Observations of H2O formation in the supersonic combustion of H2 by high-enthalpy air

We have investigated and compared the dynamics of supersonic H-2-air combustion for compression and expansion swept-ramp, three-hole injector configurations in a laboratory shock tunnel. Hydrogen fuel was injected into a Mach 3 flow of 1200 K air at 0.67 atm. The experiments used a combination of imaging and line-of-sight optical diagnostics at different locations downstream of the point of injection. Images of OH(A(2)Sigma) and OH(X(2)Pi) spatial distributions provide information on the near-field mixing and ignition characteristics and far-field Vertical spreading of the reacting layer, while spectral measurements of H2O(nu(2)) emission protide the far-field temperatures and H2O yields in the reacting layer The two injector configurations display markedly different ignition characteristics but similar near-field air-fuel mixing behavior and far-field product yields. The far-field measurements at long convective how times give final H2O concentrations, temperatures, and OH(A) concentrations that are greatest near the bottom wall and decrease with increasing height. H2O and OH(A) are observed only in the lower half of the duct; thus, complete mixing of the fuel with the main flow is not achieved. For both injectors, the efficiency of H2O production compared to full equilibrium for an idealized premixed system is 30-40%. Kinetic limitations due to incomplete radical removal are relatively minor. The primary factor limiting the far-field combustion efficiency appears to be poor mixing due to the slow vertical propagation of the reacting layer, which is similar for the two injectors despite the differences in their near-field ignition behavior.