Trans/supercritical injection has great potential for improving the formation of combustible gas mixtures and emission performance. In our work, based on the sufficient validation of the current numerical framework, we compared the PR EoS with the RK-PR EoS and applied them to simulate the injection events under trans/supercritical conditions. The effects of different nozzle diameters and chamber conditions on jet characteristics and pseudo-boiling were investigated. The results show that RK-PR EoS has higher prediction accuracy. The nozzle diameter has a significant effect on fuel injection characteristics, and the time required to undergo the pseudo-boiling process becomes longer with increasing nozzle diameter. Compared with chamber temperature, chamber pressure has a greater effect on the fuel breakup. The high pseudo-boiling intensity caused by the low supercritical pressure significantly increases the jet length and reduces the mixing layer thickness. In addition, unlike the single-component case, the occurrence of mixing affects both pseudo-boiling and its intensity.