SUBSECTION 11A
GENERAL INFORMATION
pression and power strokes respectively
GENERAL
as shown in Figure 11A-1. In contrast,
a four cycle engine requires four piston
This subsection contains information on
strokes to complete an operating cycle;
principles of operation, serial number in-
thus, during one half of its operation,
formation and general procedures that
the four cycle engine functions merely as
apply to all of the subsections in Section
an air pump.
11 (Disassembly, Cleaning, Inspection,
Assembly and Safety).
A blower is provided to force air into the
cylinders for expelling the exhaust gases
and to supply the cylinders with fresh
PRINCIPLES OF OPERATION
The cylinder wall
air for combustion.
contains a row of ports which are above
The diesel engine is an internal com-
the piston when it is at the bottom of its
bustion power unit, in which the heat of
These ports admit the air from
stroke.
fuel is converted into work in the cylin-
the blower into the cylinder as soon as
der of the engine.
the rim of the piston uncovers the ports
as shown in Figure 11A-1 (scavenging).
In the diesel engine, air alone is com-
pressed in the cylinder; then, after the
The unidirectional flow of air toward the
air has been compressed, a charge of fu-
e x h a u s t v a l v e s p r o d u c e s a scavenging
el is sprayed into the cylinder and ig-
effect, leaving the cylinders full of clean
nition is accomplished by the heat of
air when the piston again covers the in-
compression.
let ports.
In the two-cycle engine, intake and ex-
haust take place during part of the com-
F i g u r e 11A-1. The T w o Stroke Cycle
Subsection 11A
