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Abstract

Studies have been made of the effects of a varied selection of organo-silicon compounds on the combustion of a pure hydrocarbon fuel, viz. 2-methy1pentane, in the laboratory. Engine experiments have also been carried out, involving other hydrocarbons.

The Introduction outlines the various combustion phenomena associated with engine knock, and discusses different methods by which knock can be suppressed. An account is given of the environmental problems associated with the continued use, as antiknocks, of lead alkyls, which are believed to constitute a danger to health and mental development, particularly in children. Efforts to find alternative antiknock additives are described. In particular, many organic compounds which exhibit antiknock activity can be used only as blending agents which is not, at present, economical in view of the large quantities required. There is thus still a great need for research into systems with good antiknock potential and no adverse environmental or other problems. The last section in the Introduction consists of a general review of the chemistry of organosilicon compounds with emphasis on thermal and thermoxidative reactions, especially those occurring in the gas phase; this discusses in particular the role of the various transient species involved.

The Experimental Section deals with the synthetic methods used for the preparation of many of the compounds tested. It also discusses the apparatus used in this work, which was an injection system. Liquid fuel mixtures could be injected into a reaction vessel containing oxidant gases and the pressure history of the reaction was then measured by means of a pressure transducer. A CFR engine was used to determine the Research Octane Number of various systems.

The Results Section shows, in tabular form, the two-stage ignition limits found in this work as well as various associated kinetic para-meters. These limits were found to constitute a good measure of the antiknock effectiveness of these additives. Solid formation and de-position within the cylinder during experiments in a CFR engine in the presence of silicon-based additives caused unreliability in the RON results obtained. Various experiments were subsequently designed to show the validity of the assumption that ignition limit shifts were a good measure of antiknock activity.

The Discussion Section shows, by means of experiments involving the use of organic additives of known antiknock properties, in both the laboratory injection system and the CFR engine, that similar and proportional effects are obtained on the combustion of the base fuel. This indicates the validity of the use of the laboratory experimental set-up. The antiknock activity of the organosilicon compounds investigated is explained in terms of their structure and the different electron densities resulting from the presence of silicon. Whenever possible, comparisons have been made of the behaviour and structure of the silicon-based additives with those of the analogous purely organic compounds.

Publication Type:	Thesis (Doctoral)
Subjects:	Q Science Q Science > QD Chemistry
Departments:	School of Science & Technology > School of Science & Technology Doctoral Theses Doctoral Theses

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