Development of a Spark-Ignited Combustion Strategy for 100% Ammonia (NH3) Operation in Internal Combustion Engines

Ammonia (NH$_3$) is a promising carbon-free fuel for internal combustion engines, but its low reactivity and poor ignition properties present significant challenges for stable operation. This study presents the development and experimental validation of a spark-ignited combustion process that enables stable engine operation using 100% liquid NH$_3$ as a single fuel. A modified single cylinder research engine, equipped with NH$_3$ port fuel injection and a high-energy capacitive ignition system was used to investigate combustion behavior under various load conditions. The results show that stable, knock-free combustion with pure NH$_3$ is feasible at every operating point without any ignition aids like diesel fuel or hydrogen (H$_2$). The full load conditions of a diesel engine can be represented with an indicated efficiency of 50% using this combustion process. The emission measurements show nitrogen oxides (NO$_x$) and NH$_3$ emissions in a 1:1 ratio, which is advantageous for a passive SCR system. Increased nitrous oxides (N$_2$O) formation occurs at low loads and cold combustion chamber temperatures. This work demonstrates the technical viability of carbon-free NH3 combustion in spark-ignited (SI) engines and represents a promising step towards net-zero combustion.