Numerical and experimental investigation of throttleable hybrid rocket motor with aerospike nozzle

https://doi.org/10.1016/j.ast.2020.105983Get rights and content

Abstract

Hybrid rocket motors (HRMs) easily achieve variable thrust by changing oxidizer mass flow rate. This paper represents numerical and experimental studies on the throttleable HRM with aerospike nozzle, which can enhance the performances of the throttleable HRM theoretically. By comparing the performance of the throttleable HRM with the aerospike nozzle and that with the de Laval nozzle, the characteristics of the aerospike nozzle applied to the throttleable HRM are explored. Both numerical and experimental investigations are conducted. In the simulation part, characteristic velocity, combustion efficiency, thrust coefficient and specific impulse of the HRM with the two types of nozzles at different oxidizer mass flow rate are obtained. Comparing with the HRM with the de Laval nozzle, the HRM with the aerospike nozzle can improve specific impulse by about 8.9%∼23.4% when the working pressure ratio is lower than the design pressure ratio. The combustion efficiency of the throttleable HRM with the aerospike nozzle is 3.9%∼8.6% higher than that with the de Laval nozzle because of the core structure of the aerospike nozzle. When the oxidizer mass flow rate is 50 g/s, the thrust coefficient of the aerospike nozzle is increased by 12.3% relative to that of the de Laval nozzle which flow separation occurs in. The corresponding firing tests are performed by the lab-scale motor with 90% hydrogen peroxide (HP) and polyethylene (PE) grain. The numerical and experimental results agree well. The combination of the throttleable HRM and the aerospike nozzle has the advantages to improve the performance of HRMs.

Introduction

Hybrid rocket motor (HRM) is a rapid-developing propulsion technology that owns many advantages over conventional liquid rocket engine and solid rocket motor [1], [2], such as low cost, safety and simplified throttling. The HRM is becoming more and more popular, and it is considered as a promising technology [3], [4]. The HRM can simply adjust thrust by changing the oxidizer mass flow rate [5], [6], [7]. However, the chamber pressure of the throttleable HRM changes when the oxidizer mass flow rate is adjusted. The throttleable HRM with the de Laval nozzle is over-expanded at a small chamber pressure and thrust. The performance loss of de Laval nozzle is inevitably in that condition.

With the altitude compensation effect, the aerospike nozzle can maintain high performance in a wide altitude range [8]. It has the advantages of compact structure and small size. When the nozzle-exit pressure is equal to the ambient pressure, the working pressure ratio pc/pe is the design pressure ratio. The altitude compensation performance is related to the design pressure ratio. When the working pressure rate pc/pe is not lower than the design pressure ratio, the thrust characteristics of the aerospike nozzle are the same as those of the conventional de Laval nozzle; when the working pressure ratio pc/pe is lower than the design pressure ratio, the aerospike nozzle possesses attitude compensation characteristics due to the special structure and aerodynamic phenomenon [9].

Combining the HRM with the aerospike nozzle is a new development field. California State University of Technology used the oxidizer (N2O) of the HRM to cool the aerospike nozzle for reusable [10]. The University of Washington proved that the aerospike nozzle can be well integrated with the HRM through firing tests [11]. Arizona State University conducted a firing test on the HRM with an aerospike nozzle and found that the thrust coefficient of the HRM with an aerospike nozzle was 6.4% higher than that of HRM with a de Laval nozzle in over-expanded state [12]. Utah State University designed the HRM with the aerospike nozzle for small satellites; the HRM used oxidizer (N2O) to regeneratively cool the aerospike nozzle, and thrust vector adjustment was achieved through the secondary injection; the firing test results showed that the HRM had thrust vector adjustment capability and the regenerative cooling system worked normally [13].

Our previous work analyze the effects of aerospike nozzle structure on HRM performance through simulation research [14]. Nozzles with three different expansion ratios were selected, corresponding to design conditions of high altitude and ground. The above study did not involve the combination of the aerospike nozzle and the throttleable HRM. The attitude compensation performance of aerospike nozzle makes the HRM maintain high nozzle performance when the working pressure ratio is lower than the design pressure ratio. Therefore, this paper explores the impact of the performance of the throttleable HRM with the aerospike nozzle.

Through numerical simulations and test researches, this paper compares the performance of the throttleable HRM with aerospike nozzle and de Laval nozzle. The aerospike nozzle and the de Laval nozzle are designed with the same throat area and area expansion ratio. Numerical simulations of the throttleable HRMs with the aerospike nozzle and the de Laval nozzle are carried. The parameters such as combustion efficiency, thrust coefficient and specific impulse are obtained. On this basis, firing tests are carried out. The laboratory scale motors are tested under different oxidizer mass flow rate with 90% hydrogen peroxide (HP) and tubular polyethylene (PE) grain.

Section snippets

Geometry models and numerical models

The geometry model of the lab-scale motor with aerospike nozzle and the geometric parameters is shown in Fig. 1, and the unit is mm. The geometry model and the geometric parameters of the HRM with de Laval nozzle are the same as that of the HRM with aerospike nozzle except the nozzle. The throat area and area expansion ratio of the de Laval nozzle are the same as that of the aerospike nozzle. The throttleable HRM adjusts thrust by changing the oxidizer mass flow rate. The variation range of the

Experimental setup

Fig. 14 shows the test platform (a), the lab-scale motor (b) and the firing test (c). The lab-scale motor and the aerospike nozzle have been introduced in 2.1 geometry model. The de Laval nozzles are made by C-C composite material, whose area expansion ratio is 3 and throat diameter is 15 mm. The throat area of the aerospike nozzle and the de Laval nozzle are the same. The area expansion ratio of the aerospike nozzle is 3.48. The drop-shaped plug and the ring throat are made of copper

Conclusion

This paper focuses on performance comparison of the throttleable HRM with the aerospike nozzle and that with the de Laval nozzle, including comparison of characteristic velocity, combustion efficiency, thrust coefficient and specific impulse. Conclusions can be drawn as follows:

  • (1)

    The simulation results show that the combustion efficiency of the throttleable HRM with the aerospike nozzle is 3.9%∼8.6% higher than that with the de Laval nozzle. The test combustion efficiency of the HRM with the

Declaration of Competing Interest

No conflicts of interest to declare.

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