Numerical analysis of localized fin cooling for thermal, power and emissions improvements of UAV Wankel rotary engines

Wankel rotary engines (WREs) have become an important research focus for unmanned aerial vehicle (UAV) propulsion systems owing to their exceptional power-to-weight ratio. However, combustion heat release and complex heat transfer result in persistently high thermal loads in local regions, seriously impairing engine reliability and performance. This study employs a 1D 3D coupled simulation approach. First, enhanced cooling fins are introduced to optimize the cooling water jacket structure of the WRE. Subsequently, based on the optimized structure, the effects of fin configurations on WRE performance and emission characteristics are investigated at various engine speeds. At 3000 r/min, rectangular straight fins exhibit significant cooling enhancement: the average temperature of the cylinder wall decreases by 23 K, while the in-cylinder mean pressure and heat release rate increase by 3.8% and 4.5%, respectively. By lowering the in-cylinder mixture temperature, rectangular straight fins suppress NOₓ formation, reducing NOₓ concentration by 5.11%. Analysis under variable-speed conditions reveals that the optimization benefits of rectangular straight fins on WRE performance and emissions are maintained across the entire speed range, with the most pronounced improvement observed at 4000 r/min. The rectangular straight fin structure effectively improves the thermal load distribution on the cylinder wall, reducing the average cylinder wall temperature and maximum temperature difference by 5.7% and 15.8%, respectively. In addition, it increases the indicated power of the engine by 4.01% and reduces NOₓ and CO emissions by 5.90% and 6.80%, respectively.