THE DIESEL SELF-IGNITING ENG/RE You will remember I told you in the first and second chapters about how the Diesel oil engine fired its fuel charge by compressing the air in the cyl inder, which raised its temperature, and you know that all other types of internal combustion engines use some kind of an igniter for this purpose.
Now, while this difference in the methods of igni tion between the Diesel and other oil engines is the most important one, there are several other factors that are found in the former which are of interest, and these will be described in due time as we push along. , If you ever had anything to do with a gasoline or oil engine or drove a motor car you know that when the engine is running at low speed with the throttle wide open and the engine is laboring under an excessive overload it will begin to knock, and this is caused by premature ignition. Now, prema ture ignition has long been a great problem in build ing internal combustion oil engines, and it was only solved when Diesel invented the engine now under discussion. The Diesel engine is the most econom ical engine that has yet been made for producing power where crude fuel oils can be had to run it.
Diesel engines are built in both the vertical and the horizontal types, have one or more cylinders, and are made on both the two and four stroke cycle principles.
How the Diesel Four Stroke Cycle Engine Works. —In this engine the cycle of operations is as fol lows: (1) on the suction stroke the air inlet valve opens and air is drawn into the cylinder; at the end of the suction stroke the inlet valve closes, and (2) on the compression stroke the piston compresses the air to upwards of 500 pounds to the square inch, and this raises the temperature to about 1,000 degrees Fahrenheit, which is far above the ignition point of the heaviest fuel oils.
Just before the end of the compression stroke, the fuel valve is opened and the fuel oil, which is in jected under pressure into the cylinder in a, fine spray, instantly catches on fire; then (3) the power stroke begins, and the spray of fuel oil is injected during about of the length of this stroke.
Hence, the oil burns instead of exploding, as in gas and gasoline engines, and the result is that the temperature of the fuel is kept about the same and the pressuro on the piston is more nearly uniform throughout the length of the stroke instead of being set up by a sudden blow, as in an ordinary gas or gasoline or oil engine. This makes the engine ran
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 cyl inder 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 ad mission 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 ci 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 pis ton itself as in the ordinary two stroke cycle engine which I described in Chapter IL 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 en gine of the four stroke cycle type has four and some times five poppet valves, and these are (1) the air inlet valve, (2) the fuel injector valve, (3) the ex haust valve, (4) the air starting valve and (5) a safety valve.