Wind Tunnel Measurements of Ignition Delay, Using Shock-Induced Combustion

摘要

Shock-induced combustion of fuel-air mixtures in a pebble bed-heated wind tunnel was utilized to obtain values of induction time, permitting an evaluation of the importance of certain kinetic parameters and qualitative evaluation of the effect of small contamination levels. Fuels tested were hydrogen, ethylene, acetylene, propane, and methane. Certain tools of research commonly used with shock tubes were adapted for these measurements. In particular, a traveling monochromator was used to observe the distribution of characteristic emissions and a traveling OH absorption apparatus indicated OH radical densities, both in the flame zone and in the induction zone. Other necessary measurements, both upstream and downstream of the shock, included static and impact pressures, Mach number, fuel concentration, and stagnation temperature. The usual kinetics calculation with time as the independent variable was modified to predict the streamwise distribution of chemical species behind the shock, in the presence of velocity, temperature and pressure gradients, as well as various ambient densities of OH radicals. The latter may be caused by the dissociation of very small amounts of water vapor, or by a partial reaction between the fuel jet and air, without exothermic effects. (Author)