Effects of the cold wall boundary on the flame structure and flame speed in premixed turbulent combustion

Theoretical background, details of implementation and validation results of a computational model for turbulent premixed gaseous combustion at high turbulent Reynolds numbers are presented. The model describes the combustion process in terms of a single transport equation for a progress variable; closure of the progress variable’s source term is based on a model for the turbulent flame speed. The latter is identified as a parameter of prime significance in premixed turbulent combustion and is determined from theoretical considerations and scaling arguments, taking into account physico-chemical properties of the combustible mixture and local turbulent parameters. Specifically, phenomena like thickening, wrinkling and straining of the flame front by the turbulent velocity field are considered, yielding a closed form expression for the turbulent flame speed that involves, e.g., speed, thickness and critical gradient of a laminar flame, local turbulent length scale and fluctuation intensity. This closure approach is very efficient and elegant, as it requires only one transport equation more than the non-reacting flow case, and there is no need for costly evaluation of chemical source terms or integration over probability density functions. The model was implemented in a finite-volume based computational fluid dynamics code and validated against detailed experimental data taken from a large scale atmospheric gas turbine burner test stand. The predictions of the model compare well with the available experimental results. It has been observed that the model is significantly more robust and computationally efficient than other combustion models. This attribute makes the model particularly interesting for applications to large 3D problems in complicated geometries.

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Evaluation of CH4/NOx Reduced Mechanisms Used for Modeling Lean Premixed Turbulent Combustion of Natural Gas

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2818457 ◽

1998 ◽

Vol 120 (4) ◽

pp. 703-712 ◽

Cited By ~ 33

Author(s):

H. P. Mallampalli ◽

T. H. Fletcher ◽

J. Y. Chen

Keyword(s):

High Pressure ◽

Natural Gas ◽

Gas Turbine ◽

Turbulent Combustion ◽

Gas Turbines ◽

Flame Structure ◽

Computational Cost ◽

Premixed Turbulent Combustion ◽

Reduced Mechanism ◽

Lean Premixed

This study has identified useful reduced kinetic schemes that can be used in comprehensive multidimensional gas-turbine combustor models. Reduced mechanisms lessen computational cost and possess the capability to accurately predict the overall flame structure, including gas temperatures and key intermediate species such as CH4, CO, and NOx. In this study, four new global mechanisms with five, six, seven, and nine steps based on the full GRI 2.11 mechanism, were developed and evaluated for their potential to model natural gas chemistry (including NOx chemistry) in gas turbine combustors. These new reduced mechanisms were optimized to model the high pressure and fuel-lean conditions found in gas turbines operating in the lean premixed mode. Based on perfectly stirred reactor (PSR) and premixed code calculations, the five-step reduced mechanism was identified as a promising model that can be used in a multidimensional gas-turbine code for modeling lean-premixed, high-pressure turbulent combustion of natural gas. Predictions of temperature, CO, CH4, and NO from the five-to nine-step reduced mechanisms agree within 5 percent of the predictions from the full kinetic model for 1 < pressure (atm) < 30, and 0.6 < φ < 1.0. If computational costs due to additional global steps are not severe, the newly developed nine step global mechanism, which is a little more accurate and provided the least convergence problems, can be used. Future experimental research in gas turbine combustion will provide more accurate data, which will allow the formulation of better full and reduced mechanisms. Also, improvement in computational approaches and capabilities will allow the use of reduced mechanisms with larger global steps, perhaps full mechanisms.

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RANS Simulations of Statistically Stationary Premixed Turbulent Combustion Using Flame Speed Closure Model

Flow Turbulence and Combustion ◽

10.1007/s10494-014-9585-x ◽

2014 ◽

Vol 94 (2) ◽

pp. 381-414 ◽

Cited By ~ 10

Author(s):

E. Yasari ◽

S. Verma ◽

A. N. Lipatnikov

Keyword(s):

Turbulent Combustion ◽

Flame Speed ◽

Closure Model ◽

Premixed Turbulent Combustion ◽

Rans Simulations

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A Modeling Approach for Hydrogen-Doped Lean Premixed Turbulent Combustion

Heat Transfer, Volume 2 ◽

10.1115/imece2006-13861 ◽

2006 ◽

Author(s):

Siva P. R. Muppala ◽

Miltiadis V. Papalexandris

Keyword(s):

Turbulent Combustion ◽

Turbulent Flame ◽

Turbulent Flames ◽

Flame Speed ◽

Hydrocarbon Mixtures ◽

Empirical Constant ◽

Premixed Turbulent Combustion ◽

Turbulent Flame Speed ◽

Preferential Diffusion ◽

Model Predictions

In this study, we investigate some preliminary reaction model predictions analytically in comparison with experimental premixed turbulent combustion data from four different flame configurations, which include i) high-jet enveloped, ii) expanding spherical, iii) Bunsen-like, and iv) wide-angled diffuser flames. The special intent of the present work is to evaluate the workability range of the model to hydrogen and hydrogen-doped hydrocarbon mixtures, emphasizing on the significance of preferential diffusion, PD, and Le effects in premixed turbulent flames. This is carried out in two phases: first, involving pure hydrocarbon and pure hydrogen mixtures from two independent measured data, and second, with the blended mixtures from two other data sets. For this purpose, a novel reaction closure embedded with explicit high-pressure and exponential Lewis number terms developed in the context of hydrocarbon mixtures is used. These comparative studies based on the global quantity, turbulent flame speed, indicate that the model predictions are encouraging yielding proper quantification along with reasonable characterization of all the four different flames, over a broad range of turbulence, fuel-types and for varied equivalence ratios. However, with each flame involved the model demands tuning of the (empirical) constant to allow for either or both of these effects, or for the influence of the burner geometry. This provisional stand remains largely insufficient. Therefore, a submodel for chemical time scale from the leading point analysis based on the critically curved laminar flames employed in earlier studies for expanding spherical flames is introduced here. By combining the submodel and the reaction closure, the dependence of turbulent flame speed on physicochemical properties of the burning mixtures including the strong dependence of preferential diffusion and/or Le effects can be determined.

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Flame Speed Closure Model of Premixed Turbulent Combustion : Further Development and Validation(S.I. Engines, Flame Propagation)

The Proceedings of the International symposium on diagnostics and modeling of combustion in internal combustion engines ◽

10.1299/jmsesdm.2004.6.583 ◽

2004 ◽

Vol 2004.6 (0) ◽

pp. 583-590 ◽

Cited By ~ 3

Author(s):

Andrei N. Lipatnikov ◽

Jerzy Chomiak

Keyword(s):

Flame Propagation ◽

Turbulent Combustion ◽

Flame Speed ◽

Closure Model ◽

Premixed Turbulent Combustion ◽

Development And Validation ◽

Further Development

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An Efficient Computational Model for Premixed Turbulent Combustion at High Reynolds Numbers Based on a Turbulent Flame Speed Closure

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2818178 ◽

1998 ◽

Vol 120 (3) ◽

pp. 526-532 ◽

Cited By ~ 116

Author(s):

V. Zimont ◽

W. Polifke ◽

M. Bettelini ◽

W. Weisenstein

Keyword(s):

Computational Model ◽

Transport Equation ◽

Turbulent Combustion ◽

Turbulent Flame ◽

Reynolds Numbers ◽

Flame Speed ◽

Closed Form Expression ◽

Turbulent Length Scale ◽

Premixed Turbulent Combustion ◽

Turbulent Flame Speed

Theoretical background, details of implementation, and validation results for a computational model for turbulent premixed gaseous combustion at high turbulent Reynolds numbers are presented. The model describes the combustion process in terms of a single transport equation for a progress variable; turbulent closure of the progress variable’s source term is based on a model for the turbulent flame speed. The latter is identified as a parameter of prime significance in premixed turbulent combustion and determined from theoretical considerations and scaling arguments, taking into account physico-chemical properties and local turbulent parameters of the combustible mixture. Specifically, phenomena like thickening, wrinkling, and straining of the flame front by the turbulent velocity field are considered, yielding a closed form expression for the turbulent flame speed that involves, e.g., speed, thickness, and critical gradient of a laminar flame, local turbulent length scale, and fluctuation intensity. This closure approach is very efficient and elegant, as it requires only one transport equation more than the non reacting flow case, and there is no need for costly evaluation of chemical source terms or integration over probability density functions. The model was implemented in a finite-volume-based computational fluid dynamics code and validated against detailed experimental data taken from a large-scale atmospheric gas turbine burner test stand. The predictions of the model compare well with the available experimental results. It has been observed that the model is significantly more robust and computationally efficient than other combustion models. This attribute makes the model particularly interesting for applications to large three-dimensional problems in complicated geometries.

Download Full-text