Study on the combustion mechanism in SCRAMJET

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Scramjet has been recently paid attention concerning with the "space plane" concept. There are, however, several important problems to be solved before its development. They are the mixing, ignition, combustion, and so on. First of all, the ignition problem is studied by looking at silane as an ignition aid of oxyhydrogen combustion unfer the low density and low temperature atmosphere. A group of NASA developed a silane/oxygen/hydrogen/nitrigen ignition mechanism by using a similarity in the mechanism of mechane combustion. Their numerical modeling in the ignition delay of the SiH4/O2/H2/N2 mixture simulated well their experimental results at the temperature of 800-1000 K. However their modeling could not show the ignition delay at the high temperature of 1000-1700 K because the thermodynamic data of silane and its related compounds were not true. They used their data obtained by approximating the methane data. The correct thermodynamic data are developed theoratically using RRKM theory. It can be said from our experimental results that the reaction mechanism of SiH4/O2/H2/N2 mixture is changed at the border of 1000 K and the silane additivity works for enhancing the hydrogen ignition at the lower temperature than 1000 K.Besides the ignition problem, the mixing problem is studied by numerically simulating the helium injection vertically into the supersonic air flow. The numerical results show the high frequency oscillation due to the interaction between the injected helium and the main air flow and several circulations which dominate the physics of the flow field.