A team from Tsinghua University, with colleagues from BYD research, investigated the impact of NH₃ 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. A paper on their work is published in the journal Fuel.

The experimental investigation was complemented by chemical kinetic calculations. The results showed that NH₃ 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 NH₃ was blended, NO_x emissions decreased with advancing spark timing, indicating a negative correlation with pressure.

The NH₃ 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 NH₃ 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 three-body reactions. Interestingly, NO_x emissions initially increased with increasing nh3 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.

—Liu et al.

Resources

• Shang Liu, Zhelong Lin, Yunliang Qi, Guoxiang Lu, Bo Wang, Li Li, Zhi Wang (0024) “Combustion and emission characteristics of a gasoline/ammonia fueled SI engine and chemical kinetic analysis of NO_x emissions,” Fuel, Volume 367, doi: 10.1016/j.fuel.2024.131516.