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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 2-D phase doppler technique was used for the measurements of the velocity, size, and flight direction of droplets in diesel sprays. The data acquisition rate of the phase doppler system was 250 kHz. Diesel fuel sprays injected intermittently into the atmosphere were investigated. The injector orifice was 0.113 mm in diameter. The rail pressure was set at 40 MPa by using a common rail system. The injection period was 3.0 ms and the time interval between injections was 330 ms. Measurement position was located at 40 mm from the nozzle exit for free sprays. In order to evaluate velocity vectors of each droplet, velocity components with angles plus and minus 45 degrees to the spray axis were measured. The data measured at each position was 10,000 and was accumulated over about 1,000 injections. It was found that most droplets near the spray center had velocity vectors along the spray axis.