The effect of a cold temperature valley on pulsating flame spread over propanol

Abstract

The transient three-dimensional structures of velocity and temperature created by a pulsating flame spread over normal propanol were constructed from five independent transient measurements using five different techniques: laser sheet particle tracking (LSPT): smoke tracing (ST); dual wavelength holographic interferometry (DWHI): infrared thermography (IR): and high-speed photography (HSP). These measurements showed that the pulsating flame spread consists of five distinctly different steps. The first step is the onset of pulsation created by the stagnation of flame spread over the liquid, which is followed by the second step, formation of a cold liquid valley near the flame's leading edge, and the third step, accumulation of liquid fuel vapor over the liquid surface. In the fourth step, the flame jumps through the formed premixed gas layer, leading to the final step, the cessation of spread. After the fifth step, the process returns to the first step, completing the entire pulsation cycle. Our experimental data confirm the formation of a small gas-phase circulation cell, as predicted by the University of California, Irvine, numerical model, and support the idea that the pulsating spread is triggered by the subsurface liquid convection that affects the gas-phase flow and the fuel vapor concentration. The second result is unique and suggests that a cold temperature valley formed on the liquid surface would play an important role in the mechanism of pulsating spread.