United States Environmental Protection Agency Environmental Sciences Research Laboratory Research Triangle Park NC 27711 Research and Development EPA-600/S3-83-104 Dec. 1983 Project Summary Effect of Load Simulation on Auto Emissions and Model Performance Peter Gabele and Richard Snow A study was undertaken to examine the accuracy of an automobile emission rate model and the water brake dyna- mometer procedure used in the model's development. Using wheel torque- meters, actual road loads were recorded and later simulated with the vehicle on an electric dynamometer. Emissions results from tests using this load simu- lation were compared with results from tests using water brake simulation. Emission results were also compared to values predicted using the Environmen- tal Protection Agency's Automobile Exhaust Emission Modal Analysis Mod- el. This Project Summary was developed by EPA's Environmental Sciences Re- search Laboratory, Research Triangle Park, NC, to announce key findings of the research project that is fully docu- mented in a separate report of the same title (see Project Report ordering infor- mation at back). Introduction Ambient air concentrations of CO with- in urban areas are often significantly higherthan those predicted by dispersion models. Because CO is emitted predomi- nantly by motor vehicles, models used to predict CO emission rates from groups or classes of motor vehicles could be contrib- uting substantially to the shortfall and should be examined for inaccuracies. Two widely used models for estimating emissions are MOBILE2 and the Inter- section Midblock Model (IMM). Both models employ the EPA Automobile Ex- haust Emission Modal Model which is used to predict emissions for any given speed-time driving sequence. This "Modal Model" has been criticized because it was developed using precata- lyst cars which were tested on water brake dynamometers. In this study, the Modal Model is evaluated by measuring emission rates from a late model vehicle and comparing these with values predicted using the model. The effect of water brake dyna- mometer load simulation versus actual road load simulation on regulated emis- sions is also examined. Conclusions and Recommendations Investigation of the effect of dynamom- eter load characteristics upon regulated emission rates and an evaluation of the EPA Modal analysis Model were com- pleted. Based upon the study's findings the following is concluded: 1. The load applied by the water brake and the tire rolling resistance losses on the dynamometer was approxi- mately equal to the actual road load measured in highway tests. 2. Regulated emission rates for the Celebrity are not significantly differ- ent when tested using the water brake simulation versus actual road load simulation on an electric dyna- mometer. 3. The EPA Exhaust Emissions Modal Model is an inaccurate predictor of regulated emissions from the Celeb- rity. The conclusions suggest that water brake dynamometers adequately simulate actual road loads for emissions test ------- purposes. This should hold true for vehi- cles such as the Celebrity which have large inertia load components relative to aerodynamic load components. When the aerodynamic load component becomes a significant portion of the total road load, dynamometer absorbed power theoreti- cally deviates with speed from the actual road load. The tendency for this occur- rence, which makes simulation of road loads with water brake dynamometers more difficult, increases for extremely lightweight cars. Because most data collected for use in MOBILE2 have been from vehicles roughly equal in size to or larger than the Celeb- rity, inaccuracies in load simulation have no significant effect on the accuracy of MOBILE2. However, should minicars (<2000 Ib) ever occupy a significant percentage of the vehicle miles traveled (VMT), a re-evaluation of dynamometer load simulation will become necessary. With regard to the Modal Model evalua- tion, results in tests on only one vehicle cannot in themselves disprove the model. This is true because the model was recommended for prediction of vehicle group emissions and not individual vehi- cle emissions. However, because high tech emission control systems have changed the relationship between vehicle speed and emissions since the model's development, the Modal Model should be updated. The EPA author. Peter Gabefe (also the EPA Project Officer, see below), is with Environmental Sciences Research Laboratory, Research Triangle Park, NC 27711, and Richard Snow is with Northrop Services Inc., Research Triangle Park. NC 27701. The complete report, entitled "Effect of Load Simulation on Auto Emissions and Model Performance," (Order No. PB 84-120 369; Cost: $8.50, subject to change) will be available only from: National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 Telephone: 703-487-4650 The EPA Project Officer can be contacted at: Environmental Sciences Research Laboratory U.S. Environmental Protection Agency Research Triangle Park, NC 27711 #U.S. GOVERNMENT PRINTING OFFICE: 1983-759-015/7248 United States Environmental Protection Agency Center for Environmental Research Information Cincinnati OH 45268 Official Business Penalty for Private Use $300 « ------- |