Trap-Oxidizer Feasibility Study March 1982 Standards Development and Support Branch Emission Control Technology Division Office of Mobile Source Air Pollution Control Office of Air, Noise and Radiation U.S. Environmental Protection Agency ------- Trap-Oxidizer Feasibility Study March 1982 Standards Development and Support Branch Emission Control Technology Division Office of Mobile Source Air Pollution Control Office of Air, Noise and Radiation U.S. Environmental Protection Agency ------- CHAPTER I EXECUTIVE SUMMARY This study analyzes the technological feasibility of trap-oxidizers and the 1985 light-duty diesel particulate standards. The 1985 particulate standards were promulgated on March 5, 1980, and were set at 0.2 gram per mile for diesel-powered light-duty vehicles and 0.26 gram per mile for diesel-powered light-duty trucks. EPA acknowledged the technology-forcing nature of these standards at the time of promulgation, but projected that trap-oxidizers would be successfully developed iti time to permit compliance with the 1985 particulate standards. The feasibility of the 1985 particulate standards has continued to be a source of controversy within the automotive industry and EPA has monitored the research of vehicle manufacturers throughout the last two years in order to assess the progress of trap-oxidizer development. On June 17, 1981, EPA announced that it would prepare this study, and invited interested parties to submit any new data or information not considered during the original rulemaking, and to respond to specific questions about their trap-oxidizer research programs. This study is based predominantly on the submissions received from trap and vehicle manufacturers, as well as data from EPA's own test programs. Trap-oxidizer research has been concentrated primarily on two distinct designs. One involves a porous ceramic honeycomb monolith material similar to the monolith substrate used for catalytic converters on many gasoline-fueled vehicles. These monoliths have had alternate channels blocked in order to maximize particulate filtering. To this point most ceramic monolith traps have not utilized catalytic material. Corning and NGK have been the leading suppliers of prototype ceramic monolith traps. The second design utilizes compacted alumina-coated wire mesh as the filter and storage medium. Johnson Matthey has been the primary supplier of catalyzed wire mesh trap prototypes while Texaco has produced many non-catalyzed wire mesh traps• This study analyzes the most important issues involved in trap-oxidizer development. The largest part of the report summarizes the current status of trap-oxidizer development and evaluates the overall feasibility of the technology. The study also analyzes the various leadtime issues and determines when trap-oxidizers will be available for production application. The state of trap-oxidizer development has advanced significantly, over the last two years. Particulate collection efficiencies of new trap-oxidizers are quite high, ranging from 70 to 90 percent for ceramic monolith traps and 50 to 80 percent for wire mesh traps. Zero-mile backpressure levels are acceptable for ------- -2- the various trap designs. More importantly, there is a near-consensus among researchers that high efficiency and low backpressure can be maintained throughout repetitive regenerations for all trap designs when regeneration can be properly controlled. The conditions necessary for regeneration of non—catalyzed traps were found to be temperatures in the range of 500°C to 650°C and oxygen levels of 3 to 4 percent maintained for 2 to 10 minutes. It is also necessary to control the maximum temperatures in the trap to prevent uncontrolled regeneration and possible trap failure. Several systems to initiate and maintain regeneration conditions have been investigated. Some of these designs, such as fuel burners and electrical heating, appear workable but involve higher relative cost or the need for greater vehicle modifications. Other systems, such as intake air throttling and exhaust stroke fuel injection, would likely be simpler and less expensive but are further from being proved feasible on in-use vehicles. Research is continuing in an effort to identify and optimize the most promising regeneration mechanism. Probably the most undefined area of development involves the sensors, controls, and control logic which would be necessary parts of any regeneration system. Ideal sensors for the initiation of the regeneration process would be trap loading or backpressure sensors, but at this time such sensors are not commercially available and alternatives such as engine revolution and mileage counters, in combination with temperature sensors, are being examined. Integrating the proper sensors, controls, and system logic within a total regeneration system and onto vehicles is the last major technical problem in trap-oxidizer development. Trap durability is dependent upon the success of regeneration system design. It appears that, with sufficient control over the regeneration process, trap durability is sufficient. Manufacturers have reported several on-road vehicle tests and dynamometer simulations where traps have survived upwards of 30,000 miles, and many of these tests occurred in 1979 and 1980. Johnson Matthey has successfully completed a 50,000-mile durability test with its catalyzed wire mesh trap. The durability testing utilized a first-generation regeneration system, and thus did not demonstrate a production-ready overall design, but it did prove the general durability of the trap's filter structure, catalyst and washcoat formulation, and mounting system. Based on the information submitted to EPA, this study concludes that regeneration is the most significant remaining technical problem and that there is a high likelihood that manufacturers will be able to design a successful trap-oxidizer system. The determination of when trap-oxidizers could be ready for integration with production vehicles requires a projection of the amount of time still needed for development purposes, as well as an analysis of "production" leadtime issues such as a.ssurance ------- -3- testing, tooling, and certification. In view of the significant progress that has been achieved.during the last four years and the determination that only regeneration initiation and control remains unresolved, this study projects that manufacturers will be able to optimize trap systems and begin assurance testing by January 1983. Because trap-oxidizers are a new technology, EPA believes it important to allow time for field assurance testing. The first phase of assurance testing should take 7 to 9 months. At this point, manufacturers will be able to make initial tooling commitments. EPA projects that a total of 18 to 24 months will be necessary for tooling. If necessary, manufacturers will be able to carry out a second phase of assurance testing concurrently during the initial stages of the tooling period. Certification should take approximately 12 months to complete, but this can likewise take place during the extended period available for tooling. Thus, the critical path for leadtime involves the first phase of assurance testing and tooling, and EPA estimates that trap-oxidizer systems could be available for use on production vehicles within 25 to 33 months after a successful prototype system had been developed. Assuming a successful trap prototype design by January 1983, traps would be available for production application sometime between February 1985 and September 1985. 1986 model year production would begin in July/August 1985, so the shorter leadtime projection could result in 1986 model year introduction, but the longer leadtime projection would not allow introduction until the 1987 model year. Because of this range of leadtime projections, and the technical and economic risks inherent in the introduction of new technologies, the study concludes that trap-oxidizers will not be feasible on production vehicles until the 1987 model year. The fact that this conclusion is based on several conservative production leadtime assumptions is balanced by the uncertainty inherent in the development leadtime analysis, i.e., it is possible that unforeseen difficulties might occur in the final stages of trap development. ------- -4- CHAPTER II INTRODUCTION The emission of particulate matter from diesel vehicles has been a major concern to EPA for several years. Research into the environmental impacts of diesel particulate emissions began in the late 1970s when it became known that several passenger car manufacturers were seriously considering manufacturing large numbers of diesel vehicles. This work culminated in a Notice of Proposed Rulemaking (44 Federal Register 6650), published on February 1, 1979, which proposed particulate standards of 0.6 g/mi in 1981 and 0.2 g/mi in 1983 for both diesel passenger cars and light trucks. Thirty-two oral and written submissions were received on the proposed regulations from automotive manufacturers, federal agencies, environmental groups, Congressmen, and private citizens during the public comment period which ended on April 19, 1979. After reviewing these comments and reanalyzing the environmental and economic impacts and technological feasibility of the proposed standards, EPA published a Final Rule (45 Federal Register 14496), on March 5, 1980. The Final Rule delayed the implementation dates for the particulate standards. It established a standard of 0.6 g/mi for all 1982 through 1984 diesel passenger cars and light trucks. The 1985 standards were set at 0.2 g/mi for diesel passenger cars and 0.26 g/mi for diesel light trucks. EPA identified the 1985 standards as "technology-forcing," i.e., while EPA could not show that the 1985 standards were technically feasible at the time of promulgation, EPA projected that the standards would be achievable by the 1985 model year. EPA's technical projection was based on the expectation of successful development . of trap-oxidizers by 1985. It is this projection of trap-oxidizer feasibility which has been disputed by automotive manufacturers, and which is the subject of this study. The only other EPA rulemaking action affecting light-duty diesel particulate regulation was a Notice of Proposed Rulemaking (46 Federal Register 62608) issued on December 24, 1981, which proposed to allow light-duty diesel manufacturers to meet the 1985 particulate standards by averaging the emissions of their diesel engine families. EPA has not yet made a final determination with respect to averaging. General Motors petitioned EPA for reconsideration of the Final Rule on May 5, 1980, in part on the basis that the 1985 standards were infeasible. EPA denied this petition on June 27, 1980 (45 Federal Register 48133). In the spring of 1980 General Motors, joined by other diesel vehicle manufacturers, sued to overturn the Final Rule. Oral arguments were heard on October 28, 1980 before the United States Court of Appeals for the District of Columbia Circuit. The Court of Appeals upheld the Final Rule in its entirety on April 22, 1981. General Motors petitioned the ------- -5- United States Supreme Court for certiorari review of the Court of Appeals decision on July 31, 1981; this petition was denied on November 2, 1981. Because the feasibility of the 1985 particulate standards was dependent upon a projected rate of technological development, EPA was prepared to review the progress the industry was making in trap-oxidizer development. EPA published a Request for Information (46 Federal Register 31677) on June 17, 1981, which announced that EPA would be undertaking this study of the feasibility of trap-oxidizers and the 1985 particulate standards, as well as three other unrelated studies. The request notice included a list of questions concerning trap-oxidizer development (see Appendix A). EPA invited interested parties to submit any new data or information not considered during the original rulemaking, as well as direct responses to the questions listed. EPA asked that all comments be submitted by October 1, 1981 to EPA Docket A-81-20. EPA received a total of 21 submissions from 15 different parties during the time period from September 9, 1981, to November 23, 1981. Since November 23, three commenters have updated their original submissions. The Agency's policy has been to accept all submissions, even those received while the study was in progress. Parties which submitted comments, the dates of the submissions, and the corresponding EPA docket identification numbers are all given in Table II-l. The rest of this study is divided into two chapters. Chapter III, Stage of Development, will summarize the current status of trap-oxidizer development and will make an overall evaluation of the ultimate feasibility of trap-oxidizers. Chapter IV, Leadtime, will determine the model year when traps will be available for production application. This will involve projecting how much additional development leadtime is necessary to optimize trap-oxidizer design as well as determining the amount of leadtime necessary for the vehicle manufacturers to integrate traps with vehicle production. ------- -6- Table II-l Commenters to the Trap-Oxidizer Feasibility Study (EPA Docket A-83-32) EPA IH Ho. II-D-1 II-D-2 II-D-3 II-D-4 II-D-5 II-D-6 II-D-7 II-D-8 II-D-8a II-D-9 II-D-10 II-D-11 II-D-12 II-D-13 II-D-14 II-D-15 II-D-16 II-D-17 II-D-18 II-D-19 II-D-20 II-D-21 II-D-22 II-D-23 II-D-28 II-D-31 Commenter Renault USA National Automobile Dea2ers Assoc. Volkswagen of America, Inc.* Toyota Motor Co., Ltd. Chrysler Corporation* Johnson Matthey, Inc.* Ford Motor Company Texaco Inc.* Texaco Inc.* Nissan Motor Company, Ltd. Natural Resources Defense Council, Inc. U.S. Technical Research Company (Peugeot)** BMW AG*** General Motors Corporation* General Motors Corporation* Johnson Matthey, Inc.* Hogan and Hartson (Daimler-Benz AG) Volkswagen of America, Inc.* General Motors Corporation* Chrysler Corporation* Johnson Matthey, Inc.* Corning Johnson Matthey, Inc.* General Motors Corporation* Johnson Matthey, Inc.* Johnson Matthey, Inc.* Date of Comment September October 1, September September October 1, October 1, October 2, October 2, October Ik October 1, October 13 9, 1981 1981 30, 1981 29, 1981 1981 1981 1981 1981 , 1981 1981 , 1981 October 12, 1981 October 23, 1981 September 30, 1981 October 20, 1981 October 29, 1981 November 1, 1981 November 16 November 5, November 25 October 8, November 23 December 2, December 15 January 25, February 12 .1981 1981 1981 1981 , 1981 1981 , 1981 1982 » 1982 * This commenter submitted more than one document. ** This submission included confidential material which could not be used in the study. *** This entire submission was confidential and could not be used in the study. ------- -7- CHAPTER III STAGE OF DEVELOPMENT A. Different Trap Designs Conceptually the diesel trap-oxidizer can be considered to be somewhat analogous to the oxidation catalytic converter now used on gasoline-fueled passenger cars. The oxidation catalytic converter consists of a supporting structure (such as alumina pellets or a ceramic honeycomb monolith) coated with a thin layer of catalytically active material (platinum, palladium), providing a large surface area for the oxidation of exhaust gas hydrocarbons (HC) and carbon monoxide (CO) to water and carbon dioxide. Particulate matter, composed primarily of solid carbonaceous soot, cannot be oxidized as easily as gases such as HC and CO. This problem is further exacerbated by the lower exhaust gas temperatures of diesel vehicles relative to gasoline-fueled vehicles. Thus, continual oxidation of diesel particulate is impossible, and the alternative solution is a mechanism which collects the particulate on a filter structure and periodically oxidizes the collected particulate when proper conditions (high exhaust gas temperature, sufficient oxygen content) are reached. Thus, the trap-oxidizer utilizes filter/oxidation/filter/oxidation cycles to reduce particulate emissions while the catalytic converter utilizes continual and near-instantaneous oxidation to reduce HC and CO emissions. Since trap-oxidizer development began in the mid-1970's, many different designs have been investigated. The most fundamental parameter of trap-oxidizer design is the filter material. Nearly all work in this area is now focused on two materials—ceramics and alumina-coated wire meshes. These materials will be discussed in turn with specific designs described in some depth. 1. Ceramic Traps Although several manufacturers have stated that they are focusing their development programs on ceramic trap designs,[1, p. 5; 2, p. 6] Corning Glass Works was the only manufacturer of ceramic traps to submit information to EPA and the following description relies heavily on Coming's own discussion of their trap. [3, p. 2] Coming's trap is very similar to its support structure for catalytic converters for gasoline-fueled vehicles, which is a square, cell-shaped honeycomb with parallel channels running the length of the unit. The structure is basically a porous cordierite (2MgO - 2AI2O3 - 5Si02) material and is shown in Figure III-ld.[8, p. 42] As shown in Figure III-2[4, p. 19], the trap filter concept involves blocking alternate cell channel openings in "checkerboard" fashion on both the front and rear faces of the monolith, with the plugs on the front face one ------- Figure III-l a.'Alumina Coated Metal Mesh c. Foam Filter bi Alumina Coated Steel Wool d.i Honeycomb Filter Configuration of Various Trap Materials ------- -9- Figure III-2 P 4r-'S5 ------- -10- cell displaced from the plugs on the rear face. Therefore, each channel is blocked either at the front or rear face, and as Figure III-2 shows, exhaust gas cannot flow directly through any one channel and must pass through one of the porous walls of the honeycomb in order to exit through an adjacent channel. The forcing of the exhaust gas through the ceramic walls is the primary filtering mechanism of the trap. At first, the very small diesel particles (typically smaller than 1 micrometer in diameter) are trapped in the internal pores of the porous cell walls. As particulate continues to be collected, it begins to form a layer on the surface of the ceramic wall. It is fairly typical for collection efficiency to increase as this particulate "blanket" forms as there are more obstructions to the flow. Of course, there is a limit to how much particulate can be trapped before backpressure levels become prohibitive, and the trap must be regenerated before that point. Based on a fairly comprehensive characterization program, Corning identified a candidate filter material, designated EX-47, for further testing by themselves and vehicle manufacturers. The EX-47 design includes 100 cells per square inch, a 0.017 inch wall thickness, a mean pore size of 12 to 13 micrometers, 50 percent porosity, and an overall honeycomb dimension of 5.66 inches in diameter and 12 inches in length. [3, p. 9] Many of the test results which will be discussed later in this report will be with the Corning EX-47 trap, but variations in cell density, wall thickness, pore size, porosity, and overall dimensions have been tested as well. The ceramic can be, and has been, coated with catalytic material as well. Corning has produced nearly 2,000 prototype units of various sizes and shapes and has supplied traps to "[vjirtually every automaker in the world who has or expects to have a diesel engine option in 1985."[5, p. 1] A number of vehicle manufacturers commented on the Corning trap in particular, or else on ceramic honeycomb monoliths in general. (It should be noted that NGK. Insulators, Ltd. has also supplied traps of this basic design.) There is a consensus that ceramic honeycomb monoliths provide high collectiar. efficiency and that, accordingly, their primary drawback is relatively high backpressure. (4 j p. 6; 6, p. 3; 7, p. 3; 8, p. 6] These issues will be discussed in later sections. Other ceramic designs besides the honeycomb monoliths have been built and tested though no trap, manufacturer submitted information on them. Probably the most promising of these other designs is the ceramic foam filter, shown in Figure III-lc, which relies on "tortuous path" impaction for particulate removal. At least two vehicle manufacturers have tested ceramic foam filters.[8, p. 5; 9, p. 7] Also, ceramic fiber filters and porous ceramic tube elements have been tried, though again few specifics are known about their construction.[6> p. 2; 7t p. 3; 9, p. 8] ------- 2. Wire Mesh Traps The second general type of trap-oxidizer utilizes alumina-coated wire mesh as the filtering mechanism (see Figure Ill-la) • Johnson Matthey, Inc. and Texaco, Inc. both make wire mesh traps and both reported on their developments to EPA. Johnson. Mattheyfs original development work was with a trap that could be placed in the exhaust manifold as shown in Figure III-3.[10, p. 40] It is referred to as the JM4 trap. The JM4 trap is a long, cylindrical wire mesh filter with a hollow central core. The flow through the filter is radial, that is, the exhaust gas enters on the outside of the cylindrical filter but must pass through the wire mesh to exit through the hollow core. The structure of the wire mesh yields a random path for the exhaust gas to follow. Particulate filtration is due primarily to impingement on the mesh fibers. ¦ Inherent in the Johnson Matthey concept is a catalytic coating which lowers the temperature necessary for oxidation of the collected particulate matter.[10, p. 2] Johnson Matthey has performed considerable development testing which resulted in a "second-generation" trap, the JM13. The JM13 is similar to the JM4 described above but involves a graduated wire mesh bulk density and a graduated surface-to-volume ratio. Thus, the exhaust gas first enters a relatively low density, low surface-to-volume ratio section of wire mesh but, closer to the corej the density and surface-to-volume ratio of the wire mesh both increase. Thus, larger particulate tends to be trapped on the outer section of the filter and finer particulate is trapped on the inner sections. The JM13 design has also been adapted for placement in the exhaust system underneath the vehicle, similar to where catalytic converters are placed on gasoline-fueled vehicles. The underfloor trap, shown in Figure III-4[10, p. 43J with two wire mesh filters instead of one (two filters may be necessary only on the largest vehicles), resembles a conventional muffler in shape. The trap inlet has baffles to force the exhaust gas to flow around the perimeter of the can, through the mesh filter, and out through the hollow central core.[10, pp. 12-14] Finally, Johnson Matthey has developed a "third-generation trap," the JM41. The JM41 differs from the JM13 in that it would be somewhat easier to mass produce. Thus, data on Johnson Matthey traps will involve JM4, JM13, and JW41 designs. Whether traps will ultimately be installed in the exhaust manifold or underneath the vehicle will be decided by the vehicle manufacturers. The primary advantage of exhaust manifold placement is that the exhaust gas temperature is higher, making trap regeneration somewhat easier. Placing the trap farther back in the exhaust system, underneath the vehicle, is simpler to ------- Figure III-3 Schematic of a JM Manifold System ------- — J. J — Figure III-4 Schematic of a Large Capacity JM Underfioor System Inlet i i / \ \ / / \ \ / \ H \ / / \ \ \V }/ ,N / I Exhaust i } i ------- -14- integrate with the vehicle, however, and may be absolutely necessary on some vehicles due to space limitations in the manifold. Johnson Matthey has continued to optimize its trap-oxidizer design, and "numerous testing programs are underway with most of the major diesel automobile manufacturers throughout the world."[10, p. 32] Several commenters specifically discussed Johnson Matthey's design. The distinguishing characteristic of the trap is Johnson Matthey's catalytic coating. The primary advantages of the coating are a reduction of the minimum "light-off" temperature and lower HC and CO emissions; the primary disadvantage is greater sulfate emissions.[9, p. 7,20; 6, p. 2) The second alumina-coated wire mesh design for which EPA received information is the Texaco trap-oxidizer. As shown in Figure III-5,[H, p. 5] the Texaco design consists of a muffler-type container packed with alumina-coated metal wool or wire. Unlike the Johnson Matthey design, the Texaco trap permits exhaust flow straight through the filter although there is a "gas spreader" to force the flow over the entire filter face. Texaco stated that their traps have been constructed in a wide range of sizes and shapes from 16-inch diameter round units to exhaust manifold-packed units.[11, p. 1] Only one commenter mentioned the Texaco trap by name, reporting it to have moderately low backpressure and backpressure rise rates, but expressing a concern about its physical integrity and high thermal mass.[6, p. 1] Now that we have described the two general types of trap-oxidizers and a few specific designs, we can turn to the important technical parameters of trap operation—efficiency, backpressure, regeneration, and durability. These will be discussed in the following sections. Some vehicle manufacturers identified their prototype traps by name (e.g., Corning, Johnson Matthey, Texaco, etc.), others did not. Whenever possible, we will identify the trap manufacturers in the following discussions, but often it will be possible only to name the general design involved. B. Efficiency and Backpressure Efficiency and backpressure are two of the most basic trap-oxidizer performance parameters. Efficiency is a measure of the particulate reduction capability, which is the driving force for trap usage. The effect of traps on exhaust gas backpressure is a fundamental concern as the trap filter medium is an "artificial" obstruction in the exhaust system and excessive backpressure can adversely impact engine performance and fuel consumption. The determination of the efficiency and backpressure of a filter material when new is an appropriate first step toward analyzing a trap design. Thus, much data has been generated concerning zero-mile efficiency and backpressure levels. But, ------- Figure III-5 TYPICAL TEXACO DIESEL EXHAUST FILTER DESIGN ALUMINA-COATED METAL WOOL SUBSTRATE INSULATION INLET GAS PERFORATED BAFFLES AND RETAINERS GAS SPREADER OUTLET ^ 6AS Ln I ------- -16- just as critical, and far more time consuming, is determining whether the trap material can maintain acceptable efficiency and backpressure over the lifetime of the vehicle on which it is used. Accordingly, this section will examine the data on trap efficiency and backpressure in two sections—at zero-mile conditions and after significant mileage accumulation. 1. Zero-Mile Efficiency and Backpressure It has been known for some time that filter materials are available which, when new, can significantly reduce diesel particulate emissions without raising exhaust gas backpressure to unacceptable levels.[12, pp. 48-49] Table III-l summarizes zero-mile efficiency and backpressure data which were submitted by vehicle and trap manufacturers for this study. Unless otherwise noted, the efficiency data were all generated over EPA's Urban Dynamometer Driving Schedule, under either the Federal Test Procedure or hot start LA-4 conditions. The backpressure data were generated in various ways and, where stated by the commenters, are also listed in Table III-l. Except for Johnson Matthey and Texaco, which design metal mesh traps, every commenter listed in Table III-l reported data on ceramic monolith traps. Most of the ceramic monolith data are for the Corning design, with the remaining data unidentified by manufacturer. It is clear that the ceramic monolith design is a very effective particulate trap when new—the reported data range from General Motors' 60 to 80 percent to Daimler-Benz' 86 percent. EPA has recently tested a Corning ceramic monolith trap and found efficiency to be 90 percent when new. [27, p. 3] No vehicle manufacturer has stated that zero-mile trap collection efficiency is a problem, and it is likely that it is the ceramic monolith's high efficiency that has made it a favorite candidate trap for many vehicle manufacturers. Backpressure is a somewhat more complex issue. The first issue to be resolved must be the determination of "acceptable" backpressure. EPA did not specifically ask commenters to address this issue, and none did so directly. However, a few commenters did shed some light on this issue. In its development testing of its ceramic monolith prototype traps, Corning used a trap pressure drop of 103 mm Hg as the endpoint for trap filtering. This value was suggested by the manufacturer of the engine Corning was using (Oldsmobile 5.7-liter V-8 diesel) as .the maximum tolerable pressure drop.[3, p. 3] Ford, in its initial testing of the Corning ceramic monolith, apparently decided that a 75 mm Hg pressure drop at 40 mph was the limit.[13, p. 8] Johnson Matthey, in its trap development work, regenerates its trap when the pressure drop across the trap reaches about 41 mm Hg.[10, p. 24] Thus, there apppears to be quite a range of values for "acceptable" backpressure levels. ------- Table III-l Zero-Mile Efficiencies and Backpressures for Various Trap Designs Commenter (Reference) Type of Trap Daimler-Benz[2, pp. 6-8] Ceramic monolith Corning[3, p. 5] Ceramic monolith Volkswagen[A, pp. 21-22] Alumina-coated wire mesh with catalyst Ceramic monolith Ceramic monolith with catalyst Ford[6, p. 5] Nissan[7, pp. 9-10] Toyota[8, pp. 7-8] Alumina-coated wire mesh Alumina-coated wire mesh Porous ceramic tubes Ceramic monolith Steel wool Ceramic monolith Ceramic fiber Ceramic-coated steel wool Alumina-coated metal mesh Alumina-coated steel wool Ceramic monolith with catalyst Ceramic foam Manufacturer of Trap Corning Corning Zero-Mile Efficiency* (%) 86 Zero-Mile Backpressure Increase ( mm Hg) 80 7.5 (steady-state) (steady—state) Johnson Matthey (JM13) 51-61 Corning Corning with catalyst Texaco Johnson Matthey NGK Corning/NGK 77 78 115 (maximum, LA-4) 185 (maximum, LA-4) 23-71 21-58 77 80 53 (steady-s tate) 72-74 69 60 48 55 80 55 15 {40 mph) 26 (40 mph) 249 (40 mph) 26 (40 mph) 20 (55 mph) 170 (45 mph) 30 (maximum, LA-4) Remarks VI I ------- Table III-l (cont'd) Zero-Mile Efficiencies and Backpressures for Various Trap Designs Commenter (Reference) General Motors [9 pp. 5,9) Johnson Matthey [10, pp. 17,34-37,44, 50,86-87) Type of Trap Texaco[ll, p. 2] Metal mesh Ceramic monolith Ceramic foam Ceramic fiber Alumina-coated metal mesh with catalyst Alumina-coated metal mesh with catalyst Alumina-coated metal mesh with catalyst Alumina-coated metal mesh with catalyst Alumina-coated metal mesh with catalyst Alumina-coated metal mesh with catalyst Alumina-coated metal mesh with catalyst Alumina—coated wire mesh Manufacturer of Trap Johnson Johnson J ohnson Johnson Johnson Johnson Johnson Matthey Matthey Matthey Matthey Mat they Matthey Matthey Texaco (JM13) (JM13) (JM13) (JM13) (JM41) (JM41) (JM41) Zero-Mile Efficiency* (%) 45-65 60-80 45-55 40-80 73 80 55 51 68 58-80 Zero-Mile Backpressure Increase ( mm Hg) 0.15 27 41 18 13 (60 mph) 38 (60 mph) 8 (60 mph) 84 (60 mph) 145 (60 mph) 31 (60 mph) 38-79 (40 mph) Remarks EPA testing NA - Underfloor NA - Underfloor NA - Manifold TC - Underfloor NA - Underfloor NA - Manifold TC - Underfloor Efficiency data reported for FTP or LA-4 testing unless noted otherwise. ------- -18- It ¦ can be seen in Table I1I-1 that the zero-mile incremental backpressure values for the non-catalyzed ceramic monolith traps were 7.5 mm Hg (Corningj under steady-state conditions), 26 mm Hg (Ford., 40 taph), 27 mm Hg (General Motors), and 115 mm Hg (Volkswagen, maximum pressure drop during LA-4 cycle). Only the VW figure is high enough to warrant discussion. It is important to keep in mind that "acceptable" backpressure is very dependent on the vehicle being considered * For example, the 115 nun Hg pressure drop for the ceramic monolith trap reported by VW resulted in an approximate doubling of the total exhaust backpressure. But, as "Volkswagen stated in its comment, "[t]he exhaust gas backpressure at a level of two times higher than normal does not yet essentially affect the fuel economy, EC emissions, or engine power output".[4, p. 22] Thus, on this vehicle at least, VW did not consider a 115 nun Eg pressure drop increase to be unacceptable. Daimler-Benz, which reported very high efficiency for the ceramic monolith trap, stated that the backpressure of the trap "seems to be acceptable when the filter is new."(2, p. 7] Thus, the data reported to EPA indicate that the zero-mile uncatalyzed ceramic monolith trap is very efficient arid produces acceptable backpressure levels. Zero-mile backpressure data in Table 111-1 for catalyzed ceramic monolith traps are less positive—185 mm Hg (Volkswagen, maximum during LA-4 cycle) and 170 mm Hg (Toyota, 45 mph)• VW did. not comment on this backpressure level while Toyota claimed that the 170 cm Hg pressure drop would result in a 10 percent fuel economy penalty. One reason for this apparent discrepancy between the two manufacturers is that the VW value is the maximum obtained over the LA.-4 driving cycle while the Toyota value was taken at 45 mph operation and might well have been much higher at some point during LA-4 operation. Incremental backpressures near 200 mm Hg would likely not be acceptable for most vehicles and thus the use of a catalyst for ceramic monolith traps does not now appear to be a promising option. However, this conclusion is based on very limited data and it is quite possible that further research will produce a successful way of catalyzing ceramic monolith traps. Only a sparse data base was reported for other types of ceramic traps. Toyota and GM reported efficiencies between 45 and 55 percent and incremental backpressures of between 30 end 41 ram Hg for ceramic foam traps at zero-mile. Nissan and GM reported zero-mile efficiencies between 40 and 80 percent for ceramic fiber traps, with GM reporting a zero-aile backpressure increase of 18 mm Hg. These data warrant further consideration of ceramic foam and fiber traps; thus far their development has lagged behind ceramic monoliths. Ford was the only manufacturer to report on porous ceramic tubes; their efficiency was quite good at 77 percent but the incremental backpressure of 249 mm Kg was very high. This backpressure would have to be reduced for this trap to be successful. ------- -19- Most commenters also reported data for alumina-coated metal mesh traps. There were considerable data reported on the Johnson Matthey catalyzed metal mesh trap. Johnson Matthey submitted detailed data on their various trap designs and some of them are summarized in Table III-l. An attempt was made to categorize the Johnson Matthey data by basic design (JM13 vs. JM41), trap placement (manifold vs. underfloor), and by whether the trap was used on a naturally-aspirated or turbocharged vehicle. (Considerable concern has been expressed in the past regarding the additional complexity of utilizing trap-oxidizers on turbocharged vehicles. It is noteworthy that both Volkswagen and Daimler-Benz reported trap data for turbocharged vehicles and neither discussed any particular problems with such applications.) It can be seen in Table III-l that Johnson Matthey reported zero-mile collection efficiencies of between 50 and 80 percent for their traps under various conditions. EPA testing of an underfloor JM13 trap on a 1978 Fiat 131 diesel passenger car resulted in a 73 percent particulate reduction. Two vehicle manufacturers also reported data on the Johnson Matthey design. Volkswagen reported zero-mile efficiencies of between 51 and 61 percent and Ford listed efficiencies of between 21 and 58 percent for the Johnson Matthey design. Finally, GM reported efficiencies of 45 to 65 percent for metal mesh traps, and GM tested several Johnson Matthey traps. Based on the weight of these data, we can conclude that the Johnson Matthey trap-oxidizer is capable of 50 to 80 percent collection efficiency when new. - Johnson Matthey and Ford were the only commenters to submit information on zero-mile incremental backpressure levels for the former's trap design. As shown in Table III-l all of the reported backpressure levels were less than 40 mm Hg except for the JM41 design on naturally-aspirated vehicles. Even these higher values—84 and 145 mm Hg at 60 mph—might be acceptable (see discussion above), but the large discrepancy in incremental backpressure levels between the JM13 and JM41 traps on naturally-aspirated vehicles suggests that improvements in the latter's design are likely. Based on the data in Table III-l, we conclude that the Johnson Matthey trap provides good collection efficiency with acceptable incremental backpressure levels under zero-mile conditions. Texaco and Ford reported test data for Texaco's non-catalyzed wire mesh trap. Texaco reported efficiencies of between 58 and 80 percent and Ford reported efficiencies of 23 to 71 percent for the former's design. Texaco reported backpressure increases of 38 to 79 mm Hg while Ford realized a 15 mm Hg increase. Toyota and General Motors also reported data on wire-based traps without elaborating on the traps on which the data were collected. Toyota reported efficiencies of 48 to 55 percent and GM 45 to 65 percent, all at relatively low backpressure increases. These data are not ------- -20- significantly different than the results discussed above for the Johnson Matthey catalyzed design which indicate that the fundamental collection efficiency characteristics of the wire mesh filters ,are very similar and that, unlike ceramic traps, the use of a catalyst does not appear to significantly affect wire mesh backpressure levels. In conclusion, it can be confidently stated that ceramic monolith traps are 70 to 90 percent efficient and wire mesh traps are 50 to 80 percent efficient when new. Both designs have acceptable backpressure increases at zero-miles. 2. Efficiency and Backpressure After Mileage Accumulation Having determined in the previous section that both ceramic monolith and alumina-coated wire mesh trap-oxidizers are capable of providing high collection efficiencies with acceptable backpressure increases at zero-mile levels, the issue becomes whether a trap-oxidizer can maintain these characteristics over the useful life of the vehicle. As no trap-oxidizer has been developed which can continuously oxidize particulate matter, a trap reaches a point after mileage accumulation where the amount of particulate contained in the filter medium becomes excessive and backpressure increases to unacceptable levels. It is at this point that the trap has to be regenerated, with the goal being to return the efficiency and backpressure to as close to zero-mile levels as possible. Several vehicle manufacturers commented on the ability of ceramic monolith traps to return to zero-mile efficiency and backpressure levels. General Motors stated that "[i]n general the collection efficiencies and backpressure levels return to zero-mile levels after repeated regeneration.... Only in cases of incomplete regeneration, trap deterioration, or where additives have been used which collect on the trap, have we seen increasing backpressure levels with repeated regeneration."[9, p. 21) To illustrate its point, GM submitted a series of graphs showing the particulate emission levels and backpressure levels during 180 hours of dynamometer testing of a vehicle equipped with a Corning ceramic monolith trap. Two of these graphs have been reproduced as Figures III-6 and III-7. Figure 6 shows that during the first 12 hours of testing (involving 6 regenerations) the vehicle emitted between 0.09 and 0.12 g/mi particulate and had post-regeneration backpressure levels of between 36 and 41 mm Hg. Figure III-7 gives data for the same vehicle at hours 142 to 160. It shows that the vehicle was then emitting between 0.07 and 0.12 g/mi particulate with post-regeneration backpressure levels of 25 to 38 mm Hg. The data between hours 12 and 142 were in similar agreement. Thus, during the 180 hours of testing, which simulated approximately 7000 miles of driving at 40 mph and which included approximately 80 regenerations with a manifold burner, the ceramic monolith trap maintained its zero-mile efficiency and backpressure characteristics following regeneration. ------- Figure .111-6 "Cfell 6 H Olcls Y- ^t-O mph!R,L. 8> Jl 80' ------- Figure III-7 I'M : ' > i ¦ ' : i " ¦ r" ¦ i 1 1 :!ii .Mi |-T !| j ! rt- i i rr i t: rr i ! i ! i. I.L » I lit- i > i ; i l!' ! i1 in-- r ¦ -U- 11 4 i: i'' '!' H" 1 : I i ; 1 i Tt I -1- Loaded at AO MPH, Regenerated at 25 MPH : I 4' i : : ! I V! t ! i I I : I ; I : : II Li.;.;. |.| "iTi! Jl!.!. Jii.i. I i : i lt"T i ~C£LL C fi/\ , .AT/V-ArOZ/O. i! I .± I I ( ! }{^ap: ------- -23- Ford reports a similar conclusion—"With adequate regeneration temperatures and time intervals, backpressure levels can be returned to levels very close to the clean trap backpressure levels for the ceramic honeycomb trap, likewise, collection efficiency only slightly decreases with regeneration."[6, p. 8] Ford's position is supported in Figure III-8 which shows efficiency and backpressure data for a test vehicle equipped with a Corning ceramic monolith trap. The vehicle was driven on the road for over 10,000 miles and the trap underwent approximately 100 regenerations before the test was ended due to trap failure. Figure III-8 shows a very slight increase in post-regeneration backpressure levels and a slight decrease in collection efficiency over the 10,000 miles, though these trends are subject to data scatter, especially with respect to efficiency. Other vehicle manufacturers' data on ceramic monolith traps support the conclusions made by GM and Ford. Nissan reported results for the ceramic monolith trap with two different methods of regeneration. Using a burner to initiate regeneration, it reported virtually no change in efficiency or clean trap backpressure over a testing period of 500 miles. Nissan also modified engine operating conditions so that the exhaust gas temperature would be sufficient for regeneration. This resulted in the ceramic monolith trap maintaining its clean-trap efficiency and backpressure performance throughout a 5000-mile testing period involving 54 regenerations.[7, pp. 23-24] Toyota regenerated a ceramic monolith trap after approximately 100 miles of operation and found that the trap collection efficiency actually stabilized at a somewhat higher level than at zero-mile while the clean trap backpressure returned to the zero-mile level.[8, p. 15J EPA testing of a Corning ceramic monolith trap also supports the thesis that zero-mile collection efficiency can be maintained. Testing at 5,000, 10,000, and 15,000 miles has resulted in the same 90 percent collection efficiency that existed at zero-miles.[27, p. 3] Volkswagen was the only manufacturer to state that it could not return efficiencies and backpressure levels of ceramic monolith traps to zero-mile levels. It commented that "[p]otential trap collection efficiencies and backpressure levels never return to zero-mile levels following use and regeneration.... Ricardo has determined that at filter temperatures of 700°C approximately 4 percent of the particulate material collected remains in the filter. This applies to ceramic-type filter elements with high pore density."[4, p. 31] Volkswagen also supported its conclusion with data showing that the air flow through catalyzed and non-catalyzed ceramic monoliths never returned to zero-mile levels even after external flame regeneration and reverse air blasting. The fact that 4 percent of the particulate matter remained in the filter medium should not necessarily affect backpressure significantly and could actually ------- 6o 50 1+0 30 20 10 0 00 80 6o l+o 20 0 BACKPRESCtiRE g C-1+0 mph AFTER TRAP REGENERATION R106 • » » 5 i » * r 3-3 in Hg/100 Mi @ CbO mph 109 Mi Interval Average ' R122 10 12 MILES (X10 3) DURABILITY TRAP - D1 119 cu.in. Corning Ceramic Honeycomb 2.3L Opel Diesel Vehicle O o_ o o o o CVS-C/H o SVL ^'ETL O Limited Durability MILES (X10 3) — AVG.E7F. 81.6;"!- °v 10,337 mi. Ther!r:?.l Shock : Failure AMA Durability ------- -25- improve collection efficiency. The air flow results are the more significant and deserve some examination. VW did perform the regeneration and air flow tests after 180 miles of operation, which is a fairly high testing period for the efficient ceramic monolith trap. The trap would have been loaded very heavily. Regeneration after a short mileage interval might have produced different results. Otherwise,' no explanation is readily available as to why the other vehicle manufacturers which directly measured efficiencies and backpressure levels for ceramic monolith found post-regeneration levels to be at or near the zero-mile levels, while Volkswagen, using more indirect analytical methods, found otherwise. Given the near consensus of data from the vehicle manufacturers, especially those data which involve direct measurement of efficiency and backpressure, it can be concluded that ceramic monolith traps are capable of maintaining high collection efficiencies and acceptable backpressure levels through repetitive regenerations. The only commenters to submit information on wire mesh traps were Johnson Matthey and Texaco. The nature of trap-oxidizer research has been that the vehicle manufacturers perform most of the vehicle/trap integration work. Since no vehicle manufacturer reported on the ability of wire mesh traps to maintain acceptable efficiencies and backpressures throughout mileage accumulation and repetitive regenerations, the data base for metal mesh traps is much more sparse. Johnson Matthey submitted much information on the collection efficiencies of its catalyzed wire mesh trap designs during mileage accumulation.[10, pp. 46-49, pp. 52-57] Its data generally show that its trap designs maintain, and in some cases improve, zero-mile collection efficiency with mileage. Figure III-9 is a graphical illustration of the efficiency of a JM13 manifold trap over 1000 miles of hot-start LA-4 operation. There is some data scatter, but most of the efficiencies are between 65 and 75 percent and there is no discernible negative trend with mileage accumulation. These data are representative of the data base for efficiency which Johnson Matthey provided. Johnson Matthey also provided data on the backpressure levels of its traps with mileage accumulation. Its most comprehensive data are shown in Figures 111-10 and III-ll [10, p. 123, p. 125] which give the backpressure levels for the first 11,000 miles of Johnson Matthey's durability testing at Southwest Research Institute (which will be discussed in more detail later). Figure 111-10 shows that the trap had to be externally regenerated only 3 times during the 11,000 miles, at 6310, 8125, and 9220 miles. The zero-mile backpressure level of the test vehicle was 21 mm Hg at 40 mph. After the first regeneration at 6310 miles the backpressure was 27 mm H.g (Figure 111-10), after the second regeneration at 8125 miles it was 26 mm Hg (Figure III-ll), and after the third regeneration at 9220 miles it was approximately 32 ------- Figure III-9 Vehicle GF101 Manifold JM13 Miles ------- Figure III-1Q JM13/11 Durability Test Back Pressure vs Mileage First 10,000 Miles On Board Pressure Measurement Vehicle GW101 lO-i 1st Reqenoralion 6310 Miles Daclc Pressure In H20 At 40 MPH 2nd Regeneration 0125 Miles I ho I 3rd Regeneration 9220 Miles i i i \ i i i i i i r 1000 2000 3000 4000 5000 6000 7000 6000 9000 10000 11000 Mileage ------- Figure III-ll JM13/II Durability Test Stabilized Back Pressure vs Mileage 1000 Mile Detail On Board Pressure Measurement Vehicle GW101 ------- -29- mm Hg (Figure XII-10). Recently Johnson Matthey reported the final data on the 50,000-mile durability vehicle. Over the 50,000 miles the trap was externally regenerated 37 times. After regeneration the vehicle backpressure ranged from 24 mm Hg to 39 mm Hg with all but two of the levels between 24 mm Hg and 32 mm Hg.[28, p. 27] There was very little increase in post-regeneration vehicle backpressure levels and no upward trend with mileage over the 50,000-mile durability test. Texaco reported on two durability tests with its non-catalyzed wire mesh trap-oxidizer—one was an on-highway program which achieved 10,000 miles before trap failure and the second was a steady-state dynamometer program which lasted 30,000 miles before trap failure. In both cases, Texaco's data indicate that collection efficiencies were maintained at levels very near to zero-mile levels while clean-trap backpressure levels tended to stablize somewhat above zero-mile levels.[3, pp. 6-7] Based on the foregoing discussion, it can be stated that, given a successful on-vehicle regeneration system, trap-oxidizers are now available which can maintain high collection efficiencies at acceptable backpressure levels throughout mileage accumulation and repetitive regeneration cycling. This conclusion is most supportable for ceramic monolith traps, as there is a near consensus from the vehicle manufacturers on this issue. There is a much smaller data base with respect to metal mash traps, though Johnson Harthey1s data strongly support this conclusion. C. Regeneration 1. The Need for Regeneration Because of the lower exhaust gas temperatures of diesel vehicles and the more difficult physical task of particulate matter oxidation, the trap-oxidizer cannot continually oxidize particulate emissions. But the need for periodic oxidation of the collected particulate or regeneration of the trap is clear. For example, the Corning ceramic monolith trap tested by Ford, which was 5 inches in diameter and 9 inches long and which contained 100 cells per square inch with a wall thickness of 0.017 inches, has 43.4 cubic inches of void space within the filter for particulate storage. Assuming an average particle density of 0.92 grams per cubic inch, this trap would only be able to store a maximum of approximately 40 grams of particulate matter before simply running out of space within the trap. If this trap collected particulate at 80 percent efficiency on a vehicle which emitted 0.40 g/mi, then the trap storage volume would be completely filled after approximately 125 miles of vehicle operation for this specific trap design and size. [13, p. 8] Trap-oxidizers could be made to be bigger with correspondingly larger storage volumes, but it can be easily seen that regeneration is ultimately necessary simply from a physical standpoint. ------- -30- A second factor which affects the need for trap regeneration is exhaust gas backpressure. As greater amounts of particulate matter collect on the filtering medium, the exhaust gas stream must pass through more material and exhaust gas backpressure rises. Excessive backpressure can worsen fuel economy and engine performance. Third, the amount of particulate collected is a strong determinant of the maximum temperatures reached in the trap during the regeneration process. The greater the amount of particulate collected, the greater the temperature reached during regeneration. Both backpressure and regeneration temperature characteristics can result in regeneration interval requirements even more stringent than those which would be defined by total trap storage space. Thus, there are several benefits of frequent trap regeneration. Alternatively, there are reasons why the number of regenerations should be minimized. Since the regeneration process involves high-temperature oxidation during relatively short periods of time, it would be expected that the greatest physical stresses on the trapping materials (filter medium, filter/canning interface, etc.) would exist during regeneration. Thus, it has been hypothesized that trap durability is not so much a function of mileage accumulation as it is the number of regeneration cycles it must survive.[3, p. 3] Thus, the fewer regeneration cycles the better. Also, most methods being investigated for regeneration initiation and control involve some deleterious effects (increased fuel consumption, power loss) during the regeneration cycle which would be minimized by maximizing regeneration intervals. 2. Factors Affecting Regeneration Frequency The optimum regeneration intervals for any specific vehicle/trap combination will be a function of all of the above parameters and must be determined by the vehicle manufacturers. Generally, it seems reasonable to project that most vehicle manufacturers will choose to minimize the number of regenerations while not allowing excessive backpressure or particulate loadings. Several commenters reported information concerning which factors were most critical in defining trap regeneration intervals for various trap/vehicle combinations. A brief survey of these comments will summarize the latest data on trap regeneration frequency. Host of the specific comments regarding the "critical loading" and frequency of trap regeneration concern ceramic monolith traps. These comments will be discussed, first followed by comments concerning other trap designs. Two manufacturers, Nissan and General Motors, stressed the primary importance of limiting the particulate trap loading in controlling the maximum trap temperatures reached during regeneration. Figure 111-12 shows graphs from Nissan which give ------- -31- Figure 111-12 • Regenerated by Burner ^Engine : LD 2 S •1400- r-- • 12 00 -1000- ] -600 - - 6 0 0 _.-400-. o- C e r am i c" Coa t'e d ' S t ee 1 Woo! Filter 10 20 30 40 .Particulate Loading ( grams) 1400-r ¦1200 • 1000 ¦ -6 00- -600 ¦ thermal stack-rwtsrffnt Limit ¦ 400 Ceramic Monolith Filler t 10 20 30 40 Particulate LondLnq ( qrtimi ) ------- -32- the maximum trap regeneration temperatures for various particulate loadings for both ceramic coated steel wool and ceramic monolith traps.[7, p. 32] It can be seen that there is a definite relationship between maximum trap temperature and particulate loading. Based on their concerns, Nissan stated that regeneration should take place about every 50 miles and General Motors commented that regenerations should occur at 40- to 100-mile intervals.[7, p. 28; 9, p. 32] Nissan and General Motors also stated that on some trap designs excessive backpressure might also mandate regeneration, but they did not elaborate as to the types of traps or operating conditions for which backpressure would be the critical parameter. The rest of the manufacturers which commented on ceramic monolith traps all reported that exhaust gas backpressure levels were the most critical factor in determining the need for regeneration, with increased fuel consumption being the primary result, although impaired engine performance and driveability were also frequently mentioned. Suggested regeneration intervals ranged from 30 to 50 miles for Toyota, approximately 90 miles for Ford, and from 60 to 100 miles for Volkswagen.[8, p. 17; 13, p. 8; 4, p. 34] It can be concluded from these comments that the mass of particulate collected and exhaust gas backpressure are the two most important factors defining when ceramic monolith trap regeneration must occur and that with most current trap/vehicle combinations the regeneration interval would be approximately 50 to 100 miles. Fewer data were reported to EPA on this issue for wire mesh trap-oxidizers. Texaco reported that it is the maximum regeneration temperature which limits the amount of particulate which can be collected in its non-catalyzed alumina-coated metal mesh trap. With the engines Texaco used in its development programs, typical regeneration intervals were 150 to 200 miles.[11, p. 4] Johnson Matthey's catalyzed metal mesh trap design appears to oxidize particulate much more frequently during normal vehicle operation. General Motors has reported the melting of several Johnson Matthey traps, and it would seem plausible that overloading in the trap might have been a serious problem, especially for those traps which were designed to be self-regenerating and which had no external regeneration mechanism. In its recent durability testing Johnson Matthey has utilized an external regeneration system which is manually operated when backpressure rises to a certain level. Johnson Matthey has only found it necessary to utilize the regeneration mechanism approximately once every 1,350 miles, though the regeneration frequency increased with mileage accumulation.[28, p. 27] This interval is much longer than for any other trap design, though the fact that the vehicle used for the durability testing, a Volkswagen Rabbit, has low engine-out particulate levels certainly contributes to the long regeneration interval. Given the rather scarce data base, it can only be tentatively concluded ------- -33- that the temperature resulting from regeneration is the primary limit on the particulate loading for wire mesh traps as well, and that regeneration intervals for mesh traps will likely be considerably longer than for ceramic monolith traps. 3. Conditions Necessary for Regeneration There are two conditions which must exist in order for trap-oxidizer regeneration to occur: the exhaust gas temperature must be high enough and there must be sufficient oxygen in the exhaust to initiate and sustain particulate oxidation. A third important factor is time. Both the temperature and oxygen content of the exhaust must be maintained for an adequate length of time in order for complete (or as near complete as feasible) regeneration to occur. The first issue is the exhaust gas temperature necessary for trap regeneration. Table II1-2 summarizes the statements of the commenters on this issue. It can be seen that for non-catalyzed ceramic monolith traps, the minimum ignition temperatures range from 500°C to 650°C. It would be expected that by impregnating the trap-oxidizer with catalytic material the minimum ignition temperature of the ceramic monolith trap could be lowered. However, the only data reported for such an attempt, by Ford, do not support this thesis. Ford impregnated ceramic monolith traps with both platinum and lead catalysts and found' that neither material lowered the temperature required for regeneration. Ford stated, "Since the catalyst was impregnated into the ceramic trap material, only the first layer of particulate material was in contact with the catalyst.... Since successive layers of collected particulate material were not in contact with the catalyst, significant advantages from an impregnated catalyst would not be expected. Methods to improve contact between the catalyst and a larger amount of the particulate material may have the potential to reduce the particulate ignition temperature."[13, p. 12] Thus, at this time it is not clear how successful catalytic material would be in reducing ignition temperatures for ceramic monolith t.raps. Table III-2 reports minimum ignition temperature data for other ceramic trap designs as well. Two manufacturers reported data on ceramic foam traps, with and without catalytic treatment. The non-catalyzed ceramic foam traps needed temperatures in the 500°C to 550°C range while catalyzed versions regenerated at 300°C to 500°C« Thus, the catalyst material does appear to have an effect on ceramic foam traps. Two points should be made in this regard. First, the structure of the ceramic foam trap, being a "tortuous path" design similar to wire mesh designs, might well be simply better suited for effective catalytic treatment. Second, it should be noted that both of the manufacturers which reported ceramic foam trap data, Toyota and General Motors, noted that while significant particulate oxidation occurred at lower ------- Table III-2 Minimum Temperatures Necessary for Regeneration of Various Trap Designs as Reported by Commenters Commenter (Reference) Renault[14, p. 2] Texaco[ll, p. 9] Corning[3, p. 8] Johnson Matthey [10, p. 30] Daimler-Benz[2, p. 8] Volkswagen[4, p. 27] Toyota[8, p. 13] Type of Trap Alumina-Coated Wire Mesh w/o Catalyst Ceramic Monolith w/o Catalyst Alumina-Coated Wire Mesh w/o Catalyst Alumina—Coated Wire Mesh w/Catalyst Ceramic Monolith w/o Catalyst Ceramic Monolith w/o Catalyst Alumina-Coated Wire Mesh w/Catalyst Ceramic Monolith w/o Catalyst Ceramic Foam w/o Catalyst Ceramic Foam w/Catalyst Manufacturer of Trap Texaco Corning Johnson Matthey Corning Johnson Matthey Minimum Temperature Required for Ignition °_C 600 540 540 600 350 500-650 500 350 600 500 300-500 Nissan[7, p. 20] — — 550 Ford[13, pp. 9,12] Ceramic Monolith w/o Catalyst Corning 500 Ceramic Monolith w/Catalyst — 500 General Motors Ceramic Monolith w/o Catalyst — 600 [9, p. 20] Alumina-Coated Wire Mesh w/o Catalyst — 580 Alumina-Coated Wire Mesh w/Catalyst — 310 Ceramic Foam w/o Catalyst — 550 Ceramic Foam w/Catalyst — 420 Ceramic Fiber w/o Catalyst — 600 Ceramic Fiber w/Catalyst — 450 ------- -35- regeneration temperatures with the catalyzed traps, complete regeneration required temperatures in the 500°C to 700°C range regardless of whether catalytic material was present.[8, p. 13; 9, p. 16] With ceramic foam traps the overall evaluation of catalyst effectiveness may depend upon whether "complete" regeneration is essential or whether something less is acceptable in terms of backpressure, efficiency, etc. General Motors also reported minimum ignition temperature data for ceramic fiber traps. The non-catalyzed version required a temperature of 600°C while the catalyzed trap needed 450°C. Again, GM reports that the catalyst did not significantly reduce the temperature necessary for complete regeneration. Three manufacturers reported data on alumina-coated wire mesh traps without catalysts. All found the minimum temperatures for regeneration to be between 540°C and 600°C, regardless of the manufacturer of the trap. Three manufacturers also provided such information on catalyzed wire mesh traps, with two of the manufacturers identifying the Johnson Matthey trap by name. All three reported the minimum ignition temperature for the catalyzed wire mesh trap to be in the range of 310°C to 350°C. Again, GM qualifies its data by pointing out that complete regeneration does not occur at these temperatures. Nevertheless, the catalyst seems to be successful in lowering the necessary temperature for significant particulate oxidation in metal mesh traps. In summary, we can conclude from the data in Table III-2 that non-catalyzed traps, whether ceramic or wire mesh based, require minimum ignition temperatures of 500°C to 650°C. Catalyzed traps appear to promote particulate oxidation at temperatures of 300°C to 500°C, with the catalytic material more effective on "tortuous path" trap designs like foam or wire designs than on ceramic monolith designs. In addition, it seems to be generally accepted that complete regeneration requires temperatures on the order of 600°C to 700°C, whether catalysts are used or not. The need for complete regeneration, as opposed to nearly complete regeneration, may not be absolutely essential, but cannot be firmly concluded at this time. A second condition which must exist for regeneration to occur is that sufficient oxygen must be available in the exhaust gas stream. Two trap suppliers, Texaco and Corning, submitted graphs indicating the requisite exhaust oxygen levels for regeneration at various exhaust gas temperatures for non-catalyzed traps.[11, p. 9; 3, p. 8] The two graphs are essentially identical and Texaco's graph is reproduced as Figure 111-13. At a temperature of approximately 550°C there must be at least 4-1/2 percent oxygen for regeneration to occur, but at 600°C only 3-1/2 percent oxygen is required. Coming's submission extrapolated its own results to higher temperatures and hypothesized that at 700°C only 2 percent oxygen would be required for oxidation. ------- Figure 111-13 DEF REGENERATION CONDITIONS *5 12 P z~ o 1 1 - h— < 10 cr i - f— z UJ 9 - u z 8 o - o z: 7 - UJ o >- 6 - X o 1— 5 - CO ZJ 4 < X X ¦a UJ 800 A A O DEF REGENERATED A DEF DID NOT REGENERATE- 900 1000 1100 EXHAUST TEMPERATURE, °F t LO ON I 1200 ------- -37- The third requirement for trap regeneration is that the requisite exhaust gas temperature and oxygen content be maintained for a sufficient length of time. It had been hypothesized by some researchers that once trap-oxidizer "light-off" occurred, the particulate oxidation process would be self-sustaining. Several commenters have found that this is not true, however, and that the temperature and oxygen content necessary for particulate ignition must be maintained throughout the regeneration cycle in order for regeneration to continue to completion. [ 2, p. 10; 4, p. 27] Eow long regeneration takes depends on the temperature and oxygen content of the exhaust flow, as well as on the amount of particulate to be oxidized. Generally, the commenters' data do not address the latter. Typical of the commenters' responses were those of Texaco and Ford. Texaco stated that exhaust at 600°C containing 7 percent oxygen required less than 3 minutes to regenerate its non-catalyzed wire mesh trap, while lowering the temperature of the exhaust to 540°C raised the regeneration time to 3-1/2 minutes.[11, p. 4] Ford reported that complete regeneration of the Corning ceramic monolith trap at 540°C with sufficient oxygen took over 10 minutes, while at 600°C it took less than 2 minutes.[6, p. 7] Nissan, Toyota, and General Motors all reported regeneration times of from 2 to 10 minutes.[7, p. 30; 8, pp. 22-24; 9, p. 33] From the above discussion, it can be concluded that successful trap regeneration requires maintaining exhaust gas temperatures of between 500°C and 650°C for non-catalyzed traps (possibly as low as 300°C for some catalyzed traps, depending on the need for complete regeneration) and oxygen levels of at least 3 to 4 percent for between 2 and 10 minutes. 4. Attaining Regeneration Conditions In-Use Having defined the exhaust gas temperature and oxygen content conditions necessary for successful trap regeneration, the issue becomes whether such conditions can be attained on light-duty diesel vehicles and trucks in use. It would be most desirable to fulfill the requirements for particulate oxidation without having to design additional hardware for the diesel vehicle. Unfortunately, the commenters were nearly unanimous in stating that in-use diesel vehicle exhaust gas temperatures are too low to allow for successful trap-oxidizer regeneration. Table III-3 summarizes typical exhaust gas temperature ranges for different diesel vehicles and testing conditions as reported by various commenters. Very few vehicles ever reach temperatures of 500°C, the minimum particulate ignition temperature for non-catalyzed traps, and those that do exceed it do so only for short periods of time. Even temperatures of 300°C to 350°C, which seem capable of significant regeneration for some catalyzed trap designs, are not reached by some- of the vehicles listed and clearly would not be maintained for the lengths of time necessary ------- -38- Table III-3 Exhaust Gas Temperatures for Various Diesel Vehicles as Reported by Commenters Exhaust Gas Commenter (Reference) Vehicle/Engine Test Conditions Temperatures °C General Motors [9, p. 19] Mercedes 300D Opel Rekord Olds 88 Isuzu Chevette VW Rabbit Isuzu Gemini 10-55 mph 10-55 mph 10-55 mph 10-55 mph 10-55 mph 10-55 mph 200-400 125-320 180-260 190-360 190-290 180-340 Volkswagen [A, pp. 27,29] 1.6-liter, naturally aspirated FTP "City" "Highway 160-360 130-320 260-440 Johnson Hatthey [10, p. 80] Turbocharged vehicle Engine Mapping 100-350 Daimler-Benz [2, p. 8] — FTP 100-500 (median-200) T oy ot a [8, p. 14] 2.2-liter Toyota FTP 100-650 (mean-250) Ford 2.3-liter Opel FTP 100-500 [13, p. 10] ------- -39- for successful regeneration for most of the vehicles listed. It is this fundamental problem of low diesel exhaust gas temperatures which has convinced most of the commenters that some form of "positive" regeneration, i.e., some method of specifically creating the requisite exhaust gas conditions for regeneration, is needed. Besides the temperature requirements discussed above, the exhaust gas must also contain at least 3 to 4 percent oxygen in order for regeneration to occur. Because the diesel engine utilizes very high air-fuel ratios, there is normally considerable oxygen in diesel exhaust. However, there is the likelihood that at certain operating modes, such as hill climbing in low gear or at high altitude, there might not be sufficient excess oxygen for regeneration. No commenter expressed much concern about oxygen levels in general. Clearly, the primary concern has been attaining and maintaining the requisite exhaust gas temperatures in the trap-oxidizers. In addition to having to raise exhaust gas temperatures and oxygen levels to minimum levels so that particulate oxidation can be initiated and maintained, it is also necessary to limit the maximum temperatures reached during trap regeneration in order to prevent melting and/or thermal fracture of the trapping material. Vehicle manufacturers reported that they have experienced maximum regeneration temperatures of 1400°C to 1500°C.[2, p. 11; 6, p. 13; 9, p. 33] The melting point of the cordierite material used in ceramic traps is reported to be approximately 1300°C to 1400°C, while metal mesh traps are thought to have lower melting temperatures. [2, p. 11; 6, p. 10; 7, p. 30; 9, p. 33] Accordingly, to prevent trap failure, General Motors stated that its design goal is to limit the maximum regeneration temperatures to 900°C for wire mesh traps and 1100°C for ceramic traps. [9, p. 33] Nissan believes that 900°C is an appropriate design goal for ceramic traps. [7, p. 30] In addition to the possibility of trap melting, rapid and uncontrolled temperature rises in ceramic traps also raise the possibility of trap fracture from thermal stresses induced by thermal gradients within the filter itself. Fortunately, those actions implemented to prevent trap melting should also help ameliorate thermal gradients in the trap as well. The maximum temperature reached during trap regeneration is a function of several parameters. The particulate loading in the trap is very important, as the greater the amount of oxidizing particulate the greater the amount of energy released and thus the higher the temperature within the trap. The exhaust flow rate is relevant as a high flow rate is able to withdraw excessive heat out through the exhaust system much more effectively than a low flow rate. The exhaust gas temperature and oxygen content initiating regeneration are also important since moderate levels can produce a relatively controlled regeneration process while much higher levels can promote rapid and uncontrolled oxidation. ------- -40- A worst-case scenario would involve a heavily loaded trap which is exposed to exhaust that is very hot but devoid of much excess oxygen (such as during hill-climbing or high-altitude operation); under such conditions the particulate would get very hot but would not oxidize. Then, upon a change in engine/vehicle operation which would produce much excess oxygen, the hot particulate could undergo very rapid oxidation with a high probability of trap damage.[6, pp. 10-11] Thus, it can be seen that not only must exhaust gas temperature and oxygen content be maintained above minimum levels so that the regeneration process can be initiated and sustained, but these levels, as well as total particulate loading and exhaust gas flow rate, must also be controlled so as to avoid excessive maximum regeneration temperatures and resultant trap damage. It can be concluded that a satisfactory regeneration system should be able to do all the following. It must be able to initiate regeneration with satisfactory frequency so that the particulate trap loadings do not become excessive. It must have the ability to maintain a sufficiently high, but not excessive, exhaust gas temperature for the time necessary to complete regeneration. Finally, it must be able to provide sufficient oxygen to the trap both to sustain the regeneration process and to avoid oxygen-deficient particulate heating which can lead to trap failure. These are the design goals that any successful regeneration system would have to achieve in-use. 5. Specific Regeneration Mechanisms Now that we have identified the relevant parameters in the trap-oxidizer regeneration process, we can examine the various regeneration mechanisms which have been investigated by the vehicle and trap manufacturers. Most of the systems discussed below have the primary goal of raising the temperature of the exhaust in the trap to the extent that regeneration occurs. As was discussed earlier, there must also be adequate oxygen in the exhaust and the temperature/oxygen conditions must be maintained for a sufficient length of time. However, researchers in this area have found that generating the requisite exhaust gas temperature is the most challenging technical problem. The issues of oxygen content and regeneration time are still important, however, and will be considered at various points in the following discussion. Six regeneration mechanisms will be considered in turn: engine parameter changes, intake throttling, fuel burner, exhaust stroke fuel injection, electrical heating, and fuel additives. Several manufacturers considered the possibility of modifying certain engine parameters as the means of increasing exhaust gas temperature and initiating regeneration. Such a mechanism might have the advantage of requiring no major new hardware. The design change mentioned most frequently was injection timing retard, but ------- -41- both Daimler-Benz and Volkswagen have noted that the retard necessary for the requisite exhaust gas temperature increases would significantly impair fuel economy and performance.[2, p. 3; 4, p. 37] The silence of other commenters on this possibility lends credence to the conclusion that modifying engine parameters is an unacceptable way of initiating trap regeneration. Intake air throttling has probably been investigated as much or more than any other regeneration mechanism. Throttling reduces the overall air flow to the engine and thus reduces the air-fuel ratio of the mixture in the combustion chambers. This lower air-fuel ratio in turn results in higher average combustion gas temperatures and subsequently higher exhaust gas temperatures. The primary advantages of throttling are its relative simplicity and low expense compared to other regeneration systems. However, there were three primary concerns expressed about throttling. First, and most important, was simply whether throttling alone could provide the certainty of reaching regeneration conditions with sufficient frequency so as to avoid excessive particulate accumulation in the trap. GM implied that this was a concern, but did not elaborate.[9, p. 34] Ford determined that utilizing throttling on a 2.3-liter Opel diesel still required relatively high speed/high load operation to reach the necessary exhaust temperatures to regenerate non-catalyzed ceramic monolith traps. For example, at steady-state operation the minimum vehicle speed that resulted in regeneration of the ceramic trap was 55 mph.[13, p. 14] Since ceramic traps might have to be regenerated as often as every 50 miles, there would be much concern over whether such high speed/high load operation could be counted on to occur before the buildup of excessive particulate loadings in the trap. The success of throttling might well hinge on the success of catalytic coatings. As discussed previously, some catalyzed traps at least partly regenerate at temperatures in the 300°C to 350°C range. Throttling would almost certainly produce temperatures in this range for any but the lowest speed/load operations. Thus, to the extent that catalysts can be successfully utilized to lower the necessary exhaust gas temperatures, and assuming that other problems discussed below are solved, throttling should continue to be investigated as a possible regeneration mechanism. A second primary concern with throttling is that by its very nature it reduces the oxygen content in the exhaust gas. This raises the possibility of major trap failure when large amounts of hot particulate which had been exposed to heavily-throttled and oxygen-deficient exhaust is then quickly exposed to hot, oxygen-rich exhaust resulting in uncontrolled oxidation. Clearly this must not be allowed to happen. This concern is so strong that Johnson Matthey, whose catalyzed trap appears to regenerate at temperatures of 300°C to 350°C, commented that throttling is "unacceptable."[ 10, p. 23] The issue may not be so clear-cut, however. Ford hypothesized that the maximum amount of throttling should be limited to an exhaust oxygen concentration of no lower ------- -42- thar. 2 percent as a way to avoid such a problem.[13, pp. 14-15] In additioiij avoiding excessive particulate accumulation in the trap would reduce the likelihood of uncontrolled oxidation. Finally, the possibility of adding additional oxygen to the trap at heavy throttle conditions is a possibility, if it could be done while still maintaining temperatures sufficient for regeneration. Third3 several commenters deplored the loss of driveability during heavy throttling conditions-[4, p. 36; 9, p. 34; 10, p. 23] But no commenter supported its position with any data or analysis and we are unable to deal with this issue. It is likely that trap-oxidizers will generally be utilized on those diesel vehicles with the highest particulate emission rates, the most powerful engines, and the highest performance levels; such vehicles would be more capable of overcoming a slight power loss during throttling than small displacement, less powerful diesel vehicles. Another regeneration system which has received wide attention is the external fuel burner. The concept is to actually ignite an air-fuel mixture near the trap inlet whenever regeneration is required. The combustion raises the exhaust gas temperature to the necessary level. Ford has described two types of fuel burners, air-fed and exhaust-fed burners.[13, pp. 16-17] The air-fed burner utilizes an injector to provide fuel, a pump to supply combustion air, and a glow plug or spark plug to ignite the mixture, all placed just upstream of- the trap inlet. With this design the burner air flow and fuel flow must be carefully controlled to ensure adequate exhaust temperatures for regeneration. The advantages of a burner system are the clear ability to raise exhaust gas temperatures to necessary levels and the lack of any adverse effect on engine performance. But the drawbacks of burner systems are very cleaT—of all the regeneration systems considered the external fuel burner would easily be the most complex and expensive system due to . the additional hardware and controls which would be necessary for successful burner operation. At this time the fuel burner is General Motors' preferred regeneration system.[20] In an attempt to simplify burner operation, Ford also evaluated an exhaust-fed burner. The exhaust-fed burner would be the same as the air-fed burner discussed above except that, instead of utilizing atmospheric air for combustion, the process would rely on the excess air inherent in diesel exhaust. This simplifies the process by removing the need for the supply and control of air for the burner. Since there is much more excess oxygen in diesel exhaust at low speed/low load conditions, regeneration becomes possible even under these conditions. It appears that this type of burner is also workable, but it still retains most of the complexity and expense of any burner system. Of course, all burner systems result in some increased fuel consumption. ------- -43- A fourth type of regeneration system has been proposed by Johnson Matthey and can be termed "exhaust stroke fuel injection." The concept is to create the diesel equivalent of a misfire, with the resulting hydrocarbons lighting-off the catalytic material in the trap and providing sufficient temperature in the trap for regeneration. Johnson Matthey suggests injecting additional fuel into one cylinder at the end of the combustion stroke before bottom dead center and the start of the exhaust stroke. This fuel is cracked into smaller hydrocarbons by the heat and pressure which still exist in the combustion cylinder. These hydrocarbons are then exhausted on the piston upstroke and burned when they reach the catalyst in the trap. This raises the trap temperature and initiates regeneration.[10, p. 23] Johnson Matthey has stated that the exothermic reaction of the hydrocarbons/catalyst light-off produces a temperature rise of approximately 150°C to 200°C. Since their trap begins to oxidize particulate at approximately 350°C, the system can regenerate at exhaust temperatures as low as 200°C. This temperature is reached frequently by all diesel vehicles. It must be noted that the 150°C to 200° C temperature rise would likely not be sufficient for non-catalyzed trap designs. Johnson Matthey utilized a "first generation" version of this system on its recent 50,000-mile durability vehicle that was tested at Southwest Research Institute. A backpressure sensor was used with a read-out placed in the driver's compartment. When the backpressure reached a certain level, the driver operated a manual lever which injected additional fuel into one combustion chamber and initiated the regeneration process. Johnson Matthey attempted 46 regenerations during the course of the durability test, the system did not function completely nine times.[28, p. 15] Johnson Matthey believes that this system deserves serious consideration. Volkswagen was the only vehicle manufacturer to address this system; it stated that "this system shows some promise but as yet is only a system which will cause regeneration to begin."[4, p. 36] Unfortunately, little development work has been done with this concept. The most important requirement would be to automate the system. It is possible that modifications could be made to the injection pump so that when regeneration was desired the pump would automatically inject extra fuel into one cylinder. Two signals would be necessary to initiate the process. First, there would have to be some way of determining when regeneration was required. Johnson Matthey utilized a backpressure sensor in its initial work and this continues to be a possibility. Although backpressure devices of sufficient durability are not now available, alternatives are now being considered. One promising alternative would be an engine revolution counter. A worst-case scenario could be defined to determine the minimum number of revolutions which would require ------- -44- regeneration, and then regeneration could be initiated whenever that level was reached. Even with the Johnson Matthey trap, however, the temperature of the normal exhaust must be at least 200°C, and so the injection pump would also require a signal that the temperature of the exhaust was above 200°C before injecting additional fuel. Finally, some control over the duration of the special fuel injection would be necessary. As Volkswagen pointed out, it is necessary not only to initiate regeneration but also to sustain it. Thus, the pump should continue to inject additional fuel until the oxidation process is completed. • Yet, continuing the extra injection after the regeneration had concluded would simply be wasting fuel. Thus, some standard duration of injection or some measure of the completeness of the regeneration would be necessary. The primary advantage of this regeneration concept is that, like the fuel burner, it can create the conditions necessary for regeneration with certainty throughout almost all " vehicle operating modes (of course this is true only for traps which can successfully utilize catalyzed material) while avoiding much of the complexity and expense of the fuel burner. If indeed the injection pump can be modified to handle the extra injection, the only new hardware needed would be in the sensors and controls discussed above. This is in marked contrast to the fuel burner which would require an additional injector, fuel lines, a spark or glow plug, possibly an external air supply and possibly an exhaust bypass. Volkswagen was the only vehicle manufacturer to comment on the Johnson Matthey system and it concluded its discussion of the concept by stating, "Work is continuing on systems which will monitor criteria indicating the need for regeneration and trigger the activity of this system."[4, p. 37] Clearly, the primary question about this system is whether it can be successfully integrated with injection pump design. A fifth regeneration mechanism which has been investigated is electrical heating. This would involve the placement of an electrical resistance heating element at the trap inlet which would be powered by the vehicle's electrical system and would be able to raise the temperature inside the trap to the proper regeneration level. The advantages of electrical heating are that it can be a relatively simple system without requiring any engine design changes and without requiring any additional fuel combustion. The primary difficulty is its rather large power requirement. In its response of April 1979 to the light-duty diesel particulate NPRM, General Motors stated that without any assistance from any other method, '8.5 kilowatts of power would be necessary to raise the total exhaust of a test vehicle at 25 mph to the 480°C it then believed was necessary for regeneration. GM found that by utilizing a dual path trap, where a flap valve would route only a small part of the total exhaust flow to the path of the trap being regenerated, it could lower the maximum power requirements to 500 watts. Still, GM stated that "such a load is ------- -45- still near the limit of the capabilities of a vehicle electrical system."[15, pp. 116, 119] GM reaffirmed its concern over the necessary power requirements in its recent submission, but did not present any details.[9, p. 34] Volkswagen stated that electrical heating would "probably not be feasible" considering the power requirements.^, p. 37] Toyota, the onl}' other commer.ter to discuss electrical heating, did not express concern about power requirements,[8, p. 23] Given the scarcity of comments concerning electrical heating, it is difficult to judge its potential as a regeneration mechanism. At mini-mum, because of its relative simplicity, it seems to be a "fall-back" option, though it would likely require a more powerful (and thus more expensive) vehicle electrical supply system. Finally, Ford and General Motors both discussed the possibility of utilizing a fuel additive to aid the regeneration process. Ford found that by adding one gram of lead (as tetraethyl lead) to one gallon of diesel fuel, the temperature necessary to regenerate its Corning trap was reduced by over 150°C. The advantage of using a catalyst in the fuel itself is that the catalytic material is distributed on the carbon particles and can have the intimate contact with the particulate which is necessary for maximum ignition temperature reduction. From the standpoint of the vehicle manufacturers, fuel additives are the simplest regeneration mechanisms available since they might not affect vehicle or engine design whatsoever and would likely not add to vehicle cost. But additives have not been shown to be reliable for regeneration under all vehicle operating conditions. The use of additives would raise several as yet unanswered concerns about their effects on engine, trap, and fuel injection system durability. Most important, the use of additives could raise very significant environmental concerns. Lead, for example, is widely recognized as a dangerous environmental contaminant and is one of the six pollutants for which EPA has promulgated Rational Ambient Air Quality Standards. It is possible that other, less objectionable additives could be developed. Regardless of which regeneration system is adopted by vehicle manufacturers to raise exhaust gas temperatures to necessary levels, two other issues must be addressed with respect to the regeneration systems — 1) oxygen supply and 2) sensors and controls. As has been mentioned several times earlier, hot temperature, low oxygen content exhaust can result in uncontrolled regeneration and catastrophic trap failure. Due to the extremes of real-world vehicle operation such conditions would likely take place, for example, during high-altitude or hill-climbing operation. The simplest way to avoid such problems would be to ensure an adequate oxygen supply under hot exhaust temperature conditions. Such a solution should not be difficult, as it is very analogous to the need for extra oxygen in oxidation catalytic converters on gasoline-fueled cars. Johnson Matthey has suggested two ways to ensure sufficient oxygen in the trap. One system uses ------- -46- a gasoline engine air pump to inject air in front of the trap. A diverter valve coupled to the throttle activates the air stream at two-thirds power. This way the extra air is provided only under conditions where high temperature, low oxygen content conditions might occur and is not supplied when it is unnecessary and would only serve to lower the temperature of the exhaust. Johnson Matthey also suggests the possibility of using a simple venturi in the exhaust system to pull in extra air.[10, p. 22] If workable, the venturi would be simpler and cheaper than an air pump. The only vehicle manufacturer to address this concern was Volkswagen, which stated that the "development of a durability system which would add additional air to the exhaust system under high load conditions is necessary."[4, p. 35] It will also be necessary to utilize sensors and controls as part of the regeneration process, regardless of what type of system is ultimately adopted. The most obvious requirements are those which would be used to initiate, the oxidation process. Toyota reported the most research on this subject.[8, pp. 19-20] Given the importance of backpressure on fuel economy and performance, and its direct relationship to trap loading, a backpressure sensor would be an important part of an ideal regeneration system. Unfortunately, pressure sensors available today have insufficient durability and reliability for this usage. This fact has caused researchers to examine other control mechanisms. Both mileage counters and engine revolution counters have been considered as methods of determining regeneration •frequency. Neither is as direct a measure of trap loading as backpressure, but both types of counters are available and durable. General Motors has considered a "particulate loading sensor" but did not describe how such a sensor worked or whether it was successful.[9, p. 32] At this time, it would seem that the mileage and engine revolution counters are most workable. The latter is probably preferable because it would better deal with idle conditions, as the mileage counter would not account for idle. All of these mechanisms are ones which would only signal when a regeneration ought to occur, they would not indicate whether a regeneration was possible. For many regeneration systems, such as throttling or exhaust stroke fuel injection, regeneration can still take place only when the exhaust gas stream is at a certain temperature before the operation of the regeneration mechanism. Thus, there would also have to be a signal when the exhaust gas temperature was high enough for the regeneration process to begin. This would require a temperature sensor in the exhaust. This should not be a technical problem. Whether or not these initiation and control mechanisms can be handled mechanically or whether they will have to be electronically controlled is not yet clear. Volkswagen believes that "an electronic control system which can interpret an exhaust backpressure map relating engine speed, load, and power" will be required. [4, p. 47] GM also mentioned the need for electronic controls under the burner regeneration scenarios.[9, p. 44] Given ------- -47- the sophistication of electronics systems which have been developed for three-way-catalyst, closed-loop systems on gasoline-fueled cars, it would not seem overly difficult to develop electronic controls over exhaust gas temperature, engine revolutions, mileage, etc. and possibly over backpressure and particulate loading as well. In conclusion, several regeneration systems have been investigated though few were described in depth to EPA. Two regeneration mechanisms, fuel burners and electrical heating, are definitely workable, but the former is both complex and costly and the latter would likely require more powerful and expensive electrical supply systems. They may be necessary for non-catalyzed traps. Intake air throttling is well understood, and may be feasible if catalyst systems can lower the necessary exhaust gas temperatures and if adequate oxygen can be maintained during throttling. For catalyzed traps, Johnson Matthey's exhaust stroke fuel injection system is promising and deserves further investigation. The likelihood of utilizing fuel additives or engine parameter modifications as the primary regeneration mechanism is small. No matter what regeneration system is ultimately adopted, an adequate oxygen level must be maintained at high temperature operation. This will likely require either an air pump or venturi in the exhaust. Finally, sensors will be required to initiate and control the regeneration process with temperature, engine revolution, and possibly backpressure sensors being of most importance. Electronic control of these parameters may be necessary. D. Durability During the original particulate rulemaking, EPA considered durability to be the most critical unresolved technical issue with respect to trap-oxidizer development.[16, p. 14498] At that time the best durability that had been reported was 12,800 miles by General Motors for a metal mesh trap.[12, p. 51] EPA's position at that time was that the primary reason there were few positive durability results was that few resources had been expended on durability testing while other more basic issues had been the focus of trap development programs.[16, p. 14498] Clearly trap-oxidizers must be durable for the useful life requirements for light-duty vehicles and light-duty trucks. Several manufacturers have submitted information on the durability of various trap designs, and the following discussion will again be divided into sections on ceramic and wire mesh trap designs. We will not -attempt to summarize, the histories of all of the trap-oxidizers which have been submitted to EPA for two reasons. Frist, it would simply be too burdensome. Second, and more importantly, such an analysis would not be particularly helpful. In the development of any new technology, there will likely be many failures before success is achieved. Multiple failures do not prove that success is impossible, yet positive demonstrations ------- -48- tend to indicate that success is probable. There have been many trap failures during durability testing as well as many promising results. In identifying the most probable trap designs, the successful tests are most relevant. The failures will be discussed only if their examination aids the analysis of a particular design. 1. Ceramic Traps Three manufacturers reported on the durability of ceramic monolith traps in some depth—Daimler-Benz, General Motors, and Ford. Other manufacturers had either not seriously undertaken durability testing of ceramic monolith traps or else had not yet reached the point in their programs where durability testing was a priority. Daimler-Benz has reported the most promising durability data for ceramic monolith traps. [2, p. 7] They were able to achieve over 33,500 miles of durability accumulation on an unidentified vehicle equipped with a Corning ceramic monolith trap. The emission levels for this vehicle/trap system at various points during the mileage accumulation are shown in Figure III-14[2, p. 7] taken from Daimler-Benz1 submission. The data corresponding to the ceramic monolith trap are identified by x's. As can be seen, the particulate emissions for this vehicle were consistently maintained around 0.05 g/mi, and the NOx emissions were generally well below 1.0 g/mi, the level that, barring changes in the Clean Air Act, diesel passenger cars will have to meet in 1985. Also worthy of note is that the graph supplied' by Daimler-Benz was dated November 26, 1979, well over two years ago. Daimler-Benz reports several qualifications with respect to the use of this data. First, the standard AMA durability cycle was not used in the mileage accumulation; instead, Daimler-Benz used a "special driving cycle" which they did not describe. Second, Daimler-Benz retarded injection timing (in order to raise the exhaust gas temperatures for regeneration) to a degree that it considers unacceptable for production vehicles. Finally, and most importantly, Daimler-Benz was not able to duplicate the positive results discussed above with "other vehicles equipped with basically identical trap-oxidizers." For example, they report that a second trap was "mechanically destroyed " at approximately 3,000 miles and a third trap was "thermically destroyed" at approximately 3,700 miles. A fourth trap lost its collection efficiency after less than 1,000 miles. The fact, that one trap survived 33,500 miles in Daimler-Benz' testing is an important indicator that such traps have some potential of lasting 50,000 and 100,000 miles. The fact that this trap was so durable over 2 years ago is also impressive. Unfortunately, Daimler-Benz has not stated whether the testing of the successful trap continued, failed, or was simply halted. It ------- ..•¦•A (••«« »• ¦! Figure 111-14 • •*»««l»**»t •••'• •••••••ft. ••••.•!•••» .••••*••• • ••»••?«•. • t •« M ^ I : - • • ' : ; ! 1 * " ; ' : : : " ''•'" ! ••:••"!¦— I : ' • : : I : J • ! • . * • 4 : ' ¦ 1 : 1 • • • • » : 1 : »- : ?—t—i—: ; ' • i ¦:.. LJ-' : i i i • I I ¦ * • « • : 1 :. . * i : j i ¦ : { : f : T : | : ' • ¦ ¦ 4- :• •:..j j—L_- ft • i "' •; /: — • • • X ¦ For assessment of these results it has to be..rioted .thati ; i ; ; ( - Special Driving Cycle (not AMA-Cycle) vith-fp;dsitive z-e-j-j generation of the soot filter: City 80 # +.-;Autobihn 20#.' with the following schedule: k days city delving,'_.l day...; " I m * : • • ' « Autobahn Drawbacks of the system used: i: PH—0v6-i (g/ki-- ;¦• * I ' -7-O.iH Retarded begin of injection necessary, thus•worsened • - j- combustion Li i—. .;I. i higher noise . i 5 : i ; ' w .<••••• • • • • • —» worsened cold start characteristics ' . ! i risk of damage for cylinder head gasket ~j ! increase of back press, up to>1 bar caused by soot accumulation resulting in deteriorated combustion j ¦« pover loss, may lead to stalling j. 1 risk of mechanical damages wlch ' ¦ Fiihr Ceiamfc \kh I—~ I— —I ..S...L.1.32 r »i 18 H2U-: - 30 • I -' » * t •42 Running Distance Durability test results with sand- wich and ceramic soot filter VINA. 26.11.79 ------- -50- also has not reported any more recent durability data in the two years that have passed, except to describe a test program in Denver the results of which have not been submitted to EPA. The only conclusion that can be drawn is that one ceramic monolith trap survived at least 33,500 miles over two years ago. Before continuing our discussion of ceramic monolith trap durability, we must address one other feature in Figure 111-14, which was taken directly from Daimler-Benz' submission to this study. We have just discussed the ceramic monolith durability data indicated in Figure 111-14 by the x's. But it can also be seen that there are data for a "sandwich filter," most likely a wire mesh trap, indicated by small squares. It appears that this trap accumulated over 55,000 kilometers (or over 34,000 miles) of durability testing as of late 1979. Yet Daimler-Benz does not mention these data anywhere in its submission. We regret that we will not be able to include these data in the discussion on wire mesh traps. General Motors reported durability testing with ceramic monolith traps.[9, p. 10] Its most impressive data involved dynamometer testing. GM states that ceramic monoliths have survived simulated mileages up to 37,200 miles on dynamometers. GM points out that "these were performed under controlled laboratory conditions. The simulated AMA duty cycle was not as rigorous or unpredictable as real-life driving, the traps were not subjected to the vibration and temperature extremes encountered in a vehicle, and the system could be shut down automatically if any of the monitored parameters indicated a potential problem."[9, p. 10] GM points out further that no ceramic monolith has survived past 1860 miles in its vehicle testing, and that during a recent Denver test program no ceramic trap survived the entire trip and 18 traps failed.[9, p. 10] From an examination of GM's subsequent submission of test data sheets it appears that the trap failures GM experienced were generally due to regeneration occurring with too much particulate in the trap or due to operation at high altitude.[17, p. 9B] We have discussed earlier the likelihood of trap failure when the trap is overloaded. Similarly, GM does not mention whether precautions were taken to avoid low oxygen conditions which could lead to uncontrolled regeneration. At high altitude the low oxygen problem is even more likely to occur. Despite these problems, GM does report successful ceramic monolith operation on at least one vehicle in Denver. The vehicle was an Oldsmobile Omega with the new 4.3-liter, V-6 engine. The regeneration system was an inline fuel burner. Quoting GM: "After three early (50-100 km each) trap failures on a Denver test trip, modifications were made which resulted in successful operation in Denver and at altitudes up to 11,000 feet."[17, p. 10A] ------- -51- GM's problems with obtaining good durability with ceramic monolith traps may actually be a problem with regeneration control. No trap can survive uncontrolled regenerations due to particulate overloading or oxygen deficient/oxygen rich conditions. GM's 37,200-mile dynamometer test shows that ceramic monoliths can survive several hundred regenerations if those regenerations are controlled properly. As discussed in a preceding section, no manufacturer has yet been able to control on-board regenerations successfully. Ford tested a 2.3-liter Opel diesel equipped with a Corning ceramic monolith trap. A total of 10,000 miles was accumulated with normal highway usage. Ford regenerated the trap every 100 miles on-board by operating under high speed/high load conditions. After 10,000 miles had been reached, Ford began using the AMA durability cycle for mileage accumulation, continuing to use high speed/high load operation to regenerate the trap every 100 miles. Early in this process the trap cracked and failed. Ford attributes the failure to thermal shock.[6, p. 6] No explanation was offered as to why the trap failed so soon after AMA testing began when it had been performing well before. It is possible that some on-board regeneration was naturally occurring during the course of the highway operation, thus slowing the loading of the trap under those conditions, while during the AMA testing such was not occurring and the trap was overloaded prior to regeneration. EPA is in the process of durability testing a Corning ceramic monolith trap on a Mercedes 300 SD. As of February 10, 1982, the trap had maintained 90 percent collection efficiency through 15,000 miles of durability testing. Throttling is being utilized for regeneration and no difficulties have arisen during the first 18,000 miles of operation.[27, pp. 1-3] In summary, the vehicle durability testing by Daimler-Benz and Ford and the ongoing EPA testing indicate that with control over the regeneration mechanism the ceramic monolith trap has the potential to survive the vehicle environment for thousands of miles. The dynamometer testing by General Motors supports this thesis. Alternatively, the vehicle testing by General Motors shows that the durability of ceramic monolith traps is very poor in real-world operation with imperfect controls over the regeneration process. Clearly the durability of a trap-oxidizer is very dependent on the efficiency of its regeneration system. 2. Wire Mesh Traps The two wire mesh traps which have been discussed in this study—the Johnson Matthey and Texaco designs—have had durability results reported to EPA. Since all of the wire mesh durability data reported to EPA have identified the trap manufacturers by name, the Johnson Matthey and Texaco designs will be discussed in turn. ------- -52- The first durability testing reported for a Johnson Matthey trap design was on a JM4 trap in a program involving Volkswagen.[4, p. 25] This trap' was successfully operated on the road for approximately 12,500 miles during 1979. At 12,500 miles the trap was reducing particulate levels by 52 percent, and HC and CO levels by 60 percent. [10, p. 7] At this point, the trap sat dormant for approximately 4 months. When testing resumed another 10,000 miles were accumulated before testing proved that the catalyst material had failed. Particulate levels had increased throughout the latter 10,000-mile accumulation, and analysis determined that these increased levels were due to the catalyst washcoat becoming brittle and flaking off of the wire mesh. Despite the fact that the JM4 trap ultimately failed, Johnson Matthey was encouraged by the results and continued its optimization program. This culminated in their JM13 design, .which involves a graduated wire mesh bulk density, a graduated surface-to-volume ratio, and an improved washcoat formulation. By the spring of 1981 Johnson Matthey was confident that their trap design was sufficiently optimized to attempt a 50,000-mile durability test. The program was initially described to EPA in Johnson Matthey's original submission to this studj'.[10s p. 24] This 50,000-mile testing was completed in January 1982 and Johnson Matthey has reported the results to EPA in a letter to the Administrator dated January 25, 1982.[18, p. 1] Johnson Matthey contracted with the Southwest Research Institute, an independent facility, to perform the durability testing and emission tests were performed per Federal Register requirements. The vehicle used was a 1981 Volkswagen Rabbit, with a 1.6-liter, 4-cylinder engine. The car was tested by Southwest as delivered with the only changes being the addition of the JM13 trap and the modifications necessary for Johnson Matthey's prototype exhaust stroke fuel injection regeneration system. Johnson Matthey has described the vehicle changes: "The trap itself, 14 inches long and 5 1/2 inches in diameter, was easily mounted in the exhaust pipe next to the gear shift linkage in the existing floor hump. Insulation was wrapped around the car and all piping back to the exhaust manifold. An air pump and diverter valve were installed using a mechanical link up to a microswitch to activate the valve allowing air into the exhaust at two-thirds throttle or higher. The regenerator, in this case manually operated by a lever in the car, was installed. A check valve and ball valve were installed on tees between the injector lines for cylinders two (2) and four (4)."[10, p. 24] The fuel used during the testing conformed to EPA durability specifications for diesel fuel. The durability trap/vehicle system successfully completed the 50,000-mile AMA durability cycle testing. Tables II1-4 and III-5 were provided to EPA by Johnson Matthey and summarize the emissions and fuel economy results for the baseline and trap ------- -JJ- Table III-4 DURABILITY TEST RESULTS AT SOUTHWEST RESEARCH INSTITUTE VEHICLE ~ VOLKSWAGEN RABBIT CATALYST - JM-13/II UNDERFLOOR FEDERAL TEST PROCEDURE CONDITION NOMINAL MILEAGE PARTICULATE G/MILE HC G/MILE CO G/MILE NOx G/MILE SULFATE G/MILE FUEL ECONOMY MPG BACK FRESSUR MM HG 1985 Standard 0.20 0.41 3.4 1.0 - Baseline 0 0.225 0.24 1.01 0.90 0.0036 37.9 19 Baseline 5,000 0.259 0.19 0.82 0.89 0.0055 36.2 Baseline 10,000 0.211 0.19 0.84 0.90 0.0137 37.7 3aseline 15,000 0.227 0.23 0.92 0.81 0.0110 38.1 Baseline 20,000 0.275 0.19 0.79 1.00 0.0124 36.9 Baseline 25,000 0.220 0.21 0.87 0.81 0.0086 38.5 Baseline 40,000 0.213 0.17 0.85 0.85 0.0021 37.1 Baseline 50,000 0.277 0.22 0.92 1.04 0.0093 38.3 MEAN 37.6 Catalyst 0 0.113 0.05 0.16 0. 79 0.0018 37.6 21 Catalyst 5,000 0.135 0.05 0.18 0.89 0.0073 35.6 41 Catalyst 10,000 0.129 0.06 0.24 0.94 0.0110 35.7 41 Catalyst 15,000 0.111 0.10 0.31 0.79 0.0095 37/6 34 Catalyst 20,000 0.111 0.05 0. 27 0.87 0.0048 35.1 34 Catalyst 25,000 0.114 0.11 0.48 0.87 0.0032 37.9 32 Catalyst 30,000 0.144 0.13 0.49 0.82 0.0098 38.4. 52 Catalyst 35,000 0.174 0.07 0.45 0.83 0.0244 37.9 50 Catalyst 40,000 0.099 0.10 0.49 0.92 0.0017 35.5 24 Catalyst 45,000 0.153 0.11 0.56 0.94 0.0066 34.3 60 Catalyst 50,000 0.167 0.10 0.55 0.86 0.0045 36.5 41 Cat. Repeat 50,000 0.163 0.10 0.57 0.97 0.0039 35.3 41 MEAN 36.5 ------- -54- Table III-5 DURABILITY TEST RESULTS AT SOUTHWEST RESEARCH INSTITUTE VEHICLE - VOLKSWAGEN RABBIT CATALYST - JM-I3/II UNDERFLOOR HIGHWAY FUEL ECONOMY TEST CONDITION MILEAGE PARTICULATE G/MILE HC G/MILE CO G/MILE NOx G/MILE SULFATE G/MILE FUEL ECONOMY MPG Baseline 0 0.137 0.16 0.48 0.60 0.0030 51.7 Baseline 5,000 0.166 0.06 0.37 0.62 0.0594 48.5 Baseline 10,000 0.151 0.08 0.40 0.61 0.0151 49.7 Baseline 15,000 0.143 0.08 0.43 0.55 0.0101 49.3 Baseline 20,000 0.161 0.08 0.39 0.66 0.0112 45.4 Baseline 25,000 0.132 0.08 0.40 0.56 0.0093 50.1 Baseline 40,000 0.144 0.07 0.39 0.65 0.0029 49.0 Baseline 50,000 0.171 0.10 0.49 0.70 0.0102 MEAN 51.0 49.3 Catalyst 0 0.107 0.02 0.02 0.55 0.0100 50.2 Catalyst 5,000 0.187 0.01 0.05 0.58 0.0215 48.2 Catalyst 10,000 0.267 0.02 0.10 0.63 0.0383 '45.1 Catalyst 15,000 0.150 0.02 0.26 0.56 0.0328 50.1 Catalyst 20,000 0.200 0.02 0.06 0.63 0.0411 50.2 Catalyst 25,000 0.077 0.03 0.13 0.58 0.0097 49.6 Catalyst 30,000 0.096 0.03 0.18 0.62 0.0167 49. 4 Catalyst 35,000 0.124 0.03 0.16 . 0.62 0.0059 49.2 Catalyst 40,000 0.060 0.02 0.15 0.67 0.0048 47.0 Catalyst 45,000 0.124 0.04 0.21 0.62 0.0022 45.1 Catalyst 50,000 0.105 0.06 0.21 0.66 0.0123 MEAN 48.7 48.4 ------- -55- testing over the Federal Test Procedure and Highway Fuel Economy Test.[18, pp. 4-5] Particulate reductions over the FTP ranged from 39 percent at 10,000 miles to 60 percent at 20,000 miles; the trap was 40 percent efficient at the end of the 50,000 miles. These efficiencies are not very high, but because of the low engine-out particulate levels of the Rabbit, Johnson Matthey only designed the trap to be 50 percent efficient.[10, p. 24] As Table II1-4 shows, with the trap the vehicle never exceeded the 0.2 g/mi level which was the design goal of the system. The particulate results for the highway test were not as encouraging. At the 0-mile and 50,000-mile test points, the trap particulate levels were somewhat lower than the baseline levels. But at several interim test points the trap levels were actually higher. This is a source of concern and is undoubtedly due in part to the higher sulfate levels with the catalyzed trap. The successful completion of the Johnson Matthey trap-oxidizer system is very important. It shows that the basic JM13 design can survive the vehicle environment for 50,000 miles if regeneration is successfully controlled. It proved the general durability of the Johnson Matthey filter structure, catalytic coating, and mounting system and brings the process forward to the point where vehicle manufacturers can seriously attempt to integrate traps and on-board regeneration systems into their diesel vehicles. General Motors received 11 Johnson Matthey traps for testing during the period from October 1980 to April 1981. None of these traps performed satisfactorily with the longest durability trap lasting only 1,290 miles.[9, p. 17] Six of these traps were intended to be self-regenerating traps, i.e., requiring nothing more than high vehicle speeds and loads for regeneration. Given the difficulties in assuring regeneration without the aid of additional heat or hydrocarbons, it may not be surprising that these traps ultimately failed. Johnson Matthey has even come to the conclusion that it is necessary to have some form of positive regeneration system to inhibit trap overloading. The other five Johnson Matthey traps were to be regenerated by intake air throttling. As has been discussed above, one primary problem with throttling is that it tends to starve the exhaust of excess oxygen just when the trap requires it for regeneration. Accordingly, at first particulate can get very hot but not oxidize due to lack of oxygen, leading to uncontrolled oxidation when oxygen rich exhaust enters the hot trap. GM does not offer enough information for us to determine exactly what the failure modes were for each of the traps regenerated with throttling, but there was one trap failure for which some information was provided. Referring to trap JM-13-1 in their original submission.[9, p. 17] GM's subsequent submission of data sheets states the following: "This trap would not regenerate in early testing, even at speeds up to 88 km/hr. ------- -56- After accumulated particulate increased backpressure to about 8 kPa, regeneration would occur, but still required speeds of 80 km/hr or higher. In attempts to regenerate at lower speeds, particulates continued to accumulate, overloading the trap and increasing backpressure. When regeneration did finally occur, the heat of combustion of the particulates melted the trap (at about 1,240 miles)."[17, p. 5F-1] Thus, at least in this case of a trap/throttling system, GM agrees that the primary problem was regeneration with an overloaded trap. Thus, again, the problem is not so much the durability of the trap material and design itself but with the inability to control the regeneration conditions to acceptable levels. The only two commenters to address the durability of Texaco's wire mesh trap design were Texaco and General Motors. Texaco reported the results of two trap durability programs.[11, pp. 2-3] The first involved a Texaco trap in the exhaust system of a dynamometer-mounted 5.7-liter Oldsmobile diesel engine. Particulate was collected under 40 mph steady-state conditions. The trap survived for the equivalent of 30,800 miles before being damaged during a regeneration. This trap was regenerated every 200 miles so the trap successfully underwent approximately 150 regenerations before failing. Texaco offered no analysis of the failure. This trap maintained its collections efficiency over the entire test while exhaust gas backpressure rose slightly with mileage. Texaco's second durability program also involved a Texaco trap and a 5.7-liter Oldsmobile engine, but in this case, the vehicle was driven on the road at 50 to 55 mph to accumulate mileage. After approximately 2,500 miles one filter cartridge of the two-cartridge trap was replaced with a slightly different design in order to eliminate filter matrix compaction. The trap survived a total of 10,000 miles before a portion of the filter was damaged during regeneration. This trap was regenerated every 150 miles, so it survived approximately 65 regenerations. Again, the trap maintained its collection efficiency throughout the test except for one incomplete regeneration which temporarily decreased efficiency.[11, p. 6] General Motors reported on the durability testing of a Texaco wire mesh trap coated with a catalyst material to aid regeneration. [9, p. 14; 17, p. 3A] This trap was placed in the exhaust manifolds of a 5.7-liter Oldsmobile vehicle. No positive regeneration system was utilized on the vehicle. Quoting GM: "This system would regenerate on the standard AMA test cycle, but it would not regenerate on a modified cycle from which the more demanding modes were deleted. After 19,000 miles, the trap was loaded so heavily that it had to be removed from the vehicle and "regenerated" in an oven before the durability test of the metal mesh could be continued. Because it had been anticipated that regeneration would not occur without some demanding driving modes, ------- -57- this system was never intended as a candidate for production, but it was a means of evaluating durability of metal mesh as a trapping material without the need for a complicated regeneration system."[9, p. 14] This trap accumulated 34,100 miles before failing due to disintegration of part of the wire mesh, resulting in "excessive backpressure and poor performance."[17, p. 3A] Two points should be made with respect to this durability test. Most important, the fact that the trap became overloaded at 19,000 miles and had to be regenerated in an oven is not a problem with trap durability; clearly it was due to the lack of a positive regeneration system. As GM stated, the system, lacking any positive regeneration method, was never intended as a production system, but rather was simply a means for evaluating wire mesh durability. However, the fact that the trap did survive 34,000 miles without a positive regeneration system indicates that with such a system the trap might well have lasted 50,000 miles or more. It is also worthwhile to note that this durability testing ended in October of 1980,[17, p. 3A-24) thus 1-1/2 years have been available with which to continue work with this design. Both the Texaco and General Motors durability testing indicates that the Texaco trap design is capable of surviving many thousands of miles of on-road operation. The GM results, i.e., the trap surviving 34,000 miles with no positive regeneration system and having to take the trap off the vehicle just once to externally regenerate it, are the most promising. E. Overall Evaluation The previous sections of this chapter have examined the most important technical issues with respect to trap-oxidizers— efficiency, backpressure, regeneration, and durability. This section will summarize the conclusions from the preceding analyses and will provide an overall evaluation of the current status of trap-oxidizer development. The particulate collection efficiencies of new traps are quite good. The consensus of many commenters was that zero-mile ceramic monolith traps are approximately 70 to 90 percent efficient and that zero-mile wire mesh traps are 50 to 80 percent efficient, regardless of whether either trap design is catalyzed or not. The efficiencies of both types of traps can be varied by the sizes of the traps and by the relative porosities of ceramic monolith traps and the relative mesh densities of wire mesh traps. Generally, the zero-mile backpressure levels of the various trap designs were found to be acceptable to the vehicle manufacturers, with the one possible exception being catalyzed ceramic monolith traps. A very limited data base indicates that catalyzing can significantly increase zero-mile backpressure levels of ceramic monolith traps. Generally, the wire mesh traps ------- -58- exhibited lower zero-mile backpressure increases than ceramic monolith designs. Even more important, there was a near consensus among the commenters that the zero-mile efficiency and backpressure characteristics of the various trap designs could be maintained throughout repetitive regenerations. General Motors, Ford, and Nissan all provided strong evidence supporting this conclusion for ceramic monolith traps, and Johnson Matthey and Texaco both provided similar data for wire mesh designs. Volkswagen was the only dissenter on this point. Its position was based on air flow tests as opposed to actual trap/vehicle tests which the other manufacturers relied on. The submissions were in fair agreement on the conditions necessary for the initiation of trap regeneration. Non-catalyzed traps, regardless of design, require minimum exhaust gas temperatures of 500°C to 650°C while some catalyzed traps only require temperatures in the 300*0 to 500°C range. Oxygen levels in the exhaust must be 3 to 4 percent or greater, and the re-quisite temperatures and oxygen levels must be maintained for 2 to 10 minutes for sufficient regeneration to occur. The comments were also consistent on the need to control the maximum temperatures reached in the trap during regeneration. The trap inlet exhaust gas temperature and oxygen content, total trap particulate loading, and exhaust gas flow rate must be controlled such that excessive regeneration temperatures are avoided. (General Motors suggested maximums of 1100cC for ceramic monolith traps and 900°C for wire mesh designs.) Several possible regeneration systems have been identified. Research continues on the development of a catalytic treatment which could significantly reduce the exhaust gas temperature required for regeneration, but at this time all trap designs need some form of positive regeneration mechanism. Two concepts, fuel burners and electrical heating, appear to be technically feasible but are relatively complex and would likely involve costly vehicle modifications. They may be the best candidates for non-catalyzed traps which need relatively high exhaust gas temperatures. There are' problems with utilizing intake air throttling as a regeneration initiation mechanism, but it might yet prove to be acceptable for catalyzed traps where the lower requisite exhaust gas temperatures would reduce the need for excessive throttling. Johnson Matthey's exhaust stroke fuel injection, if it can be achieved through internal injection pump modificationsj may well be the most promising mechanism for catalyzed traps which only require moderate exhaust gas temperature increases. Regardless of which regeneration system is used, sufficient oxygen levels must be maintained in the trap during periods of high exhaust gas temperatures. This may well require an air pump or some other mechanism for oxygen addition to the trap. Except ------- -59- for Johnson Matthey's recent suggestion, all of the regeneration systems described above have been considered for several years now and are well understood. Probably the most undefined area of research involves the sensors and controls which would be an integral part of any regeneration system. The ideal sensors for the initiation of the regeneration process would be trap loading or backpressure sensors. At this time such sensors are not available, however, and engine revolution and mileage counters are being examined instead. Temperature sensors would also be required, but these should not pose any great technical problems. Integrating proper sensors and controls within a total regeneration system onto vehicles is the last major technical problem in trap-oxidizer development. Many promising durability data were reported to EPA. Daimler-Benz submitted information on a ceramic monolith trap which accumulated 33,500 miles of on-vehicle durability as of late 1979. Daimler-Benz did not state whether the trap testing continued, failed, or was simply halted. Ford ran a ceramic monolith trap on a vehicle for 10,000 miles before trap failure. EPA has an ongoing ceramic monolith durability program with 18,000 miles of successful operation as of February 1982. General Motors simulated over 37,000 miles on a ceramic monolith trap under dynamometer testing, though it has not achieved good durability on vehicles on the road. Johnson Matthey reported the first successful 50,000-mile durability demonstration of trap technology. This demonstration proved the general durability of Johnson Matthey's wire mesh filter structure, catalyst and washcost formulation, and mounting system. It did not involve an entire vehicle system as regeneration was initiated by the driver and involved a very crude, first-generation design. Nevertheless, the program showed that durability can be achieved if regeneration is properly controlled. General Motors recorded over 34,000 miles on a Texaco trap with a catalyst coating before the trap failed. The trap had to be externally regenerated at 19,000 miles; it is likely that both the 19,000-mile regeneration and the ultimate failure were due to overloading since no positive regeneration system was used during the testing. Texaco reached 30,000 miles on a non-catalyzed trap in a dynamometer simulation and 10,000 miles during vehicle testing. Despite the fact that nearly all of the durability testing reported to EPA resulted in trap failures, it appears that trap durability is not the primary problem so much as is control over the regeneration process. It has been shown that both ceramic monolith and wire mesh trap designs can survive the vehicle environment for tens of thousands of miles, and up to 50,000 miles for the Johnson Matthey design, if the regeneration process is properly controlled. ------- -60- In conclusion, the data submitted to EPA are encouraging and indicate that substantial progress has been made in the last two years. Efficiency and backpressure are no longer serious problems even after repetitive regenerations.. The evidence indicates that the durability of various trap designs may be acceptable if regeneration can be adequately controlled, though improvements are both possible and likely being made. The most important area of ongoing research is regeneration initiation and control. This is the most significant remaining technical problem. ------- -61- CHAPTER IV LEADTIHE A. Development Leadtime The previous chapter summarized the current status of trap-oxidizer development. It concluded that trap-oxidizers hold significant promise but that technical improvements must still be made. The issue this section will address is how much leadtime is still required for the vehicle manufacturers to optimize trap-oxidizer systems to the point where assurance testing of the most promising trap system concepts can begin. Projection of future technical advances is admittedly a difficult task. Yet the determination of achievable emission reductions is an integral part of motor vehicle emission regulation and Congress has generally delegated such determinations to EPA. Uncertainty and lack of proof are inherent in predicting technical improvements. If technological progress could indeed be proven, then the improvements would not be true "progress" so much as simply application of existing technology. Given the data which have been submitted to EPA, and our experience in motor vehicle emission technology issues, we believe that vehicle manufacturers are near the stage where the most promising trap-oxidizer systems can be identified and can begin to be integrated into overall engine and vehicle designs. This position is based on the following considerations. Most importantly, trap-oxidizers are at a very advanced stage of development. Trap and vehicle manufacturers have been performing research and development of traps for over four years and have resolved most of the basic technical issues. As was shown in Chapter III, significant advances have been achieved with respect to trap-oxidizer efficiency, backpressure, and durability for both ceramic monolith and wire mesh trap designs. The efficiency and backpressure characteristics of traps have advanced to the stage where they are not only acceptable at zero-mile levels but are also able to be maintained throughout mileage accumulation and repetitive regenerations. Durability was a major concern when the original particulate final rule was published; at that time the best durability that EPA was aware of was 12,800 miles.[12, p. 51] Since that time, manufacturers have reported several on-road vehicle tests and dynamometer simulations where traps have .survived upwards of 30,000 miles, and it is significant to note that many of these durability tests were performed in late 1979 and early 1980 and that much time has passed for even further improvements. Johnson Matthey has produced a trap design which, in combination with a rather crude regeneration system, has completed a 50,000-mile durability test. It is clear that significant progress has been made with respect to trap ------- -62- durability, and that the primary concern with durability is whether a regeneration system can be designed with sufficient control so as to maintain trap durability. As concluded in Chapter III, the primary technical task facing vehicle (and trap) manufacturers is the development of positive regeneration systems, including accompanying sensors and controls, which can be successfully integrated with diesel engine and vehicle design. Although no one regeneration system has yet been developed which is workable, simple, and inexpensive, the conditions and controls necessary for successful trap regeneration have been defined. Several candidate regeneration systems have been identified and tested. Some systems, such as fuel burners and electrical heating, appear quite workable with their primary drawbacks being higher cost and/or the need for greater vehicle modifications. Other systems, such as intake air throttling and exhaust stroke fuel injection, are much more promising but as yet are not completely proven. Still, all of these concepts are now well understood, and the hardware necessary for their utilization is generally available. For example, a fuel burner system would require an injector, a fuel pump, an air pump, a glowplug or sparkplug, and possibly an exhaust bypass, along with the requisite controls. Throttling would require a throttling motor with the necessary controls. Basically, these hardware items are all available off-the-shelf today. Probably the most undefined area involves the sensors and controls which would be used with any regeneration system. Even here manufacturers have identified many possibilities, and the experience with electronic controls on gasoline-fueled vehicles should be of great assistance. Now that more basic concerns such as efficiency, backpressure, and durability have been resolved, vehicle manufacturers will be able to concentrate their efforts on optimizing and integrating regeneration systems. Based on the solid progress of the last four years in trap-oxidizer development, and the narrowing of the technical areas where research need be concentrated, we believe it is quite reasonable to expect progress to continue and solutions for on-board regeneration initiation and control to be found in the near future. Once complete regeneration systems are developed, the vehicle manufacturers can proceed with assurance testing in the field in order to comprehensively evaluate the entire trap/regeneration system design in-use. It is not necessary that the manufacturers have production-ready trap systems available for the assurance testing fleets, since assurance testing is itself a part of the final evaluation process. Rather, the manufacturer must select the most promising trap design/regeneration system combination(s) so that the assurance testing process may begin. The manufacturer may need to include more than one concept in its assurance testing if it is unable to identify one most promising concept, or if it wants to be "safe" in case of failure of any particular design. Our analysis of the time necessary for assurance testing leaves ------- -63- the manufacturer enough latitude to perform the testing in two separate phases, so improvements may be made in the midst of the program. The technical advances which still need to be achieved do not appear overly formidable or unreasonable in light of the technical capability of the automotive industry in other areas of engineering. One commenter quotes a top General Motors engineer as saying that the company is now able to produce a different engine model from scratch in two years.[19, p. 18] GM has stated that its first two diesel engines, the 5.7-liter and 4.3-liter (which has since been replaced by a newer 4.3-liter design) engines introduced in 1978 and 1979, respectively, both took only three years to develop.[15, pp. 129-130] Finally, and most analogous to the issue at hand, it is' important to consider the requisite trap-oxidizer improvements in light of the achievements manufacturers have made with respect .to emission control on gasoline-fueled passenger cars. Beginning with most passenger cars sold in California in 1980 and extending to nearly all passenger cars nationwide in 1981, the vehicle manufacturers have integrated sophisticated electronics on-board in order to maintain tight control over the air-fuel ratio based on the oxygen level in the exhaust and other engine parameters. This precise control of air-fuel ratio is necessary for successful operation of three-way-catalysts to oxidize HC and CO and reduce NOx simultaneously. Control over the initiation and extent of particulate oxidation during regeneration may or may not entail similar levels of electronics and overall sophistication, but in any case the experience the manufacturers have gained in electronic controls on . gasoline-fueled vehicles should aid their work on trap regeneration systems. This experience should indicate that it is highly likely that success will soon be achieved. Given that 1) trap-oxidizer development has advanced to the stage where only regeneration remains as a major technical problem, 2) that significant progress has taken place during the last four years in all areas of trap design and that research may now be concentrated on the issue of regeneration, and 3) that the necessary technical improvements are not unrealistic given the technical capabilities of the automotive manufacturers with respect to engine design and emission control, the EPA technical staff projects that another one and one-half years of development leadtime is sufficient for the vehicle manufacturers to identify and optimize regeneration systems for the beginning of assurance testing. Since the data reported to EPA by the vehicle manufacturers were generally inclusive up to about the summer of 1981, the one and a half years of development leadtime projection would result in assurance testing beginning in January 1983. ------- -64- Th e . only vehicle manufacturer to comment directly on the issue of development leadtime was General Motors. GM reported that a "product design development program" of 24 months was underway which, if successful, could result in a production design.[9, p. 44] Subsequent communication with General Motors disclosed that this 24-month program began in September 1981.[20] Applying GM's timetable, a design would not be available for assurance testing until . September 1983. Unfortunately, GM provided no details as to the specifics of the program or why it would take 2 years to complete. Thus, we cannot analyze GM's position in any detail, but we believe it may be too pessimistic in view of the discussion above. In addition, past experience has shown that the automotive industry has often been too pessimistic in terms of its technical capabilities for emission control. Since the benefits of emission control equipment and lower pollutant levels are realized by society as a whole and not by . individual vehicle purchasers, the marketplace does not provide an incentive for vehicle manufacturers to develop and install pollution control equipment. In fact, since emission controls often increase vehicle prices, there is actually a marketplace disincentive for emission control improvements, which encourages the industry to downplay its technical capabilities.[19, p. 11] It was concern about this tendency for the automotive industry to be pessimistic about technological improvements in emission control which guided Congress in its development of the motor vehicle provisions of the Clean Air Act of 1970 and subsequent amendments. Inherent in the motor vehicle provisions of the Act is the concept of technology-forcing, i.e., setting standards which cannot be met at the time of promulgation but which reasoned technical analysis projects can be met by the time the standards take effect. Technology-forcing has proved to be the most effective strategy available to encourage the research and use of better emission control systems. Technology-forcing was utilized in our original particulate rulemaking and because of its application the automotive industry is now very close to a production trap design. Trap manufacturers have stated that much of their trap-oxidizer research would net have been funded if the particulate standards had not been in place.[22] The tendency for the automotive industry to be pessimistic with respect to emission control development was demonstrated in the early 1970's when the feasibility of catalytic converters and the 197 5 statutory emissions standards were being debated. In March and April, 1972, five motor vehicle manufacturers filed for suspension of the 1975 statutory standards on the basis that the development of catalytic converters was insufficiently advanced for successful use in the field. On April 11, 1973, the Administrator granted a one-year suspension of the 1975 statutory standards and promulgated a set of interim standards which he ------- -65- believed would require catalytic converters only on California vehicles* Nevertheless, over 85 percent of all 1975 model passenger cars successfully employed catalytic converters. One other fact involving the catalyst analogy should be noted. Even though catalytic converters were ultimately used on 1975 production, the first successful 50,000-mile durability demonstration of a catalyst did not take place until the spring of 1973, only 1 1/2 years before 1975 production.[22] Alternatively, there has already been a successful 50,000-mile trap—oxidizer durability test as of January 1982. The only other parties which have commented on development leadtime requirements have been the trap manufacturers. Johnson Matthey has stated that "our experience shows that the trap-oxidizer can be integrated into a given vehicle system within four months" and that "[mjore than adequate time remains to carry out the necessary steps to ensure that effective control systems are properly integrated on 1985 model year production vehicles."[21, p. 2] Other trap manufacturers have projected that additional development leadtime is needed, resulting in introduction on 1986 or 1987 production vehicles.[22] We believe these statements generally support our development leadtime projections. In summary, EPA projects that one and a half years of development leadtime is sufficient for the vehicle manufacturers to identify and optimize regeneration systems. This projection would allow assurance testing to begin by January 1983. B. Assurance Testing After successful trap-oxidizer prototypes have been developed, the vehicle manufacturers must then undertake a program of "assurance testing." This will begin when the manufacturers identify the physical specifications for the prototype trap-oxidizer model(s) for each vehicle family, and these prototype traps are fabricated by the suppliers. The desired trap model(s) are installed on the vehicles and the testing program can begin. Assurance testing allows the vehicle manufacturer to evaluate the trap-oxidizer models available in actual operating conditions on its own vehicles, identify specific improvements which could be made to optimize the engine/trap-oxidizer system for its vehicles, and to develop greater confidence in the performance of trap-oxidizer systems. The ultimate goal of assurance testing is to further prove and optimize the prototype design in an effort to provide the necessary degree of particulate control over the useful life at the lowest cost. Factors such as production economies of scale and potential warranty implications will also impact the choice of trap-oxidizer systems and the direction of the assurance testing program. For example, if one trap-oxidizer ------- -66- system will work successfully on all of a manufacturer's vehicle families, this could be preferable to developing a specific system optimized for each family. In testing such as this there are several factors which must be considered. Here, we are primarily interested in the factors bearing on the amount of assurance testing deemed necessary. The scope of a manufacturer's assurance testing program will vary according to factors such as; 1) the number of vehicle/engine configurations being evaluated, 2) the degree of experience with light-duty diesels, 3) the number of specific trap-oxidizer models being evaluated, and A) other concerns such as testing in various climatic regions, geographical areas, and special applications. These will be discussed further below. It is clear that the amount of assurance testing required will vary with the number of vehicle/engine configurations being evaluated. A manufacturer planning to certify several size passenger cars and light-duty trucks will have a much larger job and much more to gain than a smaller manufacturer. The task will be- especially important because of the potential economic jeopardy of an unsuccessful program and the potential, cost-saving gains associated with minimizing the number of systems certified. A manufacturer's degree of experience with light-duty diesel vehicles/engines will also impact the scope of the program. Manufacturers with limited experience in diesel engine technology will probably require more assurance testing than their experienced counterparts. This need for more testing would arise from a lack of historical data and vehicle performance experience on which to base judgments. In sotae cases a manufacturer may choose to evaluate both wire mesh and ceramic trap-oxidizer designs. In this case, the scope of the testing program would expand, but it is most likely that the initial evaluations being conducted on current prototypes would allow the manufacturers to choose between the two basic designs prior to the beginning of assurance testing. However, it is likely that manufacturers could choose to evaluate more than one configuration of the same basic trap-oxidizer design, for example, trap-oxidizers of different volume, trapping material density, or shape. Also, evaluations of different regeneration systems or trap-oxidizer placements could occur. Often a manufacturer's assurance testing program will be broad enough to also cover operations in different areas of the country and special applications. For example, manufacturers may choose to send fleets to specific areas in hot or cold climates or send fleets to operate in high-altitude areas. Another possibility is to place fleets in applications which are extremes from the operating norm. For example, a fleet could operate in all urban or all inter-city driving to determine performance in ------- -67- more rigorous operational environments. What is desired in an assurance testing program will be based on a manufacturer's specific goals. As was stated above, the program should ultimately lead to recommendations for trap-oxidizer specifications so that commitments leading to production and tooling can be made. However, it is not certain to what point each manufacturer must go to reach this decision, and this point is likely to be different for each manufacturer. Given this discussion on assurance testing, what is a reasonable time period for manufacturers to complete the anticipated program? There are several factors which will affect the time required. As was mentioned above, the degree of assurance desired by a manufacturer will have an influence on the amount of time necessary to complete the program. This will vary according to the manufacturer's policy, the manufacturer's experience with diesels, and the manufacturer's degree of experience with trap-oxidizer systems. Obviously these factors are different for each manufacturer. The length of time to complete assurance testing would also depend on the number of vehicle/engine-system models to be evaluated (size of the program). When practical, the best use of time would require these models to be evaluated concurrently such that they are completed at about the same time, but this may not be practical for other reasons as will be discussed below. The characteristics of the assurance program will also affect its length. This includes the manner of mileage accumulation (test track versus over the road), the amount of mileage desired per vehicle, and the amount of emissions testing and maintenance. EPA expects these programs will be quite similar to the current durability testing procedure for certification, with the exception of those cases where a manufacturer may choose to place a fleet in a special application. One final aspect which needs consideration is the current financial condition of the auto industry. Manufacturers may not have the resources to conduct concurrent evaluations of their entire product lines. Instead, they may be forced to evaluate worst case configurations first, make modifications and improvements, and then evaluate the remainder of the models. This could be a.more financially conservative approach but would likely require more time. Financial considerations may also limit the scope of the manufacturers' test programs in various geographic areas, climatic regions, and rigorous applications. This may be partially compensated for through in-house dynamometer simulation testing. ------- -68- As will be discussed below, EPA now estimates that an adequate assurance testing program would require approximately 10-14 months. The actual length of time would vary as described earlier, so this estimate uses somewhat conservative assumptions. As shown in Table IV-1, Phase I of the program would require 3 1/2 to 5 months for mileage accumulation, maintenance, and testing. The amount of mileage which could be accumulated in this period would depend upon the daily mileage accumulation rate. Based on past EPA analyses, in 3 1/2 to 5 months manufacturers could accumulate 50,000 miles operating one shift per day and 100,000 miles operating two shifts.[25, p. 28] After Phase I is completed, the results of the program are analyzed, the vehicle-engine/trap oxidizer system is evaluated, and further improvements and optimizations can be recommended. EPA believes a thorough engineering analysis of these results plus development of recommended changes in design or hardware would take 3-4 months. In some cases manufacturers may choose to conduct a follow-up (Phase II) program for further evaluation of the refined systems. For other manufacturers Phase II may consist of special applications testing as described above. Some manufacturers may choose to completely forego Phase II testing. This program may be of greater or lesser scope than Phase I, but should be achievable within a similar timeframe. In any event, after Phase I and the analysis of the results, most manufacturers will have adequate information to make initial commitments for production tooling. EPA's estimate of 10-14 months provides adequate time for assurance testing even if a manufacturer's plans on how to conduct assurance testing are substantially different than outlined above. EPA's time estimate is supported by those provided by GM[9, p. 45] and Toyota[8, p. 36] which both stated that one year would be sufficient for assurance testing. C. Preparation for Trap-Oxidizer Production Once the manufacturers have trap-oxidizer basic designs and specifications which can be committed to production, the actual preparation for mass production is a relatively straightforward process. This step is far more straightforward because no technological advances are necessary as in the developmental phase. Depending on the anticipated production volumes and the number of different sizes and models to be built, trap-oxidizer suppliers must procure facilities, make any necessary facility modifications, and install tooling and other equipment. Some components and materials may be procured from other production facilities but others may have to be produced from the basic specifications. Decisions must also be made with regards to which components will be produced internally and which will be purchased from sub-contractors. Sub-contractors in turn must prepare their own facilities and equipment. Many of these initial facility, ------- -69- Table IV-1 Time to Complete Fleet Assurance Testing Phase I (50,000 miles) 3.5-5 months Supplemental data analysis 3-4 months and system refinement/ optimization Phase II (5.0,000 miles) 3.5-5 months 10-14 months ------- -70- tooling, and equipment actions can be taken before the manufacturers have their final trap-oxidizer specifications (after the completion of Phase I but before the completion of Phase II of assurance testing). Once these final specifications have been received, any final tooling or equipment can be purchased and any last minute modifications can be made. After production personnel have been hired and received some initial training, production dry runs can be conducted for additional training, improvements in the production process, and quality control. Even though all of the components needed in the final product have their own separate leadtime requirements, the composite leadtime necessary to supply the final trap-oxidizer system is the controlling leadtime determinant. Although almost all of the commenters addressed the leadtime topic, few specifically addressed the manufacturing component of the leadtime. These comments are summarized below. Johnson Matthey, Inc.: "Johnson Matthey could be producing these diesel trap-oxidizers 12-18 months upon receipt of an order."[10, p. 1] Corning Glass; "Corning plans development and building of prototype process equipment by 1982, transfer to a production plant by 1983 1/2 and production beginning in 1984."[5, p. 2] Daimler-Benz: "The final version of a trap-oxidizer vehicle system ready for series production will require four years after a system meeting the design and regeneration requirements has been found."[2, p. 20] Ford Motor Co. ; "Upon successful completion of the demonstration of a feasible research prototype, five additional years are required to bring the components into production."[6, p. 24] Toyota Motor Co.; "Examination for manufacturing and assurance of reliability will take approximately 3 years."[8, p. 36] Volkswagen; "Once a workable system has been developed, it will take 3 years to put into production."[ 4, p. 58] An earlier submission by VW estimated a manufacturing leadtime of 18-24 months.[23, p. 40] General Motors; GM requires 24 months to validate the product design (including EPA certification) and to design, build, and try out facilities for mass producing the design.[9, p. 44] In an earlier comment GM estimated 2 1/2 to 3 years production leadtime after an acceptable method is defined.[23, p. 41] ------- -71- Clearly the leadtime estimates provided by the commenters are not directly comparable. Each estimate incorporates different aspects of the total leadtime picture. Johnson Matthey's estimate of 12-18 months is the manufacturing leadtime. Coming's statement can be interpreted to estimate a leadtime of about 2 years for manufacturing. VW's earlier submission estimated a manufacturing leadtime of 18-24 months. If it is assumed that Toyota and VW would conduct their assurance testing and then make their initial tooling commitments, a period of 1 1/2 to 2 years would be anticipated for manufacturing leadtime. GM estimated 24 months for this phase, but their estimate also included certification. Comments from Ford and Daimler-Benz were not detailed enough to be useful in this portion of the leadtime analysis. These will be considered when the total leadtime estimate is examined. Taking the useful comments en masse, it would appear that most commenters anticipated manufacturing leadtime requirements of 18-24 months. This period would begin when the vehicle manufacturers place their initial orders and end when the first production trap-oxidizers are constructed. This estimate of 18-24 months is corroborated well by manufacturers' comments in a recent EPA rulemaking of a similar nature, "Gaseous Emission Regulations for 1984 and Later Model Year Heavy-Duty Engines." The emission standards promulgated in that rulemaking required oxidation catalysts for heavy-duty gasoline-powered trucks and buses which were to be uniquely designed and built for the heavy-duty operating environment. GM estimated a tooling leadtime of 15 months (assuming substantial component carry across from light-duty), International Harvester estimated 21 months and Ford estimated 26 months.[24, p. 177] Given the general agreement in the commenters' manufacturing leadtime estimates and the corroboration of these estimates by the heavy-duty engine oxidation catalyst comments, EPA agrees that a manufacturing leadtime of 18-24 months is reasonable. D. Vehicle/Engine Modifications Both vehicle and engine modifications will be likely as a result of trap-oxidizer technology. These will be related to the trap-oxidizer system itself and the ' regeneration system(s) utilized. Any vehicle modifications will be related to changes in the underfloor area to accommodate the trap-oxidizer system and potential engine compartment changes primarily caused by the regeneration system. Since most diesel-powered vehicles are also sold with gasoline-fueled engines, they could accommodate ------- -72- trap-oxidizer systems with no major vehicle modifications by placing the trap-oxidizer system in approximately the same location as the catalytic converter. The situation with engine modifications is more complex. Engine modifications may be required by the trap-oxidizer itself and the regeneration system. The trap-oxidizer is likely to require exhaust manifold modifications for proper and efficient operation. Stainless steel exhaust pipes may also be required to help ensure the effective operation of the trap-oxidizer system over the vehicle's useful life. Since only potential regeneration systems have been identified, it is difficult to precisely identify these engine modifications. Potential areas for regeneration system-related engine modifications include the fuel system, the addition of a fuel burning system, a throttling mechanism, an air injection system, electronic engine controls, and/or other sensing devices. No submissions to the study specifically address the time required for any vehicle or engine modifications. EPA recognizes that these modifications will need to be made. However, these tooling and equipment changes can be made in parallel with tooling for the traps themselves. Since the 18-24 months allotted for tooling for trap-oxidizer production should be more than enough to accommodate these engine/vehicle modifications, this should not directly affect the necessary leadtime requirements. E. Certification In order for a vehicle manufacturer to introduce new vehicles into the consumer market, it must first describe these vehicles in a prescribed format and then show that representative vehicles meet EPA emission standards. The process of obtaining EPA approval of the vehicles for release to the consumer market is called the certification process. The certification process is essentially the same for both passenger cars and light-duty trucks whether they are gasoline or diesel-powered. Differences between the two lie in the emission and fuel economy standards which must be met, and in the details of the test procedures. At the same time, all new vehicles introduced to the market must be labeled with a fuel economy rating. In this case also, the vehicles are described in a prescribed format, and fuel economy ratings are determined by tests of representative vehicles. Certification and fuel economy approvals apply for one model year only. Although the model year may begin any time, it ends on the last day of the same calendar year. Any vehicles manufactured after that are considered to be new models. New certification and fuel economy approvals are needed. If there' are no changes, there are provisions for carryover which greatly simplify the recertification and relabeling process. ------- -73- The certification procedure for the manufacturer now follows an abbreviated procedure whereby the manufacturer completes all of the paper work and testing before any formal application is made to EPA. Previous procedures required interfacing with, and receiving approval from, EPA at a number of steps in the process. The entire process for the manufacturer consists of completing an application with detailed information about the particular engine family-exhaust emission control system combination for which a certificate is being sought. It must demonstrate, with actual data, the lifetime emission control durability of the various components by conducting a 50,000-mile vehicle test. It must also demonstrate with actual data that all variations of the emission control systems do, indeed, control exhaust and evaporative emissions so that they do not exceed the applicable standards. This is done by conducting 4,000-mile vehicle tests and applying deterioration factors determined in the durability test. All substantiating data must be submitted with the application. The most time-consuming part of the process is the durability demonstration. One durability test vehicle must be run for each engine displacement-system combination. The test is conducted by actually driving the vehicle the equivalent of a 50,000-mile distance. At specified periods, the driving is stopped and tests are conducted to determine the emission levels of the system at that point. A deterioration factor is determined by statistically analyzing the changes in the emission levels at each of these test points over the 50,000-mile test run. At the rate of driving 500 miles per work shift, it can be seen that such a test can take more than four months at one shift per day. Of course, double shifts and overtime can speed the process at increased expense to the manufacturer. Time must also be allowed for other factors. Driving is stopped to conduct each required periodic test. Maintenance on the vehicle must be performed as would be expected of the consumer-owner. Unscheduled maintenance problems occur which sometimes require that EPA review the situation to determine whether or not the vehicle might have to be rejected as unrepresentative, and a new test vehicle be started. Also, it is not unusual that the periodic tests indicate that the emissions are increasing to the point where they will exceed the standards further along in the test, and invalidate the particular engine family-emissions control system combination. If this situation develops, a new test vehicle must be initiated with a modification in the emission control system. Often, a manufacturer will run one or two backup durability vehicles which are designated as representing different families. The emission data test vehicles which are run for 4,000 miles are not tested until the durability engine test has been completed and deterioration factors have been established. The emissions ------- -74- from the emission data test vehicles are measured at the end of the 4,000 miles. Then the deterioration factors are applied to the test data so that a prediction can be made as to what the emissions would be after a 50,000-mile run. These are the results that must meet the emission standards. In a program of about the same length and scope as the emission data vehicle requirements, manufacturers must also demonstrate the fuel economy performance of their vehicles and trucks. These results are used for the fuel economy label and are a necessary component of the Department of Transportation's Corporate Average Fuel Economy (CAFE) program. After all of this testing is completed, detailed information and test data are submitted to EPA for review and evaluation. At this stage, EPA may accept the data as is or call for confirmatory testing at EPA. Confirmatory testing at EPA can involve several weeks due to scheduling considerations and potential testing complications. Should the test vehicle fail to meet emission standards under EPA testing, the vehicle data will not be accepted. Modifications must be made to the emissions control system and data from a new 4,000-mile vehicle must be submitted. Similar confirmatory testing is sometimes done on fuel economy vehicles and trucks. After all the data is accepted by EPA, the manufacturer may now complete the certification application and submit it. A certificate of conformity is issued shortly thereafter. At this point it would be useful to review the steps involved in the formal emissions and fuel economy certification processes and to estimate the time required using current certification procedures. In this analysis we will first view the process considering the time requirements for a manufacturer's entire product line and from that draw an estimate of the time required to certify its light-duty diesel vehicles and light-duty diesel trucks. Intermediate milestones in the process will be determined presuming that the manufacturers require their certificates of conformity by the August prior to new model introduction. All time periods will be measured back from that date, which will be referred to as the desired certificate date. Based on EPA experience with the process, the certification of a manufacturer's entire product line would roughly follow the schedule shown in Table IV-2. Using this schedule, EPA anticipates that a manufacturer would require about 14 months to complete a given model year's certification program. This, of course, would vary by manufacturer and would depend on factors such as the size of the product line and the resources a manufacturer wishes to expend. ------- -75- Table IV-2 Product-Line Certification Schedule Period Prior to Desired Certification Date Event Beginning Ending Intention to certify 14 months 13 months Certification application preparation 13 months 2 months Durability vehicles 13 months 3 months Emission-data vehicles 7 months 2 months Fuel economy vehicles 6 months 1 month Confirmatory testing (if necessary) 1 month 0 month Table IV-3 Engine Family Certification Schedule Event Time Required for Completion Durability Testing and Application Preparation 6 months Emission Data Vehicle 1 month Fuel Economy Vehicle 1 month Confirmatory Testing 1 month Application Processing 1 month 10 months ------- -76- Intent to certify would be submitted 13-14 months prior to the desired certificate date and work on durability vehicles would begin immediately. Development of each family's durability vehicles together with mileage accumulation and testing would take about 6 months per engine family. During durability testing the certification application would be prepared. As durability testing ends manufacturers will be identifying their emission-data vehicle requirements and preparing vehicles for emission-data testing. For the earliest durability fleets, emission-data vehicle testing could begin about 7 months prior to the desired certificate date- and would require approximately 1 month per vehicle. An additional month would also be required to finalize the application and processing at EPA. Fuel economy certification could begin as emission-data testing is completed and would also take approximately 1 month. Given this information, EPA estimates that a vehicle/truck family could move through the certification process in approximately 10 months (see Table IV-3). This would allow 6 months for durability testing, 1 month each for emission data and fuel economy testing, and 1 month for possible confirmatory testing. In addition, it is reasonable to allow an extra month for items such as manufacturer and EPA processing of the certification application, confirmatory testing for both emissions and fuel economy, or perhaps other, as of yet unidentified, delays. Under the schedule outlined above, manufacturers would have to begin the light-duty diesel vehicle and truck certification processes about 10 months prior to the desired certificate date. In an analysis such as this it is reasonable to consider that manufacturers must schedule their light-duty diesel certification as only one part of their total certification process. As a result, manufacturers may not always be able to give light-duty diesel certification top priority. Since it is estimated that the certification of a manufacturer's entire product line would take approximately 14 months and certification of any one family would require about 10 months, it is reasonable to allow a leeway of an additional 2 months to allow for potential scheduling and priority conflicts. Therefore, EPA considers 12 months a comfortable period for certification of a manufacturer's light-duty diesel vehicle and light-duty diesel truck families. F. Estimate of Total Leadtime Requirements Having determined the leadtime requirements for trap-oxidizer development, assurance testing, production tooling and certification, it is now possible to determine the total leadtime still required before trap-oxidizer systems can be used on production vehicles. As discussed above, EPA now estimates that the development of workable trap-oxidizer prototypes will require until January ------- -77- 1983. This basically requires the manufacturers to identify their choices of trapping material, determine the models/sizes of trap-oxidizers which could be used, and identify one or more successful trap-oxidizer regeneration mechanisms. The major effort still required lies in the third area. Once the workable prototype systems have been developed, vehicle manufacturers can begin assurance testing. This will allow vehicle manufacturers to determine the operational success of these prototype systems on their own vehicles/engines. After Phase I assurance testing is complete, manufacturers will be able to identify any needed refinements or optimizations on the trap-oxidizer system, engine, or vehicle. At this point, which should take approximately 9 months, manufacturers will be able to make initial commitments for tooling and other equipment necessary for suppliers to produce the trap-oxidizer system. Some manufacturers may choose to conduct a second phase of assurance testing (Phase II) to further evaluate the refinements and optimizations or to test vehicles in more extreme climatic, geographic, or operating environments. It is probably not necessary to complete Phase II testing (5 months) before committing a design to initial tooling. After completion of Phase II testing manufacturers can supply final details on system specifications so any remaining tooling actions can be finalized. Tooling and equipment for trap-oxidizer system production including production dry runs and employee training would take 18-24 months after initial tooling commitments are made. During this period production lines would be developed to: 1) build the components of the trap-oxidizer system (including the regeneration mechanism) and 2) assemble the complete trap-oxidizer. This 18-24 months would also allow time for the vehicle manufacturers to assess any vehicle or engine modifications required and to plan for such changes during normal model year changeover. Finally as described above, vehicle manufacturers would require 12 months to certify their light-duty diesels for emissions and fuel economy. To determine the required total leadtime we must identify the critical path within the different components of the leadtime picture. Figure IV-1 shows the critical path timeline for total leadtime. The solid lines represent the critical path. The broken lines represent other time necessary but not on the critical path. As can be seen in Figure IV-1, the critical path is first dependent on the development leadtime assumed to require until January 1983. Vehicle manufacturers will then require at most 9 months to complete Phase I assurance testing and analysis of the results of such testing. After this, initial tooling commitments can be made. Tooling and equipment preparation for mass ------- JAN 1982 : ¦ ¦ i . t ; ; Ul ¦l ! l ¦¦ . I i ! Mill! TTTT , i ! . . , Figure IV-1 Trap-Oxidizer Leadtime •i I ¦ • • = i . . . . : i \ \ ¦ • : . i j ; i •: it '• l i • I ¦: t , |-| I' ,ili! i ; i: r;:r<"' ..A I , : : — U_ _ 1. — Certification i 1 i x- Tooling/Equipment r K- Phase jl Phase II _A. ¦ i i Agsurartce Testing ! Development . i I j- - ; :•: ' y: '¦ ! : ! : j JAN :1983 ! ! I . ;!:!• ' ! I..! • [. 1 1 I [ ! i i 1 ! 1 . ; ' n: I : ill; ! -i ' : .! i J I • .\.A if ; j JAN |l984 lit i i i-l -i IN! '!¦! Mil !_LI_L_L. :_L ! : . JAN 1985 t JAN 1986 H-j ; i" i : I ¦< | '"! ' 1 ' 1 t 1 I ' ' !;'I i j!; job ij.f fj H 1986 MYh : • : r -^1 ; oo ------- -79- production of trap-oxidizer systems and preparation for vehicle/engine modifications will require another 18-24 months. Theoretically, certification could begin any time after completion of Phase II assurance testing, and is therefore not a critical path item. Based on this analysis, EPA estimates that trap-oxidizer systems could be available for use on production-line vehicles and trucks 25-33 months after a successful prototype system has been developed. Using first the shorter total leadtime estimate, if a successful prototype is available by the end of 1982, 25 months of additional leadtime would allow trap-oxidizer systems to be available on production vehicles and trucks by February 1985. Under this scenario, trap-oxidizers could be used on 1986 model year light-duty diesel vehicles and trucks. Job 1 for the 1986 model year would begin in late July-early August of 1985. With the longer total leadtime estimate (33 months) trap-oxidizer systems would be available during September 1985. This would miss the 1986 model year by 2-3 months, so under these conditions, trap-oxidizers could be used on 1987 model year light-duty diesel vehicles and trucks. In making the choice of which model year is preferable for a possible deferral of the 1985 particulate standards there are several other factors which deserve consideration. The technology development still required cannot be "scheduled" but must proceed at its own pace. Economic pressures bearing on the automotive industry and its suppliers could slow the pace of the entire process. In addition, as mentioned previously, manufacturers entering the light-duty diesel market in the mid-eighties might require a little more time to develop their vehicles/trap-oxidizer systems than their more experienced counterparts. And, of course, there is the real economic risk of a manufacturer not being able to certify and sell one or more engine families in 1986 if its efforts are unsuccessful. Considering all of these factors, plus the fact that the longer range in the leadtime estimates brings us early into the 1987 model year, it would probably be wiser to choose the more conservative 1987 model year. Most of the comments related to the achievable model year were keyed to the development of a successful prototype. If one assumes that a successful prototype and' regeneration system are achieved by the end of 1982, then the comments received can be used to conclude the following model years as achievable; VW 1986 [A, p. 58] D-B 1987 [2, p. 20] ------- -80- GM 1987 [9, p. 45] Ford 1988 [6, p. 24] NAS 1988 [26, p. 35] VW's estimate supports our 1986 model year conclusion, and both D-B's and GM's estimates support EPA's more conservative 1987 model year conclusion. Neither Ford nor NAS included any data to justify the need for five years leadtime beyond a successful prototype so EPA can neither affirm nor refute their estimates. ------- -81- References 1. "Petition to Suspend Application of 1985 Diesel Particulate Standards," Submitted to EPA by General Motors Corporation on September 30, 1981 (EPA Docket A-81-20, II-D-31). 2. "Submission of Daimler-Benz A.G. on the Technological Feasibility of the 1985 Light-Duty Diesel Particulate Standard," October 21, 1981, Submitted to EPA by Hogan and Hartson on November 2, 1981 (EPA Docket A-81-20, II-D-37). 3. "Cellular Ceramic Diesel Particulate Filter," John S. Howitt and Max R. Montierth, Corning Glass Works, SAE Paper 810114. 4. "Comments on the Technological Feasibility of the 1985 Light-Duty Diesel Particulate Standard," November 1981, Submitted to EPA by Volkswagen of America, Inc., on November 16, 1981 (EPA Docket A-81-20, II-D-46). 5. Letter from John S. Howitt, Corning Glass Works to Jeff Alson, EPA, Concerning the Trap-Oxidizer Feasibility Study, November 23, 1981 (EPA Docket A-81-20, II-D-64). 6. "Study of the 1985 Light-Duty Diesel Particulate Standard," Submitted to EPA by Ford Motor Company on October 2, 1981 (EPA Docket A-81-20, Il-D-24). 7. "The Technological Feasibility of 1985 Light-Duty Diesel Particulate Standard," October 1981, Submitted to EPA by Nissan Motor Co., Ltd., on October 1, 1981 (EPA Docket A-81-20, II-D-26). 8. "The Technological Feasibility of the 1985 Light-Duty Diesel Particulate Standard," Submitted to EPA by Toyota Motor Co., Ltd., on September 29, 1981 (EPA Docket A-81-20, II-D-20). 9. "General Motors Response to EPA Questions on Feasibility of 1985 Light-Duty Diesel Particulate Standards," October 1981, Submitted to EPA by General Motors Corporation on October 20, 1981 (EPA Docket A-81-20, II-D-32). 10. "Control of Particulate, Hydrocarbon, and Carbon Monoxide Emissions from Diesel Engines," Submitted to EPA by John- son Matthey, Inc., on October 1, 1981' (EPA Docket A-81-20, II-D-22). 11. Letter from Richard K. Meyers, Texaco, Inc., to EPA Public Docket No. A-81-20 Concerning the Trap-Oxidizer Feasibility Study, October 2, 1981 (EPA Docket A-81-20, II-D-25). ------- -82- 12. "Regulatory Analysis of the Light-Duty Diesel Particulate Regulations for 1982 and Later Model Year Light-Duty Diesel Vehicles," EPA, OANR, OMSAPC, February 20, 1980 (EPA Docket OMSAPC-7 8-3). 13. "Diesel Particulate Trap Regeneration Techniques," W. R. Wade, J. E. White, and J. J. Florek, Ford Motor Company, SAE Paper 810118. 14. "Renault's Comments Regarding EPA Studies on Light Duty Diesel Particulate Requirements for 1985," Submitted to EPA by Renault USA on September 9, 1981 (EPA Docket A-81-20, II-D-16). 15. "General Motors Response to EPA Notice of Proposed Rulemaking on Particulate Regulation for Light-Duty Diesel Vehicles," Submitted to EPA on April 19, 1979 (EPA Docket OMSAPC-78-3). 16. "Standard for Emission of Particulate Regulation for Diesel-Fueled Light-Duty Vehicles and Light-Duty Trucks," 45 Federal Register 14496, March 5, 1980. 17. "Addendum to General Motors October 20, 1981, Submission on Technology for Controlling Particulates from Light-Duty Diesels," Submitted to EPA on December 15, 1981 (EPA Docket A-81-20, II-D-66). 18. Letter from, B. E. Enga, Johnson Matthey, Inc., to Anne M. Gorsuch, Administrator, EPA, Concerning the 1985 Light-Duty Diesel Particulate Standards, January 25, 1982 (EPA Docket A-81-20, II-D-75). 19. "Memorandum in Opposition to General Motors' Petition for Suspension of the 1985 Diesel Particulate Standards," Submitted to EPA by the Natural Resources Defense Council, Inc., on October 13, 1981 (EPA Docket A-81-20, II-D-27). 20. Personal Communication Between John Nolan, General Motors, and Jeff Alson, EPA, January 29, 1982. 21. Letter from Dr. George McGuire, Johnson Matthey, Inc., to Anne M. Gorsuch, Administrator, EPA, Concerning the 1985 Light- Duty Diesel Particulate Standards, October 8, 1981 (EPA Docket A-81-20, Il-D-63). 22. Memo from Maureen D. Smith, EPA. to the Record, "Record of January 27., 1982 Meeting with the Manufacturers of Emission Controls Association (MECA) on Trap-Oxidizers," February 24, 1982 (EPA Docekt A-81-20, II-E-2). 23. "Summary and Analysis of Comments on the Notice of Proposed Rulemaking for the Control of Light-Duty Diesel Particulate Emissions from 1981 and Later Model Year Vehicles," EPA, OANR, OMSAPC, October 1979 (EPA Docket 0MSAPC-78-3). ------- -83- 24. "Summary and Analysis of Comments to the NPRM: 1983 and Later Model Year Heavy-Duty Engines, Proposed Gaseous Emission Regulations," EPA, OANR, OMSAPC, December 1979 (EPA Docket OMSAPC-78-4). 25. "Summary and Analysis of Comments on the Notice of Proposed Rulemaking for Gaseous Emission Regulations for 1983 and Later Model Year Light-Duty Trucks," EPA, OANR, OMSAPC, May 1980 (EPA Docket OMSAPC-79-2). 26. "Diesel Cars - Benefits, Risks and Public Policy," Final Report of the Diesel Impacts Study Committee, National Research Council, 1981 (EPA Docket A-81-20, II-A-2). 27. "Light-Duty Diesel Organic Material Control Technology Investigation Program," Southwest Research Institute, EPA Contract No. 68-03-2873, Monthly Progress Report No. 28 for the period of January 1 through January 31, 1982, dated February 10, 1982 (EPA Docket A-81-20, II-B-1). 28. "Final Report on 50,000 Volkswagen Rabbit Durability Test," (Preliminary Draft) June 1981 to January 1982, B. E. Enga, Johnson Matthey, Inc., and B. B. Bykowski, Southwest Research Institute, submitted to EPA by Johnson Matthey, Inc., on February 12, 1982 (EPA Docket A-81-20, II-D-78). ------- |