Investigation of the Series Hybrid Electric Powertrain Architecture with Wankel Engine as a Range Extender

In this study, a conventional vehicle is converted into a series hybrid electric vehicle. Electric motor power, battery pack capacity, range extender operating condition is determined; a computational model of the vehicle is built and simulations are conducted using Worldwide Harmonized Light Vehicles Test Procedure (WLTP). Power rating of the electric motor is calculated as 120 kW for the same acceleration performance. Wankel engine data available in the Automotive Laboratory of Istanbul Technical University are used. Energy capacity of battery pack is determined according to the daily driving distance of the WLTP. Engine on-off control strategy is used to control range extender operation. Wankel engine is operated at a speed of 4000 rpm and load of 5.15 bar, hence it is tuned to deliver an output power of 22.3 kW. Simulation results show that the performance of Wankel engine is validated as range extender by using engine on-off control strategy. State of charge of battery pack is set as minimum (30%) at the beginning of simulation and the state of charge of the battery pack charged by the range extender is assumed to be approximately 50% at the end of the cycle. For comparison, performance of Wankel engine is compared to the range extender of a mass-produced series hybrid electric vehicle, which has a battery pack capacity of 18.8 kWh. In conclusion, it is shown that a more compact range extender unit with a battery pack of 35 kWh is advantageous from the perspective of the packaging of the battery pack.