Jackson, Simon David; (1997) Mixture preparation process in SI engines with particular reference to an air-assisted fuel vaporiser. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis describes the problems encountered during cold-start operation of a SI engine and details an alternative fuelling system designed to reduce unburned hydrocarbon emissions throughout this period. The system is able to produce vaporised fuel during start-up conditions by incorporating an electrical heating element which may be switched off once the catalyst has reached its light-off temperature. Air assistance has been incorporated into the design to ensure good atomisation of the liquid fuel when operating with the heating element disabled. Characterisation of the liquid fuel spray and measurement of the efficiency of the heating element was performed. The device was tested to characterise its performance and applied to an engine to provide comparison of UHC emissions during a cold-start with the standard fuel system. Further tests were performed to analyse the vapour flow of fuel within the intake port of a running engine of the device in both air atomisation and fuel vaporisation modes and compared with that obtained from the standard pintle injector. Two major factors influence the mixture preparation, namely backflow and port temperature. These effects were isolated and removed for the final test programme by the use of a pulsating flow rig. A means of procuring a pressurised air supply for the device instead of relying on an atmospheric bleed was also investigated. The method was to provide a tapping into the combustion chamber via a restriction so to control the bleed rate. The tests identified reduction of engine out UHC emissions during the cold-start period of operation. Results from intake port FRFID tests indicated the vapour flow of fuel within the port, clarified the mixture preparation process and identified the major contributors to fuel vapour formation and movement. The cylinder pressure tapping experiments revealed the possibilities and benefits of such an arrangement.

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