Enhancement of Low Operating Load Limit and Engine Characteristics by Hydrogen Addition in a Biogas-Fueled Spark-Ignition Engine

Biogas is a renewable gaseous fuel and has the potential to replace fossil fuels for spark-ignition engines; however, a higher volumetric proportion of CO₂ in biogas degrades the engine characteristics significantly. Biogas upgradation techniques are limited by higher fuel costs, and strenuous modifications would be required for improving engine physical parameters. In this study, experimental investigations were performed with hydrogen-enriched biogas to enhance low operating load limit and engine characteristics, and to the best of authors' knowledge, studies related to operating range and low load enhancement by hydrogen addition in biogas fueled engines are not reported in literature. Gaseous-fuels blending setup was developed to fabricate the gaseous fuel mixtures in desired proportions and moderate amounts of hydrogen (5, 10, 20, and 30% by vol.) were blended with biogas. The experiments were conducted on a single-cylinder SI engine operated at the compression ratio of 10:1 and 1500 rpm for stationary applications. It was found that the coefficient of variation (COV) of indicated mean effective pressure decreased from 10% in case of biogas to 8.69, 6, 3.05, and 1.66%, respectively, for 5, 10, 20, and 30% hydrogen cases at 6 N·m loading condition. Low operating load limit enhanced from 6 N·m in case of biogas to 5.3, 2.2, 1.5, and 0.8 N·m, respectively, for 5, 10, 20, and 30% of hydrogen share in the fuel mixture and brake thermal efficiency also improved with hydrogen enrichment. Carbon-based emissions decreased with hydrogen addition, whereas oxides of nitrogen increased but it was well below the baseline case with pure methane. Overall results indicated that hydrogen enrichment enhances the low load limit and engine characteristics of biogas-fueled SI engines for stationary power generation applications in rural areas.