Diesel Generator Engine is commonly called “Auxiliary Engine” and employs a 4-
stroke cycle internal combustion engine. They are classified as medium and high
speed engine.
A 4-stroke cycle engine is an engine employing two revolution of crankshaft and four
stroke of piston (intake, compression, power, and exhaust) to complete a cycle. This
cycle is required to produce the output requirement for the operation of the
generator. One primary difference with the 4-stroke engine is the cylinder liner does not have the inlet ports machined into it. Another is the combustion air being drawn into the cylinder by the piston. This action is controlled by an inlet valve in the cylinder head,The cycle comprises of: two crankshaft rotation and four change of direction by the piston. With the start from the inlet stroke at top dead center (TDC). See the diagram below for a visual representation.
At TDC the inlet valve is open allowing air to flow inside the cylinder. The downward action of the piston creates a vacuum which draws air into the cylinder. Shortly before the piston reaches bottom dead center (BDC), the inlet valve is closed. The piston at BDC begins it’s upward travel, beginning the compression stroke. The piston compresses the original air volume by about 17:1 to 23:1, to about 42 bars (~600 psi). The air’s volume reduction crushes the air molecule together and as result they build up heat. At 10 degrees before TDC injection of atomized fuel begins, it burns, ignited by the high temperature from to the air being compressed. Injection stops around about 35 degrees after
TDC, depending on the engine’s load. The fuel continues to burn and expands which increase the cylinder temperature and pressure. Around 35 degrees after TDC injection stops, and shortly after maximum pressure is reached within the
cylinder .
The fuel used is either fuel oil or diesel oil. But for economical purposes, a F.O. to D.O. (vice versa) change over system is provided so that when the load of the D/G
engine is more than 30% of the rated power fuel oil is used. And when the load is
reduced to 30% or less, diesel oil is used until the D/G engine will stand still. This process provides protection to the D/G engine to prevent various troubles that may effect due to the usage of low quality fuel oil.
The air requirement for combustion process is supplied by a turbocharger connected
to the exhaust gas outlet side of the engine. The air taken from the atmosphere by
the blower attached to the turbocharger is being pressurized, cooled by a cooler and
supplied at suitable amount to the engine intake side. This process improves the
combustion quality of the D/G engine.
The starting requirement is being supplied by the starting air system which is
employing compressed air to start the operation of the D/G engine through the
starting air valve. Pressurized compressed air (about 2.5 MPa) is taken from the air
reservoir tank which is generated by an auxiliary air compressor.
A governor is attached to the D/G engine to provide control for speed (to maintain at
720 rpm) and throttles the fuel oil supply to suit the power requirement of the
generator.
A lubrication oil system is provided to serves as lubrication and cooling to various
moving parts of the D/G engine. This requirement is achieved by an attached or
separate lube oil pump and the sump tank. Lube oil filters are also included in this
system to maintain the cleanliness of the lubrication oil circulating in the engine.
Effect of Improper L.O. Management
A four-stroke cycle medium-speed engine (trunk-piston type) has a structure in which
the system oil directly makes contact with the combustion chamber and the
combustion gas. A characteristic of system oil for medium-speed engines is that
fouling and deterioration continue as a result of the direct contact of combustion gas
and the ingress of combustion residues, such as carbon, in which heavier
degradation of system oil takes place compared with low-speed engines.
Improper system oil management may lead to serious accidents, such as burnt
bearings, cracks in the crankshaft, and fractures of the connecting rod. The design of
the engine has also a significant effect on the causes of failure in the bearing. On a
crankcase and the cylinder block with low rigidity, vibration causes unstable bearing
clearances, resulting in abnormal wear.
Cooling fresh water system serves as cooling system for the cylinder covers and the
cylinders. The heat that is being generated during combustion is dissipated to the
fresh water that is circulating to the different parts of the D/G engine.
Sea water cooling is also provided and being supplied to various coolers (air, L.O.,
CFW, etc.) being attached to the D/G engine or as separate auxiliary devices to
serve as cooling medium for the lubrication oil, cooling fresh water and the air for
combustion.
The D/G engine is classified as “Critical Machinery” in the engine department. The
personnel who are to conduct operation of this device require proper understanding
and familiarization of the device itself. This is to ensure that this machinery is to be always available at all times and no troubles must arise during the operation.
7.2.2 Procedure for Operation
a. Preparation
i. For initial start-up, i.e., after overhaul, turning of the engine crankshaft is requires to ensure smooth rotation and to prevent possible damage to moving parts such as piston, cylinder liner etc., Operate the turning gear with greater caution and return all the parts in proper position.
ii. Confirm proper supply and level of lubrication oil into the system and check any
existence of dirt or contaminants, e.g., water, etc.
iii. Carry out priming of the lubrication oil system by the following:
a. Detach bonnets and crankcase side covers, and set indicator valves in the
“Open” position for all cylinders.
b. While turning the flywheel of engine, operate an auxiliary pump and confirm that
oil is coming out from the under side of pistons, bearings, cams, etc. inside the
engine.
c. Purge the air from the delivery side lubricating oil strainer.
d. After priming of lubricating oil, return bonnet covers and crankcase side covers in place and fasten them properly.
iv. Confirm that cooling water system is properly established and air has been
eliminated from the system. Bleed off air from the highest point of the cooling
system during filling and by opening the air vent valve to release air.
v. Confirm that fuel oil is properly supplied and the system is vented without any dirt or contaminants that will cause running trouble to D/G engine.
vi. Confirm that starting air pressure (minimum 1.5 MPa) in the tank is sufficient and water contamination has been drained off totally. Check the starting air system
line for any leakage while carrying out air running of the D/G engine.
vii. Finally, confirm all the parts condition and ensure that all in order, starting and running the D/G engine is readily available.
b. Starting (Machine Side Operation)
Starting operation discussed here is for machine side operation only. If remote
control operation is available, follow the maker’s instruction manual for proper
guidance.
i. Start D.O. pump and confirm that diesel oil has been supplied to D/G engine F.O.
system. It is always a practice that diesel oil is used for starting the D/G engine.
ii. Make sure that the engine is warm and the Jacket Cooling F.W. temperature is
above 50oC.
iii. Confirm that the lube oil pressure is suitable as per machinery parameters when
engine is in idle condition.
iv. Drain out moisture in the air tank, open the starting air root valve and confirm
suitable pressure at the engine gauge board.
v. Confirm that indicator cocks are open and carry out air blowing. When air blowing
is completed and engine condition is confirmed in good order, close the indicator
cocks and engine is ready for fuel running.
vi. Start the D/G engine by operating the starting air handle while the fuel handle is in “Stop” position. When the flywheel rotates, the fuel handle can be released
gradually to avoid speeding of the crankshaft rotation. When the engine is in fuel
running condition, release the operation of the starting air handle and hold the
fuel handle gradually until the engine reached its rated speed. When the engine
has reached its rated speed, the fuel handle is on top position and should be
fixed into the markings.
vii. When the engine has run, confirm that pressure of lubricating oil, valve rocker
arm lub. Oil, cooling water, fuel oil etc. has risen to the specified values.
viii. Check that all the temperatures of lube oil, cooling water, exhaust, etc. are within
the specified parameters.
ix. When the D/G engine is newly overhauled, re-adjustment of various clearances
and parameters e.g. tappet clearance, P-max, etc. has to be observed before
putting load to the D/G engine. Greater caution has to be followed when doing
this and should always consult with maker’s instruction manual.
x. When all checks have been done and D/G engine conditions are all in order, the
D/G engine can be now engaged for load operation. For load operation, follow
the procedures of the “Main Switchboard” operation.
c. Stopping
i. When the engine has to be stopped make sure that the load has been removed
and the engine is running in diesel oil. Under any circumstances, D/G engine
should not be stopped when having loads and running in fuel oil.
ii. Run the D/G engine for a few minute after removal of loads and make sure that
the temperature has decrease and stable at its lowest point prior stopping.
iii. When above conditions are met, stopping operation can proceed by putting the
fuel handle to “Stop” position and by opening the indicator cocks. When the
engine has stopped, carry out air running for few seconds to release excess
gases in the cylinder.
iv. If the D/G engine has a remote operation control, make sure to close the indicator
cocks, the D.O. valves should be opened, lube oil and cooling system is under
warming condition and various switches (Local ~ Remote, etc.) are in order.
v. If the starting operation is on local side only, indicator cocks can be left open until the next starting but the D/G engine must be in warming and ready to start condition at all times.
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