Application of Raman/Rayleigh/LIF diagnostics in turbulent stratified flames

Stratified flames are common in practical combustion systems. However, relatively little is known about the detailed structure of turbulent stratified flames. Multiscalar laser diagnostics, consisting of simultaneous line imaging of Raman scattering, Rayleigh scattering, and two-photon laser-induced fluorescence (LIF) of CO, combined with crossed planar imaging of OH LIF, are applied to turbulent premixed and stratified CH(4)/air flames stabilized above a slot burner. A new detection system for the line-imaged measurements allows a pixel resolution of 0.104 mm in the results for temperature, major species concentrations, and the local equivalence ratio. Results from premixed flames demonstrate that this diagnostic system is capable of resolving the internal structure of stratified flames at atmospheric pressure. In particular, the local equivalence ratio and the gradient in temperature are measured with good accuracy on a single-shot basis. Results from stratified flames reveal a broad range of-instantaneous conditions, and show that significant gradients in equivalence ratio can occur within the instantaneous thermal thickness of turbulent stratified flames. (c) 2009 The Combustion Institute. Published by Elsevier Inc. All rights reserved.