Hydrogen autoignition and combustion in supersonic flow at low equivalence ratio

A supersonic high-enthalpy tunnel developed at CNPM-CNR to test hydrogen autoignition and combustion under simulated flight conditions in the high supersonic - low hypersonic range is capable of sustaining supersonic combustion for 10-30 ms, the flow residence time being about 1 ms. A simple but effective procedure for data analysis based on detailed static and total pressure measurements provides information on the one-dimensional quasisteady thermofluid-dynamic field inside the tunnel as a function of the upstream stagnation conditions. An efficient-mixing discrete-hole cross-stream injector was adopted , which also allowed hydrogen preheating. The equivalence ratio was limited to values < 0.15 to keep the airstream supersonic in the constant cross-sectional portion of the tunnel. Autoignition delay data were obtained (0.1-1 ms) and correlated with the local static temperature. The results agree with experimental and theoretical literature data available for cold hydrogen. A strong effect of fuel temperature was observed, suggesting that a meaningful database for scramjet applications should always include, if appropriate, fuel preheating. Overall reaction times were also evaluated for different fuel temperatures, whose remarkable influence was confirmed.