Study on decarbonizing ocean shipping propulsion power by liquid ammonia with centralized jet-flame controlled combustion strategy

Abstract

Nowadays, the ocean shipping carbon emission accounting for 2∼3% of global carbon emission. As a zero-carbon fuel with higher volumetric heat density than hydrogen, ammonia has the potential to serve for marine engines, thereby aiding in the decarbonization of ocean shipping. However, as a fuel with weak flammability, ammonia engine still faces the problem of how to organize its combustion. This study investigates the feasibility of utilizing ammonia as the main fuel for marine engines and its combustion characteristics. A centralized jet-flame controlled combustion strategy for two-stroke marine engine are proposed to better organize the ammonia combustion in large combustion chamber. Firstly, the relative injection direction of ammonia and diesel was researched, ammonia and diesel injected in an opposite direction has better performance as the ignition happens downstream of ammonia spray with better fuel-air mixture for ignition and flame transport from downstream to upstream preventing flame hitting liner to avoid extinguishing. Secondly, centralized jet-flame controlled combustion strategy was researched in engine model. There are two phases of this combustion strategy, premixed combustion and diffusion combustion. The ITE and unburn ammonia most related to the premixed ammonia which was influenced by ammonia injection timing. The unburn ammonia most related to diffusion combustion. Ammonia injection direction concentrating in the center and flame transport from downstream to upstream can preventing ammonia flame from hitting liner and better the diffusion combustion efficiency than existing ammonia-diesel injected in same direction mode. A replacement rate of up to 98% for ammonia can be achieved while maintaining an indicated thermal efficiency (ITE) ranging from 43.7% to 50.4%. Unburned ammonia can be optimized from 4.4% to 0.18%.