Combustion Chemistry and Decomposition Kinetics of Forest Fuels

AbstractA brief review is given of the studies in combustion chemistry and decomposition kinetics of forest fuels (FF). The methods used in the study to investigate the FF pyrolysis kinetics and the combustion of the Siberian forests are described. The experiments on FF pyrolysis were conducted at high heating rates (150K/s) in a flow reactor by the method of differential mass-spectrometric thermal analysis (DMSTA) in situ using probe molecular-beam mass spectrometry, and at low heating rates (0.17K/s) by the thermogravimetric method. The kinetic parameters of Siberian FF pyrolysis have been determined for oxidative and inert media and simulation of FF pyrolysis has been conducted using the multi-component devolatilization mechanism. The flame structure of a pine branch has been studied by probe molecular-beam mass spectrometry. Species have been identified in the dark and luminous flame zones; the width of the flame zone has been measured

The effect of methyl pentanoate addition on the structure of a non-premixed counterflow n‑heptane/O2 flame

The influence of methyl pentanoate (MP) addition to n-heptane on the species pool in a nonpremixed counterflow flame fueled with n-heptane at atmospheric pressure has been investigated experimentally and numerically. Two non-premixed flames in counterflow configuration have been examined: (1) n-heptane/Ar (5.3%/94.7%) vs O2/Ar (24.1%/75.9%) and (2) n-heptane/MP/Ar (2.5%/2.5%/95%) vs O2/Ar (19.6%/80.4%). Both flames had similar strain rates and stoichiometric mixture fractions to allow an adequate comparison of their structures. The mole fraction profiles of the reactants, major products, and intermediates in both flames were measured using flame sampling molecular beam mass spectrometry. These experimental data were used for validation of a detailed chemical kinetic mechanism, which was proposed earlier for prediction of combustion characteristics of n-heptane/iso-octane/toluene/MP mixtures. The addition of MP to n-heptane reduced the flame temperature and the peak mole fractions of many flame intermediates, responsible for the formation of polycyclic aromatic hydrocarbons, specifically, of benzene, cyclopentadienyl, acetylene, propargyl, and vinylacetylene. Significant discrepancies between the calculated and measured mole fractions of cyclopentadienyl and benzene were found. A kinetic analysis of the reaction pathways resulting in formation of these intermediates in both flames and a sensitivity analysis of cyclopentadienyl and benzene were carried out to understand the origins of the observed discrepancies. The peak mole fractions of the major flame radicals (H, O, OH, CH3) were found to decrease with MP addition. The influence of MP addition on the relative contributions of the primary stages of n-heptane consumption is discussed

Influence of Triphenyl Phosphate on Degradation Kinetics of Ultrahigh-molecular-weight Polyethylene in Inert and Oxidative Media

AbstractThe kinetics and the mechanism of thermal decomposition of ultrahigh-molecular-weight polyethylene without additive and with TPP additives in oxidative and inert media has been studied using the method of differential mass-spectrometric thermal analysis at a high heating rate and the method of thermogravimetric analysis at a low heating rate, aimed at understanding the mechanism of reducing combustibility of UHMWPE with TPP additives. The results of the study may testify to the fact that not the thermal polymer degradation reactions but the gas-phase reactions in the UHMWPE flame with TPP participation are responsible for flame retardancy of UHMWPE

Experimental study and a short kinetic model for high-temperature oxidation of methyl methacrylate

Synthetic and natural polymeric esters find applications in transport and construction sectors, where fire safety is an important concern. One polymer that is widely used is poly (methyl methacrylate) (PMMA), which almost completely undergoes thermal decomposition into methyl methacrylate (its monomer) CH2¼ CðCH3Þ Cð¼ OÞ O CH3 (MMA) at ,250–300C. In order to analyze the high-temperature gas-phase oxidation of PMMA, and thereby predict its fire behavior (such as burning rate, temperature of the material, and heat fluxes) with less computational effort, a compact kinetic model for the oxidation of its primary decomposition product, MMA, is most essential. This is accomplished in the present work by obtaining a reduced mechanism for MMA oxidation from a detailed mechanism from the Lawrence Livermore National Laboratories group. To extend the available data base for model validation and present validation data at atmospheric pressure conditions, for the first time, (i) detailed measurements of species profiles have been performed in stoichiometric laminar flat flames using flame sampling molecular beam mass spectrometry (MBMS) technique and (ii) laminar burning velocities have been obtained using the heat flux method for various unburnt mixture temperatures. Evaluating the model against these data sets point to the need to revise the kinetic model, which is achieved by adopting rate constants of key reactions among analogous molecules from recent literature. The updated compact kinetic model is able to predict the major species in the flat flame as well as the burning velocity of MMA satisfactorily. The final “short MMA mechanism” consists of 88 species and 1084 reactions

The Effect of Methyl Pentanoate Addition on the Structure of a Non-Premixed Counterflow <i>n</i>‑Heptane/O₂ Flame

The influence of methyl pentanoate (MP) addition to <i>n</i>-heptane on the species pool in a nonpremixed counterflow flame fueled with <i>n</i>-heptane at atmospheric pressure has been investigated experimentally and numerically. Two non-premixed flames in counterflow configuration have been examined: (1) <i>n</i>-heptane/Ar (5.3%/94.7%) vs O₂/Ar (24.1%/75.9%) and (2) <i>n</i>-heptane/MP/Ar (2.5%/2.5%/95%) vs O₂/Ar (19.6%/80.4%). Both flames had similar strain rates and stoichiometric mixture fractions to allow an adequate comparison of their structures. The mole fraction profiles of the reactants, major products, and intermediates in both flames were measured using flame sampling molecular beam mass spectrometry. These experimental data were used for validation of a detailed chemical kinetic mechanism, which was proposed earlier for prediction of combustion characteristics of <i>n</i>-heptane/iso-octane/toluene/MP mixtures. The addition of MP to <i>n</i>-heptane reduced the flame temperature and the peak mole fractions of many flame intermediates, responsible for the formation of polycyclic aromatic hydrocarbons, specifically, of benzene, cyclopentadienyl, acetylene, propargyl, and vinylacetylene. Significant discrepancies between the calculated and measured mole fractions of cyclopentadienyl and benzene were found. A kinetic analysis of the reaction pathways resulting in formation of these intermediates in both flames and a sensitivity analysis of cyclopentadienyl and benzene were carried out to understand the origins of the observed discrepancies. The peak mole fractions of the major flame radicals (H, O, OH, CH₃) were found to decrease with MP addition. The influence of MP addition on the relative contributions of the primary stages of <i>n</i>-heptane consumption is discussed