Abstract
In this Letter, we demonstrate a 5 kHz 1D Raman instrument for temporally and spatially resolved quantitative measurements of temperature and all the major species (${{\rm N}_2}$, ${{\rm O}_2}$, ${{\rm H}_2}$, and ${{\rm H}_2}{\rm O}$) concentration in ${{\rm H}_2}$-air flames. The major constituents of the system are a pulse-burst laser operated at 5 kHz and four back-illuminated CCD cameras operated in subframe burst-gating mode. The use of CCD cameras allows achieving a high sampling rate with no compromise on instrument precision, but it requires one camera for each species of interest. A cascade of dichroic mirrors and bandpass filters spectrally separates the Raman signal associated with each of the four species and directs it to a separate camera. Measurements in a well-characterized ${{\rm H}_2}$-air premixed flat flame show that the system has precision comparable with the low-speed Raman system. The measuring uncertainty of the species mole fraction ranges between 1% (${{\rm N}_2}$) and $3 {\sim} 4\%$ (${{\rm O}_2}$ in lean flames). Measurements in laminar and turbulent ${{\rm H}_2}/{{\rm N}_2}$ jet flames show good agreement with the theoretical prediction. By measuring all species simultaneously, important combustion quantities such as the mixture fraction are also derived.
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