Efficiency of sustained burning of layered leaf fuels under external radiant heat flux

摘要

Efficiency of energy release by burning of layered leaf fuels under external radiant heat flux was studied using a cone calorimeter. By performing the ignition and sustained burning measurements with coniferous and broadleaf plants, a method was developed to determine the combustion efficiency during sustained burning chi(c). Experimental results showed that at the same radiant heat flux, an increase in the sample mass (density) leads to substantial decrease in chi(c) followed by a level-off, and the increase in leaf moisture content results in significant reduction of chi(c). Analysis indicated that chi(c) is essentially independent to the sample mass when a sample is constituted by three layers. By defining a ratio of the amount of CO produced to that of O-2 consumed during measurement phi(CO/O2), chi(c) was found to be well correlated by phi(CO/O2) with the form chi(c) = 0.2166ln[0.4655/(phi(CO/O2) - 0.03177)], thereby highlighting that energy release efficiency of a sample mainly relies on the extent of O-2 consumed to convert into CO. The parameter chi(c) acts as an indicator to reveal the combustion states of a fuel during testing, and the parameter phi(CO/O2) can be used as an index to evaluate the capacity of leaf fuels to emit toxic gases in specific fire scenarios.