Experimental study of impulse and heat transfer on pulse detonation engines

The pulse detonation engine (PDE) has recently become recognized as a possible new aerospace propulsion system. In the PDE system, self-sustained detonation waves propagate in tubes and burned gases are repeatedly exhausted backwards from behind the detonation. The PDE system produces a momentum whose absolute value is equal to the exhausted gas momentum, but whose direction is opposite it. The PDE system has high thermal efficiency on account of its constant-volume combustion and has a simple structure composed of tubes. Although the high efficiency of the PDE system has been confirmed, few experimental reports have been based on a fundamental cyclic theory. In the present paper, we apply Endo-Fujiwara simple cycle theory to the PDE in order to analyze the pressure history at an end wall (thrust wall) of the detonation tubes, the net momentum obtained on the PDE by direct-velocity measurement, and heat transfer from the burned gases to the tubes. As well, we estimated the PDE's specific impulses. Although the model overestimated the constant-pressure time duration by over 25% and simplified the exhaust phase as linear decay, the specific impulse obtained from the present experiments (187-361 sec) are roughly identical to the theory (-23% to +49%). It would be considered that the pressure overestimation by the model was balanced by the experimentally obtained higher specific impulse due to the small filling rate of the PDE. The net specific impulse based on net impulse measurement (direct-velocity measurement) was 67-147 sec, which was 28-60% of the Endo-Fujiwara theory. The difference between the two specific impulses is due to the momentum transfer on the sidewall of the tubes that was neglected in the pressure measurement. Heat, 11-15 MJ/kg, was transferred from the burned gases to the tubes during one-cycle operation. This value was 8-11% of the gross calorific value of 2H₂+O₂.