Laminar premixed flame fuel consumption rate modulation by shocks and expansion waves

The main contributing effects leading to premixed laminar flame fuel consumption rate changes following variable strength shock or expansion wave passage were studied analytically and numerically. The effects were separated into two groups: gas compression, or one-dimensional effects, and flame front distortion, or two-dimensional effects. The first group was examined analytically using a one-dimensional flame model and solution of shock and expansion wave refraction. Two-dimensional effects were examined numerically using both shock and expansion wave passage through a sinusoidally perturbed propane-air laminar flame. Flame fuel consumption amplification due to the gas compression increased rapidly (from 1.3 to 24 times for Mach 1.1–1.7 shocks), while flame length amplification peaked (∼15 times) at a given shock strength (∼Mach 1.3). Thus gas compression became the dominant effect for stronger shocks. In contrast to the shocks, a slower reaction kinetic produced by the expansion wave passage allowed for a significantly longer period of flame length growth. This resulted in a temporary burning rate increase above initial values. The negative chemical kinetic effect of the weak expansion wave passage was temporarily offset by the flame length increase. The overall reaction rate amplification was up to four times stronger in fast/slow refractions. Also, the observed values of the flame stretch are reported in the paper.