Stratified combustion optimization in ammonia/hydrogen rotary engines through asynchronous dual-direct-injection with thermal load management

The downsizing of engines is confronted with the challenges of high local thermal load and poor fuel economy, which are particularly pronounced in rotary engines under the influence of strong unidirectional flow. To address these issues, this study investigates the impact of dual direct injection on the combustion process of the ammonia-hydrogen rotary engine. For this purpose, a three-dimensional model was established to ensure that the deviation of ammonia-hydrogen fuel is within 1 % under ignition timing. The research findings indicate that the hydrogen direct injection parameters play a decisive role in mixture formation and flame propagation, due to the combined effects of the high diffusion rate and the laminar flame speed of hydrogen. At H1, an ideal fuel distribution characteristic is achieved, where ammonia and hydrogen are highly uniformly distributed and concentrated in the front and middle parts of the combustion chamber, with a corresponding reduction in fuel allocation in the combustion dead zone. Moreover, the heat release rate curve at this point is more moderate, alleviating the problem of excessively high local thermal load. In terms of direct injection angles, compared to H+30° and H-30°, H0° can reduce NOx formation without sacrificing the heat release rate during the main combustion phase. This reduction ranges from 6.3 % to 39.5 %. In terms of asynchronous injection, injecting ammonia first and then hydrogen improves fuel mixing in the cylinder, reducing unburned NH3 emissions by 74.6 %. However, this approach may lead to higher NOx emissions.