Optical Diagnostics Applied to Internal Combustion Engines: Catalysis, Sprays and Combustion
Sammanfattning: Gasoline direct injection with spray-guided charge formation is one of the most promising concepts to reduce fuel consumption and CO2 emissions of spark ignited engines. The advantages with the system are owing to un-throttled operation and stratification of the injected fuel resulting in a globally lean combustion. In these engines, the mixture formation, which is controlled by the fuel injection system, play a crucial role for the success of the combustion event. The stratification of the fuel creates locally fuel rich areas promoting efficient soot formation, and one of the drawbacks of stratified combustion is increased engine-out soot levels. In this work optical diagnostics were applied to fuel sprays in order to investigate the overall spray formation, the internal structure and to some extent the rate of evaporation. The formation of hollow cone sprays from an outward opening injector, at conditions corresponding to start-up in stratified mode, was studied in more detail. Sprays of gasoline-ethanol blends and ethanol were compared to sprays of gasoline. The obtained sprays were highly reproducible and had large recirculation zones that were somewhat reduced for low fuel temperatures. Optical diagnostics were also applied to investigate stratified combustion inside a firing engine. The aim was to investigate the sources of soot formation at stratified combustion. The charge formation, and the OH chemiluminescence and soot luminescence of the flame were visualized from below, through a quartz window in the piston. The in-cylinder observations showed that the fuel formed a compact cloud in the centre of the cylinder with fuel rich islands. Soot was efficiently formed and also efficiently oxidized except late in the cycle. The in-cylinder observations were compared to engine out emissions. Engine-out emissions of HC, CO and NOX may be removed by oxidation or reduction promoted by a catalyst. The amount of desorbed species outside a catalyst gives information about the reaction kinetics. In this work the concentration of desorbed OH molecules, formed during the water formation reaction, was measured outside a platinum catalyst using cavity ringdown spectroscopy.
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