smoother and gives it more of the steady pulling quality of the steam engine. Finally (4) the exhaust valve opens on the exhaust stroke and the burnt gases are pushed out of the cylinder into the open air, as in any ordinary four stroke cycle engine. How the Diesel Two Stroke Cycle Engine Works. -The action of a Diesel two stroke cycle engine is very like that of an ordinary engine of the same type, that is, the exhaust of the burnt gases, the admission of fresh fuel oil and the ignition of the latter all take place during a single stroke. The cycle of operations is this: (1) on the first, or compression stroke, the piston compresses the air that is in the cylinder just as it does in a Diesel four stroke cycle engine to about 500 pounds per square inch, when the temperature of the latter rises to about 1,000 degrees Fahrenheit. Then (2) on the start of the second stroke the fuel valve is opened, the oil is injected into the cylinder, when it is fired and then the power stroke takes place. When the piston is near the end of its stroke both the air inlet and the exhaust valves are opened at the same time; the air rushes in and pushes out the burnt gases so that when the compression stroke is made only fresh air remains in the cylinder. The Construction of the Diesel Engine. The Valves of a Two Stroke Cycle Engine.-A two stroke cycle Diesel engine has two poppet valves in the head of the cylinder, and these are (1) the fuel admission valve and (2) the air starting valve, which is used to start the engine. The air inlet valve and the exhaust valves are opened and closed by the piston itself as in the ordinary two stroke cycle engine which I described in Chapter II. The Valves of a Four Stroke Cycle Engine.While an ordinary four stroke cycle engine has only a fuel inlet valve and an exhaust valve, a Diesel engine of the four stroke cycle type has four and sometimes five poppet valves, and these are (1) the air inlet valve, (2) the fuel injector valve, (3) the exhaust valve, (4) the air starting valve and (5) a safety valve. How the Valves Work.-The valves of both the two stroke and the four stroke cycle engines are worked by levers or cams which are operated by gears driven by the crankshaft. The fuel valve is formed of a needle valve fitted in a nozzle which has a very small opening in it like those described for the larger makes of oil engines in the preceding chapter. Since the compression stroke compresses the air in the cylinder the fuel oil must be injected into the air charge by a blast of air which is under a much higher pressure, and to do this an air compressor pump, called an injector pump, is used. In the original Diesel engine1 the needle valve 1U. S. Patent No. 542,846 granted to Diesel explains this fuel valve fully. You can get it by sending five cents in coin to the Commissioner of Patents, Washington, D. C. sets upright in a little cylindrical fuel reservoir which has a small hole in the bottom of it; the fuel reservoir is fixed in the cylinder head and is connected to the injector pump by a pipe. When the pump makes its suction stroke it pulls a small amount of fuel oil into the reservoir. The lift of the needle valve is regulated by the governor, which determines the length of time and the distance it is opened, and, hence, the amount of oil that is pulled into the reservoir. The instant the needle valve opens, the fuel oil in the reservoir is driven in a fine spray into the compressed air charge in the cylinder by the blast of high pressure air, when it ignites. The Air Compressor, or Injector Pump.-This pump is generally a built-in part of the engine, and is driven by a crank on one end of the crankshaft, as shown in the side cross-section view Fig. 66 and end cross-section view Fig. 67. The air compressor is of the two, or three stage type, that is the air is compressed twice and sometimes three times by a succession of pistons and cylinders, each succeeding one being smaller than the other. The one shown in Fig. 66 is a two stage air compressor. The pressure of the air needed to spray the oil into the red-hot air charge in the cylinder of the engine is between 800 and 1,200 pounds to the square inch, the pressure depending very largely on the nature of the fuel oil that is used. The air com |