UC Berkeley

Fire whirls have long been a fascination in the field of fire science, but few studies have been conducted with the intention of creating fire whirls at the field scale, and even fewer with associated measurements of emissions. Fire whirls are known to increase the flame length and burning rate for flames over liquid fuel pools, with recent research indicating that they reduce the amount of particulate soot emitted by the flame. These properties make it desirable for the process of in-situ burning, where air pollution and burning duration both must be minimized. In this study, the sensitivity of fire whirl behavior and burning characteristics to the dimensions of a fixed-frame fire whirl generator were first investigated at the laboratory scale. Fire whirls were found to enhance burning rates and reduce emissions when burning slicks of crude oil over water when compared to pool fires, regardless of the thickness of the oil slick. Further increases in slick thickness improved the burning rate, but with diminishing returns. Flame lengths, burning rates, and quantities of particulate soot production were found to be sensitive to the height of the fire whirl generator’s enclosure. Higher walls increased the burning rate and flame lengths while decreasing the emissions of soot to a minimum value. This is inferred to be due to an increase in effective circulation within the enclosure. This trend held until a critical wall height, above which the flame shrinks and weakens. This critical wall height is dependent on the size of the enclosure footprint. One of the largest controlled fire whirl experiments was conducted at the field scale, with instrumentation used to collect the flame height, temperature, burning rate, emissions pro- duction, and heat flux. The desirable traits of the fire whirl were still present at this scale, with burning rates increased by a factor of up to 141% and reducing particulate soot emission to a minimum of 53% of the pool fire’s soot emission per mass of fuel burned. However, these improvements were limited to specific cases as some tests experienced premature burnout.