Impact of Hydrogen Energy Fractions on Cycle-to-Cycle Variations in Biogas-Fueled Spark Ignition Engine

The limitations related to the cost-effectiveness and technological feasibility of upgrading biogas to bio-methane for rural power generation applications have prompted researchers to explore alternative approaches for improving the quality of biogas fuel. This study focuses on evaluating the effect of hydrogen enrichment on combustion characteristics and cycle-to-cycle combustion variations in a single-cylinder spark ignition engine fueled with biogas (60% CH₄ and 40% CO₂). The engine was run at a constant operating load of 6 Nm, with a compression ratio of 10:1 and an engine speed of 1500 rpm. To establish a baseline for comparison, engine characteristics were initially assessed using pure methane fuel. Subsequently, the share of hydrogen in the biogas fuel mixture was incrementally increased on the volumetric basis from 0% to 30% and experiments were performed to study the effects of these variations on combustion behavior. The statistical approach was adopted for analyzing cycle-to-cycle variations by considering 120 consecutive engine cycles. The results of this study showed that increasing the H₂ share from 0% to 30% in an SI engine powered by biogas improved the combustion characteristics (increment in peak in-cylinder pressure; reduction in COV_IMEP from 9.9% to 1.7%; improvement in combustion phasing). With the addition of H₂, flame propagation speed increased and combustion time decreased. Results indicated that hydrogen enrichment resulted in lower cycle-to-cycle variations (CCVs) of pressure and combustion-related parameters.