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In order to utilize bio-alcohols as the fuel for diesel engines, combustion characteristics of alcohol blended with gas oil were compared between ethanol and n-butanol in a direct injection diesel engine. In the case of the same cetane number between ethanol and butanol blends, the time-history of combustion, in other words, the ignition delay, the diffusion combustion and the combustion duration, coincided almost completely in both blend fuels. However, the smoke density of the butanol blend was smaller than that of the ethanol blend. This result must be caused by difference in soot formation process between ethanol and butanol blends. Thus, it is difficult to predict the trend of the soot emission in combustion of alcohol blends only by using the existing phenomenological model of the soot formation in the combustion of gas oil.

A laser 2-focus velocimeter (L2F) was used for measurements of velocity and size of droplets in diesel sprays. The L2F has a micro-scale probe which consists of two foci. The focal diameter is about 3 μm, and the distance between two foci is 18 μm. The data acquisition rate of the L2F was increased to 15 MHz in order to capture every droplet appearing in the measurement volume. Diesel fuel was injected intermittently into the atmosphere using a 5-hole injector nozzle. The diameter of the nozzle orifice was 0.113 mm. The injection pressure was set at 80 and 120 MPa by using a common rail system and the ambient pressure was varied from 0.1 to 3 MPa. The period of injector solenoid energizing was set at 3.0 ms. Droplets were evaluated in a period of 0.2 ms just after the spray tip passed the measurement position. Measurement positions were located at 6, 9 and 12 mm from the nozzle exit. The effect of ambient pressure on the droplet velocity in the near-nozzle region was unremarkable.