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Title: A fundamental investigation of microflow and atomisation processes in automotive injectors
Author: Khoo, Yong Chuan
Awarding Body: Loughborough University
Current Institution: Loughborough University
Date of Award: 2005
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Recent developments in automotive engines have been directed towards the reduction of engine emissions in order to minimise their effect on the environment. A major part of this advancement has been the improvement of new direct injection injectors providing improved atomisation and better control of the fuel delivery into the combustion chamber. To aid the injector design process, it is vital to understand the fundamental fluid dynamic processes controlling atomisation of high-pressure fluids in Direct Injection injectors. The research effort is directed towards the ability to link changes to the internal nozzle geometry and flow field to the external atomisation processes. This thesis presents a detailed laser diagnostic investigation of Diesel and gasoline direct injectors for automotive applications. There is a need to increase our understanding of injector flow processes occurring both internally and externally to a high-pressure fuel atomiser and the physical phenomena in generating atomised fuel in the combustion chamber. The characterisation of Diesel injector flow was achieved by the use of series of real-sized, optically accessible sapphire Diesel injectors, capable of operating at realistic driving pressures through orifice nozzles of 0.15 mm and 0.3 mm diameter. High-speed, laser-illuminated flow visualisation was used to study the effect of injector geometry on the internal flow field and the nearfield external spray structure. Data in this thesis shows that operating an injector with a counterbore provides a methodology for controlling spray angle. The study of gasoline injectors was to develop and apply innovative measurement techniques, using a series of real-sized (1 mm diameter) optical nozzles, to provide data to link the internal flow structure to the external spray development. The investigation of non-swirl flow with sharp-edged inlets nozzle showed that cavitation completely controls the flow development. Fluorescent Particle Image Velocimetry (FPIV) experiments on all chamfered inlet nozzles (30°, 45° and 60°) showed that the total velocity increased linearly with driving pressure. High-speed flow visualisation study showed that high-pressure swirl injectors generate tapered aircore in the 30° and 45° chamfered inlet orifice and parallel aircores for 60° chamfered inlet orifices. The results also showed that the film thickness was dependent of driving pressure and nozzle geometry. Application of fluorescent particle image velocimetry (FPIV) was used to provide results for internal flow velocity field for the full range of injector geometries studied. A semi-empirical relationship was used and the empirical constants was modified to fit the current experimental results. For the final optical diagnostic tool, phase Doppler anemometry (PDA) was used to provide profiles of particle size in the external spray. Examples of particle size results were shown that matched findings presented in the literature.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available