R. Reid

Bio: R. Reid is an academic researcher from Vaughn College of Aeronautics and Technology. The author has contributed to research in topics: Premixed flame & Flow velocity. The author has an hindex of 1, co-authored 1 publications receiving 50 citations.

Turbulent flows with premixed reactants

Abstract: This chapter considers turbulent flows in which the reactants have been fully mixed prior to reaction. Application to combustion is emphasized both because many practical combustion systems require the fuel and oxidizer to be premixed, and also because the premixed flame provides a convenient test for contemporary ideas about turbulent reacting flows. Only gaseous species are considered. The rates of the chemical kinetic processes leading to combustion are strongly dependent on temperature. Consequently, the propagation of a premixed laminar flame requires thermal conduction and diffusion from the hot products to preheat the reactive mixture. In a turbulent flame, these molecular processes are augmented both indirectly, by distortion of flame surfaces, leading to an increase in their area, and directly, by turbulent mixing. The result is that the mean rate of heat release is generally more strongly influenced by the turbulence than by chemical kinetic factors so that premixed turbulent combustion is primarily a complex fluid mechanical problem. However, ignition and flame quenching provide examples of situations in which both chemical kinetics and fluid mechanics are likely to be important. Premixing leads to a significant simplification in the analysis as the composition of the flow is essentially uniform, in terms of the elements involved, i.e., the Z[s of (1.19) are constants. It also causes complications; the scalar thermodynamic variables of temperature, density, and composition often fluctuate strongly within this type of flame, between values characteristic of the unburned and fully burned mixtures. These intense scalar fluctuations pose theoretical and experimental difficulties, some of which have not yet been solved. Following a review of knowledge concerning premixed turbulent combustion, this chapter concentrates on theoretical models which are based on prior specification of a probability density function for the fluctuating thermodynamic state of the mixture. It is argued that such models provide the best available compromise between complexity and generality of application.

Interaction effects in turbulent premixed flames

Abstract: The Bray–Moss model for turbulent, premixed combustion is applied to plane, oblique combustion waves. The analysis takes into account the influence of turbulence and inhomogeneity on the effective rate of heat release, and also the competing effects of dilatation and turbulent production due to shear in the turbulent kinetic energy balance. Predictions are made of the flame speed and the structure of the reaction zone in cases where turbulent mixing is rate limiting. Qualitiative agreement is found with relevant experimental data.