scholarly journals Numerical investigation of the effect of pressure on heat release rate in iso-octane premixed turbulent flames under conditions relevant to SI engines

2017 ◽  
Vol 36 (3) ◽  
pp. 3543-3549 ◽  
Author(s):  
Bruno Savard ◽  
Simon Lapointe ◽  
Andrzej Teodorczyk
Keyword(s):  
Heat Release ◽  
Numerical Investigation ◽  
Heat Release Rate ◽  
Release Rate ◽  
Turbulent Flames ◽  
Effect Of Pressure ◽  
Premixed Turbulent Flames ◽  
Si Engines

Effects of Flame Development and Structure on Thermo-Acoustic Oscillations of Premixed Turbulent Flames

Volume 4 ◽  
2004 ◽  
Author(s):  
Pratap Sathiah ◽  
Andrei N. Lipatnikov ◽  
Jerzy Chomiak
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Turbulent Flame ◽  
Kinematic Model ◽  
Turbulent Flames ◽  
Flame Speed ◽  
Oncoming Flow ◽  
Turbulent Flame Speed ◽  
Premixed Turbulent Flames

Non-stationary confined premixed turbulent flames stabilized behind a bluff body are studied. A simple kinematic model of such flames was developed by Dowling [9] who reduced the combustion process to the propagation of an infinitely thin flame at a constant speed. The goal of this work is to extend the model by taking into account the structure of premixed turbulent flames and the development of turbulent flame speed and thickness. For these purposes, the so-called Flame Speed Closure model for multi-dimensional simulations of premixed turbulent flames is adapted and combined with the aforementioned Dowling model. Simulations of the heat release rate dynamics for ducted flames due to oncoming flow oscillations have been performed. Typical results show that the oscillations of the integrated heat release rate follow the oncoming flow velocity oscillations with certain time delay. The delays computed using the Dowling and the above approach are different, thus indicating the importance of resolving flame structure when modeling ducted flame oscillations.

scholarly journals Predicting the consumption speed of a premixed flame subjected to unsteady stretch rates

2021 ◽  
Author(s):  
Meysam Sahafzadeh ◽  
Seth B. Dworkin ◽  
Larry W. Kostiuk
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Time Scale ◽  
Transfer Functions ◽  
Laminar Flame ◽  
Premixed Flames ◽  
Turbulent Flames ◽  
Response Analysis ◽  
Phase Lag

The stretched laminar flame model provides a convenient approach to embed realistic chemical kinetics when simulating turbulent premixed flames. When positive-only periodic strain rates are applied to a laminar flame there is a notable phase lag and diminished amplitude in heat release rate. Similar results have being observed with respect to the other component of stretch rate, namely the unsteady motion of a curved flame when the stretch rates are periodic about zero. Both cases showed that the heat release rate or consumption speed of these laminar-premixed flames vary significantly from the quasi-steady flamelet model. Deviation from quasi-steady behaviour increases as the unsteady flow time scale approaches the chemical time scale that is set by the stoichiometry. A challenge remains in how to use such results predictively for local and instantaneous consumption speed for small segments of turbulent flames where their unsteady stretch history is not periodic. This paper uses a frequency response analysis as a characterization tool to simplify the complex non-linear behaviour of premixed methane air flames for equivalence ratios from 1.0 down to 0.7, and frequencies from quasi-steady up to 2000 Hz using flame transfer functions. Various linear and nonlinear models were used to identify appropriate flame transfer functions for low and higher frequency regimes, as well as extend the predictive capabilities of these models. Linear models were only able to accurately predict the flame behaviour below a threshold of when the fluid and chemistry time scales are the same order of magnitude. Other proposed transfer functions were tested against arbitrary multi-frequency stretch inputs and were shown to be effective over the full range of frequencies.

Determination of the Heat Release Distribution in Turbulent Flames by a Model Based Correction of OH* Chemiluminescence

2011 ◽  
Vol 133 (12) ◽  
Author(s):  
Martin Lauer ◽  
Mathieu Zellhuber ◽  
Thomas Sattelmayer ◽  
Christopher J. Aul
Keyword(s):  
Strain Rate ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Correction Method ◽  
Turbulent Flames ◽  
Lookup Table ◽  
Rate Model ◽  
Model Based

Imaging of OH* or CH* chemiluminescence with intensified cameras is often employed for the determination of heat release in premixed flames. Proportionality is commonly assumed, but in the turbulent case this assumption is not justified. Substantial deviations from proportionality are observed, which are due to turbulence-chemistry interactions. In this study a model based correction method is presented to obtain a better approximation of the spatially resolved heat release rate of lean turbulent flames from OH* measurements. The correction method uses a statistical strain rate model to account for the turbulence influence. The strain rate model is evaluated with time-resolved velocity measurements of the turbulent flow. Additionally, one-dimensional simulations of strained counterflow flames are performed to consider the nonlinear effect of turbulence on chemiluminescence intensities. A detailed reaction mechanism, which includes all relevant chemiluminescence reactions and deactivation processes, is used. The result of the simulations is a lookup table of the ratio between heat release rate and OH* intensity with strain rate as parameter. This lookup table is linked with the statistical strain rate model to obtain a correction factor which accounts for the nonlinear relationships between OH* intensity, heat release rate, and strain rate. The factor is then used to correct measured OH* intensities to obtain the local heat release rate. The corrected intensities are compared to heat release distributions which are measured with an alternative method. For all investigated flames in the lean, partially premixed regime the corrected OH* intensities are in very good agreement with the heat release rate distributions of the flames.

Influence of Lewis Number on Heat Release Rate in Premixed Syngas Flames

2019 ◽  
Author(s):  
Kedar G. Bhide ◽  
Sheshadri Sreedhara
Keyword(s):  
Heat Release ◽  
Fuel Consumption ◽  
Heat Release Rate ◽  
Release Rate ◽  
Consumption Rate ◽  
Lewis Number ◽  
Turbulent Flames ◽  
Attractive Alternative ◽  
Differential Diffusion ◽  
Fuel Consumption Rate

Abstract Syngas is an attractive alternative to currently popular hydrocarbon fuels due to its ability to be synthesized from multiple sources and lower carbon content. Direct Numerical Simulation (DNS) studies on premixed and non-premixed syngas flames have recently received attention. In this light, DNS of turbulent premixed syngas has been performed. Influence of turbulence and differential diffusion effects on chemical pathways of fuels like Hydrogen and methane has been studied in the past. Similar study on syngas flame has not been reported in the literature. Two cases with variation in the intensity of turbulence have been reported in this study. Effect of differential diffusion and turbulence on heat release rate and fuel consumption rate has been discussed. The behavior of heat release rate and fuel consumption rate was largely similar between laminar and turbulent flames considered in this study. Influence of species Lewis number was found to be more pronounced than that of turbulence.

On the Adequacy of Chemiluminescence as a Measure for Heat Release in Turbulent Flames With Mixture Gradients

2010 ◽  
Vol 132 (6) ◽  
Author(s):  
Martin Lauer ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Wavelength Range ◽  
Heat Release Rate ◽  
Turbulence Intensity ◽  
Release Rate ◽  
Reference Method ◽  
Turbulent Flames ◽  
First Law Of Thermodynamics ◽  
Spatially Resolved

The determination of the heat release in technical flames is commonly done via bandpass filtered chemiluminescence measurements in the wavelength range of OH∗ or CH∗ radicals, which are supposed to be a measure for the heat release rate. However, these indirect heat release measurements are problematic because the measured intensities are the superposition of the desired radical emissions and contributions from the broadband emissions of CO2∗. Furthermore, the chemiluminescence intensities are strongly affected by the local air excess ratio of the flame and the turbulence intensity in the reaction zone. To investigate the influence of these effects on the applicability of chemiluminescence as a measure for the heat release rate in turbulent flames with mixture gradients, a reference method is used, which is based on the first law of thermodynamics. It is shown that although the integral heat release can be correlated with the integral chemiluminescence intensities, the heat release distribution is not properly represented by any signal from OH∗ or CH∗. No reliable information about the spatially resolved heat release can be obtained from chemiluminescence measurements in flames with mixture gradients.

Determination of the Heat Release Distribution in Turbulent Flames by a Model Based Correction of OH* Chemiluminescence

2011 ◽  
Author(s):  
Martin Lauer ◽  
Mathieu Zellhuber ◽  
Thomas Sattelmayer ◽  
Christopher J. Aul
Keyword(s):  
Strain Rate ◽  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Correction Method ◽  
Turbulent Flames ◽  
Lookup Table ◽  
Rate Model ◽  
Non Linear

Imaging of OH* or CH* chemiluminescence with intensified cameras is often employed for the determination of heat release in premixed flames. Proportionality is commonly assumed, but in the turbulent case this assumption is not justified. Substantial deviations from proportionality are observed, which are due to turbulence-chemistry interactions. In this study a model based correction method is presented to obtain a better approximation of the spatially resolved heat release rate of lean turbulent flames from OH* measurements. The correction method uses a statistical strain rate model to account for the turbulence influence. The strain rate model is evaluated with time-resolved velocity measurements of the turbulent flow. Additionally, one-dimensional simulations of strained counterflow flames are performed to consider the non-linear effect of turbulence on chemi-luminescence intensities. A detailed reaction mechanism, which includes all relevant chemiluminescence reactions and deactivation processes, is used. The result of the simulations is a lookup table of the ratio between heat release rate and OH* intensity with strain rate as parameter. This lookup table is linked with the statistical strain rate model to obtain a correction factor which accounts for the non-linear relationships between OH* intensity, heat release rate, and strain rate. The factor is then used to correct measured OH* intensities to obtain the local heat release rate. The corrected intensities are compared to heat release distributions which are measured with an alternative method. For all investigated flames in the lean, partially premixed regime the corrected OH* intensities are in very good agreement with the heat release rate distributions of the flames.

scholarly journals Predicting the consumption speed of a premixed flame subjected to unsteady stretch rates

2021 ◽  
Author(s):  
Meysam Sahafzadeh ◽  
Seth B. Dworkin ◽  
Larry W. Kostiuk
Keyword(s):  
Heat Release ◽  
Heat Release Rate ◽  
Release Rate ◽  
Time Scale ◽  
Transfer Functions ◽  
Laminar Flame ◽  
Premixed Flames ◽  
Turbulent Flames ◽  
Response Analysis ◽  
Phase Lag

The stretched laminar flame model provides a convenient approach to embed realistic chemical kinetics when simulating turbulent premixed flames. When positive-only periodic strain rates are applied to a laminar flame there is a notable phase lag and diminished amplitude in heat release rate. Similar results have being observed with respect to the other component of stretch rate, namely the unsteady motion of a curved flame when the stretch rates are periodic about zero. Both cases showed that the heat release rate or consumption speed of these laminar-premixed flames vary significantly from the quasi-steady flamelet model. Deviation from quasi-steady behaviour increases as the unsteady flow time scale approaches the chemical time scale that is set by the stoichiometry. A challenge remains in how to use such results predictively for local and instantaneous consumption speed for small segments of turbulent flames where their unsteady stretch history is not periodic. This paper uses a frequency response analysis as a characterization tool to simplify the complex non-linear behaviour of premixed methane air flames for equivalence ratios from 1.0 down to 0.7, and frequencies from quasi-steady up to 2000 Hz using flame transfer functions. Various linear and nonlinear models were used to identify appropriate flame transfer functions for low and higher frequency regimes, as well as extend the predictive capabilities of these models. Linear models were only able to accurately predict the flame behaviour below a threshold of when the fluid and chemistry time scales are the same order of magnitude. Other proposed transfer functions were tested against arbitrary multi-frequency stretch inputs and were shown to be effective over the full range of frequencies.

On the Adequacy of Chemiluminescence as a Measure for Heat Release in Turbulent Flames With Mixture Gradients

2009 ◽  
Author(s):  
Martin Lauer ◽  
Thomas Sattelmayer
Keyword(s):  
Heat Release ◽  
Wavelength Range ◽  
Heat Release Rate ◽  
Turbulence Intensity ◽  
Release Rate ◽  
Reference Method ◽  
Turbulent Flames ◽  
First Law Of Thermodynamics ◽  
Spatially Resolved

The determination of the heat release in technical flames is commonly done via bandpass filtered chemiluminescence measurements in the wavelength range of OH* or CH* radicals, which are supposed to be a measure for the heat release rate. However, these indirect heat release measurements are problematic, because the measured intensities are the superposition of the desired radical emissions and contributions from the broadband emissions of CO2*. Furthermore, the chemiluminescence intensities are strongly affected by the local air excess ratio of the flame and the turbulence intensity in the reaction zone. To investigate the influence of these effects on the applicability of chemiluminescence as a measure for heat release rate in turbulent flames with mixture gradients, a reference method is used, which is based on the first law of thermodynamics. It is shown that although the integral heat release can be correlated with the integral chemiluminescence intensities, the heat release distribution is not properly represented by any signal from OH* or CH*. No reliable information about the spatially resolved heat release can be obtained from chemiluminescence measurements in flames with mixture gradients.

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