Robert Vidon

Influence of driving cycles on unit emissions from passenger cars

Abstract Small samples of petrol engine or diesel cars, equipped with or without catalysts, were tested over 36 driving cycles divided into four categories – standard cycles and three sets of cycles more representative of real-world driving conditions. The tests addressed standard gaseous pollutants and fuel consumption and also less frequently measured pollutant such as CH4. In the first part of this paper we examine cold emissions in order to assess the duration of the cold start impact and the representativity of the cold ECE15 cycle. Then unit emissions are compared over the four driving cycle families. As compared to representative cycles, the standardised cycles underestimate hot emissions by almost 50% for petrol engine cars and 30% for diesel vehicles. Conversely, the results obtained for the three representative cycle families are in relatively close agreement with each other – within approximately 10%. However, the cinematic properties of the three families differ. Finally, we demonstrate that weighting all emission data equally, not taking into account the weight of each cycle in overall traffic, introduces significant biases, particularly when plotting emission vs. average speed curves.

Reliability of the current models of instantaneous pollutant emissions

Pollutant emissions and fuel consumption of passenger cars are usually assessed as a function of average as a function of average speed. Nevertheless a number of attempts were made to take into account the driving pattern using emission vs. instantaneous speed and acceleration models. Five quite similar models were developed in Europe. To which extent these instantaneous models are innovative as compared to conventional models? In a first step the various development stages of an emission-based model and the various associated errors are presented. Among the possible sources of error, we selected modelling-induced errors, enabling to compare rigorously the various model types in terms of performance. The analysis was performed using the Modem model, developed from the measurement results obtained over a sample of 150 vehicles, representative of French, English and German fleets, over 14 representative driving cycles under urban conditions. Average emissions as measured over these 14 cycles are compared to emissions calculated over same cycles using this model. Modelling errors range from -51% to +57% as a function of the considered cycle and the vehicle type. This inaccuracy is quite similar for the other four European models. This demonstrates the low reliability of the models used, which cannot be used to assess the impact of slight changes in the driving pattern, sometimes leading to completely false conclusions. These models are barely more precise than average speed based models. In a second step, a number of alternatives liable to improve the reliability of instantaneous models are contemplated: for example using another method for calculating acceleration, or increasing the number of speed and acceleration classes significantly. But this does not improve significantly the model reliability. Limited measurements performed on a catalyst vehicle demonstrated that very high engine loads, even if not frequent, play a significant role in emissions: sometimes they yield emission values a thousand times higher. It is therefore of prime interest to study them in a comprehensive manner. In addition, this demonstrates that each model should be developed from measurements carried out over a set of representative driving cycles under real-world driving conditions.

Evaluation and optimization of a hybrid urban Microbus

Urban buses have nowadays an important challenge which is to respect the local nuisances such as air pollution and noise while offering to their passengers a high level of accessibility and comfort. Hybrid drivelines are one potential alternative to respond to these constraints. In that context, the Transport and Environment Laboratory (LTE) of the INRETS is collaborating with an urban buses manufacturer with the aim to develop and optimize a 5.5 m, 22 passenger series hybrid plug in microbus. This paper presents the first phases of our research. Firstly, the microbus components description, the actual energy management and the traction motor working are presented. Secondly, the measurement phase carried out on the GRUAUs test bus site in Laval elaborates a start point to understand the various energy flows. After that, the model of the microbuss processing is developed using the LTE library VEHLIB and validated with measurements. Thus, some suggestions about new energy management laws are proposed in order to optimize the consumption of the internal combustion engine together with the battery behavior.

Evolution des émissions de polluants des voitures particulières lors du départ à froid

Abstract Evolution of pollutant emissions from passenger cars under cold start conditions. CO, CO 2 , HC, CH 4 , NO x and N 2 O emissions were measured on ten conventional petrol-engined passenger cars, ten vehicles equipped with a three-way catalyst, and five diesel-engined vehicles over a great number of driving cycles under hot or cold start conditions: two standardized European and American cycles, four hot cycles representative of real-world driving conditions, and three representative mini-cycles, which were repeated 15 times after a cold-start. Simultaneously, water and oil temperatures were measured to assess engine temperatures. The analysis of the results enabled the follow up of emission and temperature changes with time for various kinematic types. The limit of hot temperature, the duration of cold-start emissions (over about 6 km) and excess emission rates under cold start conditions could be thus determined. These parameters significantly vary a lot according to vehicle technology, driving behaviour and pollutant type. These results should allow an accurate modeling of excess emissions under cold start conditions.

Test d'une méthode alternative de mesures des émissions de polluants des voitures particuliéres Testing of an alternative method of pollutant emission measurement for passenger cars

An on-board sampling system (mini-CVS), an alternative method for measuring passenger car pollutant emissions to the CVS, has been tested. Firstly, the emissions of a specific vehicle were compared according to the representative driving cycles on a chassis dynamometer using a mini-CVS and then a CVS. Secondly, the reliability of the mini-CVS system has been tested through measuring pollutant emissions of three vehicles over about 20 trips, according to three different methods; on-road mini-CVS sampling, then CVS and mini-CVS sampling on a chasis dynamometer using the same speeds. In addition, the relation between the number of on-road tests and the accuracy of the measurement average has been determined. It can be noted that the measurement using a mini-CVS are reliable and close to the measurements carried out with a CVS, provided that the number of rules are met. On road, only five to six trips are required to assess with a 10% margin, the emissions of a vehicle for specific traffic conditions. Finally, the method has been tested during a measurement campaign (about 150 trips) in Mexico City to obtain emission factors representing the actual use conditions of Mexican vehicles.