SIMULTANENOUS IMAGING OF SOOT CONCENTRATION AND TEMPERATURE IN ETHYLENE DIFFUSION FLAMES Q.N. Chan 1,2* , P.R. Medwell 1,3 , P.A.M. Kalt 1,3 , Z.T. Alwahabi 1,2 , B.B. Dally 1,3 , G.J. Nathan 1,3 1 Centre for Energy Technology Schools of 2 Chemical and 3 Mechanical Engineering The University of Adelaide Adelaide, 5005 S.A. Australia * Email: qing.chan@adelaide.edu.au ABSTRACT Non-linear excitation regime two-line atomic fluorescence (NTLAF) is a laser-based thermometry technique that enables temperature measurement in sooty conditions. However, the emission signals of the NTLAF technique might be affected by soot interferences or fluorescence, when the soot level within the flame is high. To examine this effect, the emission signals for both on- and off-wavelength measurements are presented in this paper. The average radial profiles of these measurements are presented and compared as well. The radial profiles suggest that fluorescence from condensed species (CS) could be responsible for the emission signals observed for off-wavelength measurements. The radial profiles indicate that interferences due to the spurious scattering and incandescence from soot are not significant for the present flame of interest. The magnitude of perturbation of the off-wavelength to on-wavelength measurements are observed to reach a maximum of ~3 to 5 %. INTRODUCTION Laser diagnostic measurements are well-suited to provide simultaneous, well-resolved, multi-dimensional measurements. Application of common laser diagnostics in flames containing soot, however, has been problematic due to various interference issues such as absorption and scattering (Hartlieb et al., 2000). These issues lead to the application of laser diagnostics often restricted to idealised clean flames, thus excluding many flames of practical significance. There is therefore a need to develop alternative laser diagnostic methods to complement and to extend those already in common use. Two-line Atomic Fluorescence (TLAF), with indium as the seeded thermometric species (Dec & Keller, 1986; Kaminski et al., 1998), is one of the laser diagnostic techniques that have been shown to hold promise in sooting environments. The inelastic nature of the technique enables optical filtering to be used to minimise spurious scattering, thus allowing temperature measurements to be performed in particle-laden environments. By extending the technique into the nonlinear excitation regime, the capability of TLAF in providing single-shot imaging has been further improved by the authors (Chan et al., 2010a; Chan et al, 2010b; Medwell et al., 2009; Medwell et al., 2010). Non-linear excitation regime two-line atomic fluorescence (NTLAF) has been shown to provide significant improvement on the signal-to-noise ratio (SNR) and hence better precision when compared to the conventional linear regime approach (Medwell et al., 2009).