Comparative investigation of energy balance and heat losses in a single-cylinder hydrogen- and gasoline-fueled SI engine

This study presents an experimental and numerical investigation of the energy balance and heat losses in a singlecylinder spark-ignition engine operated on hydrogen and gasoline under matched conditions. Experiments were conducted at indicated mean effective pressures (IMEP) of 3 and 5 bar over 1000-5000 rpm and were supported by a validated one-dimensional (1-D) simulation model that showed close agreement with measurements. The comparative analysis indicates that hydrogen alters the distribution of the fuel-supplied energy, yielding higher coolant and exhaust fractions when expressed relative to input energy, while absolute heat rejection is comparable to or lower than gasoline. Variations in coolant parameters produce only minor effects: increasing flow rate has a negligible impact on efficiency and heat rejection, whereas elevating inlet temperature moderately reduces coolant losses, with more pronounced effects at lower load. Overall, hydrogen enhances combustion efficiency and reduces residual losses, while gasoline imposes greater absolute thermal loading. Uniquely, this work provides a direct, head-to-head comparison on the same single-cylinder SI engine and delivers a validated, single-framework integration of combustion, cooling, and lubrication circuits, jointly resolving coolant, exhaust, and oil heat-loss pathways for both fuels. It quantitatively maps how coolant flow rate and inlet temperature govern total and fractional heat-loss pathways. These findings provide actionable guidance for thermalmanagement system design in hydrogen engines.