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Q. How can oil be introduced to the crankcase interior in emergencies?

A. Practically all power plants utilizing the constant level splash or manifold supply systems in which the oil is carried in a

H

To Crank Case

From Auxiliary Tank

Fig. 126.-Hand Pump Sometimes Used to
Inject Oil to Engine Base as an Auxil-

container integral with the crankcase have a filler tube or funnel that communicates directly with the crankcase interior, through which the lubricating oil is poured. In some forms of power plant where the feed is by individual pump mechanical oilers that are set for normal operating conditions it is sometimes desirable to provide a hand operated pump of the simple plunger type that may be used to draw oil from an auxiliary tank and force it to the crankcase interior in order to help out the lubricating system under abnormal operating conditions such as speeding and long

iary to the Regular Lubrication System. stretches of low speed gear work where the engine must run fast and pull hard. A simple form of oil pump adapted for this purpose is clearly outlined at Fig. 126.

LESSON THIRTEEN

COOLING THE GASOLINE ENGINE BY AIR

Q. Why is it necessary to cool the cylinder of a gas engine? A. The rapid succession of explosions taking place in the combustion chamber, which means that temperatures higher than 2000 degrees F. exist at that point, temporarily causes the cylinder to become heated, and some method of absorbing the surplus heat must be provided.

Q. What part of the cylinder is hottest?

A. The combustion chamber or cylinder head is hotter than the rest of the cylinder because it is exposed directly to the hot gases at all times and is subject to the maximum temperature.

Q. What would be the effect on the valves, if the engine was not cooled?

A. If no provision was made for absorbing the excess heat present in the combustion chamber the inlet and exhaust valves would warp, the valve head seats would become burnt so these members could not hold compression and the stems would be liable to stick while in action.

Q. What would happen to the piston if cylinder was not cooled?

A. The piston would expand to such a point that it would have much friction in the cylinder and on account of the high temperature, which would burn away the lubricating oil, it would not be long before the piston would seize in the cylinder and perhaps become expanded by the heat to such a point that it could not move. Q. Describe the possible methods of cooling.

A.

Gas engine cylinders may be cooled by direct application of currents of air or by circulating water through a suitable jacket around the hot portions.

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Fig. 127.-Simple Air-Cooled Engine With Radiating Flanges Cast Integral With Cylinders and Air Blast for Cooling From Friction Driven Fans.

Q. What is the simplest method?

A. The system of direct cooling by air is simpler than the indirect systems of cooling by water.

Q. Will air absorb heat as readily as water?

A. The heat absorbing power of air is very much less than that of a similar volume of liquid such as water or oil.

Q. What is necessary in order to cool successfully by air? A In order to compensate for the lessened power of heat absorption possessed by air it is necessary to provide more radiating surface from which the heat can be taken and also to use rapidly moving currents of air passing over the augmented surface.

Q. Can an engine cylinder be cooled too much?

A. It is possible to cool a gas engine cylinder to such a point that the efficiency of the motor will be greatly reduced and cause it to lose power.

Q. What is the permissible temperature of an air-cooled cylinder?

A. Theoretically a cylinder may become heated to the point where the cylinder oil is not affected unduly by the heat, but in actual practice owing to the facility w th which metals may become distorted by expansion due to heat it is not recommended that temperatures exceeding 325 to 350 degrees F. be exceeded.

Q. What is the temperature of a water cooled cylinder?

A. The temperature of a water cooled cylinder must a ways remain below 212 degrees F. or the boiling point of water because if the cylinder is allowed to become hotter than this it will produce boiling and rapid evaporation of the cooling liquid.

Q. What percentage of heat is lost through the cooling system?

A. The amount of heat lost through the jacket water of the average internal combustion cylinder is given a different value by various authorities, this ranging from 40 to 55% of the total heat generated by the combustion of the gas in the cylinders.

Q. Is it desirable to reduce this heat loss?

A. If it is possible to reduce the loss of heat units one will obtain greater efficiency from a given amount of fuel because more heat is turned into power. As a rule the loss with an air cooling system is considerably less, and air-cooled engines are more efficient than the water-cooled forms.

Q. How many methods of air cooling are used?

A. There are two methods of air cooling, one depending on the radiation of heat from a largely increased surface alone, the other by convection and radiation, this involving passing a current of air at high velocity over the radiating surfaces.

Q. Describe simple radiating systems.

A. A simple radiation system is used only in some forms of stationary engines of small power. To cool by radiation it is merely

VANE

VANE

Fig. 128.-Air-Cooled Engine Utilizing Air
Blast From Blower Type Fan Flywheel.

necessary to increase the external area of the cylinder by any suitable means. The air immediately surrounding the cylinder is heated by contact with it and as it is lighter than cool air it rises and its place is taken by cooler, heavier air which in turn becomes heated and makes way for more air at a lower temperature than that surrounding the cylinder. As should be expected cooling by this method is too sluggish for general use, so the combined radiation

and convection systems are generally employed in motor vehicle service.

Q. Describe air cooling by radiation and convection.

A. A simple single cylinder air cooling engine in which the heat absorption is by radiation and convection is outlined at Fig. 127. In this power plant the cylinder is provided with radiating flanges, which are swept by air blasts set up by cooling fans placed at each side of the cylinder and driven by frictional contact with the

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