During the last decades, decreased emission levels of vehicles were achieved with more sophisticated engine technology, high efficient exhaust after treatment systems and complex engine control systems. Therefore the demand on models to simulate real-world emissions increased and the established models became increasingly inaccurate. Since flexible and accurate instantaneous emission models help to reduce the number of tests necessary for estimating vehicle emission factors, research to improve the models is necessary. Requirements on modern models are the simulation of fuel consumption and emissions for all possible combinations of driving cycles, vehicle loadings, road gradients and thermal conditions with adequate accuracy needing a few measurements as model input only. The model PHEM (Passenger car and Heavy duty vehicle Emission Model) is based on the simulation of the actual engine power demand and of the engine speed over a cycle. The thermal condition of the vehicle is simulated via a simplified heat balance. Thus it has a physically correct approach for all possible driving situations. A main problem for all approaches is to reach a satisfactory accuracy for modern gasoline cars CO, HC and NOx emissions under hot running conditions. The emission curves for those components are highly influenced by transient effects on the air-fuel ratio and the resulting changes in the efficiency of the catalytic converter. To predict such transient effects, the model was extended by adding correction functions, based on several transient parameters, such as derivates of the engine power and engine speed over different time spans. It was investigated, that improvements on the instantaneous emission models first of all need improved (i.e. corrected) instantaneous measurement data. Functions to correct for the effects of turbulent gas transport and analyzer response times on the measured emission concentration signal were elaborated. It has been shown, that it is possible to reconstruct the emission signals at the tailpipe location with a time quality of about 2 seconds from the diluted measurements out of an overall delay of up to 25 seconds. The improved measurement signals allow the emission data to be correlated to the correct state of engine power and engine speed. After correcting the instantaneous measurement signals, the emission maps for PHEM can be gained from standard tests of dynamic cycles on the roller test bed. Average engine maps and transient correction functions for EURO 0 to EURO 4 were elaborated successfully using the 'Common ARTEMIS Driving Cycle, CADC' to fill the engine emission maps. The model was already used in ARTEMIS to simulate all emission factors for HDV (Heavy Duty Vehicles) and to assess the correction factors for road gradients and loading for cars.
Improving an instantaneous emission model for passenger cars
Verbesserung des Momentanemissionsmodelles für Personenkraftwagen
incl. COST 346 - Final Conference, Transport and Air Pollution, International Symposium, 14 ; 167-176
2005
10 Seiten, 10 Bilder, 11 Quellen
Conference paper
English
Exploring ways to improve instantaneous emission models for passenger cars
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