01 Notes - The Diesel Engine

8/2/2019 01 Notes - The Diesel Engine

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TTTHHHEEE DDDIIIEEESSSEEELLL EEENNNGGGIIINNNEEE

This short course deals with the actual prime mover of propulsion systems, generators and otherdriven equipment. The prime mover is the DIESEL ENGINE

What does a Diesel Engine do? The diesel engine converts the energy in fuel oil to a useful form

of energy by combining the fuel oil with oxygen and heat, from the heat of compression,resulting in a reciprocating motion that is then converted into a rotary motion. The rotary motion

is used to provide power to the ships propulsion system or to an Alternator or Generator to

provide electrical power to a ship.

The reason that the prime mover is called a Diesel engine is that Doctor Rudolph Diesel was the

first person to patent the principal of compression ignition to be used in an engine. Prior to the

time that the Diesel Engine was patented, there were several variations of the same theme inproduction and operation. Dr. Diesel saw the financial gain to be made with the production of

the engine and hence applied for and received a patent for his system.

To better understand what a prime mover accomplishes, we first must know the component parts

of such a machine. As noted above, the main purpose of the Diesel engine is to convertreciprocating motion into rotary motion. To accomplish this end, pistons, which are enclosed ina cylinder liner, are subject to explosive forces on the upper part of the piston, known as the

crown and the piston then travels down the cylinder liner due to the explosive force created. The

piston is connected to what is known as a crankshaft by a connecting rod. The forces producedon the piston crown are transmitted to the crankshaft by the connecting rod and the crankshaft

then turns. To be useful the power produced has to be controlled. This is accomplished by

regulating the amount of fuel provided to the cylinders.

We have accomplished the required result and have converted reciprocating motion into rotary

motion.

The component parts used to accomplish the required result are many and complex. The pistons,

liners and crankshaft are the main components but there are many more. To hold the pistons,

liners and crankshaft in place while in the stationary and dynamic (running) mode, we must havean enclosure of sufficient strength to contain all the necessary components that make the engine

run. This is known as the crankcase or in some circles as the entablature or the block. Thispart of the engine must be able to endure the forces produced by the combustion process and alsoto contain the reciprocating and dynamic forces produced by the pistons and rods turning the

crankshaft and to support the crankshaft itself.

CRANKCASE - There are two types of crankcase one is the fully cast usually made from cast


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alignment of the component parts. At the high Horsepower per cylinder produced in bothexamples, the forces are considerable when rotating at 520 RPM.


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FIGURE 1 MACHINED CAST CRANKCASE / BLOCK OF A 9 CYLINDER IN LINE MAN ENGINE

FIGURE 2 16CYLINDER PIELSTICK PC2.5 CRANKCASE


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The following is a compilation of the stationary components of the engine whether the engine bea two stroke or a four stroke model. These components are in addition to the crankcase

CYLINDER LINERS AND JACKETS Cylinder Liners are usually constructed of specialalloy Cast Iron, and are machined to fit into the cylinder block or crankcase. In many instances,

especially with the larger power output engines, the cylinder liners are spun cast. This procedure

necessitates the mold being set up in such a manner that as the molten metal is being poured intothe mold, the mold itself is spinning and continues to spin until the material has solidified. This

allows the liner structure to have an even grain and have greater strength than a straight poured

unit. The liner is machined inside and out to accommodate the piston and so that the liner will fit

correctly into the machined apertures in the block. The Liner is, on the larger medium speedengines, surrounded by a water jacket which is fitted to the top of the liner and rests on the

crankcase or block. Cooling water passages are also machined (drilled) into the liner so that the

temperature of the running surface of the Liner will be correctly maintained. Temperature of thecooling water is extremely important since this will affect the temperature of the operating

surface of the Liner. Temperature of the cooling water should be in the region of 185 F at the

outlet from the liner. Note that the size of the engine and its power output does not really enterinto the equation regarding cooling water temperature. The thermostat on your car will be

probably 180-190 F. The larger slow speed cathedral engines, which operate at some 4000 HPper cylinder, run at the same temperature.


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FIGURE 3 CYLINDER LINER

AND JACKET BEING

ASSEMBLED

FIGURE 4 - CYLINDER LINER AND JACKET CROSS SECTION ASSEMBLY

FROM PIELSTICK PC2


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CYLINDER HEADS Cylinder heads are usually constructed of Nodular Iron or in someinstances Cast Steel. The main function of the head is to contain the explosion of the fuel which

in turn drives the piston down the liner. The other functions are to keep the liner and jacket inplace, to form a seal between the liner and the head and to hold the inlet and exhaust valves inthe case of a 4 stroke engine, and also to house the starting air valve, the relief valve and the fuel

injection nozzle(s) In the case of the 38D81/8 opposed piston 2 stroke engine, the forces

promulgated by the explosion of the fuel in the cylinder is used to drive the upper piston andproduce power from the upper crankshaft, hence a cylinder head is not used.

FIGURE 5 - CYLINDER HEAD FROM MAN ENGINE


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FIGURE 6 - CYLINDER HEAD FROM MAN ENGINE, RUSTY TOP SHOWING

FIGURE 7 - CYLINDER HEAD FROM AN EMD ENGINE

On engines equipped with cylinder heads the actual head is held in place by heavy duty studs

which should have their nuts torqued to the manufacturers specification. Cylinder head studsmust be treated with great respect and must be free of all types of nicks, gouges and otherblemishes as these types of damages can cause stress risers which in turn can cause breakage

of the component when under load. Always remember that the forces acting on the underside of

the cylinder head during the firing part of the cycle are horrendous and that these forces are takenup by the cylinder head studs. In modern day medium speed engines the cylinder head studs are


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FUEL INJECTORS -

FIGURE 8 FUEL INJECTOR IN THE TEST STAND


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Top picture is of Injector in the test stand. Bottom picture is of a fuel pump. Center pictureshows the component parts fuel injector.

Fuel valves or injectors and fuel pumps - Manufactured from high quality hardened steel.

Although a stationary component, these pieces of equipment are said to be the heart of a dieselengine. The machining tolerances specified for both the injector and pump are extremely fine,

and the least bit of dirt or drop of water can cause irreparable harm to the running surfaces of the

plunger and barrel of the fuel pump and the surfaces of the nozzle and needle of the injector.Component parts are not interchangeable. i.e. the nozzle and needle for an injector must always

stay together as must the barrel and plunger of a fuel pump. Metal to metal joints are used

instead of gasketed surfaces since the gaskets would tend to blow out under the high pressuresbeing generated. The topic noted above is applicable to engines with jerk pumps for each

individual cylinder. Many of the lower output smaller engines are equipped with en bloc fuelpumps of different types and styles. The principal of operation and the detriments are the same

for all fuel pumps. The fuel used for the engine must be absolutely clean, free of water be of the

correct viscosity and have sufficient lubricity to allow the components in the fuel pump andinjector to operate as designed.


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Journal Bearings; Are stationary. The actual bearing is usually of a tri metal formation. The

three layers being a steel backing, a copper or bronze flash and a layer of white or Babbitt metalon top of that. A run in flash or overlay is added to aid in the run in of the bearings. The steel

back gives the bearing strength and allows it to be fitted correctly to the cap and saddle on amain bearing. The copper flash is to allow the white metal to be boded to the steel and also to

act as a tell tale for bearing wear. Some engines use aluminum bearings, the Fairbanks Morse

38D81/8 being a prime example.

FIGURE 11 - SADDLE AND BEARING CAP OF AN MAN ENGINE. THIS IS WHERE

THE JOURNAL BEARING FOR THE CRANKSHAFT FITS.

Journal Bearings in diesel engines, whether tri metal or aluminum, are held in place by thebearing saddle and cap in the case of a crankshaft bearing or by the rod and cap in the case of a

con rod. This situation is applicable to all engines no matter what the output. In days past,


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split housing into which the bearing will fit and then tightening the holding bolts to a specifiedtorque.


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become too hot and cause an ignitable vapor to be generated. Classification Societies specify theactual opening size that the cover fits and also the pressure at which the explosion door lifts.

Most engines are fitted with explosion doors manufactured by BICERA (British InternalCombustion Engine Research Association). The number of explosion doors depends upon theinternal volume of the crankcase.


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FIGURE 13 - CRANKCASE DOOR (LEFT) AND EXPLOSION DOOR FROM A

PIELSTICK PC2 ENGINE.


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Cylinder head is to relieve any excess pressure within the cylinder. Excess pressure can becaused by water in the cylinder which, when the barring gear is engaged and the crankshaft

turned, will tend to hydraulically lock the cylinder.

FIGURE 14 - PIELSTICK STARTING AIR VALVE; AIR IS ADMITTED THROUGH

THE LOWER LARGE OPENING AND CONTROLLED BY CONTROL AIR

THROUGH THE UPPER SMALLER OPENING


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usually located on the end of a camshaft. On smaller lower powered engines, starting isaccomplished either with an electrically operated or air operated Bendix drive.

STAIONARY COMPONENTS - One major stationary component is the sump or oil pan. Thisitem is bolted to the bottom of the crankcase or block and catches the oil from crankshaft and

piston lubrication. On the larger engines the oil pan main rail or flange, is used in a support

function in that this rail sits on the foundation with the crankcase above it with its flange boltedthrough the sump flange and foundation. This assembly of the crankcase and the oil pan is

supported on chocks between the bottom of the oil pan flange and the top of the foundation.

Chocks are another stationary component that form part of the complete engine installation.

On smaller Horsepower prime movers for generators the complete engine and generator

assembly are mounted on what is termed a skid. The whole unit is mounted in a vessel and the

skid mounted to the deck. On some engines resilient mounts are fitted which in one type consistof springs and plates and in another consist of steel plates and rubber

The generator shown below is a skid mounted unit. Notice item 13 which are denoted asFlexible Mountings


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FIGURE 15 DIESEL GENERATOR

Other stationary components are all the pipes for all the systems. These include Fuel Oil (bothhigh and low pressure) and Lube Oil, Fresh Water (Jacket Water and Fuel valve cooling), Airand Exhaust piping, Starting Air piping, Drain piping and Control air piping

The cutaway picture of the generator set shown above shows most of the dynamic components

inside the engine. These are the reciprocating and revolving parts that make the production of

power to spin the generator / alternator to produce amperage and voltage.

FIGURE 16 - CRANKSHAFT FROM AN MAN MEDIUM SPEED ENGINE, NOTE THE

TIMING GEAR AND THE BOLTED ON COUNTERWEIGHTS.

CRANKSHAFT - The major component is the Crankshaft. Manufactured from 4140 forgedsteel or from a Nodular Iron Casting. Forged Crankshafts can either be straight forged or Built

Up. Built up means that the shaft is made up of pre machined webs and journals and then fitted

together with extremely tight tolerances. In the case of straight forged crankshafts the forge

bends, twists and hammers a piece of steel into the base shape of the crankshaft required andh i i hi d h h d j l h i Th b i id


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The item that drives the crankshaft is the piston and rod assembly. Pistons shown are for aTrunk Piston Engine. Pistons can be manufactured from Aluminum, Cast Iron or a mixture of

Steel/Cast Iron and Aluminum. The Steel and Aluminum style pistons are known as TWOPIECE pistons, the crown or top is manufactured from cast steel and the skirt is manufacturedfrom Aluminum. 3500 series Caterpillar Engines and GE 250 engines have a two piece piston

with basically a floating skirt. The picture below is of an MAN two piece piston, note that the

rod (which connects the piston to the crank) is not suspended from the piston although thisassembly has just been drawn from the engine.

FIGURE 17 - TWO PIECE PISTON FROM AN MAN ENGINE

CONNECTING ROD - As previously mentioned the con rod is attached to the piston and the

crankshaft. The connection to the piston is known as the TOP END. The connection to theCrankshaft is known as the BOTTOM END. The basic nomenclature is correct for all engines

no matter how large or small or what the power output is.


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FIGURE 18 - CONNECTING ROD FROM MAN ENGINE, TOP END APPEARS TO BE

MISSING SOMETHING?The top connection is missing in the previous picture. MAN has a design which permits the

piston to be drawn from the engine without removal of the bottom end bearings and

consequently with out the removal of the bottom end half of the rod bearing bottom end cap.


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The piston pin can be seen in the picture of the piston for this type engine.

FIGURE 20 - PIELSTICK CONNECTING ROD FOR A PC2 ENGINE OIL FLOW IS

FROM THE LARGE END TO THE SMALL END.


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CAMSHAFT - Camshafts are manufactured from forged 4140 steel. Each shaft (One per side

on a V engine) is driven by gears from the Crankshaft. The cams are shrunk onto the shaft in

the example shown and consist of an inlet cam, an exhaust camshaft and a fuel pump cam.Camshafts for smaller output engines can be forged, cast or built up in sections, but the principle

of operation is the same in each case. The camshaft rotates and the cams operate inlet and

exhaust valves and fuel pumps on a 4 stroke engine. On a 2 stroke engine the camshaft operatesfuel pumps and exhaust valves if fitted. Inlet air is admitted by ports in the cylinder liner.

Exhaust Ports can be used to expel the exhaust gases to the exhaust manifold.

FIGURE 22 - CAMSHAFT TO MATCH THE CRANKSHAFT SHOWN PREVIOUSLY


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FIGURE 23 - CYLINDER HEAD SHOWING INLET AND EXHAUST VALVES

Exhaust valves are at the bottom of the picture. In this design the Inlet valves are fitted with

rotational devices.


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CAGE FROM MAN ENGINE NOTE THE ACTUATOR ABOVE THE

SPRING, THIS IS THE MEANS USED TO

TURN THIS VALVE IN ITS CAGE AS

OPPOSED TO THE SPINNER TYPE

TURNER IN THE EXHAUST VALVE

ASSEMBLY.

Note the Spinner at the bottom of the exhaust aperture. Instead of a Physical actuator with

balls and springs the valve is turned by the exhaust gases from the cylinder acting upon the

spinner forged into the valve stem. This action ensures that hot spots are not developed on

the seat of the cage or the valve which could cause burning of the valve seat. Burning of thevalve and seat usually ends up with a hole cut into the assembly which allows hot gases to pass

through and is denoted by exceedingly high exhaust temperatures for that particular cylinder.

In the examples shown both the Inlet and Exhaust valves are caged so that the valves can be

removed from the cylinder head, should the need arise, without actually removing the head from

the engine.

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The drawings below show an Inlet Valve and an Exhaust Valve from a Pielstick Engine Vintage

1971. Note that the Inlet valve fits directly into the cylinder head without a cage. This means

that should an Inlet Valve fail for whatever reason, the cylinder head must be removed to changethe valve out.

The second drawing is of a water cooled Exhaust Valve from the same type of engine and as canbe seen this valve has its own cage. This particular type of valve was used on engines burning

what is known as Heavy or High Viscosity Fuel.

Exhaust valves have over the years evolved so that the mating surfaces are kept cool. One of thebest designs is a water cooled valve cage and a rotating spindle. Modifications have also been

made to the inlet valves such that the valves are now caged and also rotate.

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FIGURE 28 - INLET VALVE AND AN EXHAUST VALVE FIGURE 29 WATER COOLED EXHAUST VALVE


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FIGURE 30 - ROCKER BOX MOUNTED TO CYLINDER HEAD, MAN ENGINE

NOTE THE ROCKER ARM SHAFTS GOING THROUGH THE ROCKER BOX, MAN

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FIGURE 31 - VIEW SHOWING ROCKER ARMS AND ACTUATORS FOR INLET AND

EXHAUST VALVES, MAN ENGINE

The drawings below are of a Rocker Assembly from a Pielstick PC2 engine together with the

associated Tappet Assemblies. Previously it had been noted that the Camshaft was equipped

with cams which operated push rods for the actuation of the inlet and exhaust valves. TheTappet assembly is the base component that carries out this function. The Tappet Assembly

consists of a roller and spring plus a carrier. The Tappet Assembly roller rides on the back of thecamshaft and lifts the assembly up as the camshaft rotates.

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FIGURE 32 ROCKER ARM ASSEMBLY

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FIGURE 33 ROCKER ARM

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FIGURE 54 ROCKER ARM

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The Tappet Assembly forces the pushrod upwards and in turn actuates the rocker gear to openthe requisite valve. The Rocker arm is basically a bar with a pivot point somewhere near the

center so that when force is applied to one end that force is transmitted to the other end in the

opposite direction. As one end goes up, the other end goes down.

Another style of Tappet Assembly is used for the fuel pump, this is shown directly above. Note

that the basic assembly is the same as the one for the push rod Tappet Assembly but with thisunit the height of the assembly can be adjusted to give a running clearance on the back side of

the actual cam. Since the actual camshaft is very highly loaded it is supported between two

camshaft support bearings. Load on the camshaft is produced by the action of the camshaft

through the Tappet Assembly to the plunger and barrel in the fuel pump. Pressures up to 3500PSI are generated, which equate to a load of approximately 1 3/4 tons. At 520 engine rpm this

occurs 260 times a minute therefore the camshaft and tappet assembly must be adequately

supported.

TURBOCHARGERS - The following Figure show different types of Turbochargers. The one

shown in Figure 55 is an example of an MAN style center bearing type. Exhaust gas enters theunit from the right and spins the Gas Turbine end of the shaft. This causes the compressor on the

left, to turn, since it is mounted on the same shaft. Air is drawn into the compressor and fed tothe Inlet Manifold of the engine. The use of a Turbocharger allows a greater amount of fuel tobe burned for the same sized engine therefore increasing the Horsepower output of the engine.

Oil is fed to the bearings of this Turbo from the engine lubricating system.

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FIGURE 55 TURBOCHARGER CUTAWAY, MAN STYLE CENTER BEARING

TYPE

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FIGURE 56 -TURBOCHARGER

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An example of a turbo charger with independent oil reservoirs is shown above. Principle of operation is the same. This picture is onits side. The axis should be horizontal. Benefits are that the oil system is separate from that of the engine and hence cleaner.

Disadvantage is that when stopped for a long time period the bearings must be hand lubricated prior to start up.

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FIGURE 57 - CENTER BEARING TURBOCHARGER BY ABB

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ENGINES

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FIGURE 58 - CUTAWAY SECTION OF MAN 48 / 60 INLINE ENGINE

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FIGURE 59 - CUTAWAY SECTION OF PIELSTICK PC2.5 ENGINE

01 Notes - The Diesel Engine

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