SFOC Optimisation Methods

SFOC Optimisation MethodsFor MAN B&W Two-stroke IMO Tier II Engines

MAN B&W Diesel3SFOC Optimisation Methods For MAN B&W Two-stroke IMO Tier II Engines

Content

Introduction .................................................................................................5

Influence of NOx Regulations on Reduced SFOC ...........................................6

Engine Tuning Methods Available ..................................................................6

Exhaust Gas Bypass (EGB) .....................................................................6

Variable Turbine Area or Turbine Geometry (VT) ........................................8

Engine Control Tuning (ECT) ....................................................................9

Potential Fuel Savings on Low-Load Operation ........................................... 10

Summary ................................................................................................... 13


SFOC Optimisation MethodsFor MAN B&W Two-stroke IMO Tier II Engines

Introduction

One of the goals in the marine industry

today is to reduce the impact of CO2

emissions from ships and thereby to re-

duce the fuel consumption for the pro-

pulsion of ships to the widest possible

estimate at any load.

This drive may often result in operation

of the ship at reduced ship speed and,

consequently, at reduced engine load.

This has placed more emphasis on op-

erational flexibility in terms of demand

for reduced SFOC (Specific Fuel Oil

Consumption) at part/low-load opera-

tion of the main engine. However, on

two-stroke engines, reduction of the

SFOC is affected by NOx regulations in

order to maintain compliance with the

IMO NOx Tier II demands.

Depending on the intended operation

range of the main engine, the engine

may be SFOC-optimised in the follow-

ing percentage SMCR (Specified Maxi-

mum Continuous Rating) ranges shown

in Table 1a.

The high-load range corresponds to a

normal, standard-tuned engine of today.

For part-load and low-load optimisa-

tion, the following engine tuning meth-

ods are available, see Table 1b.

The above-described engine tuning

methods are only available for engines

with high-efficient turbochargers, and

will only be introduced for engines in

compliance with the IMO NOx Tier II re-

quirements.

As an example, Figs. 1a and 1b show

the impact on the SFOC curves valid

for ME/ME-C and MC/MC-C/ME-B en-

gines in general, based on a standard-

tuned engine (high load), VT part load

and VT low load, respectively. They are

available for both nominally rated and

derated engines.

Engine load65 70 80 100 % SMCR

High-load optimisedPart-load optimised (VT tuning)Low-load optimised (VT tuning)

1 g/kWh

3 g/kWh

5 g/kWh

Fig.1a: Example of SFOC reductions for ME/ME-C engines with VT Fig.1b: Example of SFOC reductions for MC/MC-C/ME-B engines with VT

Table 1a

Table 1b

SFOC

Engine load35 65 70 80 100 % SMCR

High-load optimisedPart-load optimised (VT tuning)Low-load optimised (VT tuning)

1 g/kWh

2 g/kWh

3 g/kWh

SFOC-optimised load rangesHigh load 85-100% SMCR (standard-tuned engine)

Part load 50-85% SMCR

Low load 25-70% SMCR

Engine tuning methods availableEGB Exhaust Gas Bypass

VT Variable Turbine Area or Turbine Geometry

ECT Engine Control Tuning (only for ME/ME-C)

6 SFOC Optimisation Methods For MAN B&W Two-stroke IMO Tier II Engines

An SFOC reduction of 5 g/kWh makes

it possible to obtain a fuel cost reduc-

tion of up to approx. 3% of the specific

consumption. The daily consumption

will of course be reduced further due to

the low load.

The influence of NOx regulations and

the engine tuning methods available

for ME/ME-C and MC/MC-C/ME-B en-

gines are described below.

Influence of NOx Regulations on Reduced SFOC

As mentioned, the SFOC is limited by

NOx regulations on two-stroke engines.

In general, the NOx emission will in-

crease if the SFOC is reduced and vice

versa. In the standard configuration, our

engines are optimised close to the IMO

NOx limit, which is why the NOx emis-

sion cannot be increased.

The IMO NOx limit is given as a weight-

ed average of the NOx emission cycle

values at 25, 50, 75 and 100% load,

5% x NOx (25) + 11% x NOx (50) + 55%

x NOx (75) + 29% x NOx (100).

This relationship can be utilised to shape

or tailor the SFOC profile over the load

range, i.e. the SFOC can be reduced at

low load at the expense of higher SFOC

in the high-load range without exceed-

ing the IMO NOx limit.

Compared with MC/MC-C/ME-B en-

gine types, the SFOC reduction po-

tential is better for the ME/ME-C type

engines because variable exhaust valve

timing is available.

Engine Tuning Methods Available

The engine tuning methods available

are described in more detail below.

Exhaust Gas Bypass (EGB)

This method requires installation of an

EGB, individually tailored at approx 6%

EGB. The EGB technology is available

for both the ME/ME-C and MC/MC-C/

ME-B type engines. The SFOC poten-

tial is better on the ME type engine,

where EGB is combined with variable

exhaust valve timing.

The turbochargers on the ME/ME-C

engines for part load and low load are

matched at 100% load with fully open

EGB. At approximately 90% load, the

EGB starts to close and is fully closed

below about 80% load. For MC/MC-C/

ME-B engines, the similar engine load

figures are about 90%/70% for part

load and 85%/65% for low load. For

MC6/MC-C6, it is about 85%/70% for

part load and 85%/65% for low load.

The above description of open/closed

EGB is shown in graphical form in Fig. 2.

With this technology, the SFOC is de-

creased at low load at the expense of

higher SFOC at high load.60 70 80 90 100% SMCR

ME/ME-C

Exhaust Gas Bypass, EGB open and closed EGB

60 70 80 90 100% SMCR

MC/MC-C/ME-B

60 70 80 90 100% SMCR

MC6/MC-C6

: Low load

: Part load

Engine load

: Low load

: Part load

Engine load

: Low load

: Part load

Engine load

Closed

Based on ISO ambient conditions and for guidance only.

Partly open Open

Fig. 2: Exhaust Gas Bypass (EGB) open and closed EGB


SFOC g/kWh

Engine shaft power % SMCR25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100

164

163

162

159

160

161

166

167

168

169

170

171

172

173

174

175

176

165

StandardEGB, part loadEGB, low load

ISO ambient conditions

SMCR: 25,080 kW x 78 r/min

Fig. 2a: Example of SFOC reductions for 6S80ME-C8.2 with EGB Fig. 2b: Example of SFOC reductions for 6S80MC-C8.2 with EGB

SFOC g/kWh

Engine shaft power % SMCR

25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100164

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

165

StandardEGB, part loadEGB, low load



With part-load optimisation and com-

pared with a standard engine, the

SFOC is reduced at all loads below

about 85%.

With low-load optimisation, and com-

pared with part-load optimisation, the

SFOC is further reduced at loads below

about 70%, at the expense of higher

SFOC in the high-load range.

The most optimal method depends on

the operating pattern.

As an example, Fig. 2a shows the

SFOC curves valid for a nominally rated

6S80ME-C8.2 engine based on stand-

ard high load, EGB part load and EGB

low load, respectively. Fig. 2b shows

the similar SFOC curves valid for the

nominally rated 6S80MC-C8.2.


Variable Turbine Area or Turbine

Geometry (VT)

This method requires special turbo-

charger parts allowing the turbocharger(s)

on the engine to vary the area of the

nozzle ring. The VT method is available

for both the ME/ME-C and MC/MC-C/

ME-B type engines. The SFOC potential

is better on the ME/ME-C type engines,

where VT is combined with variable ex-

haust valve timing.

The nozzle ring area has a maximum at

the higher engine load range. When the

engine load for ME/ME-C engines for

part load and low load is reduced below

approx. 90%, the area gradually starts

to decrease and reaches its minimum at

about 80% engine load. For MC/MC-C/

ME-B engines, the similar engine load

figures are about 90%/70% for part

load and about 85%/65% for low load.

60 70 80 90 100% SMCR

ME/ME-C

Variable Turbine Area or Turbine Geometry (VT) Nozzle Ring Area

60 70 80 90 100% SMCR

MC/MC-C/ME-B

60 70 80 90 100% SMCR

MC6/MC-C6

: Low load

: Part load

Engine load

Minimum area Intermediate area Maximum area

: Low load

: Part load

Engine load

: Low load

: Part load

Engine load

Based on ISO ambient conditions and for guidance only.

SFOC g/kWh


164

163

162

159

160

161

166

167

168

169

170

171

172

173

174

175

176

165

StandardVT, part loadVT, low load


Fig. 3a: Example of SFOC reductions for 6S80ME-C8.2 with VT Fig. 3b: Example of SFOC reductions for 6S80MC-C8.2 with VT

SFOC g/kWh


164

166

167

168

169

170

171

172

173

174

175

176

177

178

179

180

165

StandardVT, part loadVT, low load



Fig. 3: Variable Turbine area or turbine geometry (VT) nozzle ring area


For MC6/MC-C6, it is about 85%/70%

for part load and 85%/65% for low load.

The above description of the VT nozzle

ring area is shown in graphical form in

Fig. 3. With this technology, the SFOC

is reduced at low load at the expense of

higher SFOC at high load.


pared with a standard engine, the

SFOC is reduced at all loads below

about 85%.

With low-load optimisation and com-


SFOC is further reduced at all loads

below about 70%, at the expense of

higher SFOC in the high-load range.

The most optimal method on a specific

engine depends on the operating pattern.

As an example, Fig. 3a shows the

SFOC curves valid for a nominally rated


ard high load, VT part load and VT low

load, respectively.

Fig. 3b shows the similar SFOC curves

valid for the nominally rated 6S80MC-

C8.2.

Engine Control Tuning (ECT)

This method can be implemented with-

out change of engine components, and

can be implemented as an engine run-

ning mode. Only pmax and engine con-

trol parameters are changed.

The method uses the possibility of vari-

able exhaust valve timing and injection

profiling, and is only available for ME/

ME-C engine types. Two different service

optimisation possibilities are available.

SFOC g/kWh


164

163

162

159

160

161

166

167

168

169

170

171

172

173

174

175

176

165

StandardECT, part loadECT, low load



Fig. 4: Example of SFOC reductions for 6S80ME-C8.2 with ECT


pared with a standard-tuned engine,

the SFOC is reduced at all loads below

about 85%.

With low-load optimisation and com-


SFOC is further reduced at all loads

below about 70%, at the expense of

higher SFOC in the high-load range.

The most optimal method on a specific

engine depends on the operating pat-

tern.

Random shifting between the part-load

and low-load modes is not allowed by

the authorities. A mode shift in case of

a change in trade pattern is permitted if

reported and approved by the flag state

representative, usually a classification

society. Hence, on a longer term basis,

the owner can select one or the other of

the modes for the engine, provided the

authorities are informed.

Both modes will need to be verified on

test bed if decided in time. Otherwise, a

special, approved process is called for.

As an example, Fig. 4 shows the SFOC

curves valid for a nominally rated


ard high load, ECT part load and ECT

low load, respectively.


Potential Fuel Savings on Low-Load Operation

Today, a reduction of CO2 emissions,

and thereby a reduction of the fuel con-

sumption of a ship, is an increasing de-

mand that will be even stronger in the

future. This may result in lower service

ship speeds compared with earlier ship

speeds. Thus, the lower the ship speed,

the lower the required propulsion power

and, thereby, the lower the fuel con-

sumption is.

Main engine 6S80ME-C8.2 IMO Tier llSMCR = 25,080kW x 78r/min

Standard engine, high load optimised

Engine load % SMCR 35% 50% 65% 85% 100% Total fuel consumption

Engine power kW 8,778 12,540 16,302 21,318 25,080

SFOC g/kWhRe LCV = 42,700 kJ/kg

171.4 167.0 164.3 165.0 168

Fuel consumption t/day 36.1 50.3 64.3 84.4 101.1

Days in service day/year 40 100 90 15 5

Fuel consumption t/year 1,444 5,030 5,787 1,266 506 14,033 t/year

VT, low load optimised


Engine power kW 8,778 12,540 16,302 21,318 25,080


166.4 162.0 159.3 165.3 168.5




Fuel savings t/year 44 150 180 -3 -1 370 t/year

Fuel savings %/year 3.0 3.0 3.0 -0.2 -0.3 2.6%/year

Table 2a: Savings in fuel consumption for 6S80ME-C8.2 with VT, low load compared with a standard engine

However, shipowners will still mostly

require the possibility of operating the

ship at the earlier higher ship speed,

if occasionally needed. This means

that the SMCR power of the main en-

gines may still be maintained, while the

changed trading pattern of the ship may

result in operation with a relatively lower

load of the main engine, with only few

days of operation on high engine loads.

Under such conditions, the application

of one of the previously described en-

gine tuning methods, e.g. the Variable

Turbine area, VT, optimised for low-load

operation, will add to reduce the fuel

consumption.

Table 2a shows, as an example, the cal-

culations of the potential fuel consump-

tion savings for a 6S80ME-C8.2 by us-

ing the VT low-load optimised method,

compared with a similar engine with the

standard high-load optimised version.


Main engine 6S80MC-C8.2 IMO Tier llSMCR = 25,080kW x 78r/min

Standard engine, high load optimised


Engine power kW 8,778 12,540 16,302 21,318 25,080


175.2 171.0 168.7 168.3 171.0




VT, low load optimised


Engine power kW 8,778 12,540 16,302 21,318 25,080


172.2 168.0 165.7 168.8 172.0




Fuel savings t/year 24 90 108 -4 -3 215 t/year

Fuel savings %/year 1.6 1.7 1.8 -0.3 -0.6 1.5%/year

Table 2b: Savings in fuel consumption for 6S80MC-C8.2 with VT, low load compared with a standard engine

For the given trading pattern, the po-

tential specific fuel saving found for the

6S80ME-C8.2 engine type is approx.

2.6%.

Table 2b shows the corresponding cal-

culations, but now valid for a 6S80MC-

C8.2 engine.

For the given trading pattern, the po-

tential specific fuel savings found for the

6S80MC-C8.2 engine type is approx.

1.5%.

The corresponding potential relative

fuel saving for other engine types are

of the same magnitude, with the higher

savings valid for the ME/ME-C engine

types and the lower savings valid for the

MC/MC-C/ME-B types.

Of course, in all cases, the daily fuel

consumption will be lowered mostly

due to the lower ship speed, i.e. lower

power needed.


Please note that the reduced SFOC on

low-load operation, when using one of

the engine tuning methods available, in-

volves a correspondingly lower exhaust

gas temperature at low-load operation,

which has to be considered at the de-

sign state of the exhaust boiler of the

ship.

As an example, the influence on the

exhaust gas temperature of the engine

tuning methods valid for 6S80ME-C8.2

with VT, low load compared with a

standard engine is shown in Fig. 5a.

The similar exhaust gas temperature

influence for 6S80MC-C8.2 is shown

in Fig. 5b, and the same tendency is

also applied to the EGB and ECT tuning

methods.

C

Engine shaft power % SMCR3025 35 40 45 50 55 60 65 70 75 80 85 90 95 100

200

240

260

280

220

Standard VT, low load

6S80ME-C8.2SMCR: 25,080 kW x 78 r/min

6S80MC-C8.2SMCR: 25,080 kW x 78 r/min

C


200

240

260

280

220




C


200

240

260

280

220


6S80ME-C8.2SMCR: 25,080 kW x 78 r/min

6S80MC-C8.2SMCR: 25,080 kW x 78 r/min

C


200

240

260

280

220




Fig. 5b: Exhaust gas temperature after t/c for 6S80MC-C8.2 with VT, low load compared with a stand-

ard engine

Fig. 5a: Exhaust gas temperature after t/c for 6S80ME-C8.2 with VT, low load compared with a stand-

ard engine


Summary

The introduction of the described main

engine tuning methods EGB, VT and

ECT makes it possible to optimise the

fuel consumption when normally op-

erating at low loads, while maintaining

the possibility of operating at high load

when needed, for example when the

time schedule is tight.

In this way, the MAN B&W two-stroke

engine is meeting the more stringent

demand of the future for reduction of

CO2 emissions and thereby the fuel

costs. A reduction of up to 3% of the

specific fuel consumption is possible.

MAN Diesel & TurboTeglholmsgade 412450 Copenhagen SV, DenmarkPhone +45 33 85 11 00Fax +45 33 85 10 [email protected]

MAN Diesel & Turbo a member of the MAN Group

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. 5510-0099-00ppr Aug 2012 Printed in Denmark

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