Effects of Hydrogen Addition on Combustion Efficiency Enhancement and Emission Reduction in Natural Gas Engines

This work describes the inherent restrictions of natural gas engines regarding poor flame propagation velocity and poor lean-burn capability. A systematic research analysis was performed to explore the combustion behavior, performance benefits, and emissions changes with varying degrees of hydrogen enrichment. Experimental validation was performed using a six-cylinder Spark Ignition natural gas engine with varying levels of hydrogen enrichment (between 0% and 30%). Experimental validation included systematic changes in engine speed, load conditions, and equivalence ratios. The results clearly identified 20% hydrogen enrichment as optimal. Compared with natural gas operation, with 20% hydrogen enrichment, an 8.6% improvement in BTE efficiency, 29% reduction in combustion duration, and 45% reduction in cycle-to-cycle variations were achieved. Carbon dioxide emissions were found to reduce by 18.5%, largely aided by the substitution effect and efficiency gains. Sizable reductions in emissions of carbon monoxide (36%) and unburned hydrocarbons (42%) were also observed. An increase in nitrogen oxide emissions due to combustion at stoichiometric conditions with enriched mixes was effectively managed with proper operation at a lean ratio of 1.35. This ensured no increase in emissions while maintaining the achieved efficiency gains.