Relations between Light Hydrocarbon, Carbon Monoxide, and Carbon Dioxide Concentrations in the Plume from the Combustion of Plant Material in a Furnace

Abstract

To systematically explain relations between light hydrocarbons, CO, and CO2 concentrations/emissions of biomassburning, we measured concentrations/emissions of carbon gases – CO,CO2, light hydrocarbons (CH4, C2H6,C2H4, C2H2, C3H8, C3H6,n-C4H10, i-C4H10, n-C5H12,i-C5H12), and THC (total hydrocarbon) – in the burning of dead plant material, mainly Imperata grass, byclosed-chamber experiments and by time-series analyses of gas concentrations in combustion plumes in relatively efficient and inefficient combustion situations. Concentrations of hydrocarbons measured were well correlated to [CO] although [C2H2] was exceptionally well correlated to[CO2]. The phase diagrams (relation between [CO]/Δ [CO2] and [hydrocarbon]/Δ [CO2]) obtained by the time-seriesexperiments well illustrated the variation in the overall emission rates of the closed-chamber experiments. The higher rates of decrease in hydrocarbon concentration with increasing carbon number in the efficient case compared with the inefficient case probably reflected the rate of oxidation and the amount of radicals. The overall concentrations (or emissions) of C2H4 and C3H6 were higher thanthose of C2H6 and C3H8, suggesting a linkage to mechanisms in whichthe predominant path of hydrocarbon oxidation is through the degradation of alkyl radicals, which can be immediately converted into or formed from alkenes. For C3 and C4 species, normal-chain species hadhigher emissions than iso-chain species under lower combustion efficiency. This may be attributable to the presence of tertiary C–H bonds in iso-species,which show more reactivity in the abstraction of H than secondary C–H bonds unless the carbon number is large.