Daisuke Nakata
(Muroran Institute of Technology, Japan)

The rocket sled is a well known device to verify the aerodynamic characteristics of full-scale aircraft or spacecraft at super sonic condition. In the past, the re-entry capsule of the Mercury spacecraft or the nose part of Space Shuttle was tested by U.S. rocket sled. In Japan, Muroran Institute of Technology newly constructed 300 m length rocket sled system. We adopted N2O-plastic hybrid rockets as an acceleration system in order to reduce the operation cost of rocket sled. The thrust performance of the hybrid rocket on the rocket sled is different from that of typical launch condition. That is, the rocket body and oxidizer tank feel strong horizontal G-force at both of acceleration phase and deceleration phase (water braking is used to stop the rocket sled). We estimated the correct thrust performance of hybrid rocket under such a condition based on the numbers of experimental trial.

Yuichi Noguchi
(IHI Aerospace Co., Ltd., Japan)

The authors have researched and developed a supercritical LOX/methane combustor for rocket engines for several years. Although the preliminary design of the coaxial injector element was conducted in this research and development, the understanding of some effects of some parts of the element such as a recess and chamfer for combustion characteristics was not enough. In order to investigate them, single element firing tests were carried out. In the tests, the data were acquired which were used for evaluating combustion characteristics such as flame holding, efficiency and combustion stability at the condition of supercritical and subcritical pressure. In addition, shadowgraphs and CH radical images of the flame were taken with the high speed cameras through the visualization chamber window. The situation of the atomization at the time of injection and the flame patterns under combustion became clear from the images. Moreover, the firing tests were conducted for the swirl type element as well. It was compared with the other type elements on the combustion characteristics. The data acquired as a result of the tests are useful for designing coaxial injector elements and correlating combustion analysis results. The authors describe the result of the firing tests on this paper.

Takahiro Hayashida
(Kyushu University, Japan)

In order to improve regression rate of hybrid rockets, a new method for enhancement of combustion has been proposed. The new method is to introduce swirling flow throughout a fuel grain through multi-section swirl injection ports, which are placed at several locations along the fuel grain. The key point of the method is to cause swirling flow in the cavity of the fuel grain at several cross sections. In the grain case, the fuel grain is mounted and gaseous oxygen is introduced through holes located in the gap between the grain case and the inner fuel grain, and oxygen gas injected into the inner fuel grain cavity through multiple injection ports. Four injection ports are located at each four cross sections along the axis of the fuel grain. The method has been applied for high density polyethylene fuel with pressurized gaseous oxygen. The average regression rate which the combustion test of the 200 mm length fuel with the post-combustion chamber has been 1.8 times compared with that of the 400 mm length fuel without the post-combustion chamber (0.77 mm/s to 1.4 mm/s). Also the present regression rate is 3.5 times compared with that of the conventional no-swirl injection method.

Yutaka Wada
(Akita University, Japan)

This paper introduces the application to hybrid rocket fuel of low melting point thermoplastics (LTP). The hybrid rocket has some benefits; for example, low cost, simplicity, throttling ability. However, the system has still not practical realization as large boosters due to difficulty of large-thrust generation. Main factors of small-thrust are low combustion efficiency and low regression rate. The hybrid rocket fuel requires higher regression rate, excellent mechanical physical properties, and good adhesion characteristics with other materials. LTP fuel has a prospect of high regression rate because it has a similar physical property with low melting point of paraffin fuel which was shown in a previous report to have high regression rate probably due to the entrainment mass transfer mechanism that droplets continuously depart out of the surface melt layer. Several different types of LTP developed by Katazen Corporation have been evaluated in the measurements of regression rate, mechanical physical properties, and the calculation of theoretical performance. These results suggest the LTP has better specific impulse, the regression rate and mechanical physical properties comparing with conventional hybrid rocket fuels.