This paper presents the capability of improving the diesel spray atomization and dispersion process by dissolving N2 gas or liquefied CO2 into diesel light oil, n-tridecane, in order to obtain the lean and homogeneous mixture inside the combustion chamber. The new injection system for gas dissolved fuel and liquefied CO2 dissolved fuel was developed, and the dissolved fuel was injected into a vessel with a certain temperature and pressure. Then, spray characteristics were observed by several optical photographing methods. At first, N2 gas was dissolved into ntridecane under pressurized state by bubbling way. Here prompting the spray atomization should be expected by the effect of separated N2 gas in the spray after injection. However, in N2 gas dissolved fuel spray, negative effects for spray atomization appears to be due to the increase in fuel viscosity by the formation of bubbling flow inside the spray. Secondly, liquefied CO2 was mixed into n-tridecane under pressurized state in order to promote the spray atomization and evaporation, and to control the combustion process by the effect of internal EGR due to separated or flash boiled CO2 gas around the spray. As expected here, the characteristics of the spray with liquefied CO2 dissolved are extremely better than those of n-tridecane spray. The phenomena are promoted as the ambient pressure decreases, and the molar fraction of CO2 and the fuel temperature increase. Therefore, the reduction of soot and NOx believed to be achieved effectively by use of this liquefied CO2 mixed fuel injection system.