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

The H₂O concentration ( x H 2 O ) 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 x H 2 O based on the flame infrared emission image. The relative error between the x H 2 O reconstructed and that measured by the spectrometer was 4.73%, which confirmed that infrared thermometry was suitable for measuring x H 2 O of supersonic combustion flames. In situ measurements of the x H 2 O were conducted in the scramjet with different equivalence ratios (ER) of struts. The experimental results revealed that the peak x H 2 O 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 x H 2 O 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%.