The structure of premixed and stratified low turbulence flames

Practical combustion systems typically operate in stratified regimes to leverage the advantages of a spatially varying mixture fraction field. Although these benefits are well known in industry, the fundamental physics underpinning these effects are currently an area of active research. In this paper simultaneous Rayleigh–Raman–LIF measurements of temperature and major species concentrations along a line are used to investigate the structure of a weakly turbulent stratified flame. Concurrent cross-planar OH-PLIF enables the extraction of flame orientation relative to the measurement line, as well as flame front curvature. The behavior of major species concentrations with respect to temperature is found to agree well with laminar flames at the local mixture fraction, even in stratified flows. However, measurements of the surface density function, ∣∇c∣, and scalar dissipation, χc, suggest that both premixed and stratified flames are spatially thicker at the microscale than corresponding laminar flames.