Ammonia thermal atmosphere compression ignition engine: Stable combustion mechanism and intake control strategy

Abstract

Ammonia is a promising carbon-free fuel for internal combustion engines (ICEs). However, existing research has not yet provided satisfactory solutions for ammonia combustion, a crucial gap that significantly limits its practical application. In this study, ammonia thermal atmosphere compression ignition (TACI) combustion mode was proposed as a promising solution to achieve efficient and clean ammonia diffusion combustion in ICEs. This study investigates the stable combustion mechanism of ammonia spray, the formation characteristics of nitrogen oxides, and the greenhouse gas (GHG) reduction potential of the ammonia TACI combustion mode. Experimental results of the TACI mode demonstrate high thermal efficiency, low NO_x emissions, ultra-low N₂O emissions, and negligible unburned ammonia slip. Intake control strategies, including intake pressure and intake temperature, are explored to further improve the ammonia substitution ratio (ASR) and GHG reduction performance. Intake air heating significantly improves the ASR, but must be coupled with high intake pressure to ensure sufficient oxygen supply. The combined strategy of intake air heating and high intake pressure increases the ASR by 17% and the GHG reduction ratio by 9%. Under medium-load conditions, this approach achieves an ASR over 80% and GHG reduction exceeding 70%, meeting the International Maritime Organization (IMO) 2040 GHG reduction target.