The flow of high-speed unsteady jets are analyzed by using computational fluid dynamics for incompressible flow with k-ε turbulence model. The pseudo-nozzle concept is applied to the inlet condition with large pressure gradient. The results show that the time history of jet development is successfully agreed with experimental data for methane and hydrogen fuels. The effects of inlet condition of turbulence intensity and scale on flow are investigated. Also, to calculate this type of jet minimum requirement of grid resolution is revealed