Phenomenological regression rate model in axial injection end-burning hybrid rocket motor using different oxidizers

Abstract

Compared with conventional configurations, axial-injection end-burning hybrid rocket motors work with multiport fuel grains, which mainly burn in the axial direction. The consumption rate is controlled by the several flames developed at the end of each port. Although many studies of performance and flame stability have been carried out in the past, a phenomenological model of the axial regression rate was never provided in the past, which is the objective of the current work. The validation of the physical model is performed by a comparative study between firing tests using gaseous oxygen and nitrous oxide. Two experimental campaigns performed by a pressure-controlled combustion chamber are carried out with a single port grain in operative conditions equivalent to the multiport configuration. The axial regression rate was measured by varying the port diameter in a range between 0.5 and 4.6 mm, the mass flow rate between 0.004 and 1.7 g/s, and the chamber pressure between 0.1 and 3.4 MPa. The measured axial regression rate was quantitatively lower with nitrous oxide than oxygen, and the pressure sensitivity exponent decreased from 1.85 to 1.5, respectively. The physical reason has been attributed to the decomposition reaction of nitrous oxide occurring upstream of the flame front. In addition, a general methodology for fuel grain design is given, highlighting the benefits and drawbacks of introducing multiport grains and the effect of the oxidizer choice on the motor geometry. Finally, multiport firing tests were carried out to confirm the evidence observed in the simplified single-port campaigns.