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.

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.

scholarly journals The Role of Triple Helix Actors for Agro-Tourism Development in West Sumatera

2017 ◽  
Vol 33 (2) ◽  
pp. 217
Author(s):  
Widya Fitriana
Keyword(s):  
Triple Helix ◽  
Agricultural Sector ◽  
Group Discussion ◽  
Tourism Development ◽  
Essential Element ◽  
Government Support ◽  
Small Scale ◽  
Literature Study ◽  
High Level

Agricultural sector as a main contributor to GDP formation in West Sumatera is required to be able to diversify its business in order to highest achieving economic and social development. One diversified agricultural business prospective to be developed is agro-tourism. The development of agro-tourism requires collaboration and synergy between academician, businessman and government as known as triple helix actors. This study is designed with aim to (i) map the agro-tourism potential in west Sumatera; (ii) analyze the role of each actors, so they may take action in accelerating Agro-tourism development. This research uses observation, depth interview method, literature study and focus group discussion. The result shows that agro-tourism in West Sumatra is more prominent of great natural and cultural value, small scale and lack of local facilities. It also requires relatively high level of investment relative to its return. Therefore government support is likely an essential element of agro-tourism development and the effort may be better directed toward consolidating with intellectual and business also.

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.

The structure of a premixed turbulent flame

1979 ◽  
Vol 367 (1730) ◽  
pp. 353-380 ◽  
Keyword(s):  
Turbulence Intensity ◽  
Structural Characteristics ◽  
Turbulent Flame ◽  
Pressure Gradients ◽  
Turbulence Scale ◽  
Air Stream ◽  
Wide Range ◽  
Total Magnitude ◽  
Premixed Turbulent Flame ◽  
Definition Of

An experimental study of the structure of a premixed turbulent flame propagating in a duct-confined, stoichiometric propane-air mixture has been carried out. Care was taken to reduce any effects of axial pressure gradients. By suitable changes in grid geometry, the turbulence intensity and scale of the approach flow were varied independently over a wide range. The results of these experiments show a strong link between the mechanisms of turbulent flame propagation and the flame-generated turbulence. Thus, three distinct regions, each having different structural characteristics in regards to the effects of turbulence scale on flame-generated turbulence, may he identified. The physical processes for each region, namely a ‘wrinkled-pulsating’ behaviour of region 1, the ‘jet-like’ characteristics of region 2 and the ‘eddy entrainment - combustion in depth’ mechanism of region 3 are described. A comparison between the mean and the turbulence properties of a flame and of a coaxial jet of lighter fluid (hydrogen) spreading into a turbulent, co-flowing air stream has been made. Based upon this, the contribution of shear-generated turbulence to total flame turbulence is calculated. A definition of flame-generated turbulence is then proposed. It is shown that in some cases the flame damps the turbulence whereas in most other instances it generates additional turbulence. The total magnitude of the relative flame-generated turbulence intensity does not exceed about 12 %. Finally, it is shown that the flame damps the unburnt stream fluctuating vorticity in region 1, has no effect in region 2 and augments the vorticity in region 3.

scholarly journals Role of small addition of liquefied petroleum gas (LPG) on laminar burning velocity of hydrous ethanol

2019 ◽  
Vol 3 (8 (99)) ◽  
pp. 56-62
Author(s):  
Muh Nurkoyim Kustanto ◽  
Mega Nur Sasongko ◽  
I Nyoman Gede Wardana ◽  
Lilis Yuliati
Keyword(s):  
Burning Velocity ◽  
Small Addition ◽  
Laminar Burning Velocity ◽  
Liquefied Petroleum Gas ◽  
Hydrous Ethanol

The influence of laminar burning velocity on the structure and propagation of turbulent flames

1979 ◽  
Vol 367 (1731) ◽  
pp. 485-502 ◽  
Keyword(s):  
Turbulence Intensity ◽  
Burning Velocity ◽  
Diffusion Mechanism ◽  
Turbulent Flames ◽  
Laminar Burning Velocity ◽  
Premixed Turbulent Flames ◽  
Region Model ◽  
High Turbulence ◽  
Model Region ◽  
Turbulent Burning Velocity

An experimental study of the influence of laminar burning velocity on the structure and propagation of duct-confined premixed turbulent flames has been carried out. Propane, acetylene and hydrogen were used as fuels to vary the laminar burning velocity in the range from 20 to 280 cm/s. These experiments fully verify the three region model (region 1: u ' < 2 S L , η > δ L ; region 2: u ' ≈ 2 S L , η ≈ δ L to η ≫ δ L ; region 3: u ' > 2 S L , η < δ L ) of turbulent flames proposed earlier by Ballal & Lefebvre. Since a large increase in the laminar burning velocity has a stabilizing influence it is possible to suppress the ‘instability’ of region 1 and the ‘eddy entrainment’ of region 3. The ‘turbulent diffusion’ mechanism then becomes solely dominant, and the flame shows a ‘jet-like’ behaviour. For such a flame (i) both the burning velocity and flame turbulence intensity are independent of scale, (ii) the equations developed by Karlovitz and Ballal for regions of stable combustion accurately predict all the experimental data on turbulent burning velocity and flame turbulence, respectively, and (iii) the laminar burning velocity remains an important parameter of flame propagation even at very high turbulence intensity. Finally the important role of shear-generated turbulence and the ability of the flame either to dampen or to generate additional turbulence has been fully confirmed.

Sign in / Sign up

Export Citation Format

Share Document