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Mathematical Modelling of Thermal NOX Emissions in Combustion Chambers

  • K. A. Pericleous
  • I. W. Clark
  • N. C. Markatos
Conference paper
Part of the EUROTHERM Seminars book series (EUROTHERM, volume 17)

Abstract

A mathematical model of combustion in typical burners is presented. The model differs from other similar ones presented by other investigators, in that it features a two-step approach, which allows the calculation of the main exothermic reactions of fuel in air, and of those responsible for the formation of pollutants, specifically nitrogen oxides (NOx) to be performed in tandem. The model uses CFD techniques to compute the flowfield in the burner and transport equations are solved for all relevant reacting species. To ensure industrial relevance all factors affecting combustion performance and heat transfer have been included, i.e. three- dimensionality, an exact representation of geometry, the air swirler, turbulence and radiation.

In the first step, the calculation deals with the combustion of methane in air for which a global, single step reaction is assumed. The limiting effect of turbulence on reaction rate is taken into account using an eddy-break-up model. Radiation between the burner walls, the flame and intervening gas is accounted for using a flux model.

In the second step, the product stream resulting from the first step calculation is analysed to determine the concentrations of O, OH and H radicals, subsequently used in a Zeldovich type scheme to form oxides of nitrogen. The convective and diffusive transport terms of the first step are used to solve conservation equations for N and NO.

The paper illustrates the technique in an application to an axial recirculating burner.

Keywords

Flame Structure Furnace Wall Burner Design Turbulent Exchange Coefficient Furnace Size 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.

Nomenclature

Nomenclature

CR

Empirical expression in combustion model

F

Species concentration

k

Turbulent kinetic energy per unit mass, J/kg

M

Mole fraction

m

Mass fraction

R

Ideal gas constant

R

Reaction rate per unit volume, kgs/m3

s

Stoichiometric oxidant to fuel ratio

Sϕ

Source term in finite difference equations

T

Temperature, K

Tact

Activation temperature, K

\(\vec v\)

Velocity vector

Greek Symbols

Гϕ

Turbulent exchange coefficient for variable ϕ

ε

Turbulence energy dissipation rate per unit mass, W/kg

μ

Dynamic viscosity, Ns/m2

ρ

Density, kg/m3

ϕ

General dependant variable

Subscripts

fu

Fuel

MO

Nitrogen oxides

N2

Nitrogen

OX

Oxygen

ox

Oxidant

pr

Product

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Copyright information

© Springer-Verlag Berlin, Heidelberg 1991

Authors and Affiliations

  • K. A. Pericleous
    • 1
  • I. W. Clark
    • 2
  • N. C. Markatos
    • 3
  1. 1.Centre for Numerical Modelling and Process AnalysisThames PolytechnicLondonUK
  2. 2.Flomerics Inc.USA
  3. 3.National Technical UniversityAthensGreece

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