Flame temperature and residence time of fires in dry eucalypt forest

Abstract

Temperature profiles of flames were measured using arrays of thermocouples on towers located in experimental bushfires of varying intensity, carried out in dry eucalypt forest of different fuel age and structure. In-fire video of flame-front passage and time series data from very fine exposed thermocouples were used to estimate the duration of passage of the main flaming front in these experimental fires. Flame temperature measured at points within the flame was found to vary with height; maximum flame temperature was greater in the tall shrub fuel than in the low shrub fuel sites. A model to estimate flame temperature at any height within a flame of a specific height was developed. The maximum flame temperature observed was ~1100°C near the flame base and, when observation height was normalised by flame height, flame temperature exponentially decreased to the visible flame tip where temperatures were ~300°C. Maximum flame temperature was significantly correlated with rate of spread, fire intensity, flame height and surface fuel bulk density. Average flame-front residence time for eucalypt forest fuels was 37 s and did not vary significantly with fine fuel moisture, fuel quantity or bulk density.