G de sercey g j awcock and m heikal university of brighton school of engineering uk
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s. OSAV’2004 International Topical Meeting. Toward A Calibrated LIF Image Acquisition Technique For In-Cylinder Investigation Of Air-to-fuel Mixing In Direct Injection Gasoline Engines. G. De Sercey, G. J. Awcock and M. Heikal University of Brighton School of Engineering UK

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G de sercey g j awcock and m heikal university of brighton school of engineering uk

s

OSAV’2004 International Topical Meeting

Toward A Calibrated LIF Image Acquisition Technique For In-Cylinder Investigation Of Air-to-fuel Mixing In Direct Injection Gasoline Engines

G. De Sercey, G. J. Awcock and M. Heikal

University of Brighton

School of Engineering

UK

[email protected]

This Work Conducted In Association With Ricardo Consulting Engineers, UK


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Toward A Calibrated LIF Image Acquisition Technique For In-Cylinder Investigation Of Air-to-fuel Mixing In Direct Injection Gasoline Engines

  • Introduction

  • The Laser Induced Fluorescence (LIF) Technique

  • The Optical Set-up for Quantitative Measurement

  • Calibration Strategy

  • Tracer Optimisation

  • Calibration Process

  • Conclusion; - Discussion Of Results


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Evolution Of European

Emission Standards For

Gasoline Engines (2.0 l)

Introduction I

The Pressure for Better, Cleaner Engines

  • User Demand

    • Rocketing Fuel Cost

      • 1970’s Onwards

    • Better Economy Is A Selling Point

  • Imposed Pollution Limits

    • Widespread Legislation

  • Manufacturers MUST Develop Cleaner Engines To Continue To Sell Cars!

 Fuel Injected (PFI) Engines

 GDI Engines


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Intake Port

Spark Plug

Injector

Exhaust

Air Flow

Bowl-In-Piston

Introduction II

Gasoline Direct Injection Engine: Injection Directly In The Engine Cylinder

  • Better Control Over Injection

  • Less Heat Losses

  • Lower Consumption

  • Reduced Emissions

  • Achieved By Concentrating FuelAround The Spark Plug

    • Complex Geometry

    • Complex Air Flow

    • Complex Air / Fuel Mixing

 Stratified Mixture


Lif technique

excited electronic state

Rotational

vibrational

transitions

LI Emission

Fluorescence

Quenching (losses)

Absorption

(Colour shift)

ground electronic state

Excited molecule (Tracer)

Laser light

Fluorescence

LIF Technique


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Qualitative LIF

Shows Relative Distribution At A Particular Piston Position, Or Crank Angle (CA)

Why Quantitative LIF?

  • Quantitative LIF

  • Shows Absolute Distribution At Any Engine Position

  • Gives Actual Fuel Concentration

  • Allows Comparison Between Crank Angles

  • Allows Comparison Between Experiments

  • No Comparison Between Crank Angles

  • No Comparison Between Experiments


Optical set up i

Optical Set-up I

Lens-coupled gated image intensifier

Beam dump

532nm ‘filter’

CooledCamera

motor

Schott filter

PC

Engine withquartz annulus

Sheet forming optics

Laser Nd:YAG, 266nm

Coated mirror(+ beam monitortap)

Shutter


Optical set up ii

Optical Set-up II


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Calibration Strategy

 Best Practice So Far: Measure Of T & P Dependency In A Pressure Vessel, BUT…

Must Compensate For Dependence Of Fluorescence On T & P

  • Optical Set-up Different From The One Of The Experiment

  • Unrealistic, As T & P Varies Spatially In The Engine!

In-Cylinder Calibration

  • Same Optical Set-up

  • No Need To Measure P & T Provided Calibration And Experimental Images Are Acquired At The Same Crank Angle


Calibration loop

Exhaust

Insulation layer

2’’ ID Pipe

Heating tape

Ball valve

Injection hole

Evaporation crucible

Intake plenum

Intake air

Ball valve

Engine

Calibration Loop


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Choice of Tracer

Characteristics Sought For The Tracer

  • Absorption Wavelength Achievable With A Laser

  • Enough Fluorescence To Be Detectable With Decent SNR

  • Low Sensitivity To Quenching

  • Similarity To Fuel In Term Of Physical And Vaporisation Properties

  • Non-Hazardous!


Lif tracer possibilities

LIF Tracer Possibilities


Tracer optimisation i

Crank

Angles

What Is

Equivalence

Ratio?

Tracer Optimisation I

Test With Pure Acetone  Saturation


Tracer optimisation ii

1600

1400

1200

100CA

1000

180CA

280CA

Fluorescence Intensity (a.u)

800

300CA

600

400

200

0

100%

90%

80%

70%

60%

50%

40%

30%

20%

10%

0%

Acetone Concentration

Tracer Optimisation II

Test With Various Acetone Concentrations In Iso-Octane  Optimum Between 2 And 10%


Calibration process overview

Calibration Process Overview

  • Engine Motored In Closed-Loop Mode

    • Calibration Images Acquired (For Each CA And Equivalence Ratio) And Processed To Extract Average Intensity

    • Average Intensities Plotted And Piece-Wise Linear Fitted

    • Calibration Look-Up-Table (LUT) Generated

  • Engine Motored In Normal Mode

    • Fuel Mixing Experiments Performed & Images Acquired

    • (Error Images Derived, At Each CA, Mid-Term, BUT In Closed Loop Mode)

    • Error Image Corresponding To The Same CA Subtracted

    • Calibration Map Applied

 Quantitative Air-to-Fuel Ratio Maps


Calibration process summary

Error Image

Raw Experiment Image

-

Calibration

Corrected Image

Calibration Process Summary

Error Subtraction

Quantitative Data


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Qualitative LIF

Shows Relative Distribution At A Particular Crank Angle

Review; - Why Quantitative LIF?

  • Quantitative LIF

  • Shows Absolute Distribution At Any Engine Position

  • Gives Actual Fuel Concentration

  • Allows Comparison Between Crank Angles

  • Allows Comparison Between Experiments

  • No Comparison Between Crank Angles

  • No Comparison Between Experiments


Quantitative results i

Quantitative Results I

Equivalence Ratio Scale:


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Quantitative Results II

  • Crank-Angle Compensation Allows Valid Fuel Mixing Studies To Be Conducted Over All Relevant Crank Angles

    • A Range of Injection Strategies (At 1500 RPM)

      • Start of Injection (SoI) At 0.5º, 30º, 60º ATDC

    • A Range of Engine Speeds (At SoI 60º ATDC)

      • 1500, 1000, 500 RPM

Uncalibrated Fluorescence

Calibrated Fluorescence; - Equivalence Ratios


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Qualitative LIF

Shows Relative Distribution At A Particular Crank Angle

Review; - Why Quantitative LIF?

  • Quantitative LIF

  • Shows Absolute Distribution At Any Engine Position

  • Gives Actual Fuel Concentration

  • Allows Comparison Between Crank Angles

  • Allows Comparison Between Experiments

  • No Comparison Between Crank Angles

  • No Comparison Between Experiments


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Quantitative Results III

Comparison With Dynamic Flow Visualisation Rig (DFVR)

  • DFVR Is A PIV Technique Using Water Seeded With Particles To Visualise Flow

  • LIF And DFVR Results Are Compared At The SAME Crank Angle

    • Good Correspondence

  • Rich Mixture (1.2<Φ<1.8) On Exhaust Side

    • Carried With Flow Out Of Bowl

  • Lean (Φ<0.5) On Intake Side

    • Dilution By High Velocity Air From Open Intake Valve

Mixture Distribution at 90º CA For A SoI At TDC, With Superimposed DFVR Air-Flow Predictions


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Injection at 30CA

Injection at TDC

Injection at 60CA

25%

10%

0%

Quantitative Results VI

  • Coefficient of Variation (CoV) Can Be Determined To Study Stability Of The Mixing Process

    • CoV Is The Image RMS Difference Values Divided By Image Mean

CoV Mixture Stability for Various Start of Injection Timings (White = >25%)

  • These Results Suggest That 30CA Is The Most Stable Scenario

  • Tests Performed On A Firing Engine Support This Evidence

    • Injection At 30CA Gives Best Emissions Performance And Minimum ‘Knock’ (Pre-ignition)


G de sercey g j awcock and m heikal university of brighton school of engineering uk

Conclusions

  • A New Strategy Has Been Developed For Calibration of LIF Measurements

    • Critical To Understanding Air-Fuel Mixing In The Cylinder

  • It Is Efficient And Realistic

    • Thanks To Calibration At Full Range Of Equivalence Ratios, Crank Angles And Engine Speeds

  • It Is Effective

    • Predictions From Motored Test Engine Give Good Agreement With Independent Investigations


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