The effect of ethanol, butanol addition on the equivalence air-fuel ratio, engine performance and pollutant emission of an SI engine using gasohol fuels

Ethanol-gasoline and butanol-gasoline blended fuel was tested in a conventional engine under various air-fuel equivalence ratios for its performance and emissions. The results of engine performance tests showed that torque output would increase slightly at seventy percent throttle valve opening when ethanol-gasoline and butanol-gasoline blended fuel was used. It was also shown that CO and HC emissions were reduced with the increase of ethanol/butanol content in the blended fuel, which resulted from oxygen enrichment. At an air-fuel equivalence ratio slightly larger than one, the smallest amounts of CO and HC and the largest amounts of CO_R2R resulted. It was noted that under the lean combustion condition, CO_R2R emission was controlled by air-fuel equivalence ratio; while under the rich combustion condition, CO_R2R emission is offset by CO emission. From the experimental data, the optimal ethanol, butanol content in the gasoline and air-fuel equivalence ratio in terms of engine performance and air pollution was found.