Flame image velocimetry: seedless characterization of post-reflected-shock velocities in a shock-tube

The use of a laser-ignited expanding flame as a virtual particle for seedless velocimetry of a flammable mixture is described and demonstrated, a method referred to as flame image velocimetry. Within an expanding flame, the burned gas is nominally stagnant relative to the local flow field, such that the motion of the flame centroid can be interpreted as an advected particle and serve as the basis of a single-point velocity measurement. This technique is applied to study the post-reflected-shock (region-5) environment in a shock tube using propane and n -heptane as fuels, lean equivalence ratios (0.3 ≤ϕ≤ 0.9), and oxidizers consisting of 18.1