Premixed laminar flames and kinetic studies

The implicit numerical solution of the time-dependent conservation equations provides the most powerful general method of solving premixed laminar flame problems in systems of (in principle) arbitrary chemical complexity. Indeed, with the simultaneous development of improved diagnostic techniques for the measurement of flame profiles, the possibility of obtaining such solutions has opened the way to realistic studies of reaction mechanisms even in hydrocarbon flames. The choice of solution method and transport flux formulation involves compromise between precision and cost, which becomes a matter of considerable import when modeling hydrocarbon oxidation in flames, which may involve some 25 chemical species and 80 or so elementary reactions. 

The implicit solution approach has been used successfully for onedimensional premixed flame modeling of flames in hydrogen-bromine (Spalding and Stephenson, 1971), hydrogen-air (Stephenson and Taylor, 

Following a series of flame computations over an extended range of initial compositions and conditions, the validity of an assumed kinetic mechanism and set of rate parameters may be tested by comparison of computed properties with experiment. In the case of the flame profiles there must be comparison not only for major reactants and products, but also for reactive intermediates. It is necessary to be circumspect as far as minor intermediates are concerned (for example, with mole fractions less than about 10 ), since there may be large uncertainties in the measurements themselves. When assessing rate parameters it is also necessary to carry out sensitivity analyses (Chapter 7) to determine the relative importance of each elementary reaction and intermediate in the mechanism. The final mechanism and rate parameters must, further, be consistent with results from studies of other combustion phenomena, such as data obtained from shock tube, explosion limit, or fast flow studies. 

To illustrate the degree of agreement with experiment which is achieved by current methane-air kinetic models. Fig. 7 compares predicted and measured burning velocities of methane-air flames at atmospheric pressure, and Figs. 8 and 9 compare predicted species profiles for a stoichiometric methane-air flame at atmospheric pressure with measurements by Bechtel et al (1981). 

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