Review of combustion technologies for ammonia-diesel compression ignition engines: Approaches to achieving high ammonia substitution

Abstract

Ammonia, as a zero-carbon fuel, has great potential for meeting decarbonization targets in the internal combustion engine sector. This paper summarizes recent studies in which ammonia is used as a fuel for compression-ignition engines. Due to its low combustion reactivity, ammonia must be used in conjunction with a high reactivity fuel, such as diesel, to ensure stable engine operation. Currently, two main approaches are used to supply ammonia to the engine combustion chamber: ammonia port injection and in-cylinder direct injection. In the two routes, ammonia-diesel engines commonly face challenges such as low ammonia energy rate (AER), limited thermal efficiency, and high emissions of nitrogen-containing pollutants, especially under high ammonia substitution conditions. To address these challenges, this study reviews combustion technologies capable of achieving relatively high AER, such as premixed charge compression ignition (PCCI) and reaction-controlled compression ignition (RCCI), and analyzes their impact on combustion and emissions characteristics. This paper also examines combustion technologies under ultra-high AER conditions and finds that technologies such as diesel pilot injection and ammonia-diesel stratified injection can support stable engine operation. This review provides insights into current progress, remaining challenges, and future directions in ammonia-diesel engine combustion technologies.

Graphical abstract

Keywords

dual fuel engine / ammonia energy rate (AER) / compression ignition / combustion technology / emissions control

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