Modelling and prediction of the filling characteristics of modern diesel fuel injection equipment

Soteriou, Cecilia Catherine Elizabeth (1990) Modelling and prediction of the filling characteristics of modern diesel fuel injection equipment. University of Southampton, Doctoral Thesis.

Abstract

The filling systems incorporated in traditional diesel fuel injection equipment (FIE) have been either fairly simple in design, or have not been required to function under demanding conditions, such as high speed. As such, detailed theoretical investigations into their performance characteristics have been unwarranted, and computer simulations of FIE have concentrated on the high pressure injection aspects of the system. More recent developments, however, have resulted in the filling system being called upon to play an increasingly complex and critical role, and one which has a direct bearing on the performance of the engine. This is due to the development of FIE to meet the requirements of the small high speed and other high performance diesel engines, whilst complying with the more stringent emissions and noise legislation being brought into force. Special control devices have been incorporated into filling systems as a result, and at high speed, filling must be completed in less than two milliseconds. The greater demands placed on the filling system by these developments have emphasized the need for a full understanding of filling systems, which is only possible by means of a detailed, accurate mathematical model. This work describes the development of a general purpose computer simulation of diesel FIE filling systems and its experimental verification on the most complex system currently available. An example is given of how the model was used to investigate and solve an existing problem on a modern high performance system. Details are also given of how a significant improvement was made in the accuracy of an existing simulation of the injection system, as a result of the filling system investigation. Furthermore, new information is included on the flow characteristics of certain orifices peculiar to diesel FIE systems. The simulation consists of a library of modules, each of which represents an individual device or feature. The networks module simulates flow in the system of branching, merging and recirculating fuel passages and drillings, which are subject to pressure transients and cavitation. The compressible flow model adopted is one which had proved the most successful when applied to the high pressure injection side of FIE, and is based on the finite difference technique. The basic method has been considerably extended and modified in order to cope with the more topologically complex and varied configurations encountered in filling systems. An improvement in the treatment of cavitation has also been incorporated. Other modules cater for the valves, orifices, volumes, displacing elements and other components, which may be situated as required according to the configuration of the particular filling system in question.

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