Numerical simulations, based on an engine where data can be obtained from the literature, were used to obtain detailed data of the variables in the interior of the engine. Visualization of relevant variables were used to in detail analyze the events going on in a pulsejet. In the simulations propane was used as fuel. It was found that the efficiency of the operation of the engine was markedly improved when the equivalence ration was reduced from stoichiometric to a lean value of 0.6. The numerical results could be used to provide an understanding of this behavior; it was shown that at stoichiometric conditions a rather large part of the combustion occurred at a pressure below ambient, whereas for the leaner case this "low pressure burning" was reduced to a high degree. This result compares well with the claim in a thesis from University of Texas, "The synchronous injection ignition valveless pulsejet", 1987, that an improved strategy for injection and ignition could improve the performance of a pulsejet to equal that of a turbojet. And according to this thesis this improvement should be achieved by forcing the combustion to occur at a more favorable time in the cycle (when the pressure is higher). This particular result was reproduced with a performance model developed in this study.