Internal combustion engine plants
operate with the combustion of fuel taking place within the prime
mover. The fuels commonly employed include natural gas, gasoline,
petroleum and its distillates, alcohol, and by-products of industrial
and other operations.
The fuels used may be in a gaseous
state originally; they may be liquid fuels gasified by evaporation;
or they may be heavy fuel oils injected into the cylinders of the
(Diesel) engines by means of a fuel pump or air jet.
The combustion of the fuel may take
place within one or both ends of its one or more cylinders. Although
their utilization of the heat energy of the fuel is usually better
than that found in steam plants (as the intermediate steps with the
heat losses are not necessary), their initial cost, maintenance
charges and depreciation restrict their employment to relatively
small units for emergency purposes.
Classification
Internal combustion engines may be
classified as to:
1. Cycles of combustion: Regular or
constant volume; and, heavy oil (Diesel) or constant pressure.
2. Cycles of operation: Two stroke and
four stroke cycles.
3. Cylinders: Number (one, two, four,
etc.); arrangement (vertical, horizontal, V, single-acting,
double-acting).
4. Fuel handling: Vaporizer,
carburetor, solid injection, air injection.
5. Cooling: Water, liquid compounds,
air.
6. Power output (in horsepower) and
speed (in revolutions per minute).
Cycles of Combustion
The combustion of fuel in an internal
combustion engine may be accomplished in two ways:
1. The fuel in gaseous or vaporized
form is intimately mixed with a suitable quantity of air and the
mixture compressed in the cylinder. It is then ignited by an electric
spark and the resultant explosion causes a rise in pressure that is
practically instantaneous, with a nearly constant volume.
2. Air only is compressed in the
cylinder at a very high pressure so that its temperature is
sufficient to ignite the fuel without the aid of an electric spark.
At the instant this high compression
pressure is attained, the fuel is sprayed or injected into the
cylinder, at the same time the piston begins to move on its power
stroke.
The ignition of the fuel produces a
further increase in temperature and a practically constant pressure
in maintained during this portion of the stroke of the piston; fuel
injection can continue and pressure maintained until all the oxygen
available is consumed.
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