On The Determination Of Carbon Emission Factor And The Correlation With Burning Behavior Of Wildland Fuels

Carbon emissions from forest fire play a significant role in the greenhouse effect and the global climate change,for the great contribution of carbon dioxide to atmosphere.Carbon emission factors?or carbon conversion rates?of various types of forest fuels are key parameters for determining the magnitude of carbon emissions released from forest fire by the estimation.This paper handles the research on the carbon emission factors under the theme of carbon emission of forest fire.In recent years,a lot of work has been done on carbon emission factors of forest fire by making use of two major methods,i.e.the in-door combustion experiment and the out-door combustion experiment.The method of in-door combustion experiment owns the characteristics of good repeatability and economy,but there exists more or less differences between its environment and the real fire.While the environment of the out-door combustion experiment is correlated well with the real fire,it faces the problem that the repeatability and economy of the method is not so good.On this basis,a new method is proposed to detect the carbon emission of plant combustion by using a cone calorimeter,which is not only exhibits good features of the indoor experiment,but takes into account the environment effect of a real fire.Typical forest plants of Guang Dong province were tested by using cone calorimeter.Through repeated test and tests with different sample loads,the feasibility of this method and the well-correlation with a real fire was proved.And by analyzing data obtained at different radiation flux,moisture content and combustion condition,we study the varying pattern of carbon emission factors influenced by these variables.Analysis results show that with the variation of external radiant heat flux for a measurement and the moisture content of a sample,the conversion rate of the consumed carbon to CO(?_CO)fluctuated between 0.01 and 0.10,and that to CO₂(?_CO2)fell within the range between 0.05 and 0.85,and both increased with the increase in the level of external radiant heat flux.A decrease in the moisture content of a sample enhanced the transfer of the combustion state of a sample from smoldering to the flaming combustion,thus promoting the formation of CO and CO₂,which was closely related to the combustion efficiency of pyrolysis products and the percentage of carbon soot formed during the combustion of leaf samples in the open environment.Using energy and element mass conservation equations,a mathematical model was developed to correlate the carbon conversion rates with the fire behavior parameters,including flame length and temperature.The computations were preceded with the typical surface fuels in Guangdong forest area with their known property data.It was observed that with the increase in flame length or flame temperature,the combustion efficiency increases,which results in an increase in the conversion rate of consumed carbon to CO₂(?_CO2);for the surface fire with flame temperature fluctuating between 1000 K and 1200 K,the conversion rate of the consumed carbon to CO₂ varies between 0.44 and 0.95,whereas the emission ratio of CO to CO₂ falls in the range between 0.02 and 0.20.Further analyses indicate that,an increase in flame length or flame temperature implies a more complete combustion occurring in the flame zone,which causes a lower percentage of carbon emitted in the form of CO and soot,and consequently leads to an increase in ?_CO2.It has been confirmed that the carbon conversion rates in the fire spread over wildland fuels is in fact the reflection of their fire behavior,which well explained the variation patterns of the field experimental data reported in the literature.The mathematical model developed lays the foundation for accurately evaluating the amounts of carbon emitted by individual wildfires.