Gas temperature and boundary layer thickness measurements of an inert mixture using filtered broadband natural emission of species at Rapid Compression Machine conditions (Part II)

Abstract Our understanding of the combustion process is hindered by the boundary layer at the optical access. To be detected by the camera, the infrared emission of the mixture (or the laser) should pass the boundary layer at the window of the combustion system. Regardless of the type of experimental techniques used (either the laser or natural emission of the species), part of the emission could be absorbed by the boundary layer due to its low temperature. Hence, the measured data includes some uncertainty and errors due to the boundary-layer absorption and its thickness (it reduces the optical length), which have not yet been quantified due to the unavailability of the boundary layer thickness, especially during a transient process such as engine compression stroke. A new methodology was used to measure the gas mixture temperature and boundary layer thickness using the Rapid Compression Machine (RCM). The methodology is based on filtering and measuring the infrared natural emission of the species at two different band-pass wavelength ranges. The new methodology was applied to measure the gas temperature and boundary layer thickness by measuring the filtered infrared emission of methane, carbon monoxide and carbon dioxide at two compressed gas pressures and two compressed gas temperatures in this work. The measured and modeled gas temperatures were compared during the post compression. An excellent agreement within 1% between the measured and modeled gas temperatures were reached at all of the studied conditions.