To model combustion, the information related to the fluid mechanics of the system must be known. All the transport phenomena such as convection, diffusion as well heat should be accurately incorporated in such models. Chemical reaction schemes must also be known so as to estimate the formation of combustion products and species and also to predict ignition, stabilization and extinction of flames. Radiation also takes place due to presence of soot formed during combustion and also there is radiative heat transfer from wall of the combustion chamber. Combustion of fuels comes under multiphase system, where liquid fuels is a two phase system consisting of liquid and gas phases while solid fuel belongs to a three phase system. The challenges faced are to model breaking up of the liquid fuel, its reaction and distribution of the reactants in three dimensional spatial systems. These models which form part of CFD, has become an indispensable tool for combustion modelling. For my blogs kindly visit: https://www.learncax.com/knowledge-base/blog/by-author/ganesh-visavale

1. Recent Trends in Modeling of Combustion
learncax.com /blog/2013/10/21/recent-trends-in-cf d-modeling-of -combustion/
Ganesh Visavale
Recent Trends in Modeling of Combust ion : Challenges and Highlight s of CFD Simulat ion Applied t o
St udy Combust ion
Computational fluid dynamics (CFD) when saw its development on the peak, was meant to merely validate
simulations with the experimental results. But the recent trends have shown that confidence in CFD has grown and its
use is on the rise to simulate physics problems which have very limited experimental data for its validation.
Combustion is one such field where application of CFD and this recent trend has proved to be a boon. A genre of
sophisticated codes for modelling combustion phenomenon has been developed in the last few decades. The
challenges faced by engineers and developers is to develop such codes that will represent “perfectly” the
observed temperature and concentration profile and to use this codes or models to further simulate and predict the
events where no measurements are possible or no data is available. The reader is expected to already have some
exposure about CFD modeling and its understanding before proceeding with this article. To model combustion, the
information related to the fluid mechanics of the system must be known. All the transport phenomena such as
convection, diffusion as well heat should be accurately incorporated in such models. Chemical reaction schemes
must also be known so as to estimate the formation of combustion products and species and also to predict ignition,
stabiliz ation and extinction of flames. Radiation also takes place due to presence of soot formed during combustion
and also there is radiative heat transfer from wall of the combustion chamber. Combustion of fuels comes under
multiphase system, where liquid fuels is a two phase system consisting of liquid and gas phases while solid fuel
belongs to a three phase system. The challenges faced are to model breaking up of the liquid fuel, its reaction and
distribution of the reactants in three dimensional spatial systems. These models which form part of CFD, has
become an indispensable tool for combustion modelling. Before we begin a detailed review of CFD applied to
combustion phenomenon a few points to note for beginners to CFD: 1. CFD finds its application in sciences involving
fluid dynamics. 2. Prediction of heat transfer, mass transfer, chemical reactions are carried out by solving governing
equations. 3. The programs or the models use finite volume methods to solve the Navier- Stokes equations &
energy equations.
CFD f or combust ion in power plant
CFD modelling is used to simulate the combustion of coal in boilers of power plants. Coal undergoes pyrolysis,
followed by combustion of coke. Hence the accuracy of the result depends on the sub- models chosen for
devolatalisation, char combustion and soot formation. Also heat transfer models and turbulence model, if chosen
accurately gives reasonable results. As turbulence affects the heat transfer and chemical processes occurring in
pulverised coal boiler, three dimensional flow field is assumed. The transport property of solid fuel is different than
the gas surrounding it. Hence for simulation, they are generally modeled as it is and then coupled using a source
term in transport equation. Radiation and turbulence find dependence on one another in combustion CFD. Radiation
effects come into picture due to fluctuation of temperature and species concentration which are in turn affected due to
turbulence. This links up turbulence with radiation.Application areas:
Below are some of the areas where CFD finds direct application within power plant industry:
1. Coal burning and combustion analysis.
2. NOx burner design and analysis of its effect on combustion and thermal performance.
3. Draft loss and ductwork analysis
4. Coal flow distribution, improvement in pulveriz er performance, and reduce coal pipe and burner head erosion.
5. Analysis of gas flows in a furnace
6. Design of emission control systems for coal- fired power plants (NOx, SOx, mercury, CO2)
7. Design of thermal and fluid problems of nuclear reactors
8. Efficiency improvements for turbines
9. Design of combustion and power generation equipments
10. Modeling of vibration, fatigue and thermal stress in welded components, piping systems, connections, tanks,
reactors and pressure vessels
11. Design of wind power systems including turbine blades, components, electronic systems and towers.
12. Development of solar collection panels and storage systems
13. Design of hydropower plants and surrounding waterways
(Image source: Combustion modelling opportunities and

2. (Image source: Combustion modelling opportunities and
challenges for oxy-coal carbon capture technology P. Edgea, M.
Gharebaghia, R. Ironsb, R. Porter, R.T.J. Porter, M.
Pourkashaniana, D. Smithc, P. Stephensond, A. Williamsa)
The article DEVELOPMENT OF THE ADVANCED SIMULATOR
FOR FLY ASH MODIFICATION IN THE PULVERIZED COAL
COMBUSTION FURNACE describes simulation approach to
model fly ash modification behavior by direct injection of Ca
fine particles in coal combustion furnaces. Also the Role of
Engineering Simulation in Clean Coal Technologies is a nice
article on application of CFD to come up with clean technology
solutions for power industry.
Ve l o ci ty a n d te m p e r a tu r e p r o fi l e a t b o tto m a n d to p
r e s p e cti ve l y
Combust ion modeling in CFD f rom saf et y point of view
Hydrogen, as a fuel has found its application as a clean source of energy. Hydrogen being a light gas has high
transport properties such as thermal conductivity, diffusion coefficient and has wide range of flammability limits.
Hydrogen which is used in light water reactor in nuclear power plant when undergoes combustion, results in high
pressure loads acting on the container. The pressure loads are a function of the turbulent flame speed. This is where
CFD is applied to predict the pressure loads accurately. For this, hydrogen deflagration and its various regimes are
identified. While resolving combustion, in which turbulence plays a vital role, the accuracy of the results largely
depend on the mesh siz e and the time step resolution, as well as, on the initial turbulence conditions. This initial
turbulence conditions are measured from the experiments which are used to validate the CFD result. Resolving the
turbulent flame thickness by the mesh siz e helps in predicting the results accurately.Application areas:
1. CFD has application in safety systems designs in below areas:
2. Hydrogen Management
3. Boron Dilution Transients
4. Pressuriz ed Thermal Shock
5. Thermal Fatigue
6. Air and water pollution control equipment
7. Recycling and waste management systems
8. Chillers, scrubbers and spray towers
CFD analysis of a combust ion chamber t o model f luid f low
Combustion taking place in a combustion chamber is accompanied with high amount of turbulence. To simulate the
piston motion, dynamic mesh is used i.e the mesh generation approach can be used to treat the moving piston as a
moving solid body in the computational domain without generating new meshes every time at each crank angle. The
finite volume method can accommodate any type of grid. Thus, it is suitable for complex geometries. This fluid flow
can be simulated and visualiz ed along with temperature distribution in the combustion chamber.
Application areas:
Below are some of the application areas of CFD within combustion systems
1. Intake systems
2. Ports
3. In- cylinder flow and combustion
4. Engine block, head, components
5. Exhaust and after- treatment
6. Fuel supply
7. Engine ancillaries
8. Improvement of burner configurations in industrial furnaces
9. Reduction of NOx emissions from petroleum refineries
10. Investigation of novel clean energy technologies
11. Prediction of CO emission rates
12. Model and minimiz e thermal stresses in combustion equipment
13. Reduction of soot formation in furnaces
(Image source: CFD

3. (Image source: CFD
modeling of heat transfer
and fluid flow inside a pentroof type combustion
chamber using dynamic
model; Yasin Varol, Hakan
F. Oztop, Mujdat Firat,
Ahmet Koca)
The article Simulation of
Flow and Combustion in
Internal Combustion
Engines describes
modeling approach for flow
and combustion within an IC
engine.
Fl u i d fl o w p r o fi l e a n d te m p e r a tu r e d i s tr i b u ti o n i n s i d e a p e n t-r o o f typ e co m b u s ti o n ch a m b e r
(Image source- Mixing
models for the two-waycoupling of CFD codes and zerodimensional multi-zone codes to
model HCCI combustion H. Barths,
C. Felsch, N. Peters)
Simulat ion of spray f lames
In space shuttle engines, the
combustion chamber has many
individual elements which are used
to inject fuel and oxidiz er in the
high pressure chamber. The
degree of mixing and the extent of
combustion determines the thrust
generated. These conditions
therefore need to be known
accurately. Also practical simulation
of these space shuttles is not
possible. Hence engineers have
Fu e l m i xtu r e d i s tr i b u ti o n
largely become dependent on
CFD. The distribution of droplets as
well as the particle siz e in the combustion chamber cannot be
i n a co m b u s ti o n ch a m b e r o f HCCI e n g i n e

4. well as the particle siz e in the combustion chamber cannot be
measured due to presence of many injector elements. Hence
investigators have used a simplified way of assuming the fuel
to exist in gaseous state, which is sensible as the fuel droplet
would enter and evaporate instantly at such high pressures and
temperatures. The new spray flame model is computationally
efficient for three- dimensional injector flow field simulations. An
interesting article about premixed combustion modeling is
provided at the link: PROGRESS IN THE SELF- SIMILAR
TURBULENT FLAME PREMIXED COMBUSTION MODEL
(Image source- CFD analyses of complex flows, Richard Farmer,
Ralph Pike, Gary Cheng)
To summariz e this article, we have seen the different areas
where combustion modeling is applied as a design tool to
come up with new designs within various industries. We also
discussed different challenges that one encounters an engineer
while applying CFD for simulating combustion. We also
reviewed the progress in development of new models for
combustion simulation and hope the article threw some light on
highlights of combustion modeling and its application within
industry.
Ref erences:
Co m p u ta ti o n a l m e s h o f a n e n g i n e
1. CFD analyses of complex flows – Richard Farmer, Ralph
Pike, Gary Cheng 2. CFD modeling of heat transfer and fluid
flow inside a pent- roof type combustion chamber
using dynamic model – Yasin Varol, Hakan F.
Oz top, Mujdat Firat, Ahmet Koca 3. Combustion
modelling opportunities and challenges for oxycoal carbon capture technology P. Edgea, M.
Gharebaghi, R. Ironsb, R. Porter, R.T.J. Porter, M.
Pourkashanian, D. Smith, P. Stephenson, A.
Williams 4. The role of CFD combustion modeling
in hydrogen safety management—Part I:
Validation based on small scale experiments
Pratap Sathiah, Ed Komen, Dirk Roekaerts 5.
Mixing models for the two- way- coupling of CFD
codes and z ero- dimensional multi- z one codes
to model HCCI combustion H. Barths, C. Felsch,
N. Peters 6. Effect of fuel injection timing and
intake pressure on the performance of a DI diesel
engine – A parametric study using CFD B.
Jayashankara, V. Ganesan 7. www.ansys.com
8. www.cd- adapco.com
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