effect of fuels and detergent oils on engine deposits The following are some extracts from a paper by R. S. Spindt and Court L. Wolfe, both of the Multiple Fellowship of Gulf Research & Development Company presented at a recent meeting of the Society of Auto mobile Engineers at Seattle. The effects of detergent oils on piston varnish are illustrated, and it is seen how the heavier concentra tions of detergent additive reduce this. The engine used for this work is shown in diagrammatic form. It was originally a two cylinder engine equipped with Chevrolet pistons and overhead valves, but for the tests one piston is replaced by a balancing assembly made from a conventional piston except that the head is cut out and the ring grooves are eliminated. Oil-laden vapours from the crankcase pass through In another test in which the balancing assembly this unit. A heavy coating of varnish builds up on was used, the lead salts on the power piston gave a both the sliding unit and the cylinder wall and also chalky deposit, while the dummy assembly had a on the head. The latter looks like a sludge but has clear orange varnish, typical of unleaded operation. properties paralleling those of th e piston varnish. Detergent Oils Remove Deposits. The results illustrated were not separate tests, they show that the use of these detergent oils reduced the amount of deposits formed by the original straight I t was supposed that the lead salts entering the crankcase have a mild polishing effect on piston skirts which tends to reduce varnish, and the dummy assembly, which is perhaps not subjected to as great an amount of lead salts, therefore retains a heavier, more varnish-like deposit. mineral oil. It must of course be remembered that these are laboratory deposits and they are not baked Effect of Individual Hydrocarbons. down as are those in service. Different fractons in petrol seem to affect the amount of varnish formation differently. A number Effect of Leaded Petrol. of compounds were evaluated in the tes t engine for their depositing characteristics. Surprisingly, mono- The other diagram shows the effect of adding olefins in general did not increase varnish but seemed tetraethyl lead to th e fuel, and in this test the engine to make the fuel cleaner. Di-isobutylene and was run with two power cylinders. The insoluble isoheptane gave little deposit. Vinyl Cyclohexane can piston varnish was increased by th e leaded fuel, bu t increase varnish considerably, as also does alipha- the soluble varnish was reduced so that the total methylstryene. deposit remained constant. Scientific LUBRICATION 29 December, 1951
Industrial Lubrication and Tribology – Emerald Publishing
Published: Dec 1, 1951
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