In situ determination of N2 broadening coefficients in flames for rotational CARS thermometry

Abstract

Total N2 S-branch broadening coefficients have been measured in situ as a function of radial position in a highly sooting ethylene diffusion flame by the use of time-resolved dual-broadband picosecond pure rotational CARS (RCARS). Time-domain measurements of the J-dependent N2 rotational coherence decays in the flame were used to determine the broadening coefficients, and these coefficients were then used in the spectral fitting routine for the determination of temperature and [O2]/[N2] ratio in the flame. Corrections of up to 125K are found when compared to spectral fitting using an ECS self-broadened N2 linewidth model. The presented technique effectively takes into account contributions to the N2 linewidths from all collision partners without any a priori knowledge of relative species concentrations.