Emission Laboratory Correlation Study Between EPA and Audi - NSU Auto Union by Richard E. Lowery June 1974 Environmental Protection Agency Office of Air and Waste 'Management Programs Office of Mobile Source Air Pollution Control Emission Control Technology Division Regulations Development and Support Branch Ann Arbor, Michigan ------- Emission Laboratory Correlation Study Between EPA and Audi - NSU Auto Union ABSTRACT This report presents the results of a laboratory correlation study between EPA and Audi - NSU Auto Union of Germany. An attempt is made to isolate equipment, procedure, and ambient differences which affect the degree of emission result correlation. A research vehicle tested at both Audi and EPA revealed a good HC emission correlation, but significant discrepancies in measurements of CO and NOX. Differences in dynamometers and ambient conditions seemed to be the most important factors affecting the degree of emission cor- relation. ------- Emission Laboratory Correlation Study Between EPA and Audi - NSU Auto Union Introduction: In an attempt to ensure a good laboratory correlation between Audi- NSU and EPA, a program was initiated to exchange information with Audi and relate that information to the emission test results of a research vehicle tested at both laboratories. The findings of that program, in- cluding conclusions regarding the factors affecting the degree of cor- relation, are the substance of this report. Organization and Sequence of Testing; Because Audi's request for correlation information was made during peak demand for EPA certification work, a small scale testing program was a necessity. Also, since OMSAPC's Test and Evaluation Branch had already scheduled the Audi vehicle for evaluation testing, the correlation testing had to be arranged within the limitations of the vehicle's availability. Under these restrictions, EPA and Audi representatives agreed on the fol- lowing program: (1) Audi and EPA would exchange information relating to their facilities, equipment, and procedures. (2) EPA would conduct three valid hot-start emission tests on the Audi vehicle on a certification site. Audi would provide data of similar tests at the Audi - NSU laboratory. (3) Audi would submit static gases to EPA for analysis and comparison with values generated at the Audi laboratory. Steps 1 and 2 of the program were initiated simultaneously on May 31. The gases required for Step 3 arrived at EPA on June 17, and their analyses was completed on EPA's Train - 15 on June 24. Teat Procedures; The vehicle emission tests conducted for this study were hot-start tests over the LA-4 cycle using only one set of collection bags. Sample collection was begun upon vehicle ignition as is done in 1975 federal tests. CVS flow rates were adjusted to accommodate the usage of only one sample bag. These vehicle tests were run at EPA on certification site #5. ------- -2- Test Vehicles; The vehicle used for correlation testing was a modified 1974 Audi Fox equipped with an oxygen - sensor system which controlled air-fuel ratio. The following data apply to this vehicle. Model: Audi Fox V.I.D: 8442000011 C.I.D: 97.0 Inertia Weight: 2500 pounds Transmission: 4-speed manual No. of Cylinders: 4 In testing this vehicle, dynamometer horsepower was set at 7.0 at 50 mph, a value different than Federal Register specifications. This was done because Audi had supplied appropriate data to EPA's Certification Branch such that their 1975 certification fleet will be tested at that setting. N Analysis of Data: The analyses of Audi - NSU facilities data reveals the following comparative differences with the EPA facility. EPA Audi - NSU Dynamometer Drive Type Direct Belt Roll Spacing 17.25 in. 20.25 in. Driver's Aid Chart Speed 4 in./min. 4.72 in./min. Resolution 60 mph=5.00 in. 60 mph=4.56 in. Facility Altitude (ft.) 897.5 1276.3 Analyzers Span Gases (%Full Scale) 75-96 47-97.5 # Calibration Points HC and NOX 6 2 CO and C02 6 8 Complete Audi - NSU and EPA facility data may be found in the Appendix. ------- -3- In general, average emission levels measured on the Audi correlation vehicle were higher at the Audi facility than at EPA. Specifically, com- paring average levels of three tests at each facility showed Audi 3.8% higher on HC, 19.3% higher on CO, and 56.6% higher on NOX. No C02 values from the tests at Audi were available, so no comparison of CC>2 levels was possible. Complete vehicle emission test data are summarized in Table 1. The static gas checks compared measurements of four span gases at EPA, Volkswagen, and two Audi analysis sytems. The largest discrepancies were revealed in HC (C3H8) measurements, where Audi's values were 5.2% and 4.3% lower than the EPA measurement. All CO and C02 values obtained at Audi and Volkswagen were lower than correponding readings at EPA, the maximum dif- ference being 3.1%. The NO correlation was quite good, with Audi's Train II measuring the largest deviation from EPA's value, 2.3%. A summary of these calibration gas data is presented in Table 2. Discussion: Significant CO and NOX emission level differences between EPA and Audi-NSU were observed in this program, and several factors were documented which could possibly contribute to this problem. The most important factor is probably the dynamometer roll-spacing difference, Audi's 20.25 inch span . vs. EPA's 17.25 inch. This difference significantly affects the tire-roll friction, especially since the test vehicle was equipped with relatively small tires (13" rims; approximately 11" inch rolling radius). The result of this difference is that the work necessary to complete the LA-4 driving cycle is significantly higher on the rolls of wider spacing. Thus the effect of the wider roll span would probably be higher levels of all emittants, the magnitudes of which would depend on the particular vehicle's character- istics. The Audi-EPA NOX discrepancy, although larger than would be ex- pected because of roll spacing difference, may have been largely attributable to this factor. Perhaps the Audi vehicle was particularly sensitive to the effects of increased loading. Another factor which may have significantly affected the correlation results is the difference in barometric pressure (facility altitude) between the two laboratories. Although Audi's oxygen - sensor emission control system should compensate for barometric differences, its effectiveness is not certain. A trend toward higher CO and HC measurements at Audi than at EPA would be a result of Audi's lower barometric pressure if the altitude com- pensation was not effective. The influence of analyzer calibrations could also have had a significant effect on the emission correlation. The static checks showed that Audi would measure higher NOX levels (approximately 2%), and lower HC concentrations ------- -4- (4-5%) than EPA, which would account for a minor portion of the NOX emission discrepancy. However, it would increase the HC emission difference. The effect of different HC and NOX analyzer techniques might also be.important, since Audi's two point calibrations are not as accurate as EPA's six - point technique. One other factor may have contributed significantly to the NOx emission differences, that being the test cell relative humidity. Audi typically tests their vehicles at humidity near 75 grains of water per pound dry air, while the EPA test cell measured an average of about 50 grains during testing. If the Audi vehicle was substantially less NOX sensitive than t^he correlation factor assumes, then the NOx factor over - corrected EPA results. Other correlation studies with American manufacturers have indicated that NOX measurements at EPA were frequently over - corrected. Conclusions: A comparison of laboratory test equipment and procedures and vehicle emission levels has indicated correlation problems between EPA and Audi-NSU. The most significant problem was revealed by Audi's average measurement of 56.6% higher NOX on the correlation vehicle. Audi's large dynamometer roll spacing is the most probable cause of the NOX discrepancy. The difference in barometric pressures between the EPA and Audi - NSU laboratories did not seem to have a major effect on the degree of correlation on the vehicle tested, but it should be realized that this factor could be of greater importance on other control system configurations. Differences between EPA and Audi - NSU analysis systems were discovered, but their effect on the emission discrepancies were minimal. However, Audi - NSU should be encouraged to compare the effects of six - point HC and NOX instrument calibrations to their current two - point technique. Effects of ambient test cell humidity may have contributed slightly to the NOX correlation problem. EPA should continue its efforts to improve the consistency of its humidity controls and to bring the ambient condition of its test cells nearer the 75 grains of moisture specification. ------- TABLE 1 AIIDT CORRELATION Vehicle Audi - Fox 8442000011 Test 1972 Hot - Start Test Laboratory Audi - NSU 3 Dynamometers •3 Drivers EPA 1 Dynamometer 1 Driver Test No. 1 2 3 AVE 1 2 • 3 AVE HC 1.19 1.11 0.94 1.08 1.01 1.03 1.07 1.04 CO 13.89 14.41 11.81 13.37 11.25 11.23 11.16 11.21 NOx 3.66 3.33 3. 30 3.43 2.22 2.13 2.23 2.19 C02 • 346 343 344 345 Fuel Consumption 24,2 24.3 24.3 24.3 Barometric Pressure 28.78 28.80 28.84 28.81 NOx Factor 0.8872 0.8792 0.9289 0.8984 Emission Values in grams/mile Fuel Consumption in miles/gallon Barometric Pressure in inches of mercury ------- TABLE 2 Audi Correlation Calibration Gas Data Facility Readings Deviation from Cyli 100 200 100 100 nder No. 098 178 030 053 Contents EPA Reading £3^8 116.19 ppm CO 1874.96 ppm NO 122.7 ppm C02 3.538 % VW 114 1825 122 3.43 % -1. -2. -0. -3. 7 7 8 1 Audi Train 111 1855 124.5 3.43 I -4 -1 +1 -3 and EPA % .3 ,1 .5 .1 Percent Reading Audi Tra i n 110 1862 125.5 3,47 II -5 -0 +2 -2 % .2 J .3 .0 ------- APPENDIX ------- LABORATORY CORRELATION DATA SUMMARY TEST FACILITY . EPA #6 A. Dynamometer Manufacturer Clayton Model CTE - 50 Absorber HP 50 Torque Bridge Strain Gage Inertia Style Direct Drive Auto Loader Not Used Roll Diameter 8.65 in. Roll Spacing 17.25 in. Calibration Procedure Coast - downs at 4,8, and 14 indicated horsepower used to calculate actual absorbed horsepower vs. indicated horsepower for each inertia weight. B. Driver's Aid Manufacturer Varian Control Manual Scaling 5 inches = 60 mph, 4 inches/minute Speed Signal Origin Rear Roll C. Ambient Monitors Facility Altitude 897.5 feet Location of: Barometer W&11 of Test Cell . Humidity Sensors 1) Center of Cell - Ambient, 2) Dilution Air Inlet Nominal Test Cell Humidity See Test Results D. Analysis System 1. HC Analyzer Manufacturer Beckman Model 400 H2 / N2 A4 Fuel Used Zero Gas Alr ------- Ranges Used 50/100 Span Gas (es) 41/89.5 Curve Fit Linear # Cal. Points 6 2. CO Analyzers Manufacturer Bendix Hi 98.05 Ranges Used 500/1000 Span Gas (es) 427/923 // Cal. Points_ Curve Fit Zero Gas Hi 3 rd Order Manufacturer Beckman Range Used Span Gas 2500 2112 3. NOX Analyzer Manufacturer Teco Zero Gas 2 Range (s) Used 10° Span Gas (es) # Cal. Points 95.8 Hi 4. C02 Analyzer Manufacturer_ Zero Gas Beckman Ranges Used_ 3.3% Span Gas (es) 2.5% # Cal. Points Hi 470 91.2 Lo 10'24 Model . - 85° Lo 94 Model 315A Model 10A Curve Fit Linear Lo 8.5 Model 315A Curve Fit 3rd Order 3-33 Lo .78 ------- E. CVS System Manufacturer Air Monitoring, Inc. Model 705-G Calibration Date 5/17/74 Calibration Technique Laminar Flow Element & Propane Injection. Results of Last 3 Propane Injections: Date 5/20/74 5/21/74 5/31/74 % Error -1.92 0.326 0.946 P 8.25 8.20 5.10 ------- LABORATORY CORRELATION DATA SUMMARY TEST FACILITY Audi NSU Ingolstadt #3 A. Dynamometer Manufacturer Clayton ModelEC 200 modified Absorber HP 50 Torque BridgeSpring loaded coikiertia Style mech - V - Belt Auto Loader none Roll Diameter 8.65" ROH Spacing 20.25" Calibration Procedure Coast down at 4, 8 and 12 indicated hp used to calculate actual hp vs. indicated hp for 2000, 2500 and 3000 Ibs B. Driver's Aid Manufacturer with°ff Control manual Scaling 12° mm=100 km/hr (63 mph), 2 mm/sec Speed s±gnal Origin rear ro11 C. Ambient Monitors Facility Altitude 12?6-3 feet Location of: Barometer Wal1 of Test Lab Humidity Sensors Test cel1 near dilution air inlet Nominal Test Cell Humidity 50% ± 5 D. Analysis System Train II 1. HC Analyzer Manufacturer IPM Model RS 5 Fuel Used 2 Zero Gas Air ------- Ranges Used 20° PPm Span Gas (es) 94 Curve Fit Linear # Cal. Points 2 Hi X 98 Lo ?1 2. CO Analyzers Manufacturer H & B Model _ URAS I] Ranges Used 75° PPm Span Gas (es) # Cal. Points 8 Hi 745 Lo 74'5 Curve Fit Linearized N Zero Gas 2 Manufacturer H & B Model URAS II Range Used 3000 ppm Span Gas 1895 3. NOX Analyzer Manufacturer Teco Model 10A Zero Gas - Curve Fit linear Range (s) Used _ 100 Span Gas (es) _ 97.5 # Cal. Points 2 Hi 97.5 Lo 48.75 4. C02 Analyzer Manufacturer H & B Model URAS 2T Zero Gas N2 Curve Fit Linearized Ranges Used 5.^ Span Gas (es) 3-65% // Cal. Points 8 Hi 5'0% Lo °'5% ------- E. CVS System Manufacturer Audi Model Mk II Calibration Date last; 4-30-74 Calibration Technique Laminear flow element and propane injection Results of Last 3 Propane Injections: Date 8-9-73 1-11-74 4-30-74 % Error 0.97 1.02 0.97 P 0.5" 0.5" 0.5" ------- |