Increasing Efficiency and Reducing Emissions in a Small Displacement Gasoline Engine With Hydrogen-Enriched Natural Gas

There is currently a gap in the available literature on retrofitting engines with less-advanced control systems to run on hydrogen-enriched natural gas. Potential advantages of hydrogen-enriched natural gas in these engines may not be realized without altering parameters such as spark-timing, exhaust gas recirculation, or the air/fuel ratio. However, in such engines, changes in spark-timing and exhaust gas recycle are often cost-prohibitive, leaving equivalence ratio adjustments as one of the few remaining viable operational strategies. In this study, a small-displacement (319 cc), naturally aspirated, single-cylinder gasoline engine without spark-timing control was converted to run on a 10 vol% blend of hydrogen-enriched natural gas. Stoichiometric operation improved thermal efficiency, fuel consumption, and total hydrocarbon emissions, but higher NO_x emissions resulted. Despite no spark-timing control, lean-burn operation at an equivalence ratio of 0.7 was found to maintain performance improvements while also lowering emissions: fuel consumption was lowered versus the methane base case by 11%, and NO_x and hydrocarbon emissions were both decreased by approximately 70% below the base case. This study concludes that in a scenario even without spark-timing control, the addition of 10 vol% hydrogen can improve power, emissions, and efficiency of a spark-ignited natural gas engine, which serves as a proof-of-concept that even fairly simple, small-displacement engines can benefit from switching from gasoline to hydrogen-enriched natural gas operation.