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Diesel and Petrol Engine Lubrication
Published in W. S. Robertson, Lubrication in Practice, 2019
As discussed earlier, the lubricant in the combustion zone has to work in a very hostile environment giving rise to severe oxidative attacks. This is particularly true in the piston ring zone area where the first ring groove temperatures can easily reach 250 °C. This gives rise to acids, which promote corrosion of engine parts, and insoluble polymeric materials, which promote piston deposits. Anti-oxidants help to combat both these effects. Detergent-dispersants keep the insoluble products in suspension in the oil and thus prevent the formation of deposits in critical engine parts. The detergents with high basicity help in minimising corrosive wear. Anti-wear additives help in reducing mechanical wear of heavily loaded components, such as piston rings/cylinder liners and valve trains. Viscosity index improvers impart suitable viscosity characteristics, particularly important in automative petrol and diesel engines for cold starting. Other additives are added to improve low-temperature fluidity and foaming characteristics of the lubricating oils.
Hydraulic Fluids and Fluid-Handling Components
Published in Qin Zhang, Basics of Hydraulic Systems, 2019
Irrelevant to its viscosity, the lubricity of a hydraulic fluid is a special property used to measure the antiwear performance of the fluid. The pump is the critical dynamic element in any hydraulic system, and each pump type has different requirements for wear protection. Compared to piston pumps, vane and gear pumps require more antiwear protection because they operate with inherent metal-to-metal contact. As stated in Section 6.1.1, an ideal fluid should be able to form a full film between two facing surfaces of all motion pairs. Normally, most hydraulic fluids require use of some special additives to improve their antiwear performance, especially for the water-based fluids. The most frequently used antiwear additive is probably zinc dithiophosphate (ZDP). However, the ashless antiwear hydraulic fluids have become a popular means of reducing waste-treatment loads.
Long-Term Additive Trends in Aerospace Applications
Published in Leslie R. Rudnick, Lubricant Additives, 2017
Carl E. Snyder, Lois J. Gschwender, Shashi Kant Sharma
The most important additive for a space lubricant is an antiwear additive [7]. Spacecraft mechanisms generally operate on a very small quantity of lubricant. With lubricant depletion due primarily to evaporation or lubricant creep, the lubricated components experience a higher degree of boundary lubrication. Effective antiwear additives are required for prolonged life of these components. As a general rule, perfluoropolyalkylether (PFPAE) lubricants are not used in applications where the bearing contact stress is over 100,000 psi because they may undergo tribocorrosion-induced failure. An antioxidant is often used to protect a spacecraft’s hydrocarbon oil and its antiwear additive for the time the formulation is on the earth, waiting for launch, but is not essential in space, where little oxygen is available.
The Importance of Temperature in Generating ZDDP Tribofilms Efficient at Preventing Hydrogen Permeation in Rolling Contacts
Published in Tribology Transactions, 2018
Vlad Bogdan Niste, Hiroyoshi Tanaka, Joichi Sugimura
Zinc dialkyldithiophosphates (ZDDPs) contain both sulfur and phosphorous in their molecules and are the most common antiwear additives used due to their large contact pressure range of efficient protection. Previous studies have shown that in optimum conditions of temperature, pressure, and sliding, ZDDP can generate thick films that cover the metal surface uniformly and provide competition for the decomposition of hydrogen-containing molecules (Tanaka, et al. (27)). The hydrogen content in the substrate when using ZDDP was much lower compared to the pure base oil, indicating that antiwear tribofilms can be an efficient way to prevent hydrogen embrittlement by interfering with the initial step of atomic hydrogen production (Niste, et al. (26); Tanaka, et al. (27)).