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Recent pressures on vehicle manufacturers to reduce their average fleet levels of CO2 emissions have resulted in an increased drive to improve fuel economy and enable use of fuels developed from renewable sources that can achieve a net reduction in the CO2 output of each vehicle. The most popular choice for spark-ignition engines has been the blending of ethanol with gasoline, where the ethanol is derived either from agricultural or cellulosic sources such as sugar cane, corn or decomposed plant matter. However, other fuels, such as butanol, have also arisen as potential candidates due to their similarities to gasoline, e.g. higher energy density than ethanol. To extract the maximum benefits from these new fuels through optimized engine design and calibration, an understanding of the behaviour of these fuels in modern engines is necessary.

Levels of liquid fuel impingement on in-cylinder surfaces in direct injection spark ignition engines have typically been higher than those in port-fuel injection engines due to in-cylinder injection and higher injection pressures. The result is typically an increase in the levels of un-burned hydrocarbons and smoke emissions which reduce the potential fuel economy benefits associated with direct injection engines. Although different injection strategies can be used to reduce these effects to some extent, full optimisation of the injection system and combustion process is only possible through improved understanding of spray development that can be obtained from optical engine investigations under realistic operating conditions. To this extent, the spray formation from a centrally mounted multi-hole injector was studied in a single-cylinder optical direct-injection spark-ignition engine under part-load conditions (0.5 bar intake plenum pressure) at 1500 RPM.