A two-eddy theory of premixed turbulent flame propagation

1981 ◽  
Vol 301 (1457) ◽  
pp. 1-25 ◽  
Keyword(s):  
Experimental Data ◽  
Reynolds Number ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Experimental Measurements ◽  
Laminar Burning Velocity ◽  
Turbulent Reynolds Number ◽  
Theoretical Predictions ◽  
Premixed Turbulent Flame ◽  
Turbulent Burning Velocity

Available experimental data on the turbulent burning velocity of premixed gases are surveyed. There is discussion of the accuracy of experimental measurements and the means of ascertaining relevant turbulent parameters. Results are presented in the form of the variation of the ratio of turbulent to laminar burning velocities with the ratio of r.m.s. turbulent velocity to laminar burning velocity, for different ranges of turbulent Reynolds number. A two-eddy theory of burning is developed and the theoretical predictions of this approach, as well as those of others, are compared with experimentally measured values.

Further development of the three-region model of a premixed turbulent flame III. Eddy entrainment, combustion in depth process of region 3

1979 ◽  
Vol 368 (1733) ◽  
pp. 295-304 ◽  
Keyword(s):  
Burning Velocity ◽  
Turbulent Flame ◽  
Small Scale ◽  
Laminar Burning Velocity ◽  
Turbulence Scale ◽  
Advection Term ◽  
Region Model ◽  
Premixed Turbulent Flame ◽  
High Level

An experimental study of the turbulent kinetic energy balance for the eddy entrainment, combustion in depth process of region 3 has been carried out. The influence of approach turbulence scale, intensity and laminar burning velocity on each term in the balance equation has been examined for propane-air and acetylene-air flames and the important role of small scale turbulent motion is highlighted. It is observed that either an increase in intensity or a reduction in scale of approach turbulence increases the magnitude of all terms except that for convection. The core region of the flame shows jet-like behaviour. The entrainment, combustion in depth process produces a very high level of fluctuating vorticity. Therefore, the dominant terms appear to be those of viscous dissipation and advection. Finally, a large increase in laminar burning velocity enhances the contribution of the advection term at the expense of a reduction in the convection term.

Further development of the three-region model of a premixed turbulent flame I. Turbulent diffusion dominated region 2

1979 ◽  
Vol 368 (1733) ◽  
pp. 267-282 ◽  
Keyword(s):  
Turbulence Intensity ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Turbulent Energy ◽  
Variable Density ◽  
Turbulent Flames ◽  
Laminar Burning Velocity ◽  
Advection Term ◽  
Set Up ◽  
Premixed Turbulent Flame

A study of the balance equation for turbulent kinetic energy of a premixed turbulent flame has been carried out. Various parameters constituting each term have either been measured or have been calculated from previously measured values. Propane and hydrogen were used as fuels, and the turbulence intensity of the approach flow was varied. Thus, an energy balance of turbulence in a flame has been set up. These results show that increase in both approach turbulence intensity and laminar burning velocity reduce the ratio of production/dissipation in a flame. Thus the stabilizing influence of laminar burning velocity is fully confirmed. The turbulent convection term is found to remain substantially unaltered. The advection term, on the other hand, changes from a loss to a gain in the turbulent energy of the flame. Finally, it is shown that significant differences exist between a flame and a non-reactive variable density axisymmetric jet. These conclusions make the study of turbulent flames unique in that theories that do not accommodate their special features should either be modified or abandoned.

Further development of the three-region model of a premixed turbulent flame II. Instability dominated region 1

1979 ◽  
Vol 368 (1733) ◽  
pp. 283-293 ◽  
Keyword(s):  
Energy Balance ◽  
Viscous Dissipation ◽  
Balance Equation ◽  
Large Scale ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Flame Structure ◽  
Small Scale ◽  
Laminar Burning Velocity ◽  
Premixed Turbulent Flame

An analysis of the balance equation for turbulent kinetic energy of an instability dominated region 1 is presented for a turbulent, premixed propane-air flame. The effects of intensity, scale and laminar burning velocity on the energy balance are also examined. Specifically, the nature of instability in a turbulent flame and its influence on the flame structure are highlighted. These results show that either increase in scale or reduction in intensity of approach turbulence increases the magnitude of all the terms in the balance equation. The core region of the flame is unaffected by a small scale instability, whereas, for a large scale instability, the ratio of turbulence production/viscous dissipation remains independent of scale. The dominant terms in the energy balance are found to be those of convection and advection when the structure of the flame turbulence consists mainly of a large scale fluctuating motion. Finally, increase in laminar burning velocity restores stability and causes transition to region 2, in which production and viscous dissipation predominate over convection and advection terms, respectively.

Study of Thermo-Diffusive Effects on Iso-Octane/Air Flames at Fixed Turbulence Karlovitz Number

2011 ◽  
Author(s):  
Akihiro Hayakawa ◽  
Tomohiro Takeo ◽  
Yukito Miki ◽  
Yukihide Nagano ◽  
Toshiaki Kitagawa
Keyword(s):  
Equivalence Ratio ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Turbulent Flames ◽  
Laminar Burning Velocity ◽  
Markstein Number ◽  
Flame Stretch ◽  
The Mean ◽  
Diffusive Effects ◽  
Turbulent Burning Velocity

Spherically propagating laminar and turbulent flames were studied using iso-octane / air mixtures with and without dilution. The main purpose of this study is to clarify the influence of thermo-diffusive effects on the turbulent flames. In order to examine the thermo-diffusive effects solely by separating them from the effects of flame stretch, turbulent burning velocities were compared at constant flame stretch factors. The mean flame stretch factor acting on turbulent flame front may be represented by the turbulence Karlovitz number. Thus, turbulent explosions were carried out at fixed turbulence Karlovitz numbers. The ratio of turbulent burning velocity to unstretched laminar burning velocity increased with the equivalence ratio for non-diluted mixtures at fixed turbulence Karlovitz numbers. And this ratio for CO2 diluted mixtures was larger than N2 diluted mixtures. The Markstein number that denotes the sensitivity of the flame to thermo-diffusive effects depends on the equivalence ratio and diluents of the mixture. The ratio of turbulent burning velocity to unstretched laminar one increased with decreasing Markstein number. Especially, it changed stepwise around Markstein number of zero. However, the burning velocity ratios did not increase with increasing mixture pressure although the Markstein number decreased with pressure.

scholarly journals Bioinspired aerofoil adaptations: the next steps for theoretical models

2019 ◽  
Vol 377 (2159) ◽  
pp. 20190070 ◽  
Author(s):  
Lorna J. Ayton
Keyword(s):  
Experimental Data ◽  
Theoretical Models ◽  
Theoretical Modelling ◽  
Experimental Measurements ◽  
Far Field ◽  
Acoustic Analogy ◽  
Trailing Edge ◽  
Trailing Edge Noise ◽  
Theoretical Predictions ◽  
Field Noise

The extended introduction in this paper reviews the theoretical modelling of leading- and trailing-edge noise, various bioinspired aerofoil adaptations to both the leading and trailing edges of blades, and how these adaptations aid in the reduction of aerofoil–turbulence interaction noise. Attention is given to the agreement between current theoretical predictions and experimental measurements, in particular, for turbulent interactions at the trailing edge of an aerofoil. Where there is a poor agreement between theoretical models and experimental data the features neglected from the theoretical models are discussed. Notably, it is known that theoretical predictions for porous trailing-edge adaptations do not agree well with experimental measurements. Previous works propose the reason for this: theoretical models do not account for surface roughness due to the porous material and thus omit a key noise source. The remainder of this paper, therefore, presents an analytical model, based upon the acoustic analogy, to predict the far-field noise due to a rough surface at the trailing edge of an aerofoil. Unlike previous roughness noise models which focus on roughness over an infinite wall, the model presented here includes diffraction by a sharp edge. The new results are seen to be in better agreement with experimental data than previous models which neglect diffraction by an edge. This new model could then be used to improve theoretical predictions for far-field noise generated by turbulent interactions with a (rough) porous trailing edge. This article is part of the theme issue ‘Frontiers of aeroacoustics research: theory, computation and experiment’.

A predictive combustion model for one-dimensional gasoline engine simulation

2020 ◽  
pp. 146808742094590
Author(s):  
Yoshihiro Nomura ◽  
Seiji Yamamoto ◽  
Makoto Nagaoka ◽  
Stephan Diel ◽  
Kenta Kurihara ◽  
...  
Keyword(s):  
Gasoline Engine ◽  
Early Stage ◽  
Burning Velocity ◽  
Turbulent Flame ◽  
Operating Conditions ◽  
Combustion Model ◽  
One Dimensional ◽  
Turbulent Reynolds Number ◽  
Proposed Model ◽  
Wide Range

A new predictive combustion model for a one-dimensional computational fluid dynamics tool in the multibody dynamics processes of gasoline engines was developed and validated. The model consists of (1) a turbulent burning velocity model featuring a flame radius–based transitional function, steady burning velocity that considers local quenching using the Karlovitz number and laminarization by turbulent Reynolds number, as well as turbulent flame thickness and its quenching model near the liner wall, and (2) a knock model featuring auto-ignition by the Livengood–Wu integration and ignition delay time obtained using a full-kinetic model. The proposed model and previous models were verified under a wide range of operating conditions using engines with widely different specifications. Good agreement was only obtained for combustion characteristics by the proposed model without requiring individual calibration of model constants. The model was also evaluated for utilization after prototyping. Improved accuracy, especially of ignition timing, was obtained after further calibration using a small amount of engine data. It was confirmed that the proposed model is highly accurate at the early stage of the engine development process, and is also applicable for engine calibration models that require higher accuracy.

scholarly journals The Effect of Hydrogen Addition on Low-Temperature Combustion of Light Hydrocarbons and Alcohols

Energies ◽  
2020 ◽  
Vol 13 (15) ◽  
pp. 3808
Author(s):  
Fekadu Mosisa Wako ◽  
Gianmaria Pio ◽  
Ernesto Salzano
Keyword(s):  
Experimental Data ◽  
Burning Velocity ◽  
Engine Performance ◽  
Pollutant Emissions ◽  
Low Temperature Combustion ◽  
Laminar Burning Velocity ◽  
Nox Formation ◽  
Hydrogen Addition ◽  
Temperature Combustion ◽  
Fuel Mixtures

Hydrogen is largely considered as an attractive additive fuel for hydrocarbons and alcohol-fueled engines. Nevertheless, a complete understanding of the interactions between blended fuel mechanisms under oxidative conditions at low initial temperature is still lacking. This study is devoted to the numerical investigation of the laminar burning velocity of hydrogen–hydrocarbon and hydrogen–alcohol fuels under several compositions. Estimations were compared with experimental data reported in the current literature. Additionally, the effects of hydrogen addition on engine performance, NOX, and other pollutant emissions of the mentioned fuels have been thermodynamically analyzed. From the study, it has been observed that the laminar burning velocity of the fuel mixtures increased with increasing hydrogen fractions and the peak value shifted to richer conditions. Besides, hydrogen fraction was found to increase the adiabatic flame temperatures eventually favoring the NOX formation for all fuel blends except the acetylene–hydrogen–air mixture where hydrogen showed a reverse effect. Besides, hydrogen is also found to improve the engine performances and helps to surge thermal efficiency, improve the combustion rate, and lessen other pollutant emissions such as CO, CO2, and unburned hydrocarbons. The model predicted well and in good agreement with the experimental data reported in the recent literature.

Numerical Modeling of Stationary But Developing Premixed Turbulent Flames

2006 ◽  
Author(s):  
Pratap Sathiah ◽  
Andrei N. Lipatnikov
Keyword(s):  
Bluff Body ◽  
Burning Velocity ◽  
Rectangular Channel ◽  
Turbulent Flame ◽  
Flame Stabilization ◽  
Turbulent Flames ◽  
Turbulent Diffusivity ◽  
Flame Thickness ◽  
Premixed Turbulent Flames ◽  
Premixed Turbulent Flame

A typical stationary premixed turbulent flame is the developing flame, as indicated by the growth of mean flame thickness with distance from flame-stabilization point. The goal of this work is to assess the importance of modeling flame development for RANS simulations of confined stationary premixed turbulent flames. For this purpose, submodels for developing turbulent diffusivity and developing turbulent burning velocity, which were early suggested by our group (FSC model) and validated for expanding spherical flames [4], have been incorporated into the so-called Zimont model of premixed turbulent combustion and have been implemented into the CFD package Fluent 6.2. The code has been run to simulate a stationary premixed turbulent flame stabilized behind a triangular bluff body in a rectangular channel using both the original and extended models. Results of these simulations show that the mean temperature and velocity fields in the flame are markedly affected by the development of turbulent diffusivity and burning velocity.

Sign in / Sign up

Export Citation Format

Share Document