Regime transition from premixed to flameless oxidation in turbulent JP-10 flames

An opposed jet configuration featuring fractal generated turbulence was used to characterise premixed fuel lean JP-10 flames with equivalence ratios (ϕ) from 0.20 to 0.80 stabilised against combustion products with a temperature of 1720K. The cold flow turbulent Reynolds (Re_t) number was set to 122 and the estimated Damköhler (Da) numbers varied from below 0.3 (ϕ=0.20) to 6 (ϕ=0.80) with laminar flame parameters obtained from computations of the corresponding opposed jet configuration. The gradual transition from a turbulent flame to a supported burning mode related to the Homogeneous Charge Diffusion Ignition (HCDI) flameless oxidation regime was detected with features typical of conventional flames gradually disappearing for ϕ<0.60. A second mode transition to the corrugated flamelet regime at ϕ=0.80 is shown to coincide with a gradual change from gradient to counter-gradient turbulent transport. A density segregation based technique was applied to Particle Image Velocimetry (PIV) images to detect the instantaneous location of reaction zones and to provide conditional and unconditional statistics to illustrate the combustion regime transitions. Flame surface area characteristics and turbulent burning velocities were also derived to further characterise the burning modes.