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Measurements of temporal and spatial changes in the velocity and size of droplets of diesel fuel sprays under two injection pressures were conducted near the nozzle orifice by a laser 2-focus velocimeter (L2F). The result showed that the size of droplets under higher rail pressure was larger than that under lower rail pressure at the spray center and was smaller than that under lower rail pressure at the spray periphery. It was found that the size of droplets deceased in the downstream direction of the spray and the decrease rate increased with the rail pressure. The cross-sectional average velocity increased and the cross-sectional average size decreased with the rail pressure in the spray near the nozzle exit.

In order to realize a premixed compression ignition (PCI) engine by utilization of bio-alcohol, combustion characteristics of bio-alcohol blended with gas oil were compared between ethanol and n-butanol in a diesel engine. The effects of the ethanol blend ratio and the butanol blend ratio on ignition delay, premixed combustion, diffusion combustion, fuel consumption and exhaust emissions such as smoke density and NOx were investigated experimentally. It is found that ethanol almost burns out together with combustion of low evaporation temperature composition of gas oil in the premixed combustion period and the heat release in the diffusion combustion is based on mainly high evaporation temperature composition of gas oil, then, soot is formed in the diffusion combustion of gas oil. On the other hand, a part of butanol burns in the diffusion combustion, however, the combustion of butanol in the diffusion stage is not the cause of soot formation.