Fuel droplet vaporization and spray combustion theory

Turbulent combustion modelling

Turbulent combustion occurs in a majority of industrial devices. Many prediction methods have been proposed in recent years, and at the same time much experimental investigation has been performed. However, the physical structure of turbulent flames cannot be regarded as completely understood at present due to the complexity of the relevant experimentation.

On the Structure and Morphology of Turbulent Premixed Flames

The effects of chemical heat release on the large-scale structure in a chemically reacting turbulent mixing layer have been studied using three-dimensional time-dependent simulations. Moderate heat release is found to slow the development of the large-scale structures and to shift their wavelengths to larger scales. The results suggest that previously unexplained anomalies observed in the mean velocity profiles of reacting jets and mixing layers may be the result of vorticity generation by baroclinic torques.

Effects of heat release on the large-scale structure in turbulent mixing layers

A numerical method for accurate simulation of the time and spatial characteristics of the inner and outer vortex structures in transitional H 2 /N 2 jet diffusion flames is presented. The direct numerical simulation, incorporating buoyancy, a simple one-step chemistry model, coefficients that depend on temperature and species concentration, is described in detail. The species and energy equations are simplified by introducing two conserved scalars β 1 and β 2 and by assuming that the Lewis number of the flow is equal to unity. An implicit, third-order-accurate, upwind numerical scheme having very low numerical diffusion is used to simulate the inner small-scale structures and the outer large-scale structures simultaneously

Numerical investigations of transitional H2/N2 jet diffusion flames

The transition between laminar and turbulent flow in a round jet flame is studied experimentally. Comparison is made between transition in nonburning and burning jets and between jet flames with systematic variation in initial Reynolds number and equivalence ratio. Measurements are made using laser anemometry, miniature thermocouples, ionization probes, laser Schlieren, and high-speed cine films. Compared with the cold jet, the jet flame has a longer potential core, undergoes a slower transition to turbulence, has lower values of fluctuating velocity near the burner with higher values further downstream, and contains higher velocity gradients in the mixing layer region although the total jet width does not alter greatly in the first twenty diameters. As in the cold jet, transitional flow in the flame contains waves and vortices and these convolute and stretch the initially laminar interface burning region. Unlike the cold jet, which has Kelvin-Helmholtz instabilities, the jet flame can contain at least two initial instabilities: an inner high-frequency, combustion-driven instability and an outer, low-frequency instability that may be influenced by buoyancy forces.

Combustion-Transition Interaction in a Jet Flame

A light scattering technique is combined with a tomographic transformation to convert line of sight integrated data, measured in sprays, to measurements of droplet size and concentration in volume elements within the spray. The technique is developed and assessed by systematic experiments in axisymmetric sprays generated by twin-fluid atomisers. The good agreement found shows that, provided certain conditions are satisfied by the local spray structure, the technique provides information on spray structure, similar in detail and extent to that derived by photography, but with reduced experimental time. The technique is applied to an investigation of a kerosene spray vaporizing in a hot gas stream.

A laser tomographic investigation of liquid fuel sprays

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Combustion-transition interaction in a jet flame

Ionization probes were used to measure mean ionization current and frequency spectra, auto-correlations and cross-correlations in jet flames with variation in the initial Reynolds numbers and equivalence ratios. Special attention was paid to the transitional region between the burner exit plane and the plane of onset of turbulence.

A. J. Yule

Papers

Combustion-Transition Interaction in a Jet Flame

A laser tomographic investigation of liquid fuel sprays

A laser tomographic investigation of liquid fuel sprays

Combustion-transition interaction in a jet flame

The investigation of time dependent flame structure by ionisation probes