Experimental study on the combustion and emission characteristics of ammonia-diesel dual fuel engine under high ammonia energy ratio conditions

Abstract

Ammonia (NH3) is considered one of the most promising carbon-free fuels for internal combustion engines. Adopting diesel-NH3 dual fuel combustion mode is the most convenient way to utilize NH3 fuel in compression ignition engines. Increasing the proportion of NH3 fuel is a key factor in effectively reducing carbon emissions. Therefore, in this paper, the combustion and emission characteristics of the engine under high proportions of NH3 ratios were investigated. Compared to conventional diesel combustion (CDC), diesel-NH3 dual fuel combustion leads to a significant increase in the ignition delay. High NH3 energy ratio (ER) at low loads result in deteriorated combustion, whereas as the load increases, the fuel concentration in the cylinder increases and the reactivity strengthens, leading to enhanced combustion performance. At an indicated mean effective pressure (IMEP) of 10 bar and an NH3 ER of 0.6, the indicated efficiency can reach 44.5%. Increasing the intake pressure can improve the in-cylinder thermal atmosphere but reduces the equivalence ratio of the premixed NH3 fuel, resulting in deteriorated combustion and a continuous decrease in indicated thermal efficiency. Therefore, the impact of the NH3 fuel equivalence ratio is greater compared to the in-cylinder temperature and pressure environment under medium engine load conditions.