SL2008-501.pdf

Service Letter SL08-501/SBE

Action code: WHEN CONVENIENT

Low Load Update

Down to 40% load

SL08-501/SBE

October 2008

Dear Sirs

Concerns

Owners and operators of MAN B&W

two-stroke marine diesel engines.

Types: MC/MC-C and ME/ME-C

Generally, MAN B&W MC/MC-C and ME/ME-C engines can operate

down to 40% load without any engine modiications. As an example,

a 24% speed reduction can cut a container vessel’s fuel consumption

per travelled nautical mile in half.

Summary

Long-term low load operation down to

40% load is generally feasible without

any engine modiications.

A 24% speed reduction may cut a con-

tainer vessel’s fuel consumption in half!

Today, the only issue with long-term low load operation is to avoid soot

fouling of the gas ways, turbocharger and boiler/economiser in particular.

Slide type fuel valves provide the optimal protection against soot devel-

opment at any load level. By delivering eficient injection at all load levels,

slide type fuel valves set new and very excellent fuel injection standards.

Our low load recommendations boil down to two:

Retroit slide type fuel valves, if not already installed

Monitor the gas ways for fouling

Part load optimisation and engine de-rating can reduce fuel consumption

further, also at loads below 40%. Questions and requests concerning

part load optimisation and long-term operation below 40% load can be

directed to our Technical Service Department at ae-cph@mandiesel.com

Yours faithfully

Mikael C Jensen

Vice President, Engineering

Stig B Jakobsen

Senior Manager, Operation

Long-term low load operation is feasible for

most ME/ME-C and MC/MC-C engines

Head ofice (& postal address)

MAN Diesel

Teglholmsgade 41

2450 Copenhagen SV

Denmark

Phone: +45 33 85 11 00

Fax: +45 33 85 10 30

mandiesel-cph@mandiesel.com

www.mandiesel.com

PrimeServ

Teglholmsgade 41

2450 Copenhagen SV

Denmark

Phone: +45 33 85 11 00

Fax: +45 33 85 10 49

PrimeServ-cph@mandiesel.com

Production

Teglholmsgade 35

2450 Copenhagen SV

Denmark

Phone: +45 33 85 11 00

Fax: +45 33 85 10 17

manufacturing-dk@mandiesel.com

Forwarding & Receiving

Teglholmsgade 35

2450 Copenhagen SV

Denmark

Phone: +45 33 85 11 00

Fax:

MAN Diesel

Branch of MAN Diesel SE, Germany

CVR No.: 31611792

Head ofice: Teglholmsgade 41

2450 Copenhagen SV, Denmark

German Reg.No.: HRB 22056

Amtsgericht Augsburg

MAN Diesel – a member of the MAN Group

•

+45 33 85 10 16

Service Letter SL08-501/SBE

Contents

Low Load Beneits

page 2

Soot

Soot formation in the gas ways constitutes a potential risk

when operating at low load. Soot deposits may impair tur-

bocharger performance, and imply a risk of boiler soot ires.

Always ensure that turbocharger and boiler heat surfaces

are clean and soot free!

Soot

page 2

Slide Type Fuel Valves

page 3

Other Issues

page 3

Further Information

page 3

Low Load Beneits

Operation down to 40% load is feasible for all ME/ME-C and

most MC/MC-C engines without any engine modiications.

Boiler types

Soot formation is in general very limited in modern smoke

tube exhaust gas boilers/economisers.

In water tube boilers with ins, more soot may be deposited

at low load operation. Thus, water tube boilers may require

extra attention and more cleaning during long-term low load

operation.

The container vessel example in Fig. 1 shows the beneits of

low load operation: A 24% speed reduction can reduce fuel

consumption per travelled nautical mile to approximately 50%.

A further 3g/kWh fuel, approximately, can be saved by part

load optimisation and by de-rating the engine. Such engine

component alterations require a new IMO NO X certiicate.

% fuel per

nautical mile

100

Fig. 2: Smoke tube boiler inside, after 7 days below 40% load.

Limited soot deposits.

5 49

Inspections

We generally recommend operators to follow the boiler and

turbocharger manufacturers’ instructions for monitoring and

cleaning.

However, during an introductory low load period, we recom-

mend increasing the gas way and turbocharger inspection

frequency. If no or limited fouling is observed, inspection

intervals may be re-extended and/or adjusted to the general

service routines on board.

25 knots 19 knots

19 knots

Engine

part load

optimised

Same

engine matching

A gas way soot inspection includes:

exhaust gas boiler/economiser

exhaust gas receiver with turbine inlet grid

Fig. 1: Example showing a container vessel’s fuel consumption

in relation to its speed

Blow back and reduced scavenge air velocity may increase

sludge deposits in the scavenge air receiver during long-term

low load operation. This increased fouling is harmless; no ac-

tion is required to prevent or remove it.

Low Load Update. Down to 40% load. Page 2 of 3

•

Service Letter SL08-501/SBE

Load ups

From an engine point of view, regular load ups are not

necessary when operating at 40% load and above.

Other Issues

Auxiliary blowers

Generally, auxiliary blowers are switched off automatically

well below 40% engine load. However, in a few cases the

engine rating differs from the standard rating, which may

cause the blowers to switch off around 40% engine load.

However, boiler manufacturers and some turbocharger

manufacturers recommend regular load ups during low load

operation as part of the cleaning procedure. In such cases,

we recommend this procedure:

Manual load up procedure

Duration

If the blowers switch off near or at the desired load level,

e.g. 42%, the blowers may continuously switch on/switch

off while operating at 42% load. To avoid this unfortunate

condition, we recommend adjusting the engine load, in this

example to 40% or 44%, so that the blowers are either con-

tinuously running or permanently switched off.

Load up, 40 → 75% load

60 minutes

Load down

30 minutes

Slide Type Fuel Valves

The risk of soot development during long-term low load

operation depends on engine type and fuel valve type.

Combustion chamber components

Combustion chamber components are generally lower

loaded when operating at low load. We have observed minor

exhaust valve temperature elevations during low load, but

none above our recommended range.

Engine type

Soot development

ME/ME-C engines

Very low

MC/MC-C engines with slide valves Generally low

MC/MC-C, former standard or mini sac valves Higher

Please note, that a higher average exhaust valve temperature

may increase the valve spindle wear, thereby reducing the

time between overhaul.

All ME/ME-C engines are equipped with slide type fuel

valves. Slide type fuel valves were introduced in MC/MC-C

engines in the late 1990s, and have been standard on all

new MC/MC-C engines since 2005.

Further Information

In this service letter, emphasis is on what to expect and

consider when initiating long-term low load operation of

ME/ME-C and MC/MC-C engines, down to 40% load.

Compared to former fuel valve types, slide type fuel valves

have improved injection quality dramatically, thereby reduc-

ing soot development in the gas ways. Slide type fuel valves

have also proved to be very well suited for low load operation.

For further information on long-term low load operation,

please refer to the following:

Before initiating long-term low load operation on MC/MC-C

engines itted with our former standard or mini-sac valves,

we recommend retroitting slide type fuel valves.

Paper: Low Container Ship Speed Facilitated by Versatile

ME/ME-C Engines, 2008

The paper can be downloaded here:

www.mandiesel.com/article_008410.html

Service letter: SL07-480

Our service letters are available online.

Please register here to get online access to service letters:

www.mandiesel.com/sl-registration

Fig. 3: Slide type fuel valve and HIP-compound nozzle

By registering, you get online access to our service letters,

and you will be notiied by e-mail when new service letters

are published.

Low Load Update. Down to 40% load. Page 3 of 3

Plik z chomika:

Inne pliki z tego folderu:

Inne foldery tego chomika: