Numerical investigation on multiphase momentum coupling and transient combustion in a dual-fuel compound injection rotary engine

Achieving high-power-density propulsion under low-altitude-economy conditions remains a major engineering challenge for unmanned aerial vehicle Wankel rotary engines (WREs). This inherently stems from the severe spatial paradox within their crescent-shaped chambers: apex-seal flame quenching compounded by trailing-end unburned gas autoignition. To physically uncouple ignition enhancement from mitigating auto-ignition propensity, a customized gasoline/n-butanol compound injection strategy is proposed and evaluated. A high-fidelity three-dimensional computational-fluid-dynamics framework is adopted for this investigation. The model incorporates a detailed 110-species chemical mechanism and is thoroughly calibrated against Z160F engine bench-test data, with peak-pressure prediction error below 5.14%. This framework is used to clarify multiphase-flow characteristics and transient combustion dynamics. The investigation reveals that a reverse-direct injection topology of n-butanol makes full use of the WRE's dominant unidirectional bulk flow. As predicted by the CFD model, this aerodynamic interaction produces secondary turbulent kinetic energy up to 125 m 2 /s 2 and reduces wall-film formation. Consequently, a reactivity-stratified field is sustained: volatile gasoline accelerates early flame kernel development at the front, whereas high-latent-heat n-butanol is stably confined at the rear to weaken thermodynamic preconditions for end-gas auto-ignition. At the baseline speed of 4000 rpm, the B N30 strategy advances the main combustion phase and achieves a peak indicated thermal efficiency of 25.33%. Furthermore, thermal NOx, CO, and CO 2 emissions are concurrently mitigated by 24.72%, 17.23%, and 15.08%, respectively. Evaluated via the proposed specific thermo-environmental cost index (STCI), the B N30 strategy provides a comparative numerical multi-physics reference for optimizing active mixture stratification for low-carbon aero-rotary propulsion systems.