High-speed 1D Raman analyzer for temperature and major species measurements in a combustion environment

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 (N2, O2, H2, and H2O) concentration in H2-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 H2-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% (N2) and 3∼4% (O2 in lean flames). Measurements in laminar and turbulent H2/N2 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.