Development of an Engine-Vehicle Simulation Model for Prediction of Transient Performance 2019-01-1428
Transient engine/vehicle operation is challenged by off-design operating conditions. Consequently, it results in non-optimum performance and emissions. Experimentation on a vehicle under transient conditions is complex and hence robust computer models can be used for such studies. In this work, a transient engine simulation model was developed using commercial software called AVL Cruise. The model was validated using transient experiments from the engine test-bed. The reference engine’s ECU logic and control map values were used in the engine model. The fuel consumption, torque response, IMEP, turbocharger operating conditions and smoke emissions could be predicted fairly well under steady and transient conditions. Another flexible MATLAB model of the vehicle was also developed in order to provide the required inputs for the transient engine simulation code such as load torque, engine speed and gear ratios once the vehicle speed and road terrain were known. The coupled engine-vehicle models were able to predict the fuel consumption rate, emissions and also the influences of gear changes and drive ratio changes of the transmission.
It was observed that smoke spikes were common during transient operations. Hence, the default boost pressure demand from the ECU was corrected based on the rate of change of throttle position applied by the driver during transient operation. This enabled the smoke levels to be diminished considerably in the IDC, but with a marginal increase in the overall fuel consumption. Studies were also conducted on the influence of different gear shifting strategies on performance and fuel consumption, with the gear change happening at different engine speed ranges. Gear shifting strategies which keep engine speed at lower BSFC regions were identified. It was also found that by altering the final drive ratio and the 1st gear ratio, the vehicle can become more fuel efficient without losing its gradient climbing ability. On the whole, the developed methodology can be used as a preliminary step to predict the fuel economy and emissions of a vehicle as it is run on any given terrain.