LESSON CONTENT
Part B.
Diesel Engines. Upon completion of Part B, you will be able to explain the
principles of operation of twostroke and fourstroke cycle diesel engines.
The diesel engine bears the name of Dr. Rudolph Diesel, a German engineer. He
is credited with constructing, in 1897, the first successful diesel engine
using liquid fuel. His objective was an engine with greater fuel economy than
the steam engine, which used only a small percentage of energy contained in the
coal burned under its boiler. Dr. Diesel originally planned to use pulverized
coal as fuel, but his first experimental engine in 1893 was a failure. After a
second engine failed, he changed his plan and used liquid fuel.
a. Characteristics of Diesel Engines. Diesel engines are similar to
gasoline engines and are built in both two and fourstroke designs. They may
be water or air cooled. In general, they are heavier in structure to withstand
the higher pressures resulting from the increased compression ratios used. In
some diesel engines, the compression ratio may be as high as 18 to 1.
(1) Fuel Intake and Ignition of AirFuel Mixture. The main difference
between gasoline and diesel engines (Figure 112) is in the method of
introducing fuel into the cylinders and igniting the airfuel mixture. Fuel
and air are mixed together before they enter the cylinder of the gasoline
engine. The mixture is compressed by the upstroke of the piston and is ignited
within the cylinder by a spark plug. Air alone enters the cylinder of a diesel
engine. The air is compressed by the upstroke of the piston and the diesel
fuel is injected into the combustion chamber near the top of the upstroke
(compression stroke). The air becomes hot enough (1000 to 2000 F) to ignite
the fuel as it is sprayed into the combustion chamber by the injector
(compression ignition). No spark plug is used in the diesel engine; ignition
is by contact of the fuel with the heated air.
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