Laura Kranendonk and Scott T. Sanders Wavelength-Agile H2O Absorption Spectrometer for Thermometry of General Combustion Gases Laura Kranendonk and Scott T. Sanders Spectral Results: Introduction: 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 Experimental Setup: 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. Plot A shows a measured absorption spectrum (red) taken 12o before top dead center, and the corresponding spectrum (black) from the HITEMP database. Plot B shows differences in line widths (due to pressure) of the measured (red) and database (black). Plot C shows the smoothed, differentiated spectra. These are the plots used to calculate temperature. Precision: Calculating Temperature: Conclusions: 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, multi-species concentration measurements Single shot (grey) shows, at best, ±3% precision, and as poor as 50% (low XH2O and low P). 50 averaged spectra (red) are better than ± 1% precision throughout engine cycle. Accuracy: Using a well defined shock tube, the absolute accuracy was measured to be ±2.2% up to 1000K (with 30 averages).