CHAPTER XCOOLING SYSTEMS
Proper cooling is a necessary feature of all gasoline motors, otherwise the intense heat of the burning fuel would expand the pistons to such an extent as to prevent their free motion in the cylinders, as well as destroy the spark plugs, injure the springs, and make lubrication a difficult matter, if not impossible, by burning up the oil.
Air Cooling.—Cooling was originally obtained by using air, which was blown against the cylinders; but this was not generally developed to a satisfactory degree except for small motors.
Air does not take up heat readily, whereas water is the greatest absorbent known, and in the primary stages of the art water was objected to on account of its weight, and for the further reason that the jacketing of the engine was considered a needless expense.
One of the best known devices to increase the cooling capacity with air cooling, and now largely used in motorcycles, is to provide the cylinderswith a plurality of thin broad ribs, annularly-disposed, as shown in Fig. 72a.
Fig. 72a. Increasing Cooling Area.
Fig. 72a. Increasing Cooling Area.
Air-Cooling Devices.—A highly-heated metallic surface actually repels such a subtile fluid as air, hence it is necessary to supply the cylinders with a blast of air, and also provide a greater cooling area, so that if the ribs themselves can be cooled, the temperature will be decreased in proportion to the enlarged surface thus provided.
In using water this artifice is not necessary, because it will absorb heat instantly along the surface in contact with the metal, and quickly change the heated particles in favor of the cooler portions.
Water Cooling.—While heat will cause a circulation of water in a definite direction, for the foregoing reason, it has been found that, in practice, it is more practical to keep up the movement by mechanical means.
This is done by a pump placed in the line of the circulating pipe, and usually so arranged that the cold, or coldest, water is forced into the circulating area around the cylinders.
Fig. 73. Movement of Heated Water.
Fig. 73. Movement of Heated Water.
Gravity System.—The natural circulation is founded on the principle of the well known law, that heated water will flow upwardly, hence, if a cylinder, such as A, Fig. 73, which has a water jacket around it, has its lower end connected by a pipe B, from the bottom of a water reservoir C, and the upper end of the jacket is provided with a pipe connection D, with the upper part of the reservoir, the water will flow from the bottom of the reservoir to the jacket, and from the top of the jacket to the reservoir, in the direction of the arrows.
Locating the Reservoir.—This flow would bematerially increased if the reservoir should be located a considerable distance above the jacket. But in an automobile it would be difficult to use an elevated reservoir, and, furthermore, as means must be provided to cool the water, such disposition of the reservoir would be still more impracticable.
Fig. 74. Cooling System.
Fig. 74. Cooling System.
The area forward of the engine is the most available space for placing the water tank, and, especially for the reasons that the radiator itself may be utilized for inclosing the engine hood, and because the air, which is only partially heatedin passing through the radiator, serves to keep the space within the hood reasonably cool.
Force System of Cooling.—Under the circumstances the water should be caused to circulate by mechanical means, which, while it adds another operative element to the machinery, is nevertheless so much more effective that it is worth the care, attention and expense which are involved.
The Radiator Connection.—In Fig. 74 a radiator, engine and circulating system are connected together to show the relative arrangement of the various elements, in which the pump A is placed in the pipe line B running from the lower end of the radiator C to the manifold D at the lower end of the water jacket of the engine.
The upper end of the radiator is connected by a pipe E with the top of the jacket, and the pipes are thus so disposed as to be free of the other mechanism, and are all contained within the hood of the engine.
A fan F, suitably geared to the crane shaft of the engine, provides a means for inducing an air current through the radiator whenever the engine is running.
Radiators.—Much time and money has been spent in developing a simple and efficient type of radiator. As, of necessity, it must be made up of a multiplicity of parts, leakage is apt to occur, andwhile in the past most of the constructions depended on soldering together the various portions, it will be seen how insecure such a system of construction must be necessarily.
Construction of Radiator.—In Fig. 75, is shown a front and a sectional view of portion of a simple type, which is made up of square tubes A, their ends being fitted into square holes formed through front and rear plates B C, and the tubes are so arranged that there are small spaces D between the tubes.
Fig. 75. Radiator Type.
Fig. 75. Radiator Type.
When water enters through the inlet tube E, it fills the spaces, and being cooled moves downwardly, while the air rushing through the open-ended tubes, cools down the water over the large area thus afforded.
All radiators employ substantially the same construction, the illustration given being merely to show the principle of the device.
A drain cock G, Fig. 74 should be placed in thesystem below the radiator, in the pipe line B, so that water can be drained off from all the pipes, to prevent liability of freezing. The diagram shows the fan shaft connected and run by a belt H. This is not the best construction, as it is not a positive drive. Most cars are provided with gearing for this purpose.
Operation of Radiator.—The water is thus carried from the bottom of the radiator to the water jacket space, and from the upper end of the jacketed area to the top of the radiator, and used over again.
More or less of the water is lost by evaporation, so more must be added from time to time, and the radiator should be kept as full as possible to get the best results. If the water level falls too far below the return pipe at the top of the radiator, the area of the heating surface and the decreased quantity of water exposed to the cooling surface, are likely to cause undue heating, or vaporization.
The Pump.—A variety of pumps are used, but they are generally based on the principle of the turbine impelling system, or on centrifugal action. A type which utilizes both these principles is shown in Figs. 76 and 77, in which the former is a cross vertical section of 77 along line 1, and the latter is a central vertical section on line 2 of Fig. 76.
The device comprises a cylindrical shell A, with an inlet B, at one edge near the front wall, and an outlet C at the upper edge near the rear wall.
Pump Construction.—Within is a revoluble tubular hub D, with one end E projecting, to which power is applied. A disk partition G is secured to this hub, midway between its ends, and on each side of the partition is a pair of oppositely-projecting convolute blades, those on the inlet side, indicated by H, and the ones in the discharge side by I.
Fig. 76. Side View of Pump.Fig. 77. Section.
Fig. 76. Side View of Pump.
Fig. 76. Side View of Pump.
Fig. 77. Section.
Fig. 77. Section.
It will be noticed that the blades H on the intake side are so disposed that their concave surfaces are on the advance sides while those in the discharge end of the shell have their convex faces in the retreating side.
Action of Pump.—The hub has inlet ports J below each blade, and discharge ports K between each of the blades I. When rotating the points of the blades H catch the water at the inlet and drive it inwardly through the ports J, from which it passes through the hub to the ports K, and is then violently thrown by centrifugal motion, and by the action of the blades I to the discharge opening C.
Should the pump cease working there is always a free passage way for the natural circulation of water through the pump.