Infrared imaging in internal combustion engines: Advanced techniques for vapor phase visualization and CO2 detection

As the technical level of modern engines increases to fulfill the emissions requirements, the techniques used to investigate in-cylinder phenomena need to update and to improve. Optical diagnostics provide precious information about the injection and combustion processes. To visualize the fuel vapor phase, a light source with specific wavelength and energy is needed; multiple optical accesses and additional optical components are required; the techniques are susceptible to the directionality of the light source and to the fuel composition. Recently, Infrared imaging has been used to overcome some of the drawbacks of well-known optical techniques. A peculiarity of infrared imaging is the ability to detect the energy emitted by a body as electromagnetic waves, from 0.76 to 1000 ?m wavelength. This work illustrates the application of infrared imaging in a compression ignition engine for the analysis of the injection and combustion processes. The diesel fuel vapor penetration is experimentally measured and then compared to a 1d model of spray injection. Another application of IR can be the evaluation of the CO2 in the cylinder, that is a key species in the combustion process, the wavelength of 4.2 ?m, relative to the asymmetric stretch of this molecule, is investigated to follow its distribution within the cylinder for different, conventional and non-conventional combustion modes.