Influence of Ambient
Temperature Conditions
Main engine operation of MAN B&W two-stroke engines
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
Influence of Ambient Temperature Conditions
Main engine operation of MAN B&W two-stroke engines
Introduction
our paper “Ambient Temp–air tempera-
80 cm, and may with benefit also be
Diesel engines used as prime movers
ture as a common parameter.
applied for engines with a smaller bore.
The three chapters are entitled:
However, if needed, the existing load-
on ships are exposed to the varying climatic temperature conditions that prevail in different parts of the world, and
must therefore be able to operate un-
up programme recommendation (from
„„
der all ambient conditions from winter
Temperature Restrictions and Load-
90% to 100% in 30 minutes) is still valid
up Procedures at Start of Engine
for engines with bore sizes from 70 cm
to summer and from arctic to tropical
areas.
and down.
„„
Engine Room Ventilation
Note: The below recommendations are
As the temperature variations on the
surface of the sea are rather limited, the
„„
Ambient Temperature Operation and
based on the assumption that the en-
Matching
gine has already been well run in.
diesel engine will not normally be exStart of warm engine – normal load-
other things, cause a change in the
Chapter 1
Temperature Restrictions and
Load-up Procedures at Start of
Engine
specific fuel oil consumption, the ex-
In order to protect the engine against
gine are shown in Fig. 1.
haust gas amount and the exhaust gas
cold corrosion attacks on the cylinder lin-
temperature of the diesel engine. These
ers, some minimum temperature restric-
Recommended start of engine at normal en-
changes are already described in our
tions and load-up procedures have to be
gine load operation
Project Guides and will therefore not be
considered before starting the engine.
Fixed pitch propellers
Below stated load-up procedures are
Normally, a minimum engine jacket wa-
Also the scavenge air, compression and
valid for MAN B&W two-stroke engines
ter temperature of 50oC is recommend-
maximum firing pressures of the diesel
with a cylinder bore greater or equal to
ed before the engine may be started
posed to really extreme temperatures.
However, the changes that do occur
in the ambient conditions will, among
up procedures
As a summary, the load-up procedures
recommended for normal start of en-
discussed in this paper.
and run up gradually from 80% to 90%
engine will change with climatic changes
and, at very low ambient air temperatures, unrestricted engine operation
requires adjustments of individual engine parameters.
This paper describes our recommendations of load-up procedures on
engine startup, the supply of ventilation air to the engine room and engine
Start of warm engine (normal load-up procedures)
Required jacket water temperature at normal start of engine: minimum 50oC
FPP:
Fixed Pitch Propeller
CPP:
Controllable Pitch Propeller
Recommended start of engine
1. at normal engine load operation
A. Run up slowly
minimum
temp. 50oC
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
conditions.
C. Run up slowly,
(minimum 60 min)
FPP – From 90% up to 100% SMCR speed
CPP – From 75% up to 100% SMCR power
The paper is divided into three chap-
A. Run up slowly
operation under normal, high and
extremely low ambient temperature
2. at normal very low engine load operation
ters which, in principle, may be read
independently of each other. Thus,
Chapter 3 is more or less a copy of
If normally 10% to 40% engine low load operation
(slide fuel valves needed) extra slowly load-up procedure is recommended: minimum 30 min from 10% to
40% load and minimum 60 min from 40% to 75% load
Fig. 1: Temperature restrictions and load-up procedures at normal start of engine
Influence of Ambient – Temperature Conditions
5
of specified MCR speed (SMCR rpm).
during 30 minutes.
Start of cold engine (exceptional load-up procedures)
Required jacket water temperature at start of cold engine: minimum 20 o C
SMCR = Specified Maximum
FPP:
Fixed Pitch Propeller
CPP:
Controllable Pitch Propeller
Recommended start of engine at normal engine load operation
Continuos Rating.
A. Run up slowly
Minimum
temp. 20oC
FPP – From 0% up to 80% SMCR speed
CPP – From 0% up to 50% SMCR power
= revolutions per minute
B. Run up slowly,
(minimum 30 min)
Minimum
temp. 50oC
FPP – From 80% up to 90% SMCR speed
CPP – From 50% up to 75% SMCR power
For running-up between 90% and
C. Run up slowly,
(minimum 60 min)
rpm
100% of SMCR rpm, it is recommended that the speed be increased slowly
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
over a period of 60 minutes.
Controllable Pitch Propellers
Fixed pitch propellers
The time period required for increasing
Normally, a minimum engine jacket wa-
In exceptional circumstances where it is
the jacket water temperature from 20°C
ter temperature of 50oC is recommend-
not possible to comply with the above-
to 50°C depends on the amount of wa-
ed before the engine may be started
mentioned normal recommendations,
ter in the jacket cooling water system,
and run up gradually from 50% to 75%
a minimum of 20oC can be accepted
and on the engine load.
of specified MCR load (SMCR power)
before the engine is started and run up
during 30 minutes.
slowly to 80% of SMCR rpm.
For running-up between 75% and
Before exceeding 80% SMCR rpm, a
45 days), it is recommended to keep
100% of SMCR power, it is recom-
minimum jacket water temperature of
the engine preheated, the purpose be-
mended that the load be increased
50oC should be obtained before the
ing to prevent temperature variations in
slowly over a period of 60 minutes.
above-described normal start load-up
the engine structure and corresponding
procedure may be continued.
variations in thermal expansions, and
Preheating during standstill periods
During short stays in ports (i.e. less than
Recommended start of engine at normal very
thus the risk of leakages.
low engine load operation
Controllable Pitch Propellers
For engines normally running at 10%
In exceptional circumstances where it is
The jacket cooling water outlet temper-
to 40% engine low load operation an
not possible to comply with the above-
ature should be kept as high as possi-
extra slowly load-up procedure is rec-
mentioned normal recommendations,
ble (max. 7580°C), and should – before
ommended compared with above de-
a minimum of 20oC can be accepted
startup – be increased to at least 50°C,
scribed load-up procedures, and is
before the engine is started and run up
either by means of the auxiliary engine
also shown in Fig. 1.
slowly to 50% of SMCR power.
cooling water, or by means of a builtin
Start of cold engine – exceptional
Before exceeding 50% SMCR power,
load-up procedures
a minimum jacket water temperature
As a summary, the load-up pro-
of 50oC should be obtained before the
cedures
above described normal start load-up
preheater in the jacket cooling water
recommended
for
ex-
ceptional start of cold engine are
shown in Fig. 2.
6
Influence of Ambient – Temperature Conditions
procedure may be continued.
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
preheater in the jacket cooling water
system is shown schematically in Figs.
Preheater
pump
3 and 4, respectively.
Preheater
bypass
For system A, the circulating water flow
is divided into two branches, one going through the engine and one going
through the cooling water system outside the engine. As the arrows indicate,
the preheater water flows in the oppo-
Jacket water main pumps
Diesel engine
site direction through the engine, com-
Direction of main water flow
Direction of preheater circulating water flow
pared with the main jacket water flow.
As the water inlet is at the top of the
Fig. 3: Preheating of jacket cooling water system – System A
engine, the engine preheating is more
effective in this way.
For system B, the preheater and circulating pump are placed in parallel with
Preheater
the jacket water main pumps, and the
water flow direction is the same as for
Preheater
pump Preheater
bypass
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,
Jacket water main pumps
Diesel engine
Fig. 4: Preheating of jacket cooling water system – System B
should be about 10% of the jacket water
main pump capacity. Based on experience, it is recommended that the pressure 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.
Influence of Ambient – Temperature Conditions
7
The preheater capacity depends on
gine room are of equal temperatures.
the main engine, auxiliary engines, boil-
the required preheating time and the
It is assumed that the temperature will
ers and other components.
required temperature increase of the
increase uniformly all over the engine
engine jacket water. The temperature
structure during preheating, for which
A sufficient amount of ventilation air
and time relationship is shown in Fig. 5.
reason steel masses and engine surfaces
should be supplied and exhausted
The relationship is almost the same for
in the lower part of the engine are also
through suitably protected openings
all engine types.
included in the calculation.
arranged in such a way that these
openings can be used in all weather
If a temperature increase of for example
The results of the preheating calcula-
conditions. Care should be taken to
35°C (from 15°C to 50°C) is required, a
tions may therefore be somewhat con-
ensure that no seawater can be drawn
preheater capacity of about 1% of the
servative.
into the ventilation air intakes.
Chapter 2
Engine Room Ventilation
Furthermore, the ventilation air inlet
When sailing in arctic areas, the re-
In addition to providing sufficient air for
tance from the exhaust gas funnel in or-
quired temperature increase may be
combustion purposes in the main en-
der to avoid the suction of exhaust gas
higher, possibly 45°C or even higher,
gine, auxiliary diesel engines, fuel fired
into the engine room.
and therefore a larger preheater capac-
boiler, etc., the engine room ventilation
ity is required. The curves in Fig. 5 are
system should be designed to remove
Major dust and dirt particles can foul
based on the assumption that, at the
the radiation and convection heat from
air coolers and increase the wear of
engine’s nominal MCR power is required
to obtain a preheating time of 12 hours.
start of preheating, the engine and en-
should be placed at an appropriate dis-
combustion
chamber
components.
Accordingly, the air supplied to the
Temperature
increase
of jacket water
o
Preheater capacity in %
of nominal MCR power
1.50% 1.25% 1.00%
C
60
0.75%
engine must be cleaned by appropriate filters. The size of particles passing
through the air intake filter should not
exceed 5µm.
An example of an engine room ventila-
50
tion system, where ventilation fans blow
air into the engine room via air ducts, is
40
shown in Fig. 6.
30
Air temperature
Measurements show that the ambient
20
air intake temperature (from deck) at sea
will be within 1 to 3°C of the seawater
10
temperature, i.e. max. 35°C for 32°C
seawater, and max. 39°C for 36°C seawater.
0
0
10
20
30
40
50
60 70 hours
Preheating time
The temperature increase and corresponding
preheating time curves are shown for the different
preheater sizes indicated in % of nominal MCR power
Fig. 5: Preheating of diesel engine
8
Influence of Ambient – Temperature Conditions
Measurements also show that, in a normal 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
Air outlet
Engine room
ventilation fans
Air inlet
Air inlet
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 ambient outside air temperature.
Air supply
In the case of a low speed twostroke
diesel engine installed in a spacious engine room, the capacity of the ventilation
system should be such that the ventilation air to the engine room is at least
1.5 times the total air consumption of
the main engine, auxiliary engines, boil-
ME
AE
AE
er, etc., all at specified maximum con-
AE
tinuous rating (SMCR).
As a rule of thumb, the minimum engine room ventilation air amount corre-
ME: Main engine
sponds to about 1.75 times the air con
AE: Auxiliary engines
sumption of the main engine at SMCR.
Main ducts for supply
Accordingly, 2.0 times the air con-
of combustion air
sumption of the main engine at SMCR
may be sufficient.
Fig. 6: Engine room ventilation system
On the other hand, for a compact engine
higher than the ambient outside air tem-
Since the air ventilation ducts for a nor-
room with a small twostroke diesel
perature. This temperature difference is
mal air intake system are placed near
engine, the above factor of 1.5 is rec-
even higher for winter ambient air tem-
the turbochargers, the air inlet temper-
ommended to be higher, at least 2.0,
peratures, see Fig. 7. In general, the en-
ature to the turbochargers will be lower
because the radiation and convection
gine room temperature should never be
than the engine room temperature. Un-
heat losses from the engine are relatively
below 5°C, which is ensured by stopping
der normal air temperature conditions,
greater than from large twostroke
one or more of the air ventilation fans,
the air inlet temperature to the turbo-
engines, and because it may be difficult
thus reducing the air supply to and
charger is only 13°C higher than the am-
to achieve an optimum air distribution
thereby the venting of the engine room.
bient outside air temperature.
in a small engine room.
This means that the average air tem-
This means that the turbocharger suc-
To obtain a correct supply of air for the
perature in a ventilated engine room will
tion air temperature will not be higher
main engine’s combustion process,
not be lower than 5°C and not higher
than about 39 + 3 = 42°C (ref. 36°C
about 50% of the ventilation air should
than 39 + 12 = 51°C, say 55°C (ref.
S.W.), say 45°C.
be blown in at the top of the main en-
36°C S.W.), as often used as maximum
gine, near the air intake to the turbo-
temperature for design of the engine
For arctic running conditions, a ducted
room components.
air intake system directly to the turbo-
chargers, as shown in Fig. 6.
Influence of Ambient – Temperature Conditions
9
Air pressure
Engine room temperature TER
and difference T
The air in the engine room should have
a slightly positive pressure, but should
o
C
60
not be more than about 5 mm WC (Water Column) above the outside pressure
TER
at the air outlets in the funnel.
50
Accommodation quarters will normally
40
have a somewhat higher overpressure,
so as to prevent oil fumes from the en-
30
gine room penetrating through door(s)
20
into the accommodation.
T = TER Tamb.
The ventilation air can be supplied, for
10
example, by fans of the lowpressure
Amb. air temp. Tamb.
0
axial and highpressure centrifugal or
20
0
o
40 C
20
The engine room temperature TER and the engine
room/ambient air temperature difference T are shown
as functions of the ambient air temperature Tamb
axial types. The required pressure head
of the supply fans depends on the resistance in the air ducts.
All ventilation air is normally delivered
by lowpressure air supply fans which,
to obtain sufficient air ventilation in all
Fig. 7: Engine room temperature
corners of the engine room, may require extensive ducting and a pressure
Otherwise, this can have a negative ef-
Moreover, a sufficient amount of air
fect on the main engine performance.
should be supplied to areas with a high
Thus, the maximum firing pressure will
heat dissipation rate in order to ensure
Lowpressure fans,
be reduced by 2.2% for every 10°C the
that all the heat is removed, for instance
∆p = 60100 mm WC
turbocharger air intake temperature is
around
raised, and the fuel consumption will go
and boilers. Ventilation ducts for these
For further information, please consult
up by 0.7%.
areas are not shown in Fig. 6.
engine room ventilation standard ISO
Furthermore, a correct air supply near
In the winter time, the amount of air
the turbochargers will reduce the dete-
needed to remove the radiation/con-
rioration of the turbocharger air filters
vection heat from the engine room may
(from oil fumes, etc., in the engine room
be lower.
auxiliary
head as stated below.
engines/generators
8861: 1998 (E).
air), and a too draughty engine room
can be avoided.
10
Influence of Ambient – Temperature Conditions
Chapter 3
Ambient Temperature Operation and
Matching
Standard ambient temperature
The above tropical ambient relative hu-
10°C (to the scavenge air cooler), the
midity of 60% at 45ºC is theoretically
specific fuel oil consumption (SFOC)
the absolute limit at which it is possible
will increase by approx. 2 g/kWh, see
for humans to survive. The correspon-
Fig. 8. Any obtained gain in reduced
ding wet bulb temperature is 36.8ºC.
electric power consumption, therefore,
matched engine
will be more than lost in additional fuel
MAN Diesel & Turbo has never measured
costs of the main engine.
Standard unrestricted service demands
levels above 50% at 45ºC, and humidity
For a standard main engine, the engine
levels above standard tropical ambient
The above ISO, tropical and winter
layout is based on the ambient refer-
conditions will never occur.
ambient reference conditions are used
ence conditions of the International
Standard Organization (ISO):
by MAN Diesel & Turbo for ships, and
When applying the central cooling wa-
MAN B&W two-stroke engines com-
ter system which, today, is more com-
ply with the above rules. MAN B&W
ISO 3046-1:2002(E) and
ISO 15550:2002(E):
ISO ambient reference conditions
monly used than the seawater system,
engines matched according to the
the corresponding central cooling wa-
above rules are able to operate con-
ter/scavenge air coolant temperature is
tinuously up to 100% SMCR in the
Barometric pressure:
4ºC higher than the seawater tempera-
air temperature range between about
ture, i.e. equal to 36ºC.
-10 and 45ºC.
1,000 mbar
Turbocharger air intake
temperature:
25ºC
Charge air coolant temperature:
The winter ambient reference condi-
Often the engine room temperature is mi-
25ºC
tions used as standard for MAN B&W
staken for being equal to the turbocharger
Relative air humidity:
30%
two-stroke engines are as follows:
air intake temperature. However, since the
air ventilation duct outlets for a normal
With this layout basis, the engine
Winter ambient reference conditions
air intake system are placed near the
must be able to operate in unrestrict-
Barometric pressure:
turbochargers, the air inlet temperature
ed service, i.e. up to 100% Specified
Turbocharger air intake
temperature:
Maximum Continuous Rating (SMCR),
within the typical ambient temperature
1,000 mbar
to the turbochargers will be very close
10ºC
Cooling water temperature:
(minimum for lub. oil cooler)
10ºC
range that the ship is exposed to, operating from tropical to low winter ambi-
Relative air humidity:
60%
to the ambient outside air temperature.
Under normal air temperature conditions, the air inlet temperature to the
ent conditions.
According to the International Associa-
Shipyards often specify a constant
tion of Classification Societies (IACS)
(maximum) central cooling water tem-
rule M28, the upper requirement, nor-
perature of 36°C, not only for tropical
mally referred to as tropical ambient ref-
ambient conditions, but also for winter
erence conditions, is as follows:
ambient conditions. The purpose is to
SFOC
g/kWh
Turbocharger air intake temperature: 10°C
36°C C.W
reduce the seawater pump flow rate
IACS M28 (1978):
Tropical ambient reference conditions
when possible, and thereby to reduce
Barometric pressure:
to reduce the water condensation in the
1,000 mbar
Air temperature:
45ºC
Seawater temperature:
32ºC
Relative air humidity:
60%
2 g/kWh
10°C C.W
the electric power consumption, and/or
air coolers.
However, when operating with 36°C
cooling water instead of for example
40
50
60
70
80
90 100% SMCR
Engine shaft power
Fig. 8: Influence on SFOC of the cooling water
(scavenge air coolant) temperature
Influence of Ambient – Temperature Conditions
11
turbocharger is only 13°C higher than
in some inland, gulf, bay and harbour
perature conditions
the ambient outside air temperature.
areas, the maximum power output of
Usually, higher or lower turbocharger
the engine should be reduced to an
air intake temperatures may result in
The classification society rules often
engine load resulting in a scavenge
lower or higher scavenge air pressures,
specify an engine room air temperature
air temperature below the level of the
respectively, and vice versa.
of 0-55ºC as the basis for the design
scavenge air temperature alarm.
of the engine room components. The
An increase of, for example, 5ºC of the
55ºC is the temperature used when
Nevertheless, the engine’s obtainable
tropical air temperature from standard
approving engine room components.
load level will in all cases be much
45ºC to special 50ºC will result in a too
This, however, must not be mistaken
higher than required to ensure a safe
low scavenge air pressure at 50ºC.
for the above tropical air intake tempe-
manoeuvrability (46 knots) of the ship
rature of 45ºC specified when related to
even at an extreme seawater tempera-
However, the pressure reduction can
the capacity or effect of the machinery.
ture of for example 42°C.
be compensated for by specifying a
correspondingly higher (turbocharger)
In recent years, owners/shipyards have
When sailing in, for example, the har-
scavenge air pressure at ISO ambient
sometimes required unrestricted ser-
bour area during manoeuvring, the en-
reference conditions. This involves that
vice on special maximum ambient tem-
gine load will normally be relatively low
the engine, instead of being matched
peratures higher than the tropical am-
(1530% SMCR), and the correspond-
for the ISO-based design air tempera-
bient temperatures specified by IACS
ing scavenge air temperature will then
ture of 25ºC, has to be matched for the
M28. In such cases, the main engine
only be slightly higher than the scav-
25 + 5 = 30ºC turbocharger air intake
has to be special high temperature
enge air coolant temperature. There-
temperature.
matched, as described later in this pa-
fore, a seawater temperature as high
per.
as for example 42°C in harbour areas
The original ISO-based heat load con-
is not considered a problem for the
ditions will then almost be obtained
Furthermore, operation in arctic areas with
main engine, and a special temperature
for this higher design air temperature.
extremely low air temperatures has also
matching is not needed under these
The principles for standard and special
sometimes been required by owners/
operating conditions.
high (or low) ambient air temperature
shipyards, and the measures to be taken
are also described later in this paper.
matched engines are shown in Fig. 9.
In general, when sailing in areas with a
high seawater temperature, it is pos-
At the other end of the air temperature
Operating at high seawater temperature with
sible to operate the standard ambient
range, the increase of 5ºC of the de-
standard matched engine
temperature matched main engine at
sign air intake temperature will involve
An increase of the seawater tempera-
any load as long as the scavenge air
a too high scavenge air pressure when
ture and, thereby, the scavenge air
temperature alarm limit is not reached.
operating at -10ºC. Operation below
temperature has a negative impact on
If the alarm is activated, the engine load
-10 + 5 = -5ºC will then only be pos-
the heat load conditions in the combus-
has to be reduced.
sible when installing a variable exhaust
gas bypass valve system for low air
tion chamber. Therefore, all MAN B&W
twostroke engines for marine applica-
Non-standard ambient temperature
tions have an alarm set point of 55°C
matched engine
for the scavenge air temperature for pro-
If unrestricted loads are desired in a
Fig. 9 may in a similar way also be
tection of the engine, as described later.
temperature range different from the
used to explain a special low tempera-
standard, different matching possibili-
ture matched engine. For example, if
ties are available.
the standard tropical air temperature
For a standard ambient temperature
needed is reduced by 10ºC, from 45ºC
matched engine operating at an increased seawater temperature existing
12
Influence of Ambient – Temperature Conditions
temperatures, as described later.
Engine matching for non-standard air tem-
to 35ºC, the engine matching design
Turbocharger
air intake temperature
65
60
Standard
ISO temperature
matched engine
55
50
45
Special
Low temperature
matched engine
40
35
Max.
Special
tropical
temperature
30
25
20
15
Special
design
temperature
Max.
45 °C
Standard
design
Temperature
ISO
25 °C
ISO based
design
layout
5
0
-5
Min.
-10 °C
-10
-15
-25
-30
-35
Min.
Lowest
ambient air
temperature
Max.
Normal
tropical
temperature
Special
tropical
temperature
Special
design
temperature
ISO
design
layout
For engine loads
higher than 30% SMCR
a low scavenge air
coolant temperature
is recommended
(Giving low SFOC and
low scav. air press.)
10
-20
Special
High temperature
matched engine
Normal min.
ambient air
temperature
Possible low ambient
air temperature
exhaust gas bypass for
operation under
extremely low ambient
temperature conditions
Min.
ISO based
design
layout
Lowest
ambient air
temperature
Low ambient air
temperature exhaust
gas bypass will be
needed below min.
temperature
-40
-45
-50
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
Fig. 9: Principles for standard and special high (or low) ambient air temperature matched engines
Influence of Ambient – Temperature Conditions
13
air temperature can be reduced to
perature, which has a negative impact
A temperature difference of 8ºC is con-
25 ˉ 10 = 15ºC.
on the combustion chamber tempera-
sidered to be the lowest possible tem-
tures. Therefore, for all marine applica-
perature difference to be used for a
This involves that the exhaust gas tem-
tions, an alarm set point of 55ºC for the
realistic specification of a scavenge air
perature will increase by about 16ºC
scavenge air temperature is applied for
cooler. Accordingly, the 48 ˉ 8 = 40ºC is
compared with a standard ISO tem-
protection of the engine.
the maximum acceptable scavenge air
perature matched engine, whereas the
SFOC will increase.
coolant temperature for a central coolThe standard marine scavenge air cooler
ing water system, see the principles for
is specified with a maximum 12ºC tem-
layout of the scavenge air cooler in Fig. 10.
Engine matching for high tropical seawater
perature difference between the cooling
temperature conditions
water inlet and the scavenge air outlet
The demand for an increased tropi-
For long time operation in an area with
at 100% SMCR, which gives a maxi-
cal scavenge air coolant (central cool-
high tropical seawater temperatures,
mum scavenge air temperature of 36 +
ing water) temperature of up to 40ºC,
the following should be observed.
12 = 48ºC for the scavenge air cooler
layout and, accordingly, a margin of 7ºC
therefore, can be compensated for by a
An increase in the seawater tempera-
to the scavenge air temperature alarm
of the scavenge air cooler. This can be
ture and, thereby, of the scavenge air
limit of 55ºC.
obtained by means of an increased wa-
coolant temperature will involve a similar increase in the scavenge air tem-
Temperature °C
Standard 55 °C
56
ter flow and/or a bigger scavenge air
Standard ISO temperature
matched engine
Special high temperature
matched engine
Standard air cooler design
Special air cooler design
Scavenge air temperature limit
reduced design temperature difference
Scavenge air temperature limit
cooler.
Max. 55 °C
54
52
50
Standard 48 °C
48
46
Maximum
scavenge air
temperature
at 100% SMCR
Maximum
scavenge air
temperature
at 100% SMCR
Max. 48 °C
High tropical
scavenge air
coolant
temperature
Max. 40 °C
High tropical
seawater
temperature
Max. 36 °C
44
42
40
38
Standard 36 °C
36
34
Standard 32 °C
32
30
Standard
tropical
scavenge air
coolant
temperature
Up to 100% SMCR running is
allowed (scavenge air)
Standard tropical
seawater
temperature
High scavenge
air coolant
temperature
28
Standard
basis 25 °C
26
24
ISO based
scavenge air
coolant
temperature
Up to 100% SMCR running is
not allowed (scavenge air)
ISO
design
layout
ISO based
design
layout
Max. 29 °C
Up to 100% SMCR running is
allowed (scavenge air coolant/central
cooling water)
Up to 100% SMCR running is
allowed (seawater)
22
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)
14
Influence of Ambient – Temperature Conditions
Design recommendations for opera-
porated in the Engine Control System
sure is close to the corresponding pres-
tion at extremely low air temperature
(ECS) as an add-on.
sure on the scavenge air pressure curve
which is valid for ISO ambient condi-
When a standard ambient temperature
matched main engine on a ship occa-
Engine load, fuel index and scavenge
tions. When the scavenge air pressure
sionally operates under arctic condi-
air pressure signals are already availa-
exceeds the read-in ISO-based sca-
tions with low turbocharger air intake
ble for the ME software and, therefore,
venge air pressure curve, the bypass
temperatures, the density of the air will
additional measuring devices are not
valve will variably open and, irrespec-
be too high. As a result, the scavenge
needed for ME engines.
tive of the ambient conditions, ensure
that the engine is not overloaded. At the
air pressure, the compression pressure
and the maximum firing pressure will be
In general, a turbocharger with a nor-
same time, it will keep the exhaust gas
too high.
mal layout can be used in connection
temperature relatively high.
with an exhaust gas bypass. However,
In order to prevent such excessive
in a few cases a turbocharger modifica-
The latest generations of turbochargers
pressures under low ambient air tem-
tion may be needed.
with variable flow, e.g. the VTA (Variable
Turbine Area) system from MAN Diesel
perature conditions, the turbocharger
The exhaust gas bypass system ensures
& Turbo, can replace the variable by-
high as possible (by heating, if possi-
that when the engine is running at part
pass and ensure the same scavenge air
ble).
load at low ambient air temperatures,
pressure control.
air inlet temperature should be kept as
the load-dependent scavenge air presFurthermore, the scavenge air coolAir intake casing
ant (cooling water) temperature should
be kept as low as possible and/or the
engine power in service should be reduced.
Exhaust gas bypass
Exhaust gas system
Exhaust gas
receiver
B
Turbine
However, for an inlet air temperature
below approx. ˉ 10ºC, some engine design precautions have to be taken.
1 C1+2
Turbocharge r
Main precautions for extreme low air temperature operation
D1
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 bypasses the turbocharger turbine, giving
less energy to the compressor, thus reducing the air supply and scavenge air
pressure to the engine.
For the electronically controlled ME
2
Scavenge
air receiver
D2
Diesel engine
B
Scavenge
air cooler
Compressor
Exhaust gas bypass valve
Controlled by the scavenge air pressure
C1+2 Control device
Ensures that the loaddependent scavenge air pressure
does not exceed the corresponding ISO based pressure
D
D1
D2
Required electric measuring device
Scavenge air pressure
Engine speed and engine load
engine (ME/ME-C/ME-B), the load-dependent bypass control can be incor-
Fig. 11: Standard loaddependent low ambient air temperature exhaust gas bypass system
Influence of Ambient – Temperature Conditions
15
Other low temperature precautions
Ships with ice class notation
For other special ice class notations,
Low ambient air temperature and low
For ships with the FinnishSwedish ice
the engines need to be checked indi-
seawater temperature conditions come
class notation 1C, 1B, 1A and even
vidually.
together. The cooling water inlet tem-
1A super or similar, all MAN B&W
perature to the lube oil cooler should
twostroke diesel engines meet the
The exhaust gas bypass system to be
not be lower than 10°C, as otherwise
ice class demands, i.e. there will be no
applied is independent of the ice class-
the viscosity of the oil in the cooler will
changes to the main engines.
es, and only depends on how low the
be too high, and the heat transfer in-
specified ambient air temperature is
adequate. This means that some of the
However, if the ship is with ice class
expected to be. However, if the ship is
cooling water should be recirculated to
notation 1A super and the main engine
specified with a high ice class like 1A
keep up the temperature.
has to be reversed for going astern
super, it is advisable to make prepara-
(Fixed Pitch Propeller), the starting air
tions for, or install, an exhaust gas by-
Furthermore, to keep the lube oil vis-
compressors must be able to charge
pass system.
cosity low enough to ensure proper
the starting air receivers within half an
suction conditions in the lube oil pump,
hour, instead of one hour, i.e. the com-
Increased steam production in wintertime
it may be advisable to install heating
pressors must be the double in size
During normal operation at low am-
coils near the suction pipe in the lube
compared to normal.
bient temperatures, the exhaust gas
temperature after the turbochargers will
oil bottom tank.
The following additional modifications
of the standard design practice should
be considered as well:
„„
Steam production
kg/h
6S60MC-C7/ME-C7
SMCR = 13,560 kW at 105 r/min
2,500
Air intake temperature: 0 °C
Cooling water temperature: 10°C
Larger electric heaters for the cylinder lubricators or other cylinder oil
ancillary equipment
„„
2,000
Surplus steam
Total steam production,
without bypass
Cylinder oil pipes to be further heat
traced/insulated
„„
Total steam production,
with exhaust gas bypass
1,500
Steam consumption
Upgraded steam tracing of fuel oil
pipes
Extra steam needed
1,000
„„
Increased preheater capacity for
jacket water during standstill
„„
Different grades of lubricating oil for
500
turbochargers
„„
„„
Space heaters for electric motors
Sea chests must be arranged so that
0
40
50
60
70
80
90
100% SMCR
Engine shaft power
blocking with ice is avoided.
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
16
Influence of Ambient – Temperature Conditions
decrease by about 1.6ºC for each 1.0ºC
Closing Remarks
reduction of the intake air temperature.
Diesel engines installed in oceangoing
The load-dependent exhaust gas by-
ships are often exposed to different cli-
pass system will ensure that the exhaust
matic temperature conditions because
gas temperature after the turbochargers
will fall by only about 0.3ºC per 1.0ºC
of the ship’s trading pattern, but as the
drop in the intake air temperature, thus
temperature variations on the sea sur-
enabling the exhaust gas boiler to pro-
face are normally relatively limited, the
duce more steam under cold ambient
engines will normally be able to operate
temperature conditions.
worldwide in unrestricted service without any precautions being taken.
Irrespective of whether a bypass system is installed or not, the exhaust gas
Even if the ship has to sail in very cold
boiler steam production at ISO ambient
areas, the MAN B&W two-stroke en-
conditions (25ºC air and 25ºC C.W.) or
gines can, as this paper illustrates, also
higher ambient temperature conditions,
operate under such conditions without
will be the same, whereas in wintertime
any problems as long as special low
the steam production may be relatively
temperature precautions are taken.
increased, as the scavenge air pressure
is controlled by the bypass valve.
The use of the standard loaddependent
low ambient air temperature exhaust
As an example, Fig. 12 shows the influ-
gas bypass system may – as an ad-
ence of the load-dependent exhaust gas
ditional benefit – also improve the ex-
bypass system on the steam production
haust gas heat utilisation when running
when the engine is operated in winter-
at low ambient air temperatures.
time, with an ambient air temperature of
0ºC and a scavenge air cooling water
Furthermore, at the other end of the
temperature of 10ºC.
temperature scale, if the ship should
need to sail in unrestricted service in ar-
The calculations have been made for a
eas with very high ambient air tempera-
6S60MC-C7/ME-C7 engine equipped
tures, higher than 45°C, this will also be
with a high-efficiency turbocharger, i.e.
possible provided a high temperature
having an exhaust gas temperature of
matching of the engine is applied. Even
245ºC at SMCR and ISO ambient con-
when sailing should be needed at very
ditions.
high seawater temperatures, this will be
possible provided a specially designed
Fig. 12 shows that in wintertime, it is
scavenge air cooler is installed on the
questionable whether an engine with-
diesel engine.
out a bypass will meet the ship's steam
demand for heating purposes (indicated for bulk carrier or tanker), whereas
with a load-dependent exhaust gas bypass system, the engine can meet the
steam demand.
Influence of Ambient – Temperature Conditions
17
All data provided in this document is non-binding. This data serves informational
purposes only and is especially not guaranteed in any way. Depending on the
subsequent specific individual projects, the relevant data may be subject to
changes and will be assessed and determined individually for each project. This
will depend on the particular characteristics of each individual project, especially
specific site and operational conditions. Copyright © MAN Diesel & Turbo.
5510-0074-00ppr Sep 2014 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.marine.man.eu
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