Mechanism of Induction System Deposit Formation

Basic information on gasolines which cause damaging induction system (intake port and valve) deposits in ground vehicle engines was obtained. Several fuels of known depositing tendencies were charcoal filtered and the absorbant extracted with chloroform and acetone. Theadsorbant was then eluted with isopropyl alcohol in a silica gel column to obtain a concentrate. This concentrate was further subdivided in a column of magnesium silicate by a repeated elution sequence using n-pentane and methanol, obtaining a about 10-500 ppm of the fuel. The results were confirmed by both bench and engine tests. An identification of these induction system deposit precursors was made by all inclusive induction system means of elemental, nuclear magnetic resonance, infrared and mass spectral analyses. The induction system deposit precursors were found to consist primarily of long chain oxygen and nitrogen containing compounds such as amides and carboxylic acids. Representative samples of these compounds were purchased or synthesized and their induction system deposit tendencies determined. Electron spin resonance experiments were conducted which showed that the conversion of the induction system deposit precursors to induction system deposits is a free radical reaction. The induction system deposits were analyzed, and their chemical composition determined. Finally, the mechanism of induction system deposit formation in terms of its chemistry was formulated.