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COMBUSTION DIAGNOSTICS – LIF. Dr. 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.

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COMBUSTION DIAGNOSTICS – LIF

Dr. Jimmy Olofsson


Outline
Outline

  • Why combustion diagnostics?

  • Molecular spectroscopy in brief

  • Combustion LIF system

  • Time-resolved Combustion LIF

  • Coffee break

  • Applications

  • Related Techniques



Benefits of analysing combustion
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 for combustion diagnostics
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
Combustion diagnostic techniques

Combustion Radicals - LIF

Soot LII

Combined Measurements

Fuel Tracer LIF

Rayleigh Temperature



Combustion species
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 Molecule

Photon

Fluorescence

Emission

Laser-Induced Fluorescence

Excited State

  • Species selective measurements

  • (OH, formaldehyde, fuel tracers, etc.)

Ground State

Absorption


Molecular energy states electronic

e-

e-

Molecular energy states: Electronic


Molecular energy states vibrational and rotational
Molecular energy states:Vibrational and Rotational


Oh absorption spectrum several absorption lines around 283 nm
OH absorption spectrumSeveral absorption lines around 283 nm

Air Wavelengths

Excitation in UV

Wavelength (Å)


Oh absorption spectrum two narrow absorbtion regions within 100 nm range
OH absorption spectrumTwo narrow absorbtion regions within 100 nm range

~283 nm

0.05

0.04

0.03

0.02

0.01

0.00

O–H

Optical Density

240 260 280 300 320 340 360

Wavelength (nm)


Temperature dependence
Temperature dependence

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

in the measured temperature range


Acetone absorption spectrum larger molecules have wider absorption range
Acetone absorption spectrumLarger molecules have wider absorption range

0.05

0.04

0.03

0.02

0.01

0.00

Optical Density

240 260 280 300 320 340 360

Wavelength (nm)


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.

Selection of excitation wavelength


Laser induced fluorescence1
Laser-Induced Fluorescence must be precisely tuned to match molecular energy transition.

Laser

line

1,0

0,8

Detected LIF

0,6

Residual laser light

0,4

Wavelength

/nm

l

0,2

0

Bandpassfilter

Fluorescence

spectrum

Absorption

spectrum

Normalised intensity

200

250

300

350

400

450

500

550

600


Combustion LIF system must be precisely tuned to match molecular energy transition.


Combustion lif system
Combustion LIF system must be precisely tuned to match molecular energy transition.

Image Intensifier

UV Camera Lens

Optical Filter

CCD Camera

Nd:YAG Laser

Burner

Sheet Optics

Dye Laser


Standard nd yag pumped dye laser
Standard Nd:YAG pumped dye laser must be precisely tuned to match molecular energy transition.

1090 mm

3ω/4ω

Nd:YAG laser

250 mm

Dye laser

744 mm

Dye laser UV beams or 266nm or 355nm

250 mm

Beam combining output bench

840 mm

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


Tuneable dye laser oscillator

  • Tuning mirror must be precisely tuned to match molecular energy transition.

  • Grazing incidence grating

  • Beam expander prism (NBP Option)

  • Flowing dye cell

  • High reflectivity mirror

  • Focusing lens

Tuneable dye laser oscillator

Dye Laser


Tuning curves for laser dyes
Tuning curves for laser dyes must be precisely tuned to match molecular energy transition.


Species and excitation wavelengths
Species and excitation wavelengths must be precisely tuned to match molecular energy transition.

Our refecence species which we use during the lab training


Light sheet forming optics
Light sheet forming optics must be precisely tuned to match molecular energy transition.

Sheet height adjuster

Beam waist adjuster

Standard mount

Holder & fixation system

  • Quartz optics for UV/visible transmission

  • Parallel light sheet

  • - Better control of reflections

  • - Enhanced energy distribution


Detecting laser induced fluorescence
Detecting Laser-Induced Fluorescence must be precisely tuned to match molecular energy transition.

  • Sensitive, high-resolution CCD camera

CCD Camera

  • 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

Image Intensifier

UV Camera Lens

Spectral Filter

  • UV camera lens required for detection of UV fluorescence

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


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

Optical filters


Combustion lif software and timing
Combustion LIF: Software and timing wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

  • 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
Laser control from the software wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

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 wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm


Framing rate requirements
Framing rate requirements wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

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.

  • Resolution used in the study: 0.5CAD

  • This corresponds to a 14kHz

Time-resolved Formaldehyde LIF

J.Olofsson et al SAE 2005


High speed nd ylf laser
High-speed Nd:YLF laser wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

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


Pumping of dye lasers

Pulse separation: 75 µs wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

Rep. Rate: 13kHz

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


Tr c lif yag based pump lasers
TR C-LIF: YAG-based pump lasers wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

IS Series

  • Repetition rate up to 10kHz

  • Pulse length: ~10ns

  • Pulse energy @ 4kHz: 8mJ

HD Series

  • Repetition rate up to 10kHz

  • Pulse length: ~10ns

  • Pulse energy @ 10kHz: 12mJ

  • Pulse energy @ 5kHz: 20mJ


Tr c lif dye laser
TR C-LIF: Dye laser wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

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
TR C-LIF: SpeedSense camera series wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm


Tr c lif image intensifiers
TR C-LIF: Image intensifiers wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm


COMBUSTION DIAGNOSTICS – APPLICATIONS wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

Dr. Jimmy Olofsson


Scalar imaging applications
Scalar imaging applications wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

Gaseous flows

(non reactive)

Gaseous flows

(reactive)

Liquid flows

Applications

Mixing and heat transfer

Pre- / Post-combustion

Combustion

Hardware

Nd:YAG Laser

Image intensifier unit

Tuneable Dye Laser


Fuel tracer lif
Fuel Tracer-LIF wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

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 wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm

Formaldehyde fluorescence spectrum

A: in a flame

B: in an engine

Fluorescent tracer spectra


Application example 1 wavelength interval of the fluorescence from the molecular species of interest, typically some few 10 nm


How to acheive homogeneous acetone concentration for calibration
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 University

Beijing, China




Formaldehyde visualization in an hcci engine
Formaldehyde visualization in an calibrationHCCI 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

J.Olofsson et al SAE 2005


Formaldehyde lif in an engine
Formaldehyde LIF in an engine calibration

High-speed laser

Field-of-view

Wavelength: 355 nm

Fuel: N-Heptane

J.Olofsson et al SAE 2005


Cycle resolved formaldehyde consumption
Cycle-resolved calibrationFormaldehyde consumption

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

J.Olofsson et al SAE 2005


Fluorescence spectra diatomic radicals

OH radical calibration

Fluorescence spectra diatomic radicals



Piv plif investigation of two phase vortex flame interactions
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, andWright-Patterson Air Force Base, OH, USA


Simultaneous ch plif and piv
Simultaneous CH PLIF and PIV interactions

By courtesy of

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


Application example 4 interactions



Combined oh lif fuel tracer lif and piv1
Combined OH LIF, fuel tracer LIF and PIV interactions

OH radical

Flow velocity field

Fuel tracer / Acetone

  • Local flame extinction events

  • Create a data base of measurement data

  • Data used for model comparison

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.


Air&Burnt interactions

OH

OH

Coflow

Burnt

Unburnt: Methane&Air

Simultaneous PIV and TR OH LIF local flame extinction

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
Multi-dye laser cluster interactions

J.Olofsson


Application example 5 interactions


Combined tr piv and tr oh lif with lund university sweden
Combined TR PIV and TR OH LIF interactionswith Lund University, Sweden

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.


Flow field and flame front at 4 khz
Flow field and flame front at 4 kHz interactions

Lund University P.Petersson and J.Olofsson


COMBUSTION DIAGNOSTICS – RELATED TECHNIQUES interactions

Dr. Jimmy Olofsson



Soot in combustion
Soot in combustion interactions

  • Soot is a hazardous pollutant emission

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


Laser indusced incancescence

Size decreases interactions

Laser-Indusced Incancescence

  • Soot particles are heated up by laser radiation

  • The increased particle temperature results in increased emission of Plank radiation

LII intensity (a.u.)

0 100 200 300 400 500

Time (ns)


Lii measurement systems
LII measurement systems interactions

Image Intensifier


Application example 6 interactions



Quantitative lii
Quantitative LII interactions

Soot-volume-fraction in a Diesel engine

  • Soot formation at different EGR rates

  • Soot formation at different piston bowl geometries

Soot volume fration (ppm)

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


Rayleigh Thermometry interactions


Rayleigh Thermometry interactions

  • 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 for rayleigh thermometry

Measurement image interactions

Reference image

Required data sets forRayleigh Thermometry


Results of rayleigh thermometry analysis

Mean: 1350 K interactions

RMS: 106

Mean: 1120 K

RMS: 61,3

Mean: 295 K

RMS: 12,2

Results of Rayleigh Thermometry analysis


Rayleigh thermometry results
Rayleigh Thermometry results interactions

Takes into account:

  • Scattering cross-section

  • Pressure

  • Laser pulse energy


Thank you for your attention
Thank you for your attention! interactions

DANTEC

DYNAMICS


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