Full cycle CFD modeling of a Wankel engine for UAV applications

Rotary engines represent a very attractive solution for uncrewed aerial vehicle applications (UAV) and portable power generation thanks to their compact size, high power-to-weight ratio, reduced moving parts and possibility to operate with multiple fuels. Despite very promising, such technology needs to be improved in different areas to reach same efficiency and lifespan of reciprocating IC engines. In particular, fuel consumption is affected by the heat losses resulting from the high combustion chamber surface-to-volume ratio and by the unfavorable interaction between rotor and stator slowing down the flame propagation. Within this context, computational fluid dynamics (CFD) represent a valuable tool to study and design Wankel engines, understanding how fuel efficiency is affected by the complex interplay between combustion chamber design, flame propagation, flow and turbulence distribution. This work presents a CFD methodology for the simulation of gas exchange and combustion in Wankel engines: a single working chamber was considered in the CFD domain whose mesh is deformed over the whole cycle and dynamically connected with the intake and exhaust ports. Flame propagation is described by a flame area model. Validation was carried out in operating conditions representative of UAV operation at constant speed and variable loads. CFD simulation results were compared with experimental data of in-cylinder pressure and heat release rate. For a complete assessment and to validate the cylinder pressure during the gas exchange process, results were also compared with 1D engine simulation data. Satisfactory results were achieved demonstrating that the proposed approach could be applied to design and optimize Wankel engines with high degree of accuracy and reduced computational costs.