Laminar diffusion flamelet models in non-premixed turbulent combustion

Turbulent jet diffusion flames

Counterflow diffusion flames

Model-free simulations of turbulent reactive flows

The prediction of laminar jet diffusion flame sizes: Part II. Experimental verification

Three theoretical models of plane flames burning on a cooled porous-plug type of flame-holder are reviewed and compared with experimentally observed relationships between stand-off distance, flame speed and temperature.
It is shown that for most practical burners their conductance is large and that for near adiabatic conditions, the order of the non-dimensional stand-off distance ceases to be O (1), but is O (O) where O is the non-dimensional activation energy.

Starting in 1946 as the College of Aeronautics, the Cranfield Institute of Technology was granted university status in 1969. In 1993 it changed its name to Cranfield University.

Second order theory of unsteady burner-anchored flames with arbitrary Lewis Number

The stability of burner flames for arbitrary Lewis number is considered on the basis of large activation energy modelling. Previous leading-order-only approaches are now extended to second order in Math (the inverse activation energy). The assumption that the unsteady perturbations are small (order e) means that one must discuss the distinguished limit implicit in the product Math. lt is demonstrated here that different governing equations (and in particular the inner zone equation) are obtained in the two cases, θ1e → 0 and θ1e → ∞. It is shown that there are two complex frequency relations governing the behaviour of flames near burners. It is found that for free flames a dispersion relationship specifically dependent on activation energy is obtained which is similar though not identical to the classical relationship. For near-free flames, the complex frequency obeys a "composite" dispersion relation, the solution to which clearly indicates the destabilizing effect of heat losses to the burner. ...

Second Order Theory of Unsteady Burner-Anchored Flames With Arbitrary Lewis Number

Results of an experimental investigation of the structure of flat diffusion flames on a Parker-Wolf hard burner are compared with theoretical predictions of perturbation solutions which incorporate realistic schemes for the chemical kinetics. Measurements of hydroxyl radical concentrations show that the flames are reaction-broadened for temperatures below I950°K, while at higher temperatures reaction zone structure is of equilibrium-broadened type. Experiment also shows that, close to extinction, there is significant convective transfer of material from one stream to the other at the flame base. It is suggested that the consequent disruption of mixing in, or shielding of, the reaction zone makes extinction a progressive process. Complementary studies of spherical and counter flow diffusion flames suggest that the former geometry is preferable in future studies designed to test hypotheses about the role of kinetics in diffusion flame extinction.

The Structure of a Reaction-Broadened Diffusion Flame

Hydrogen gas is assumed to be injected through the surface of a ‘fuel spher’ into a pure oxygen atmosphere, and so to give rise to a spherical diffusion flame. The combustion process is presumed to be sustained by a set of five reactions which involve the six species H2, O2, O, H, OH and H2O, and a proper multi-component, variable diffusion-coefficient, description of the diffusion processes is therefore adopted. Use of the method of matched asymptotic expansions to solve the governing conservation equations makes it possible to deal analytically with this problem and, by focussing attention on the dominance of certain physical phenomena in special regions of the field, reveals the influence of chemical kinetics on flame structure. For example, inner region (i.e. intense reaction zone) behaviour indicates the crucial role played on the O2-rich side of the flame by the reaction OH + H; in one case it may produce O + H2 and in the other (with the aid of a third body) it may result in H2O and so act...

On the Structure of a Spherical H2—O2, Diffusion Flame

A streamwise laminar diffusion flame in a boundary layer flow is modelled for a hydrogen-oxygen system with six step reaction kinetics. The method of matched asymptotic expansions, based on the existence of a large value of the Damkohler number, provides first order inner and outer temperature and concentration solutions from which composite series are constructed for a range of fresstream reactant concentrations, some of which are chosen to coincide with experimental situations. In these cases comparisons between theoretical and experimental results are made

J. F. Clarke

Papers

Second order theory of unsteady burner-anchored flames with arbitrary Lewis Number

Second Order Theory of Unsteady Burner-Anchored Flames With Arbitrary Lewis Number

The Structure of a Reaction-Broadened Diffusion Flame

On the Structure of a Spherical H2—O2, Diffusion Flame

Theory of a Hydrogen-Oxygen Diffusion Flame Part I: Profiles from a Large Damkohler Number Model