Combustion:

Defined as an Exothermic Chemical Reaction of a fuel (For example CH4) with an oxidant (For example O2) to form products.

Modes of Combustion:

• Flame Mode: Thin Zone of intense chemical reaction called ‘flame’ exists.

• Non-Flame Mode: Volumetric Combustion Process.

Applications for Combustion Modeling

Wide range of reacting flows:

• Furnaces

• Boilers

• Process heaters

• Gas turbines

• Rocket engines

Predictions of:

• Flow field and mixing characteristics

• Temperature field

• Species concentrations

• Particulates and pollutants

Eddy Dissipation and Finite Rate Chemistry Combustion Model

1. We will discuss the theory of Eddy Dissipation (EDM) and the Finite Rate Chemistry (FRC) Models

2. Outline how to setup gaseous combustion processes in CFX.

PDF Flamelet: NonPremixed Combustion

1. We will discuss the PDF Flamelet (PFM) Combustion model in ANSYS CFX. This combustion model is used to analyze non

premixed gaseous combustion processes.

2. We will discuss the theory of the interaction between the PFM combustion model and turbulence in the flow field.

3. We will discuss a tool called “CFX-RIF” which is used to generate input files (Libraries) for the PFM combustion model.

4. We will outline the steps for setting up a PFM combustion case in CFX-Pre.

Partially Premixed Combustion

We will discuss Premixed and Partially premixed Combustion models in CFX

We will also discuss the use of PDF flamelet model to analyze a partially premixed combustion process.

We will study the setup of a partially premixed combustion case in CFX-Pre.

Pollutants Modelling,NOx and Soot

1. We will discuss the mechanism of NOx formation and outline the 4 different NOx models that can be activated in CFX

2. We will discuss the different soot models and outline how soot is modeled in CFX

Radiation Modeling

1. We will discuss the objective of and applications for radiation modeling

2. We will define radiation and outline the development of some mathematical models for radiation

3. We will review 2 solution methods for radiation: Spectral and Spatial

4. We will discuss the radiation models that are available in CFX and how to select the best model for a given case

Advanced Combustion Models and Related Features

Extended Coherent Flame Combustion Model

Shares the framework for the partially premixed combustion with the Burning Velocity Model

Transport Equations are solved for Mean Mixture Fraction, Mixture Fraction Variance and Reaction Progress

Idea of Flame Surface Density (FSD, S) is introduced in this model to describe the intensity and location of the flame. ‘FSD’ is defined as the surface area of the turbulent flame per unit volume. A transport equation is used to solve for FSD

Particle Transport Modeling for Liquid Spray and Coal Combustion

General description

Particle transport equations

Particle integration algorithm

Heat and mass transfer

Transient particle tracking

Particle injection

Particle diameter distributions

Post-Processing

Method for modelling particle laden flows

A representative sample of particles is tracked through the continuous fluid

Ordinary differential equations (ODE) are integrated for position and velocity of each particle

The overall mass flow rate of the particle phase is shared amongst the representative particles, so each particle has its own mass

flow rate, and its own number rate

Simplifying Assumptions

• Moving particle is treated as a moving mass point

• Abstraction from particle shape and volume

• Details of the flow around the particle are neglected, e.g.

• Near particle flow field

• Vortex shedding

• Flow separation

• Boundary layers

• Local properties of the dispersed phase are predicted from

spatial averaging over particle trajectories which are crossing a certain (control) volume

• Not possible to predict the tracks of all physical particles

• This would require a particle flow DNS

• Using concept of representative particle trajectories

Liquid Spray Combustion

Liquid evaporation model

Multi-component evaporation

Oil combustion modelling

Droplet break-up models

Mass Transfer – Liquid Evaporation Model

Synonym: “Spray drier model”

Main difference to simple mass transfer model:

• Particle can boil

Coal Combustion & Pollutant Modeling

Coal characterisation

Furnace types

Burner types

Coal pyrolysis modeling

Char oxidation modeling

NOx formation

Examples

Customization of multiphase reactions

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