BY : CHAM Development Team - M R Malin

FOR : Validation of Gaseous Combustion Models

The main objective of the calculations is to validate the turbulent combustion models provided in the extended SCRS attachment for gaseous combustion.
The experimental data to be simulated are the zero-swirl results for the gas-fired turbulent combustion chamber of Owen et al (16th Int. Symp. Combustion, p105, 1976).

The geometry comprises a 12.2cm diameter axisymmetric combustor into which natural gas (96% CH4) is injected centrally and axially to mix and burn with a heated, coaxial annular air stream.
The chamber length is taken as 4 diameters in the CFD simulations.
Coaxial fuel and air streams are admitted separately into the combustor and then burn in a turbulent diffusion flame. The inlet fuel/air velocity ratio is 0.05.
The fuel jet enters through a pipe of 6.3cm diameter at a temperature of 288 K. The air jet enters through an annulus at a temperature of 750 K. The furnace walls are presumed isothermal at a temperature of 600 K.
The inlet fuel/air equivalence ratio is 0.9, and the combustor operating pressure is 3.8 atmospheres.

Turbulence is represented via the k-e turbulence model.
Calculations are made with 4 different combustion models: (a) fast-chemistry model with a one-step global irreversible methane reaction to form CO2 and H2O; (b) as (a) but with an assumed double-delta probability density function to account for the influence of concentration fluctuations; (c) eddy-break-up finite-rate chemistry model with a one-step global irreversible methane reaction (CEBU=6.0); and (d) as (c) but with a two-step global reaction mechanism involving the intermediate CO (CEBU1=6.0 and CEBU2=1.0).
The calculations employ variable specific heats and heats of reaction.
The flow is treated as weakly compressible.
Radiative heat transfer is modelled via the P1 spherical-harmonics approximation for a gray medium. The wall emissivity is taken as 0.9 and the optical thickness as 0.25 based on furnace diameter.
A cylindrical-polar mesh is used with 30 radial by 40 axial cells.