The influence of air-fuel ratio on engine performance and pollutant emission of an SI engine using ethanol-gasoline-blended fuels

Ethanol-gasoline-blended fuel was tested in a conventional engine under various air-fuel equivalence ratios (lambda) for its performance and emissions. The amount of fuel injection was adjusted manually by an open-loop control system using a CONSULT controller. It was found that without changing throttle opening and injection strategy, lambda could be extended to a leaner condition as ethanol content increased. The results of engine performance tests showed that torque output would increase slightly at small throttle valve opening when ethanol-gasoline-blended fuel was used. It was also shown that CO and HC emissions were reduced with the increase of ethanol 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 CO2 resulted. It was noted that under the lean combustion condition, CO2 emission was controlled by air-fuel equivalence ratio; while under the rich combustion condition, CO2 emission is offset by CO emission. It was also found that CO2 emission per unit horse power output for blended fuel was similar or less than that for gasoline fuel. From the experimental data, the optimal ethanol content in the gasoline and air fuel equivalence ratio in terms of engine performance and air pollution was found. (C) 2004 Elsevier Ltd. All rights reserved.