Document K6Zz7KGLo1nK03qNVj96G5yww

Lubricating the Diesel Lubrication ol diesel engine breaks down into three parts: (I) providing an oil film between shafts and bearing surfoces at main, cronkpln end wristpin bearings (1)'performing the same job for camshaft, valve gear and var ious engine auiiliaries, end (3) main taining an oil film between piston and cylinder walls. Uhrlcotloa System*. Most engines have a pressure circulating system to lubricate main and connecting-rod bearings end many extend this system to include all camshaft, valve gear and auxiliary bearings. Diagrams at right show typical systems for large and small engines. Major difference lies In the provision for lubricating cylinder walls. In small engines, oil forced out of the ends of the crankpin bearings sprays Into the crankcase, filling It with an oil fog. This oily mist, plus oil from wristpln ends in some designs, lubri cates cylinder walls. Excess oil from various parts of the system returns to the crankcase for recirculation. In large engines, a separate mechan ical forced-feed system is usually in stalled for the cylinder walls. Number of feeds per cylinder depends on diam eter. Usually each feed connects by tubing to an individual pump cylinder In a mechanical lubricator. lubricators. A mechanical lubricator usually consists of a group of small reciprocating pumps mounted in a single casing, which serves as an oil reservoir.' The pumps supply a meas ured quantity of oil at each stroke and ere driven from the engine by an eccen tric, crank and ratchet, or gearing. Amount of oil fed by each cylinder is usually aeparately adjustable; control Is by varying pump stroke or changing position of sleeve ports, fn mast cases, a sight feed keeps oil flow visible. Oil particularly suited for cylinder lubrication may be used in the lubrica tors. Of the oil that is fed to the cylin ders, part stays on the walls, part Is burned by exposure to hot gas, and part drains away. In some cases, excess oil, with Its contaminants, is caught and drained off to waste or to a separate tank for reclaiming. In most cases, ex cess oil drains off cylinder wells and joins the oil in the crankcase. Wat ead Dry Sumps. Many engines hove what is known as a wet sump; that' is, oil is stored in the crankcase or <n a sump Integral with the crank case. Where it b desired to eliminate crankcase "fog," which may cause ex cessive cylinder wall lubrication, the dry sump arrangement b used. Thu includes a storage tank outside the engine end oil drains from the crank case os fast as it returns. Auxiliaries. The complete pressurelubrication system includes a pump, often a gear unit, driven from the en gine. In some cases an auxiliary pump, motor-driven, b also installed to sup ply lubrication before engine reaches speed and after shutdown. The system usually includes a strainer or o filter, or both. An oil cooler b frequently employed to hold oil temperature within desired limits. LUBRICATION PROBLEM It Is not too difficult to And a lubri cant to perform the work outlined above, nor to devise a satisfactory system for delivering the lubricant to the desired spots in the right amounts. The difficulty arises from the fact that conditions involved in engine op eration cause all known lubricants to deteriorate in service. Thb occurs in lu brication of most machinery; the high temperatures and pressures of diesel work make the action much faster. This also represents the difference be tween lubrication of large low-speed engines and small high-speed units. The same kinds of changes take place in each case, but in large engines they occur at a slower rate and in a much larger body o! oil. Consequently, the results, wbleh are much less evident over normal operating periods, are likely to be regarded es less critical. 0(1 Deterioration. Lubricating oUs deteriorate in service because of changes that take place in the oil itself and because o! contamination from outside sources. Let's look first at changes that occur in the oil itself. High temperatures, particularly in the piston-ring area, cause petroleum oils to crack or break down in molec ular structure. Carbonaceous end tarry products result that play a part in ring-sticking end other troubles. Oxidation also takes its toll. Com bination of petroleum hydrocarbons and oxygen forms organic acids of two general types: (1) volatile acids having low molecular weights end low boiling points, which are usually highly corro sive, and (3) acids having high mo lecular weights and high boiling points which ploy a part in formation of gums and lacquers. These oxidation products He at the root of a number of the diesel's lubri cation problems. If allowed to sufficiently concentrated, ormmu attack certain bearing raetST*** pitting and failure. Abo the?*1 with remaining ports of the oU^.? sludges. Chemically, sludge defined es precipitated oxrfW. drocorbons. Sludge deposits Iq chambers, sumps, on filter* and u ere, and in the oil cooter. Acid-reaction products are blamed by some for vambh dew on pistons, valve stems and other a ports. These hard, black film, , when oxidation products, ( oil up to a certain point, heated metal surfaces. On valv^ti vambh may cause sticking or bu and on pistons it promotes ring ttk. Outside Ceafarafaetlan. These V cation problems result from eta that take place in the oil Use! result of exposure to heat- ai Contamination from outside i__ contributes to these problems and i new ones. In the cylinder, | combustion -- ash. carbon partlclrs'a soot, unburned "heavy ends" of g fuel, and water--mix with the tube a Ash, carbon and soot help to build q ring deposits. Unbumed fuel msy b cracked or oxidised in the Mgh-tami eroture tone, making a resinous gunuo^ material that forms a binder f or carbon particles. Unbumed fuel thot finds 1 post the rings and Into the enn) dilutes the lube oil.. For every gsl of fuel burned, obout a gallon of a forms as a combustion product 1 normally passes out the exhaust a vapor but some of it may condense, particularly on the lower parts of the cylinder liner. This prevents proper wetting of surfaces by oil and in com bination with hydrogen sulphide <x sulphur dioxide may cause corrosion Woter that reaches' the crank** may couse moyonnabe-iike emulsions, which accumulate over screens sod b the cireulotory system. As water also tends to increase the activity of <* ganlc acids, It may accelerate eeft*. sion of bearings and other parts. The engine itself may form encth:' source of contamination. Metallic os*, ides, which accumulate in the Jubricrf in service, act as powerful catalys and hasten the oil's deterioration evto though present in amounts a* s*B **, fractions of 1%. Forelga Martor. Dirt and dust tO0- enter the cylinders through the ' intake system, particularly If . are In poor shape, and may enter * crankcase through the breather U * is not protected. Under operating dltions oil film on cylinder walls is . microscopic thickness and thus *** smallest dust particles have a deeotf^ 6 <2231 SOWER 2 <a o large angina, pump- uA*i mt|M lren twmp, luttt atl through itrelner and coaler to on angina header supplying ell bearings and working gam- Mala km of tetouopic pipe to re turn all from coated piston) separata, lubrication far1 rytlnder* ' sbruive action. Further contamination - may result from smell metal particles program of lubricating-oil purification, eliminate the unavoidable decomposi tion and contamination products, -08 weiring mrloett\ .taMig tbs froblera. Lubricating the maintaining the oil at or near its ..diesel is. on the evidence, a tough atdpunent Yet it is accomplished suecenfully. Howl For one thing, refiners err producing over better lubricants. These oils are refined to have suitable physical characteristics end, even more important, desired chemical character istics. Considerable research has been ' original state of effectiveness. lufco-Ofl Treatmsat. Various methods con be employed to remove some or most of the contamination that occurs in service. Treatment-may be carried out In any one of three ways, or in a combination of them'. (1) botch treat ment, (2) continuous total treatment, dene to increase the resistance of oils to oxidation. This hat been accom and (3) continuous bypass treatment In the first oil charge is withdrawn and plished to some extent by improved refining and also by adding oxidation Inhibitors. Still other additive com* Poind* may be used to produce to Oiled detergent oils, that Is, oils which feed to keep oxidation products dls- treated at one time for later replace ment Where rate of oil circulation U not rapid end with certain types of equipment. It may be possible to treat the entire charge as it circulates, but most common method Is to bypass a hned and suspended. The operator plays his part by main- lining engines and accessory equip* Blent in good mechanical condition, portion of flow (obout 10% say) to treating equipment With this arrange ment, condition of a portion of the oil is being restored continuously, which dw* reducing contamination by blowV. condensation and foreign matter. keeps total amount of impurities below danger point and avoids need for large Treatfsq Methods. Space does not permit discussing here the many types q( treating equipment available (see Power, July 1945, pp 88-90, Aug pp 92*94; Jan 1941, pp 70*73, Feb pp 6062). Mechanical methods include centritugfng and various forms of filtra tion. Centrifuging separates out tmpur. itiei by differences in specific gravity. In mechanical filters the oil Is passed through materials such es cotton or gloss fiber, cellulose, yam or waste, or between closely stacked disks; foreign particles are caught and held. Another class ol lube-oil purifiers uses adaorbeni materials to filter out foreign matter and to adsorb adds end oxidation products. Medium may be Fuller's earth, bauxite, bentonite, or combinations of these materials. Mechanical filtration is usually em ployed on a continuous bypass ar rangement; centrifuging ami purifica tion with adsorbents may be handled either on a batch or bypass basis. There Is a tendency to combine treating meth ods to obtain best features of each. 'kUy, he cao, by adopting a sound treating facilities. (223) V **** AAporirl l1ll7M40