CHAPTER XVFUEL AND LUBRICANTS
There is greater misconception and real ignorance about gasoline than concerning any other subject or material connected with automobiles. The explosive nature of gasoline seems to act the same as gunpowder, whereas, in fact, it is entirely different.
Knowledge on this important subject is lacking, because not enough care and study has been bestowed on it to bring out the proper information. Most people know that in order to explode gasoline in an engine, air is required; but few of them stop to consider that air is also the important thing necessary to burn gasoline in the open air.
An Experiment With Gasoline.—Experiments have been made with gasoline which show better than anything else where the danger lies, and what should be avoided. A can, partly filled with gasoline, was permitted to stand for a few minutes, until some of the gasoline was allowed toevaporate. The escaping vapor of course readily ignited and burned, but no explosion followed. It burned, but the blaze was at the top only. The gasoline in the can did not burn; only the vapor which was collecting and escaping at the top.
Gasoline was next put into a half pint cream bottle, so that it was half full. The opening of such a bottle is nearly as large diametrically as the bottle itself. After allowed to stand so as to permit evaporation to take place, a lighted match was thrust down into the gasoline. While the vapor at the top burned, the gasoline extinguished the match, the reason being that there was not enough oxygen within the bottle at the region of the surface of the gasoline to make an explosive mixture, and there was not an explosive mixture formed until the vapor had issued from the mouth of the bottle, and came into contact with the surrounding atmosphere.
Air Necessary for Explosion.—The fact is, the hydro-carbon in the gasoline needs air to support combustion, and it must have at least three parts of oxygen (which means fifteen parts of air), to one part of carbon, before it can be ignited. Air, for this purpose, cannot by any possibility, find its way down into the bottle, hence it will be seen that no danger need be anticipated from this source.
The inexperienced, however, will tell you, that he knows it will explode, because he has had some experience of that kind. Let us explain what happened in these explosions, and then the difference in the conditions will be understood.
Making an Explosive Mixture.—The same bottle used with the previous experiment was then taken, and the same amount of gasoline put into it. Air was then fanned into it, and a match applied. An explosion followed, because enough air has been admitted to make an inflammable gas.
If the mouth of the bottle is large enough to permit the products of combustion to pass out, no harm results; but if the opening of the bottle is too small, then the expanding gases will shatter the bottle.
Gunpowder.—Gunpowder acts differently, for the following reasons: Enough oxygen is compounded with the gunpowder to support combustion, and when a sufficient heat is applied it requires no outside air to cause combustion. The principal constituent of gunpowder is a fuel; so with gasoline. Every fuel requires oxygen before it will burn.
Filled Tank not Explosive.—If a tank is entirely filled with gasoline, it cannot explode. It may leak, and the escaping gasoline is thus brought into contact with sufficient air to aërateit. When this burns it develops a heat; this in turn increases the temperature of the gasoline and increases the rate of evaporation, so that it now begins to issue forth in greater volume, thus adding to the intensity of the flame; and as the evaporation increases, it reaches a point where the tank openings are not large enough to permit it to escape fast enough, and an explosion follows.
Why Gasoline will not Burn Within a Closed Tank.—Now this explosion is attributed to the burning of the gasoline within the tank. Such is not the case, for the reasons stated. It will be found that the difficulty lies in allowing the tank to become filled with an explosive gas, and it is brought about in this way:
If all the gasoline is drawn from a tank, the sides of the tank will retain enough gasoline to form a heavy vapor of hydro-carbon gases. This gas is heavier than air, and, like water, will remain in the bottom. Sooner or later some of the gas will pass out, particularly the lighter portions, and air will intermingle with the gas, and it is then in a ripe condition for an explosion.
It is obvious, therefore, that the first duty is to see that there are no leaks, and when discovered, to repair immediately.
Filling Tanks Having Dried Out Gasoline.—The second, and more important care, is, to besure and not attempt to fill a tank which has been allowed to run dry, without first blowing out the vapor, if there is any danger from lights. If there is still oil in the tank when you refill, there is no danger from explosions, because the vapor within is too heavy, and requires too much air to explode.
To Extinguish Gasoline Fires.—When a fire actually takes place in a gasoline tank, do not use water in trying to extinguish it. Dry sand, or a woolen blanket will be far more serviceable. The latter should not be applied haphazard, as so many do in the excitement of the moment. Try and remember what it is that the blanket is used for. The object is to try and prevent air from reaching the flame, hence the effort should be to so arrange the blanket that air cannot reach the burning part.
Ammonia as an Extinguisher.—It is better, therefore, to place the blanket around the lower part of the tank, or below the flame itself, so as to prevent air from rushing up into the burning zone. The air coming in from above will soon be inadequate to aërate the flame, and it will be smothered.
A bottle of ammonia, and one should always be kept handy, is the best, in the absence of regular extinguishers, to kill the flame.
The lesson learned from the experiments show, that a large amount of air is necessary to make an explosive compound.
Leaks.—Leaks in tanks can be repaired temporarily, with tire cement, and patches, but as gasoline affects the rubber it should be properly soldered up at the first opportunity.
Water in gasoline is the most serious trouble. All fuel of this kind should be strained through chamois leather. This will effectually prevent water from getting in.
Lubricants.—A necessary element in gasoline engines, is a lubricant. This is as essential as the fuel itself. The object is to remove friction between the moving parts. Cylinders of engines are heated to high temperatures, and this makes wear between the parts not lubricated a most serious one.
While ordinary gasoline would be a good lubricant for some uses, it would be of no avail in the cylinders of an explosion engine, for two reasons: First, it has but little viscosity,—that is, it has no body which holds together so as to produce a film on the surface of the contacting metals.
Viscosity.—The film produced by gasoline, for instance, is very thin, but that of castor oil is very thick. The latter, therefore, has greater viscosity. Then again, gasoline, is readilyaffected by temperature. If it ignites readily, and thus loses its character as a lubricant, it can be of no service.
It is necessary, therefore, that the lubricant should not be affected or changed in its character at a low heat.
Carbonization.—Some oils when subjected to heat, or when exposed to air, will become sticky or gummy. This is one of the most serious things possible in a gas engine cylinder, because a deposit is formed which causes carbonization through the continued application of heat, resulting in the scratching of the cylinder by breaking the packing rings.
Acid in Lubricants.—In the early production of lubricants, acid was one of the elements in oils not carefully guarded against; and even now, with all the skill of the manufacturer, a small percentage will be found in most products. The presence of this produces corrosion, or pitting of the working parts. This, and the presence of foreign matter, will condemn any oil for cylinder purposes.
Composition of Lubricants.—Lubricants are composed of either animal, vegetable, or mineral matter, and they may be liquids or solids, or a combination of both.
Of the latter, graphite is the best and most widely known. It is one form of carbon, and isused in a finely-divided state, either dry, or mixed with a good lubricating oil.
Soapstone is also frequently employed and generally with a liquid lubricant.
Grease.—Grease, usually of animal origin, used in connection with graphite, makes by far the best lubricant for bearings, and for similar purposes, as it can be readily retained in the bearings.
Graphite.—On the other hand, graphite, if introduced in a cylinder with a good liquid lubricant, will, in time, fill up the pores of the metal, and thus produce a good surface, and it also protects the cylinders from carbonizing, and prevents the pistons from “Freezing” as it is called when it is caused to stick together by the heat.
The Test of Cylinder Lubricants.—For cylinders the lubricant should have a flash point of at least 375, and a fire test of 430 degrees, Fahrenheit.Flashpointhas reference to the temperature at which it will give off inflammable vapor.Fire testhas reference to the temperature at which the oil will actually ignite and burn.
Any oil, in burning, will deposit more or less carbon, because being a fuel, it must have carbon. As mineral oils will stand higher temperatures before igniting, than animal or vegetable oils they are best suited for cylinders.
Lubricating Systems.—Various systems are employed in automobiles. Thesplashsystem has the advantage of simplicity since the cylinders, as well as the bearings, are provided with a modicum of oil at every revolution of the crank, the latter, or the connecting rods, being adapted to strike the pool of oil in the bottom of the chamber.
The cylinder walls do not get the greatest benefit from this method of distributing the lubricant, as the splash is at the point when the piston reaches the lowest turn, so the lubrication on the cylinder is effectual only so far as the piston is able to draw it up or entrain it in its upward movement.
Pressure Method.—Supplementing the splash, and frequently used as the sole mean is the plan adopted by many, and known as the pressure system, which not only lubricates the bearings and cylinders, but also the other mechanism in the car, is the use of pressure, which may be exerted by gravity, or by the use of hand pumps.
Some employ the exhaust of the engine to draw up the oil. This requires ducts leading to all the parts which are adapted to take a liquid lubricant.
The Precision System.—The most positive method is that which has a pump connected with the engine, which forces the oil to all the bearings at each turn of the engine, and for that reason iscalled theprecisionsystem. It has the advantage that every bearing must get a certain portion of the lubricant, and as arrangement is made to catch and return the unused oil, it is also economical in use, although more expensive to apply.
Fig. 106. Lubricating System.
Fig. 106. Lubricating System.
Combined Force Feed and Splash System.—In Fig. 106 is illustrated one of the latest improved systems, in which there is utilized an internal force feed and a constant level splash system. In this equipment a reservoir under the crank case contains the supply of oil.
From the reservoir the lubricant is pumpedthrough a tube extending the entire length of the crank case, with lateral connections leading directly to each main bearing and to each cam shaft bearing. Any surplus to the bearings drips into small pans directly under the connecting rods.
An open end tube projects from the connecting rod, and leads to the connecting rod bearing. At each revolution of the crank shaft this tube dips into the pan and forces sufficient oil directly to the connecting rod bearing for lubrication.
There is a constant circulation of oil directly to and through every bearing in the motor, by means of a pump driven from the cam shaft. The oil pressure gauge on the dash, and the gauge on the crank case, will instantly tell what is going on. This is a very economical system.