Abstract: The injection of supercritical n-decane into a quiescent atmospheric environment was experimentally investigated to study the jet structures and phase transition process near the nozzle exit.It was found that supercritical n-decane jets injected above the critical point underwent ideal gas-like expansion and exhibited visible Mach disk shock structures.The axial location of the Mach disk increases with the growing injection pressure,and the injection temperature has little effects on the axial location of Mach disk.The phase transition process analysis reveals that,the supercritical n-decane is penetrated directly into the gas region from the supercritical region at the nozzle exit,without passing through the two phase region at higher injection temperature.Supercritical n-decane condensation phenomenon occurs in the nozzle and the outlet,and the fuel passes through the two phase region when fuel is injected near the critical point.