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 COR2R resulted. It was noted that under the lean combustion condition, COR2R emission was controlled by air-fuel equivalence ratio; while under the rich combustion condition, COR2R 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.