Influence of Ambient
Temperature Conditions
Main engine operation of MAN B&W two-stroke engines
2 Influence of Ambient Temperature Conditions
MAN B&W Diesel
3Influence of Ambient Temperature Conditions
Contents
Introduction .................................................................................................5
Chapter 1 ....................................................................................................5
Temperature Restrictions and Load-up Procedures at Start of Engine ..............5
Start of warm engine – normal load-up procedures ..................................5
Start of cold engine – exceptional load-up procedures .............................6
Preheating during standstill periods .........................................................6
Jacket cooling water systems with a built-in preheater .............................7
Preheater capacity ..................................................................................7
Chapter 2 ....................................................................................................8
Engine Room Ventilation ...............................................................................8
Air temperature .......................................................................................8
Air supply ...............................................................................................9
Air pressure ..........................................................................................10
Chapter 3 ..................................................................................................11
Ambient Temperature Operation and Matching ...........................................11
Standard ambient temperature matched engine ....................................11
Non-standard ambient temperature matched engine .............................12
Design recommendations for operation at extremely low air temperature ....... 15
Closing Remarks ........................................................................................17
4 Influence of Ambient Temperature Conditions
MAN B&W Diesel
5Influence of Ambient Temperature Conditions
Influence of Ambient Temperature Conditions
Main engine operation of MAN B&W two-stroke engines
Introduction
Diesel engines used as prime movers
on ships are exposed to the varying cli-
matic temperature conditions that pre-
vail in different parts of the world, and
must therefore be able to operate un-
der all ambient conditions from winter
to summer and from arctic to tropical
areas.
As the temperature variations on the
surface of the sea are rather limited,
the diesel engine will not normally be
exposed to really extreme tempera-
tures. However, the changes that do
occur in the ambient conditions will,
among other things, cause a change
in the specific fuel oil consumption, the
exhaust gas amount and the exhaust
gas temperature of the diesel engine.
These changes are already described
in our Project Guides and will therefore
not be discussed in this paper.
Also the scavenge air, compression and
maximum firing pressures of the diesel
engine will change with climatic chang-
es and, at very low ambient air temper-
atures, unrestricted engine operation
requires adjustments of individual en-
gine parameters.
This paper describes our recommenda-
tions of load-up procedures on engine
start-up, the supply of ventilation air to
the engine room and engine operation
under normal, high and extremely low
ambient temperature conditions.
The paper is divided into three chapters
which, in principle, may be read inde-
pendently of each other. Thus, Chapter
3 is more or less a copy of our paper
“Ambient Temp–air temperature as a
common parameter.
The three chapters are entitled:
? Temperature Restrictions and Load-
up Procedures at Start of Engine
? Engine Room Ventilation
? Ambient Temperature Operation and
Matching
Chapter 1
Temperature Restrictions and Load-up
Procedures at Start of Engine
In order to protect the engine against
cold corrosion attacks on the cylinder lin-
ers, some minimum temperature restric-
tions and load-up procedures have to be
considered before starting the engine.
Below stated load-up procedures are
valid for MAN B&W two-stroke engines
with a cylinder bore greater or equal to
80 cm, and may with benefit also be
applied for engines with a smaller bore.
However, if needed, the existing load-
up programme recommendation (from
90% to 100% in 30 minutes) is still valid
for engines with bore sizes from 70 cm
and down.
Note: The below recommendations are
based on the assumption that the en-
gine has already been well run in.
Start of warm engine – normal load-
up procedures
As a summary, the load-up procedures
recommended for normal start of en-
gine are shown in Fig. 1.
Recommended start of engine at normal en-
gine load operation
Fixed pitch propellers
Normally, a minimum engine jacket wa-
ter temperature of 50
o
C is recommend-
ed before the engine may be started
and run up gradually from 80% to 90%
of specified MCR speed (SMCR rpm).
during 30 minutes.
SMCR = Specified Maximum
Continuos Rating.
rpm = revolutions per minute
6 Influence of Ambient Temperature Conditions
Start of warm engine (normal load-up procedures)
Required jacket water temperature at normal start of engine: minimum 50
o
C
FPP:
CPP:
Fixed Pitch Propeller
Controllable Pitch Propeller
Recommended start of engine
1. at normal engine load operation
A. Run up slowly minimum
temp. 50
o
C
FPP – From 0% up to 80% SMCR speed
CPP – From 0% up to 50% SMCR power
B. Run up slowly,
(minimum 30 min)
FPP – From 80% up to 90% SMCR speed
CPP – From 50% up to 75% SMCR power
C. Run up slowly,
(minimum 60 min)
FPP – From 90% up to 100% SMCR speed
CPP – From 75% up to 100% SMCR power
2. at normal very low engine load operation
A. Run up slowly
If normally 10% to 40% engine low load operation
(slide fuel valves needed) extra slowly load-up proce-
dure is recommended: minimum 30 min from 10% to
40% load and minimum 60 min from 40% to 75% load
For running-up between 90% and
100% of SMCR rpm, it is recommend-
ed that the speed be increased slowly
over a period of 60 minutes.
Controllable Pitch Propellers
Normally, a minimum engine jacket wa-
ter temperature of 50
o
C is recommend-
ed before the engine may be started
and run up gradually from 50% to 75%
of specified MCR load (SMCR power)
during 30 minutes.
For running-up between 75% and
100% of SMCR power, it is recom-
mended that the load be increased
slowly over a period of 60 minutes.
Recommended start of engine at normal very
low engine load operation
For engines normally running at 10%
to 40% engine low load operation an
extra slowly load-up procedure is rec-
ommended compared with above de-
scribed load-up procedures, and is
also shown in Fig. 1.
Start of cold engine – exceptional
load-up procedures
As a summary, the load-up pro-
cedures recommended for ex-
ceptional start of cold engine are
shown in Fig. 2.
Fixed pitch propellers
In exceptional circumstances where it is
not possible to comply with the above-
mentioned normal recommendations,
a minimum of 20
o
C can be accepted
before the engine is started and run up
slowly to 80% of SMCR rpm.
Before exceeding 80% SMCR rpm, a
minimum jacket water temperature of
50
o
C should be obtained before the
above-described normal start load-up
procedure may be continued.
Controllable Pitch Propellers
In exceptional circumstances where it is
not possible to comply with the above-
mentioned normal recommendations,
a minimum of 20
o
C can be accepted
before the engine is started and run up
slowly to 50% of SMCR power.
Before exceeding 50% SMCR power,
a minimum jacket water temperature
of 50
o
C should be obtained before the
above described normal start load-up
procedure may be continued.
The time period required for increasing
the jacket water temperature from 20°C
to 50°C depends on the amount of wa-
ter in the jacket cooling water system,
and on the engine load.
Preheating during standstill periods
During short stays in ports (i.e. less than
4-5 days), it is recommended to keep
the engine preheated, the purpose be-
Fig. 1: Temperature restrictions and load-up procedures at normal start of engine
Start of cold engine (exceptional load-up procedures)
Required jacket water temperature at start of cold engine: minimum 20
o
C
FPP:
CPP:
Fixed Pitch Propeller
Controllable Pitch Propeller
Recommended start of engine at normal engine load operation
A. Run up slowly Minimum
temp. 20
o
C
FPP – From 0% up to 80% SMCR speed
CPP – From 0% up to 50% SMCR power
B. Run up slowly, Minimum
(minimum 30 min) temp. 50
o
C
FPP – From 80% up to 90% SMCR speed
CPP – From 50% up to 75% SMCR power
C. Run up slowly,
(minimum 60 min)
FPP – From 90% up to 100% SMCR speed
CPP – From 75% up to 100% SMCR power
Fig. 2: Temperature restrictions and load-up procedures at start of cold engine in exceptional cases
MAN B&W Diesel
7Influence of Ambient Temperature Conditions
ing to prevent temperature variations in
the engine structure and corresponding
variations in thermal expansions, and
thus the risk of leakages.
The jacket cooling water outlet temper-
ature should be kept as high as possi-
ble (max. 75-80°C), and should – before
start-up – be increased to at least 50°C,
either by means of the auxiliary engine
cooling water, or by means of a built-in
preheater in the jacket cooling water
system, or a combination of both.
Jacket cooling water systems with a
built-in preheater
For two different jacket water preheater
systems, A and B, the positioning of a
preheater in the jacket cooling water
system is shown schematically in Figs.
3 and 4, respectively.
For system A, the circulating water flow
is divided into two branches, one go-
ing through the engine and one going
through the cooling water system out-
side the engine. As the arrows indicate,
the preheater water flows in the oppo-
site direction through the engine, com-
pared with the main jacket water flow.
As the water inlet is at the top of the
engine, the engine preheating is more
effective in this way.
Preheater
pump
Preheater
Preheater
bypass
Diesel engine
Jacket water main pumps
Fig. 4: Preheating of jacket cooling water system – System B
For system B, the preheater and circu-
lating pump are placed in parallel with
the jacket water main pumps, and the
water flow direction is the same as for
the jacket cooling water system.
In both cases, the preheater operation
is controlled by a temperature sensor
after the preheater.
Preheater capacity
When a preheater is installed in the jacket
cooling water system, as shown in Figs.
3 and 4, the preheater pump capacity,
should be about 10% of the jacket water
main pump capacity. Based on experi-
ence, it is recommended that the pres-
sure drop across the preheater should
be approx. 0.2 bar. The preheater pump
and the jacket water main pump should
be electrically interlocked to avoid the
risk of simultaneous operation.
The preheater capacity depends on
the required preheating time and the
required temperature increase of the
Direction of main water flow
Direction of preheater circulating water flow
Preheater
pump
Preheater
Preheater
bypass
Diesel engine
Jacket water main pumps
Fig. 3: Preheating of jacket cooling water system – System A
8 Influence of Ambient Temperature Conditions
Fig. 5: Preheating of diesel engine
Preheater capacity in %
of nominal MCR power
Preheating time
0 10 20 30 40 50 60 70
0
10
20
30
40
50
60
o
C 1.50% 1.25% 1.00% 0.75%
The temperature increase and corresponding
preheating time curves are shown for the different
preheater sizes indicated in % of nominal MCR power
hours
Temperature
increase
of jacket water
engine jacket water. The temperature
and time relationship is shown in Fig. 5.
The relationship is almost the same for
all engine types.
If a temperature increase of for example
35°C (from 15°C to 50°C) is required, a
preheater capacity of about 1% of the
engine’s nominal MCR power is required
to obtain a preheating time of 12 hours.
When sailing in arctic areas, the re-
quired temperature increase may be
higher, possibly 45°C or even higher,
and therefore a larger preheater capac-
ity is required. The curves in Fig. 5 are
based on the assumption that, at the
start of preheating, the engine and en-
gine room are of equal temperatures.
It is assumed that the temperature will
increase uniformly all over the engine
structure during preheating, for which
reason steel masses and engine surfaces
in the lower part of the engine are also
included in the calculation.
The results of the preheating calcula-
tions may therefore be somewhat con-
servative.
Chapter 2
Engine Room Ventilation
In addition to providing sufficient air for
combustion purposes in the main en-
gine, auxiliary diesel engines, fuel fired
boiler, etc., the engine room ventilation
system should be designed to remove
the radiation and convection heat from
the main engine, auxiliary engines, boil-
ers and other components.
A sufficient amount of ventilation air
should be supplied and exhausted
through suitably protected openings
arranged in such a way that these
openings can be used in all weather
conditions. Care should be taken to
ensure that no seawater can be drawn
into the ventilation air intakes.
Furthermore, the ventilation air inlet
should be placed at an appropriate dis-
tance from the exhaust gas funnel in or-
der to avoid the suction of exhaust gas
into the engine room.
Major dust and dirt particles can foul
air coolers and increase the wear of
combustion chamber components.
Accordingly, the air supplied to the
engine must be cleaned by appropri-
ate filters. The size of particles passing
through the air intake filter should not
exceed 5μm.
An example of an engine room ventila-
tion system, where ventilation fans blow
air into the engine room via air ducts, is
shown in Fig. 6.
Air temperature
Measurements show that the ambient
air intake temperature (from deck) at sea
will be within 1 to 3°C of the seawater
MAN B&W Diesel
9Influence of Ambient Temperature Conditions
temperature, i.e. max. 35°C for 32°C
seawater, and max. 39°C for 36°C sea-
water.
Measurements also show that, in a nor-
mal ventilation air intake system, where
combustion air is taken directly from
the engine room of a ship, the engine
room temperature is normally 10-12°C
higher than the ambient outside air tem-
perature. This temperature difference is
even higher for winter ambient air tem-
peratures, see Fig. 7. In general, the en-
gine room temperature should never be
below 5°C, which is ensured by stopping
one or more of the air ventilation fans,
der normal air temperature conditions,
the air inlet temperature to the turbo-
charger is only 1-3°C higher than the am-
bient outside air temperature.
This means that the turbocharger suc-
tion air temperature will not be higher
than about 39 + 3 = 42°C (ref. 36°C
S.W.), say 45°C.
For arctic running conditions, a ducted
air intake system directly to the turbo-
charger can be an advantage in order to
maintain sufficiently high temperatures
for the crew in the engine room. With
a ducted air intake, the turbocharger’s
intake air temperature may be assumed
to be approximately equal to the ambi-
ent outside air temperature.
Air supply
In the case of a low speed two-stroke
diesel engine installed in a spacious en-
gine room, the capacity of the ventilation
system should be such that the ventila-
tion air to the engine room is at least
1.5 times the total air consumption of
the main engine, auxiliary engines, boil-
er, etc., all at specified maximum con-
tinuous rating (SMCR).
As a rule of thumb, the minimum en-
gine room ventilation air amount corre-
sponds to about 1.75 times the air con-
sumption of the main engine at SMCR.
Accordingly, 2.0 times the air con-
sumption of the main engine at SMCR
may be sufficient.
On the other hand, for a compact engine
room with a small two-stroke diesel
engine, the above factor of 1.5 is rec-
ommended to be higher, at least 2.0,
because the radiation and convection
heat losses from the engine are relatively
Air inletAir inlet
Engine room
ventilation fans
Air outlet
AEAE AE
Main ducts for supply
of combustion air
ME: Main engine
AE: Auxiliary engines
ME
Fig. 6: Engine room ventilation system
thus reducing the air supply to and
thereby the venting of the engine room.
This means that the average air tem-
perature in a ventilated engine room will
not be lower than 5°C and not higher
than 39 + 12 = 51°C, say 55°C (ref.
36°C S.W.), as often used as maximum
temperature for design of the engine
room components.
Since the air ventilation ducts for a nor-
mal air intake system are placed near
the turbochargers, the air inlet temper-
ature to the turbochargers will be lower
than the engine room temperature. Un-
10 Influence of Ambient Temperature Conditions
greater than from large two-stroke
engines, and because it may be difficult
to achieve an optimum air distribution
in a small engine room.
To obtain a correct supply of air for the
main engine’s combustion process,
about 50% of the ventilation air should
be blown in at the top of the main en-
gine, near the air intake to the turbo-
chargers, as shown in Fig. 6.
Otherwise, this can have a negative ef-
fect on the main engine performance.
Thus, the maximum firing pressure will
be reduced by 2.2% for every 10°C the
turbocharger air intake temperature is
raised, and the fuel consumption will go
up by 0.7%.
Furthermore, a correct air supply near
the turbochargers will reduce the dete-
rioration of the turbocharger air filters
(from oil fumes, etc., in the engine room
air), and a too draughty engine room
can be avoided.
Moreover, a sufficient amount of air
should be supplied to areas with a high
heat dissipation rate in order to ensure
that all the heat is removed, for instance
around auxiliary engines/generators
and boilers. Ventilation ducts for these
areas are not shown in Fig. 6.
In the winter time, the amount of air
needed to remove the radiation/con-
vection heat from the engine room may
be lower.
Fig. 7: Engine room temperature
hyphenminus20 0 20 40
0
10
20
30
40
50
60
o
C
The engine room temperature T and the engine
room/ambient air temperature difference T are shown
as functions of the ambient air temperature T
ER
amb
o
C
Amb. air temp. Tamb.
Engine room temperature T
and difference T
ER
c68T = hyphenminus Tamb.TER
TER
c68
c68
Air pressure
The air in the engine room should have
a slightly positive pressure, but should
not be more than about 5 mm WC (Wa-
ter Column) above the outside pressure
at the air outlets in the funnel.
Accommodation quarters will normally
have a somewhat higher over-pressure,
so as to prevent oil fumes from the en-
gine room penetrating through door(s)
into the accommodation.
The ventilation air can be supplied, for
example, by fans of the low-pressure
axial and high-pressure centrifugal or
axial types. The required pressure head
of the supply fans depends on the re-
sistance in the air ducts.
All ventilation air is normally delivered
by low-pressure air supply fans which,
to obtain sufficient air ventilation in all
corners of the engine room, may re-
quire extensive ducting and a pressure
head as stated below.
Low-pressure fans,
?p = 60-100 mm WC
For further information, please consult
engine room ventilation standard ISO
8861: 1998 (E).
MAN B&W Diesel
11Influence of Ambient Temperature Conditions
Fig. 8: Influence on SFOC of the cooling water
(scavenge air coolant) temperature
Engine shaft power
40 SMCR50 60 70 80 90 100%
SFOC
g/kWh
36°C C.W
10°C C.W
2 g/kWh
Turbocharger air intake temperature: 10°C
Chapter 3
Ambient Temperature Operation and
Matching
Standard ambient temperature
matched engine
Standard unrestricted service demands
For a standard main engine, the en-
gine layout is based on the ambient
reference conditions of the Interna-
tional Standard Organization (ISO):
ISO 3046-1:2002(E) and
ISO 15550:2002(E):
ISO ambient reference conditions
Barometric pressure: 1,000 mbar
Turbocharger air intake
temperature:
25oC
Charge air coolant tem-
perature:
25oC
Relative air humidity: 30%
With this layout basis, the engine must
be able to operate in unrestricted serv-
ice, i.e. up to 100% Specified Maximum
Continuous Rating (SMCR), within the
typical ambient temperature range that
the ship is exposed to, operating from
tropical to low winter ambient conditions.
According to the International Associa-
tion of Classification Societies (IACS)
rule M28, the upper requirement, nor-
mally referred to as tropical ambient ref-
erence conditions, is as follows:
IACS M28 (1978):
Tropical ambient reference conditions
Barometric pressure: 1,000 mbar
Air temperature: 45oC
Seawater temperature: 32oC
Relative air humidity: 60%
The above tropical ambient relative hu-
midity of 60% at 45oC is theoretically
the absolute limit at which it is possible
for humans to survive. The correspon-
ding wet bulb temperature is 36.8oC.
MAN Diesel & Turbo has never mea-
sured levels above 50% at 45oC, and
humidity levels above standard tropical
ambient conditions will never occur.
When applying the central cooling wa-
ter system which, today, is more com-
monly used than the seawater system,
the corresponding central cooling wa-
ter/scavenge air coolant temperature is
4oC higher than the seawater tempera-
ture, i.e. equal to 36oC.
The winter ambient reference condi-
tions used as standard for MAN B&W
two-stroke engines are as follows:
Winter ambient reference conditions
Barometric pressure: 1,000 mbar
Turbocharger air intake
temperature:
10oC
Cooling water temperature:
(minimum for lub. oil cooler)
10oC
Relative air humidity: 60%
Shipyards often specify a constant
(maximum) central cooling water tem-
perature of 36°C, not only for tropical
ambient conditions, but also for winter
ambient conditions. The purpose is to
reduce the seawater pump flow rate
when possible, and thereby to reduce
the electric power consumption, and/
or to reduce the water condensation in
the air coolers.
However, when operating with 36°C
cooling water instead of for example
10°C (to the scavenge air cooler), the
specific fuel oil consumption (SFOC)
will increase by approx. 2 g/kWh, see
Fig. 8. Any obtained gain in reduced
electric power consumption, therefore,
will be more than lost in additional fuel
costs of the main engine.
The above ISO, tropical and winter
ambient reference conditions are used
by MAN Diesel & Turbo for ships, and
MAN B&W two-stroke engines com-
ply with the above rules. MAN B&W
engines matched according to the
above rules are able to operate con-
tinuously up to 100% SMCR in the
air temperature range between about
-10 and 45oC.
Often the engine room temperature is mi-
staken for being equal to the turbocharger
air intake temperature. However, since the
air ventilation duct outlets for a normal
air intake system are placed near the
turbochargers, the air inlet temperature
to the turbochargers will be very close
to the ambient outside air temperature.
Under normal air temperature condi-
tions, the air inlet temperature to the
turbocharger is only 1-3°C higher than
the ambient outside air temperature.
12 Influence of Ambient Temperature Conditions
engine load resulting in a scavenge
air temperature below the level of the
scavenge air temperature alarm.
Nevertheless, the engine’s obtainable
load level will in all cases be much
higher than required to ensure a safe
manoeuvrability (4-6 knots) of the ship
even at an extreme seawater tempera-
ture of for example 42°C.
When sailing in, for example, the har-
bour area during manoeuvring, the en-
gine load will normally be relatively low
(15-30% SMCR), and the correspond-
ing scavenge air temperature will then
only be slightly higher than the scav-
enge air coolant temperature. There-
fore, a seawater temperature as high
as for example 42°C in harbour areas
is not considered a problem for the
main engine, and a special temperature
matching is not needed under these
operating conditions.
In general, when sailing in areas with a
high seawater temperature, it is pos-
sible to operate the standard ambient
temperature matched main engine at
any load as long as the scavenge air
temperature alarm limit is not reached.
If the alarm is activated, the engine load
has to be reduced.
Non-standard ambient temperature
matched engine
If unrestricted loads are desired in a
temperature range different from the
standard, different matching possibili-
ties are available.
Engine matching for non-standard air tem-
perature conditions
Usually, higher or lower turbocharger
air intake temperatures may result in
lower or higher scavenge air pressures,
respectively, and vice versa.
An increase of, for example, 5oC of the
tropical air temperature from standard
45oC to special 50oC will result in a too
low scavenge air pressure at 50oC.
However, the pressure reduction can
be compensated for by specifying a
correspondingly higher (turbocharger)
scavenge air pressure at ISO ambient
reference conditions. This involves that
the engine, instead of being matched
for the ISO-based design air tempera-
ture of 25oC, has to be matched for the
25 + 5 = 30oC turbocharger air intake
temperature.
The original ISO-based heat load con-
ditions will then almost be obtained
for this higher design air temperature.
The principles for standard and special
high (or low) ambient air temperature
matched engines are shown in Fig. 9.
At the other end of the air temperature
range, the increase of 5oC of the de-
sign air intake temperature will involve
a too high scavenge air pressure when
operating at -10oC. Operation below
-10 + 5 = -5oC will then only be pos-
sible when installing a variable exhaust
gas bypass valve system for low air
temperatures, as described later.
Fig. 9 may in a similar way also be
used to explain a special low tempera-
ture matched engine. For example, if
the standard tropical air temperature
needed is reduced by 10oC, from 45oC
to 35oC, the engine matching design
air temperature can be reduced to
25
ˉ
10 = 15oC.
The classification society rules often
specify an engine room air temperature
of 0-55oC as the basis for the design
of the engine room components. The
55oC is the temperature used when
approving engine room components.
This, however, must not be mistaken
for the above tropical air intake tempe-
rature of 45oC specified when related to
the capacity or effect of the machinery.
In recent years, owners/shipyards have
sometimes required unrestricted serv-
ice on special maximum ambient tem-
peratures higher than the tropical am-
bient temperatures specified by IACS
M28. In such cases, the main engine
has to be special high temperature
matched, as described later in this pa-
per.
Furthermore, operation in arctic areas with
extremely low air temperatures has also
sometimes been required by owners/
shipyards, and the measures to be taken
are also described later in this paper.
Operating at high seawater temperature with
standard matched engine
An increase of the seawater tempera-
ture and, thereby, the scavenge air
temperature has a negative impact on
the heat load conditions in the combus-
tion chamber. Therefore, all MAN B&W
two-stroke engines for marine applica-
tions have an alarm set point of 55°C
for the scavenge air temperature for pro-
tection of the engine, as described later.
For a standard ambient temperature
matched engine operating at an in-
creased seawater temperature existing
in some inland, gulf, bay and harbour
areas, the maximum power output of
the engine should be reduced to an
MAN B&W Diesel
13Influence of Ambient Temperature Conditions
Turbocharger
air intake temperature
-40
-35
-30
-25
-20
-15
-10
-5
0
5
10
15
20
25
30
35
40
45
50
55
Max.
45 °C
ISO
25 °C
Min.
-10 °C
ISO
design
layout
Normal
tropical
temperature
For engine loads
higher than 30% SMCR
a low scavenge air
coolant temperature
is recommended
(Giving low SFOC and
low scav. air press.)
Normal min.
ambient air
temperature
Standard
ISO temperature
matched engine
Possible low ambient
air temperature
exhaust gas bypass for
operation under
extremely low ambient
temperature conditions
ISO based
design
layout
Special
tropical
temperature
Lowest
ambient air
temperature
Low ambient air
temperature exhaust
gas bypass will be
needed below min.
temperature
Max.
Special
design
temperature
Min.
Special
High temperature
matched engine
Up to 100% SMCR running is not allowed
Up to 100% SMCR running is allowed
Up to 100% SMCR running only allowed when low
ambient temperature exhaust gas bypass (C1+2)
is installed
Standard
design
Temperature
ISO based
design
layout
Special
tropical
temperature
Lowest
ambient air
temperature
Max.
Special
design
temperature
Min.
Special
Low temperature
matched engine
-50
-45
60
65
Fig. 9: Principles for standard and special high (or low) ambient air temperature matched engines
14 Influence of Ambient Temperature Conditions
This involves that the exhaust gas tem-
perature will increase by about 16oC
compared with a standard ISO tem-
perature matched engine, whereas the
SFOC will increase.
Engine matching for high tropical seawater
temperature conditions
For long time operation in an area with
high tropical seawater temperatures,
the following should be observed.
An increase in the seawater tempera-
ture and, thereby, of the scavenge air
coolant temperature will involve a simi-
lar increase in the scavenge air tem-
perature, which has a negative impact
on the combustion chamber tempera-
tures. Therefore, for all marine applica-
tions, an alarm set point of 55oC for the
scavenge air temperature is applied for
protection of the engine.
The standard marine scavenge air cooler
is specified with a maximum 12oC tem-
perature difference between the cooling
water inlet and the scavenge air outlet
at 100% SMCR, which gives a maxi-
mum scavenge air temperature of 36 +
12 = 48oC for the scavenge air cooler
layout and, accordingly, a margin of 7
o
C
to the scavenge air temperature alarm
limit of 55oC.
Temperature °C
42
44
46
48
50
52
54
56
Maximum
scavenge air
temperature
at 100% SMCR
ISO based
scavenge air
coolant
temperature
ISO
design
layout
Standard ISO temperature
matched engine
Standard air cooler design
ISO based
design
layout
High scavenge
air coolant
temperature
Maximum
scavenge air
temperature
at 100% SMCR
Special high temperature
matched engine
Special air cooler design
Max. 48 °C Standard 48 °C
26
28
30
32
34
36
38
40
22
24
Standard tropical
seawater
temperature
Standard
tropical
scavenge air
coolant
temperature
High tropical
scavenge air
coolant
temperature
High tropical
seawater
temperature
Max. 40 °C
Max. 36 °C
Max. 29 °C
Standard 36 °C
Standard 32 °C
Standard
basis 25 °C
Max. 55 °C Standard 55 °C
Scavenge air temperature limit Scavenge air temperature limit
Up to 100% SMCR running is
not allowed (scavenge air)
Up to 100% SMCR running is
allowed (scavenge air)
Up to 100% SMCR running is
allowed (scavenge air coolant/central
cooling water)
Up to 100% SMCR running is
allowed (seawater)
A temperature difference of 8oC is con-
sidered to be the lowest possible tem-
perature difference to be used for a
realistic specification of a scavenge air
cooler. Accordingly, the 48
ˉ
8 = 40oC is
the maximum acceptable scavenge air
coolant temperature for a central cool-
ing water system, see the principles for
layout of the scavenge air cooler in Fig. 10.
The demand for an increased tropi-
cal scavenge air coolant (central cool-
ing water) temperature of up to 40oC,
therefore, can be compensated for by a
reduced design temperature difference
of the scavenge air cooler. This can be
obtained by means of an increased wa-
Fig. 10: Principles for layout of scavenge air cooler for standard and special high scavenge air coolant temperature (illustrated for a central cooling water system)
MAN B&W Diesel
15Influence of Ambient Temperature Conditions
ter flow and/or a bigger scavenge air
cooler.
Design recommendations for operation
at extremely low air temperature
When a standard ambient temperature
matched main engine on a ship occa-
sionally operates under arctic condi-
tions with low turbocharger air intake
temperatures, the density of the air will
be too high. As a result, the scavenge
air pressure, the compression pressure
and the maximum firing pressure will be
too high.
In order to prevent such excessive
pressures under low ambient air tem-
perature conditions, the turbocharger
air inlet temperature should be kept as
high as possible (by heating, if possi-
ble).
Furthermore, the scavenge air cool-
ant (cooling water) temperature should
be kept as low as possible and/or the
engine power in service should be re-
duced.
However, for an inlet air temperature
below approx.
ˉ
10oC, some engine de-
sign precautions have to be taken.
Main precautions for extreme low air tem-
perature operation
With a load-dependent exhaust gas
bypass system (standard MAN Diesel &
Turbo recommendation for extreme low
air temperature operation), as shown
in Fig. 11, part of the exhaust gas by-
passes the turbocharger turbine, giving
less energy to the compressor, thus re-
ducing the air supply and scavenge air
pressure to the engine.
For the electronically controlled ME
engine (ME/ME-C/ME-B), the load-de-
pendent bypass control can be incor-
porated in the Engine Control System
(ECS) as an add-on.
Engine load, fuel index and scavenge
air pressure signals are already availa-
ble for the ME software and, therefore,
additional measuring devices are not
needed for ME engines.
In general, a turbocharger with a nor-
mal layout can be used in connection
with an exhaust gas bypass. However,
in a few cases a turbocharger modifica-
tion may be needed.
The exhaust gas bypass system ensures
that when the engine is running at part
load at low ambient air temperatures,
the load-dependent scavenge air pres-
sure is close to the corresponding pres-
sure on the scavenge air pressure curve
which is valid for ISO ambient condi-
tions. When the scavenge air pressure
exceeds the read-in ISO-based sca-
venge air pressure curve, the bypass
valve will variably open and, irrespec-
tive of the ambient conditions, ensure
that the engine is not overloaded. At the
same time, it will keep the exhaust gas
temperature relatively high.
Fig. 11: Standard load-dependent low ambient air temperature exhaust gas bypass system
D2
C1+2
B
D1
1
2
B Exhaust gas bypass valve
Controlled by the scavenge air pressure
C1+2 Control device
Ensures that the loadhyphenminusdependent scavenge air pressure
does not exceed the corresponding ISO based pressure
D Required electric measuring device
D1 Scavenge air pressure
D2 Engine speed and engine load
Diesel engine
Scavenge
air receiver
Scavenge
air cooler
Compressor
Turbocharger
Turbine
Exhaust gas
receiver
Exhaust gas system
Air intake casing
Exhaust gas bypass
16 Influence of Ambient Temperature Conditions
The latest generations of turbochargers
with variable flow, e.g. the VTA (Variable
Turbine Area) system from MAN Diesel
& Turbo, can replace the variable by-
pass and ensure the same scavenge air
pressure control.
Other low temperature precautions
Low ambient air temperature and low
seawater temperature conditions come
together. The cooling water inlet tem-
perature to the lube oil cooler should
not be lower than 10°C, as otherwise
the viscosity of the oil in the cooler will
be too high, and the heat transfer inad-
equate. This means that some of the
cooling water should be recirculated to
keep up the temperature.
Furthermore, to keep the lube oil vis-
cosity low enough to ensure proper
suction conditions in the lube oil pump,
it may be advisable to install heating
coils near the suction pipe in the lube
oil bottom tank.
The following additional modifications
of the standard design practice should
be considered as well:
? Larger electric heaters for the cylin-
der lubricators or other cylinder oil
ancillary equipment
? Cylinder oil pipes to be further heat
traced/insulated
? Upgraded steam tracing of fuel oil
pipes
? Increased preheater capacity for
jacket water during standstill
? Different grades of lubricating oil for
turbochargers
? Space heaters for electric motors
? Sea chests must be arranged so that
blocking with ice is avoided.
Ships with ice class notation
For ships with the Finnish-Swedish ice
class notation 1C, 1B, 1A and even
1A super or similar, all MAN B&W
two-stroke diesel engines meet the
ice class demands, i.e. there will be no
changes to the main engines.
However, if the ship is with ice class
notation 1A super and the main engine
has to be reversed for going astern
(Fixed Pitch Propeller), the starting air
compressors must be able to charge
the starting air receivers within half an
hour, instead of one hour, i.e. the com-
pressors must be the double in size
compared to normal.
For other special ice class notations,
the engines need to be checked indi-
vidually.
40
2,500
kg/h
Engine shaft power
60 80 100%
Surplus steam
Extra steam needed
Total steam production,
without bypass
Total steam production,
with exhaust gas bypass
Steam consumption
2,000
1,500
1,000
500
0
Steam production
SMCR50 70 90
6S60MC-C7/ME-C7
SMCR = 13,560 kW at 105 r/min
Air intake temperature: 0 °C
Cooling water temperature: 10°C
Fig. 12: Expected steam production by exhaust gas boiler at winter ambient conditions (0 °C air) for main
engine 6S60MC-C7/ME-C7 with/without a load-dependent low air temperature exhaust gas bypass system
MAN B&W Diesel
17Influence of Ambient Temperature Conditions
The exhaust gas bypass system to be
applied is independent of the ice class-
es, and only depends on how low the
specified ambient air temperature is
expected to be. However, if the ship is
specified with a high ice class like 1A
super, it is advisable to make prepara-
tions for, or install, an exhaust gas by-
pass system.
Increased steam production in wintertime
During normal operation at low am-
bient temperatures, the exhaust gas
temperature after the turbochargers will
decrease by about 1.6oC for each 1.0oC
reduction of the intake air temperature.
The load-dependent exhaust gas by-
pass system will ensure that the exhaust
gas temperature after the turbochargers
will fall by only about 0.3oC per 1.0oC
drop in the intake air temperature, thus
enabling the exhaust gas boiler to pro-
duce more steam under cold ambient
temperature conditions.
Irrespective of whether a bypass sys-
tem is installed or not, the exhaust gas
boiler steam production at ISO ambient
conditions (25oC air and 25oC C.W.) or
higher ambient temperature conditions,
will be the same, whereas in wintertime
the steam production may be relatively
increased, as the scavenge air pressure
is controlled by the bypass valve.
As an example, Fig. 12 shows the influ-
ence of the load-dependent exhaust gas
bypass system on the steam production
when the engine is operated in winter-
time, with an ambient air temperature of
0oC and a scavenge air cooling water
temperature of 10oC.
The calculations have been made for a
6S60MC-C7/ME-C7 engine equipped
with a high-efficiency turbocharger, i.e.
having an exhaust gas temperature of
245oC at SMCR and ISO ambient con-
ditions.
Fig. 12 shows that in wintertime, it is
questionable whether an engine with-
out a bypass will meet the ship''s steam
demand for heating purposes (indicat-
ed for bulk carrier or tanker), whereas
with a load-dependent exhaust gas by-
pass system, the engine can meet the
steam demand.
Closing Remarks
Diesel engines installed in ocean-going
ships are often exposed to different cli-
matic temperature conditions because
of the ship’s trading pattern, but as the
temperature variations on the sea sur-
face are normally relatively limited, the
engines will normally be able to operate
worldwide in unrestricted service with-
out any precautions being taken.
Even if the ship has to sail in very cold
areas, the MAN B&W two-stroke en-
gines can, as this paper illustrates, also
operate under such conditions without
any problems as long as special low
temperature precautions are taken.
The use of the standard load-dependent
low ambient air temperature exhaust
gas bypass system may – as an ad-
ditional benefit – also improve the ex-
haust gas heat utilisation when running
at low ambient air temperatures.
Furthermore, at the other end of the
temperature scale, if the ship should
need to sail in unrestricted service in ar-
eas with very high ambient air tempera-
tures, higher than 45°C, this will also be
possible provided a high temperature
matching of the engine is applied. Even
when sailing should be needed at very
high seawater temperatures, this will be
possible provided a specially designed
scavenge air cooler is installed on the
diesel engine.
Copyright
?
MAN Diesel & T
urbo · Subject to modification in the inter
est of technical pr
ogr
ess.
5510-0074-00ppr Aug. 2010 Printed in Denmark
MAN Diesel & Turbo
Teglholmsgade 41
2450 Copenhagen SV, Denmark
Phone +45 33 85 11 00
Fax +45 33 85 10 30
info-cph@mandieselturbo.com
www.mandieselturbo.com
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