Convective Froude number and Byram’s energy criterion of Australian experimental grassland fires

A subset of experimental fires, conducted in the Northern Territory, Australia, in July and August 1986, was analysed to examine the role of the convective Froude number and Byram’s energy criterion (Pw/Pf) in the behaviour of grassland fires. Forms of these dimensionless numbers were obtained from the literature as were functions relating independent variables in these formulations to measured quantities. It was found that Byram’s energy criterion is simply the inverse cube of the convective Froude number and thus, was not examined in detail. It was found that the convective Froude number is not reflected in the observed behaviour of fires, as previous authors have suggested, despite the range of experimental conditions (wind speed 1.5–7.5 ms−1, rate of spread 0.05–2.82 ms−1).