Contents

1

Very Large Diesel Engines for Independent
Power Producers and Captive Power Plants

Page

Abstract . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

3

Preface . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . · · · · · · . . . . . . . . . . . .

3

The Diesels and their Competitors. . . . . . . . . . . . . . . . . . . . . . . . . . . . .

4

Diesel Engines in Stationary Applications . . . . . . . . . . . . . . . . . . . . . . .

5

Load Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Fuel Linkage . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

6

Fuel Flexibility . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

8

Emissions . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

Two-stroke Engine Driven Plants. . . . . . . . . . . . . . . . . . . . . . . . . . . . . .

9

The Bahamas Project . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10

Conclusion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

Literature . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12

3

Croatia
Uljanik

1954

Split

1984

Poland
Cegielski

1959

Russia
Bryansk

1959

Spain
IZAR- Manises

1941

Japan
Mitsui

1926

Makita

1981

Hitachi

1951

Kawasaki

1981

!

Korea
Hyundai

1976

HSD

1983

Ssangyong

1984

China
HHM

1980

YMD

1989

! Shanghai HHM 1994

DMD

1980

Fig. 2: MAN B&W two-stroke licensee family

30,000

20,000

40,000

600

10,000

60,000

50,000

Engine output P

(kW)

mech

0

700

500

200

300

400

Medium speed

70,000

100

Low speed

Four-stroke

Two-stroke

Engine speed, r/min

Fig.1: MAN B&W engine programme

Very Large Diesel Engines for Independent
Power Producers and Captive Power Plants

Abstract

During recent years, an increasing
demand has been experienced in the
stationary diesel engine market for
large diesel units for reliable and fuel
efficient power plants in the range of
30-250 MW, based on cost effective
refinery residuals.

This demand is being met by modern
marine-derivative medium speed diesel
GenSets and, for the larger units, by
two-stroke low speed crosshead
uniflow scavenged diesel engines, the
latter capable of burning almost any
fuel available on the market, whether
liquid or gaseous.

This paper will deal with service experi-
ence gained from two-stroke low
speed diesel engines and their fuel
capability, as well as describe the latest
30 MW extension of the Clifton Pier
plant on the Bahamas, owned by the
Bahamas Electricity Corporation (BEC).

Preface

Diesel engines for power generation
from MAN B&W Diesel are offered in
the following categories, see Fig. 1:

•

High speed and medium speed en-
gines, ranging from 0.5 to 22 MW
per unit, from MAN B&W Diesel’s
companies in Germany, Denmark,
France and the UK.

•

Two-stroke MC engines from MAN
B&W Diesel, Copenhagen, Denmark.
These are low speed engines with
unit outputs of up to 68 MW. The
engines are built by MAN B&W
licensees as listed in Fig. 2.

The low speed two-stroke engines
match any requirements of medium to
large size projects, whether for island
utilities or large IPP or captive plants,
up to say 250-300 MW, Fig. 3.

Guam, Enron units

D8

D9

Availability

%

96.3

95.1

Reliability

%

99.0

97.6

Scheduled outage

hrs.

234

217

Unscheduled outage hrs.

84

207

Load factor

%

82

83

Low speed engines are particularly
suited to digest any fuels with high effi-
ciency and good reliability. Engineers
are well acquainted with the technology
through wide experience from the world
merchant fleet, which is dominated
by MAN B&W low speed two-stroke
engines.

The Diesels and their
Competitors

Looking at the prime mover options
available to the end-user today, and
comparing their efficiencies, we can see
that in the relevant range, say 12-68 MW
per unit, Fig. 4, the two-stroke diesel en-
gine is unrivalled as the most fuel efficient
prime mover, whether compared with
medium speed engines, steam turbines
or single-cycle or combined cycle gas
turbines.

4

35

30

40

100

25

50

45

Medium speed
diesel engine

20

500

Unit capacity (MW)

50

1

10

55

Thermal efficiencies %

Gas turbine

Combined cycle
gas turbine

Steam turbine

Low speed diesel engine

5

Fig. 4: Power efficiency comparison at ISO 3046

Fig. 3: Guam, 90 MW Enron power plant

Diesel Engines in
Stationary Applications

The MAN B&W Diesel engines are
always matched to the actual climatic
conditions of the site, with due al-
lowance for seasonal variations. With
demanding site conditions, medium
speed engines sometimes call for slight
derating, whereas this is not required
for low speed diesels in which an ac-
ceptable combustion chamber heat
load is maintained by modification of
the heat rate of the engine.

A comparison of deratings, as a func-
tion of ambient conditions for the various
combustion engines on the market, is
shown in Fig. 5, revealing the insensi-
tivity of the low speed diesel engines to
ambient conditions, when compared
with other internal combustion machines.
When one is comparing the various
prime movers, differences in the vari-
ous ISO standards should be consid-
ered, Fig. 6.

5

25

48

80

Air inlet temperature C

Cooling water temperature C

Ambient conditions

o

o

46

100

90

Medium
speed diesel

35
42
Design

Overall efficiency

Gas turbine

Low speed diesel

30

35

45

20

40

% Power

Power restriction

Efficiency, low speed diesel

% Power

25
35
Min.

45
52
Max.

50

49

Ambient temperature C

o

47

80

100

90

Low speed diesel

Efficiency, medium speed diesel

Medium speed diesel

(%)

Fig. 5: Influence of ambient conditions on rating of internal combustion engines

Gas turbines

ISO 3977

Diesel engines

ISO 3046

Air temperature

o

C

15

25

Coolant temperature

o

C

15

*

)

25

Barometric pressure

mbar

1013

1000

Relative humidity

%

60

60

*

)

If applicable

Fig. 6: Comparison of ISO conditions

Load Flexibility

To cater for load variation in plants, say
up to 300 MW, it is quite common to
install a number of equally-sized units.
The load fluctuations called for by us-
ers are then managed by sequential
starting and stopping of the units.

This configuration and running principle
is very often seen with the traditional
gas turbines, because of their poor
part-load efficiency behaviour.

As shown in Fig. 7, the efficiency of
diesel engines, and especially of
two-stroke low speed diesels, is almost
independent of load over a wide load
range. Furthermore, low load running
without any limitation is possible down
to approx. 20% of Maximum Continu-
ous Rating (MCR), and the engines are
able to run at 10% overload for one
hour every 12 consecutive hours. It is
therefore fully feasible to install the larg-
est two-stroke diesel units applicable,
i.e. as few units as possible for a given
plant size, thereby shortening plant
construction time, reducing the space
requirement, as well as reducing first
cost, running cost and maintenance
load, while still ensuring high efficiency
and reliability, irrespective of the plant
running programme.

Fuel Linkage

As most diesel plants are installed in
areas which depend on liquid fuels with
scarce and unstable supplies of high
quality fuels, it is of paramount impor-
tance for the feasibility of a project that
the acceptable range in the guideline
fuel oil specifications of the various
prime movers is considered at a very
early stage. Fig. 8 shows the difference
in fuels that can be used in gas tur-
bines and diesel engines in general.

Essentially, diesel engine combustion
comprises a series of batch processes,
whereas the gas turbine uses continu-
ous combustion. In the batch process,
higher initial temperatures and pres-
sures can be used than in the gas tur-
bine, since the exposed components
are cooled at the end of each process
and between processes. The thermal

6

30

20

40

100

10

60

50

0

Load %

50

% Thermal efficiencies

Gas turbine

Combined cycle gas turbine

Steam turbine

Low speed diesel

Medium speed diesel

70

60

90

80

Fig. 7: Typical part load efficiencies of prime movers

Designation

Density at 15
Kinematic viscosity at 100
Flash point
Carbon residue
Ash
Water
Sulphur
Vanadium
Aluminium + Silicon
API gravity (min)
Sodium plus potassium
Calcium
Lead

o

C

C

o

kg/m
cSt

C

% (mm)
% (mm)
% (mm)
% (mm)
ppm (mm)
mg/kg

o API
ppm (mm)
ppm (mm)
ppm (mm)

3

o

Gas turbines

ASTM 2880

Diesel engines

CIMAC-H55

* experience, no limitations in official specification
** Incl. sediment
*** on 10% destillation

1010

55
60
22

0.15

1.0
5.0

600

80

200
200

10

>

*

876

50
66

0.35
0.03

1.0
1.0

0.5-2

(10)

35

1
1
1

***

**

Fig. 8: Diesel engine and gas turbine liquid fuel guideline specification

efficiency can therefore be higher in the
diesel than in the gas turbine. Each pis-
ton stroke constitutes a batch process,
and the slower it can be while still main-
taining its adiabatic thermodynamics,
the more efficient it can be.

An added advantage of the slow pro-
cess that takes place in a low speed
engine is that the ignition delay which

may occur, depending on fuel quality
and engine geometry, has less impact
on a low speed engine.

While a low speed engine often gives a
longer ignition delay than its medium
speed counterpart with the same fuel,
the ignition delay is still proportionally
shorter in a low speed engine, in terms
of degrees crankshaft angle.

As illustrated in Fig. 9, the typical fuel
injection period in terms of milliseconds
is 3-4 times longer in a low speed en-
gine, i.e. up to 35 msec. Typical igni-
tion periods are up to 10 msec in a
medium speed engine and up to 20
msec in a low speed engine.

Hence, in a worst-case situation using
a fuel with a tendency towards long
ignition delay, all the fuel for a stroke
may have been injected in a medium
speed engine before ignition takes
place. Ignition can then take the form
of a detonation which harms the piston,
piston rings and bearings. In the low
speed engine, even with a long ignition
delay, less fuel is injected before igni-
tion. Thus, the risk of detrimental deto-
nation is over.

This is one of the reasons why a low
speed engine is considered more for-
giving than other types of machinery
when low-quality, low-cost fuels are
used, as outlined later.

7

1 rev

B

A: Fuel injection period
(~22 deg. crankshaft) ~35 msec for two-stroke

~ 9 msec for four-stroke

B: Possible max. ignition delay

~ 20 msec for two-stroke and four-stroke

Low speed (two-stroke)
60/103.4 = 0.58 sec/rev.

Medium speed (four-stroke)
60/600 = 0.10 sec/rev.

Cylinder pressure

In medium speed engines all fuel may have
been injected before ignition, i.e. detonation
may occur if delay is long due to fuel quality.

Sec

A

Fig. 9: Fuel acceptance

Fuel No.:

Units

1

2

3

4

5

6

7

8

9

10

11

12

13

Guiding fuel

specification

Viscosity

cSt/50

o

C

2.27

3.8

84

85

141

198

255

470

520

560

690

710

50,000

700

Density

kg/m

3

at

15

o

C

843

968

995

970

993

938

977

985

983

1,010

1,008

1,030

1,040

991*

Flash point

o

C

65

98

84

80

103

100

106

90

95

90

79

84

> 60

60

Conradson
carbon

% weight

0.01

0.3

17.2

12.1

13.3

9.4

14.5

16.8

14.8

17.3

22.1

24.7

24.2

22

Asphalt

% weight

0.00

0.78

15.1

8.9

9.2

3.7

10.0

11.3

12.8

14.6

19.3

29.0

-

14

Sulphur

% weight

0.22

0.10

2.72

1.16

0.91 0.83

0.87

0.90

1.18

2.22

3.52

3.30

4.8

5

Water

% weight

0.00

0.01

0.01

0.01

0.00 0.01

0.02

0.02

0.01

0.00

0.00

0.00

0.05

1.0

Ash

% weight

0.00

0.00

0.065

0.025

0.03 0.03

0.025

0.03

0.035

0.04

0.07

0.09

0.035

0.2

Aluminium

mg/kg

-

-

-

-

-

-

-

-

-

-

-

-

2.0

30

Vanadium

mg/kg

0

0

220

20

23

12

17

24

45

122

300

370

149.0

600

Fig. 10: Examples of liquid fuels burned in MAN B&W two-stroke low speed diesel engines

Fuel Flexibility

Most power plants built today are
based on the use of one or two fuels.
Such fuels are typically natural gas or
light fuels for gas turbines, coal or
heavy fuel for steam turbines, and die-
sel oil, heavy fuel oil or natural gas for
diesel engines.

The two-stroke low speed diesel engines
of MAN B&W design are able to run
on virtually any commercially available
liquid or gaseous fuel.

Fig. 8 shows a typical guideline fuel oil
specification of today for such engines.
The basic data are dictated by the
logistics of the marine market, which
require that the fuel can be transported
to the ship. This requirement, in princi-
ple, does not apply to stationary plants
which can be placed close to the source
of energy and connected to it by a pipe
that is heated by waste heat from the
engine.

Various types of refinery waste can
thus be used in low speed diesels.

Such fuel oil specifications are normally
quoted by the majority of diesel engine
designers on the market, regardless
of the number of strokes. Nevertheless,
in this connection it should be noted
that most medium speed designers
specify a max. design temperature
of HFO at injection in the range of
130-150 °C, resulting in a max. fuel
viscosity of 700 cSt at 50 °C.

For the two-stroke engines of MAN
B&W design, the max. design tempera-
ture of the fuel preheating is 250

o

C,

corresponding to a specific fuel viscosity
of approx. 70,000 cSt at 50

o

C, i.e.

a factor of 100 in admissible fuel vis-
cosity.

Fig. 10 shows examples of liquid fuels
burnt or tested successfully in MAN
B&W two-stroke low speed diesels,
while Fig. 11 shows similar data for
gaseous fuels.

Fig. 12 shows the fuel flexibility of the
MAN B&W MC-GI-S type high-pressure
gas injection, dual fuel, two-stroke
engines, which are able to burn both
liquid and gaseous fuel in almost any
ratio without influencing their power rating
or efficiency.

8

Composition:

Gas No.

1

2

3

CH

4

Vol %

88.5

91.1

26.1

C

2

H

6

Vol %

4.6

4.7

2.5

C

3

H

8

Vol %

5.4

1.7

0.1

C

4

H

10

Vol %

1.5

1.4

-

CO

2

Vol %

-

0.5

64.0

N

2

Vol %

-

0.6

7.3

Molar mass

kg/kmol

18.83

17.98

35.20

Higher calorific value

kJ/kg

49,170

48,390

11,120

Lower calorific value

kJ/kg

41,460

38,930

7,050

Density at 25

o

C/1 bar abs

kg/m

3

0.762

0.727

1.425

Density at 25

o

C/200 bar abs

kg/m

3

194

179

487

Fig. 11: Examples of gaseous fuels burned in MAN B&W two-stroke low speed diesel engines

Gas

100% load

40%

Fuel

Fuel

100%

8%

Dual-fuel mode

100% load

Fuel

Fuel

100%

Fuel-oil-only mode

100% load

Fuel

Gas

Fuel

100%

8%

Fixed-gas mode

Fig. 12: MAN B&W two-stroke low speed
diesels, fuel type mode

Emissions

In response to the increasing demand
for environmental protection, the two-
stroke low speed diesels can be delivered
with internal and external controls to
comply with virtually any emission restric-
tion requirements, including the 1998
World Bank Guideline for diesel-driven
plants.

Two-stroke Engine
Driven Plants

An example of a 40 MW medium-load
high-injection pressure two-stroke
crosshead diesel engine plant is the
Chiba plant in Tokyo (Fig. 13). This
plant is based on a 12K80MC-S en-
gine, developing 40 MW at 102.9 rpm

at an ISO efficiency of 49.3%. The
plant is equipped with extensive SCR
control of NO

x

emission in order to fulfil

the local NO

x

limit of 13 mg/Nm

3

.

9

Fig. 13: 40 MW Chiba plant in Japan

Main particulars
Prime mover:

MCR:
Engine speed:
Main effective pressure:
Cylinder bore:
Stroke:
Number of cylinders:
Fuels:

Gas compressor:
Pressure:

Generator:

De-NO

x

NO

x

limit

Main data 1994-1999
Average reliability:
Average availability:
Average load factor:
Average efficiency, gross:
Average efficiency, net:

MAN B&W 12K80MC-GI-S
Dual fuel high-pressure gas
injection engine
40 MW
103.4 r/min
17 bar
800 mm
2300 mm
12
Main fuel: LNG
Pilot fuel : Low-sulphur diesel oil
Thomassen recipro. four-stage
Suction: 4.5 bar
Delivery: 300 bar
Meidensha
Output: 40,000 kW
Voltage: 3.2 kV
Frequency: 50 Hz
Ammonia SCR
13 mg/Nm

3

97%
97%
71%

46.1%
42.6%

The Bahamas Project

At the beginning of the seventies, four
10 MW two-stroke units were installed at
the Clifton Pier power plant by Bahamas
Electricity Corporation.

In 1992 the plant was extended with
two 9K80MC-S engines (units DA 9
and DA 10), built by MAN B&W Diesel’s
Japanese licensee Mitsui Engineering &
Shipbuilding Co. Ltd and supplied by
Burmeister & Wain Scandinavian
Contractor A/S, Mitsui’s contracting
division.

In November 1996 after an extensive
international call for tenders, Bahamas
Electricity Corporation, decided to ex-
tend the plant with a new 30 MW unit,
Figs. 14 and 15.

The prime mover selected was an MAN
B&W type 10K80MC-S diesel engine,
developing 33.5 MW at 102.9 r/min at
an ISO efficiency of 49%. The engine
was built by Manises Diesel Engine
Company S.A., Spain, and the plant
order was awarded to a group of
companies led by Alstom Power
S.A., Madrid, Spain (Fig. 16).

The project was financed by the Inter-
American Development Bank and the
European Investment Bank.

The new plant, called unit DA 11, was
successfully commissioned and handed
over to the owner, Bahamas Electri-
city Corporation, in October 1999.

The plant is equipped with a large
exhaust gas boiler, utilising the exhaust
gas waste heat energy down to some
180 ° C. The energy is utilised for the
production of 10-bar steam, partly
used for heating the fuel oil, and mainly

10

415 V

BH PUMP

SWBD 2

415 V

STN AUX.

SWBD 2

415 V DA11

SWBD

415 V DA10

SWBD

415 V

CAMCC

33 kV

SWBD A

BIG POND

132 kV S/S

30

MVA

80

MVA

33 kW

SWBD B

13.5
MVA

13.5
MVA

13.5
MVA

13.5
MVA

6.3

MVA

35

MVA

35

MVA

80

MVA

80

MVA

BLUE HILLS

132 kV S/S

10MW

10MW

10MW

10MW

26.5

MW

26.5

MW

DA5

DA6

DA7

DA8

DA9

DA10

40
MVA

DA11

33kV

SWBD C

30
MW approx.

DA12

80

MVA

SPARE OHL

No. 1

132kV

LINE

SPARE OHL

No. 2

6.9 kV

STATION

SWBD 1

6.9 kV

STATION

SWBD 2

2.5

MVA

2.5

MVA

1.25
MVA

1.25
MVA

SITE

BUILDING

SERVICES

S/S 1&2

FIRE

PUMPS

EMERG. D.G.

840kVA

415 V

BH PUMP

SWBD 1

415 V

STN PUMP

SWBD 1

2000A

415 V

CAMCC

415 V DA9

SWBD

POWER

STATION’A’

415 V DA12

SWBD

30
MW

Fig. 15: Bahamas, single-line diagram

for the production of drinking water,
which is being supplied to the local
municipality (Fig. 17).

The main data of the engine and
Alstom generator are shown in Fig. 18.

During commissioning, extensive mea-
surements were taken of all guaranteed
plant values, and fulfilment has been
ascertained, ref. Fig. 19 comparing
the guaranteed and the actually
obtained data.

Of course, no plant of such size has
been commissioned without teething
troubles. In connection with the engine it-
self, tear of compensators between
turbocharger and air cooler was experi-
enced, as well as repeated accelerated
wear on two out of ten cylinders. The
difficulties have been investigated in
detail, resulting in realignment of the
compensators and the introduction of
the latest development of ceramic-coated
piston rings. Since these modifications
were carried out, the engine has been
running without any unplanned stoppage.

11

Alstom Power S.A., Spain
- Main contractor
- Generator
- Mechanical and electrical aux. systems
- Logistics
- Site erection
- Commissioning

MAN B&W Diesel A/S, Denmark
- Diesel engine design

Manises Diesel Engine Co. S.A., Spain
- Diesel engine supply
- Site erection
- Commissioning

Conceptual plant engineering

Foundation design

Commissioning assistance

Fig. 16: Bahamas, project organisation

Heat balance data:

Non-utilized
energy

Generator cooling: 1.4%

Radiation: 0.8%

Lub. oil cooling:

4.0%

Charge air cooling: 20.3%

Exhaust gas: 21.0%

Jacket water cooling: 6.4%

Station use of aux. systems: 2.0%

Total energy utilization:
Electrical output = 42.0%
Thermal

= 2.2%

Total energy utilization = 44.2%

output

Energy in fuel: 100%

Utilized
energy

2.2%

High temp.

Low temp.

Mechanical
output 45.4%

Generator
output
44.0%

Net
Electrical
output
42.0%

Engine data:

Ambient conditions:

10K80MC-S shaft power = 33,410 kW at 100% MCR

Air at blower inlet:

35 C

Air pressure at blower inlet: 1000 mbar
Charge air colant

32 C

o

o

Fig. 17: Bahamas DA 11, plant heat balance

Fig. 14: Bahamas DA 11, plant view from
outside and inside

From its commissioning in October 1999
until 31 December 2000, the engine
has accumulated 9500 running hours,
and a total of 280 hours have been spent
on scheduled and unscheduled mainte-
nance, resulting in a total plant availabil-
ity of 90% in the period.

In February 2001, BEC awarded an or-
der for an identical diesel generator unit
to the same group of companies for
delivery in 2002.

Conclusion

As shown, the two-stroke low speed
diesels of MAN B&W design are a
viable option to be investigated and
chosen by owners anywhere where
reliable, fuel-efficient diesel plants
are required, especially if the fuel is
of a poor quality and available in
scarce amounts.

The future development of such en-
gines will be dictated by the market, in
particular by the future fuel oil prices
and qualities, and the trend seems to
point in the direction of even more effi-
cient and ever larger units.

Literature

‘Diesel Engines for Independent Power
Producers and Captive Power Plants’,
issued by MAN B&W Diesel A/S,
Copenhagen, Denmark.
Publication No. P.352-99.01

‘Waste Heat to Water’, by N. Pearce of
Alfa Laval Ltd., published in ‘The Power
Engineer’, Vol. 3, No. 2, April 1999.

12

MAN B&W engine type

K80MC-S

Number of cylinders

10

MCR

kW

33,410

r/min

rpm

102.9

Bore

cm

80

Stroke

cm

230

Mean piston velocity

m/s

7.89

Mean effective pressure

bar

16.8

Length

m

18

Width

m

7.5

Height

m

14.3

Total weight

t

1,200

Heaviest weight for maintenance

t

6.3

Alstom generator type

W 950/76/70

Rated output, kVA

41,092

Power factor (overexcited)

0.8

Rated voltage (± 5%), kV

11

Rated current, A

2,156.8

Frequency, Hz

60

Number of poles

70

Rated speed, rpm

102.9

Overspeed, rpm

124

Mass moment of inertia (I), kgm

2

3,150,000 (1)

Inertia constant kWs/kVA

4.43

Insulation class (stator, rotor)

F

Design

IM 7325

Enclosure

IP 44

Cooling system

ICW-37A97 (air to water)

Total weight, tons

400

Heaviest weight for maintenance, tons

9

Fig. 18: Bahamas DA 11, engine and generator main data

Plant net efficiency

Guaranteed

%

Measured at

commissioning

%

100% MCR

40.7

42.0

80% MCR

40.8

42.4

50% MCR

38.8

40.8

Plant emissions at 15% O

2

CO

2

mg/Nm

3

(2% sulphur in fuel)

1,900

1,110

CO mg/Nm

3

150

72

NO

x

ppm/Nm

3

(incl. 0.3% fuel bound nitrogen)

1,300

1,020

HC mg/Nm

3

150

31

PM mg/Nm

3

150

140

Noise
1 m from engine, dB (A)

105

105

2 m above floor level and 1 m from engine, dB (A)

95

95

At boundary of plant, dB (A)

70

60

Fig. 19: Bahamas DA 11, plant performance