GT 2007-27990 Development and Application of an 8-Step Global Mechanism for

CFD and CRN Simulations of Lean-Premixed Combustors

Igor V. Novosselov and Philip C. Malte

University of Washington

ASME Turbo Expo

Montreal

May 14-17, 2007

Outline

• Purpose of 8-step mechanism:

– CFD and CRN predictions of NOx and CO for natural

gas-fired lean-premixed combustion turbines.

• Development of 8-step mechanism:

– Foundation in high-pressure JSR measurements.

– Chemical reactor modeling with GRI 3.0 used to

develop the “database.”

– Regression analysis used to obtain the 8 global steps.

• Application and verification of 8-step mechanism:

– 15 atm bluff body combustor.

– Gas turbine engine test rig.

– CFD model of generic can-type combustor.

The 8-Steps

Nitric Oxide Reaction Chemistry for Lean-Premixed Combustion

Foundation in High-Pressure Jet-Stirred Reactor Measurements:

Modeling of data of Bengtsson by Rutar and Malte

(phi = 0.55, T = 1828K, 88% PSR/ 12% PFR).

Chemical reactor schemes used in developing the “database” –

pressure 5-20 atm, inlet air temperature corresponding to 85%

efficient compression from 288K, phi 0.45-0.75

“Data” provided

• Temperature

• Major species concentrations: CH4, CO, CO2, O2, H2O,

N2, and OH.

• Species involved in NO formation: CH, N2O, NNH, O,

and H.

• Rates of CH4 and CO oxidation and CO2 dissociation.

• Rates of NO formation by the Zeldovich, nitrous oxide,

prompt, and NNH mechanisms.

Global Rate Expression

Obtaining the Global Rates

Example: Global Rate vs Rate by Elemental Chemistry

Bluff body combustor (Bucher et al.): methane, 680K inlet T, 14.3

atm, 1.1 kg/s air, 0.63 blockage ratio, effusion cooled.

Temperature field by 2-D CFD shown top plot: 1930K peak.

(flow from left to right)

Predicted CO (2.2% peak) and NO (14 ppm peak) also shown.

(phi = 0.59)

Bluff body: comparison of modeling results to measurements

0

100

200

300

400

500

600

700

800

0.55 0.57 0.59 0.61 0.63 0.65 0.67 0.69 0.71

premixer phi

CO

pp

mv

dry

(1

5%

O2

) .

experimental data

CFD area-average

CFD weighted to probe

CFD on centerline

0

10

20

30

40

50

60

70

80

0.55 0.57 0.59 0.61 0.63 0.65 0.67 0.69

premixer phi

NO

x p

pm

v d

ry (

15

% O

2)

.

experimental data

CFD weighted to probe

CFD without thermal NO weighted to probe

L&S high (front-end phi)

L&S low (front-end phi plus wall-cooling air)

Gas Turbine Engine Test Rig Data (Novosselov et al.): Comparison

between data and 31-element CRN predictions using full mechanism and

8-step mechanism.

0.0

0.5

1.0

1.5

2.0

2.5

0 50 100 150 200

Pilot, % of Neutral

NO

x, N

orm

alized

Em

issio

n

CRN: 8-step mechanism

CRN: GRI 3.0 mechanism

Engine test rig data

31-Element CRN for Lean-Premixed GT Combustor (Novosselov)

Application of 8-Step Mechanism in Modeling Generic Lean-

Premixed Gas Turbine Combustor (phi = 0.475, 50% pilot, 16 atm)

Application of 8-Step Mechanism in Modeling Generic Lean-

Premixed Gas Turbine Combustor (rates)

CFD Modeling Assumptions and Boundary Conditions

(bluff body at left, generic GT combustor at right)

END