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

•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.

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.