scholarly journals Turbulent Premixed Combustion in SI Engine

2018 ◽  
Vol 11 (4) ◽  
pp. 78-85
Author(s):  
Mohammed Alhumairi
Keyword(s):  
Turbulent Flame ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Exhaust Valve ◽  
Fuel Temperature ◽  
Si Engine ◽  
Lean Premixed Combustion ◽  
Turbulent Flame Speed ◽  
Combustion Simulation ◽  
Exhaust Valves

The turbulent lean premixed combustion simulation is implemented in 4- stroke spark ignition (SI) engine. The Turbulent Flame speed Closure model (TFC) is used in different turbulent flow conditions. The model is tested for a variety of flame configurations such as turbulent flame speed, the heat release from the combustion and turbulent kinetic energy in the radial direction of the cylinder at 15.5 mm below the top dead center TDC point. The simulation performs in the three cases of the (intake / exhaust) valve timing. The exhaust valve case is an essential leverage on the turbulent flame specification. The combustion period is very important factor in SI engine which is controlled especially by the turbulent flame speed. The turbulent flame speed and heat transfer is ascendant less than 10 % and 3% in case of intake and exhaust valves are closed respectively. Moreover, the results show that the brake power enhances less than 4% and more than 40% with increase fuel temperature 60 K and engine speed 3000 rpm respectively.

scholarly journals Active-grid turbulence effect on the topology and the flame location of a lean premixed combustion

2018 ◽  
Vol 22 (6 Part A) ◽  
pp. 2425-2438 ◽  
Author(s):  
Mohammed Alhumairi ◽  
Özgür Ertunç
Keyword(s):  
Turbulent Combustion ◽  
Turbulent Flame ◽  
Jet Flow ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Grid Turbulence ◽  
Closure Model ◽  
Lean Premixed Combustion ◽  
Turbulent Flame Speed ◽  
Combustion Models

Lean premixed combustion under the influence of active-grid turbulence was computationally investigated, and the results were compared with experimental data. The experiments were carried out to generate a premixed flame at a thermal load of 9 kW from a single jet flow combustor. Turbulent combustion models, such as the coherent flame model and turbulent flame speed closure model were implemented for the simulations performed under different turbulent flow conditions, which were specified by the Reynolds number based on Taylor?s microscale, the dissipation rate of turbulence, and turbulent kinetic energy. This study shows that the applied turbulent combustion models differently predict the flame topology and location. However, similar to the experiments, simulations with both models revealed that the flame moves toward the inlet when turbulence becomes strong at the inlet, that is, when Re? at the inlet increases. The results indicated that the flame topology and location in the coherent flame model were more sensitive to turbulence than those in the turbulent flame speed closure model. The flame location behavior on the jet flow combustor significantly changed with the increase of Re?.

Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model

2000 ◽  
Vol 124 (1) ◽  
pp. 58-65 ◽  
Author(s):  
W. Polifke ◽  
P. Flohr ◽  
M. Brandt
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Combustion Stability ◽  
Model Parameters ◽  
Turbulent Flame Speed ◽  
Functional Relationships

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the turbulent flame speed closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e., the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.

An Optimized Correlation for Turbulent Flame Speed for C1-C3 Fuels at Engines-Relevant Conditions

2020 ◽  
Author(s):  
Eoin M. Burke ◽  
Sajjad Yousefian ◽  
Felix Güthe ◽  
Rory F. D. Monaghan
Keyword(s):  
Entire Range ◽  
State Of The Art ◽  
Velocity Ratio ◽  
Turbulent Flame ◽  
Search Method ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Percentage Error ◽  
Turbulent Flame Speed ◽  
Wide Range

Abstract The aim of this work is to examine the state-of-the-art turbulent flame speed (ST) correlations and optimize their adjustable parameters to best match a wide range experimental turbulent premixed combustion results. Four correlations based on previous works by Zimont, Kobayashi, Ronney and Muppala have been selected for the present study. Using a Matlab-based Nelder-Mead simplex direct search method, each correlation’s adjustable parameters are optimized such that their mean absolute percentage error (MAPE) is minimized. In addition to the literature correlations, a new empirical correlation is developed using the same search method to define constants and powers in the expression. Two sets of optimized parameters are proposed to account for atmospheric and elevated (0.2–3.0 MPa) pressure flames. Each correlation is tested further, examining their ability to match ST trends for varying equivalence ratio (φ) and turbulent velocity ratio (u′/SL). It was found that a minimum of two correlations and two sets of adjustable parameters are required to accurately account for the entire range of data, thus showing that there is currently no turbulent flame speed correlation that is applicable across all engine-relevant conditions.

An Optimized Correlation for Turbulent Flame Speed for C1–C3 Fuels at Engine-Relevant Conditions

2020 ◽  
Vol 142 (11) ◽  
Author(s):  
Sajjad Yousefian ◽  
Eoin M. Burke ◽  
Felix Güthe ◽  
Rory F. D. Monaghan
Keyword(s):  
Entire Range ◽  
State Of The Art ◽  
Velocity Ratio ◽  
Turbulent Flame ◽  
Search Method ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Percentage Error ◽  
Turbulent Flame Speed ◽  
Wide Range

Abstract The aim of this work is to examine the state-of-the-art turbulent flame speed (ST) correlations and optimize their adjustable parameters to best match a wide range experimental turbulent premixed combustion results. Based on previous work, four correlations have been selected for this study. Using a matlab-based Nelder–Mead simplex direct search method, each correlation's adjustable parameters are optimized such that their mean absolute percentage error (MAPE) is minimized. In addition to the literature correlations, a new empirical correlation is developed using the same search method to define constants and powers in the expression. Two sets of optimized parameters are proposed to account for atmospheric and elevated (0.2–3.0 MPa) pressure flames. Each correlation is tested further, examining their ability to match ST trends for varying equivalence ratio (φ) and turbulent velocity ratio (u′/SL). It was found that a minimum of two correlations and two sets of adjustable parameters are required to accurately account for the entire range of data, thus showing that there is currently no turbulent flame speed correlation that is applicable across all engine-relevant conditions.

Investigation of the Turbulent Flame Speed for Natural Gas and Natural Gas/Hydrogen Mixtures at High Turbulence Levels and Volumetric Heat Release Rates

2013 ◽  
Author(s):  
Martin Zajadatz ◽  
Nikolaos Zarzalis ◽  
Wolfgang Leuckel
Keyword(s):  
Natural Gas ◽  
Heat Release ◽  
Gas Turbines ◽  
Turbulent Flame ◽  
Flame Speed ◽  
Release Rates ◽  
Fuel Gas ◽  
Lean Premixed Combustion ◽  
Number Range ◽  
Turbulent Flame Speed

In gas turbine combustion application, there is a strong tendency towards high volumetric heat release rates without compromising ignition stability and the requirement of low emission concentrations of NOx, CO and unburned hydrocarbons. In order to meet these demands for industrial gas turbines the lean premixed combustion concept has been developed. In the scope of this paper fundamental experimental work, which has been carried out in order to analyze the important topic of turbulence/chemistry interaction on a semi-technical scale, will be reported. The turbulent intensity and length scales have been varied by a generic burner system, which consists of four geometrically scaled burners. At atmospheric pressure conditions more than 700 Bunsen type flames in a Reynolds number range from 21000 to 128000 have been investigated. Gas/air mixture preheating has been included in the tests as a typical boundary condition for combustion in gas turbines. The natural gas was blended with 25 vol. % and 50 vol. % hydrogen in order to alter the kinetics of the fuel gas. The influence of the aforementioned parameters on the turbulent flame speed were assessed and compared with existing correlations for the turbulent flame speed. Special emphasis has been taken on the influence of gas/air mixture preheating and kinetics.

Transient Combustion Modeling of an Oscillating Lean Premixed Methane/Air Flame

2008 ◽  
Author(s):  
Jan A. M. Withag ◽  
Jim B. W. Kok ◽  
Khawar Syed
Keyword(s):  
Laminar Flame ◽  
Turbulent Flame ◽  
Low Frequency ◽  
Turbulence Models ◽  
Flame Speed ◽  
Combustion Model ◽  
Lean Premixed Combustion ◽  
Combustion Modeling ◽  
Turbulent Flame Speed ◽  
Lean Premixed

The main objective of the present study is to demonstrate accurate low frequency transient turbulent combustion modeling. For accurate flame dynamics some improvements were made to the standard TFC combustion model for lean premixed combustion. With use of a 1D laminar flamelet code, predictions have been made for the laminar flame speed and the critical strain rate to improve the TFC (Turbulent Flame Speed Closure) combustion model. The computational fluid dynamics program CFX is used to perform transient simulations. These results were compared with experimental data of Weigand et al [1]. Two different turbulence models have been used for predictions of the turbulent flow.

Investigation of Turbulence Models Applied to Premixed Combustion Using a Level-Set Flamelet Library Approach

2004 ◽  
Vol 126 (4) ◽  
pp. 701-707 ◽  
Author(s):  
Ulf Engdar ◽  
Per Nilsson ◽  
Jens Klingmann
Keyword(s):  
Level Set ◽  
Turbulence Intensity ◽  
Turbulent Flame ◽  
Turbulence Models ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Chemical Mechanism ◽  
Turbulent Flame Speed ◽  
The Mean ◽  
The Impact

Most of the common modeling approaches to premixed combustion in engineering applications are either based on the assumption of infinitely fast chemistry or the flamelet assumption with simple chemistry. The level-set flamelet library approach (FLA) has shown great potential in predicting major species and heat release, as well as intermediate and minor species, where more simple models often fail. In this approach, the mean flame surface is tracked by a level-set equation. The flamelet libraries are generated by an external code, which employs a detailed chemical mechanism. However, a model for the turbulent flame speed is required, which, among other considerations, depends on the turbulence intensity, i.e., these models may show sensitivity to turbulence modeling. In this paper, the FLA model was implemented in the commercial CFD program Star-Cd, and applied to a lean premixed flame stabilized by a triangular prism (bluff body). The objective of this paper has been to investigate the impact on the mean flame position, and hence on the temperature and species distribution, using three different turbulent flame speed models in combination with four different turbulence models. The turbulence models investigated are: the standard k-ε model, a cubic nonlinear k-ε model, the standard k-ω model and the shear stress transport (SST) k-ω model. In general, the computed results agree well with experimental data for all computed cases, although the turbulence intensity is strongly underestimated at the downstream position. The use of the nonlinear k-ε model offers no advantage over the standard model, regardless of flame speed model. The k-ω based turbulence models predict the highest turbulence intensity with the shortest flame lengths as a consequence. The Mu¨ller flame speed model shows the least sensitivity to the choice of turbulence model.  

Modeling of Inhomogeneously Premixed Combustion With an Extended TFC Model

2000 ◽  
Author(s):  
Wolfgang Polifke ◽  
Peter Flohr ◽  
Martin Brandt
Keyword(s):  
Laminar Flame ◽  
Mixture Fraction ◽  
Turbulent Flame ◽  
Flame Temperature ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Combustion Stability ◽  
Model Parameters ◽  
Turbulent Flame Speed ◽  
Functional Relationships

In many practical applications, so-called premixed burners do not achieve perfect premixing of fuel and air. Instead, fuel injection pressure is limited, the permissible burner pressure drop is small and mixing lengths are curtailed to reduce the danger of flashback. Furthermore, internal or external piloting is frequently employed to improve combustion stability, while part-load operation often requires burner staging, where neighboring burners operate with unequal fuel/air equivalence ratios. In this report, an extension of the Turbulent Flame speed Closure (TFC) model for highly turbulent premixed combustion is presented, which allows application of the model to the case of inhomogeneously premixed combustion. The extension is quite straightforward, i.e. the dependence of model parameters on mixture fraction is accounted for by providing appropriate lookup tables or functional relationships to the model. The model parameters determined in this way are adiabatic flame temperature, laminar flame speed and critical gradient. The model has been validated against a test case from the open literature and applied to an externally piloted industrial gas turbine burner with good success.

Investigation of Turbulence Models Applied to Premixed Combustion Using a Level-Set Flamelet Library Approach

2003 ◽  
Author(s):  
Ulf Engdar ◽  
Per Nilsson ◽  
Jens Klingmann
Keyword(s):  
Level Set ◽  
Turbulence Intensity ◽  
Turbulent Flame ◽  
Turbulence Models ◽  
Flame Speed ◽  
Premixed Combustion ◽  
Chemical Mechanism ◽  
Turbulent Flame Speed ◽  
Non Linear ◽  
The Mean

Most of the common modeling approaches to premixed combustion in engineering applications are either based on the assumption of infinitely fast chemistry or the flamelet assumption with simple chemistry. The level-set flamelet library approach (FLA) has shown great potential in predicting major species and heat release, as well as intermediate and minor species, where more simple models often fail. In this approach, the mean flame surface is tracked by a level-set equation. The flamelet libraries are generated by an external code, which employs a detailed chemical mechanism. However, a model for the turbulent flame speed is required, which, amongst other considerations, depends on the turbulence intensity, i.e. these models may show sensitivity to turbulence modeling. In this paper, the FLA model was implemented in the commercial CFD program Star-CD, and applied to a lean premixed flame stabilized by a triangular prism (bluff body). The objective of this paper has been to investigate the impact on the mean flame position, and hence on the temperature and species distribution, using three different turbulent flame speed models in combination with four different turbulence models. The turbulence models investigated are: the standard k-ε model, a cubic non-linear k-ε model, the standard k-ω model and the Shear Stress Transport (SST) k-ω model. In general, the computed results agree well with experimental data for all computed cases, although the turbulence intensity is strongly underestimated at the downstream position. The use of the non-linear k-ε model offers no advantage over the standard model, regardless of flame speed model. The k-ω based turbulence models predict the highest turbulence intensity with the shortest flame lengths as a consequence. The Mu¨ller flame speed model shows the least sensitivity to the choice of turbulence model.

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