Combustion Instability Characteristics of a Swirling Combustor

Guoqiang Li, Tongxun Yi, Ephraim GutamrkUniversity of Cincinnati

39TH AIAA/ASME/SAE/ASEEJoint Propulsion Conference and Exhibit20-23 JULY 2003Huntsville, Alabama

39th A

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Copyright ©

2003 by the Am

erican Institute of Aeronautics and A

stronautics, Inc. All rights reserved.

Introduction

Premixing lean burn combustion is susceptible to thermo-acoustic instability

The coupling between acoustic field of combustion system and the oscillation in heat release drives thermo-acoustic instability

Large coherent structures (LCS) in swirling flow and shear layer is one mechanism for driving thermo-acoustic instability

Schadow et al. identified the role of LCS to combustion instability in dump combustor; Paschereit et al studied the interaction of acoustic and unstable swirling flow

This paper focus on the identification of combustion instabilityin a swirling combustor which features DLE nozzle design

Experimental Setup

AirFuel

Air

Air

2”

5.75”, 4”

Fine Screen

Pressure Transducer1

Trigger In

Air

18.5” 25.5”

Pressure Transducer2

Emission Probe

Combustion Chamber

Gas Analyzer

39”, 28”, 26”, 18”

TARS

ICCD camera

PMT2”

Computer (dSpaceBoard)

Experimental Setup

Results and Discussions

1. Effects of combustion chamber geometry to combustion instability

2. Effects of air swirler inlet to instability

3. Phase correction of pressure signals

4. Phase-locked OH Chemiluminescence

Combustion chamber length

5.75”

39”

28”

26”

Combustion instability characteristics

Pressure Characteristics of Air Flow Rate at 19.5 SCFM

0

50

100

150

200

250

0.7 0.75 0.8 0.85 0.9 0.95

Equivalence Ratio

Peak Amplitude (Pa)

Peak Frequency (Hz)

Unstable Acoustic Frequency and Peak Amplitude for Air Flow Rate at 19.5 SCFM

Combustion instability characteristics

Φ=0.71

Φ=0.73

Φ=0.74

Effects of air swirler inlet conditions

AirFuel

Air

Air

2”Fuel

Air

Air

2”

φ=0.59 with air mass flow rate 1.2lb/min

Effects of air swirler inlet conditions

0

60

120

180

240

0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

Euqivalence Ratio

Dom

inat

e Fr

eque

ncy

(Hz)

air mass=1.2lb/min

0

10

20

30

40

0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80

Euqivalence Ratio

Mag

nitu

de o

f Dom

inat

e Fr

eque

ncy

(Pa)

air mass=1.2lb/min

airflow rate = 1.2lb/min (air swirler inlet non-blocked)

330

340

350

360

370

380

0.45 0.50 0.55 0.60 0.65 0.70 0.75Euqivalence Ratio

Dom

inat

e Fr

eque

ncy

(Hz)

air mass=1.2lb/minair mass=1.8lb/min

80

120

160

200

240

280

0.45 0.50 0.55 0.60 0.65 0.70 0.75

Euqivalence Ratio

Mag

nitu

de o

f Dom

inat

e Fr

eque

ncy

(Pa) air mass=1.2lb/min

air mass=1.8lb/min

airflow rate = 1.2lb/min and (air swirler inlet 1.8lb/min blocked)

Pressure signals from two transducers

Pressure Transducer2

Pressure Transducer1

Air

5.75”

Pressure Transducer1

20.5”

Combustion Chamber

26”

Pressure Transducer2

TARS

Fine Screen

25.5”

Phase-locked OH Chemiluminescence

364Hz,Φ=0.76

380Hz, Φ=0.84

4”18”

q’

Phase-locked OH Chemiluminescence

ICCD setup parameters:

100µs gating time

41 images

Sequential delay: 1.5ns~5.4ms

Gain: 255

On-chip accumulation: 10

Negative External Trigger Edge

Φ=0.76

Phase-locked OH Chemiluminescence

0° 36° 72° 108°

144° 180° 216° 252°

288° 324° 360°

Phase-locked OH Chemiluminescence

-1.20

-0.80

-0.40

0.00

0.40

0.80

1.20

0 100 200 300 400 500 600 700 800

Phase (degree)

Arb

itrar

y U

nit

p'q'

ICCD OH

Phase-locked OH Chemiluminescence

0.0E+00

4.0E+08

8.0E+08

1.2E+09

1.6E+09

2.0E+09

2.4E+09

0 100 200 300 400 500 600 700 800Phase (degree)

Tota

l OH

pixe

l ind

ensi

ty

Equivalence ratio=0.76Equivalence ratio=0.84

Conclusions

The combustion instability of this system changed with the combustion chamber geometry and inlet boundary conditions; its dominant frequency increased with the shortening of chamber length and its strength was stronger after the air swirler inlet blocked. The dominant frequency mode was identified to be quarter wave mode.

Phase-locked OH imaging showed that the flame intensity oscillation was strongly coupled with pressure oscillation signal and suggested this coupling may be the driven mechanism of thermo-acoustic instability in this system.

The OH imaging also indicated that the flame oscillation could coupled with vortex shedding at the dump. This may lead the way for future instability control for this system.

Future Plan

Pressure oscillation

Flame

oscillation

Vortex shedding

?

Future Plan

Fuel injection locations