Transcript Toward a calibrated LIF image acquisition

OSAV’2004 International Topical Meeting
s
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
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
Introduction I
The Pressure for Better, Cleaner Engines
User Demand
European Emission Standards for Gasoline Engines (2.0ℓ)
• Rocketing Fuel Cost
Evolution Of European
Emission Standards For
Gasoline Engines (2.0 l)
100
• 1970’s Onwards
90
80
• Better Economy Is A
Selling Point
Percentage of Reduction
70
60
50
40
Imposed Pollution Limits
30
20
• Widespread Legislation
• Manufacturers MUST
Develop Cleaner Engines
To Continue To Sell Cars!
10
NOx
0
HC
1983
1988
 Fuel Injected (PFI) Engines
CO
1991 (Euro I)
1996 (Euro II)
Year
2000 (Euro III)
2005 (Euro IV)
 GDI Engines
Pollutant
Introduction II
Gasoline Direct Injection Engine: Injection Directly In The Engine
Cylinder
• Better Control Over Injection
• Less Heat Losses
Intake Port
• Lower Consumption
• Reduced Emissions
Spark Plug
Injector
Exhaust
Achieved By Concentrating Fuel
Around The Spark Plug
• Complex Geometry
• Complex Air Flow
Air Flow
Bowl-In-Piston
• Complex Air / Fuel Mixing
 Stratified Mixture
LIF Technique
ground electronic state
Excited molecule (Tracer)
Quenching
(losses)
Fluorescence
LI Emission
Absorption
excited electronic state
Rotational
vibrational
transitions
(Colour shift)
Why Quantitative LIF?
Qualitative LIF
Quantitative LIF
Shows Relative Distribution At
A Particular Piston Position, Or
Crank Angle (CA)
Shows Absolute Distribution
At Any Engine Position
• No Comparison Between
Crank Angles
• No Comparison Between
Experiments
• Gives Actual Fuel
Concentration
• Allows Comparison Between
Crank Angles
• Allows Comparison Between
Experiments
Optical Set-up I
Lens-coupled
gated image
intensifier
532nm ‘filter’
Beam dump
Cooled
Camera
PC
motor
Schott filter
Sheet
forming
optics
Laser Nd:YAG, 266nm
Shutter
Engine with
quartz
annulus
Coated mirror
(+ beam monitor
tap)
Optical Set-up II
Calibration Strategy
Must Compensate For Dependence Of Fluorescence On T & P
 Best Practice So Far: Measure Of T & P Dependency
In A Pressure Vessel, BUT…
• 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
2’’ ID Pipe
Exhaust
Insulation layer
Heating tape
Ball valve
Injection hole
Evaporation
crucible
Intake
plenum
Intake air
Ball valve
Engine
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
Fuel or Tracer
Absorption (nm)
Emission (nm)
Boiling Point (ºC)
Gasoline
240-300
330
Various
Iso-octane
Non fluorescing
99
Biacetyl
300-360
440-480
88
DMA
240-300
335
193
Toluene
240-260
270-370
110
2-Hexanone
240-310
350-450
127
Acetone
240-340
350-450
56
3-Pentanone
240-310
350-450
102
Tracer Optimisation I
What Is
Equivalence
Ratio?
Test With Pure Acetone  Saturation
600
Fluorescence Intensity (a.u.)
500
Crank
Angles
400
80
100
180
280
300
300
200
100
0
0
0.5
1
1.5
2
2.5
Equivalence Ratio (Ø)
3
3.5
4
Tracer Optimisation II
Test With Various Acetone Concentrations In Iso-Octane
 Optimum Between 2 And 10%
Fluorescence Intensity (a.u)
1600
1400
1200
1000
800
100CA
180CA
280CA
300CA
600
400
200
0
100%
90%
80%
70%
60%
50%
40%
Acetone Concentration
30%
20%
10%
0%
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
-
Error Subtraction
Calibration
Corrected Image
Quantitative Data
Review; - Why Quantitative LIF?
Qualitative LIF
Quantitative LIF
Shows Relative Distribution
At A Particular Crank Angle
Shows Absolute Distribution
At Any Engine Position
• No Comparison Between
Crank Angles
• No Comparison Between
Experiments
• Gives Actual Fuel
Concentration
• Allows Comparison Between
Crank Angles
• Allows Comparison Between
Experiments
Quantitative Results I
Equivalence Ratio Scale:
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
Average equivalence ratio
700
3.5
600
3
500
1500-.5-61
1500-30-61
400
1500-60-61
1000-60-45
500-60-20
300
2.5
equivalence ratio
average fluorescence (a.u.)
800
1500-.5-61
2
1500-60-61
1.5
1000-60-45
500-60-20
200
1
100
0.5
0
1500-30-61
0
50
100
150
200
250
300
350
CA
Uncalibrated Fluorescence
50
100
150
200
250
300
350
CA
Calibrated Fluorescence; Equivalence Ratios
Review; - Why Quantitative LIF?
Qualitative LIF
Quantitative LIF
Shows Relative Distribution
At A Particular Crank Angle
Shows Absolute Distribution
At Any Engine Position
• No Comparison Between
Crank Angles
• No Comparison Between
Experiments
• Gives Actual Fuel
Concentration
• Allows Comparison Between
Crank Angles
• Allows Comparison Between
Experiments
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
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
Injection at TDC
Injection at 30CA
Injection at 60CA
25%
10%
0%
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)
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