Impact of Ammonia Share on Combustion, Cycle-to-Cycle Variations, and Performance Characteristics of Methane-Fueled SI Engine

Ammonia is one of the most promising zero carbon fuels for meeting carbon neutrality targets and zero carbon emissions. Ammonia has gained a lot of research interest recently as a hydrogen energy carrier, and direct use of ammonia as a fuel in engines will aid the transformation toward sustainable energy future. In this work, the effect of ammonia shares on combustion and performance characteristics of methane-fueled SI engine is evaluated by increasing the ammonia share by small fractions (0 to 30% by volume) in the fuel mixture (CH₄/NH₃ blend). Experiments were performed at constant engine load of 8 Nm (BMEP of 1.52 bar), while maintaining constant engine speed (1500 rpm), stoichiometric operation (λ = 1), and optimum spark advance for MBT conditions. Increasing the share of ammonia (0 to 30%) in the fuel mixture reduced its flame propagation speed and lowered the heating value, and thus resulted in lower peak cylinder pressures, detrimental engine performance (16.8 to 16.3% brake thermal efficiency), prolonged the combustion duration (FID and CD), and increased the cycle-to-cycle combustion variations (1.1 to 3.1% COV of IMEP). However, the COV of IMEP was observed to be within the acceptable range and the results of this study indicate that stable engine operation could be achieved by ammonia substitution in small fractions to get the benefit of clean fuel utilization.