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Page:Popular Science Monthly Volume 89.djvu/276

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Lubricating Your Automobile

By Waldemar Kacmpifert

��AN automobile engine is a heat engine. The gasoline is drawn

  • " into the cylinder in the form of

vapor, which consists of about one part of gasoline to eighteen parts of air. The vapor, when it comes in contact with the electric spark, explodes, or, more properly stated, burns with flash-like rapidity. Anything that burns generates heat, and when heat is generated the sur- rounding medium expands. It is simply the expansion of the medium in the cylinder, produced by heat, that forces the piston down against the crankshaft and ultimately turns the wheels of the automobile.

The temperature at the instant of ex- plosion is between 2000 and 3000°. If it were possible to convert the heat repre- sented by that temperature into work, the automobile engine would be marvel- ously efficient. But we have not yet learned how to handle that heat. We must waste some of it by cooling sys- tems to save our automobiles from de- struction; otherwise the cylinders of a motor would be reduced to a mass of molten metal.

The lubrication of an automobile is a particularly difficult problem because the gasoline motor is so peculiar a heat engine. It is the object of lubrication to kcoji rubbing surfaces apart. But if the lubricant is a film of oil, often less than three one-thousandths of an inch thick, as in a gasoline engine, and the rubbing surfaces are very hot, how is it possible to attain that object? It seems almost incredible that lubrication is possible at all in an automobile, once the phxsical problem is stated.

A prominent automobile manufacturer has i)rought out a motor which has a speed, muler certain conditions, of 3400 rcvohilions a minute. An equal- ly jjromincnt refiner of oils has visualized these figures in a way that shows what is demanded oi a lubricating oil. During a single minute, he |)()ints out, each cylinder passes through the four cycles of intake, compression, power and ex-

��haust no less than 1700 times! More than 28 complete cycles in each cylinder, or a total of 171 complete cycles in all six cylinders within a single second! Every second the carbureter must fur- nish 171 complete charges of gas — the magneto 171 individual sparks; and 171 times in a second the temperature at the instant of combustion reaches the almost inconceivable figure of nearly 3000° Fahrenheit. During each second the six pistons, each with a stroke of 4)4 inches, travel a lineal distance of 255 feet, rubbing over a surface equiva- lent to a path 255 feet in length and lei's inches in width — a total area of 216^ square feet a second.

Friction and Lubrication

The object of lubrication is, of course, to overcome friction, and friction in automobiles is due primarily to inequal- ities which are always found in the most highly polished surface. Even the smoothest piece of glass, when viewed under the microscope, is incredibly rough, and so are the apparent h' smooth walls of a cylinder and the surfaces of the piston rings and the piston. Press two apparently smooth pieces of metal to- gether; then slide them in opposite tlirections; the two "seize" — interlock; the inequalities on the surface of the one interniesh with those of the other. Friction is produced, which means that heat is generated. Heat causes a metal to expand. The pressure on the outer surfaces does not permit of expansion outward. "Seizing" results. That is why it is the function of a lubricant to keep tiic surfaces apart.

Tr\- to keep a red hot sto\e wet with <lr()ii])ing water, and you will realize the (lifhcultN' of lubricating a hot automobile motor. The greatest enemy of lubricat- ing oil is heat. Hence of two oils that which loses little lubricating value imder relatively high heat is the more suitable for automobile hibricalion. ("onsider the temperature to which oil is sub- jected in a motor and you will under-

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