Principles of Engine Lubrication AVI A-1065 PDF

Principles of Engine Lubrication AVIA-1065 1 Principles of Engine Lubrication Principles of Engine Lubrication the primary purpose of a lubricant is to reduce friction between moving parts liquid lubricants or oils are used universally in aircraft engine...

Principles of Engine Lubrication AVIA-1065 1 Principles of Engine Lubrication Principles of Engine Lubrication the primary purpose of a lubricant is to reduce friction between moving parts liquid lubricants or oils are used universally in aircraft engines because they can be circulated readily in theory, fluid lubrication is based on the actual separation of the surfaces so that no metal-to-metal contact occurs 2 Principles of Engine Lubrication Principles of Engine Lubrication metallic friction is replaced by the internal fluid friction of the lubricant as long as the oil film remains unbroken friction and wear are held to a minimum under ideal conditions 3 Principles of Engine 4 Lubrication Principles of Engine Lubrication oil is generally pumped throughout the engine to all areas that require lubrication overcoming the friction of the moving parts of the engine consumes energy and creates unwanted heat (Friction HP) the reduction of friction during engine operation increases the overall potential power output Principles of Engine Lubrication engines are subjected to several types of friction Types of Friction sliding friction rolling friction wiping friction 5 Principles of Engine Lubrication sliding friction occurs when one surface slides over another the surfaces are not completely flat or smooth and have microscopic defects these defects cause friction between the two moving surfaces [Figure 6-1] found in the use of plain bearings 6 Principles of Engine Lubrication rolling friction occurs when a roller or sphere rolls over another surface such as with ball or roller bearings also referred to as antifriction bearings the amount of friction created by rolling friction is less than that created by sliding friction 7 Principles of Engine Lubrication wiping friction occurs between gear teeth pressure can vary widely loads applied to the gears can be extreme the lubricant must be able to withstand the loads 8 Principles of Engine Lubrication Functions of Engine Oil reducing friction acting as a cushion between metal parts [Figure 6-2] 9 Principles of Engine 10 Lubrication Functions of Engine Oil this cushioning effect is particularly important for such parts as: reciprocating engine crankshafts connecting rods which are subject to shock loading as the piston is pushed down on the power stroke, it applies loads between the connecting rod bearing and the crankshaft journal the load-bearing qualities of the oil must prevent the oil film from being squeezed out, causing metal-to- metal contact in the bearing Principles of Engine Lubrication Functions of Engine Oil oil cooling oil circulates through the engine it absorbs heat from the pistons and cylinder walls these components are especially dependent on the oil for cooling in reciprocating engines can account for up to 50% of the total engine cooling is an excellent medium to transfer the heat from the engine to the oil cooler 11 Principles of Engine Lubrication Functions of Engine Oil prevents leakage – the oil aids in forming a seal between the piston and the cylinder wall to prevent leakage of the gases from the combustion chamber cleaning – oils clean the engine by reducing abrasive wear by picking up foreign particles and carrying them to a filter where they are removed – the dispersant, an additive to the oil, holds the particles in suspension and allows the filter to trap them as the oil passes through the filter 12 Principles of Engine Lubrication Functions of Engine Oil prevents corrosion on the interior of the engine by leaving a coating of oil on parts when the engine is shut down one of the reasons why the 13 engine should not be shut down for long periods of time is that the coating of oil preventing corrosion will not last on the parts, allowing them to rust or corrode  Rotary Gear Pump Rotary Vane Pump https://youtu.be/plxFeszbQD0 ( pumps) 14 15  Requirements and Characteristics of AVIA-1065 Reciprocating Engine Lubricants 16 Requirements and Characteristics of Reciprocating Engine there are several Lubricants important properties that satisfactory reciprocating engine oil must possess its viscosity is most important in engine operation oil that flows slowly is viscous or has a high viscosity oil that flows freely has a low viscosity 17 Requirements and Characteristics the viscosity of oil is of Reciprocating Engine affected by temperature it was not uncommon for Lubricants earlier grades of oil to become practically solid in cold weather increasing drag making circulation almost impossible other oils may become so thin at high temperatures that the oil film is broken causing a low load carrying ability resulting in rapid wear of the moving parts https://www.youtube.com/watch?v=V5a4kP-5Jiw 18 Requirements and Characteristics of Reciprocating Engine the oil selected for aircraft Lubricants engine lubrication must be: light enough to circulate freely at cold temperatures heavy enough to provide the proper oil film at engine operating temperatures it is extremely important that only the approved grade or Society of Automotive Engineers (SAE) rating be used lubricants vary in properties no one oil is satisfactory for all engines and all operating conditions 19 Requirements and Characteristics several factors must be considered in determining of Reciprocating Engine the proper grade of oil to use in an engine Lubricants the most important of which are: operating load rotational speeds operating temperatures the grade of the lubricating oil to be used is determined by: the operating conditions to be met in 20 the various types of engines  the oil used in aircraft reciprocating engines has a relatively high viscosity required by: large engine operating clearances due to: the relatively large size of the moving parts the different materials used the different rates of expansion of the various materials high operating Requirements and Characteristics temperatures high bearing pressures of Reciprocating Engine Lubricants 21 Requirements and Characteristics of Reciprocating Engine Viscosity Lubricants commercial aviation oils are generally classified by a number an approximation of the viscosity as measured by a testing instrument called the Saybolt Universal Viscosimeter 22 Requirements and Characteristics of Reciprocating Engine Lubricants Viscosity a tube holds a specific quantity of the oil to be tested the oil is brought to an exact temperature by a liquid bath surrounding the tube the time in seconds required for exactly 60 cubic centimeters of oil to flow through an accurately calibrated orifice is recorded as a measure of the oil’s viscosity http://licensewiki.blogspot.com/2018/09/saybolt-universal-viscosity.html 23 Requirements and Characteristics of Reciprocating Engine Lubricants 24 Viscosity if actual Saybolt values were used to designate the viscosity of oil, there would probably be several hundred grades of oil to simplify the selection of oils, they are often classified under an SAE system divides all oils into seven groups (SAE 10 to 70) according to viscosity at either: 130 °F 210 °F Requirements and Characteristics of Reciprocating Engine Lubricants 25 Viscosity SAE ratings: are purely arbitrary bear no direct relationship to the Saybolt or other ratings indicate only the viscosity grade or relative viscosity – they do not indicate quality or other essential characteristics Requirements and Characteristics of Reciprocating Engine Lubricants Viscosity may be: 26 an SAE number a commercial aviation grade number an Army and Navy specification number the correlation between these grade numbering systems is shown in Figure 6-3 Requirements and Characteristics of Reciprocating Engine Lubricants 27 Viscosity the SAE scale has: eliminated some confusion in the designation of lubricating oils it must not be assumed that this specification covers all the important viscosity requirements Requirements and Characteristics of Reciprocating Engine Lubricants Viscosity letters the letter W-occasionally is included in the SAE number giving a designation such as SAE 20W indicates that the oil is satisfactory oil for winter use in cold climates in addition to meeting the viscosity requirements at 28 the testing temperature specifications EX: 20W50 (20SAE in winter, 50 SAE in Summer) Requirements and Characteristics of Reciprocating Engine Lubricants Viscosity When W is placed in front of either: the grade weight number indicates the oil is of the ashless dispersant type Ie W100 or W100 Plus 29 Viscosity 101 Requirements and Characteristics of Reciprocating Engine Lubricants 30 Viscosity Index a number that indicates the effect of temperature changes on the viscosity of the oil when oil has a low viscosity index, the oil becomes: thin at high temperatures thick at low temperatures when oil has a high viscosity index, it has small changes in viscosity over a wide temperature range (can handle a greater temperature range) Requirements and Characteristics of Reciprocating Engine Lubricants 31 Viscosity Index the best oil for most purposes is one that maintains a constant viscosity throughout temperature changes oil having a high viscosity index resists excessive thickening when the engine is subjected to cold temperatures this allows for: rapid cranking speeds during starting prompt oil circulation during initial startup resists excessive thinning when the engine is at operating temperature provides full lubrication and bearing load protection Requirements and Characteristics of Reciprocating Engine Lubricants 32 Flash Point and Fire Point determined by laboratory tests that show Flash Point-the temperature at which a liquid begins to give off ignitable vapors Fire Point-the temperature at which there are sufficient vapors to support a flame or fire established for engine oils to determine that they can withstand the high temperatures encountered in an engine Requirements and Characteristics of Reciprocating Engine Lubricants 33 Cloud Point and Pour Point also help to indicate suitability cloud point is the temperature at which oil’s wax content (normally held in solution), begins to solidify and separate into tiny crystals causing the oil to appear cloudy or hazy pour point is the lowest temperature at which oil flows or can be poured Requirements and Characteristics of Reciprocating Engine Specific Gravity comparison of the weight of Lubricants the substance to the weight of an equal volume of distilled water at a specified temperature. As an example – water weighs approximately 8 pounds to the gallon; – oil with a specific gravity of 0.9 – would weigh 7.2 pounds to the gallon 34 Requirements and Characteristics Mineral Oils of Reciprocating Engine In the early years, the Lubricants performance of aircraft piston engines was such that they could be lubricated satisfactorily by means of straight mineral oils, blended from specially selected petroleum base stocks. Oil grades 65, 80, 100, and 120 are straight mineral oils blended from selected high-viscosity index base oils 35 Requirements and Characteristics of Reciprocating Engine Lubricants 36 Straight Weight Mineral Oils These oils do not contain any additives except for very small amounts of pour point depressant, which helps improve fluidity at very low temperatures, and an anti-oxidant. This type of oil is used during the break-in period of a new aviation piston engine or those recently overhauled Requirements and Characteristics of Reciprocating Engine Lubricants 37 Mineral Oils The first additives incorporated in straight mineral piston engine oils were based on the metallic salts of barium and calcium. In most engines, the performance of these oils with respect to oxidation and thermal stability was excellent, but the combustion chambers of the majority of engines could not tolerate the presence of the ash deposits derived from these metal-containing additives. Requirements Mineral Oils and To overcome the disadvantages of harmful Characteristics combustion chamber deposits, a nonmetallic of (i.e., non-ash forming, polymeric) additive Reciprocating was developed that was incorporated in blends of selected mineral oil base stocks Engine W oils are of the ashless type and are still in Lubricants use The ashless dispersant grades contain additives, one of which has a viscosity stabilizing effect that reduces the tendency of the oil to thin out at high oil temperatures 38 and thicken at low oil temperatures Requirements and Mineral Oils Characteristics The additives in these oils extend operating of temperature range and improve cold engine Reciprocating starting and lubrication of the engine during Engine the critical warm-up period permitting flight Lubricants through wider ranges of climatic changes without the necessity of changing oil. Semi-synthetic multigrade SAE W15 W50 oil for piston engines has been in use for some time. 39 Requirements and Characteristics of Reciprocating Engine Lubricants 40 Ashless Dispersant Oils Oils W80, W100, and W120 are ashless dispersant oils specifically developed for aviation piston engines. They combine nonmetallic additives with selected high viscosity index base oils to give exceptional stability, dispersancy, and antifoaming performance. Dispersancy is the ability of the oil to hold particles in suspension until they can either be trapped by the filter or drained at the next oil change Requirements and Characteristics of Reciprocating Engine Lubricants Ashless Dispersant Oils The dispersancy additive is not a detergent and does not clean previously formed deposits from the interior of the engine. 41 Requirements and Characteristics of Reciprocating Engine Lubricants Oils Some multigrade oil is a blend of synthetic and mineral based oil semisynthetic, plus a highly effective additive package, that is added due to concern that fully synthetic oil may not have the solvency to handle the lead deposits that result from the use of leaded fuel As multigrade oil, it offers the flexibility to lubricate 42 effectively over a wider range of temperatures than monograde oils Requirements and Characteristics Oils of Reciprocating Engine Compared to monograde Lubricants oil, multigrade oil provides better cold-start protection and a stronger lubricant film (higher viscosity) at typical operating temperatures. The combination of nonmetallic, antiwear additives and selected high viscosity index mineral and synthetic base oils give exceptional stability, dispersancy, and antifoaming performance. 43 Requirements and Characteristics of Reciprocating Engine Oils Lubricants Start up can contribute up to 80 percent of normal engine wear due to lack of lubrication during the start-up cycle The more easily the oil flows to the engine’s components at start up, the less wear occurs The ashless dispersant grades are recommended for aircraft engines subjected to wide variations of ambient temperature, particularly the turbocharged series engines that require oil to activate the various turbo controllers. 44 Requirements Oils and At temperatures below 20 °F, Characteristics (-6C) preheating of the engine and oil supply tank is of normally required regardless of the type of oil used. Reciprocating Premium, semisynthetic multigrade ashless dispersant Engine oil is a special blend of a high-quality mineral oil and Lubricants synthetic hydrocarbons with an advanced additive package that has been specifically formulated for multigrade applications. The ashless antiwear additive provides exceptional wear protection for wearing 45 surfaces. Requirements and Characteristics of Reciprocating Engine Lubricants 46 Oils Many aircraft manufacturers add approved preservative lubricating oil to protect new engines from rust and corrosion at the time the aircraft leaves the factory This preservative oil should be removed at the end of the first 25 hours of operation When adding oil during the period when preservative oil is in the engine, use only aviation grade straight mineral oil as required, of the correct viscosity Requirements and Characteristics of Reciprocating Engine Lubricants 47 Oils If ashless dispersant oil is used in a new engine, or a newly overhauled engine, high oil consumption could be experienced. The additives in some of these ashless dispersant oils may retard the break in of the piston rings and cylinder walls. This condition can be avoided by the use of mineral oil until normal oil consumption is obtained, then change to the ashless dispersant oil Requirements and Characteristics of Reciprocating Engine Lubricants 48 Oils Mineral oil should also be used following the replacement of one or more cylinders or until the oil consumption has stabilized. In all cases, refer to the manufacturers’ information when oil type or time in service is being considered. https://youtu.be/Q7yuDJUcJ74 The End 49