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Fuel spray breakup in combustion engines and hence all following processes are determined by the primary atomization. Due to high optical densities as well as high velocities and structures in the μm-range, the measurement of sprays in the near nozzle region is extremely challenging. Therefore, the processes of the primary breakup are not fully understood yet, although these processes are very important for simulation of spray atomization. One important property of a spray is the velocity distribution close to the nozzle outlet. With the newly developed Structural Image Velocimetry (SIV) technique it is possible to visualize spray structures in the near nozzle region and track them via cross-correlation algorithms, so that two-dimensional velocity fields of the spray can be derived. The initial SIV technique is improved with a new high-speed setup, allowing to observe also the temporal behavior of the spray velocities during the injection.

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.