기체메탄-액체산소 소형로켓엔진의 종횡비와 산화제 공급압력에 따른 성능특성

Abstract

A ground hot-firing test was conducted to examine the performance characteristics of gaseous methane and liquid oxygen bipropellant small rocket engine. As a first step, the design factors necessary for designing the thruster of methane/oxygen binary propulsion system were derived through theoretical performance analysis. In order to investigate the theoretical performance, the chemical reaction inside the combustion chamber was assumed to be in equilibrium, and the NASA ‘s CEA code was used. Since it is very costly to carry out the combustion test in a high vacuum environment, the ground hot-firing test is conducted and then the operating performance in a vacuum is inferred from the ground performance. The supersonic nozzle was designed with an expansion ratio of 50, but on the ground combustion test the bell-shaped nozzle of the expansion ratio 3.2 was employed to minimize shock waves and flow separation within the nozzle. Test equipments for performance evaluation of GCH4/LOx thruster include a Thrust Measurement Rig (TMR), Coriolis flow-meters, Data Acquisition and Control System (DACS), Flow Control Valves (FCV’s) and sensors. Combustion chambers with aspect ratio (AR=Lc/Dc) 1.5, 1.8, and 2.1 were fabricated to observe the performance change according to the AR at a fixed characteristic length of 1.71 m. The nozzle was designed and manufactured by Rao’s construction. On the ground firing-test, as the test condition LOx supply pressure increased from 220 psia to 320 psia, the specific thrust and characteristic velocity and their efficiency increased. It is noticeable that chamber aspect ratio is not that influential in thrust performance at the similar chamber pressures: this might be caused by the fixed chamber volume originating from the fixed characteristic length as mentioned earlier, or by mixing characteristics of the gaseous fuel and liquid oxidizer which have a severe difference in mass diffusivity between the two. More scrutiny needs to be made for this indefiniteness. Through the ground hot-firing test of a thruster, we could obtain an operability of stable combustion as well as acceptable performance data. Based on them, fundamental design parameters and test procedures were established that will be used for an optimization of 200 N-class GCH4/LOx thruster.