man b&w fuel pump

7/30/2019 MAN B&W Fuel pump

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u

Th

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e pump is basically a jerk type with a pl

nger to control the end of injection by u

sing the needle valve in the injector to clo

is supplied to the barrel via the spill port

en the pressure in the barrel falls below

ts are covered by plunger.

placeable erosion plugs are fitted in the p

e of the helix uncovers the spill ports at t

Operational Informa

MAN B&W MC Engine VI

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nger moving in a matched barrel, using tw

covering spill ports and causing the disch

se.

s and a suction valve. The suction valve, sit

the supply pump pressure; i.e. during down

mp housing opposite the spill ports. The hig

e end of injection, hit the plugs, which preve

ion

Fuel Pump.

avStudio. (OpenCube Inc. -

o helical grooves machined in th

rge pressure to drop rapidly, thus

ated at the top of the barrel opens

ard stroke of plunger, while spil

h pressure oil, spilling back, as th

nt damage to the pump casing


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A puncture valve is fitted in the top cover of the pump. It is

opened when compressed air from the control air system acts o

top of a piston fitted in the top cover. Fuel oil from the discharg

side is then returned to the suction side of the pump and n

injection takes place. The puncture valve is operated in the evenof actuation of the shut down system (all units), during the ai

start sequence or when excessive leakage is detected from th

double skinned fuel pipes.

Fuel oil leakage past the plunger to the cam case is prevented b

the use of an "umbrella" seal


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A

si

t

s

a

e

ARIABLE INJECTION TIMING (VIT)

e pump is capable of Variable Injection

hough the end of injection is infinitely va

mmencing shortly after the ports are cover

Quantity ControlUsing Fuel Rack

As well as havin

which rotates the

with an adjustabl

on the bottom. T

which is rotated

axially, and the

sleeve rotates, th

position of the s

start of injection.

spring loaded damper is fitted to the

de of the pump connected through to

e suction side of the pump. This

oothes out the pressure fluctuations

the high pressure fuel spills back at

d of injection.

iming (VIT). This overcomes the disadvant

riable, the start of injection is fixed by the p

ed by the top edge of the plunger.

g the normal fuel quantity control (i.e a rack

plunger in the barrel), the fuel pump is fitte

e barrel which has a large pitch thread machi

he threaded barrel is located in a threaded sle

y a second rack. As the sleeve cannot mov

arrel is prevented from rotating, then as the

barrel moves up and down, thus altering th

ill ports relative to the plunger, and varying

ge of the basic jerk pump, where

osition of the spill ports, injection

ned

eve

he Timing ControlUsing VIT Rack


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Fuel Quantity and VIT Linkages on Engine

ASON FOR USING VARIABLE INJECTION TIMING

Graph Showing Effect of VIT onMax Cylinder Pressure

The reason for using VIT is to achieve greater fuel economy.

This is achieved by advancing the injection timing so that

maximum combustion pressure (pmax) is achieved at about 85%MCR (maximum continuous rating).

The system is set up so that there is no change in injection

timing at low loads (40%MCR). This is to avoid frequent

changes of pump lead during manoeuvring.

As the engine load is increased above 40%, the start of

injection advances. When the engine has reached

approximately 85% MCR at which the engine is designed to

have reached pmax, the servos retard the injection timing so that

the maximum combustion pressure is kept constant between85% and 100%MCR.

At 90% MCR a fuel saving of 4-5g/h.p.hour is claimed to be

achieved.

Variable Injection timing also allows for small adjustments to

the fuel pump timing to be made to allow for fuels of varying

ignition qualities. Wear on the fuel pumps can also be

compensated for as can changes in the camshaft timing due to

chain elongation (up to 2 degrees)

OW VARIABLE INJECTION TIMING IS ACHIEVED

Mechanical-Pneumatic: Older System

w pressure air is fed to the pressure control valve, the output of which is fed to the VIT servos on the fuel pump. A link

m the governor output (or fuel pump control handwheel) moves a pivoted bar, the position of which determines the

put of the pressure control valve.

e position of the control valve is adjustable which can be used to allow for fuels of varying ignition qualities and

anges in the camshaft timing due to chain elongation.

e pivots are also adjustable for initial setting up of the VIT and adjustment of breakpoint position.


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Linkage Between Fuel Quantity and VIT

SITION OF VIT CONTROLLER AT VARIOUS ENGINE LOADS


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Electro Pneumatic: Later Engines.

e air signal to the fuel pump VIT actuators which operate the VIT racks is implemented within the electronic governor

an electrical signal between 4 and 20 milliamps. This signal is sent to an IP converter which generates the pneumatic

ntrol signal between 0.5 bar (min VIT setting) and 5 bar (Max VIT setting).

e essential difference between the mechanical and electrical system is the use of the breakpoint and how the pressure

e is controlled. With the mechanical system the breakpoint is fixed, with the electrical VIT system the breakpoint is

iable depending on the scavenge pressure.


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If the scavenge pressure is high, then the resulting

compression pressure within the cylinder will be higher:

This means that unless adjustments are made, the

maximum pressure in the cylinder could rise above the

design point. By altering the breakpoint to a lower

percentage point of engine load, Pmax is reached earlier

and maintained at that point until 100% load.

Similarly, if scavenge pressure is low, then the

breakpoint moves closer to 100% engine load, so thatPmax is still reached.

e electronic control is only active when running ahead when the engine is in bridge control or ECR control. When

ning astern or in local engine side control, the manoeuvring system delivers a preset pressure to the VIT actuators.

justments during running are simpler, as correction values are entered directly into the governor. Change in fuel qualitywear in the fuel pumps may make it necessary to adjust the VIT.

e correct method of doing this is as follows:

ke a set of indicator cards with engine load just above the breakpoint.

just the Pmax by altering the governor Poffset value. (this is the value by which the Pmax can be raised or lowered)

ke a further set of indicator cards to verify adjustments.

he case of badly worn liners giving poor compression, or excessively worn fuel pumps, it is recommended that the VITction is disabled in the governor settings.

OTE

el pumps mounted on the smaller MC engines are not fitted with Variable Injection Timing.

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