A diesohol fuel (10% bioethanol, 89% Thailand diesel fuel and 1% additive) may be used as an alternative fuel in a compression ignition engine. However, higher compressibility, lower energy content, and lower cetane number of the diesohol tend to increase the ignition delay and reduce engine efficiency. In this study, to get more knowledge on the diesohol combustion characteristics, an experimental study of luminous combustion in a swirl chamber of an IDI engine was performed to compare the combustion phenomena between diesel and diesohol. Two-color method was applied to obtain spatially and temporally resolved two dimentional distributions of flame temperatures and soot in flame. The imaging system used for this study was based on a wide angle endoscope that is mounted in the cylinder head of the combustion chamber. The experiments were carried out on a commercial 2.5 litre IDI engine. Through systematic experiments, it was explored the effect of ethanol in diesohol blend. Observed diesohol fuel sprays have shown either longer spray tip penetration length or wider spray angle than the reference diesel. Images of spray combustion shown in figure 1 indicate that the period of diesohol combustion phenomena occurred more retard with respect to TDC than diesel. As its consequence, together with the lower heat of combustion, the predicted combustion flame temperature and soot in flame density distribution, shown in figure 2 and 3, are lower than the reference diesel. Observation in swirl chamber shows detail of the complex inflammation and combustion processes.