PRIN. OF INTERNAL COMBUSTION ENGINES - OD1619 LESSON 1/TASK 2
(3) Power. As the piston reaches top dead center, the compression stroke ends.
Fuel is injected at this point. The intense heat of compression causes the fuel to
ignite. The burning fuel pushes the piston down, giving power to the crankshaft.
The power stroke ends when the piston gets down to the point where the intake ports
are uncovered. At about this point, the exhaust valve opens and scavenging begins
again.
c. Advantages. The two stroke cycle diesel engine has all of the advantages that
a four stroke cycle engine has over a gasoline engine, plus the following:
(1) Because it is a two stroke cycle engine, it will run smoother than its four
stroke cycle counterpart.
This is because there is a power stroke generated for
every crankshaft revolution.
(2) The two stroke cycle diesel has a less complicated valve train because it
does not use intake valves.
d.
Disadvantages.
(1) The two stroke cycle engine must use a supercharger to force in the intake
air and push out the burnt exhaust gases.
This is because the movement of the
piston is not such that it will accomplish this naturally. The supercharger uses
engine power to operate.
(2) The two stroke cycle diesel uses either two or four exhaust valves per
cylinder, which complicates the valve mechanism.
(3) As with the two stroke cycle gasoline engine, the diesel counterpart will not
produce twice as much power as a four stroke cycle engine, even though it produces
twice as many power strokes. By studying figure 33 on the following page, it can
be seen that the power stroke occupies only a portion of the downstroke of the
piston in a two stroke cycle diesel.
In a four stroke cycle diesel, the power
stroke lasts from top dead center to bottom dead center.
e. Usage. The two stroke cycle diesel is used in most of the same applications as
the four stroke cycle diesel.
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