Fig. 11.-Outlining the Two Possible Systems of Water Cooling. At Top, Thermo-Syphon or Natural Flow System of Chalmers, 30 Power Plant. Below It, the Pump Circulation System of the Dodge Brothers Motor Car is Shown.

through a pipe to the lower portion of the water jackets of the cylinder. It becomes heated as it passes around the cylinder walls and combustion chambers and the hot water passes out

of the top of the water jacket to the upper portion of the radiator. Here it is divided in thin streams by the many tubes and directed against comparatively cool metal walls, which abstract the heat from the water. As it becomes cooler it falls to the bottom of the radiator because its weight increases as the temperature becomes lower and also because of the pressure back of it. By the time it reaches the lower tank of the radiator it has been cooled sufficiently so that it may be again passed around the cylinders of the motor.

The cooling system depicted at the top of Fig. 11 is one that has demonstrated its worth conclusively in practice and is somewhat simpler than the forms in which a pump is used to maintain circulation. With this method, the fact that water becomes lighter as its temperature becomes higher is taken advantage of in securing circulation around the cylinders. The top of the water jacket of the cylinders is attached to the center of the radiator, while the pipe leading from the bottom of that member is connected to a motor inlet elbow which supplies cool water to the bottom of the cylinder jacket. With such a system it is imperative that the radiator be carried at such a height that the cool water will flow to the water spaces around the cylinders by gravity. As the water becomes heated by contact with the hot cylinder and combustion chamber walls it rises to the top of the water jackets, flows to the cooler, where enough of the heat is absorbed to cause it to become sensibly greater in weight. As the water becomes cooler it falls to the bottom of the radiator and it is again supplied to the water jacket. The circulation is entirely automatic and continues as long as there is a difference in temperature between the liquid in the water spaces of the engine jacket and that in the cooler.

Carburetion System.-There is no appliance that has more influence upon the efficiency of the internal combustion motor than the carburetor or vaporizer which supplies the explosive gas to the cylinders. It is only in recent years that engineers have realized the importance of using carburetors that are effi cient and that are so strongly made that there will be little liability of derangement. As the power obtained from the gas

engine depends upon the explosion of fuel and air mixture in the cylinders, it is evident that if the gas supplied does not have the proper proportions of elements to insure rapid combustion the efficiency of the engine will be low. When a gas engine is used in a stationary installation it is possible to use ordinary illuminating or natural gas for fuel, but when this

Fig. 12.-The Fuel System of the Overland Model 85 Cars is Typical of Standard 1917 Practice. The Interior Construction of the Vacuum Tank and the Main Fuel Container are Shown in Detail.

prime mover is applied to automobile or marine service it is evident that considerable difficulty would be experienced in carrying enough compressed coal gas to supply the engine for even a very short trip. Fortunately, the development of the internal combustion motor was not delayed by the lack of suitable fuel.

Engineers were familiar with the properties of certain liquids which gave off vapors that could be mixed with air to form an explosive gas which burned very well in engine cylinders. A small quantity of such liquids would suffice for a very satisfactory period of operation. The problem to be solved before these liquids could be applied in a practical manner was to evolve suitable apparatus for vaporizing them without waste. Among the liquids that can be combined with air and burned, gasoline is the most common and is the fuel utilized by the majority of internal combustion engines employed in self-propelled conveyances. The problem of gasoline storage and method of supplying the carburetor is one that is determined solely by design of the car. While the object of designers should be to supply the fuel to the carburetor by as simple means as possible, the fuel supply system of some cars is quite complex. The first point to consider is the location of the gasoline tank. This depends upon the amount of fuel needed and the space available in the car.

A very simple and compact fuel supply system is where the tank is placed in the motor compartment or under the cowl. The power plant in such cars is usually an engine of low power and correspondingly low fuel consumption. As it does not require much gasoline to run a small engine one can obtain a satisfactory touring radius on one filling of a comparatively small tank. When the fuel container is suspended near the dashboard and placed immediately back of and above the engine cylinders, the carburetor may be joined to the tank by a short piece of copper tubing. This is the simplest possible form of fuel supply system.

The old method of supplying gasoline to the carburetor when the tank was carried so low that the fuel would not flow by its own weight was to pump air or gas into the supply tank and displace the gasoline by its pressure, but now a vacuum feed tank is used. From the main supply tank the fuel goes to a small auxiliary tank carried on the dash of the power plant compartment. A short pipe connects this small container with the carburetor, and as this auxiliary tank is higher than the mixing device the fuel will flow to the carburetor by gravity.

If gasoline under pressure was fed directly to the carburetor it might result in an oversupply of fuel because there might exist pressure enough to force the gasoline into the float chamber because the shut-off needle valve would not seat positively. The auxiliary tank, which draws fuel by engine suction from a tank at the rear, is provided with an automatic cut-off mechanism, which interrupts the fuel supply when the small container is properly filled. The various parts of such a fuel system are shown at Fig. 12.

What a Carburetor Should Do.-While it is apparent that the chief function of a carburetor device is to mix gasoline vapors with air to secure mixtures that will burn, there are a number of factors which must be considered before describing the principles of vaporizing devices. Almost any device which permits a current of air to pass over or through a volatile liquid fuel will produce a gas which will explode when compressed and ignited in the motor cylinder. Modern carburetors are not only called upon to supply certain quantities of gas, but these must deliver a mixture to the cylinders that is accurately proportioned and which will be of proper composition at all engine speeds. Flexible control of the engine is sought by varying the engine speed by regulating the supply of gas to the cylinders. The power plant should run from its lowest to its highest speed without any irregularity in torque, i. e., the acceleration should be gradual rather than spasmodic.

A carburetor consists of a float or feed chamber which maintains a constant height of gasoline in a spray nozzle carried in a mixing compartment where gasoline is sprayed into the entering air stream drawn into the engine cylinders by the suction or pumping effect of the pistons as they descend on their suction strokes. The gasoline vapor and air mix to form a gas which can be ignited by an electric spark when it is properly compressed in the cylinders, this gas entering through the inlet valves and intake manifold which joins the vaporizing device to the cylinders. Adjustment means are usually provided on the carburetor to vary the mixture proportions by changing either the gasoline supply or air flow.