Smouldering fire and emission characteristics of Eucalyptus litter fuel

Abstract

Eucalyptus is one of the most widespread genera around the world and a key element in recent wildfires. In a Eucalyptus forest, the accumulation of litter builds up a ground fuel layer that can support both flaming and smouldering wildfires. This work investigates the smouldering wildfire on leaf, bark, and twig beds (bulk density: 70-140 kg/m3) of Eucalyptus species. Two-stage smouldering spread processes are observed. The first-stage smouldering fire has the peak temperature of 600°C-700°C and spread rate of 5-9 mm/min. The measured emission factors are 1000-1500 g/kg (CO2), 180-450 g/kg (CO), 9-16 g/kg (CH4), and 2-6 g/kg (H2), respectively. The CO/CO2 ratio ranges from 0.15 (leaf) to 0.8 (bark). Laboratory experiments demonstrate that the smouldering fire spread is slower in leaf than those in bark and twig. The burning of stringy barks is less complete, compared to smooth barks. For leaf and twig beds, the influence of Eucalyptus species and heating value on smouldering fire is negligible. This is the first work to reveal smouldering fire behaviors on different Eucalyptus litter fuels and provides valuable information for understanding the effects of Eucalyptus species and plant parts on smouldering combustion.