Download - COMBUSTION DIAGNOSTICS – LIF

| JIMMY OLOFSSON | 2013A Nova Instruments company

COMBUSTION DIAGNOSTICS – LIFDr. Jimmy Olofsson


Outline

• Why combustion diagnostics?

• Molecular spectroscopy in brief

• Combustion LIF system

• Time-resolved Combustion LIF

• Coffee break

• Applications

• Related Techniques


Why combustion diagnostics?


Benefits of analysing combustion

Combustion related applications:• Transportation• Electrical power production• Heating

Combustion analysis can be used for economic as well as environmental benefits by:

• Optimizing fuel economy• Improving performance and reliability• Reducing pollutant emissions


Benefits of using lasers forcombustion diagnostics

• Non-intrusive• High spatial resolution• High temporal resolution• High sensitivity• Species selective• 2D measurements

Laser-based measurements techniques can provide information on species concentrations, temperature fields, flow velocities etc. and the measurements often have the following properties:


Combustion diagnostic techniques

Soot LII

Rayleigh Temperature

Fuel Tracer LIF

Combustion Radicals - LIF

Combined Measurements


Molecular spectroscopyin brief


Combustion species

• Gas with chemical reactions• Production of radicals• Qualitative concentration of radical

- OH- CH- NO- etc

• Concentration of larger molecules/tracers- Formaldehyde- Acetone- etc


Laser-Induced Fluorescence

Excited State

Ground State

Photon

Absorption

Excited Molecule

Emission

Fluorescence

• Species selective measurements (OH, formaldehyde, fuel tracers, etc.)


Molecular energy states: Electronic

e-

e-


Molecular energy states:Vibrational and Rotational


OH absorption spectrumSeveral absorption lines around 283 nm

• Air Wavelengths Excitation in UV

Wavelength (Å)


OH absorption spectrumTwo narrow absorbtion regions within 100 nm range

240 260 280 300 320 340 360

Wavelength (nm)

0.05

0.04

0.03

0.02

0.01

0.00

Op

tica

l De

nsi

ty

O–H ~283 nm


Temperature dependence

Choose a peak with for which the fluorescence is independent of temperature

in the measured temperature range


Acetone absorption spectrumLarger molecules have wider absorption range

240 260 280 300 320 340 360

Wavelength (nm)

0.05

0.04

0.03

0.02

0.01

0.00

Op

tica

l De

nsi

ty


Selection of excitation wavelength

• To excite atoms or diatomic molecules the laser wavelength must be precisely tuned to match molecular energy transition.

• Larger molecules, such as Acetone, 3-pentanone or Formaldehyde, have many more close-lying states, effectively making a wide continuous absorption band. Therefore, any wavelength within the absorption band can be used to excite the molecule.


Laser-Induced Fluorescence

0

0,2

0,4

0,6

0,8

1,0

200 250 300 350 400 450 500 550

Wavelength /nm

Fluorescencespectrum

No

rmal

ised

in

ten

sit

y

Bandpass

filter

Laserline

600

Absorptionspectrum

Detected LIF

Residual laser light


Combustion LIF system


Combustion LIF system

CCD Camera

Burner

Nd:YAG Laser

Dye LaserSheet Optics

UV Camera Lens

Optical Filter

Image Intensifier


Standard Nd:YAG pumped dye laser

Nd:YAG laser• Single cavity 10 Hz• Wavelengths: 1064 nm, 532 nm,

355 nm, 266 nm• Pulse length ~10 ns• Pulse energy 400 mJ @ 532 nm

Tuneable dye laser• Tunability range of fundamental:

380-750 nm• UV extension down to 200 nm• Line width: 0.8 cm-1

• Narrow band option: 0.08 cm-1

1090 mm

840 mm

250 mm

744 mm

250 mm

Nd:YAG laser

Dye laser

3ω/4ω 2ω

Beam combining output bench

Dye laser UV beams or 266nm or

355nm


Tuneable dye laser oscillator

Dye Laser

4. Flowing dye cell5. High reflectivity mirror6. Focusing lens

1. Tuning mirror2. Grazing incidence

grating3. Beam expander prism

(NBP Option)


Tuning curves for laser dyes


Species and excitation wavelengths

SpeciesExcitation

wavelengthLaser pulse

energyProcess Type of dye

OH 283 nm 25 mJ Doubling Rh590

CH 389 nm 28 mJ Mixing Rh610+Rh640

CO 230 nm 13 mJMixing after

doublingRh610

NO 226 nm 4.5 mJMixing after

doublingRH590+Rh610

Our refecence species which we use during the lab training


Light sheet forming optics

• Quartz optics for UV/visible transmission• Parallel light sheet

- Better control of reflections- Enhanced energy distribution

Beam waist adjusterSheet height adjuster

Holder & fixation system

Standard mount


Detecting Laser-Induced Fluorescence

Image Intensifier • Image intensifier

- Amplifies the incoming light- Converts UV fluorescence to

visible light detectable by the CCD camera

- Allows gated detection with very short time gates, to minimise detection of natural flame emission

UV Camera Lens

• UV camera lens required for detection of UV fluorescence

Spectral Filter

• Spectral filter to eliminate detection of scattered laser light and flame emission

CCD Camera

• Sensitive, high-resolution CCD camera


Optical filters

• Interference filters are used to transmitt only in the wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

• All other wavelengths should ideally be blocket by the filter


Combustion LIF: Software and timing

• Synchronization unit

• Analog Input option. Includes the A/D board and software add-on

• Software:

- DynamicStudio acquisition and processing software

- Software add-ons for tracer LIF and combustion LIF


Laser control from the software

Nd:YAG laser• Automatic detecion• Auto activation at

Preview/Acquisition• Q-switch activation/de-activation

during Preview/Acquisition• Interlock messages displayed in

Log

Tuneable Dye laser• Wavelength set• Wavelength fine-tune buttons• Wavelength scan• Output wavelength calculated

from fundamental depending on frequency conversion scheme


Time-resolved Combustion LIF


Framing rate requirements

EXAMPLE

• Heat release event in combustion engine running at 1200 rpm.

• The main heat release occurs within ~5CAD out of the entire 360CAD engine cycle.

J.Olofsson et al SAE 2005

Tim

e-r

eso

lved F

orm

ald

ehyde L

IF

• Resolution used in the study: 0.5CAD

• This corresponds to a 14kHz


High-speed Nd:YLF laser

Output pulse energy (527 nm) vs repetition rate (single cavity laser)


Pumping of dye lasers

Pumping of a dye laser with high repetition rate causes two major problems:

• Decrease in pulse energy• Deterioration of beam profile

Pulse separation: 75 µs

Rep. Rate: 13kHz


TR C-LIF: YAG-based pump lasers

IS Series

• Repetition rate up to 10kHz

• Pulse length: ~10ns

• Pulse energy @ 4kHz: 8mJ

HD Series

• Repetition rate up to 10kHz

• Pulse length: ~10ns




TR C-LIF: Dye laser

Example:

Pumping with 12W @ 1kHz => 12mJ / pulse

Dye: Rhodamine 6G (~570nm) gives 3.3mJ / pulse

Frequency doubling to ~283nm for OH LIF is estimated to give ~0.5mJ / pulse

This should be compared with the corresponding ~20mJ / pulse achieved by the standard 10Hz system!


TR C-LIF: SpeedSense camera series

Model example SpeedSense v711

Maximum fps at full res.

7500 at1280 x 800

Resolution at 10kHz (example)

1280 x 600

Resolution at 15kHz (example)

896 x 544


TR C-LIF: Image intensifiers

Model H Series9138A1178

Maximum repetition rate

200 kHz

Minimum gate time

10 ns

Diameter (input/output)

24 mm

Photocathode material

Multialkali

Phosphor screen material

P46

L Series9138A1180

100 kHz

40 ns

25 mm

S20(as

Multialkali)

P46


COMBUSTION DIAGNOSTICS – APPLICATIONSDr. Jimmy Olofsson


Mixing and heat transfer Pre- / Post-combustion Combustion

Liquid flowsGaseous flows

(non reactive)

Gaseous flows

(reactive)

Image intensifier unit

Applicat

ions

Hardwar

e

Tuneable Dye LaserNd:YAG Laser

Scalar imaging applications


Fuel Tracer-LIF

Two different approaches to fuel visualization

• ”Real” fuels- Real engine conditions- Unknown fluorescent

properties (temperature, pressure, quenching etc.)

• Non-fluorescing reference fuel with added fluorescent tracer

- Well-known fluorescent properties

- Allows for quantification- Further from real engine

conditions


Fluorescent tracer spectra

• Acetone fluorescence spectrum • Formaldehyde fluorescence spectrum

- A: in a flame- B: in an engine


Application example 1


How to acheive homogeneous Acetone concentration for calibration

Example:Quantification of fuel vapour in constant pressure vessel using liquid fuel

“Iso-octane was used as substitute of real gasoline in PLIF experiment and 10% acetone was added in as tracer.”

…

“To get a homogeneous mixture, a small amount of fuel was injected into vessel. Waited about 30 seconds for vaporization, then, recorded 100 LIF signal images. After averaged the images and subtracted the background, the result gave the relationship between current equivalence ratio and the LIF signal.”

Tsinghua UniversityBeijing, China


Tracer-LIF calibration


Formaldehyde visualization in anHCCI engine

Homogeneous Charge Compression Ignition Engine

Advantages• Lower NOx levels and less soot formation

compared to the Diesel engine• Higher part load efficiency compared to the

SI engine

Disadvantage• Difficult to control ignition timing

For some fuels formaldehyde is formed in the cool-flame region



Formaldehyde LIF in an engine

Wavelength: 355 nmFuel: N-Heptane

Field-of-view


High-speed laser


Cycle-resolvedFormaldehyde consumption

Single-cycle-resolved formaldehyde fluorescence imaged with a time separation of ~70 µs (0.5 CAD).



Fluorescence spectra diatomic radicals

• OH radical


PIV/PLIF investigation of two-phase vortex-flame interactions

• Study of two-phase vortex-flame interaction in a counterflow burner

• Local flame extinction events

• PIV for flow velocity field measurements giving the local strain rates

• PLIF of CH (389.5 nm) for diffusion flame front location and flame extinction zones

Investigation done in collaboration between École Centrale Paris, France, Innovative Scientific Solutions, and Wright-Patterson Air Force Base, OH, USA


Simultaneous CH PLIF and PIV

By courtesy of

École Centrale Paris, France, Innovative Scientific Solutions, and Wright-Patterson Air Force Base, OH, USA


Combined OH LIF, fuel tracer LIF and PIV


Combined OH LIF, fuel tracer LIF and PIV

Simultaneous flow field (PIV), fuel (tracer-LIF) (blue) and OH (LIF) (green) visualisation in a turbulent atmospheric flame. Courtesy of R. Collin and P. Petersson, Division of Combustion Physics, Lund University, Sweden.

OH radical

Fuel tracer / Acetone

Flow velocity field

• Local flame extinction events

• Create a data base of measurement data

• Data used for model comparison


Simultaneous PIV and TR OH LIF local flame extinction

BurntCoflow

Unburnt: Methane&Air

Air&Burnt

OH

OH

OH: Intermediate combustion product in hydrocarbon combustion. Flame front marker.

Time-resolved OH LIF at 2.5kHz framing rate

Lund University P.Petersson and J.Olofsson


Multi-dye laser cluster

J.Olofsson


Planar Laser-Induced Fluorescence (PLIF) system

Diode pumped Nd:YAG laser is used to pump a high repetition rate dye laser.

The emitted 283 nm laser pulses excites OH radicals in the flame –> imaged on an intensified high-speed camera.

Combined with high repetition rate Nd:YLF laser for simultaneous TR PIV.

Combined TR PIV and TR OH LIFwith Lund University, Sweden


Flow field and flame front at 4 kHz

Lund University P.Petersson and J.Olofsson


COMBUSTION DIAGNOSTICS – RELATED TECHNIQUESDr. Jimmy Olofsson


Laser-Induced Incandescence


Soot in combustion

• Soot is a hazardous pollutant emission

• Soot is related to incomplete combustion which has an impact on combustor performance


Laser-Indusced Incancescence

• Soot particles are heated up by laser radiation• The increased particle temperature results in increased emission of

Plank radiation

Size decreases

Time (ns)

LII i

nten

sity

(a.

u.)

0 100 200 300 400 500


LII measurement systems

Image Intensifier


Laser diagnostics in an IC engine


Quantitative LII

Soot-volume-fraction in a Diesel engine

Work done by H. Bladh et al, at Combustion Physics, Lund University, Sweden

Soot

volu

me f

rati

on

(p

pm

)

• Soot formation at different EGR rates

• Soot formation at different piston bowl geometries


Rayleigh Thermometry


Rayleigh Thermometry

• The Rayleigh signal is dependent on:

- Laser intensity- Scattering cross section- Number density

• If species composition and pressure are known in the gas the gas temperature can be determined from imaging of the Rayleigh scattering.


Required data sets forRayleigh Thermometry

Reference imageMeasurement image


Results of Rayleigh Thermometry analysis

Mean: 1120 K

RMS: 61,3

Mean: 295 K

RMS: 12,2

Mean: 1350 K

RMS: 106


Rayleigh Thermometry results

Takes into account:• Scattering cross-section• Pressure• Laser pulse energy


Thank you for your attention!

DANTECD Y N A M I C S

Download - COMBUSTION DIAGNOSTICS – LIF

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