Proceedings of the Europort Diesel Engine Symposium'89 - ""MOTOR 2000"".

EUROPOR T DIESEL ENGINE SYMPOSIUM

'89

P19 89 -10

MOTOR 2000

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16TH NOVEMBER 1989 RAI AMSTERDAM

4

Daniel Paro

Vice President and General Manager Oy Wartsila Ab Diesel Technology

THE CNC ENGINE ROOM - A VITAL PART OF THE CC SHIP

The vision

The most important task of the responsible man on the

bridge is, has always been, and will probably always be to bring the ship from one harbour to another as safely and

economically as possible. Responsibility for the ship is always great, and in many cases, for example narrow waters,

bad weather and harbour approach, navigation calls for

total concentration. The man on the bridge should therefore not have to bother too much about other functions on the

ship.

On the manually operated ship, this was ensured by a well

developed hierarchy with clear chains of responsibility and

sufficient personnel to perform the duties.

On-board automation began with remote control of single functions. When a few controls were concentrated at the

same point, the control room was born. The next step in the

automation process was what could be called spot

automation; systems and devices were equipped with

automation systems with some built-in logic. Even in the most advanced ships of today the automation system consists of islands which are either isolated or which communicate

with each other occasionally. As the "one on bridge"

concept has already been invented, it can be taken for

granted that development will strongly go in this

direction. But if large parts of the current control room are brought up to the bridge, the poor man in charge there will be overwhelmed. The "one on bridge" concept requires

development of a hierarchy which is at least as good as

wARTSILA 01-1-,

2

that on manually operated ships. The vision is to create a system containing a master intelligence; on one hand this intelligence is the interface with the person on the

bridge, on the other hand it gives instructions and checks all existing computerized and automated systems on board. (Fig. 1) If the aim is to create a reasonable work

environment for the single man on the bridge, it is obvious that real progress must be made in the reliability and

self-correcting properties of all the ship's systems. This paper concentrates on the propulsion system and the engine room.

The prerequisites

The following are essential for the development of a CNC engine room:

The prime movers must be extremely reliable.

All systems which are in any way delicate must be

designed for maximum reliability and contain corrective

functions.

The most advanced systems, e.g. the diesel engines, must be equipped with a diagnostic

system-The reliability of the monitoring and correcting systems

must be at least

as good as that of the

monitored

function.

The medium-speed engine as a reliable prime mover

Looking at the medium-speed engines introduced in the early 70's, it is probably right to say that should they have

been operated at 60 to 70 per cent of rated load, they

t

*

WARTSILA

₃

would have been performing quite well, and the reputation

of medium-speed engines in general would have been quite different from the position today. If that reasoning is true, it indicates that the basic arguments, like low

weight, small space and low kilowatt price, have been

overdone in the generation of medium-speed engines which is

now predominant in actual ships. A further extension of the

reasoning results in the conclusion that a reliable

medium-speed engine ought to be over-dimensioned, and maybe a little bit more sturdy, heavier and even slightly more expensive than the existing ones.

The highest failure rates have probably been recorded in some of the following areas:

Bearing damage resulting in crankshaft damage

In very many cases dirty lubricating oil can be blamed. However, practical people claim that dirty oil is part of life. The conclusion must be that the medium-speed engines have been too sensitive to dirty oil. Also bearing

corrosion and plain overloading of the bearing materials

have been

contributing

to the high failure rate. The

unpopularity of this type of failure is underlined by the fact that total crankshaft damage, and in some cases even

engine

block damage, have

been a consequence of bearing

failures, resulting in long off-hire times.

- Piston seizures

This failure is very much related to aluminium alloys as the material in the piston skirt, and the very unfavourable

seizure process which this material induces. Also in this

case the consequential damage has often been much worse

wARTsiLA

4

-

Burned exhaust valves

Burned exhaust valves have certainly been irritating a lot of operational personnel. However, this type of failure has not been decisive for the bad reputation of the

medium-speed engines of the past.

Features of a reliable medium-speed engine

Thick-pad bearing technology

When the design of the engine type Vasa 46 was started one of the most important aims was to create a bearing

technology which would be on a totally different level from the existing one in medium-speed engines. After initial investigations of the possibilities, two different

development directions evolved:

* Development of a seizure-safe multilayer bearing by utilizing sputtering technology

* Drastic increase of the bearing dimensions resulting in lower bearing pressure, lower oil film pressure and increased oil film thickness

Both development directions were chosen. However, only the

larger dimensions existed as a possibility at the date of designing the engine, and were incorporated in the design.

Fig. 2, 3 and 4 show the influence of the larger dimensions of the crankshaft bearings.

wARTsiLA

5

Safe combustion

It is quite difficult to estimate what the fuel quality for marine engines will be in the long term. However, in the near future, i.e. the next five to ten years, it is obvious that heavy fuel will have a predominant role, and the

quality of heavy fuel will also deteriorate, especially if oil prices start to accelerate again. Therefore, an engine for the future, and especially for the near future, has to be designed and developed for operation on fuels with very poor ignition qualities. At the same time it is obvious that the future engine must be designed and developed for very low fuel consumption, because the current rather low price of oil will certainly not prevail during the lifetime of an entirely new product. Low fuel consumption is the result of many parameters, but at least one thing is

certain, and that is that the fuel injection process must be very quick. A quick injection process, i.e. a high rate of injected fuel, involves a risk of a knocking process if the ignition delay cannot be reduced by some means. The method chosen to control the ignition delay was the

so-called twin injection system, which means a pilot and main charge system, where a small pilot amount is injected before the real fuel charge. The main advantage of the twin

injection

system is that the ignition delay when the main charge is injected is almost negligible. This again means that the heat release into the cylinder can be very well controlled by the injection process. According to the

author's opinion there is no other method existing today by

which one can reach very low fuel consumption without introducing any risk of diesel knock. (Fig. 5 and 6)

A big step forward in piston safety in medium-speed engines

was the change from aluminium alloy as skirt material to nodular cast iron (Fig. 7 and 8). The advantages of the

nodular cast iron piston skirt are:

The thermal

expansion coefficient is low, which allows a

small piston clearance.

Less tilting results in less piston ring and liner wear.

Local overheating of the piston skirt does not result in

accelerating seizure process.

The piston material is very strong and the piston can

withstand even a seizure process.

wARTsILA lag;tr l

6

Concerning turbocharging systems, the choice is between a pulse charging system and some form of constant pressure charging system. Both have their advantages and

disadvantages. The advantage of a constant pressure charging system is high efficiency at high load of the diesel engine and the disadvantage is very poor low load performance.

The so-called SwirlEx system was introduced in the Vasa 46. The idea of this system is basically to wind a very long diffusor around the main exhaust duct, thus getting the best possible transformation of the pulses to constant pressure. The system offers clear advantages over a plain constant-pressure system. However, at the same time it must be said that its low load performance is not as good as for a pulse charging system.

Safe piston

wARTSILA

'7

Another threat towards piston safety has been piston ring scuffing. A big step forward in this area was the

introduction of the pressure lubricated piston skirt, which is patented by Wartsila Diesel. The advantages of the

pressure lubricated piston skirt are:

No risk of piston ring scuffing Lower oil consumption

Clean ring grooves and rings Less tilting, less wear

Higher maximum pressure possible -> lower fuel consumption

Altogether it is fair to say that the piston of the

medium-speed

engines

nowadays is a very safe component.

Safe cylinder heads

The introduction of a

double-bottom

cylinder head and bore

cooling in the sensitive parts of the cylinder head removed the problems encountered in the cylinder head piece itself. From that point the reliability of the head is very much related to the reliability of the valves. At higher maximum pressures, inlet valve seat wear has sometimes been

noticed, but it can obviously be solved by the right material choice and correct dimensioning of the parts involved. The exhaust valve has certainly caused more

problems to the marine industry. Good achievements have been made by introducing water cooled seats and improved materials. However, the decisive factor, according to the

author's company, is the deformation of the cylinder head, the valve seat and the valve itself during the combustion process. In this area the introduction of finite element calculation methods has meant big improvements in the possibility of optimizing the design (Fig. 9).

WARTSILA iagr-gi,

8

Conclusion

The medium-speed diesel engine stands a very good chance of being a sufficiently reliable prime mover for the CNC

engine room and the CNC ship.

Existing components for the CNC engine room

WENCOM

It is the philosophy of Wartsila Diesel that the

communication interface with the engine belongs to the

development responsibilities of the engine manufacturer.

Consequently, development of a reliable monitoring system was begun in the late 1970's. An outline for a really

realible system was presented at the 1983 CIMAC Congress in

Paris.

The WENCOM system is by nature a safety system

concentrating on monitoring of the most vital components,

such as main bearings, piston and liner, exhaust valves and load balance between the cylinders. The system has so far proved that both the sensors and the computers can be made reliable enough to meet the demands of a CNC engine room

system.

FAKS

For the "one on bridge" concept a monitoring system is not

enough because it only tells what is happening on the ship,

something the man on the bridge does not need to know. What he does need to know is whether it affects his work, in

wARTsILA Eg;51 i

9

For some time Wartsila Diesel has been working on an engine diagnosis system based on expert system technology. The

first system will be delivered this year. The prime interface with the engine comprises a large number of

sensors, about 90 (9-cylinder engine) for each engine. The information from these sensors is processed in a computer which creates a mathematical model of the operating engine. This model is compared with a mathematical model of an

ideally operating engine at the same output. The two models are compared; if there are any deviations the expert system informs its memory, which is loaded with a great number of knowledge containing cards, by means of which the expert system can make a diagnosis and also prescribe corrective actions or impose limitations for the man on the bridge. '(Fig. 10)

REMCON

It is quite obvious that not just any electro-pneumatic remote control system for the main engine is compatible with CNC technology. Together with a cooperation partner, Wartsila Diesel has therefore developed a remote control system based on microprocessor technology.

Next development steps

For the one man on bridge it is not

enough

to be served by

a CNC engine room. He also wants to be served by a CNC

system for the complete ship. The current step is therefore to communicate with suppliers of ship automation systems

and work together with them on the superintelligence which will be the partner of the single man on the bridge.

WAFrTSILA

CAPTIONS

Fig. 1 The future

working

environment for the "one on bridge"

concept.

Fig. 2 In the Vasa 46 the bearing pressures are reduced to half

compared with state-of-the-art engines, and the oil film pressure is reduced accordingly.

Fig. 3 The reduction of the oil film pressure by half more than

doubles the effect on the oil film thickness.

Fig. 4 An oil film thickness of 20 pm is a considerable

improvement compared with 4 to 5 pm, which is normal in many engines.

Fig. 5 Twin injection reduces the ignition delay when the main

fuel charge is injected and is a base for controlled combustion.

Fig. 6 Twin injection system

Fig. 7 Aluminium alloys as piston skirt material do have some

delicate properties.

Fig. 8 Nodular cast iron as piston skirt material was a big step

towards safe pistons.

Fig. 9 The Vasa 32 cylinder head has an outstanding performance

record with time between overhauls on heavy fuel of 12,000-20,000 h.

Fig. 10 The working routines of the master intelligence of a "one

MASTER

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-C421

NEW WAY OF COMBUSTION MONITORING

IN DIESEL ENGINES

EUROPORT AMSTERDAM

on 16th November 89

0

A

by

JP. BOURGOIN

4,

1

S.E.M.T. Pielstick

IELsvc

/

1 - ABSTRACT

NEW WAY OF MONITORING THE COMBUSTION IN DIESEL ENGINES

The combustion quality may deteriorate during the running of the

engine and this may result in abnormal stresses for the components.

The risk is greater with the increasingly heavier fuel oils which

are put on the market.

The combustion severity has been quantified from the vibration

le-vels of the cylinder-head.

The cylinder-head vibrations transmitted by an accelerometer are

analysed in

an equipment with microprocessors called DYNASCAN°.

The DYNASCAN , which has been used for several years on the test

benches of SENT PIELSLTICK, is being evaluated on board ships.

For the processing of the information and the software, a micro

computer compatible IBM-PC is used.

2 COMBUSTION HARDNESS

The well-known refining evolution leads to heavier fuel oils and

the use of low viscosity fitments with bad ignition quality.

Oil companies have proposed calculated values for Calculated Carbon

Aromaticity Index (C.C.A.I) and Calculated Ignition Index

(C.I.I.), both based on the fuel viscosity and density, and

therefore taking into account the aromaticity of the fuel. Both

viscosity and density are known during market operations and this

explains their increasing acceptance. SENT PIELSTICK investigated.

problems in service concerning ignition, which are summarized in

figure No 1.

In parallel with the above investigations SENT PIELSTICK carried

out a serie of tests on specially prepared fuels. The fig.2 summarizes the results of these tests.

-The high pneumatic frequencies of the air-gas mass in the cylinder, (up to 8 kHz for a 280 mm bore) are much above the values of the frequencies of mechanical vibrations of the engine components like the liner and cylinder-cover, but they are transmitted through the material. Therefore, it is possible to measure the intensity of the

internal pneumatic vibrations by measuring the intensity of the

external accelerations.

The similarity of the spectral response between

the combustion pressure,

the engine structure,

gives then a way to apprehend this phenomenon (Figures No.5 and

No. 6).

3 - DYNASCAN

An electronic equipment was developped by SENT PIELSTICK to give a

digital indication of the cylinder chamber response to the excitation created by ignition (Fig.7).

Its name is DYNASCAN which is registered mark based on and

covered by an SENT PIELSTICX patent (cf. figure No.8 and No.9).

It is very simple to fit on an existing engine only one accelerometer and one timing sensor

are

the requested inputs.

Its issues a parameter quantifying the combustion hardness (Index

of Combustion Severity), in relative unit which we have nicknamed

PICE for

Pielstick

Index of Combustion Severity.

. For each cylinder one

accelerometer is fitted on the cylinder

head. The signal from the accelerometer is filtered, calibrated and

integrated in a window of constant angular duration. The result

displayed on the device is the average cf 10C successive measures

E r13:

rNLSTC

. It is very simple to fit it on an existing engine

the accelerometer is screwed in a steel washer glued on the cylinder cover (Fig.10);

the Top Dead Center sensor is fitted on one inspection door of the camshaft (Fig No.11).

The DYNASCAN uses a monochip microprocessor.

A standard portable microcomputer can be connected to the

DYNASCAN through a serial link and allows.

the programmation (type of engine, number of cylinders, engine timing);

the reading of the records stored in the memories.

The display is made according three modes

Automatic scanning of all the cylinders;

Manual scanning of desired cylinders;

Automatic display of the cylinder which have the higher value of combustion hardness.

The electronic cards are according EUROP standards and fitted in

a 19 inches

standard rack.

The fig.12 shows the general arrangement of DYNASCAN®

The fig.13 shows the DYNASCAN installed on board a ship in

service.

4 - TESTS AND SERVICE RESULTS

Already used on SENT PIELSTICK test benches, the DYNASCAN is

under evaluation in service in order to settle practical charts and realistic limits per engine type.

The Index of Combustion Severity is the result of the vibrations

analysis given by DYNASCAN

e

, the vibration signal being given by

the external accelerometer fitted on the cylinder cover.

The same vibration analysis through DYNASCANID can be made on the

signal given by a piezo sensor placed directly in the combustion

chamber.

The vibration analysis was carried out for different values of speed and torque.

The fig.14 and 15 show the good correlation factor between the

piezo signal and the accelerometer signal.

The fig.16 and 17 show the evolution of the Index of Combustion

Severity when the cetane number is decreasing. These tests were

carried out on a SENT PIELSTICK PAS BTC engine low compression

ratio 8.5 (Bore 280mm) for NAVY applications.

The fig.18 shows the results in -service on one SENT PIELSTICK PC

2.6 engine. The indexes of Combustion Severity for the engine

running with medium Diesel Oil and with fuel oil can be compared. The influence of the partial loads and of the charging air temperature can be appreciated.

5 - CONCLUSION

DYNASCAN allows to quantify the combustion hardness with a good

industrial accuracy. The challenge is to settle the realistic

limits per engine type. The following principle could apply.

Index of Combustion Severity below A value;

Good combustion. The engine can be operated without any risk in respect with the combustion conditions.

Index cf Combustion Severity between A value and B value; The combustion is not normal. The operation of the engine permanently in these conditions is not recommanded.

C421-01

SERVICE EXPERIENCE ON BOARD SHIPS

1,01 1,00 0.99 -Or t r 0 r igit** ** **-*** *

* ** **w***

** **; :: VP: 1r 0,98 0,96 0,95 0,94 0,93

* *

.* * * DENSITY (kg/m3 15*C) * * *

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CCAI 100 200 300

400

500 BOO 700 870 aeo $50 840 830 820

A BAD COMBUSTION

* NORMAL COMBUSTION

Viscosity (cSt 50°C)

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C421-02

DENSITY 15 °C

1,010

-1,000

0,990

0,980

0,970

0,960

-0,950

-0,940

-0,930

0,920

-FUELS TESTED

830

820

N rIELSTICr' CCA1

ZONE 1: GOOD COMBUSTION

ZONE 2: RISKS OF BAD COMBUSTION

ZONE 3: BAD COMBUSTION

TESTED FUELS

ZS

100

200

no

400

560

660

₇₆₀

4. C421-03

1,01-S.E.M.T. PIELSTICK CCAI CHART

DENSITY

(kg/m3 15C)

ZONE 1: GOOD COMBUSTION

ZONE 2: RISKS OF BAD COMBUSTION

ZONE 3: BAD

COMBUSTION

Viscosity (cSt 50°C)

100

200

300

400

500

600

700

830

820

s.E.MT V . . 45' ,/ IELSTIC 1,00-0,99 0,98- 0,97-0,96

0,95-0,94

0,93-0,92

870

860

840

CCAI

C421-04

COMBUSTION TYPES

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A C.C.A.I.-chart was deducted, (see Figure No.3) indicating three

zones

good combustion;

bad combustion;

zone with uncertain effects;

and therefore the only approach available on owner side is to plot

its bunkering on this C.C.A.I. chart to roughly judge its quality.

But, nothing can advise the chief engineer if the engine itself is

not properly adjusted or well maintained. Then, the combustion

quality can worsen and leads to detrimental effects towards the

combustion chamber components. Figure No.4 shows the shape of

pressure fluctuations for normal combustion and for a degraded one.

It is therefore of the utmost interest to issue a quantified value

for the combustion hardness.

This leads to the choice of measurement to be made. Ignition

quality is linked with ignition delay. This is a first measurement possibility. Ignition delay is linked with the variable quantity of fuel injected during this delay and therefore with the degree of explosive combustion that generates the pressure gradient. This is

a second possibility. The uneven speed of ignition and explosive

combustion in the combustion chamber excites the natural frequencies of the air-gas mass.

This gives a third measurement possibility, which seems,

the best

one to describe "combustion hardness and danger for the engine.

This third possibility consists in measuring the transmitted vibrations.

The air-gas mass in the cylinder exhibits certain inherent natural

frecuencies. Those vibrations may occur according different modes (circumferential, radial).

Like any vibrations system, the intensity of the vibrations depends on the actuating forces.

C421-05

FREQUENCY ANALYSIS OF PRESSURE CYCLES

ONE DETECTION EVERY 29 CYCLES.

_

10000 HZ

A-_

ONE DETECTION EVERY 3 CYCLES.

r

VAAL

-MOO HZ

SEI-D ' E L ST I 700 RPM PRESSURE CYCLE PRESSURE CYCLE

=s- "'"'"---. - -: =.7 _ C421-06

FREQUENCY ANALYSIS OF CYLINDER-HEAD

VIBRATIONS

ONE DETECTION EVERY 29 CYCLES.

!ONO HZ

ONE DETECTION EVERY 3 CYCLES.

-=Z." -. 7 7:7 ., . - . . . 10000 HZ

6s.EMIJ

rIELTIcrs 700 RPM CYLINDER-HEAD VIBRATIONS. 700 RPM CYLINDER-HEAD VIBRATIONS. 0

C421-07

COMBUSTION HARDNESS

IRREGULAR AND / OR EXPLOSIVE

COMBUSTION

EXCITATION OF OWN

FREQUENCIES OF AIR MASS

TRANSMISSION THROUGH WALLS

ACCELEROMETER DYNAS CAN DIGITAL INDICATION

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PA6 STC ENGINE

DYNASCAN0 ANALYSIS,

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Correlation factor 20 : :

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C421-15 ISC KIESSION 30C 200 150 100 50 0

8 PC20 ENGINE

DYNASCAN

ANALYSIS

Quantity of plotted points :

15

Correlation factor

.995

Off /7/1179 //// //iM b IELsTiC

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_/

ISC YIBRATICii 0. 50. 100. 150. 200. 250. 300. 350. 400 400

0

p.

V / / / /

/ / /67

/ /

000 s.EMT IELSTIC C421-16

COMBUSTION SEVERITY INDEX

IMEP 25 20 15 10 (bar) i

Cetan

1 1

Or

index

1 1 I I

50

i 100

r

1 50 . 1 roo 1 1 1 _ 150i

1--._ 200 , A 1

1

I

ihi

_Pr

Pr

a. 400 500 800 700 8001 900 1000 1100 RPM 300

C421-17

21

1

1

5

COMBUSTION SEVERITY INDEX

400 500 600 700 600 900 1000 1100 RPM

"IMMM7M=MaMMMMIa2M=ZaZ=",_

s.E.M:r IELsTic itr tow;

index

Cetan

43

200

r

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um

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111111.

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600 500 400 300 200 100 0 C421-18

#7'

DIAGRAMS: ISC

f (engine load, fuel)

'Sc T3 : 27 .0 to 33 .0 A T3 : 40 .0 to 42 C 10 20 30 40 50 60 70 BO 90 100 7. ENGINE LOAD

s.Ettr

PIELTIc14

IIVAal

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0

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IVITU Friedrichshafen

VKTG D 2 149

EUROPORT DIESEL ENGINE-SYMPOSIUM

MOTOR 2000

16. NOVEMBER 1989 RAI AMSTERDAM

396 TE COOLING SYSTEM

Dipl. Ing. Wolfgang Rudert, MTU-Friedrichshafen

Ladies and Gentlemen,

MTU has developed a new version of the 396 engine

family for all

purposes. This TE-version will now be introduced in the market.

The letters "TE" are

standing for a new coolant

circuit especially

influencing and controlling

the combustion-air inlet

temperature

depending on engine load.

Former 396-versions have two different charge-air cooling systems.

The charge air of the TB engines is cooled down direktly by raw water

or sea water.

This system is the best for

lowest possible air inlet

temperatures and therefore highest possible output.

But there are also some disadvantages: at low load and

idling

conditions in combination

with low sea water temperatures

the

combustion suffers from the cold combustion air: the

problems

of white smoke at idling and of insufficiant combustion at part

load are growing.

Another problem is the corrosion resistance of charge air coolers

against all kinds of sea water

all over the world. Corrosion

All possible problems concerning idling, low load

combustion and

corrosion of the charge air cooler are eliminated, if engine

coolant

is used for charge air cooling. All MTU-engines in this TC-version are

running with excellent results. But the air intake temperature is

depending on the relativly high engine coolant temperature. Therefore

the output is limited. The new TE-version combines the advantages of

the TB and the TC.

But before explaining the details of the new coolant curcuit

and lift

functions first a photo of the 396 TE engine.

It could be seen the classical design of the MTU 396 engines with

it's triple wall exhaust system, the two MTU turbochargers also

with encapsulated hot parts, the charge-air cooler and the mechanisme

for sequential turbocharging that is now introduced in general for all

396 engines. (Fig. 1)

At the rear end there are arranged the raw water pump, coolant water pump,

But let's go back to the desciption of the

396-TE engine coolant

circuit: It is a very simple one with only one pump, one

thermostat, one

recooler and one expansion

tank. les

mass flow is split into two circuits

after leaving the engine itself:

About two third of the coolant with the high temperature of

the

engine-outlet directly flows back to

the water pump. The rest

of the coolant is

first passing the thermostat

controlling the engine outlet temperature.

In case of full load and opened thermostat the recooler is cooling

down this

small amount of coolant to a low temperature close to the raw water

tempe-rature. Thus the air intake temperature is low at

high load.

The lube oil heat exchanger is also arranged within the low temperature

circuit with benefits especially for the bearings. Before the coolant water

pump, the low temperature

flow is mixed together with the high temperature

flow

.

Thus the coolant intake temperature

for the engine itself is reduced.

When idling, the engine outlet temperature

becomes lower, the thermotat is

shutting down the flow through

the recooler and is opening the bypass.

Now the charge air intercooler gets water with the high temperature level of

the engine outlet. Thus the intake air

is heated for excellent conditions

for combustion. (Fig. 4)

The triple wall exhaust gas system helps to

keep the engine warm during

long idling periods.

Increasing load from idling or decreasing load

from full load gives an

intermediat situation: The thermostat is partly

opened and the charge

air temperature will be between idling and full load condition. (Fig. 5)

The flowrates of the two circuits are given by their resistance curves.

Without doubt the system can be optimired for steady state conditions.

But it is also of interest, what happens during

transient operation.

First calculations and later on experience from

teststand and operation in

heavy duty dumps trucks showed that even when accelierating the

tempera-tures of intake air, engine parts, and lube oil are well within it's

given limits. The split circuit reacts very quickly. There was no need

Thank you for your attention

-5 _

The arrangement

of

the components

of

the coolant circuit could be seen

on top of the engine.

The low temperature circuit passes the thermostat,

is recooled or

bypassed'

cooks

down charge air and tube oil and sejoins the high temperature

circuit. (Fig. 6)

Together with the TE coolant circuit a plate-core recooler is introduced.

This is a lightweight and high efficiency system that incorporates a lot

of improvements compared with a conventional system. Instead of tubes of

cupper-nickel titanium-plates with it's excellent corrosion resistance are

used. The plates can easily be disassambled for cleaning purpose.

And last not least the required capacity of the recooler can be

optimized by the number of plates. (Fig. 7)

The coolant circuit

of

the new MTU 396 TE version combines the avantages

of the internal and external charge air cooling systems.

It heats up the charge air at idling and low load for optimizing the

combustion and it cools down the combustion air at high load for low

thermal load of all parts and high output.

The number of sea water ducting parts could be minimized. The charge air

cooler has no more any contact with sea water, the recooler itself is a

uols.ian aupiew

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LoW-temperature

circuit

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Lube oil heat

Intercooler

exchanger

Coolant system, functional diagram

(full load)

irovi

p-J80°C--74116

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Recooler

85°C

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Deutsche Aerospace

ivr

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396217e3/8911

MTU Friedrichshafen

Coolant system, functional diagram

(idling)

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r:;; ;!;:1,;41, :11;:.9.

'I. Low-temperature

circuit

rrt:75-c,

pif

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I

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Thermostat

Deutsche Aerospace 3962110/891,1

MTU Friedrichshafen

_{396 TE}

Exhaust manifold

with double-wall

jacket

NT iIrs

I

MTU Friedrichshafen

Coolant system, functional diagram

(increasing load)

IS7 IMO

Low-ternberature:

,

circuit

65°

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C\kci

-Lube oil heat

Intercooler

exchanger

High-ternperature circuit

Recooler

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Eivairva- CUTLET

_{coliBusriani A (R.}

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Deutsche Aerospace Tworlaut Vo1 1 mot Vallsst Lesrlaut if*la 2100 1/1.1.1n 600 1/Stin tl TU./Coda H I

.

-4,

200.

16 V 396 TE

_{Coolant system}

Mr

396 238e/8910

row Friedrichshafen

I )'it'

MTU Friedrichshafen

Plate-core recooler diagram

Number of plates

dependent on requirements

to°

,,y1 I I_ It seste ' Deutsche Aerospace

> Lngine coolant

5 RaW water

AGE

3S.

Dipl.-Ing. R. Hafner

MaK C engines - a sound basis for the engine 2000

Development of the diesel engine for almost 100 years

When one looks at the future he will first of all examine the

past by means of comparison parameters. With regard to

four-stroke trunk piston engines, photo 1 demonstrates that

initially the ignition pressures are increasing slightly. After

introduction of the charging a steep increase of the ignition

pressures is noticed. This was necessary because the specific

outputs were increased. At the same time, however, the specific

fuel consumption was reduced on account of the improved

formation of mixtures and the increased mechanical efficiency.

But after the energy crisis in 1973 and 1979 the ignition

pressure was increased in excess of the mean effective pressure.

Now the specific fuel consumption - and not the output increase

- was of primary importance. Today, particularly in the part

load range, ignition pressure/mean effective pressure ratios

above 10 are not unusual anymore.

A very _{drastical fuel consumption reduction was achieved by the}

adaptation of the injection to engines with reduced output for

which the _{ignition pressure was maintained. In order to achieve}

low wear indices and a smooth engine operation - and this with

heavy fuel oils the ignition of which becomes worse and worse

-in spite of the relatively high ignition pressures, it was

necessary to increase the compression ratio drastically again.

As you know, when Diesel searched for an extremely economic

diesel engine, they started with a very high compression.

Increased charging in already engines running at their optimum

design limits and very cheap fuel, however, resulted in a

reduction of the compression ratio down to 8. Values of 14 are

not unusual today. In order to obtain a combustion chamber of

sufficient depth in spite of these thermodynamically and

mechanically correct high compression ratios, longer and longer

piston strokes were required also for four-stroke engines. Owing

to the long stroke _{the compression ratio can be increased and}

simultaneously the combustion chamber can be built deep enough.

Long piston strokes even with medium/high-speed engines

The design of the MaK C engines includes _{a long stroke; refer to}

table 2. Thus a modern combustion chamber is possible together

with a very high heavy fuel oil performance. Experience has

shown that larger piston diameters require relatively shorter

piston strokes, whereas the smaller engines need the larger

stroke. On one hand the surface of the combustion chamber of

larger engines, referred to the combustion chamber volume,

always becomes relatively small; on the other hand the free 'let

length of the fuel, referred to the piston diameter, _{is reduced}

for engines with increasing size.

-1-.0"

Characteristic data, constraints and general trends

There are three definitions which will characterize the diesel

engine in the future. Two of these definitions are control

quantities which are already used for a long time, i.e. DM/kW

acquisition and DM/kWh maintenance. The legal provisions for

environmental protection are the newly introduced influencing

variables.

The specific acquisition cost DM/kW is mainly derived from the

specific material utilization of material quantity kg/kW,

handling cost - i.e. manhours/kW and administration cost also

expressed in manhours/kW. The specific cost is reduced when

kW/engine is increased. Thus the trend to increase the specific

diesel engine load will proceed. At the same time, however,

considerable attempts will be made to reduce the administration

cost by a relatively high number of equal parts and reduction of

the numerous part variants. In future a clever construction is

required where by the use of relatively many equal parts the

different requirements of customers can still be met.

The specific operating cost in DM/kWh includes the fuel cost

with abt. 90 %, the cost of lubricants with abt. 6 % and the

maintenance work with abt. 4 %, followed by spare parts cost,

repair work and downtimes which can all be measured in DM/kWh.

The trend towards very low fuel and lubricant cost will surely

proceed. Consequently the trend toward high thermal efficiencies

will

remain - also and actually connected with the wish to build

clean engines at the same time. For this purpose low-deformation

engines are required.

A main line of the development is directed toward a Perfect

engine maintenance. In the days of computer technology, more

modern monitoring and expert systems are reflected.

We will hope that the legal provisions for the environmental

protection are considerably increased. This does not only apply

to the easily controllable coloring of exhaust gases. It also

concerns the toxic components which are optically not

measurable, such as nitrogen oxides, sulphur oxides and

hydrocarbons. With regard to the humanization of work a

reduction of the engine noises is more and more required. This

is in opposition to the demand for higher material utilization

and the sound and vibration levels which continuously increased

in the last years. New solutions are required, particularly

because an increasing material utilization in the shipbuilding

is less and less compatible with engine vibrations.

MaK C engines have a sound basis for low cost

Mak has further developed their proved engine up to today's C

engine program in order to be prepared for the future. As

demonstrated in diagram 3 outputs from 1 to 10 MW are possible

with reliable series engines; table 4 indicates the output data.

2

-Increasing outputs,

improved utilization of material and handling expenditure, increased ignition pressure for further reduction of the fuel consumption,

still low material expansions to ensure high operating safety

were possible owing to a careful conversion of the carrying

engine components and application of highly tough castings. At

equal piston force, for instance, all deformations resulting

therefrom were reduced by at least 30 %. Thus engine operation

is smoother than before, even if torque and ignition pressure

are increased by 10 %.

The rigidity at the engine casing provides for a rigid

environment and thus a high hydrodynamic load carrying capacity

of sliding parts such as cylinder liners and plain bearings. It

is of decisive importance to the safety of the engine that the

fatigue strength under reversed stresses has been increased many

times. Breakage will not occur even in case of overstresses,

e.g. caused by deformations of the ship sailing in stormy sea or

by incorrect installation of engine components.

MaK engines with new combustion system

The second decisive task to design the engines of today in

accordance with the customer's requirements and the engines for

tomorrow in accordance with future safety, is the new

development of combustion room, air distribution and injection.

It has always been a characteristic of the MaR combustion

chamber that the top of the piston is arranged higher at the

lateral side in order to protect the cylinder liner. This

principle has been maintained (refer to photo 5) but the

combustion chamber recess has been adapted closer to the fuel

jet. When it is feasible with regard to the geometry, the fuel

jet shall pass the combustion chamber air without disturbance

and shall only be slightly deflected by a special controlled air

swirl and surrounded by a quantity of air which is sufficient

for self-mixing. Only after a large flight distance the fuel

droplets shall be reflected by the piston to the top/to the

outside. Thereby a high quantity of air available in the piston

is used on one hand, and on the other hand the exhaust gas

valves are not exposed to striking up flames.

Normally the MaR C engines are supplied by sophisticated pulse

pressure supercharging. Since these MaK C engines are operated

at a comparably low specific _{output, this is the best system}

particularly with regard to part load operation. The highly

precompressed air is delivered to the combustion chamber with a

definite swirl. A lot of tests were necessary for optimization;

one of these tests is shown in photo 6. It was necessary to keep

the ignition delay at a minimum, not only by high compression

but also by intensive air/fuel mixture, particularly at part

load. The fuel itself is injected very intensely because small

fuel droplets required high treatment energy. The small

droplets, however, are necessary so that, particularly heavy

3

-fuel oil with poor ignition properties, can be burnt as normal

as possible. Photo 7 demonstrates the favourable effect of the

newly designed combustion on the temperatures in the combustion

room. Everywhere you can find values which on one hand exclude

hot corrosions and on the other hand avoid cold corrosion. The

next photo 8 from a great test series also demonstrates how

positive the effect of a sufficient injection energy is with

regard to fine atomization and introduction of an intense

air/fuel mixture. Beyond that photo 9 demonstrates that the

distribution of the injection energy with regard to time

-initially during the _{ignition delay a low injection energy and}

thereafter high Injection energy is required within a short time

permits an optimum utilization of the ignition design

pressure. In this case the thermodynamically optimimum

constant-pressure process is nearly reached.

MaK C engines with high inherent stability

MaK takes great efforts with regard to perfect tribologic

conditions between piston and piston ring on one hand and

cylinder liner on the other hand. This is demonstrated, for

instance, by the engine M 552 C in photo 10. Here not only the

high _{rigidity of the cylinder block supports the cylindricity of}

the liner, but also the newly developed flame ring which is

arranged between cylinder liner and cylinder head. It absorbes

most of the heat generated by the flame and leaves the cylinder

liner sufficiently cold. On the other hand it is a flexible

member to keep most of the self movements of the cylinder head

away from the _{cylinder collar. Moreover, the cylinder liner is}

provided with a special nitrating laver which was developed in

many years; on this nitrating laver the piston rings which are

chromium plated around can run _excellently. The usual wear

indices in gas oil or heavy fuel oil operation are shown in

photo 11. The maximum cylinder wear of 0,01 - 0,02 mm/1000 h is

extremely favourable. Thus the maintenance intervals can be long

and the lube oil consumption remains low throughout these

periods.

Within the scope of the above description the following can be

predicted for the engines 2000: the higher utilization of

material used in the engine will still increase in the future.

Calculations which are carried out during the design phase

provide for a detailed configuration which will be better and

better. The industry develops new technologies for the _abatement

of wear and tear. MaR is working very hard on this. We expect

further progresses with regard to injection control. The

development

will

particularly aim to the precise adaptation to

the requirements resulting from output, speed, air condition,

fuel and last but not least environmental requirements.

Altogether, lower relative acquisition cost, operating cost and

maintenance cost are to be _{expected when the labour cost and}

energy cost is neutralized. This is not applicable when the

protection of nature will be of more importance to us than

before.

Mal( C engines are "non-smokers"

High emission of smoke is clearly visible for everybody. It has

mainly formed from carbon particles, but also by heavy

hydrocarbon and traces of sulphuric acid. The two particles

mentioned first are generated at partial combustion. After the

ignition delay the flame burns in such a manner that fresh air

has to be continuously supplied to the burning fuel. This is

called a turbulent diffusion flame. When this mixing process is

too slow, more and more of the high-carbon compounds will not

find any oxygen and remain unburnt. Therefore it is necessary

-mainly by the energy of the fuel jet - to deliver the fuel as

fast as possible on one hand and to generate on the other hand a

highly-turbulent mixing process of air/fuel by the jet energy

for a quite long period of time. At part load where the

injection energy is lower, it is also required to generate the

mixing energy by definite initial movements of the air. In

addition a _{less rugged combustion chamber - as shown in photo 5}

for M 453 C - is also important.

How economical can ecology be?

It is more and more required to keep the CO2 emission very low.

With regard to the combustion of hydrocarbons this means:

Consumption as low as possible!

The diesel engine gains its unsurpassable economy because it can

achieve very high temperatures and pressures owing to its

oscillating mode of operation - working cycles and rest cycles.

The formation of nitric oxide is mainly characterized by the

Zeldovich reaction [lit. 1):

0 + N2 = NO + N

N 02 = NO + 0

It highly depends on the temperature. In an exaggerating way,

however, this means the higher the efficiency of an engine the

higher its NOx emission. This statement is easily shown by

experience (refer to photo 12), i.e. engines with increasing

diameter do not only have an improved consumption but also a

specifically higher NOx emission [lit. 2].

On account of the high _{temperature dependency,}

_{NOx is}

_mainly

generated at the beginning of combustion [lit. 3]. The quantity

of air and fuel which can be burnt down very hot in premixed

condition is decisive. After the occurrence of the flame only a

diffusion burning can take place which is relatively colder.

When for instance more than 40 of the total injection quantity

are already in the cylinder before the ignition occurs, a very

high temperature together with high pressure rise occur in the

premixed combustion phase.

- 5

-+

Thus the important factors influencing the NOx formation in the

engine are a low ignition delay and a skilled injection

characteristic: up to the ignition a low fuel injection quantity

is required. In opposition to other measures taken to reduce

Nox, these factors are very important because they scarcely

influence the consumption but in general improve the operating

conditions of the engine. A high compression discharge

temperature contribrutes to a short ignition delay. Therefore,

MaK engines are provided with a load-depending control of the

charge air temperature by a modern single-circuit cooling system

in addition to a high compression ratio [lit. 4]. On the other

hand the charge air coolers are sufficiently designed so that a

low charge air temperature is obtained at full load. It is very

positive, because it has a high effect on the temperature of the

material to be burnt.

Measures for NOx reduction

A delayed injection has a very good influence on low NOx

formation [lit. 5]. With delayed injection, not only the

compression discharge temperature is increased and the

combustion delay reduced, but the pressure cannot rise so fast

after the upper dead center because the piston descends already.

A delayed injection increases the consumption and supports the

formation of soot [lit. 6). As far as engines with optimized

consumption are concerned, they normally have very high NOx

values. First of all the emission of these engines can be

considerably improved at a reasonable increase in consumption

when the injection is delayed. As demonstrated in photo 13, a

deterioration of the fuel consumption of 1 g/kWh first of all

occurs with an improvement of 100 ppm NOx. With further NOx

reduction, however, the disadvantageous consumption will

increase fast. Any NOx improvement for each 100 ppm will then

result in an increased consumption of 2-3 g/kWh for common

engines. Within the possible limits with regard to thermal

stresses of still justifiable exhaust gas turbidity and BC

emission this would mean: a fuel consumption increase of abt. 7

g/kWh for an improvement of 100 ppm NOx [lit. 2 and 5]. Thus it

has to be noticed that the measures regarding delayed ignition

are limited.

With regard to low formation of nitric oxide it is much more

economical to add water to the combustion chamber [lit. 7]. A

reason for this could be that the water first of all absorbs

evaporation heat and dissociation heat [lit. 3) and at a later

combustion stage again dissipates combustion heat. With this

process MaK engines have shown a good effect. It is a thumb-rule

that with 10 % water content in the fuel the nitric oxide is

reduced by 10 - 15 %. But engines with a very good mixture

preparation and thus a very low fuel consumption show a fuel

consumption increase of 2 - 3 g/kWh for each 10 % water addition

(photo 14). It has to be borne in mind that when water is _added,

considerable corrosion damage might occur in case of negligence.

Moreover, the entire injection system is to be enlarged by the

water injection quantity.

In any case the combination of the two methods unfortunately

does not bring about an economic reduction of the NOx values

which are required to fulfil future requirements, e.g. "TA Luft"

of 1990. At least this is today's state of art. Therefore it is

absolutely necessary to retreat the exhaust gas in order to

really protect the environment. Presently the only question is

to what extent the NOx can be reduced in the engine and to what

extent the exhaust gas shall be retreated in order to achieve a

sound overall economy, a low emission of carbon dioixde and heat

loss as well as a preservation of our resources.

At the present time only one method seems practicable with

regard to the retreatment of exhaust gas: the selective

catalytic reduction system, briefly called SCR. In a catalyst

the quantity of ammonia is injected which approximately

corresponds to the quantity of NOx. The efficiency of a

non-contaminated catalyst amounts to more than 90 % when the

exhaust gas temperature is constantly within the range of abt.

380 °C !lit. 8]. Operation at a lower temperature is difficult

as long as a higher sulphur content is not removed in the fuel

at the same time.

The price for a kilogram of ammonia to be added approximately

corresponds to that of heavy fuel oil [lit. 7 and 9]. The

expenditure of catalyst and control units, however, is high.

With regard to the total cost,

however,

the SCR method is better

than the engine internal methods, taking into account the

present relation between fuel price and heavy fuel oil _price,

when - assuming an economically adjusted engine - the NOx

content shall be reduced by more than 25 %. Therefore it is

necessary to design the engines in future in such a manner that

a very high efficiency will be achieved in the SCR. For this

purpose a constantly high exhaust gas temperature is required. A

sophisticated supercharger system is used in the MaR C engines.

Not only a sufficiently high temperature level is available

downstream the supercharger groups, but this can also be offered

through

a relatively broad load range at a nearly constant

level. A supercharger system operating at constant temperature

downstream the turbine will be possible in the future.

It can be expected that a diesel engine of the year 2000 will

still be an engine with a very good fuel consumption. But at the

same time it will be prepared

to

cooperate

with

additional

systems in a self-optimizing manner in order to protect the

environment - and thus to protect us. It will be interesting to

determine the total cost of a diesel system with clean exhaust

gas compared to a different system with gas _{or steam turbines or}

even with a Sterling engine. With their C engines the Mal:

naturally expexts the success of the entire system "diesel

engine".

Direct flexible support against sound emission

Unfortunately it is gained from experience that the sound level

of the engines increases with increasing specific output under

equal main conditions. This applies to airborne sound as well as

to _{structure-borne noise [lit. 10]. It is very difficult to}

reduce the airborne sound at the _{engine considerably. In this}

case it _{will in future be necessary to work with sound capsules}

or passive sound reduction in the engine room. In this case it

is absolutely necessary that the engines are so reliable that

inspection work and maintenance work will not become necessary

during operation.

With regard to _{structure-borne noise which is much more}

important to the entire plant, an insulation degree of more than

95 % can be obtained with a flexible support. This _{is shown in}

photo 15 by the high level difference above and below the

flexible support.

The three larger MaK C engines are very suitable for direct

flexible support as shown in photo 16. On one hand the approved

base plate construction was maintained in spite of high cost

expenditure; on the other hand these _{base plates are made of}

rigid nodular cast iron. Thereby the motor feet _{can be directly}

placed horizontally on the rubber blocks. This considerably

reduces _{the expenditure compared to an angular support. Owing to}

the suitable selection of rubber elements with regard to _size,

number and hardness, and by additional arrangement of a few

rubber elements in _{horizontal direction, the engine can be}

operated within a large speed and output range. The natural

frequency with its 6 degrees _{of freedom can be}

placed

sufficiently above or below the important engine excitaton

frequencies (photo 17).

The advantage of horizontal antivibration blocks is their high

rigidity in direction of compression. Therefore _{the engine with}

horizontal resilient mountings is less susceptible to tipping of

the engine when the _{vessel pitches or rolls and the output of}

the engine fluctuates. But in direction _{of transverse thrust the}

antivibration blocks are more flexible than _{in direction of}

thrust. Thus a higher _{tendency to transverse}

displacement

compared to angular bearing support exists. In order to

compensate this disadvantage we have provided flexible limit

stops acting

in

the _horizontal

_plane

_{as shown in the previous}

drawing.

With flexible support most of the _{engine components are relieved}

with regard to maximum _{stresses. Driving mechanism forces and}

gas forces are distributed more equal across the length of the

engine. This is clearly visible from table 18. Part of the

deformation energy of gas forces and _forces of gravity

introdcued in the engine cannot be transferred to a rigid

foundation anymore. This partial _{energy preferably acts on the}

units which are screwed to the engine. They are liable to

increased oscillation amplitudes compared to the condition at a

more rigid arrangement. With _{a clever construction but mainly}