Precision in-cylinder H₂O vapor absorption thermometry and the associated uncertainties

Water vapor absorption spectroscopy was used to measure crank-angle resolved temperature in an internal combustion engine for two intake pressures and a range of intake temperatures from 323 to 423 K. Measurements were acquired throughout the full engine cycle, for both motored and fired operating conditions. The methodology to convert absorbance measurements to processed temperatures up to values of 650 K are detailed in this work. The sensitivity of the processed temperature to the processing parameters was analyzed and quantified. The precision of the sampled mean with 95% confidence uncertainty bounds was 0.5%, and a comparison of the temperature estimates using the band shape thermometry technique was compared to both fast-response thermocouple measurements as well as a trapped-mass thermodynamic model.