Numerical study of the compression ignition of ammonia in a two-stroke marine engine by using HTCGR strategy

Pure ammonia is challenging to utilize in internal combustion engines (ICE) due to its high auto-ignition tem-perature, long ignition delay time, and low laminar flame velocity. To overcome this, this study proposes a novel technique called high-temperature cylinder gas recirculation (HTCGR) to achieve the compression ignition of pure ammonia in a two-stroke low-speed marine engine. The fundamental idea of HTCGR is that the in-cylinder gas during the expansion stroke is recirculated to heat the working fluid during the compression stroke, which is different from the exhaust gas recirculation (EGR) method. The numerical simulation results show that the cylinder temperature can be reached up to 1200 K in CGR mode before the fuel injection while remaining at the same level of compression pressure near the top dead center (TDC) as in the original diesel mode. In HTCGR mode, the two-stroke low-speed marine engine can achieve compression ignition of pure ammonia thanks to the high in-cylinder temperatures. Furthermore, thermal efficiency can approach 50%. This paper provides a novel and reasonable solution for the application of ammonia, a carbon-free energy source, in two-stroke low-speed marine engines.