Comparison and optimization of strategies for ammonia-diesel dual-fuel engine based on reactivity assisted jet ignition and reactivity turbulent jet disturbance under high load conditions

Abstract

Ammonia (NH3), as a zero carbon, easy to synthesize, and easily obtainable fuel, is one of the choices for future internal combustion engine fuels. However, the slow laminar flames speed and high ignition temperature of NH3 seriously hinder the development of NH3 engines. Efficiently igniting NH3 and ensuring its stable combustion is currently a challenging research topic. Utilizing diesel to optimize the NH3 combustion process is one effective solution. However, the increase of unburned ammonia (UNH3) and unstable combustion, under high load conditions have always been technical challenges that constrain the development of ammonia-diesel dual-fuel (ADDF) engines. Previous studies have found that pre-chambers (PC) have a significant effect on improving ammonia combustion characteristics. Therefore, based on the PC system, this study proposes two combustion modes: Reactivity Assisted Jet Ignition (RAJI) and Reactivity Turbulent Jet Disturbance (RTJD), which greatly optimize the combustion characteristics of ADDF engines under high load conditions. The research results indicate that the RAJI mode effectively improves the thermal environment inside the cylinder. Setting the start of diesel injection of pre-chamber (SODI-PC) at −14 °CA after top dead center (ATDC) can increase the cylinder temperature by 25.05% before the start of diesel injection of main chamber (SODI-MC). The improvement of thermal environment reduces the average generation of N2O to 13.56% of the traditional mode. However, if SODI-PC is postponed to −8 °CA ATDC, the effect of creating a thermal environment is no longer significant. Research on the RTJD mode has found that adopting the RTJD mode can significantly optimize emissions. Compared with traditional modes, N2O, UNH3, and Soot decreased by 28.81%, 27.79%, and 35.08%, respectively. Additionally, SODI-PC is delayed until after 4 °CA ATDC, CO and UHC will be further reduced to 50.00% and 12.24% of the traditional mode, respectively. In addition, the RTJD mode overcomes the deficiency of the slow laminar flame speed of NH3, shortening the combustion duration by 23.46%, and effectively improving the gross indicated thermal efficiency (ITEg) by an average increase of 1.08%, with the highest increase reaching 47.57%. This paper provides ideas for optimizing the structure and strategy of ADDF engines, as well as theoretical support and empirical reference for achieving clean and efficient combustion of engines.