Optimal Energy Management for Variable Fuel Quality in Hybrid Electric Vehicles 2019-01-2219
Efficiency of Hybrid Electric Vehicles (HEV) strongly depends on the implemented energy management strategy (EMS) that splits the drivers torque request onto internal combustion engine (ICE) and electric machine (EM). While in conventional vehicles overall efficiency decreases by using low quality fuel (in terms of octane rating), in HEV this effect can amplify itself. This is due to the restricted ICE operation to higher load areas, where the risk of engine-knock is increased.
Since the EMS can set the ICE operation point flexible, the author suggests consideration of fuel quality (Research Octane Number RON) within the EMS to exploit the full fuel saving potential of HEV.
This paper examines three different fuel qualities, with varying octane rating, on the engine test bench. Results show that the operation range of optimal ICE efficiency varies significantly between them. While high octane fuel allows a broader usable area for ICE operation in HEV, low octane fuel has a negative impact in knock relevant areas. However, this peril can be avoided by adapting the EMS.
Test bench data is used to generate fuel-specific EMS for each octane rating. EMS development is done by longitudinal simulation for different driving cycles.
Furthermore, an Engine-in-the-Loop (EiL) system, capable of reproducing Full-HEV behavior, such as torque- controlled ICE starts while electric driving is evolved. Through this the EMS is evaluated on the real ICE in a simulated HEV environment.
Purely simulative results as also the results from the EiL test bench show that by adapting the EMS, fuel consumption can be kept comparable among different fuel qualities and unnecessarily high fuel consumption can be prevented. An improvement of efficiency up to nearly 10% was observed in extreme circumstances. Especially, if only low octane fuel is available, this seems to be a promising approach for using the full fuel saving potential of HEV.