Investigating the potential of two individually controlled injectors per rotor for a DI hydrogen Wankel engine

Hydrogen-fuelled rotary engines offer a promising alternative for zero-emission powertrains in commercial applications, particularly where compact packaging is required. This study presents experimental results of the further development of the naturally aspirated hydrogen rotary engine by HTM with direct injection, integrated with an electric machine into a hybrid or genset system. Despite the lower volumetric energy density of hydrogen compared to conventional fuels, the compact design of the rotary engine enables installation within the packaging of a conventional internal combustion engine with comparable power output. Initial applications, including an airport baggage tractor, have demonstrated the feasibility of the concept. However, engine calibration revealed pre-ignition phenomena that constrained the maximum achievable torque. To address this limitation, the influence of mixture formation is further investigated. An experimental engine setup is used where two individually controllable Bosch injectors are merged into the injection channel of one rotor. This study investigates the potential of this setup on operating behaviour, efficiency and NOx emissions. The testing shows that the use of two injectors significantly reduces the required injection duration, allowing a more precise spatial placement of hydrogen within the combustion chamber. This improved mixture control mitigates pre-ignition tendencies and enables a higher mean effective pressure. A systematic variation of injection timing in representative steady-state operation reveals further potential on efficiency and reduction of NOx emissions by different injection timings of both injectors. Comprehensive pressure measurement inside the combustion chamber and exhaust gas analysis provide detailed insight into the underlying combustion processes and occurring abnormal combustion events. Overall, the findings demonstrate that the double injector setup substantially enhances torque capability and operational robustness without increasing construction complexity. These results highlight the viability of hydrogen rotary engines as a compact and efficient solution for future zero-emission hybrid powertrains and stationary power generation systems.