MITSUI ENGINEERING & SHIPBUILDING CO., LTD.

DIESEL TECHNICAL INVESTIGATION GROUP.

for MITSUI MAN B&W engines, No. 179

APPROVED N. Osako
Low Load Operation
Special attention and modification based CHECKED
on recent service experience
PREPARED M. Kotake

ENGINE TYPE All engines DATE 20thAug. 2012

Revised 1: Added chapter 5. Maintenance of exhaust valve (Jan. 31st 2013)

Guidance and special attention on continuous 10% to 40% low-load operation are described in the
Service Note No.169

Recently it has been reported that vessels in service with operating continuously down to 10% engine
load has been in good condition after low load operation. Special attention about fouling of exhaust gas
ways and turbocharger(s) is directed in the service note No.169, but no major difficulties have been
reported so far.
From the experience of operating continuously down to 10% engine load, this service letter describes
the special attention newly obtained as follows.

1 Auxiliary blowers

In connection with continuous low-load operation and, thereby, increased operation time of auxiliary
blowers (A/B), an increasing number of troubles of the A/B has been reported. An increased running
hours will require increased maintenance, but still a number of troubles have been reported.

If the venting pipe is closed or plugged, the scavenge air pressure will push air, sludge and impurities
from the scavenge air through the bearing and, thereby, remove the lubricant from the bearing.

AT FIRST WHEN
IMMEDIATELY OPPORTUNITY CONVENIENT OTHERS

Issuer : Mitsui engineering and shipbuilding Co., ltd.

Diesel technical investigation group
1-1, Tama 3-chome, Tamano, Okayama 706-8651 Japan
TEL : 0863-23-2534 / FAX : 0863-23-2772
E-mail: demail @mes.co.jp
It is recommended to open the valve equipped at the top of venting hole at least once a week regularly
for drain from the venting pipe. This valve can open and close during engine operation. Change the
shaft sealing if an excessive air amount is experienced from the drain.

Shaft Shaft sealing labyrinth

Venting pipe
Ball valve
Drain

This is also described in the service note No.169, it is a general recommendation to carry a complete
spare blower on board the vessel if low-load operation is employed for longer periods
2. Flap valves- scavenge air receiver

There have been several reports of broken flap valves in connection with low-load operation

At some point in the load area around the switch point of the A/B, the flap valves (non-return valves) in
the scavenge air receiver will be continuously opening and closing due to the pressure pulsations in the
scavenge air receiver. This load area can be recognized by a distinct hammering noise from the flap
valves.

The hammering of the valves will damage and/or break the valves after a short period.
Operating the engine continuously in this load area must be avoided.

Broken and damaged valves must be changed at first opportunity, and valve pieces should be removed
from the scavenge air space to prevent them from causing damage downstream. Broken and missing
valves will have a negative impact on the engine performance when the auxiliary blowers are running.
 Cylinder lubrication

Lower-load operation will result in an increase in the specific cylinder oil dosage (g/kWh).

The intention is to switch from Mep-proportional control or Load-proportional control to

Speed-proportional control below 25% engine load. However, since the Alpha lubricator system has a
limitation of maximum 15 rev. per injection in order to avoid too long intervals between lube injections
on MC/MC-C engines, MEP-proportional control or Load-proportional control will be switched to
Speed-proportional control at 35-40 % load, depends on cylinder oil feed rate. This may result in
excessive lubrication at very low loads, which could lead to deposit build-up on the piston top lands.
We have not received any reports of damage in relation with over lubrication at low loads. However,
Deposit build-up of unused lube oil and additives may be harmful to the cylinder condition, especially in
connection with subsequent loading up to higher engine loads.

As illustrated in Fig. 3 and Fig. 4, smaller alpha lubricator pumps can be retrofitted, so that the Mep
proportional (or the load proportional) breakpoint can be moved down to a lower engine load and Mep
proportional (or the load proportional) control can be kept in more low engine load. Depending on the
load pattern of the engine, this modification could show profitable for reducing operation cost, and it
would reduce the fouling of the scavenge air space with excessive lube oil.

If mechanical lubricators are installed, it is highly recommended to retrofit the Alpha Lubricator.
Especially during low-load operation, the mechanical lubricator will have a very high feed rate
compared to the specified need.
If you need further advice and question regarding the above smaller Alpha Lubricator pump or
Alpha Lubricator retrofit, please contact with the MES TECHNOSERVICE CO., LTD.
Please refer to Service Note No. 111

For retrofitting to smaller alpha lubricator,

plunger, cylinder cover and their accessories
are replaced. (Red portion)

Plunger

Cylinder Cover
Cylinder feed rate can control
more lower during low load
operation if break point is
changed from load 35% to load
15%.
 Turbocharger cleaning by solid material and engine load-up

The tendency to form deposits of turbocharger depends on the maintenance condition of fuel injection
equipment, fuel cleaning equipment, and the quality of the fuel used. Accordingly, the cleaning interval
must be based on the experience of the turbocharger fouling in the specific plant,

Engine load-up should be not operated as much as possible in order not to compromise the cylinder
condition. Engine load-up level and frequency should be decided, depends on the actual engine
condition with trial operation to 50 – 75% load once a day.

The necessary cleaning intervals of the turbocharger are specified by the turbocharger designer, and
the latest recommendation should be followed

ABB: increase load to >50% engine load

– minimum once every 20-50 hours.
MAN: to be effected during normal service load. Not need to increase engine load. But, carry out the
cleaning during load-up operation for effective cleaning as possible.
– minimum once every 24 hours.
MET: load to be between a minimum and a maximum T/C speed depending on T/C type
– minimum once every 100 hours.

5. Maintenance of exhaust valve

In condition that exhaust valve temperature is

high continuously, burnt wear progress of
exhaust valve may increase.
In exhaust valve maintenance as shown in fig.
5, check the burnt wear amount.
If the burnt wear amount arrives to limit,
replace or repair the exhaust valve. Burnt wear
Please see the check point and the
maintenance interval in the instruction manual.