In order to understand the behavior of transient gaseous injection used in an LPG (Liquefied Petroleum Gas) engine, turbulent incompressible transient jets with butane and propane were measured and analyzed at pressures of 1.5 bar and 2.0 bar with injector diameters of 3 mm and 5 mm. Mie-scattering method with a tracer was used, and images were processed to investigate the behavior of butane and propane jets. Distances from the nozzle to transition region were measured as $L_e/d_{inj}$=4.35~19.4, where $L_e$ and $d_{inj}$ indicate respectively a distance from nozzle to transition point and nozzle diameter. Slits and tubes around jet at near-field were introduced to measure the effect of entrainment and the diameter of jet, which revealed that the entrainment of surrounding air is significant for developing jet diameter. When the entrainment is restricted, the behavior of jet became deviating from the baseline. It was found that the virtual origin located outside of a nozzle towards jet tip within the conditions of this work, and its location was estimated as $x_o/d_{inj}$=0.56~7.25, where $x_o$ is a distance from nozzle to virtual origin.