Just The Right Timing
By: Thomas Yoon
How does the engine know when to spray fuel, let in air, compress
the air, and exhaust the spent combustion product?
Obviously, there must be a certain timing for these processes to
follow in order for the diesel engine to work.
If the fuel were to be injected when the air inside the cylinders
is not sufficiently compressed, it will not ignite. Furthermore,
if the timing is not correct, some of the unburned fuel may find
their way out through the exhaust and become lost.
Inefficient combustion takes place and power will be lost.
The many components of a diesel engine must work together
properly, doing their function at the correct sequence all the
time. If any component does not function as designed, the engine
will perform poorly or even stop completely.
The main moving components of a diesel engine, i.e. the piston,
connecting rod, crankshaft, fuel pump, exhaust valves and inlet
valves are connected together through carefully designed gearing,
cams, push rods, rocker arms, and sometimes drive chains.
Adjusting the timing of the various processes of a diesel
combustion cycle involves adjustments to these linkages.
In small diesel engines, very little adjustments can be done.
However in large diesel engines, each of these components can be
adjusted for maximum efficiency.
The cams of the camshaft driving the fuel pump can be adjusted to
advance or delay the fuel injection to the engine cylinder. The
cams driving the push rods for the inlet and exhaust valves can
also be adjusted.
In doing all these adjustments, care must be taken to consider the
positions of the piston relative to the process to be adjusted.
The flywheel at the end of the crankshaft is usually marked as a
reference to show the piston at Top Dead Center. Each piston will
have its marking on the flywheel. If the engine has 6 cylinders,
then 6 markings for Top Dead Center will be marked.
From the markings on the flywheel a person can refer to it for
adjustments on the fuel pump cams, and cylinder valve cams.
Some diesel engines do not have inlet and exhaust valves. Perhaps
we will look at 2-stroke and 4-stroke diesel engine next...
Well folks, start your engines.
Until next time...
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