Combustion characterization of an ammonia-hydrogen hybrid homogeneous charge compression ignition internal combustion engine

A simulation model of a homogeneous charge compression ignition (HCCI) internal combustion engine was developed using the CHEMKIN software to investigate the effects of key parameters, including hydrogen doping ratio (α), inlet temperature, and equivalence ratio (φ), on combustion performance. The study focused on in-cylinder temperature and pressure, heat release rate and NO emissions. Results reveal that increases in α and inlet temperature lead to higher in-cylinder temperature, pressure, and heat release rate, as well as earlier ignition timing. When φ approaches 1, peak values of in-cylinder temperature, pressure, and heat release rate are maximized, while the ignition timing advances as φ decreases. In-cylinder NO formation is only slightly affected by α; however, the peak mole fraction of NO rises with increasing α. As the in-cylinder combustion concludes, NO emissions decrease significantly. Increasing α from 0 to 0.2 considerably reduces NO emission. Although the main NO formation pathways remains unchanged, the total reaction rate increases. NO in the cylinder primarily originates from HNO, while NH primarily consumes NO. These findings provide feasibility evidence for improving combustion efficiency and emission performance in future ammonia-hydrogen HCCI engines.