Optical Determination of Stagnation Temperature Behind a Gas Sampling Orifice

A technique has been developed for measuring the temperature during a transient combustion event. It combines the features of atomic resonance absorption and direct sampling to produce a relatively simple, intrusive diagnostic technique to obtain time-resolved measurements. In this study, a propagating hydrogen/air flame was used to provide a rapid temperature increase. A small fraction of krypton was added to the reactants and the absorption of resonant radiation at 123.5 nm was recorded downstream of the sampling orifice within a flow tube. Conversion from absorption measurements to temperature values was performed using a computer model of the radiation source and the absorption by the sample. The model of the source was validated by comparing predicted and recorded spectra of hydrogen Lyman-α emissions, while the absorption model for the sampled gas was tested by comparing the temperatures predicted by krypton absorption measurements with those recorded at a range of known temperatures. The direct sampling atomic resonance technique minimizes time-history distortions inherent in other direct sampling techniques, and is capable of tracking local temperatures during the passage of a propagating flame front.