Empirical Assessment of Driver-Gas Efficiency in Shock-Tube Flows over a Wide Range of Conditions

The rising cost of helium has inspired consideration of alternative driver gases to be used in shock-tube experiments, especially when conducting chemical kinetics measurements of fuel-air mixtures across engine-relevant conditions. The potential to replace helium as a driver gas altogether requires a better understanding of driver-gas performance across a wide range of shock-tube conditions. The present study utilized a diverging (A4/A1 = 0.25), high-pressure shock tube to investigate the efficiency of uncommon driver gases, namely H2, N2, and CH4, in producing desired reflected-shock conditions in common test gases such as Ar, N2, CO2, and He. Incident-shock Mach numbers ranged from 1.35 to 6.78, which produced reflected-shock temperatures up to 10,231 K. Reflected-shock pressures were varied from 0.23 to 56.75 atm. An analytical model was developed, based on measured departure function data, to accurately predict the reflected-shock conditions for a desired driver-driven gas combination. The predicted p4/p1 values from the gas-dynamic model are in excellent agreement with the measured values for p4/p1 < 1000, regardless of the diaphragm material used. Last, a comparison of several diaphragm materials and thicknesses suggests that a greater ultimate-to-yield strength ratio results in improved rupture of the diaphragm and ultimately enhances the experimental gas-dynamic performance.