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. In the present study, the concept of the threshold sooting index (TSI), which has been proposed as the sooting tendency in fuel flames, was incorporated into the soot formation model in KIVA-3V code. The soot emission trend obtained in the experiments was clearly shown in the present simulation by considering the characteristic TSI values for each alcohol and gas oil as well as the alcohol blend ratio.
