Toward zero carbon emissions: High thermal efficiency low speed two-stroke marine engine using pure ammonia fuel

As the future development trend and the crucial link to achieving the carbon peaking and carbon neutrality goals in China, the achievement of "zero carbon" emissions in low-speed two-stroke marine engines is currently in the preliminary stages of exploration. Ammonia fuel is one of the main zero-carbon energy sources of interest for marine engines. The primary challenges associated with ammonia application include its high self-ignition temperature, low laminar flame speed, and lengthy ignition delay time. Although stable combustion can be achieved with the assistance of a small amount of highly active carbon-based fuel, carbon emissions are still inevitable. To obtain "zero carbon" emissions, the high-temperature cylinder gas recirculation strategy (HTCGR) was innovatively proposed to realize the possible application of pure ammonia. However, the heat transfer loss by using pure ammonia fuel is enhanced by 289% compared to the diesel mode. Therefore, the main objective of this article is to investigate ways to decrease heat transfer loss and further improve the thermal efficiency of the two-stroke engine from the perspective of energy distribution, and the effect of the circulating high-temperature gas, swirl ratio, and fuel distribution on heat transfer loss was systematically numerically studied in this manuscript. As a result, the heat transfer losses can be decreased up to 38.80% by lowering the CGR rate and adjusting the fuel distribution, and the ITE can be improved from 48.85% in the diesel model to 51.19% in the ammonia mode. However, to avoid incomplete combustion in the engine, a minimum CGR rate of 13.3% is basically required for the compression ignition of pure ammonia fuel.