The Evaluation of a New Kinematic Emissions Model on Real and Simulated Driving Cycles 2010-01-1564

The evaluation of vehicles real emissions circulating in urban areas is a basic activity for planning and management of implemented traffic measures aiming at emission control and air quality improvement.

National, region, and city emission inventories require overall average emission estimation based on modeling technique with a few input parameters such as fleet composition and mission profile, represented by average speed.

But in the field of emission modeling an important open issue is the very expensive costs of experimental campaigns needed to obtain driving cycle statistically representative of driving behavior, also if only in a specific link of a network.

A possible approach to deal with this problem is represented by the use of traffic microscopic simulation models which are capable to simulate individual car motion on the basis of traffic conditions, road characteristics and management rules. Here we want to investigate the possibility integration of traffic simulation models and emission factors model, from the point of view of emission modeling results.

So in this paper a new statistical approach capable to consider more attributes than the simple mean speed to characterize driving behavior is considered. This meso scale emission model, named KEM, Kinematic Emission Model, is able to calculate emission factor, considering as input the driving cycle. In particular, micro-simulation models can determine instantaneous kinematic characteristics of each vehicle moving on the simulated transportation network, thus providing the needed input parameters to the emission models. Its prediction emission factor has to be estimated as a consequence of the effect of some variables characterizing the different modes, that is idling, acceleration, deceleration and cruise, better than mean velocity of driving cycle.

In this paper some results concerning regulated pollutant emission are presented. For a defined case study, that is EURO II gasoline cars in a 1200-1400 displacement, the KEM model coefficient and predicted value for emission are calculated. After, some comparison are presented between measured and predicted emission value on a urban supplementary driving cycle, and on some simulated driving cycle coming from four different car following micro-simulation models, that use the supplementary driving cycle as starting cycle. Two different types of results are obtained. From the point of view of micro simulation models, it could be asserted that at least one of them should be calibrated, based on acceleration profile rather than solely on mean velocity of driving cycle. This feature has also a strong impact on the emission values resulting from modeling phase, generally for all pollutants, but especially for NOx. In fact it shows extremely high values for a specific microsimulated cycle. In general, the goodness of fit of KEM model to experimental measured emission is good. Also a comparison with COPERT IV curve for each pollutant is presented. The sensitivity assessment of KEM model, which is able to discriminate emission predicted values, resulting from the small differences between driving cycles generated from the micro simulation, is shown. So in conclusion, these differences couldn't highlighted by emission model that using only the average speed as input parameters.