Yanmar 1GM User Manual page 75

SINGLE-CYLINDER ENGINES
4·STROKE DIESEL ENGINE PRINCIPLES
69
B
As the piston travels downward, the exhaust
valve closes and the intake valve opens,
allowing air to be drawn into the cylinder. When
the piston reaches the bottom of its travel
(SOC), the intake valve closes and remains
closed for the next 1 1/2 revolutions of the
crankshaft.
When the crankshaft continues to rotate, the
piston moves upward, compressing the air.
c
Injector
~i~~~~Exhaust
valve
o
As the piston almost reaches the top of its
travel, the injector sprays fuel into the
combustion chamber. The fuel Is ignited by the
heat of compression. The piston continues to
top dead center (TOC) and is pushed downward
by the expanding gases.
When the piston almost reaches SOC, the
exhaust valve opens and remains open until the
piston Is near TOC. The upward travel of the
piston forces the exhaust gases out of the
cylinder. After the piston has reached TOC, the
exhaust valve closes and the cycle repeats.