Infrared spectroscopic concentration measurements of carbon dioxide and gaseous water in harsh environments with a fiber optical sensor by using the HITEMP database

This study presents a method for concentration measurements of carbon dioxide and gaseous water. CO2 and H2O are infrared active substances with strong overlapping absorption bands in the spectral range at about 3700 cm−1 due to the excitation of molecule vibrations. The analysis is based on the HITEMP database which was used to quantify spectral integrated transmission measurements. A fiber optical spark plug sensor with an absorption path close to the electrodes was used for in-cylinder measurements of carbon dioxide and gaseous water. The sensor system consists of a tungsten halide lamp as a broadband source and two infrared detectors with different optical bandpass filters. The developed calibration procedure was evaluated by using a heatable optical cell. Various gas compositions were analyzed at pressures up to 1800 kPa within a temperature range from 298 to 573 K under well defined conditions. Finally, the calibration procedure was adapted for in situ measurements of CO2 and H2O concentrations in the cylinder of a spark ignited (SI) engine. Concentrations were measured time resolved for motored as well as fired engine conditions. -- Highlights: • Quantitative measurement of carbon dioxide and gaseous water. • Band integrated transmission measurements in the mid-infrared spectral range at 3700 cm−1. • Quantification by using HITEMP spectral data. • Measurements with a fiber optical spark plug sensor in a combustion engine