ABSTRACT
The Wankel rotary engine offers unrivalled power density as a consequence of having a combustion event every revolution, as well as lightness, compactness and vibrationless operation due to its perfect balance. These attributes have led to its success as a powerplant for unmanned aerial vehicles, and which should also make it an attractive proposition for range-extended electric vehicles. However, it is not currently in production for automotive applications having historically struggled with poor combustion efficiency, and high fuel consumption and hydrocarbon emissions. The purpose of this work is to study the in-chamber flow motion in order to better understand how such limitations may be overcome in future. A 225cc 30 kW Wankel rotary engine is modelled using Large-Eddy Simulation (LES) to ensure turbulent flow features are faithfully recreated, since Reynolds-averaged Navier-Stokes-based approaches are insufficient in this regard. The LES-predicted peak chamber pressure lies within 3.7% of the engine test data, demonstrating good model validation. Combustion simulation parameters are calibrated to match the measured heat release profile, for high-load engine operation at 4000 rpm. Simulation results provide insight into the generation of turbulent structures as the incoming flow interacts with the throttle, intake port, rotor and housing surfaces; how the turbulence breaks down as the combustion chamber is compressed; and how the flame propagates following ignition, leaving a pocket of reactants unburned. Indeed, the computational approach described here allows detailed understanding of the impact of design parameters on the detailed in-chamber flow phenomena, and consequently engine performance and emissions. This will enable the optimization of Wankel rotary engine geometry, port and ignition timing for maximum combustion efficiency and low emissions, reasserting its potential as an effective and efficient prime mover for hybrid and range extended electric vehicles.
