Wavelength-Agile H2O Absorption Spectrometer for Thermometry of
General Combustion Gases
Laura Kranendonk and Scott T. Sanders
Introduction:
Spectral Results:
Engine Measurements:
• Absorption spectroscopy can quantitatively measure temperature, mole
fraction, and/or pressure
• HCCI is a combustion process governed by temperature, mole fraction,
and pressure
-1
Optical Frequency [cm ]
Combustion  = 0.44
Motoring
2
0.16
0
Abs.
Pressure [MPa]
4
H 2O %
4
400
-60
-30
0
CAD [aTDC]
30
60
Temperature [K]
Smoothing: Reduces noise
Differentiate: Eliminates baseline
1355
1360
0.075
50 Averages
Single Shot
0.050
1200
0.000
1340
-0.008
1340
1345
1350
1355
Wavelength [nm]
d/d Abs (Measured)
d/d Abs (Measured)
0.000
-0.004
0.002
0.000
1360
1345
-0.002
1350
1355
1360
Wavelength [nm]
-60
-30
0
30
60
0.004
Good Fit
Accuracy:
0.002
0.000
MSE = 1
1100
M1207 K
MSE = 6.82
900
-0.006
0.002
0.004
-0.002
8.0
-0.001
0.000
d/d Abs (1207 K)
0.001
0.002
1.15
7.0
700
Theory = 628 K
Measured* = 641.2 K
600
Theory = 411 K
Measured* = 416.9 K
400
MSE
5.0
MSE
800
500
1.10
6.0
4.0
3.0
M = 2.46
M = 1.25
Theory = 1026 K
Measured* = 1002.7 K
1000
-0.004
-0.004
0.000
• 50 averaged spectra (red) are better than ±
1% precision throughout engine cycle.
0.006
-0.002
d/d Abs (367 K)
1.05
300
1.00
* = 30 spectra averaged at start of shock
0
1
2
3
4
5
6
Time [ms]
2.0
1.0
500
1000
1500
Temperature [K]
2000
HITEMP
1340
1350
1360
1370
0.00
1380 1345
0.02
1350
1355
Wavelength [nm]
C
Measured + 0.015
0.01
Residual
0.00
1330
HITEMP
1340
1350
1360
Wavelength [nm]
1370
1380
• Plot A shows a measured absorption spectrum (red) taken 12o before
top dead center, and the corresponding spectrum (black) from the
HITEMP database.
800
• Single shot (grey) shows, at best, ±3%
precision, and as poor as 50% (low XH2O and
low P).
0.025
Poor fit
-0.002
0.02
• Plot C shows the smoothed, differentiated spectra. These are the plots
used to calculate temperature.
-90
0.004
0.004
-0.004
0.08
400
0.008
Temperature [K]
1350
Wavelength [nm]
B
Conclusions:
d/d Abs
Absorbance
Abs. (smoothed)
1345
Measured + 0.08
• Plot B shows differences in line widths (due to pressure) of the
measured (red) and database (black).
CAD [aTDC]
0.000
1340
 Abs. [cm]
Temperature [K]
800
1600
0.025
0.06
Wavelength [nm]
Precision:
0.050
7250
0.04
1330
1200
Calculating Temperature:
7300
0.00
• Combustion (red) and motoring (grey)
results. Pressure (top panel) was measured
with a pressure transducer. Water mole
fraction (middle) and temperature (bottom)
were calculated using absorption spectra.
0.075
A
7350
0.04
-90
0.100
7400
1600
Experimental Setup:
Measured Spectra
7450
2
0
0.100
0.12
7500
2500
0.95
1000
1100
1200
1300
Temperature [K]
1400
1500
• Absorption spectra measured from -90 to +60 CAD (0.25 CAD
resolved)
• Temperature Measurements:
– Better than 1% precision with 50 averages
– ± 2.3% accuracy to ~1000 K with 30 averages
– Single shot measurements show potential but need
improvement
• Pros:
– Quantitative measurements
– Non-invasive measurements (optical measurement, no tracer)
– Extremely simple set-up
– Can measure wide range of conditions (entire cycle if air is
humid)
• Cons:
– Line of sight average
– Requires heavy averaging
• Potential future applications include spatial tomography, multispecies concentration measurements
• Using a well defined shock tube, the
absolute accuracy was measured to be
±2.2% up to 1000K (with 30 averages).
University of Wisconsin Engine Research Center