Planar OH density and apparent temperature measurements in a supersonic combusting flow

Distributions of the absolute density of OH and of the population densities of five OH rotational states were obtained in a supersonic H 2 -air combustion tunnel using planar laser-induced fluorescence. A tunable KrF excimer laser was used to excite, nonsimultaneously, the five separate ro-vibronic lines in the (3-0) vibrational band of OH. Measurements were calibrated against measurements in an atmospheric air furnace, where known quantities of OH are formed by the thermal dissociation of H 2 O molecules. Despite flame intermittency, a sum of each of these nonsimultaneous measurements represents the time-averaged population density of the probed state. Present results show that these time-averaged measurements of the populations of the probed states still follow a Boltzmann distribution. Therefore, measurements of the average population of any pair of states can provide the two independent average properties required to define the average thermodynamic state of OH.