Laser diagnostics applied in theLaser diagnostics applied in theafterburner of an aircraft turbofan engineafterburner of an aircraft turbofan engine

Hans SeyfriedDivision of Combustion Physics, Lund University, Faculty of Engineering

LTH, S-22 100, Lund, Sweden

Outline

• Measurement object

• Measurement techniques– Laser-induced fluorescence – Fuel visualization

• Experimental setup

• Results

• Summary and Conclusions

– Laser-induced phosphorescence – Surface thermometry• Experimental setup

• Results

• Summary and Conclusions

Volvo Aero, RM 12 turbofan engineReinforcedfan HP

compressor Combustor

Radialflameholder

Afterburner

Exhaustnozzle

HPturbine

LPturbine

Volvo Aero, RM 12 turbofan engine

Harsh environmentperforming optical/laserbased diagnostics

– Acoustic vibration due to highlevels of noise (several kW/m2)

– Absorption

– Interference of backgroundradiation

Protection for laser and detector

Laser protection

Protection for detector and optics

Thick-walled steel tubes

Measurement Techniques

Laser Induced Fluorescence (LIF) – Fuel visualization

Electron ground state

Excited electron state

Laser, λ1Fluorescence λ2 > λ1

Basic principle:

Present work:λ1 = 266 nmλ2 is shown in the diagram

Fluorescence from Jet-A afterexcitation with 266 nm:

LIF – Experimental setup

Laser type: Nd:YAGLaser wavelength: 266 nmLaser frequency: 10 HzPulse energy: ~70 mJCamera: CCD 576*384 pxExposure time: 100 nsDetections wavelength: λ > 295 nm

Afterburner Outlet

Lasersheet

A/B load A/B load

4 %

29 %

42 %

20 %

33 %

56 %

Counts

Results – Fuel visualization

Results – Fuel visualization

• Afterburner load sweep: 0%- 100% - 0%

• Afterburner outletdiameter and laser sheetare represented bydashed lines

Counts

Summary – Fuel visualization

• Non-intrusive laser diagnostics for visualization ofunburned fuel exiting the afterburner

• Unburned fuel does exit the afterburner nozzle

• The fuel is located in the outer areas of the jet-stream

• Measurable amounts at 0 – 60 % afterburner load

• Maximum of unburned fuel at about 30 % afterburnerload

Measurement techniques

Laser Induced Phosphorescence (LIP) – Surface thermometry

Thermographic phosphors– Temperature dependent light emission

– Inorganic, often ceramic, materials doped with some activator (≈ 1 %)

– Doping agent (Activator) - rare earth ion (Eu+3, Dy+3, Mn+2) absorb andemit radiation ⇒ narrow band emission

– Powder (Ø 1-10 _m)

– Excited by UV-laser light → phosphorescence in the visible spectra• Laser Induced Phosphorescence (LIP)

• Phosphorescence lifetimedecreases with temperature

• Typical lifetime: µs – ms

• Theoretical lifetime:

• Data acquired via photomultiple tube (PMT) and aoscilloscope

• Fitting measured data totheoretic model gives lifetime

Temperature measurements using lifetime method

Temperature sensitivity ofMg3FGeO4:Mn at 657 nm

τt

eII−

⋅= 0

Phosphorescence decay of the Mg3FGeO4:Mnphosphor at different temperatures.

Experimental arrangement

Lens + Filter + PMT +Transimpedance amplifier

Segment of flameholdercoated with phosphor material

Nd:Yag laserλ=266 nm

Results 1(2)

Power Level (PL) versus time for testcycle B.

Temperature data measured for testcycle B.

Temperature data (lifetime decays) was recorded at the repetition rateof the excitation laser (10 Hz).

Signals were sampled using a 1 GHz bandwidth oscilloscope (LeCroy).

Results 2(2)

a) Heating process: Power Level (PL) sweep 18 – 102.b) Cooling process: Power Level (PL) sweep 130 – 28.

Temperature data measured for a test cycle.

Summary – Surface thermometry

• Non-intrusive laser diagnostics for remote probing ofsurface temperatures on flameholder

• Quantitative temperature data for a wide engineoperational range

• Sampling rate of 10 Hz resolved temperature variationsunder engine load transitions

• Good agreement with conventional thermocouplemeasurements