In the present research, we experimentally verified the partial-fill effect in a multicycle pulse detonation rocket engine. The intermittent thrust of a pulse detonation rocket engine was measured by using a spring-damper mechanism that smoothed this intermittent thrust in the time direction. The intermittent mass flow rates were assessed by gas cylinder pressure or mass difference measurement. The maximum specific impulse was 305 9 s at an ethylene and oxygen propellant fill fraction of 0:130 0:004. When the fill fraction was greater than 0.130, the specific impulse was increased as the partial-fill fraction was decreased. When the fill fraction was less than 0.130, the specific impulse was sharply decreased as the partial-fill fraction was decreased. This decrease was due to diffusion between propellant and purge gases and the short length of the transition from deflagration to detonation. The multicycle pulse detonation rocket engine had a partial-fill effect that may have been mainly due to the suctioned air and was consistent with the single-cycle partial-fill model of Endo et al. NomenclatureA e = control-volume surface area through which an exhaust jet flows c = attenuation coefficient of a damper F f = force acting on the pulse detonation engine tube by the rail in the x direction F kc = force acting on the pulse detonation engine tube by the spring-damper system in the x direction F lc = force acting on the spring-damper system by the load cell in the x direction F p = force acting on the pulse detonation engine tube by the fluid in the x direction F t = force acting on the pulse detonation engine tube by the supplying tubes in the x direction F 0 = plateau thrust ff air;est = estimated suctioned air fill fraction ff propellant = propellant fill fraction ff purge = purge gas fill fraction g = gravitational acceleration I = impulse acting on the pulse detonation engine tube by the fluid in the x direction I sp = specific impulse I total = absolute value of the total impulse acting on the pulse detonation engine tube by the fluid in the x direction during all cycles I total;x = total impulse acting on the pulse detonation engine tube by the fluid in the x direction during all cycles k = spring constant M c = molecular weight in the cylinder m d = mass of weight m propellant = propellant mass during all of the cycles m purge = purge gas mass during all of the cycles m t = pulse detonation engine tube mass p a = ambient pressure around the control volume p e = exhausted-jet pressure on the control surface R c = gas constant of the gas in the cylinder T c = gas temperature in the cylinder t = time t cyc = period of one cycle t pl = time during which the plateau thrust is maintained t total = time during all of the cycles u e = fluid velocity component in the x direction, on the control surface u x = fluid velocity component in the x direction V = volume V c = volume of the cylinder v s = horizontal velocity of a solid element v w = velocity of the weight x = horizontal axis fixed in the control volume x p = p...

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