THE EFFECTS OF VARIOUS NOZZLE HOLE CONFIGURATIONS ON DIESEL ENGINE PERFORMANCE

Abstract: Any improvement that can be done with the diesel engine to reduce emissions and fuel consumption is of importance. The aim of the studies presented in this thesis was to determine whether changes in the nozzle geometry of the fuel injection systems used in diesel engines might improve their emissions and fuel consumption. This project started with the question if elliptical or non-circular nozzle holes instead of the conventional circular designs would have any effect on emissions and fuel consumption in a heavy duty diesel engine. It was speculated that non-circular holes might increase air entrainment in the lift-off zone and thereby reduce smoke emissions. Increased air entrainment in the lift off zone would allow more of the fuel to burn under relatively lean conditions in the rich premixed zone and thus reduce soot formation. Experiments were conducted using a single cylinder engine whose emissions and fuel consumption were measured. An optical cylinder head was also designed and manufactured, and used to investigate flame propagation during combustion using fuel injectors with non-circular nozzles. The effects of varying the nozzle hole inlet geometry were also investigated by conducting experiments with single-hole axisymmetric nozzles that had been subjected to different grades of hydrogrinding. These studies were performed using a high temperature high pressure combustion chamber, and a variety of techniques were used to characterise the resulting sprays and flames. Impingement measurements were also performed to ensure that the studied nozzles produced fuel jets with the same momentum. From the impingement measurements velocity, discharge coefficient and loss of kinetic energy was calculated. Finally, the effects of changing the nozzle hole inlet geometry were investigated using a single cylinder heavy duty diesel engine. The engine’s emissions and fuel consumption were measured and an endoscope technique was used to capture images from inside the combustion chamber during the combustion sequence. Two-colour pyrometry was used to determine the soot and temperature distributions inside the cylinder from the images, and the results of this analysis were compared to the emissions data.