Combustion and emission characteristics of a gasoline/ammonia fueled SI engine and chemical kinetic analysis of NOx emissions

Mitigating climate change involves the greater adoption of carbon - neutral and renewable energy sources within the transportation sector. Ammonia (NH 3 ), as a carbon-free and sustainable fuel, has garnered growing interest in recent years. The present study aims to investigate the impact of NH 3 blending on combustion and emission characteristics of a stoichiometric spark-ignition gasoline engine, with a particular emphasis on nitrogen-based emissions. The experimental investigation was complemented by chemical kinetic calculations. The results showed that NH 3 blending could effectively suppress engine knock, optimize combustion phase and improve thermal efficiency. For pure gasoline, advancing the spark timing resulted in increased NO x emissions. However, when NH 3 was blended, NO x emissions decreased with advancing spark timing, indicating a negative correlation with pressure. The NH 3 emission was attributed to the 'crevice mechanism ' as well as the absorption/desorption in the lubricant oil film on the cylinder wall. Chemical kinetic analysis revealed that the NO x emission from NH 3 blended combustion is closely related to reactive radicals such as OH, H and O. The reduction in NO x emissions under high-pressure conditions was primarily attributed to the consumption of these reactive radicals via threebody reactions. Interestingly, NO x emissions initially increased with increasing NH 3 blending ratio but eventually followed a decreasing trend. This can be attributed to the lower combustion temperature, lower concentration of reactive radicals, and enhanced de-NO x reactions.