Abstract

Delivery of a lubricant as a vapor mixed with a carrier gas provides a method of controlling the delivery rate of the lubricant. Temperatures in the range of 370 to 800°C are high enough to produce a lubricating film from tricresyl phosphate [TCP] vapor delivered in nitrogen as a carrier gas. The solid film lubricant formed by this delivery system provides excellent lubrication for a four-ball wear tester run at 370 C. Deposit rates are compared for TCP vapor delivered lubrication over a temperature range using stainless steel and quartz surfaces. The deposit rate is sensitive to TCP concentration in the carrier gas. The deposit rates of the TCP decomposition products versus time are reported.

Having been demonstrated in laboratory tests, the Vapor Phase [VP] concept is being pursued for hot section lubrication of the advanced (low heat rejection) diesel engines. An advanced cylinder kit, the Separated Ring Belt [SRB] concept isolates the hot combustion area from the side-force region of a conventional piston. The SRB hot zone is treated with VP tribology.

Conceptual studies and preliminary analysis examine the potential of the VP concept for engine lubrication. A tribotester has been adapted for testing of VP under simulated engine conditions. The strategy of the advanced diesel engine VP tribology approach, current status, and future plans are reported.

LUBRICATION OF HIGH TEMPERATURE INTERFACES with liquid lubricants is generally limited by the formation of excess sludge and deposit build up from lubricant degradation. Solid film lubricants for high temperatures are limited by a lack of a replenishing mechanism. One solution to these problems is a continuous lubricant delivery system that provides only enough lubricant at any time to produce the easily sheared film necessary for good boundary lubrication without an excess build up of the lubricant.

An examination of liquid lubricant behavior in boundary lubrication shows that they react chemically with or on the bearing surface to form a viscous polar or semisolid compound (friction polymer) that provides an easily sheared film. This chemical film is the lubricant which is wiped from the solid bearing surfaces. In boundary lubrication the lubricant and bearing surfaces are heated by friction to a minimum of 340^-360 C with effective boundary lubricants (1) . Similar reactions can be caused by delivering lubricant vapor (in a carrier gas) to a hot bearing surface where the lubricant can react on or with the bearing surface. This paper describes the film-forming tendencies of TCP on several substrates heated to 500 to 800°C in a tubular oven. The TCP is evaporated into a hot nitrogen gas stream and carried to the bearing surfaces where it reacts chemically to form a solid film. In addition, the use of TCP vapors to lubricate a four-ball wear tester at 370°C using M50 tool steel balls is discussed.

The paper also presents a status report on the application of the VP concept for the lubrication of the cylinder kit of an advanced diesel engine. This includes rig simulation and single-cylinder engine tests.

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