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Butanol has been proposed as a biologically derived fuel that has significant advantages over ethanol in terms of energy density and miscibility with diesel. This has generated the need to study separately and evaluate comparatively the in-engine combustion of the four isomers of butanol. Previous studies on the combustion of butanol isomers in laminar premixed flames have shown that while the isomers exhibit several similar combustion characteristics, including adiabatic flame temperature and flame speed, pollutant formation is highly dependent on the precise chemical structure of each isomer. The objective of this study is to build on these findings by investigating the effect of three of the four butanol isomers (n-butanol, isobutanol, and sec-butanol) on engine performance and emissions. The three isomers were blended as 30% butanol and 70% gasoline on a mass basis. These fuel blends were tested in a single-cylinder port-injection spark-ignition engine.

An experimental investigation was conducted using a Ford single-cylinder spark-ignition research engine to compare the performance and emissions of neat n-butanol fuel to that of gasoline and ethanol. Measurements of brake torque and exhaust gas temperature along with in-cylinder pressure traces were used to study the performance of the engine and measurements of emissions of unburned hydrocarbons, carbon monoxide, and nitrogen oxide ere used to compare the three fuels in terms of combustion byproducts. It was found that gasoline and butanol are closest in engine performance with butanol producing slightly less brake torque. Exhaust gas temperature and nitrogen oxide measurements show that butanol combusts at a lower peak temperature. Of particular interest were the emissions of unburned hydrocarbons which were between two and three times those of gasoline suggesting that butanol is not atomizing as effectively as gasoline and ethanol.