Numerical investigation on recess geometry amelioration of an ammonia-hydrogen zero-carbon Wankel engine

The optimization of combustion chamber geometry is crucial for improving the combustion efficiency of rotary engines. This study aims to investigate the combined effects of recess structure and speed on the combustion process in ammonia-hydrogen rotary engines, with particular emphasis on reducing the recess size in terms of length, width, and height. The goal is to identify the optimal balance between recess dimensions and engine performance. Adjusting the recess size to optimize the combustion chamber geometry can, to some extent, enhance engine performance, especially in terms of emissions. Under the premise of balancing operational efficiency and emissions control, a recess design with the CR9.0W at 2000 rpm is recommended. This design results in a mere 0.5 % decrease in thermal efficiency, a reduction of two orders of magnitude in unburned ammonia emissions, and NO emissions as low as 1.24993 × 10−3 g/kWh. These findings suggest a potential direction for enhancing the performance of rotary engines. However, the reduction in recess size limits the heat and mass transfer between the front and rear sections of the combustion chamber, potentially leading to significant fluctuations in the combustion process and increasing the risk of knocking.