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The Forefront of Space Science

Hybrid Rocket Will Go for the Next Generation of Space Transportation
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The second method to improve the fuel regression rate is to use Glycidyl-azide polymer (GAP)-based or WAX fuels. By blending GAP with conventional fuels, the regression rate can be raised, i.e. by using GAPís self-heating decomposition effect. On the other hand, in the case of the WAX fuel, the regression rate rises by the combination of the dynamic effect and the heat effect because of the phenomenon whereby fuel melting on the surface becomes droplets to be caught in the flow and dispersed.

HRrWG confirmed that, using swirling injection of the oxidizer into the WAX fuel, we could obtain a higher regression rate by one order of magnitude compared to the conventional hybrid rocket. We also confirmed the possibility that much higher rates could be accomplished by the multi-cross section swirling technique. Improvement of the fuel regression rate alone, however, is not enough for the rocket. Simultaneously, we must burn the fuel efficiently. To this end, HRrWG devised the baffle plate shown in Fig. 5. We confirmed that, with the baffle plate, efficiency more than 95% could be obtained for the exhaust velocity (characteristic exhaust velocity) that is theoretically determined according to combustion-gas characteristics.


Figure 5
Figure 5. Conceptual illustration of the engine using the baffle plate and visualization of WAX fuel combustion
When heated, the WAX fuel melts on its surface and is caught in droplet state in the mainstream. The droplets vaporize to combust, but if their residence time is short, they are released in pre-combustion state. To prevent this, a baffle plate is used to turn the droplets into fine particles. As a result, combustion efficiency is improved. We also succeeded in visualizing for the first time in the world the moment when the droplets were caught. (This experiment was conducted at Nakagawa Lab., Tokai University/HRrWG)


Conclusion

Since the hybrid rocket has the advantages of safety, security, environmentally and ecologically friendly, high-performance and high-functionality, it will meet the social needs of future crew space transportation and/or low-cost cargo space transportation. Comprising researchers of universities in Japan and ISAS, HRrWG is working on the demonstration of technologies to improve the fuel regression rate and combustion efficiency necessary for the practical-use rocket, while deepening our understanding of the key technology, boundary-layer combustion. As the first step, we are now fabricating a 5kN-thrust class test engine and preparing a technological-demonstration test facility (HTE-5-1). We hope to report its test in the future.

Toru SHIMADA

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