IR digital imaging for analysing in-cylinder combustion process in transparent diesel engine

The exhaust gases emitted from automobiles are one of the major sources of pollution in urban centers. Big efforts have been made to meet the strict regulations they are subjected to. However, further development of the automotive engine is necessary to meet future challenges. Recently, thermography has proved to be a powerful tool to deepen the knowledge about the chemical and physical processes that take place in automotive engine. 2D infrared (IR) chemiluminescence measurements have been performed in an optical Common Rail diesel engine in order to investigate the different processes that regulate the pollutant emission formation. The time evolution of the injected fuel, of the flames, and of the burned gases has been analyzed. Infrared images have been detected in the spectrum from 1.5 μm to 5 μm. IR imaging has allowed obtaining more information with respect to the visible imaging. In particular, it has been possible to detect the fuel vapor and the burned gas motion in the combustion chamber for a longer period with respect to visible range. Moreover, two band-pass filters have been used. One filter is at 3.9 μm, a wavelength where liquid phase has high reflectance. Using this, it is possible to isolate the shape of the injected liquid fuel from the hot gases in the combustion chamber. The second filter is at 4.2 μm, it is the wavelength where carbon dioxide (CO₂) emits. The mitigation of CO₂ is mandatory by the European committee in order to improve the engine efficiency. CO₂ evolution in the available volume during several combustion phases has been detected: the CO₂ that enters during the aspiration phase, the spatial distribution of the CO₂ that forms during the combustion phase, and, finally, the CO₂ in the burned gases cloud that moves toward the exhaust valves. The results obtained suggest IR diagnostics as useful tool for engine control.