One-dimensional analyses of pulse detonation engine (PDE) have been performed by numerous workers without considering injection phase. 1-D codes have fundamental defects in considering transport processes (viscosity, heat conductivity and diffusion) and injection phase. In studying PDE, a key issue would be how to generate a CJ/quasi-CJ detonation in a short distance. Therefore, investigation of injection and ignition has become unavoidable. In the present analysis, the performance of straight single Model PDEs having various tube lengths is studied; for combustion phase, exhausting phase and injection phase, using two-dimensional unsteady calculations, where we used a MacCormack-TVD numerical scheme to solve Navier-Stokes equations.