In the last few years, increasing concern about the harmful effects of the use of fossil fuels in internal combustion engines has been observed. In addition, the limited availability of crude oil has driven the interest in alternative fuels, especially biofuels. In the context of spark ignition engines, bioalcohols are of great interest owing to their similarities and blend capacities with gasoline. Methanol and ethanol have been widely used, mainly due to their knocking resistance. Another alcohol of great interest is butanol, thanks to its potential of being produced as biofuel and its heat value closer to gasoline. In this study, a comparative study of gasoline–alcohol blend combustion, with up to 20% volume, with neat gasoline has been carried out. A single-cylinder, variable compression ratio, Cooperative Fuel Research-type spark ignition engine has been employed. The comparison is made in terms of fuel conversion efficiency and flame development angle. Relevant information related to the impact in the combustion process of the use of the three main alcohols used in blends with gasoline has been obtained.

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Knock remains one of the main limitations for increasing the efficiency in spark-ignition engines. The use of certain alcohol–gasoline blends is an effective way to either mitigate or eliminate knock, allowing the use of higher compression ratios, therefore increasing the efficiency of spark-ignition engines. Methanol and ethanol are alcohols commonly employed for reducing knock, due to their higher octane number and vaporization heat value. Major attention is being paid recently to butanol and its blends with gasoline since they present similar characteristics to gasoline; however, it was found to be the least knock resistant among the three fuels. In the present work, a comparison between the knock performance of methanol–gasoline, ethanol–gasoline and butanol–gasoline blends is carried out, by volume concentrations up to 20 v/v%. This comparison is made in terms of knock intensity and knock probability. Tests are performed in a single-cylinder, variable-compression ratio, Cooperative Fuel Research engine equipped with port fuel injection system, facilitating the comparison against future results obtained by similar experimental facilities. Results obtained allow to reach meaningful conclusions about the capacity of each blend to mitigate knock.