THEORETICAL INVESTIGATION OF TURBULENT COMBUSTION IN STRATIFIED INHOMOGENOUS MIXTURES USING DIRECT NUMERICAL SIMULATION

Lead Research Organisation: University of Liverpool
Department Name: School of Engineering

Abstract

The aim of this project is to understand the effects of turbulence on hydrocarbon fuel combustion where the fuel and oxidizer distribution form a highly stratified mixture at the time of ignition. For stratified charge combustion the reactants are neither homogeneously mixed (premixed) nor completely separated (non- premixed). Thus the analysis of this kind of combustion has special modelling needs in comparison to fully premixed or fully non-premixed flames. Turbulent combustion in a stratified fuel-air mixture is highly relevant in the context of both spark-ignition gasoline and compression-ignition Diesel engines and has the potential for reducing fuel consumption especially at low-speed, light- load operations in automobile applications. Stratified-charge combustion can also be found in the Lean Premixed Prevaporised (LPP) combustors in aircraft gas turbines where fuel and injected secondary air form an inhomogeneous fuel-air mixture ahead of the flame front. The capability of predicting accurately the flame propagation behaviour in the presence of mixture inhomogeneities and intense turbulence would facilitate the development of low-emission, energy-efficient devices, such as automotive engines and gas-turbine combustors. The proposed research project consists of three parts. In the first, three-dimensional (3-D) Direct Numerical Simulations (DNS) with simplified chemistry, appropriate for the combustion of realistic hydrocarbon fuels, will be performed for a variety of mixing fields and turbulence intensities to enhance the present state of fundamental understanding and to create a database for the assessment of existing combustion models and to develop new models wherever necessary. Three-dimensional DNS with a reasonable degree of detailed chemistry will be carried out based on the information gained from 3-D DNS with simplified chemistry. The second part of the project involves the development of a combustion model in the context of Reynolds Averaged Navier Stokes (RANS) and Large Eddy Simulations (LES). The model will be implemented with a view to future incorporation into industry-standard Computational Fluid Dynamics (CFD) packages, which can then be used for engineering design purposes.

Publications

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Brearley P (2020) The relation between flame surface area and turbulent burning velocity in statistically planar turbulent stratified flames in Physics of Fluids

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Chakraborty N (2008) A priori assessment of closures for scalar dissipation rate transport in turbulent premixed flames using direct numerical simulation in Physics of Fluids

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Chakraborty N (2008) A priori direct numerical simulation assessment of algebraic flame surface density models for turbulent premixed flames in the context of large eddy simulation in Physics of Fluids

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Chakraborty N (2009) Physical Insight and Modelling for Lewis Number Effects on Turbulent Heat and Mass Transport in Turbulent Premixed Flames in Numerical Heat Transfer, Part A: Applications

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Chakraborty N (2009) Effects of Lewis number on the reactive scalar gradient alignment with local strain rate in turbulent premixed flames in Proceedings of the Combustion Institute

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Chakraborty N (2008) Influence of Lewis number on the surface density function transport in the thin reaction zone regime for turbulent premixed flames in Physics of Fluids

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Chakraborty N (2009) Effects of Lewis number on scalar transport in turbulent premixed flames in Physics of Fluids

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Chakraborty N (2010) The Scalar Gradient Alignment Statistics of Flame Kernels and its Modelling Implications for Turbulent Premixed Combustion in Flow, Turbulence and Combustion

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Chakraborty N (2009) Effects of Lewis number on turbulent scalar transport and its modelling in turbulent premixed flames in Combustion and Flame

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Chakraborty N (2010) Numerical Investigation of Edge Flame Propagation Behavior in an Igniting Turbulent Planar Jet in Combustion Science and Technology

 
Description Achievements

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1. Development of a three_dimensional DNS database of freely statistically

planar turbulent flames propagating through stratified mixtures in different

configurations [1,2] for different values of global mean equivalence ratio,

root_mean_square equivalence ratio, global Lewis number and turbulent

velocity fluctuations, integral length scales of turbulent velocity fluctuations

and equivalence ratio fluctuations. This provides a wealth of important

information, which can be used for the purpose of assessing existing models

and develop new models in the context of RANS and LES. The database

developed during the course of this project will continue to be a very useful

source of information for gaining fundamental understanding and model

development beyond the duration of this project.

2. The performance of the existing algebraic models for scalar variances, covariances,

dissipation rates and cross_dissipation rates have been assessed

in detail based on a_priori analysis of DNS data [1]. The existing models that

are the best suited for predicting the relevant quantities are identified and

for some quantities either new algebraic models were proposed or existing

models were modified, when existing models were found to predict the

quantities in question adequately. Transport equation based closure for

some quantities where algebraic models are found not to perform well [1].

3. Models have been proposed for all the terms for the transport equations of

fuel mass fraction variance [3,4], co_variance of fuel mass fraction and

mixture fraction fluctuations [5,6], scalar dissipation rates of mixture

fraction and fuel mass fraction [7_9] and the cross scalar dissipation rates of

fuel mass fraction and mixture fraction fluctuations [10] in the context of

RANS. The quantities such as variance, co_variance, scalar dissipation rate

and cross_scalar dissipation rate play pivotal roles in the reaction rate

closure in turbulent combustion of stratified mixtures. The aforementioned

modelling activity aided by DNS data devised a coherent unified modelling

methodology which can be used for reaction rate closure both high and low

Damkohler number conditions. This modelling exercise was also closely

related to the modelling turbulent premixed combustion because it is a

special case of turbulent stratified combustion modelling. As a result of this,

significant advances in different aspects of scalar dissipation rate [11_16],

Flame Surface Density (FSD) [17,18] and scalar flux [19_22] modelling of

turbulent premixed flames.

4. The statistics of flame propagation statistics in turbulent inhomogeneous

mixtures have been studied in terms of displacement speed and its

components [2,23] and FSD based reaction rate closure has been extended

for turbulent combustion of stratified mixtures for both high and low

Damkohler number conditions in the context of RANS. The possible

extension of the RANS models for the purpose of LES is also identified [2,23].

5. Identifying the strengths and limitations of the simplified models for

combustion (e.g. Multi_zone model) which are in use in analysing DNS data

of localised ignition of thermally inhomogeneous mixtures, which is often

realized in Homogeneous Charge Compression Ignition (HCCI) engines.

6. The newly developed models have been implemented in an industrystandard

Computational Fluid Dynamics (CFD) package so that they can then

be used for future engineering design purposes.

In addition, the models and findings have been shared with the Combustion

Research Group in Cambridge (especially with Profs. R. Stewart Cant, E.

Mastorakos and Dr. N. Swaminathan) who are also engaged in computational

and experimental analysis of turbulent combustion of stratified mixtures.



References

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1. S.P. Malkeson, N. Chakraborty, "A_priori Direct Numerical Simulation analysis

of algebraic models of variances and scalar dissipation rates for Reynolds

Averaged Navier Stokes Simulations for low Damköhler number turbulent

partially_premixed combustion", Combustion Sci. Technol. 182, 960_999,

2010.

2. S. P. Malkeson, N. Chakraborty, "Statistical analysis of displacement speed in

turbulent stratified flames: A Direct Numerical Simulation study", Combustion

Sci. Technol., 182, 1841-1883, 2010.

3. S. P. Malkeson, N. Chakraborty, "Modelling of fuel mass fraction variance

transport in turbulent stratified flames: A Direct Numerical Simulation study."

Numerical Heat Transfer A , 58, 187_206, 2010.

4. S.P. Malkeson, N. Chakraborty, "Statistical analysis of fuel mass fraction

variance transport in turbulent partially_premixed flames: A Direct Numerical

Simulation study", 33rd International Combustion Symposium, Tsinghua

University, Beijing, 1_6th August, 2010.

5. S.P. Malkeson, N. Chakraborty, "Statistical analysis of co_variance transport in

low Damköhler number number turbulent stratified flames: a DNS study",

33rd International Combustion Symposium, Tsinghua University, Beijing, 1_6th

August, 2010.

6. S. P. Malkeson, N. Chakraborty,A-priori DNS modelling of co-variance transport in turbulent stratified flames", 7th Mediterranean Combustion Symposium, Chia Laguna, Cagliari, Sardinia, Italy, 11th -15th September, 2011.

7. S. P. Malkeson, N. Chakraborty, "Analysis of Scalar Dissipation rate transport

in combusting stratified charge mixtures using Direct Numerical Simulations",

32nd International Combustion Symposium, Montreal, Canada, 3rd to 8th

August, 2008.

8. S.P. Malkeson, N. Chakraborty, "Scalar Dissipation rate transport modelling of

partially premixed flames using Direct Numerical Simulations (DNS)", 4th

European Combustion Meeting, Vienna, Austria, 14th to 17th April, 2009.

9. S.P. Malkeson, N. Chakraborty, "Statistical analysis of scalar dissipation rate

transport in turbulent partially premixed flames: A Direct Numerical

Simulation study", Flow Turbulence and Combustion, 86, 1-44, 2011.

10. S.P. Malkeson, N. Chakraborty, "Statistical analysis of cross scalar dissipation

rate transport in turbulent partially premixed flames: A Direct Numerical

Simulation study." Flow Turbulence and Combustion, 87,313-349, 2011.

11. H. Kolla, J. Rogerson, N. Chakraborty, N. Swaminathan, "Prediction of

turbulent flame speed using scalar dissipation rate", Combust. Sci. Technol.,

181,3, 518_535, 2009.

12. N. Chakraborty, J.W. Rogerson, N. Swaminathan, "APriori

assessment of closures for scalar dissipation rate transport in turbulent premixed flames

using direct numerical simulation", Phys. Fluids, 20,045106,1_15, 2008.

13. N. Chakraborty, N. Swaminathan, "Modelling of non_unity Lewis number

effects on scalar dissipation rate transport in turbulent premixed flames", 4th

European Combustion Meeting, Vienna, Austria, 14th to 17th April, 2009.

14. N. Chakraborty, M. Klein, N. Swaminathan, "Effects of Lewis number on

reactive scalar gradient alignment with local strain rate in turbulent

premixed flames." Proc. of Combust. Institute, 32,1409_1417,2009.

15. N. Chakraborty, N. Swaminathan, "Effects of Lewis number on scalar

dissipation transport and its modelling implications for turbulent premixed

combustion", Combustion Sci. Technol.,182, 1201_1240, 2010.

16. N. Chakraborty, J. Rogerson, N. Swaminathan, "The scalar gradient alignment

statistics of flame kernels and its modelling implications for turbulent

premixed combustion", Flow Turbulence and Combustion, 85,1, 25_55, 2010.

17. N. Chakraborty, M. Klein, "A Priori Direct Numerical Simulation assessment of

algebraic Flame Surface Density models for turbulent premixed flames in the

context of Large Eddy Simulation." Phys. Fluids, 20, 085108, 1_14,2008.

18. N. Chakraborty, M. Klein, "Influence of Lewis number on the Surface Density

Function transport in the thin reaction zones regime for turbulent premixed

flames." Phys. Fluids, 20, 065102,1_24, 2008.

19. N. Chakraborty, R.S. Cant, "Effects of Lewis number on the scalar flux in

Turbulent premixed Flames." 12th SIAM Numer. Combust. Conference,

Moneterey, USA, 31st March_2nd April, 2008.

20. N. Chakraborty, R.S. Cant, "Effects of Lewis number on turbulent scalar

transport and its modelling in turbulent premixed flames.", Combustion and

Flame, 156, 1427_1444, 2009.

21. N. Chakraborty, R.S. Cant, "Physical insight and modelling for Lewis number

effects on turbulent heat and mass transport in turbulent premixed flames."

Numerical Heat Transfer A, 55,8,762_779, 2009.

22. N. Chakraborty, R.S. Cant, "Effects of Lewis number on scalar transport in

turbulent premixed flames", Physics Fluids, 21, 035110, 2009.

23. N. Chakraborty, H. Hesse, E. Mastorakos, "Numerical investigation of edge

flame propagation behaviour in an igniting turbulent planar jet", Combustion

Sci. Technol., 182, 1747-1781, 2010.
Exploitation Route The major beneficiaries of this work are automotive engine and gas turbine manufacturers, who are engaged in developing new concepts for low-pollution and high-efficiency engines throughout the world. The design process of Direct Injection and Homogeneous Charge Compression Ignition engines is limited by the lack of knowledge on turbulent stratified charge combustion, and predictive capability of combustion performance based on engineering CFD calculations. Ford and Lotus are mentioned as compression-ignition engine developers, and Rolls-Royce as a gas turbine manufacturer will have interest in the outcome of this work concerning the fundamentals of turbulent stratified charge combustion. However, the benefits are not limited to the above-mentioned UK manufacturers, as all automotive manufacturers have a program on HCCI engines and all gas turbine manufacturers are interested in LPP combustors. The relevant industrial partners were made aware of the developments that took place in this research during interactions at the aforementioned international conferences and UK based meetings (e.g. Meetings organised by the British Combustion Institute ). The present fundamental findings concerning turbulent stratified combustion will be of immediate value to all the industries mentioned above. Moreover, the project outcome will be directly beneficial to industries, as the developed model will be incorporated in commercial CFD software used by industry for a-posteriori analysis. 1. High-quality journal publications

2. Dissemination through conference presentations

3. Effective UK and international collaboration

4. Industrial contacts
Sectors Aerospace, Defence and Marine,Energy,Environment,Transport
 
Description The findings of this project gave a thorough insight into the Reynolds Averaged Navier Stokes (RANS) modelling of turbulent combustion of stratified mixtures using scalar dissipation rate approach. The new closures developed in this project are robust as they have gone through a detailed a-priori test for a range of different parameters. Apart from enriching the relevant field of research, the research outcomes provided high-fidelity simulation tools for simulating premixed turbulent combustion for Internal Combustion (IC) engine (e.g. modern Direct Injection engine) and gas turbine (e.g. Lean Premixed Prevaporised (LPP) technology) manufacturers (e.g. Ford, Rolls Royce and Siemens), which will contribute to the development of energy-efficient and environment-friendly devices and wealth generation in the future. This will give rise to considerable socio-economic impact. Moreover, this project gave rise to the development of a highly skilled professional with expertise of turbulence, combustion, Direct Numerical Simulation, parallel computing etc, who is going to contribute to UK industry and economy for years to come.
Sector Aerospace, Defence and Marine,Energy,Environment,Transport
Impact Types Societal,Economic
 
Description Large Eddy Simulation modelling of scalar dissipation rate based reaction rate closure in turbulent premixed flames
Amount £158,407 (GBP)
Funding ID EP/I028013/1 
Organisation Engineering and Physical Sciences Research Council (EPSRC) 
Sector Public
Country United Kingdom
Start 10/2011 
End 03/2015