Design and testing of a novel low-cost C$$_2$$H$$_2$$–O$$_2$$ combustion driver for shock tubes

Abstract A novel combustion driver is designed and tested to replace conventional helium drivers for the hypersonic shock wind tunnels. Stoichiometric acetylene and oxygen were chosen to minimize the production of water to prevent major corrosion in facilities not made of stainless steel. A single-burst diaphragm mechanism was employed, which was found to generate a reproducible shock tube process even in the presence of small variations in diaphragm scribe depth. The driver gas mixture was proven to burn entirely deflagrative for a single spark plug configuration. This is a major advantage compared to other combustion-driven shock tube designs found in the literature using oxyhydrogen diluted with helium, which requires a carefully designed ignition system in order to avoid the formation of pressure oscillations induced by local autoignition or detonation in the driver. High levels of dilution using argon were shown to maximize the available test time to approximately 5.5 ms for low-enthalpy conditions ( h 0 $$=$$ <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"> <mml:mo>=</mml:mo> </mml:math> 1.12 MJ kg -1 ). Inhomogeneities in the driver temperature caused by the combustion in a closed vessel were correlated to the observed post-reflected-shock pressure traces in the experiments. However, the negative effects can be compensated for the given experimental setup by ignition at a single location near the diaphragm and conducting experiments at slightly undertailored interface conditions. The result of the present study is a novel, functioning combustion driver capable of replacing conventional helium drivers for low-enthalpy conditions with minimal modifications on the existing facility, which enables an experimentation at a fraction of the gas costs.