Residual gas fraction measurement inside engine cylinder using infrared absorption method with spark-plug sensor

In this study, residual gas fraction measurements in a spark-ignition engine were carried out using an optical sensor installed in the spark plug with infrared absorption method. The residual gas fraction inside engine cylinder is proportional to the CO₂ concentration. Infrared absorption method was applied and an infrared lamp and optical filter (center wavelength: around 4.3 μm) that coincides with the absorption lines of CO₂ was used as a light source.The molar absorption coefficient of CO₂ is discussed and compared to results in the HITRAN database. The effect of water vapor absorption doesn't affect the absorption of CO₂. The absorption characteristics of CO₂ were determined in advance using a constant volume vessel. Molar absorption coefficient depends on the CO₂ concentration and ambient pressure and temperature, and wavelength of absorption line. Further experiments should be carried out for the quantitative measurements of CO₂ concentration using infrared lamp and band-pass filter. The spark plug sensor for in-situ CO₂ concentration measurement was applied to a compression-expansion machine and also to a port injected SI engine. It was possible to qualify the CO₂ concentration inside residual gas during the compression stroke using the developed optical system with new spark plug sensor both in compression-expansion machine and commercial spark-ignition engine.