Experimental study on sparking ignition engine performance for optimal mixing ratio of ethanol–gasoline blended fuels

•The optimal mixing ratio of ethanol–gasoline blended fuels is proposed.•At low speed, the optimal mixing ratio will increase torque output significantly.•E40 and E50 fuels provide the highest brake thermal efficiency.•E20–E40 fuels provide the highest maximum brake torque.

The purpose of this study is to experimentally determine the optimal blend rate of ethanol–gasoline fuels in order to maximize the brake thermal efficiency of a commercial SI engine. In this study, the engine performance, in terms of brake torque and brake specific fuel consumption, has been investigated with variation of volumetric mixing ratio between 87.5-octane gasoline and 99.5%-purity ethanol (E10, E20, E30, E40, E50, E60, E70, E85, and E100). The experiment has been conducted at different engine speeds and percentages of intake-throttle opening. The tests were performed at a constant compression ratio. The relative air–fuel ratio was tuned to unity and the ignition timing was tuned for maximum engine torque. The experimental results indicated that the appropriate ethanol–gasoline mixing ratio can enhance engine torque output, especially at low engine speed. The brake thermal efficiency is maximum when the engine operates at 58–73% of WOT with an engine speed of 2000–2500 rpm, using E40 and E50 fuels. This paper also provides a guideline for a suitable ethanol–gasoline blend rate at a certain engine load and speed.