Preface 1.General Considerations 2.Basic Processes in Atomization 3.Drop Size Distributions of Sprays 4.Atomizers 5.Flow in Atomizers 6.Atomizer Performance 7.External Spray Charcteristics 8.Drop Evaporation 9.Drop Sizing Methods Index

Atomization and Sprays

Turbulent combustion modeling

A computational technique is described and demonstrated that can decrease by three orders of magnitude the computer time required to treat detailed chemistry in reactive flow calculations. The method is based on the in situ adaptive tabulation (ISAT) of the accessed region of the composition space - the adaptation being to control the tabulation errors. Test calculations are performed for non-premixed methane - air combustion in a statistically-homogeneous turbulent reactor, using a kinetic mechanism with 16 species and 41 reactions. The results show excellent control of the tabulation errors with respect to a specified error tolerance; and a speed-up factor of about 1000 is obtained compared to the direct approach of numerically integrating the reaction equations. In the context of PDF methods, the ISAT technique makes feasible the use of detailed kinetic mechanisms in calculations of turbulent combustion. The technique can also be used with reduced mechanisms, and in other approaches for calculating rea...

Computationally efficient implementation of combustion chemistry using in situ adaptive tabulation

Oxy-fuel combustion of solid fuels

Large-eddy simulation (LES) of turbulent combustion is a relatively new research field. Much research has been carried out over the past years, but to realize the full predictive potential of combustion LES, many fundamental questions still have to be addressed, and common practices of LES of nonreacting flows revisited. The focus of the present review is to highlight the fundamental differences between Reynolds-averaged Navier-Stokes (RANS) and LES combustion models for nonpremixed and premixed turbulent combustion, to identify some of the open questions and modeling issues for LES, and to provide future perspectives.

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Large-eddy simulation of turbulent combustion

The structure of turbulent nonpremixed flames revealed by Raman-Rayleigh-LIF measurements

Instantaneous and Mean Compositional Structure of Bluff-Body Stabilized Nonpremixed Flames

The mean structure of turbulent bluff-body jets and flames is presented. Measurements of the flow and mixing fields are compared with predictions made using standard turbulence models. It is found that two vortices exist in the recirculation zone; an outer vortex close to the air coflow and an inner vortex between the outer vortex and the jet. The inner vortex is found to shift downstream with increasing jet momentum flux relative to the coflow momentum flux and gradually loses its circulation pattern. The momentum flux ratio of the jet to the coflow in isothermal flows is found to be the only scaling parameter for the flow field structure. Three mixing layers are identified in the recirculation zone. Numerical simulations using the standard k-ϵ and Reynolds stress turbulence models underpredict the length of the recirculation zone. A simple modification to the C1 constant in the dissipation transport equation fixes this deficiency and gives better predictions of the flow and mixing fields. The mixed-is-b...

Flow and mixing fields of turbulent bluff-body jets and flames

Turbulent lifted flames in a vitiated coflow investigated using joint PDF calculations

This paper introduces a new experimental set-up for investigating the effects of obstruction geometry, blockage ratio and venting pressure on overpressures resulting from premixed flame deflagration. Obstructions shaped as cylinders, triangles, squares, diamonds and plates or walls are studied here covering blockage ratios ranging from about 10% to more than 75%. It is found that the deflagration overpressure increases with increasing venting pressure. Also, the maximum overpressure increases, generally with increasing blockage ratio but the rate of increase depends on the obstruction geometry. The wall/plate type obstruction leads to the highest overpressures and the cylindrical obstruction yields the lowest overpressure. The time taken to reach the maximum overpressure decreases with increasing blockage ratio and changes with obstruction geometry implying that the flame accelerates faster due to changed local turbulence levels and length scales.

Assaad R. Masri

Papers

The structure of turbulent nonpremixed flames revealed by Raman-Rayleigh-LIF measurements

Instantaneous and Mean Compositional Structure of Bluff-Body Stabilized Nonpremixed Flames

Flow and mixing fields of turbulent bluff-body jets and flames

Turbulent lifted flames in a vitiated coflow investigated using joint PDF calculations

The effects of obstructions on overpressure resulting from premixed flame deflagration