Exhaust emissions and energy release rates from a controlled spark ignition engine using ethanol blends

Abstract

Although alcohols have been considered and used as fuels for internal combustion engines for decades, their use in automotive transportation systems has been rather limited. In the past few years, ethanol has received varying amounts of attention in the United States owing to the increasing cost of gasoline fuel and legislative mandates in some states requiring the sale of alcohol-blended gasoline for light-duty vehicles. This may, in the end, help the agricultural economy in the United States. If alcohol blends are to be used in spark ignition (SI) engines designed to operate on gasoline, then it is important that engines be tuned for the fuel that is being utilized at that instant. This requires knowledge of the combustion characteristics of alcohol blends so that the engine control system can make appropriate changes according to the quality of the blend. The present investigation was conducted to evaluate the combustion and exhaust emissions characteristics of ethanol-gasoline blends in a two-valve automotive SI engine. Ethanol blends improved the specific energy consumption relative to pure gasoline fuel. At stoichiometric air-fuel ratio, the alcohol blends improved exhaust CO emissions marginally. However, there were consistent reductions in NO _x levels, particularly with the E-85 blend. The use of E-85 in the engine also resulted in a reduction in HC levels relative to neat gasoline, but E-85 produced significantly higher levels of acetaldehydes by comparison with neat gasoline and lower ethanol blends, particularly at lighter engine loads. The E-85 blend required a longer time to develop and set up the flame in the combustion chamber relative to neat gasoline. This was particularly true at lower engine loads, probably owing to cooling effects of the inducted charge. However, the rapid combustion duration did not exhibit much difference between the blends and gasoline.