For several years, shock tubes have been employed for studying ignition phenomena at temperatures routinely above 1200 K, and experimental test times are typically on the order of 1 millisecond. Autoignition in the premixer of power generation gas turbines is one application requiring ignition information at lower temperatures in addition to elevated pressures. However, at temperatures between 800 K and 1200 K, reactions are slow and autoignition times can be on the order of 10 milliseconds or greater. To study practical operating conditions such as these, it is of great importance to increase shock-tube test times, and this can be done by tailoring the interface between the driver and driven gases. As demonstrated in conventional shock-tube tailoring, it is the thermodynamics of the driver and driven gases which determine the wave conditions, and the geometry of the shock tube determines the test times.
Unfortunately, since the driver length of the present shock tube is relatively short compared to the driven length, it is the reflected expansion wave that reaches the contact surface before the reflected shock wave. The reflected expansion wave colliding and transmitting with the interface cannot be avoided, and traditional driver-gas tailoring using He and N2 will not address this problem. Therefore, an alternative using exotic driver gases such as propane and carbon dioxide was developed and demonstrated. Using this method, expansion-wave arrival was changed from 1 millisecond to 14 milliseconds, allowing lower-temperature combustion behavior to be explored. Presented in this seminar are the results of the experiments demonstrating this driver-gas tailoring approach. Some recent results from a carefully designed set of experiments using the tailoring technique and covering a comprehensive array of possible methane/hydrocarbon fuel blends are also presented.
