Kinetics of hydrocarbon combustion

Detailed kinetic mechanisms for the combustion of hydrocarbon fuels have been subjected to relatively intensive study in recent years. The mechanisms are complex and involve a variety of chain carriers. Fundamental to such studies are data on rates of elementary steps. Extensive compilations of rate information are becoming available [12], [39]-[47]. Users should realize that uncertainties remain in rates of various elementary steps. Since these uncertainties sometimes exceed an order of magnitude, studies of 

If methyl concentrations become sufficiently high, then 

The mechanism described here results in H2O and CO as reaction products. The oxidation of CO to CO2 occurs largely by 

Attempts to simplify the scheme outline here have employed a two-step process, the first typically being combustion to form H2O and CO and the 

Accurate specifications of kinetic mechanisms for combustion often are less critical to calculation of overall rates of heat release than to estimation of amounts of pollutants produced. Pollutants of primary interest are oxides of nitrogen, oxides of sulfur, unburned hydrocarbons, and particulates such as smoke or soot [12]. A primary mechanism by which nitric oxide is formed in flames is that attributed to Zel dovich, namely, 

If methyl concentrations become sufficiently high, then CH3 + O -------------------------- CH2O + H 

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Westbrook, C.K. and Dryer, F.L., Chemical kinetic modeling of hydrocarbon combustion, Prog. Energy Combust. Sci., 1984, 10, 1-57. 

C.K. Westbrook. Chemical Kinetics of Hydrocarbon Ignition in Practical Combustion Systems. Proc. Combust. Inst., 28 1563-1577,2000. 

C.K. Westbrook and F.L. Dryer, Chemical Kinetic Modelling of Hydrocarbon Combustion, Prog. Energy Comb. Sci. 10 (1984) 1. 

C. Morley, Photolytic Perturbation Method to Investigate the Kinetics of Hydrocarbon Oxidation near 800 K, 22nd Symp. (Int.) Comb. (The Combustion Institute, Pittsburgh, 1988) p. 911. 

Westbrook, C. K., and F. L. Dryer. 1981. Chemical kinetic modeling of hydrocarbon combustion. Combustion Science Technology 27 31-43. 

The kinetics of the combustion of hydrocarbons is a complex issue, the activity of a catalyst being dependant on many different factors. In determining the kinetics of combustion, therefore, each catalytic system must be considered on its own merits. 

A simulation model for the reaction-regeneration steps in the transformation of methanol into hydrocarbons has been proposed and used for predicting the behaviour of a laboratory fixed bed pseudoadiabatic reactor. Kinetic models for both the main reaction and deactivation have been used, which take into account the attenuating role of water on both the zero time kinetics and the deactivation by coke deposition. The kinetics of coke combustion and the relationship between activity and coke content have been used for the design of the regeneration. The activity-coke content relationship is different in the reaction and regeneration steps. 

Westbrook, C. K. Dryer, F. L. "Chemical Kinetics Modeling of Hydrocarbon Combustion" Lawrence Livermore National Laboratory Report No. UCRL-88651 February, 1983. 

C. Westbrook, Chemical kinetics of hydrocarbon oxidation in gaseous detonations. Combust. 

GASFLOW models geometrically complex containments, buildings, and ventilation systems with multiple compartments and internal structures. It calculates gas and aerosol behavior of low-speed buoyancy driven flows, diffusion-dominated flows, and turbulent flows dunng deflagrations. It models condensation in the bulk fluid regions heat transfer to wall and internal stmetures by convection, radiation, and condensation chemical kinetics of combustion of hydrogen or hydrocarbon.s fluid turbulence and the transport, deposition, and entrainment of discrete particles. 

The solution procedure to this equation is the same as described for the temporal isothermal species equations described above. In addition, the associated temperature sensitivity equation can be simply obtained by taking the derivative of Eq. (2.87) with respect to each of the input parameters to the model. The governing equations for similar types of homogeneous reaction systems can be developed for constant volume systems, and stirred and plug flow reactors as described in Chapters 3 and 4 and elsewhere [31-37], The solution to homogeneous systems described by Eq. (2.81) and Eq. (2.87) are often used to study reaction mechanisms in the absence of mass diffusion. These equations (or very similar ones) can approximate the chemical kinetics in flow reactor and shock tube experiments, which are frequently used for developing hydrocarbon combustion reaction mechanisms. 

At high pressures or in the initial stages of hydrocarbon oxidation, high concentrations of H02 can make reaction (3.45) competitive to reaction (3.44), so reaction (3.45) is rarely as important as reaction (3.44) in most combustion situations [4], Nevertheless, any complete mechanism for wet CO oxidation must contain all the H2—02 reaction steps. Again, a complete mechanism means both the forward and backward reactions of the appropriate reactions in Appendix C. In developing an understanding of hydrocarbon oxidation, it is important to realize that any high-temperature hydrocarbon mechanism involves H2 and CO oxidation kinetics, and that most, if not all, of the C02 that is formed results from reaction (3.44). 

There has been a great deal of research on the combustion of small hydrocarbons, including nitrogen-cycle chemistry leading to nitric-oxide formation and abatement [138]. There are a number of methane-air reaction mechanisms that have been developed and validated [274,276,278], the most popular one being GRI-Mech [366]. There is also active research on the kinetics of large hydrocarbon combustion [81,88,171,246,328-330,426]. 

P. Glarborg, M.U. Alzueta, K. Dam-Johansen, and J.A. Miller. Kinetic Modeling of Hydrocarbon/Nitric Oxide Interactions in a Flow Reactor. Combust. Flame, 115 1— 27,1998. 

E. Ranzi, M. Dente, A. Goldaniga, G. Bozzano, and T. Faravelli. Lumping Procedures in Detailed Kinetic Modeling of Gasification, Pyrolysis, Partial Oxidation, and Combustion of Hydrocarbon Mixtures. Prog. Combust. Sci. Techn., 27 99-139, 2001. 

The previous intent has been to use kinetics simply as a tool to describe qualitatively the particular aspect of combustion under study. Numerical values of the kinetic constants were thus assumed for illustrative purposes or approximated from other types of data by making admittedly questionable major assumptions. Approximations include, for example, the extrapolation of low temperature hydrocarbon oxidation rates to high temperature hydrocarbon combustion rates. Other schemes involve application of semiempirical laminar flame speed theories or of flow patterns in the wake of a bluff body immersed in an air stream (43). 

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