Flame Structure and Propagation in Turbulent Flame-Droplet Interaction: A Direct Numerical Simulation Analysis
| Autor: | Nilanjan Chakraborty, Daniel H. Wacks |
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| Rok vydání: | 2016 |
| Předmět: |
Materials science
020209 energy General Chemical Engineering Flame structure General Physics and Astronomy 02 engineering and technology Physics and Astronomy(all) Combustion complex mixtures 01 natural sciences 010305 fluids & plasmas Physics::Fluid Dynamics fluids and secretions 0103 physical sciences 0202 electrical engineering electronic engineering information engineering Physics::Chemical Physics Physical and Theoretical Chemistry Premixed flame Hull speed Turbulence Diffusion flame Mechanics Strain rate eye diseases humanities Turbulence kinetic energy Chemical Engineering(all) |
| Zdroj: | Flow, Turbulence and Combustion. 96:1053-1081 |
| ISSN: | 1573-1987 1386-6184 |
| DOI: | 10.1007/s10494-016-9724-7 |
| Popis: | Three-dimensional Direct Numerical Simulations (DNS) in canonical configuration have been employed to study the combustion of mono-disperse droplet-mist under turbulent flow conditions. A parametric study has been performed for a range of values of droplet equivalence ratio ϕd, droplet diameter ad and root-mean-square value of turbulent velocity u′. The fuel is supplied entirely in liquid phase such that the evaporation of the droplets gives rise to gaseous fuel which then facilitates flame propagation into the droplet-mist. The combustion process in gaseous phase takes place predominantly in fuel-lean mode even for ϕd>1. The probability of finding fuel-lean mixture increases with increasing initial droplet diameter because of slower evaporation of larger droplets. The chemical reaction is found to take place under both premixed and non-premixed modes of combustion: the premixed mode ocurring mainly under fuel-lean conditions and the non-premixed mode under stoichiometric or fuel-rich conditions. The prevalence of premixed combustion was seen to decrease with increasing droplet size. Furthermore, droplet-fuelled turbulent flames have been found to be thicker than the corresponding turbulent stoichiometric premixed flames and this thickening increases with increasing droplet diameter. The flame thickening in droplet cases has been explained in terms of normal strain rate induced by fluid motion and due to flame normal propagation arising from different components of displacement speed. The statistical behaviours of the effective normal strain rate and flame stretching have been analysed in detail and detailed physical explanations have been provided for the observed behaviour. It has been found that the droplet cases show higher probability of finding positive effective normal strain rate (i.e. combined contribution of fluid motion and flame propagation), and negative values of stretch rate than in the stoichiometric premixed flame under similar flow conditions, which are responsible for higher flame thickness and smaller flame area generation in droplet cases. |
| Databáze: | OpenAIRE |
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