United States Environmental Protection Agency Air and Radiation EPA420-P-99-015 March 1999 M6 STE 003 Determination of Start Emissions as a Function of Mileage and Soak Time for 1981-1993 Model Year Light-Duty Vehicles DRAFT 4^ Printed on Recycled Paper ------- EPA420-P-99-0] March 199 Determination of Start Emissions as a Function of Mileage and Soak Time for 1981-1993 Model Year Light-Duty Vehicles M6.STE.003 DRAFT Ed Glover Penny Carey Assessment and Modeling Division Office of Mobile Sources U S. Environmental Protection Agency NOTICE This technical report does not necessarily represent final EPA decisions or positions It is intended to present technical analysis of issues using data which are currently available The purpose in the release of such reports is to facilitate the exchange of technical information and to inform the public of technical developments which may form the basis for a final EPA decision, position, or regulatory action ------- EPA420-P-99-015 - Draft - Determination of Start Emissions as a Function of Mileage and Soak Time for 1981-1993 Model Year Light-Duty Vehicles Report Number M6.STE.003 March 4,1999 Ed Glover Penny Carey U.S.EPA Assessment and Modeling Division NOTICE This technical report does not necessarily represent final EPA decisions or positions It is intended to present technical analysis of issues using data which are currently available The purpose in the release of such reports is to facilitate the exchange of technical information and to inform the public of technical developments which may form the basis for a final EPA decision, position, or regulatory action M6.STE.003 March 4, 1999 ------- -2- 1.0 INTRODUCTION MOBILE6 will allocate vehicle exhaust emissions to either the "extra" emissions associated with engine start (start emissions) or the "base" emissions associated with travel (running emissions). This distinction is to some extent an artifical constraint since in reality "start" emissions in part will be released while the vehicle is in motion. However, it is a useful constraint and not too far from physical reality, in at least summer conditions, when the extra emissions from a start end after only 1 or 2 mmutes of driving. This split allows the separate characterization of start and running emissions for correction factors such as fuel effects and ambient temperature. It also allows a more precise weighting of these two aspects of exhaust emissions for particular situations such as morning commute, parking lots and freeways This document describes the methodology used to calculate start emissions as a function of mileage and soak time for use in MOBILE6 The results for model year 1981-1993 light-duty cars and light-duty trucks are presented. The deterioration of running emissions will be addressed in a separate document (Report Number M6.EXH 001) This document is organized into six sections. The first section is the short introductory section. Section 2 describes the FTP data sources and the model year and technology groups which are used Section 3 provides a definition of start emissions in mathematical terms and shows the relationship between start emissions and the Federal Test Procedure (FTP) emissions. This includes a description of the FTP cycle, the Hot505 cycle, and a definition of cold start and hot start emissions Section 4 describes the methodology used to predict start emissions as a function of soak time. Section 5 shows the algorithm used to predict start emissions versus mileage. Section 6 contains an example of the final start emission results as used in MOBILE6 as a function of both deterioration and soak time. 2.0 DATA SOURCES USED The basic datasets used to determine in-use deterioration are based on FTP testing. (I/M data from Dayton, Ohio were also used to correct the results for recruitment bias which EPA believes affects the FTP test samples - see Appendix A). Three FTP data sources were used: 1) the test results from the EPA laboratory in Ann Arbor, Michigan, 2) the data received from AAMA (American Automobile Manufacturers Association) based on testing conducted in Michigan and Arizona, and 3) the API (American Petroleum Institute) data collected in Arizona The model years in the dataset range from 1981 through 1993, and contain both cars and trucks. Table 1 gives a breakdown by vehicle type, model year, and technology for the three datasets combined. M6.STE.003 March 4, 1999 ------- -3- Table 1 Distribution of Vehicles by Model Year and Technology* Cars Cars Cars Cars Cars 1 Trucks Trucks Trucks Trucks Trucks MYR OPLP CL Carb TBI PFI ALL 1 B MYR OPLP CL Carb TBI PFI ALL 81 367 657 15 29 1068 1 I 81 124 124 82 71 71 74 8 224 I ¦ 82 45 45 83 63 57 127 62 309 1 1 83 8 3 11 84 5 30 46 35 116 1 1 84 26 22 1 49 85 24 74 56 66 220 1 I 85 33 30 13 6 82 86 7 34 60 92 193 1 I 86 14 9 23 41 87 87 1 17 76 106 200 1 I 87 6 4 10 88 15 69 113 197 I ¦ 88 0 89 22 38 103 163 I I 89 0 90 160 250 410 I ¦ 90 144 1 145 91 91 426 517 1 1 91 141 144 285 92 57 347 404 I 1 92 92 92 184 93 29 366 395 1 ¦ 93 90 93 183 ALL 538 977 898 2003 4416 ALL 250 64 509 382 1205 No entry indicates no data available for that model year/technology type in the FTP dataset used for this analysis M6 STE 003 March 4, 1999 ------- -4- In general, most of the 1990+ model year vehicle data were supplied by AAMA, and most of the pre-1990 data were supplied by the EPA laboratory testing. The API sample is a relatively small sample (99 cars and trucks). Its chief appeal is that the vehicles all have generally higher mileage readings than the rest of the sample (all over 100,000 miles). The other general trend in the data is toward PFI technology, and away from the others This is seen in the 1990+ vehicles which are predominately PFI with some TBI still present. The 1981 -1989 model years start with a high percentage of carbureted and some open loop, but end with mostly TBI and PFI technology. Although not explicitly shown in the tables, new catalyst technology was phased slowly into the fleet starting in the mid 1980's. For analysis, the cars and trucks were placed into the model year/technology groups shown below Trucks were separated into five different groups by pollutant due to differences in certification standards. CARS MY Group / Technology Type HC/CO/NOX 1988-93 PFI 1988-93 TBI 1983-87 FI 1986-93 Carb 1983-85 Carb 1981-82 FI 1981-82 Carb TRUCKS MY Groups / Technology Type HC/CO/NOX 1988-93 PFI 1988-93 TBI 1981-87 FI 1984-93 Carb 1981-83 Carb The technology groups are closed-loop ported fuel injection (PFI), closed-loop throttle body injection (TBI), and carbureted (CARB). FI refers to a combination of PFI and TBI. CARB includes both closed-loop and open-loop vehicles which are carbureted. These model year/technology grouping boundaries were selected on the basis of changes in emission standards or the development/refinement of new fuel metering or catalyst technologies. It is assumed that as of 1990, carbureted technology had a very tmy market share, and are included with the previous carbureted group. Because of the relatively large amount of 1988-93 fuel injected data, the category was split into PFI technology and TBI technology for both cars and trucks. This produces separate deterioration functions based on this fuel delivery technology and allows the modeling of the future penetration of PFI technology into the m-use fleet. M6 STE.003 March 4, 1999 ------- -5- 3.0 DEFINITION OF START EMISSIONS 3.1 Overview of the Federal Test Procedure (FTP) The Federal Test Procedure (FTP) is a test cycle which is used to certify new vehicles to emission performance standards (see 40 CFR Part 86, Subpart B, Section 86.144). The FTP consists of a cold start segment (Bag 1), a hot stabilized segment (Bag 2), and a hot start segment (Bag 3). Initially, the vehicle is stored for a minimum of 12 hours before testing to simulate a 12 hour overnight soak penod. The vehicle is then driven over the cold start segment, which lasts 505 seconds over a length of 3.59 miles, and the emissions collected as Bag 1 The latter part of the driving in Bag 1 occurs with the engine and catalyst in a hot stabilized condition. Bag 2 emissions are then immediately collected from the hot stabilized segment, which lasts 867 seconds over a length of 3 91 miles. After a 10 minute soak, the 505 seconds of the start segment is then repeated and the emissions collected as Bag 3. The FTP composite emission rate is a weighted combination of the three measured bags to represent two trips. The first trip is a cold start trip after a 12 hour soak, and the other is a hot start trip after a 10 minute soak. Each trip is a "LA4" cycle, which is a combination of the 505 cycle (either Bag 1 or Bag 3) and the Bag 2 cycle. In a typical FTP test, the Bag 2 is only measured once and the results are used for both trips. Since the 505 cycle is 3 59 miles long and the Bag 2 cycle is 3.91 miles long, each LA4 trip is 7 5 miles long. The cold start trip is weighted at 43% and the hot start trip weighted 57%. If the cold start trip is 43% of the driving, then the vehicle miles traveled (VMT) in Bag 1 (containing the cold start) is: FTP Bag 1 VMT Weighting = 43% * (3.59 miles / 7.5 miles) = 0 206 The hot start trip is 57% of driving, and the VMT weighting for Bag 3 (containing the hot start) is: FTP Bag 3 VMT Weighting = 57% * ( 3 59 miles / 7.5 miles) = 0.273 The remaining VMT is from stabilized driving, represented by Bag 2. Since Bag 2 is used for both the cold start and hot start trips, it uses VMT weighting from both. FTP Bag 2 VMT Weighting = ( 43% + 57% ) * ( 3.91 miles / 7 5 miles ) = 0 521 The standard VMT weighting of the bags reported in grams per mile for the full FTP are- M6.STE.003 March 4, 1999 ------- -6- FTP - (Bag 1 * 0.206) + (Bag 2 * 0.521) + (Bag 3 * 0.273) where the fractions represent the amount of vehicle miles traveled within the three modes during the FTP trip, and Bagl, Bag2, Bag3 and the FTP emissions are in grams per mile (g/mi). 3.2 Overview of the Hot Running 505 and Its Use The FTP testing method outlined above does not allow the precise separation of start and running emissions, since Bags 1 and 3 contain both start and running emissions. Bag 2 of the FTP does not contain an engine start; however, the driving cycle used in the second bag is significantly different from the cycle used for Bags 1 and 3. Thus, to estimate the amount of FTP emissions that can be allocated to engine start, the concept of the Hot Running 505 (HR505) is needed. The HR505 is an extra 505 cycle performed immediately following bag 3 of the FTP. It uses an identical driving cycle as the first and third bags of the FTP, but does not include an engine start. For more information, refer to the document "The Determination of Hot Running Emissions from FTP Bag Emissions", report number M6.STE 002. With a HR505 emission result, it is possible to compare the results obtained from the HR505 to the results from Bags 1 and 3 of the FTP to determine the portions of Bags 1 and 3 attributable to start emissions following a 12 hour soak and start emissions following a 10 minute soak, respectively. Since the HR505 has not historically been included in FTP test programs, a method of estimating the HR505 was developed, as described in report M6.STE.002. Briefly, HR505 emissions were measured from a sample of 77 vehicles tested under EPA contract. The results from this vehicle sample were used to develop a correlation between the HR505 and FTP bag data. This correlation was then used to estimate HR505 results for the FTP dataset used for this analysis. 3.3 Basic Start Emission Rate For MOBILE6, the basic unit of engine start emissions is defined as a start after a 12 hour soak. The units for engine start emissions will be grams, instead of grams per mile, since start emissions will not be allocated by vehicle miles traveled. The engine start basic emission rate can be determined by subtracting the HR505 emission rate from the Bag 1 emission rate (in grams per mile) using the nommal distance traveled in the 505 driving cycle: Basic Start Emission Rate (grams) = [Bag l(g/mi) - HR505(g/mi)] * 3.59 miles M6.STE.003 March 4,1999 ------- -7- For illustration purposes, the average basic start emission rates (in grams) after a 12 hour soak were calculated for each model year and are shown in Tables 2 and 3 for cars and trucks. Start emissions after a 10 minute soak can also be estimated from the Bag 3 and HR505 emission rates, analogous to the basic start emission rate: Start Emissions after 10 minute soak (grams) = [Bag 3(g/mi) - HR505(g/mi)] * 3.59 miles The average start emissions after a 10 minute soak are also shown in Tables 2 and 3 for each model year and for cars and trucks. For some FTP tests of some cars, the predicted HR505 emissions are higher than Bagl and/or Bag3 emissions. This causes the start emissions to be negative. This probably is due to intermittent emission control system defects. Except in some cases of very small samples, the negative values were retained in the analysis. 4.0 Basic Start Deterioration with Mileage 4.1 Definition of Categories The basic modeling concept behind the start emission factor methodology is that the fleet can be represented as two types of vehicle emitter categories. These two types are termed "high" emitters, and "normal" emitters. The "high" emitters have FTP average emission levels which are considerably higher than the overall mean emission levels, and significantly higher than their FTP standards, indicating that they have problems with their emission control systems The "normal" emitters are low and average emitting vehicles with emission control systems which are generally functioning properly. The overall fleet emission factor is a weighted average of the high and normal emitters. The high/normal emitter modeling concept is also used in the estimation of running emissions, and is discussed in depth in other reports. For both start and running emissions, the high/normal concept allows for corrections due to recruitment bias against higher emitting vehicles, and for more accurate estimates of the effects of I/M programs, fuel effects, temperatures, etc. In the data analysis, vehicles were defined as normal emitters for a specific pollutant if their FTP HC emissions were less than twice the applicable new car certification standard, or their FTP CO emissions were less than three times the applicable new car M6.STE.003 March 4, 1999 ------- -8- Table 2 Mean Estimated Start and FTP Emission Levels by Model Year for Light-Duty Cars in the FTP Dataset Basic start (after 12 hour soak) Start (after 10 min soak) Composite FTP grams grams grams/mile MYR HC CO NOx MYR HC CO NOx MYR HC CO NOx 81 4 002 46 419 1.373 81 0.610 5 115 0.041 81 0 706 9 667 0 897 82 2.445 36 378 1 237 82 0 373 4.843 -0 045 82 0 789 8 318 0.872 83 2.399 26 112 1 264 83 0 400 3 827 0 150 83 0.431 5 073 0.806 84 2.950 34 827 1 190 84 0513 3 418 0 047 84 0.756 9 968 0 893 85 3 468 30 353 1 204 85 0 506 4 737 0.095 85 0 533 6 935 0 770 86 2 526 26 639 1432 86 0 298 2 082 0.241 86 0 926 10.43 0 713 87 2.712 20 030 1 376 87 0 597 2.104 0 170 87 0 656 8 366 0.790 88 2 831 19 716 1 419 88 0 406 1.147 0 223 88 0 406 4 574 0.668 89 2.254 18.610 1 434 89 0 379 2 524 0216 89 0311 3.911 0.652 90 2 169 18 677 1.930 90 0.332 2219 0.611 90 0.274 3 614 0 633 91 2 183 19 494 1 443 91 0 275 2 132 0 530 91 0.237 3 145 0.525 92 2 271 18.878 1 645 92 0.304 2 595 0 485 92 0 267 4 328 0 508 93 2312 21.030 1 801 93 0.310 2 564 0 392 93 0 225 2 551 0 466 M6 STE 003 March 4, 1999 ------- -9- Table 3 Mean Estimated Start and FTP Emission Levels by Model Year for Light-DutyTrucks in the FTP Dataset Basic start (after 12 hour soak) grams Start (after 10 min grams soak) MYR HC CO NOx MY R HC CO NOx MY R HC CO NOx 81 7 342 107 501 1.055 81 1 212 14 211 0 385 81 1 275 18.158 1.752 82 7 909 116 584 -0 119 82 1489 14 189 0 006 82 1 732 16.774 1.732 83 6 537 104 817 0 796 83 1 577 18 657 -0 209 83 1 361 13.226 1436 84 5219 95.893 0 299 84 1.098 20.057 0.004 84 0.802 10.633 1 405 85 4 766 84 621 0.457 85 0.854 7 742 0 102 85 1 281 14 465 1 388 86 3.752 41 196 0 729 86 0 607 2.148 0 128 86 0 823 8.789 1.057 87 3 352 26 635 1 266 87 0 566 1433 0017 87 0 401 4 610 0.605 88 88 88 89 89 89 90 4 705 45 331 4 683 90 0 930 7 037 0 765 90 0 800 9510 0 885 91 3 521 41.128 2 761 91 0 878 7 129 0519 91 92 3 656 41446 3.054 92 0 654 5.746 0 656 92 93 3 644 40 557 2 736 93 0 589 4 634 0 676 93 0 420 5 363 0.847 Composite FTP grams/mile M6 STE 003 March 4, 1999 ------- -10- certification standard, or their FTP NOx emissions were less than twice the new car certification standard. Vehicles were defined as high emitters for a specific pollutant if their FTP HC emissions or FTP CO emissions exceeded twice or three times the applicable new car certification standard, respectively, or their FTP NOx emissions were two times the new car certification standard. Because high NOx emissions often occur with low HC and/or low CO emissions, and sometimes even HC can be high and CO normal, the three categories were kept separate. Thus, a vehicle could be a high HC emitter, but a normal CO and NOx emitter. 4.2 Calculation of Start Emission Rates for Normal Emitters Emission rates for normal emitters were calculated by least squares regression of the emissions of the normal emitters versus mileage. The regression was done for each pollutant / model year / technology group. The start emission regression coefficients for cars are shown in Table 4a and for trucks in Table 4b The column labeled ZML contains the zero mile coefficients, and the column DET contains the deterioration coefficients (slope) from the regressions. Table 4a Regression Coefficients for START Emissions from Normal Emitter CARS MY Group Tech Group HC Coefficients CO Coefficients NOx Coefficients ZML DET ZML DET ZML DET 1988-93 PFI 1 9987 0 006830 18 972 0 00703 1444 0 00220 1988-93 TBI 1 9019 0 002679 19 233 0 00000 2 300 0 00000 1983-87 FI 2 3589 0 001388 19 949 0 00000 1461 0 00141 1986-89 Carb 1 4934 0 018238 24 698 0 10947 1 405 0 00000 1983-85 Carb 1 5892 0 009408 24 442 0 10577 0 748 0 00524 1981-82 FI 2 3543 0 008533 20 038 0 22673 1 530 0.00059 1981-82 Carb 2 1213 0 013610 28 637 0 22673 1 601 0 00000 M6.STE.003 March 4, 1999 ------- -11- Table 4b Regression Coefficients for START Emissions from Normal Emitter Li^ht Trucks MY Group Tech Group HC Coefficients CO Coefficients NOx Coefficients ZML DET ZML DET ZML DET 1988-93 PFI 2 873 0 00000 32 178 0 0168 1 597 0 00000 1988-93 TBI 4 073 0 01309 42 456 0 1411 4 294 0 00324 1981-87 FI 2 599 0 00964 23 497 0 0613 1 384 0 00000 1984-93 Carb 3 916 0 00854 78.286 0 2564 0 143 0 00436 1981-83 Carb 6817 0 00154 98 432 0 3240 1 082 0 00000 4.3 Calculation of Start Emission Rates for High Emitters High emitters are the vehicles in the fleet which likely have problems with then- emission control systems, as evidenced by emission levels which are considerably higher than the FTP standards. In the analysis they were defined as those vehicles exceeding either twice FTP standards for HC or NOX or three times FTP standards for CO. The emissions line is a flat horizontal line because the emissions of a high emitter were not a statistically significant function of mileage In addition, the relatively small sample sizes of high emitters make regression determined mileage coefficients unreliable indicators of actual behavior Table 5a shows the average emissions of the high emitters (cars only) for the pollutant / model year / tech groups, and Table 5b shows the analogous results for light trucks. For NOX start emissions, the normals and the highs were combined together, and the emissions were regressed versus mileage This has the effect of eliminating the NOX high emitter group for start emissions. This combination was done for two reasons. First, for many of the model year / tech groups the average NOX start emissions were found to not be statistically significantly different from start emissions from the normals This was found to be the case even when different definitions of a high emitter were tried (IX FTP NOX, 1.5X FTP NOX, and 2X FTP NOX). This phenomenon is consistent with the mechanisms of NOX formation - higher emissions under lean high temperature / load FTP conditions, and lower during rich and cooler start conditions. Second, the sample sizes for NOX high emitters were smaller in both an absolute sense, and in comparison to the HC and CO high emitter sample. M6 STE.003 March 4, 1999 ------- -12- Table 5a Mean START Emissions of High Emitter CARS MY Group Tech Group HC Mean CO Mean NOx Mean 1988-93 PFI 4 829 38 06 Same as Normals 1988-93 TBI 3 293 27 16 Same as Normals 1983-87 FI 5 313 65 31 Same as Normals 1986-89 Carb 10 520 92 82 Same as Normals 1983-85 Carb 10 520 92 82 Same as Normals 1981-82 FI 5 313 92 82 Same as Normals 1981-82 Carb 10 520 92 82 Same as Normals Table 5b Mean START Emissions of High Emitter Trucks MY Group Tech Group HC Mean CO Mean NOx Mean 1988-93 PFI 5 212 83 862 Same as Normals 1988-93 TBI 5 212 83 862 Same as Normals 1981-87 FI 5.826 60 319 Same as Normals 1984-93 Carb 9 406 162 115 Same as Normals 1981-83 Carb 17 865 179 549 Same as Normals The other anomally in the results was the HC and CO high emitter emission levels for the 1990-93 TBI group. In both of these cases the average start emission levels of the few cars tested were judged to be unrealistically low. For the case of CO, the value was -123.84 grams, and for HC it was 0.0356 grams. These low average levels are the result of small sample size, and the possibility of negative values when the hot running 505 on a particular car is greater than Bagl of the FTP. Rather than insert negative values in the MOBILE6 model, the HC and CO high emitter emission levels from the 1988-93 PFI group were substituted in the 1988-93 TBI group. This is a M6.STE.003 March 4, 1999 ------- -13- reasonable assumption since these vehicles are generally about the same age and model year vintage, and have reasonably similar emission control technology. 4.4 Fraction of High and Normal Emitters in the Fleet The basic start emission factor is computed from a weighted average of the highs and normals. The fraction of high emitters in the fleet is the weighting factor The fraction of high start emitters is the same fraction as the one used for the running emissions calculations Appendix A presents the fraction of HC and CO high emitters in the fleet at selected mileages / ages for each pollutant (see document M6.IM.001 for further details). The fraction of NOX high emitters is not shown because for NOX the Normals and Highs are assumed to have the same emission rate (no start NOX highs are assumed to exist). 4.5 Calculation of Basic Start Emission Rates The basic start emission rate is calculated for each combination of vehicle type / pollutant / model year group / technology group. The units are start emissions in grams Equation 1 is used to calculate the basic (mean) start emission rate from the high and normal emitter emission values and the rate of high emitters in the fleet For NOX emissions a special case of this equation is used where the normal and high emission rates are set equal to each other. START = ST_High_ave * Highs + STNormave * Normals Eqn 1 Where: Highs = fraction of High emitters Normals = fraction of Normal emitters START is the basic (mean) emission rate ST_High_ave is the high emitter start emission average ST_Norm_ave is the normal emitter start emission average Where: Highs + Normals = 1 Eqn 2 M6.STE.003 March 4, 1999 ------- -14- 5.0 Start Emissions Versus Soak Time Start emissions will be a function of soak time so that MOBILE6 will be able to account for the entire distribution of soak times observed in the fleet. This ranges from a minimum soak time of zero minutes up to a 12 hour soak period (720 minutes). Soak periods exceeding 12 hours will be assumed to be the same as for a 12 hour soak. To develop the relationship between start emissions and soak time, the FTP database was used only to determine the engine start emissions after a 10 minute soak and a 12 hour (720 minute) soak (these are the only data points available). To predict start emissions for the entire range of soak duration, a model was developed from the two FTP points, and from testing done by California of the effect of soak time on engme start emissions (see CARB report "Methodology for Calculating and Redefining Cold and Hot Start Emissions") The model which was developed uses the FTP start emission data from the two FTP soak times to adjust the curves presented in the California report. The start emission data points at 10 minutes and 720 minutes are derived from the FTP dataset described earlier and are a function of pollutant, technology, model year group, and mileage. The California interpolation curves (California Soak Function) is a function of pollutant and catalyst type Mathematically, the start emissions of a given pollutant (in grams) as a function of soak time is shown as: Start Emissions (@ soak time) = Basic Start Emissions (@ 12 hour soak) * Soak Function where the Soak Function is a multiplicative factor used to calculate start emissions for other soak times. The Soak Function is calculated by dividing the grams for the soak time of interest by the grams for a soak time of 12 hours. Therefore, at a 12 hour (720 minute) soak time, the Soak Function is equal to 1.0. Mathematically, for the first domain of the California Soak Function (see Table 6 for the two domains for each pollutant and catalyst type) the Soak Function is defined as: Soak Function = California Soak Function * [Ratio+(l-Ratio)*((SoakTime-10)/(X-10))] For the second domain of the California Soak Function (i e., HC for catalyst equipped vehicles the second domain is 90 minutes through 720 minutes) the Soak Function is M6.STE.003 March 4,1999 ------- -15- Table 6 Coefficients for Adjusting Engine Start Emissions for Soak Time (from "Methodology for Calculating and Redefining Cold and Hot Start Emissions", CARB) Non-Catalyst Vehicles HC Curve 1 HC Curve 2 CO Curve 1 CO Curve 2 NOX Curve 1 NOX Curve 2 Constant 0 38067 0 43628 0 43803 -0 08541 1 31568 2 48061 minutes -0 00163 0 00078 -0 00998 0 00303 0 02752 -0 00018 minutes2 6 64E-05 0 7 01E-05 -2 11E-06 -0 00015 -2 6E-06 domain(min) 0-52 53-720 0-119 120-720 0-119 120-720 Catalyst Equipped Vehicles HC Curve 1 HC Curve 2 CO Curve 1 CO Curve 2 Nox Curve 1 NOx Curve 2 Constant 0 0 57130 0 0 70641 0 11796 112983 minutes 0 01272 0 00072 0 01195 0 00033 0 02967 2 21E-05 minutes2 -6 30E-05 -1 76E-07 -4 76E-05 1 0OE-O7 -0 00021 -3 04E-07 domain(min) 0-89 90-720 0-116 117-720 0-61 62-720 Electrically Heated Catalyst Equipped Vehicles HC Curve 1 HC Curve 2 CO Curve 1 CO Curve 2 Nox Curve 1 NOx Curve 2 Constant (a) 0 0 50641 0 0 44733 1 05017 1 37178 minutes (b) 0 00561 0 00069 0 00707 0 00162 0 00362 0 00027 minutes2 (c) -5 09E-06 0 -1 33E-05 -1 18E-06 -5 57E-06 -1 09E-06 domain(min) 0-117 118-720 0-107 108-720 0-113 114-720 California Soak Function = a + b * minutes + c * minutes2 (where minutes is time since last engine operation (i e , soak time)) The Soak Function is the grams per soak time i divided by the grams per overnight soak (720 minutes or 12 hours M6.STE.003 March 4, 1999 ------- -16- defined as: Soak Function = California Soak Function where- California Soak Function: The values developed by the California Air Resources Board to adjust the start emissions for soak times other than 12 hours. This is a function of soak time in minutes. The coefficients for catalyst vehicles, non-catalyst vehicles, and electrically heated catalyst vehicles are given in Table 6. The coefficients for catalyst-equipped vehicles are for the model year/technology groups examined in this report. For example, for HC on a catalyst equipped vehicle at a soak time of 100 minutes, the value is 0 57130 + 0.00072*100 + (-1.76E-07)*(100)2 = 0.64154 Ratio: This parameter is calculated by dividing the EPA ratio of start emissions at 10 minutes to start emissions at 12 hours by the California Soak Function at 10 minutes. Mathematically, it is given by: Ratio = (Start @10 minutes / Start @720 minutes) / California Soak Function @10 mmutes The numerator in the above equation (Start @10 minutes/ Start @720 minutes) was developed from FTP data using the equations in Sections 3.3, and dividing the Start @10 minutes by the Start @ 720 minutes. One value for each pollutant was developed that included all technologies and vehicle types These values, used m the numerator of the equation, are: HC= 0.160, CO = 0.112, and NOx = 0 204. The California Soak Function is the value obtained from the coefficients in Table 6 at a 10 minute soak point. The California Soak Function values at a 10 minute soak point for catalyst- equipped vehicles, used in the denominator of the equation, are. HC=0.1209, CO=0 1147, and NOx=0 3937. Therefore, the Ratios obtained are: HC=1.3234, CO=0 9765, and NOx=0.5182. SoakTime: The time duration in minutes of the soak which is to be calculated (range zero minutes to 720 mmutes). X term: This term is defined to be zero for soak times from 0-10 minutes. For the range from 10 minutes to 720 minutes, it is set equal to the highest minute in the domain of the California Soak Function For example, HC emissions from catalyst equipped vehicles have two time domains m Table 6. These are 0-89 minutes and 90-720 M6 STE.003 March 4, 1999 ------- -17- minutes. Thus, for this example, X = 0 for times of 10 minutes or less, and X = 89 for times from 11 minutes through 89 minutes No soak adjustment is applied for the remaining soak period of 90 minutes through 720 minutes. Only the California Soak Function is used. For all three pollutants, the difference between the MOBILE6 soak function and the California soak function will generally be small for the entire range of soak times. If any difference exists it will reach its highest magnitude in the range of 10 minutes to about 60 minutes. 6.0 START EMISSION RESULTS Start emissions are both a function of vehicle deterioration represented by mileage, and soak time In previous sections the results were shown separately. In this section, examples of the results are shown with both effects combined. Shown in the linked EXCEL spreadsheets (CAR_BER.xls and TR_BER.xls) is a sample calculation of the basic emission start factors for the various model year groups and pollutants It mcludes calculations for both start and running emissions The calculations in the spreadsheet use Equation 1 in this document, and show the magnitude of the start emission factors that will be used in MOBILE6. The statistical results and output are too voluminous to present directly in this document. However, they are available in the linked document (stat.lst). The statistical software SPSS was used to perform the linear regressions and compute the means In general, the regression correlation coefficients (r-squared) are not high (< 0.10), and reflect the tremendous scatter in emissions data. However, virtually, all of the regression coefficients of the normal emitters are significant at least at a 90 percent confidence level On the other hand, the confidence intervals around the average start emission levels of the high emitters are quite large due to high scatter and small sample sizes. Shown below for illustration purposes is a sample calculation of start emissions. It illustrates the soak function equations and methodology shown in Section 5. Example: Calculate HC start emissions at a soak time of 88 minutes for a 1991 model year PFI-equipped car with 60,000 miles. M6.STE.003 March 4, 1999 ------- -18- Start Emissions (@88min) = Basic Start Emissions (@12hr) * Soak Function From Tables 4a, 5 a and A-l: Basic Start Emissions = High ave * Highs + Norm ave * Normals START = 4.829*0.0987 + (1 999 + 0.00683*60)(1.0 - 0.0987) = 2.647 g HC Soak Function = California Soak Funct * [Ratio+(l-Ratio)*((SoakTime-10)/(X- 10))] From Table 6, using the coefficients for catalyst-equipped vehicles: California Soak Funct = 0.000 + (0.01272)*(88) + (-6.30E-05)*(88)2 = 0.63149 Ratio = (Start@10min / Start@12hr) / California Soak Funct@10min = 1.3234 for HC as given m Section 5.0 SoakTime = 88 minutes X = 89 minute HC time domain (from Table 6). Soak Function = 0.63149 * [1.3234 + (1-1.3234) * ((88-10) / (89-10)j] = 0.63407 Start Emissions(@90min) = 2.647 * 0.63407 = 1.679g HC M6 STE.003 March 4, 1999 ------- -19- Appendix A Fraction of High and Normal Emitters in the Fleet The fractions of high and normal emitters in the fleet were calculated based on the running emission estimates. For consistency, these fractions were also used for start emissions. The fractions were based on the running estimates, because the running estimates were corrected to account for the recruitment bias inherent m the FTP data. A large amount of IM240 data from the Dayton, Ohio I/M program (211,000 initial tests) were used to correct the recruitment bias inherent in the FTP type data The recruitment bias is believed to exist in the EPA and AAMA FTP samples because of (1) their relatively small size in comparison to the likelihood of selecting a high emitter, (2) the belief that motorists with poorly maintained or tampered vehicles will be reluctant to volunteer them to a government entity like the EPA or even the vehicle manufacturer, and (3) the relatively low mileage levels of the EPA and AAMA sample (relatively few over 100,000 miles). Since the Dayton sample contains virtually the entire vehicle fleet (or a randomly selected 50 percent) of the city these issues of recruitment bias should be minimal. For example, the sample size is quite large (211,000 vehicles). Even if high emitters are just a few percent of this sample, they should be well characterized Also, I/M is not a voluntary program in Ohio; thus, a motorist cannot simply decline to participate. Unless they have intentionally tampered the vehicle and have an expectation of failure, it is unlikely that they would seek to avoid the program since the data is from the first year of I/M testing m Dayton. Although the mileage data from Dayton are highly suspect and not useful, the vehicles of a given model year vintage are older than the vehicles of the same model year vintage in the EPA and AAMA databases. Thus, they should provide a more representative cross- section of the m-use fleet. The derivation of the average running emission rates, with the adjustments based on the Dayton IM240 data, are discussed in EPA document M6.EXH 001. Tables A-l and A-2 show the fraction of HC and CO high emitters in the fleet. The use of these to develop start emission factors are discussed m Section 4 4 and Section 4.5. The derivation of these high emitter fractions is discussed in detail in EPA document M6 IM 001. However, a brief description and the mathematical equation is shown below. The number of High and Normal emitters is calculated at each age point for each combination of vehicle type / pollutant / model year / technology group using the following general equations. M6.STE.003 March 4, 1999 ------- -20- Where: Highs is the fraction of High emitters. Normals is the fraction of Normal emitters. RLA4 is the average running emission rate, after adjustment based on IM240 data from Dayton, OH. High_ave is the high emitter running emission average estimated from the FTP data. Norm_ave is the normal emitter running emission average estimated from the FTP data. Highs + Normals = 1 Eqn A-l and RLA4 = Highave * Highs + Norm ave * Normals Eqn A-2 Solving for the variables Highs and Normals produces: Highs = (RLA4 - Norm ave) / (Highave - Norm_ave) Eqn A-3 Normals = 1 - Highs Eqn A-4 M6 STE.003 March 4, 1999 ------- -21- Table A-l Estimated Fraction of HC High Emitters in the Fleet HC HC HC HC HC HC HC MILEAGE 88-93 PFI 88-93 TBI 83-87 Fl 86-89 Carb 83-85 Carb 81-82 Fl 81-82 Cart> 2142 0 0184 0 0239 0 0223 0 0052 0 0232 0 0203 0 0282 12 823 0 0227 0 0251 0 0157 0 0197 0 0158 0 0654 0 0543 29 335 0 0422 0 0270 0 0406 0 0526 0 0047 0 1613 01580 50 0 0800 0 0386 01003 01042 0 0917 0 2861 0 2906 60 006 0 0987 00458 01298 01296 01348 0 3485 0 3560 74 239 01260 0 0561 01723 0 1661 01972 0 4393 0 4503 87 786 01525 0 0661 0 2078 0 2012 0 2578 0 5275 0 5416 100 01 01770 0 0753 0 2346 0 2334 0 3135 0 6094 06253 112 948 0 2036 0 0851 0 2634 0 2678 0 3737 0 6986 0 7152 124 625 02280 0 0940 0 2898 0 2992 0 4290 0 7812 0 7976 135 738 0 2518 0 1026 0 3153 0 3295 0 4826 0 8620 0 8772 146 315 0 2748 01110 0 3400 0 3586 0 5345 0 9407 0 9539 156 38 0 2972 01190 0 3638 0 3866 0 5847 1 0000 1 0000 165 96 0 3189 01267 0 3868 0 4135 0 6332 1 0000 1 0000 175 077 0 3398 01341 0 4089 0 4393 0 6801 1 0000 1 0000 183 753 0 3601 0 1412 0 4303 0 4641 0 7253 1 0000 1 0000 192 01 0 3798 01480 0 4508 0 4879 0 7690 1 0000 1 0000 199 869 0 3988 0 1546 0 4706 0 5108 08111 1 0000 1 0000 207 349 04171 01609 0 4896 0 5327 0 8516 1 0000 1 0000 214 466 0 4348 01669 0 5079 0 5537 0 8907 1 0000 1 0000 221 241 04519 01727 0 5255 0 5738 0 9284 1 0000 1 0000 227 688 0 4683 01782 0 5425 0 5931 0 9646 1 0000 1 0000 233 823 0 4842 01836 0 5587 0 6116 1 0000 1 0000 1 0000 239 663 04994 01887 0 5743 0 6293 1 0000 1 0000 1 0000 245 22 0 5141 0 1936 0 5893 0 6462 1 0000 1 0000 1 0000 250 509 0 5283 01982 0 6036 0 6624 1 0000 1 0000 1 0000 M6.STE.003 March 4, 1999 ------- -22- Table A-2 Estimated Fraction of CO High Emitters in the Fleet CO CO CO CO CO CO CO MILEAGE 88-93 PFI 88-93 TBI 83-87 Fl 86-89 Carb 83-85 Carb 81-82 Fl 81-82 Carb 2 142 0 0093 0 0552 0 0180 0 0103 0 0130 0 0119 0 0508 12 823 0 0082 0 0553 0 0123 0 0388 0 0093 0 0511 0 1102 29 335 0 0241 0 0553 0 0357 0 0929 0 0473 0 1334 0 2441 50 0 0458 0 0554 0 0889 0 1741 0 1783 0 2466 0 4138 60 006 0 0566 0 0555 0 1150 0 2140 0 2430 0 3024 0 4969 74 239 0 0721 0 0555 0 1496 0 2715 0 3364 0 3830 0 6163 87 786 0 0872 0 0556 0 1765 0 3270 0 4271 0 4611 0 7312 100 01 0 1010 0 0556 0 2012 0 3778 0 5102 0 5327 0 8360 112 948 0 1159 0 0557 0 2276 0 4323 0 5998 0 6097 0 9479 124 625 0 1296 0 0558 0 2518 0 4822 0 6819 0 6802 1 0000 135 738 0 1429 0 0558 0 2751 0 5302 0 7614 0 7484 1 0000 146 315 0 1556 0 0559 0 2976 0 5764 0 8381 0 8141 1 0000 156 38 0 1680 0 0559 0 3193 0 6210 0 9121 0 8775 1 0000 165 96 0 1799 0 0560 0 3402 0 6638 0 9836 0 9387 1 0000 175 077 0 1914 0 0560 0 3602 0 7050 1 0000 0 9976 1 0000 183 753 0 2025 0 0561 0 3795 0 7445 1 0000 1 0000 1 0000 192 01 0 2132 0 0561 0 3981 0 7825 1 0000 1 0000 1 0000 199 869 0 2235 0 0561 0 4159 0 8191 1 0000 1 0000 1 0000 207 349 0 2334 0 0562 0 4330 0 8541 1 0000 1 0000 1 0000 214 466 0 2429 0 0562 0 4495 0 8877 1 0000 1 0000 1 0000 221 241 0 2521 0 0562 0 4653 0 9200 1 0000 1 0000 1 0000 227 688 0 2609 0 0563 0 4804 0 9510 1 0000 1 0000 1 0000 233 823 0 2693 0 0563 0 4949 0 9806 1 0000 1 0000 1 0000 239 663 0 2774 0 0563 0 5089 1 0090 1 0000 1 0000 1 0000 245 22 0 2852 0 0564 0 5222 1 0363 1 0000 1 0000 1 0000 250 509 0 2927 0 0564 0 5350 1 0623 1 0000 1 0000 1 0000 M6.STE.003 March 4, 1999 ------- |