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.

中文翻译：

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不同氧化剂轴向喷射端燃混合火箭发动机唯象回归率模型

与传统配置相比，轴向喷射端燃式混合火箭发动机采用多端口燃料颗粒，主要沿轴向燃烧。消耗速率由每个端口末端产生的多个火焰控制。尽管过去已经进行了许多关于性能和火焰稳定性的研究，但过去从未提供轴向回归率的唯象模型，这是当前工作的目标。物理模型的验证是通过使用气态氧和一氧化二氮的燃烧测试之间的比较研究来进行的。由压力控制燃烧室执行的两个实验活动是在与多端口配置等效的操作条件下使用单端口颗粒进行的。通过在 0.5 至 4.6 mm 范围内改变端口直径、0.004 至 1.7 g/s 之间的质量流量以及 0.1 至 3.4 MPa 之间的腔室压力来测量轴向回归率。一氧化二氮测得的轴向回归率在数量上低于氧气，压力敏感性指数分别从 1.85 降至 1.5。物理原因归因于火焰锋上游发生的一氧化二氮的分解反应。此外，还给出了燃料颗粒设计的一般方法，强调了引入多端口颗粒的优点和缺点以及氧化剂选择对电机几何形状的影响。最后，进行了多端口发射测试，以证实在简化的单端口活动中观察到的证据。