City Research Online

Abstract

Engine manufacturers have acknowledged that in order to meet future strict emission regulations, greater optimisation of the combustion process is necessary. They are also aware that in a direct injection diesel engine, the Fuel Injection Equipment (FIE) plays the most critical role in the combustion efficiency and the formation of exhaust pollutants. In fact, the engine torque curve, fuel consumption, smoke, noise and exhaust emissions are all determined by the quantity and manner in which the fuel is injected into the engine cylinder. In modern high speed diesel engine applications, it is the inwardly-opening needle valve which fulfils this purpose. Its location, being situated within the tip of a fuel injector nozzle, ensures that the needle valve is the ultimate link between the FIE and the combustion process. This arguably makes this valve the single most important component within the whole fuel injection system, or in other words, the most important piece of the puzzle.

This thesis details a series of experimental projects which were carried out to study the internal flow inside some common types of valves found within diesel FIE. Although primarily focusing on the needle valve design, both ball and cone check valves were also considered. The typical approach of visualising the internal flow structure involved the use of enlarged transparent models and a refractive index matched working fluid. Laser Light sheet illumination and Particle Image Velocimetry techniques were adopted to provide qualitative and quantitative analysis of the internal flow structure within the aforementioned types of valves. In the case of the needle valve, two reported flow phenomena, the ‘flow transition’ and the ‘flow overshoot’ were confirmed to occur within the nozzle sac, whilst a third previously unknown flow structure, the ‘reverse overshoot’ was exposed. PIV analysis has quantified flow structures within the injection holes and these have been associated with vortical structures known to exist within the emerging spray plumes. Additional observations were made of the growth of the separated region and the influence of hole entry cavitation on the bulk flow within the injection hole. In the case of an un-sprung ball check valve, a novel design of lift stop was put forward and found during steady-state flow to improve the operational performance and neutralise some undesirable behaviour. This effect was especially apparent at the full lift condition.

It is anticipated that knowledge gained and described within this thesis will have commercial value to assist with design optimisation of future FIE components and for the validation of simulation data, in particular with regard analysis of the flow within the injection hole.

Publication Type:	Thesis (Doctoral)
Subjects:	T Technology > TA Engineering (General). Civil engineering (General)
Departments:	Doctoral Theses School of Science & Technology > Engineering School of Science & Technology > School of Science & Technology Doctoral Theses

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