Visible and Infrared Imaging for In-cylinder Visualization of Diesel Jet Liquid and Vapor Phases with varying Swirl Motion

Investigation of the processes that take place inside an internal combustion engine finds a powerful tool in the optical diagnostics. Different techniques have been developed for the identification of the species present in the cylinder during fuel injection and combustion. Most of the well-known techniques are very complex and sophisticated (schlieren, laser-induced fluorescence, X-rays, etc.), but recent studies have demonstrated that infrared (IR) imaging is relatively easy to apply and very effective for the investigation of these processes. In particular, it does not require an external light source or extensive use of optical components, the original fuel can be used instead of a surrogate pure one, and the number of required optical access point is reduced to just one. In this work high speed visible/IR imaging was used to undertake optical diagnostics on an internal combustion engine. A single cylinder research engine with optical access from the piston was used. A sapphire window assured the view of the combustion chamber and of the fuel injector. The engine runs an operating condition of the homologation cycle, which it consists of three injection events. Moreover, the air motion around the cylinder axis (swirl motion), which manages air-fuel mixing, is varied. The aim of this work was to make a preliminary analysis of the effect of two swirl motion rates on the liquid and the vapor phases of the fuel. A Photron SA-X2 high-speed visible camera was used to detect the liquid phase of the fuel jets, and a Telops FAST IR-2K camera with sensitivity range of 3-5 ?m was used to detection of the vapor phase. To this end, a band pass filter at 3.32 ?m was applied to the IR camera, as this wavelength is proven to be sensitive to the C-H single bond stretch absorption. This work shows that more information about fuel jets is obtained using IR imaging than visible imaging. The air motion affects the jets differently depending on the distance from the injector and the fuel phase. The fuel vapor at the jet tip is more influenced by air motion and a higher swirl level results in a better air-fuel mixing