Transient Spray Mode Fuel Injection

Licentiate thesis, 2023

This research examines the pivotal role of transient fuel spray in internal combustion engines, primarily focusing on their influence on dual-fuel (DF) engines. In the case of dual-fuel (DF) engines functioning in a gas mode, the controlling of the primary fuel’s ignition is usually managed through the direct injection of liquid pilot fuel. The initial penetration and overall quantity of liquid pilot fuel play a significant role in influencing both the emissions released in the exhaust and the stability of combustion. Different methodologies are employed here to comprehensively explore spray characteristics from multi-
hole diesel fuel injectors within a constant-volume spray chamber. The first methodology involves using a nozzle equipped with a thimble structure to isolate a single plume. In contrast, the second approach, known as plume-blocking, entails sealing the orifices of the multi-hole nozzle to generate a single spray plume. Comparisons between these methods reveal that plume-blocking achieves superior spray penetration, although with potential limitations in its applicability to single-spray studies. Furthermore, the research highlights that a clogged nozzle displays distinct spray characteristics compared to an multi-hole (MH) nozzle, whereas a thimble-equipped nozzle yields similar outcomes to the standard MH nozzle. The blocking of orifices within the nozzle modifies the flow distribution within the sac volume, thereby influencing spray characteristics.
Another aspect of this study addresses concerns arising from inconsistent performance attributed to manufacturing variations in diesel injectors. The research carefully examines sprays from four different injectors. Experimental studies are conducted under diverse injection conditions, including varying ambient gas densities, injection pressures. Root Mean Square Error (RMSE) analysis is employed to investigate variations in spray penetration length among the injectors, providing details on both symmetric and asymmetric spray behaviours. Furthermore, the study investigates into the behaviour of transient single spray, utilizing a thimble approach, under high-pressure and high-temperature conditions. To maintain an inert and reactive atmosphere, pre-combustion of a lean hydrogen-air mixture is thoroughly achieved. The evaporating and non-reacting spray investigation takes place with the gas composition inside the chamber maintained at approximately 0% oxygen.
Spray vapour phases are captured using shadowgraph and Schlieren imaging techniques. Additionally, the study explores the reactive spray with increasing oxygen levels above 0%, employing natural luminosity and Schlieren imaging.
The conditions include a temperature range between 400 and 1000 K and fuel injection pressures ranging from 1700 to 2100 bar, resulting in simulated mixture densities ranging from approximately 14.62 to 27.69 kg/m3. The study emphasizes the considerable effects that temperature, density, and injection pressure have on the characteristics of these sprays.