Mineral Oils

Early jet engines used a petroleun based oils as lubricant. Containing no highly loaded bearings or gears, they operated at comparatively low temperatures. Bulk oil temperatures approached 200°F (90°C). The mineral lubricant, generally used, was a low pour point material having a viscosity of 2.5 as at 210°F (99°C). Later engines containing heavily loaded gears, required an oil of higher viscosity to meet the load carrying requirements. The one chosen had a viscosity of 9 as at 210°F (99°C). Mineral lubricants still employed today are used in some of the lower-powered aircraft and industrial gas-turbines.

As engine power output increased, operating temperatures rose and the resultant increase in bearing oil temperatures and gear and bearing unit loads revealed distinct shortcomings in mineral lubricants. In addition to meeting these higher operating temperature requirements, the lubricant had to remain fluid at the low temperature encountered during starting on the ground.

Aviation Synthetic Lubricants

Of the many problems facing the jet engine designer, lubrication was considered to be one of the least important. But as engine development progressed, it was quickly realized that lubrication could become a limiting factor unless improved lubricants were forthcoming. The arduous operating conditions imposed on the lubricant plus the need to achieve increasingly better engine performance, reliability and economic operation, virtually eliminated mineral-based oils, and a new type of lubricant was introduced. Developed from non-petroleum sources, these synthetic lubricants, as they are now known, have given excellent performance in both subsonic and supersonic planes over the last 30 years, and without their timely introduction, development of the jet engine could have been severely retarded. Recently developed turbofan engines of 18-20,000 1b thrust, high performance engines for the SST, the "Jumbo Jets" and high-speed military aircraft have posed further problems to the lubricant supplier. These problems have been met by developing a range of high-temperature synthetic lubricants. A number of carried out performance trials indicate that these should meet all the requirements of the jet engine designer and operator.

Exercise 15. Put all types of questions to the texts above.

Supplementary reading Active vocabulary

1.aircraft noise reduction (mitigation, abatement)	зниження рівня шуму літака
2.acid rain	кислотний дощ
3.ban	заборона
4.boundarу	кордон, межа
5.cause	причина; спричиняти
6.compliance	відповідність
7.emission	емісія, викид
8.endanger health	бути небезпечним для здоров’я
9.environmental pollution	забруднення навколишнього середовища
10.environmental protection	охорона навколишнього середовища
11.be exposed to	зазнавати впливу
12.health hazard	небезпека / ризик для здоров’я
13.hushkitted aircraft	літак, який обладнано пристроєм для зниження шуму
14.incorporate	об’єднувати, включати
15.ozone depletion	зменшення озонового шару
16.pollutant	забрудник
17.preserve investments	зберігати інвестиції
18.proliferation	розповсюдження, поширення
19.Committee for Aviation Environmental Protection (CAEP)	Комітет з питань охорони довкілля від впливу авіації
20.retrofit	модернізація (повітряного судна)
21.transition	перехід