12/16/12 Fuel Pump - Marine Engineer  

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Fuel Pump

effective stroke & idle stroke of fuel pump

effective stroke is travel of the plunger in mm from beginning of injection to

termination of injection and idle stroke is upward travel of plunger during which fuel is

pressurised but not injected.

now da generator n main engine both have same pumps..... so how u check in

generator engine...??????

told abt da mark on da fuel pump body n plunger to coincide n check da flywheel

mark n compare it with da shop tr ial report.... itna hi pata tha mujhe..

Fuel pump lead and fuel cam lead, and what is effective stroke and effective lead ?

 Amol Chagas Silva effective stoke of a fuel pump is the stoke for which

the fuel is pressurized to injection pressure....i.e. the length of the

stoke for which the fuel is injected....

October 11, 2011 at 11:59pm · LikeUnlike

 Amol Chagas Silva

whereas the fuel pump lead a (= the effective lead)

is defined as the distance the top of the fuel

pump plunger is lifted above the upper 

edge of the upper cut-off holes in the fuel

pump barrel when the piston of the cylinder 

... concerned is in TDC. means the length from which the fuel is being

pressurized...hence it should be greater than the effective storke....

which is only length for which the fuel is injected....understood?See

More

October 12, 2011 at 12:00am · LikeUnlike

Taufiq Chougle significance is to check the correct volume of fuel is

injected. we r checking the quantity of fuel injected and not timing.

quantity is changed due to elongation in chain.

October 12, 2011 at 12:39am · LikeUnlike · 1

Ravish Ramakrishnan Amol Chagas Silva yaar i think u defined both

correctly...but injection stops after tdc so effective stroke will be

greater than eff lead.

October 12, 2011 at 10:46am · LikeUnlike

Ravish Ramakrishnan please tell me about fuel cam lead too

 

Search this s ite

 

12/16/12 Fuel Pump - Marine Engineer  

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October 12, 2011 at 10:47am · LikeUnlike

 Amol Chagas Silva

so what if injection stop after tdc, that dosent matter, so long as the

fuel is being pressurized to injection pressure...and in the above

definition TDC does not mean exactly at TDC....cause if it was, then

the piston is at TDC for hardly ...1degree of rotation, while the injection

takes place for 10 to 15 degrees of rotation....that tdc thing is just

given to tell that the fuel pump in question is of the piston which is

closest to tdc and about to fire...not of anyone else.... See More

October 12, 2011 at 3:10pm · LikeUnlike

 Amol Chagas Silva and fuel cam lead is the movement of the plunger 

from the bottom postion to the peak....i.e. the measured distance of 

the plunger when the cam is at its base circle to the distance it

reaches its peak... .

October 12, 2011 at 3:14pm · LikeUnlike

Irfan Solkar can any one explain more about the fuel cam lead

October 12, 2011 at 3:28pm · LikeUnlike

अम  ृत पंवार The fuel cam lead is the the total stroke of the plunger when the

concern unit piston is at TDC ...that means it is of prime importance

for checking fuel pump timing as we have to cross check with flywheel

markings....if cam is slipped fuel... cam lead will either advance or 

retard there effecting timing.......hope this is correct...guys correct if 

am wrong.....and fuel pump lead i am not sure as there is only fuel

cam lead in KMC series which i have worked onSee More

October 12, 2011 at 10:20pm · LikeUnlike · 1

 Amol Chagas Silva your right amrat...whether pump lead or cam lead

both are use to time the fuel pump injection....and that is taken with

respect to the flywheel....or using a pin gauge...

October 12, 2011 at 10:25pm · LikeUnlike · 1

अम  ृत पंवार  Amol Chagas Silva ....Correct but pin gauge is used t check

cam slippage.....pin gauge is used only when fly wheel markings are

not matching with records....

October 12, 2011 at 10:28pm · LikeUnlike

अम  ृत पंवार Ravish Ramakrishnan ...dont get confused.....in SULZER

there is something call idle stroke and effective stroke....idle stroke

where the fuel is pressurized but not injected ..where as the effective

stroke is the plunger travel in mm in which fuel is injected.....But in

 

12/16/12 Fuel Pump - Marine Engineer  

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MAN B&W there we measure only fuel cam lead...so 4gt abt eff lead

and eff stroke.

October 12, 2011 at 10:31pm · LikeUnlike

अम  ृत पंवार other than what Amol Chagas Silva has said is correct

October 12, 2011 at 10:32pm · LikeUnlike

 Amol Chagas Silva you right....main thing what we want is the relation

between flywheel which is fixed rigidly on the crankshaft and the

camshaft which controls the fuel pump.... so using pin gauge we

check whether the camshaft has rotated(due to elongation of the

chain) with respect to the flywheel or not....

October 12, 2011 at 10:34pm · LikeUnlike

Ravish Ramakrishnan thnx guys..

October 12, 2011 at 11:39pm

 

fuel pump timing

engine flushed with d.o n v/vs closed,immobilize,prop clear,main air n st.air shut,ind

cock open n t/g engaged,special tools n manual along with v/v setting table kept

ready ,understand the procedure n get ready ,telegraph ahd,turn eng ahd so that run

dir int c/o,servomotor cut off n l.o p/p kept running,put vit to zero posn by a

spacer,fuel lever to be at posn-8 as per v/v setting table,remove cover belw fuel p/p n

check alignment of cam n roller,also check no spacers r there if present have to be

removed,remove suc dis n spill v/vcovers,remove spring v/v n pressure bushes by

special tools,put v/v n bush put gauges on all 3,take p/p to bdc such that cam is on

base circle n adjust dial gauge to zero here spill v/v closes,turning in ahd dirn bring

piston to tdc such that cam is at peak and adjust dial to zero,again in ahd dir bring

cam to base circle n check for zero error,turn in ahd dir until reading on suc v/v is

0.02 and see crank angle,take reading as S1,turn engine so that reading on spill v/v

is 0.02 and check crank angle,take reading as S2.DIFF BET TWO READING WILL

GIVE EFFECTIVE STROKE.

zero cut out n fuel pump cut out manually

by raising roller of cam by turning it in anticlock dirn abt 100deg,

how will u knw its cut off 

said the pin protrudes out.

UseUse of VIT

Super VIT mechanism fitted to advance fuel injection at lower loads for increasing

maximum firing pressure resulting better fuel economy.

VIT has been introduced to reduce the specific fuel oil consumption by raising the

combustion pressure.

VIT AND SVIT

Before the Super VIT was introduced variable injection timing was obtained by

means of a special profile on the fuel pump plunger. Hence there was a fixed

relationship between the injection timing and the fuel index. Thus it was not possible

to adjust the fuel index of the individual pumps without also altering the injection

timing. For this reason the Super VIT was introduced, where it is possible to adjust

the fuel index and the injection timing independently.

The Super VIT is available in both a mechanical and a electronic version. In the

 

 

Fuel Pump - Marine Engineer 

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electronic version an I/P converter supplies the pilot air pressure to the individual

servo cylinders, instead of the pilot valve activated by the fuel rack used in the

mechanical version. The I/P converter receives its pilot signal from the governor 

system.

The advantage of the electronic version is that the break-point is calculated from the

actual conditions, why the ambient conditions are taken into account. The engine

load is calculated from the engine speed and the fuel index, while the compression

pressure is calculated from the scavenging air pressure. Based on these

calculations the governor calculates the output to the I/P converter.

what is break point

The breakpoint is the point where the maximum cy linder pressure has been reached

and the injection timing is advanced the most. Above the breakpoint the injection

timing is gradually retarded back until it reaches its original setting at 100% MCR

load. The position of the breakpoint is determined by the layout of the engine.

Formerly it was generally considered to be at approximately 85% MCR load, but it

also has to be ensured that the maximum pressure rise from compression to

maximum cylinder pressure is 35 bar or less (recommended by MAN B&W Diesel

 A/S). For this reason the breakpoint has tended to be somewhat higher on the latest

engines (approximately 90% MCR load).

Does the MAN B&W engine have a fuel quality setting lever on the VIT control

similar to that used on the Sulzer RTA, or must the fuel pumps be adjusted

individually if a fuel of differing ignition quality is bunkered.

In order to compensate for fuel related differences in the maximum cylinder pressure

it is possible to adjust the VIT according to the experience with the different fuels.

In case of the mechanical VIT an offset is introduced by moving the pilot valve

bracket horizontally towards or away from the lever, by means of the adjusting

screws.

In case of the electronic VIT it is possible to adjust an offset value on the governor 

panel.

What is fuel index and how is it adjusted?

The fuel index is an indication of the active stroke of the fuel pump. This is controlled

by push rods on the individual fuel pumps connected to the fuel rack, which in turn is

controlled by the engine governor.

When the engine is given a speed command the governor increases the fuel index,

subject to certain limitations, untill the requested engine speed is reached.

Why Negative cam or Inward cam used in Air distributor of the MAN B&W Starting

 Air System.Why not a positive cam?

The cam for the air distributor serves its purpose only while starting the engine,

reversing and again starting. Actually if you see there is no other requirement of this

particular cam while the Engine is in continuous operation. Therefore if a cam (

normal positive ) is used then the wear of this particular cam will be obviated and will

be expensive to repair/replace this cam. So when the engine has started, and the

vessel is en-route a voyage, then this particular cam turns without ant running gear 

touching it. It comes into play while starting.

 Advantages of using Wasted studs for securing main bearing top keep in MAN

B&W.Why not jacking bolts?

Previously, you might be knowing that the main bearing keeps were held down by

Jacking bolts (eg. Sulzer RND ). The reason behind that was the the kind of 

construction of the bed plate itself. When a cylinder fires, the pressure not only

forces the main journals down but there is also a component of force which pushes

the cylinder head up. Now the Cylinder Head, entablature and the bed plate is tied

and precompressed by the TIE RODS. Now when the firing forces come, then there

is a couple formed- a) One component of force tries to push the journal down and b)

the other component tries to Push the Tie Rods up. Now at the bottom, the tie rods

are bolted to the bed plate so a couple thus formed will try to rock the bed plate and

thus the engine. To counter attack this problem, the tie rods were kept as close to

 

12/16/12 Fuel Pump - Marine Engineer  

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the centerline of the engine as possible and due to space restrictions, the jack bolts

were used to keep the bearing top covers tight(reaction force through the

entablature). Note that there was only one cover for the main bearing having two jack

bolts. Now recent development has waisted studs on the main bearing cap but the

are OFFSET FROM the transverse centerline of the engine. Waisted s tuds give

more comression as they have more elasticity and resilience. As a matter of fact,

from the foundation bolts to the con rod bolts, the x-head bolts etc are all waisted

studs. So care has to be taken while working as the necked region should not be

marked, scored or cracked as due to reversal os stresses, fatigue will cause a crack

initiation and finally fracture.

Does the Sulzer engine have Super VIT?If yes, then what is the difference between

VIT and super VIT in Sulzer?

When Sulzer introduced their VIT it had the pssibility of adjusting the beginning and

end of fuel injection independent of one another i.e. it had the same features as the

MAN B&W super VIT. Hence there is no question of a "super VIT" in a Sulzer 

engine. The only change the Sulzer made was to replace the mechanical control of 

the VIT by an elctronic control in their later engines.

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