Experimental detection of two-dimensional H2O distribution in jet flame of scramjet based on the infrared imaging technology

The H2O concentration (xH2O) is a key parameter for monitoring the combustion process and quantifying the combustion efficiency. To study the combustion behavior of the complex supersonic flame in the scramjet, a new radiation thermometry combined with Line-by-line (LBL) method and Newtonian iteration was proposed to measure the xH2O based on the flame infrared emission image. The relative error between the xH2O reconstructed and that measured by the spectrometer was 4.73%, which confirmed that infrared thermometry was suitable for measuring xH2O of supersonic combustion flames. In situ measurements of the xH2O were conducted in the scramjet with different equivalence ratios (ER) of struts. The experimental results revealed that the peak xH2O of the jet flame increased from 0.175 mol/mol to 0.219 mol/mol as the ER of strut I increased from 0.2 to 0.6, while the peak xH2O decreased from 0.210 mol/mol to 0.151 mol/mol as the ER of strut II increased from 0 to 0.4. The vortex generated by the strut I mixed the fuel with the supersonic air to achieve the scramjet ignition, and the strut II formed a localized reflux zone at the nozzle to ensure the stable combustion. With an ER of 0.4 for strut I and 0.2 for strut II, the maximum combustion efficiency reached 85.66%.