An investigation into the atomisation of emulsified fuels

Abstract

It has been recognised for a number of years that the use of water-in-oil emulsified fuels in diesel engines provides the advantages of improved engine combustion and emissions. At the present time, it is a general practice to burn W/O emulsions on shipboard propulsion diesel engines. To meet the requirements of environmental protection, there exists the possibility of using emulsified fuels on road vehicles in the future. The Department of Marine Technology of The University of Newcastle upon Tyne has been involved in this subject for many years, initially concentrating on the production of emulsions using surfactants, and later using mechanical devices, subsequently concentrating on the engine performance study using W/O emulsions. A multiplicity of experimental data has been obtained from a broad range of diesel engines. In the mean time, there have been many reports in this field from other investigators. It is safe to say that the research on engine performance using emulsified fuels has been comprehensive. This project is a continuation of the application of W/O emulsions in diesel engines. As there is a lack of investigation into W/O emulsion atornisation and combustion, the project alms to a). study the effect of water on fuel atomisation; b). develop the mathematical models for spray atornisation of emulsified fuels; c). investigate the phenomena concerned with the combustion and emissions observed by previous researchers. In the atornisation study of emulsified fuels, it has generally been assumed that the benefits associated with improvements in fuel atomisation are brought about by what is termed the "micro-explosions" effect as observed ill boiler/furnace applications. It has been reported that the positive effect of the micro-explosions in an engine combustion chamber exists only under limited conditions. It is therefore questionable as to whether micro-explosions actually occur in the real engine combustion chamber or not. Even if they do take place it is likely that the explosions are very weak. There is some justification to support the thesis that the perceived benefits of using emulsified fuels may be derived from sources other than micro-explosions. This thesis presents a systematic and detailed investigation on the atornisation of water-in-oil emulsified fuels, which includes the properties of W/O emulsions, atomising fundamentals, test rigs for fuel spray atomisation, mathematical model development and regression of the models, etc.. A novel, less expensive and effective method for studying fuel atomisation, is achieved by a high speed camera with a micro lens and an extensive tube, and this has successfully been used in the tests. Test results obtained from the non-combusting bomb indicate that the atornisation of emulsified fuel contributes a major part in the improvements of engine combustion and emissions in the following respects: 1). longer spray penetration; 2). Iarger spray angle; 3). larger fuel specific area/small Sauter mean diameter; 4). more air is available in the spray for combustion. Results are in good agreement with the theoretical study, and explain the mechanisms of the phenomena observed in engine tests by previous researchers. There is also a good consistency between the results and the quantitative descriptions of the models.