Two-Stroke versus four-stroke. A summary of the technical state-of-the-art of marine diesel engines

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May 1999

TUDelft

Two-stroke versus Four-stroke

A summary of the technical state-of-the-art of marine diesel

engines

D_E.J. Knops

OVS

98/30

Faculteit Ontwerpen, Constructie en Productie Maritieme techniek

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TABLE OF CONTENTS 1

SUMMARY

Merges of marine diesel engines manufactures led to a clear power overlap of the two-stroke and four-stroke propulsion engines. Ships tend to get larger and propulsion power demands change for different kinds of ships. To create an insight in which propulsion suits the power demands best, a survey will have to make clear what the differences are between the

two-stroke and four-two-stroke marine diesel engines. A theoretical approach has been verified by

means of a database of marine diesel engine data.

This paper summarises the technical state-of-the-art two-stroke and four-stroke marine diesel engines. First different kinds of ship types have been distinguished and an insight on their

power demands has been created.

The ships with a high power/deadweight ratio are mainly propelled with a four-stroke diesel engine and the ships with a low power/deadweight ratio are mainly propelled with two-stroke diesel engines. For ships with a power/deadweight ratio in between, both the two-stroke and four-stroke engine principle is used. There is no clear conclusion about the power/deadweight ratio in relation with the ship speed. This relation is troubled by differences in manoeuvrability

requirements, ship resistance or a powerbuffer among the different types of ships.

An historical review creates insights in the marine diesel engines developments. There has

been focused on the marine diesel engines installed in ships from 1988 till 1997.

During those years an average increase of 30% more power per engine has been established.

Also an increase in propulsion power per ship and a higher power/deadweight ratio can be

seen in the focus.

A theory about marine diesel engine performance and its dimensions has been verified by an empirical survey. A database with engine parameters has been made and differences between the two-stroke and the marine diesel engines can be obtained.

For a certain engine brake power, the two-stroke marine diesel engines need more space and

are heavier than the four-stroke engines. But concerning a certain brake cylinder power, the two engine principles do not differ that much from each other in size or weight.

The differences between the engine dimensions in theory and in practice can be explained by the support function components and the number of cylinders, which are both disturbing

factors for the engine dimensions.

Apart form the engine dimensions, a further comparison of two-stroke and four-stroke marine

diesel engines has been made.

Initial costs are higher for the stroke engines and operating costs are lower for the two-stroke engines compared to the four-two-stroke engines. Further more, two-two-stroke engines need

no gear box and are more reliable than a four-stroke engine.

In the future marine diesel engines will have more electronic devices and will get more flexible.

Maintenance will consume less time and new environmental demands will influence the brake

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INTRODUCTION 4

1 INTRODUCTION

From the first diesel engines till the newest ones, the engine has been split up into two principles, the two-stroke and the four-stroke principle. In the marine diesel engines market, this split up has been carried through and so even the engine manufactures are divided into two parts; the two-stroke and four-stroke marine diesel engines manufactures with separate markets and customers. Shipowners usually installed only one of the two principles in their

ships and bought these engines mostly at one single company.

Within the past five years, merges of companies occurred and this led to companies producing as well two-stroke and four-stroke marine diesel engines. With those two principles in the engine portfolio, power overlap got clear and competition between the two principles could start. Recently a large four-stroke marine diesel engine has been developed and this even

enlarged the power overlap.

Fascinated by the power overlap of the two-stroke and four-stroke marine diesel engines, an investigation has been launched at the Technical University of Delft in September 1998. The purpose of this investigation is; creating an insight on the market position of the two-stroke (low-speed) versus the four-stroke (medium speed) marine diesel engine in the light of the recent developments. Supported by the Section for Ship Design, Marine Engineering and Sub-Section Technical Marketing, the investigation is carried out as a Master thesis subject.

The investigation will involve a technical state-of-the-art inquiry of the two-stroke and

four-stroke marine diesel engines and a market inquiry.

A first survey has been done and the results are published in this paper.

In chapter 2, the problem and thesis description will be explained for the whole investigation and the first survey. Chapter 3 distinguishes the ships where propulsion marine diesel engines are installed in. A brief historical review of the marine diesel engine is given in chapter 4 and the developments of the propulsion marine diesel engine during the past ten years is

described. In chapter 5, some theory about the marine diesel engines is explained. This theory is used in chapter 6 and has been verified, also differences between the two-stroke and four-stroke state-of-the-art marine diesel engines are described in this chapter. More comparisons of the two principles have been done and are described in chapter 7. Conclusions can be

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PROBLEM AND THESIS DESCRIPTION 5

2 PROBLEM AND THESIS DESCRIPTION

In the 100 years of diesel engine development the engine has been split up into two principles: the two-stroke and the four-stroke principal. The two-stroke is in general a slow rotating engine

(50 250 rpm) of the crosshead type. It has a relatively 'simple' construction and its stroke/bore ratio is between 2,5 and 4,5. The four-stroke diesel engine is in general a fast

rotating engine (300 2000 rpm) of the trunk piston type. It has a more complex construction

and its stroke/bore ratio is between 1 and 1,5.

In the marine diesel engine market these two principles are both used for the propulsion of ships. When purchasing diesel engines for propulsion, it's often not clearly argumented which of the two principles suits the requirements best. The following list summarises the main facts

of why an investigation is welcome:

nowadays engines are often purchased with oldtimes repeating arguments

there is a considerable overlap of power-ranges for the two-stoke and four-stroke diesel

engines (roughly between 1500 and 40000 kW) bigger ships will be built

higher ship speeds are demanded

the diesel-electric-propulsion gets wider attention

there is no clear insight in the costs of the marine diesel engine

The purpose of the whole investigation is to create a clear insight into the marine diesel engine market and it's developments. This results in arguments, which can be used when making

purchase decisions for a two-stroke or four-stroke marine diesel engine. This has to be achieved by investigating three issues:

The technical state-of-the-art of the marine diesel engine. The market and its parties.

How the technical state-of-the-art and the market demands can be merged.

These three issues will be investigated by means of three surveys and this paper contains the results of the first survey namely the technical state-of-the-art of the marine diesel engine. The

thesis description of this first survey is as follows:

Summarise the technical state-of-the art of the two-stroke and four-stroke diesel engines in the light of recent developments. Also give an outlook in the near future. Address the subject from the viewpoint of technical requirements from the marine

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MARINE DIESEL ENGINES IN SHIPS 6

3 MARINE DIESEL ENGINES IN SHIPS

3.1 Introduction

"Nowadays 98% of the world's merchant fleet is powered by diesel engines and 2/3 of all the

marine diesel engines has the four-stroke principle" [Hoeschen, 1998]. Thus the marine diesel

engine is the most frequently used engine in the merchant fleet and when looking at the total

power of a ship. the four-stroke principal has a large share in that market.

To create an insight in why certain engine models have been developed, it is useful to look at the different kinds of ships and what type of marine diesel engines is installed. Because the

main engine in a ship is the propulsion engine, the focus will be on the propulsion engines and not on all the engines which produce power on board ships.

In paragraph 3.2 various types of ships have been distinguished, paragraph 3.3 focuses on the

future ship sizes and demands. Paragraph 3.4 gives a more extensive insight on a specified

ship type. Conclusion of this chapter can be found in paragraph 3.6.

3.2 Distinguishing various ship types

Since there are a lot of different tasks to fulfil on the seas and waters, there are different types of ships built, which have different propulsion power demands. A distinction can be made

between two main tasks for ships nowadays: offshore dredging / oil drilling and transportation.

Offshore dredging or oil drilling is a special task, which requires a total different kind of ship than the transportation task. The ships are called "special task ships" and they are mostly equipped with four-stroke marine diesel engines due to space requirements and the presence of many auxiliary machines, which have to be driven on board. Because engines with the four-stroke principle have a high power density (power per engine volume) and can easily run at

part loads, they satisfy the space requirements and driving speeds of auxiliary machines.

About 10% of all ship types built is a special task ship. This is a niche compared to the whole

marine diesel engines market and therefore is not covered in this inquiry. The focus lies on the transportation ships and

especially their propulsion power requirements. To be able to distinguish various ship types, data from ships and their propulsion power must be examined. Plotted are charts with data

drawn from a database with about 5500 ships of

different types, except the special tasks ships [Fairplay. 1998].

Chad 3 1 displays the deadweight (see Definitions & Nomenclature) plotted versus the ship speed. Chart 3.2 displays the total propulsion power of a ship plotted versus the deadweight and Chart 3.3 displays the total propulsion power plotted versus the ship speed.

Puke: carfare: tanker pass ferry

x dry cargo 4fishing vessel - reeler 400000 350000 300000 2 150000 to. 200000 150000 100000 50000 Chart 3,1 0 0 10 20 30 40 50 80

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-MARINE DIESEL ENGINES IN SHIPS 7

Chart 3.2 _{Chart 3.1}

The database contains the types op ships required for the transportation of various cargos like:

Sulkers for the transportation of bulk (grain, ore, coal).

Tanker ships for the transportation of liquids or gases (oil, LPG).

'Container ships for the transportation of containers (Twenty-foot Equivalent Unit (TEU)).

Dry cargo ships for the transportation of various kinds of (unit) freight.

IRoRo's for the transportation of trailers and trucks.

at Reefers for the transportation of cooled freight (fruit, meat).

Passenger ferries (including Cruise-liners) for the transportation of people, cars and trucks. Fishing vessels for the catching, processing and transportation of fish.

Examining Chart 3.1, 'Chart 3.2 and Chart 3.3 the following' gets clear:

Bulkers and Tankers, no matter their deadweight, have ship speeds around 14 knots. The total propulsion power increases when the deadweight increases and the total propulsion' power,is

not related to the ship speed.

For Container ships, Dry cargo ships, Reefers and RoRo's, the ship speed increases when the'

deadweight increases. The total propulsion power increases when the deadweight increases and the total propulsion power increases when the ship speed increases.

For Passenger ferries and Fishing vessels, a zoomed in look (not plotted) displays two groups. A group for which the ship speed increases when the deadweight increases and a group with

very low deadweights and' very high ship speeds. The Fishing vessels are all situated in the

group with increasing ship speeds and deadweights and the Passenger ferries are situated in both groups. This suggests the presence of "Very Fast Ferries" in the database. For

Passenger ferries the total propulsion power seems not to be related to the deadweight, but this insight could be troubled by the Very Fast Ferries which have a lot of propulsion power compared to their deadweight. For Fishing vessels, an increasing deadweight involves an increasing total propulsion power. For both ship types, the total propulsion power increases

when the ship speed' increases. The Ferry' Fast Ferries can clearly be distinguished.

In general it can be stated that when the deadweight increases the ship speed increases so larger ships sail at higher speeds. Further that when the deadweight increases the total propulsion power increases, which is a trivial statement because when increasing the ship

speed and the deadweight, more propulsion power is required. And that when the ship speed' increases, the total propulsion power increases, which also is a trivial statement which will be. explained.

Fxluter i container diet s pass ferry dry cargo - roro a fishing vessel -reefer

80000 /0000 F ," 60000 ._ 3 0 50000 o. 240000t Ti S 12-30000 -es ia. Tr 20000 -__Niigei.a.3, ....,!?WI

t

10000 _47'._{.'1"le n} 0 , 10003C1 2occoo 300003 '432003 cleadweigth [ton/

I

c 0

t

_ = gr 1 t;

- burger container tanker pass ferry Sdry cargo - rote .shehria vessel - reefer

Fr c. 80000 70000 60000 50000 -I I

I

ca. 40000 30000 20000 s - a 7' _{a. .11}t 10000, ₁ _sie a l' 0 / 0 20 30 40

ship speed [Mots]

SD 60

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In Chart 3.3 the relation between the total propulsion power and the ship speed is plotted. The following equation describes the relation between the propulsion power and the ship speed

[Basic Principals of Ship Propulsion, 1996]:

i

a

v:31

Equation 3.1

So when the ship speed (va increases the propulsion power (P) needed, increases to the third power. The factor a is a constant, which has to be determined for each ship. It must be emphasised that the equation is an approximation and in fact, a is not constant and depends

on the ship speed and varies per ship.

When examining Chart 3.2, categories can be created. One can distinguish three main lines. Splitting up the transportation ships. which create these lines, three categories can de created:

Ships with a little deadweight and a !ot of propulsion power installed, called the "high power/deadweight ratio ships".

Ships with more deadweight and less propulsion power installed, called the "medium

power/deadweight ratio ships"

Ships with a lot of deadweight and little propulsion power installed, called the low

power/deadweight ratio ships".

The three power/deadweight ratio categories mentioned, contain mainly the following ship

types:

Table 3.1 ship types in categories

The power/deadweight ratios of the ships are plotted versus the ship speed in the following

charts: 350 loo 250 14 200 761 V 150 100 '3) ea_ 50 Ch- ar-t 3.4 10 20 30 40 50

ship speed [knots]

eo

Chart 3.5

In Chart 3,4 the total propulsion power divided by the deadweight (power/deadweight ratio) is plotted versus the ship speed. When taking a closer look on the high power/deadweight ratio ships, one should exclude the Passenger ferries (which include Cruise-liners and Ferry Fast Ferries) out of that category. Passenger ferries belong to the category of a high/deadweight ratio but compared to the other two ship types in that category (RoRo's and Fishing vessels). they have very high ship speeds. And if propelled with a waterjet system, they need different

f

1. high power/deadweight 2. medium power/deadweight 3. low power/deadweight

(Passenger ferries) Container ships Sulkers RoRo's Dry cargo ships Tankers Fishing vessels Reefers

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' . . . : x IN. I e -1". L':... g", -ll' 211 0 . ar_,..-' , -':- vir... bulker zsdry cargo cortainer roro

tanker pass ferry

. fishingvessel -reeler

biker

dry callo

- contauer

roro

tanker pass ferry + fishing %easel -reefer

10 15 20 25 30

ship speed [knots]

2,0 11.8 Z 16 2 1,4 1,2 1.o .g 0,8 0,6 0,4 EL 0,2 0,0 cr, 'I 1 0

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MARINE DIESEL ENGINES MI SHIPS 9

engine specifications. Passenger ferries require also very low specific engine weights and so are mainly equipped with high-speed marine diesel engines or gas-turbines.

Therefore included in this survey are seven

types of ships, belonging to three different

power/deadweight categories.

Chart 3.5 and Chart 3.6 display a zoomed in look on Chart 3.4 without the Passenger ferries.

In these charts the power/deadweight ratio plotted is from 0 to 2 and the ship speeds from 0 to 30 knots. Chart 3.6 displays the mean data (the dot) and the standard deviation (the vertical and horizontal lines) of the ship data in the database. The ellipses drawn, cover the main data plotted and give an indication of the power/deadweight ratio trend regarding to the ship speed within a category.

Because the power is divided by the deadweight, the (actual) relation between power and speed gets clear. As mentioned before and explained by Equation 3.1. in

general the propulsion power increases when ship speed increases. This is true within the medium arid high power deadweight ratio category. Within the low power/deadweight ratio category, there are different relations between the propulsion power and the ship speed. This is caused by the variance in the category data, which will be explained in the following

paragraphs.

When merging the ship types into the three power/deadweight ratio categories, recapitulating

the insights obtained, gives:

Within the high and medium power/deadweight ratio category: when the deadweight

increases, the ship speed increases.

Within all power/deadweight ratio categories; when the deadweight increases, the total

propulsion power increases.

Within high and medium power/deadweight ratio category; when the ship speed increases, the

total propulsion power increases.

From examining Chart 3.6, it can not be said what the relations are between the categories. It seems trivial that ships with high power/deadweight ratios use their abundance of power to develop high ship speeds. But Chart 3.6 suggests that this is not true because when

compensated by the deadweight, the high power/deadweight ships don't have the highest ship

speeds.

To give an explanation for the power/deadweight ratio categories versus ship speed relations,

the ship types in each category are described.

3.2.1 high power/deadweight

ratio ships

The average ship speed for RoRo's is 17 knots. Besides the propulsion power needed for the relative high ship speed, the high power/deadweight ratio can be explained by a high ship resistance due to a not economical hull shape. a high manoeuvrability requirement or a

"powerbuffer" for compensating time lost.

Fishing vessels too have a high power/deadweight ratio because of a high ship resistance and

the need to drag fishing nets.

So the high power/deadweight ratio ships use their abundance of propulsion power for;

developing a relative high ship speed, compensating for a high ship resistance, a powerbuffer

or a high manoeuvrability requirement.

I 0.8 .! 0,6 0,4 S. 0,2 0,0 5 10 15 20 25

ship speed [knots] 2,d 1,8 1,6 1,4 1,2 -0 Chart

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3.2.2 medium power/deadweight ratio ships

The average ship speed (19 knots) of Container ships is the highest of all categories. Most economical ship speeds lie below 26 knots, when desiring speeds above this value, propulsion power has to increase enormously or a non displacement ship hull has to be applied. A low ship resistance, a lower manoeuvrability requirement or lower powerbuffer than RoRo's have, can explain the medium power/deadweight ratio. So more propulsion power can be used for

developing the ship speed.

The same goes for Dry cargo ships, but because they have a lower average ship speed than

Container ships, their power/deadweight ratio is also lower.

Reefers have an average ship speed of 17 knots. Their power/deadweight ratio is higher than that of Container ships and Dry cargo ships. This can be explained by a high auxiliary power

requirement for cooling the freight.

So the medium power/deadweight ratio ships have a lower ship resistance, a lower

manoeuvrability requirement or a lower powerbuffer, and all the propulsion power is used for developing the required speed or in the case of Reefers, for producing auxiliary power.

3.2.3 low power/deadweight ratio ships

Bulkers are almost all situated at a ship speed of 14 knots and a power/deadweight ratio that

lies under 0,3.

Most tankers are also situated around a ship speed of 14 knots and most values of the

power/deadweight ratio lie under 0,4 but there is a lot more variance than for Bulkers. Because the ship speed doesn't vary much, a higher manoeuvrability, redundancy or auxiliary power

requirement (onboard pumps) could be the cause of this variance.

So low power/deadweight ratio ships have a fixed relative low ship speed and all the power is

used to develop this speed or in case of the Tankers for producing auxiliary power.

3.3 _{Two-stroke and four-stroke engines in ships}

Both the two-stroke and four-stroke marine diesel engines are installed in the three

power/deadweight categories mentioned in the previous paragraph. When investigating the

ship data (obtained from the database) per category, a trend can be seen.

High power/deadweight ratio ships have few two-stroke propulsion engines and mainly four-stroke marine diesel engines are installed. The medium power/deadweight ratio ships have no clear main share of two-stroke or four-stroke propulsion engines installed. Both principles are installed and have about equal shares. For ships with a low power/deadweight ratio, mainly

two-stroke engines are used as propulsion power producer.

The engine choices made all depend on different factors like; propulsionpower required, ship

speed required, engine performance, engine room space, brake specific fuel-oil consumption,

maintenance, reliability and redundancy and the costs related to these factors.

Because every factor has different importance for different shipowners, it is difficult toname the most important ones.

This survey will try to get some insights in some of the differences between the two-stroke and

four-stroke marine diesel engines.

3.4 _{Future ship sizes and demands}

In the near future, ship sizes will change. Transportation over_{sea can get more economical by} increasing the amount of cargo that can be transported per ship. Also the ship speed_{can be a}

parameter in achieving higher economical demands.

The demand of transporting more cargo per ship will have its influenceon the ship's size.

Because most harbours are not deeper than 14 m, ship draughts will have to be in

accordance. So when ship draughts are restricted, that leaves ship widths and lengths to_be varied. A restriction on the ship widths is the Panama Canal with_{a width of 32,3 m. So when}

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using this passage, ship widths are also restricted. That leaves the ship's lengths to be varied. But this cannot be done freely due to ship stability requirements and quay wall limited lengths Some ship types need to have a double hull instead of a single hull, when transporting a

specified amount of cargo; this will demand a larger ship than a single hull ship.

When not using the Panama Canal and if harbours get deeper or new harbours are to be

situated in deep water areas, ship sizes can be increased. This will have large effects on the propulsion power needed and new engines or more engines per ship will have to be applied. Table 3.2 displays some dimensions of future ships [Elshof, 19981:

Table 3.2 dimensions of future ship sizes

The ship speed demands are changing for some types of ships. Some ships do not get more economical by increasing their ship speeds and some do. A survey will have to be done to

determine which ship types will have economical benefits by changing their ship speeds.

3.5 Container feeders

To narrow the scope of the whole investigation. a ship type and sub-type must be chosen to have a closer look at. The type Container ships and the sub-type Container feeder have been chosen. This is done in accordance with the focus of the second and third survey mentioned in chapter 2.

Container feeders are 'small' Container ships with a cargo capacity between 200 TEU and 1000 TEU (see Definitions & Nomenclature). Since they are of the Container ship type, they belong to the medium power/deadweight ratio ships.

The capacity of Container ships is often measured in container capacity (TEU) in stead of deadweight. Chart 3.7 displays the relation between the capacity measured in TEU and the

deadweight of the ship. Because the relation is a fairly linear one, especially for the smaller Container ships (Container feeders), the capacity will be displayed in TEU in stead of

deadweight. From Chart 3.7 a relation of 14 ton deadweight per TEU can be obtained. 10000 9000 8000 7000 =tamer] 0 20000 40oo3 60000 80000 100000 120000 deactwegth [ton]

ship type length [m] width [m] depth [m] speed [knots] power WIN]

Sulkers ₃₄₃ ₆₃ ₂₃ ₁₄ ₁₈₃₂₀

Tanker ships (liquid/gas) 230 36 14 19 13460 Container ships 400 69 14 25 132400 General cargo ships

RoRo's 290 32 12 17 34570

Passenger ferries Reefers

Fishing vessels

Chart

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In Chart 3.8 the total propulsion power and the ship speed of the Container ships are plotted versus the capacity. The propulsion power and

the ship speed are increasing with the capacity

of the ship. There are parabolic trends, which indicate; the more capacity, the higher ship

speed and so the more propulsion power. The

relations between speed and power have already been explained by Equation 3.1. By plotting Chart 3.9, one can see that the Container feeders (between 200 TEU and 1000 TEU) can be propelled by as well the two-stroke as the four-stroke marine diesel engine. This poses the question why one of these principles is chosen and this question will hopefully be answered in the third inquiry mentioned in

chapter 2. Chart 3.8 80000 70000

F

60000 50003 2 40000 a 30000 2 a. 20300 10000 Chart 3.9 F;-ntainer j 4000 two capacity (Tall 8000 10003 80000 70000 60000 1 50000 5 40000 't1 30000 ra. T! 20003 10000 12000 Ft, 10000 3 8000 6000 4000 :000 Chart 3.10

container power container speed!

container power container speed]

35 30 25

20.

15 5 0 0 2000 4030 8000 8000 10000 capacity (MU] 35 30 25 20 'II 1:1 0 15 .o. 10 .5 5

Chart 3.10 is a zoomed in view of Chart 3.8 and displays the Container feeders with a capacity to 1000 TEU. For a Container feeder with a capacity of 200 TEU, the charts displays a

propulsion power around 1800 kW and a ship speed around 14 knots. A Container feeder with 1000 TEU has a propulsion power around 10000 kW and a ship speed around 17 knots.

A calculation made with data out of Chart 3.10 leads to the conclusion that the

power/deadweight ratio increased. This is caused by the demand for more power to increase the ship speed (Equation 3.1).

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3.6 Chapter conclusions

Most of the merchant fleet is propelled with marine diesel engines. The amount of propulsion power installed in a ship not only depends on the ships' deadweight and speed, but also on the type of ship. Dividing the propulsion power by the deadweight of the ship gives the

power/deadweight ratio. This ratio has three categories; the high, medium and low

power/deadweight ratio. Each of these categories contains several ship types.

Within the high and medium power/deadweight categories, an increasing deadweight involves an increasing of the ship speed and an increasing of the propulsion power. Within the low power deadweight category, an increasing deadweight has no effect on the ship speed. but will

involve more propulsion power.

The relation between the ship speed and the power/deadweight category is troubled by the different demands of the ship types in the categories. The ships in the high power/deadweight

ratio category need besides developing a relative high ship speed, a lot of propulsion power for compensating a high ship resistance or a high manoeuvrability requirement. Also the presence of a powerbuffer can cause the high power/deadweight ratio. The ships in the medium

power/deadweight ratio category have a lower ship resistance or manoeuvrability requirement. They have almost all propulsion power for achieving a relative high ship speed. The ships in the low power/deadweight ratio category have a relative low ship speed. No powerbuffer or

manoeuvrability requirement is demanded and so all the propulsion power can be used to

achieve the required ship speed.

Though it can be seen which engine principle (two-stroke or four-stroke) is most common for

category, it is difficult to say why they are chosen that way.

In the future, dimensions and ship speeds of some ship types will change and so will their

propulsion power. This will lead to new demands on the marine diesel engine market.

Container feeders belong to the medium power/deadweight ratio category. They can be propelled by as well the two-stroke as the four-stroke marine diesel engines. Again the

question poses, why an engine principle has been chosen

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4 HISTORICAL REVIEW OF THE MARINE

DIESEL ENGINE

4.1 Introduction

When trying to understand how something has developed and will develop in the future, it is useful to have a brief look at its history. This will give insights in possible trends and problems that have been encountered and solved. Also the present status of the marine diesel engines

gets clear.

Paragraph 4.2 describes Rudolf Diesel's first running engine and paragraph 4.3 describes the first diesel engines installed in ships. Paragraph 4.4 gives an overview of the marine diesel

engines installed over the past 10 years. Conclusions of this chapter are described in paragraph 4.5.

4.2 Rudolf Diesel invents

On February the 28th 1892 Rudolf Diesel patented his new combustion engine, nowadays known as the "Diesel engine". It took him 5 years to make a good working engine. During

those 5 years, Diesel experimented with several parameters and constructions. The first

running engine was a 1-cylinder four-stroke crosshead engine with a bore of 150 mm and a stroke of 400 mm. At zero power takeoff, it ran at a rotational speed of 88 rpm and had a pme of

4,3 bar. The second one had a bore of 250 mm and a stroke of 400 mm. Fuel was injected with a high-pressure air nozzle. This engine reached an effective efficiency of 17% and a

mechanical efficiency of 54%, but these values are without the processing of the high-pressure air compressor. After a lot of modifications the engine reached an effective efficiency of 16,5% and a mechanical efficiency of 67%. The third engine featured a charge pump under the piston. It had separate inlet- and outlet valves and 4 piston rings on the piston. The engine directly drove the high-pressure air compressor. It reached a pme of 10, 6 bar. Modifications on the fuel nozzle made the engine smoke less at a pre, of 8 bar and after disconnecting the air charging, the fuel consumption was halved.

The thermal efficiency of the diesel engine was twice that of steam engines in those days. The

diesel engine was borne [Verkleij, 1997].

4.3 _{The first generation marine diesel engines}

In 1903 the first diesel engine was installed in the French ship "Petit Pierre". Although a reversible diesel engine was built in 1897, a reversible propeller was installed for moving backwards. In 1905 a machine factory in St. Petersburg was trying to build a reversible

two-stroke diesel engine. The engine was equipped with a variable moving camshaft so the valve timing could be changed. The "Selandia" is considered to be the first ship with reversible four-stroke diesel engines [Dieselmotor hat grofle Zukunftschancen', 1993].

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4.4 Marine diesel

_{engine power during the past 10 years}

To get an insight in the amount of marine diesel engines and ships built with these engines a survey has been done. This survey consists of gathering data concerning marine diesel engines of the two-stroke and four-stroke principle built ['Annual Analysis installed output' & Doughty & 'Engine Analysis', 1988-1998]. This survey focuses on the propulsion power of

ships above 2000 ton deadweight.

4.4.1 marine diesel engines

The main task of these engines is delivering propulsion power. The power installed of the auxiliary engines in a ship is 10% to 40% of the power the propulsion engine produces in that

ship ['Mehr Shiffsdieselmotoren geliefert*, 19981. About 10% of the new built ships are special

task ships with a much higher auxiliary power demand as described in chapter 3.

1200 I loop

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i

/

t

A 59 .511 _'483 40 , 31 mg-114 371 12 44tok.1 159 0 1907 1080 1001 1990 1001 1992 1093 1094 1995 096 1927 YOU

Chart 4.1 displays the number of propulsion diesel engines built per year. It shows that

there is an increase of about 40% in the total number of propulsion diesel engines built per

year over the past 10 years. Where in the late 80-ies and early 90-ies the number of

two-stroke and four-two-stroke propulsion engines built

per year is quite the same, the latest trend shows a decrease in four-stroke propulsion

diesel engines and an increase in the number of two-stroke propulsion diesel engines built per

year.

Chart 4.2 displays the propulsion diesel power installed per year over the past 10 years. There is an increase of 53% in the total diesel

propulsion power installed per year. This

Chart 4.1 Chart 4.2

increase is mainly caused by an increase in the propulsion power installed by two-stroke propulsion diesel engines. The increase of two-stroke propulsion power installed is no only

caused by the number of two-stroke propulsion engines installed (as seen in Chart 4.1), but also by an increase of power per engine, which can be seen in Chart 4.3.

HISTORICAL REVIEW OF THE MARINE DIESEL ENGINE 15

2-4944+0 - 4- Mt oks 12000000 it 10000000 000000(1 6000(00 4000000

L

0 1987 1908 1989 1990 1991 9992 1993 1994 1995 1996 1997 Yew 14000 moo them 14 C 2 _moo 3 2 6000

I

4000 N 0 --4-stakei 1987 1988 /999 1990 1991 1992 1993 1994 1995 1996 1997 YOU. Chart 1

(17)

Chart 4.3 displays the power per propulsion diesel engine installed. Here the power installed' is

divided by the number of engines installed. It shows that the two-stroke and four-stroke propulsion diesel engines both increase in power per engine installed. For the four-stroke propulsion engines there is a dip in the power per engine from 1990 to 1994. This suggests that smaller engines or engines with less power per engine were installed in those years. A two-stroke propulsion diesel engine produces nowadays about 30% more power and a four-stroke propulsion diesel engine produces about 35% more power than 10 years ago. How this power increase per engine is achieved is not clear from this data. Whether larger engines were built or more power was produced by a diesel engine can not be said. Larger engines have

more stroke volume or more cylinders and power per engine can be increased by a higher

mean effective pressure or mean piston speed'. Chapter 5 will display these relations.

4.4:2

ships with marine diesel engines

I1-cia1 -a-2-18okt -4-strakei

/70 2 371 _.-386 1:14-12 367 .-325 "314 - 287-- _{' 293.277} 290 go--.904,w216 1 7 .1.67 1 6 1987 1988 1989 19110 991 1992 1903 1994 1995 1996 1097, 1997 1993 I1639; 1090 991 1062 1983, /904 1995 1008 1807 Ow Chart 4.5 Chart 44

Chart 4.4 displays the number of ships built with diesel 'propulsion engines per year. Over the

past 10 years an increase of about 45% in ships with diesel propulsion engines built can be seen. Two-stroke propelled ships were more numerous than ships with four-stroke propulsion engines. Especially after 1993 the number of ships with two-stroke propulsion diesel engines

installed increased and the number of ships with four-stroke propulsion engines (installed decreased.

This could be caused by improvements of the two-stroke engine, like the low level of maintenance needed or the ability of burning HFO (see Definitions), which made the two-stroke engine more popular than the four-two-stroke engine. Or a demand for more power in the top of the power range occurred. Because only two-stroke marine diesel engines can deliver this power, their number increased and the demand for the four-stroke engines propulsion

engine decreased'.

When dividing the number of propulsion engines built by the number of ships built, one tan plot Chart 4.5. It displays the average number of propulsion diesel engines per ship.

'It can be stated that a two-stroke propulsion diesel engine is the single operating' main engine' in a ship. The number of four-stroke propulsion engines in a ship varies between 1,18 and 1',67 over the past 10 years. A roughly decreasing trend in the number of four-stroke propulsion

diesel engines per ship can be seen. This can be explained by the increase of the power per

engine (Chart 4.3), so fewer engines are needed, to produce the required propulsion, power.

Ye?,

2

...

0 e" m 403 - 284 1,0 11.3

I

(18)

When dividing the propulsion power by the number of ships built, Chart 4.6 can be plotted. In this chart the propulsion power installed per ship is displayed. Because two-stroke

propulsion engines operate alone in a ship, the power per ship increased due to the increase of power per engine (see Chart 4.3).

For the four-stroke engines propelled ships, the power per ship increased from 1987 till 1989, decreased from 1990 till 1994 and increased

again from 1995 till 1997. This is the same trend as the power per engine as seen in Chart 4.3. But the number of four-stroke propulsion engines per ship trouble the insight for the power per ship. When taking this into account, the following can be said about the propulsion

power for four-stroke engines propelled ships.

When dividing the propulsion power by the deadweight of a ship, this leads to the

power/deadweight ratio wic,h is plotted in Chart

4.7. Unfortunatly, there are no split-up figures of

the two-stroke and the four-stroke propulsion engines.

It gets clear though that modem ships have more propulsion power per deadweight unit. This could be due to an increasing of ship speeds or a demand for a "power-buffer", as described in chapter 3.

A difficult question remains, who dictates whom? Are developments in the marine diesel engines manufacturing business dictating the shipowners and builders, or can the shipowners and builders dictate the marine diesel engines manufactures which engine requirements have to be developed? a 14000 12000 4000 2000 0,35 0.30 0 25 0.20 0 15 0.10 0.05 Chart 4.7 tow stroke 1987 1988 1989 1990 1991 1992 1993 1994 1995 1990 1997 yeir

The increase from 1987 till 1989 was caused by Chart 4.6

a high number of four-stroke propulsion engines

per ship together with an increasing power per engine. The decrease from 1990 till 1994 was

caused by a lower number of porpuision engins per ship together with a decreasing power per

engine. The increase from 1995 till 1997 was caused by an increasing number of propulsion engines per ship and an increasing power per engine

0.00-,

1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997

yaar

4.5 Chapter conclusions

Though only a 100 years old, the diesel engine has made a fast evolution and delivers about 30% more power than 10 years ago.

From 1987 till 1997 for the two-stroke propulsion engines the number and propulsion power installed per year increased. The number of four-stroke propulsion engines installed decreased per year, but the four-stroke propulsion power installed, increased slightly per year.

Nowadays ships tend to have fewer propulsion diesel engines installed and at the same time have more propulsion power per ship. This leads to the conclusion that more power is produced by a propulsion diesel engine installed in a ship. How this increase in power per engine is achieved is not clear from these data.

The power/deadweight ratio increased from 1992 till 1997. This could be caused byan

increasing ship speed or a demand for a powerbuffer in those years.

-4I-4-strake

0,

0,3

.428

(19)

THEORY OF THE STATE-OF-THE-ART MARINE DIESEL ENGINES 18

5 THEORY OF THE STATE-OF-THE-ART

MARINE DIESEL ENGINES

5.1 Introduction

In order to get a grip on the marine diesel engine state-of-the-art, ills necessary to give some

theory which will be used in this survey.

Paragraph 5.2 gives some basic theoretical considerations needed to create a clear insight on the marine diesel engine performance and its size. Paragraph 5.3 describes the theory around the engine performance. In paragraph 5.4 relations between engine sizing parameters are displayed and paragraph 5.5 displays the specific engine sizing parameters. A frequently used factor indicating the 'level of technology' used in an engine, is explained in paragraph 5.6. In

paragraph 5.7, conclusions of this chapter are described.

5.2 Theoretical considerations

Some general relations for piston combustion engines must be explained. The relations will create an insight on the engine performance and engine sizing parameters, which are

important for marine diesel engine purchasers and builders.

When looking from a market point of view, it is assumed that a marine diesel engine purchaser first approaches the engine like a black box. Its main task is delivering power at a certain

rotational speed, the engine performance. This has to be fulfilled by the engine, which has to have certain dimensions. The parameters concerning the black box approach are called the

engine external parameters.

The main engine external parameters have been drawn in Figure 5.1.

engine width

engine height

Figure 5.1

When zooming in on the 'engine black box', the internal mechanism of the engine gets visible. The engine consists of a cylinder and piston system, which transforms chemical energy into mechanical energy. The parameters in this process are called the design parameters. These design parameters

can be influenced by the dimensions of

the cylinder and piston system, which are called the size parameters. Drawn in Figure 5.2 are the main design and the main engine size parameters.

engine length

bore diameter

stroke length

Figure 5.2

engine brake power

rotational speed

mean effective pressure

(20)

So three kinds of parameters are distinguished; engine external parameters, design parameters and size parameters. The following table displays all the relevant engine parameters:

engine external parameters:

design parameters:

Table 5.1 three kinds of parameters

The basic relations between the parameters displayed in Table 5.1, will be given:

, Ls = Equation 5 1 = 2 Ls Equation 5.2

p

P = I Vs n k Equation 5.3

Pb engine brake power

rotational speed engine length

engine width [mm]

engine height [mm]

engine volume

engine weight [ton]

mean effective pressure [bar]

cm mean piston speed [m/s]

As stroke/bore ratio

number of revolutions per cycle

number of cylinders H

with:= )1.

L5 D2

4

5.3 Engine performance in theory

The engine performance can be expressed by the engine brake power (Pb), or without the number of cylinders (i), by the brake cylinder power (Pbcyl). Always included in an equation is a combination of the design parameters. The engine performance can be displayed in two ways;

with engine external parameters or with size parameters, both include a combination of design

parameters [Stapersma, 1998]; 7I pm, C3 1 = ₃₂ k . As2

rr

Equation 5.4 3

ltPmeCm

1 bCyo 32 , 2 n2 Equation 5.5

or with size parameters:

Pb

8'

ekC m D2

Z 10 me Cm 2

=

""' 8 k

From these equations one has an insight in how changing a parameter changes the engine brake power or brake cylinder power.

When examining the equations, increasing the mean effective pressure (One), mean piston

speed (cm) or bore (D) will increase the brake cylinder power. Apart from those, increasing the

size parameters: bore diameter [mm]

Ls stroke length [mm] [mm] -k

p

Pme

(21)

number of cylinder (i) will increase the engine brake power. Increasing the number of

revolutions per cycle (k) will decrease the brake cylinder power or engine brake power.

It must be emphasised that engine parameters can not be freely chosen. There are

mechanical and technical limits the engine builder has to comply with. When looking from purchasers' point of view, there are also economical restraints.

Recapitulating:

Pb is proportional with i, pme, cm, D2 and and

Pbcyi is proportional with pm, cm, D2 and k1

Because choosing cm and k can not be freely done due to mechanical and technical limits,

changing the engine brake power (Pb) will have to be done by changing the brake cylinder power (Pbcyl) by means of the bore (D) or the by changing the number of cylinders (i).

5.4 Engine sizing (engine external parameter) relations

Besides the engine performance, the size of the engine is an important issue. An engine builder will have to transform the external parameters, given by the engine purchaser, into the design parameters and the size parameters (Table 5.1). Relations between these three kinds of engine parameters have been derived in a previous inquiry and will be displayed in this

paragraph. For a more detailed derivation of the equations, refer to [Stapersma, 1998].

Note:

In all equations the engine brake power (Pb) and the brake cylinder power (Pbo), which are

engine external parameters, are placed on the right hand side to create the absolute

values on the left hand side of the equations.

The number of cylinders (i), is a special parameter, it has direct influence on the engine

brake power without changing any other design or size parameters. So it can be chosen

independently and should be give special attention when investigation the engine

performance or the engine sizing parameters.

The relations, which will be given, do not give the real values for the engine sizing parameter relations but approximations of these values. To obtain the real values for the engine external parameters (like L, H. W, V and M), the approximations will have to be

multiplied by an engine construction factor. Extra material and support-function

components which are needed on a marine diesel engine are taken into account in this construction factor. It is not known whether this factor will be constant or varying for different engine sizes. It is assumed that because each engine manufacturer has it's own way of designing marine diesel engines, the construction factor will certainly differ for each engine brand. An empirical survey will have to be done to determine the construction

factor.

5.4.1 engine length

When focusing on an engine with a line-configuration, an approximation for the engine length (L) is given by the bore (D) times the number of cylinders (i). To obtain the real engine length,

this approximation will have to be multiplied with a construction factor.

The approximation for the engine length can be displayed by the following equations, expressed with engine brake power (Pb) or with brake cylinder power (Pbco):

!LatiDI

Equation 5.6

Equation 57

or with Pbcyl. i = 8

ki

pme

THEORY OF THE S TA TE-OF- THE-ART MARINE DIESEL ENGINES 20

-D =

pme-c Vi liFT, I

(22)

L is proportional with and

L is proportional with i and

To determine the construction factor, an empirical survey will have to be carried out. This can also reveal how the equation for the engine length suits for engines with a vee-configuration.

5.4.2 engine height & engine width

When focusing on a crosshead engine with a line-configuration, the engine height (hi) has to be at least three times the stroke length (Ls) [Oyamada, 1998].

The engine width (W) has to be at least the stroke length due to the geometrical relations of

the driving shaft as displayed in Figure 5.3.

So an approximation for the engine length (H) and engine width (W) is the stroke length (Ls).

stroke length Figure 5.3

8 k22

1 i Ls sr pm@ Equation 5.10 V

The following equations display the engine height and engine width approximated as a function of the stroke length. The stroke length is displayed as a function of the engine brake

power or brake cylinder power:

H Ls

Equation 5.8

V Lsi

Equation 5.9

or with Pbco:

H and Ware proportional with

and IF,

H and W are proportional with VP,

Both the construction factor for the engine height and engine width will have to be determined by an empirical survey. But already it can be said that, for the engine height the factor will have to be at least; 3 and for the engine width; 1. The empirical survey can also reveal how the equations for the engine height and engine width suit for trunk-piston engines and engines with

a vee-configuration.

(minimal) engine height

(minimal) engine width

Ls =

k.2,2

pm. cm

118

*

'*

(23)

5.4.3 engine volume 8, engine weight

An approximation for the engine volume (V) can given in two ways: by the stroke volume (Vs) times the number of cylinders (i):

i

Equation 5.11

by the engine length (L) times the height (H) times the width (W), which are related to the

number of cylinders (i). bore (D) and stroke length (Ls) as derived in Equation 5.6, Equation 5,8 and Equation 5.9, this yields the following equation:

V121 =L-1-1W:4-DL,21 Equation 5.12

Remarkable is that the difference between the engine volume (V) as derived in Equation 5.11

and Equation 5.12 i.s This yields the following relation: VE21 = - -11,1 .

Jr

The engine weight (M) is assumed to be correlated by a density factor times the engine volume (V). The equation for the engine volume and engine weight is displayed by the

following equations:

rr. density factor I

Equation 5.13

And when focusing on the engine volume approximated by means of Vol:

Equation 5.14

V and thus M are proportional with and 11 P,3

i V and thus M are proportional with i and

An empirical survey has to be carried out to display the relation between V[l] and V[21 and the

two construction factors involved. Also the engine density factor will have to be determined by

this survey.

5.5 Specific engine sizing parameter relations

The brake engine power (Pb) and the number of cylinders (i) both trouble a clear look on the engine sizing parameter relations. To create a clear insight on the engine sizing parameters,

one wants to exclude the number of cylinders and the engine brake power or brake cylinder

power (Pbeyi). The relations without the number of cylinders and the brake engine power or

brake cylinder power have also been derived in a previous inquiry [Stapersma, 1998] and will be displayed in this paragraph. In fact they are the (absolute) engine sizing parameter relations

divided by the engine brake power or brake cylinder power. Note:

Like for the equations derived in the previous paragraph, the equations in this paragraph

don't give the real values but the approximations for the specific engine sizing parameters. To obtain the real values, they will have to be multiplied with the construction factor.

Because both sides of the equation are divided by the same value (engine brake power),

32 k3 .252 1 Fr:7 /7 N Ai or with Pbcyl: i Vs = 32 k3252

_."

3 i V, = ₃ ₃ cm 3 3 pme Om

*

(24)

the construction factor for each specific engine sizing parameter will be the same factor as the construction factor in each (absolute) engine sizing parameter, which will have to be

determined by an empirical survey.

5.5.1 specific engine length

Like with the engine length (L), an approximation for the specific engine length (LP) is given by the bore (D) times the number of cylinders CO, divided by the brake engine power (Pb). Of

course to obtain the real specific engine length, the theoretical specific engine length will have

to be multiplied by the construction factor.

%."'i D.C) Equation 5.15 II 118 k Pi,

pcm

Pb Equation 5.16

L proportional with 7 and 1

1/Pb

LP is proportional with which is remarkable because L is proportional with D

5.5.2 specific engine height 8, specific engine width

An approximation for the specific engine height (Fe) and specific engine width (We) can be obtained from the specific stroke length (Le). The following equations display the relations

between them: Lsa Equation 5.17 114e° -41-s$11 'Equation 5.18 Ls$ k its2 1 1

z

_Pb Equation 5.19

Due to mathematical relations where the engine brake power is implemented, the number

of cylinders (i) can not be excluded in the equation without Pb.

Equation 5.20 without Pb displays a relation between the specific stroke length (Le) and

the (absolute) engine length (L) due to the parameters i and D in the denominator.

1

He and Vie are proportional with

1

and

VF)b

Ha and V1.e are proportional with -1 and I/ andthus with D without i and Pb : without Pb:

i D

8 k 1 Pb

pme-c, D

e 8 k 1 1 Ls pimcm

i D

p

(25)

5.5.3 specific engine volume 8, specific engine weight

An approximation for the specific engine volume No?) is the specific stroke volume (Ve)

times the number of cylinders (i) divided by the engine brake power (Pb). For the specific engine volume calculated by means of (V[216), the approximation is

7I"

The specific engine weight (Ma) is correlated to the specific engine volume and thus also to the specific stroke volume. This is displayed in the following equations:

MG density factor Equation 5.20

i

Vs V[11 p Equation 5.21 Vs 132 k 2 Pb P me3 Cm 3

vi

I r- b Equation 5.22 or without i and Pb:

it

Vs and thus Ms are proportional with and VP,

1 i

* Vs and thus VI' are proportional with D

5.6 Compensated technology factor

A frequently seen combination of the design parameters; mean effective pressure (pme) times

mean piston speed (co), gives an indication of the 'amount of technology' used in an engine.

The higher the pm, or cm, the higher the technical and mechanical demands on the engine. The product of these two parameters is called the technology factor.

Because a four-stroke engine needs twice the number of revolutions (k = 2) compared to the two-stroke engine (k = 1) to complete a combustion cycle, dividing the technology factor with k

creates an insight on the engine performance. The expression for the compensated technology factor is give by Equation 1.23:

Pine Cm

compensated technology factor -Equation 5.23

When the compensated technology factor is expressed in an equation for the engine performance, the following can be stated; the engine performance increases, when the

compensated technology factor increases.

The inverse of this compensated technology factor or a related combination of design parameters is frequently used in the previous engine sizing parameter relations. When an engine sizing parameter is expressed with the inverse of the compensated technology factor, the following can be stated; the size of the engine decreases when the compensated

technology factor increases.

Vs 2 k D

Pb

(26)

5.7 Chapter conclusions

Distinguished are three kinds of parameters; engine external parameters, design parameters

and size parameters. These parameters are related to each other by equations which can displayed in many ways.

The engine performance has two main indicators; the engine brake power and the brake cylinder power. They can be expressed with design parameters or size parameters. Also the

compensated technology factor is an engine performance indicator.

Engine sizing parameters belong to the engine external parameters and their relation with the

other parameters can be given on absolute or specific basis.

The specific engine sizing parameters give a relation of the engine's size relative to its

performance. They give the "space" needed to produce a certain power and except for the specific engine height and width, can be expressed without the number of cylinders.

The values obtained from the (absolute or specific) engine sizing parameters are approximations. The real value can be calculated by multiplying the approximations by a

construction factor. It is not known whether this factor is constant of varies for each engine size. An empirical survey will have to be carried out to determine these construction factors.

(27)

DATA INQUIRY OF THE STATE-OF-THE-ART MARINE DIESEL ENGINES 26

a

_{DATA SURVEY OF THE}

STATE-OF-THE-ART MARINE DIESEL ENGINES

6.1 Introduction

Besides the theory there is the practice and so this chapter focuses on the relation between

the theory, described in the previous chapter, and the state-of-the-art marine diesel engines in

practice. It involves an empirical survey which gives insights on how the real engine sizing parameters suit the theoretical ones it gives the construction factors.

To create these relations, a database with engine data from two-stroke and four-stroke marine

diesel engines manufactured nowadays, has been made. The engine data is obtained from

product guides of marine diesel engines manufactures [MaK & MAN B&VV & MTU & Wartsila

MD] and Jane's Information Group Limited [Henderson].

Paragraph 6.2 describes the data from the data base used in the engine data survey to display

the relations between the theory and practice. In paragraph 6.3 the engine performance

relation is described and in paragraph 6.4 the stroke volume in theory and practice is

examined. Paragraph 6.5 describes the engine length and paragraph 6.6 the engine height. In paragraph 6.7 the engine width is described and so is the engine volume in paragraph 6.8 and

the engine weight in paragraph 6.9. Paragraph 6.10 describes the brake specific fuel oil

consumption and paragraph 6.11 is about the overall efficiency. In paragraph 6.12 the technology factor is described and in paragraph 6.13 the wear rate. The chapter conclusions can be found in paragraph 6.14.

6.2 Data used in the engine data survey

Engine models of four major marine diesel engines companies are used in this data survey. Two of the companies produce as well the two-stroke as the four-stroke marine diesel engines

and the other two produce only four-stroke engines. About 70 engine models were looked at. Most engine models can be built with different numbers of cylinders and in two configurations;

line-configuration or vee-configuration. The engine data contains values for the lowest and the highest number of cylinders as well for the line-configuration as the vee-configuration, if an engine is built in these configurations. This results in a maximum of four data values per

engine model, visualized in Table 6.1.

engine model

line-configuration

vee-configuration Table 6.1 data values per engine model

lowest number of cylinders highest number of cylinders lowest number of cylinders highest number of cylinders I

This way, a view can be created on the total power range of the two-stroke and four-stroke

marine diesel engines manufactured nowadays.

(28)

Stroke (Ls) and bore (D) are frequently used

engine data, plotting these versus each other gives us Chart 6.1. This chart gives an insight in the number of engine models used in the data

survey.

One can see that the two-stroke data has more variation, this is due to the market demands for

difference in rotational speeds at certain bore

diameters. When keeping the mean piston

speed the same, changing the stroke length changes the rotational speed. This is often used

for matching the driving shaft speed to the ship

speed desired.

From Chart 6.2 where the stroke/bore ratio (As)

is plotted versus the bore, it gets clear that for two-stroke engines, bigger bore engines have

smaller stroke/bore ratios.

The two-stroke biggest bore engines are mainly installed in large Container ships which have a

relative high ship speed and thus require a relative high rotational speed. This is done by changing the stroke like previously described.

Resume: a relative short stroke will influence the

stroke/bore ratio and produce a relative high rotational speed when keeping the mean piston speed constant.

In Chart 6.3, the mean effective pressure (p,) is plotted versus the bore. By doing so an insight is created in how this parameter creates

differences between the two-stroke and four-stroke engines. It gets clear that in general the

mean effective pressure of the four-stroke engines is higher than that of the two-stroke

engines. This is caused by the fact that four-stroke engines can produce higher charging

pressures than two-stroke engines due to a larger effective stroke volume four-stroke engines have.

Because the mean effective pressure can not be

freely changed due to technical and mechanical

limits, the differences this parameter creates between the two engine types will maintain in a

way. 2 stroke 4 stroke 500 1000 bore (trim] 1500 Chart 6.1 2 stroke stroke I.: .2....

500 woo 1500 bore [mm] Chart 6.2 3500 3000 2500 2000 2 1500 1000 500 4,5 4,0 3,5 .2 3,0 2,5 -43 2,0 2 _1,5 1,0 0,5 0,0 2 stroke - 4 stroke 35 -^ 30 25 20 2'4 15 10 5 0 0 500 1000 1500 bore !rem] Chart 6.3 0

-a

(29)

-6,3

Engine performance

6.3.1

engine brake power

The engine performance can be expressed by the equations defined in chapter 5 Recalling

the equations for the engine brake power:

.it Ar. cm'

11

= I

32

k252

nP

By plotting the brake engine power versus the rotational speed or the bore, the power overlap of the two-stroke and four-stroke engines gets obvious. Chart 6.4 and Chart 6.5 display this

overlap. Chart 6.6 displays the variation in the number of cylinders since the engine brake power is plot versus the brake cylinder power.

80000 70000 F 60000 swop 40000 a, 30000 It '0000 0000 I-2 stroke. choke 1 500 1000 1500 2000 2500 rotational speed [rpm]

When verifying the database data plotted in Chart 6.4 and' Chart 6.5 to the engine brake

power equation, all the data is exactly suited to the equations. The deviation is 0.

Because the theory suits the practice exactly, this verification has not been plotted.

Because it seems that increasing the rotational speed, decreases the engine brake power, one should realize that the other parameters were not kept constant and so influenced the brake engine power apart from the rotational speed.

Chart 6,4 _{Chart 6.5} $0000 70000 F 60000 50000 di 40000 30000 E 20000 10000 OF Chart 6.6 g = cm D2 k 2 stole stro 41.1` 2000 4030 6000 8000

brake cylinder power [kWicyl]

2 stroke stroke.3 80000 70000 60000 50000 :I 40000 3 0000 2 0000 ' . 10000

;

0 500, 1000 1500 bore Irnnil

p

0 8 -0

(30)

6.3.2 brake cylinder power

A more advanced look on the performance of the-state-of-the-art marine diesel engines can be obtained by examining the brake cylinder power plot versus the rotational speed or bore. This

indicates how much power a single cylinder produces. The amount of data for the minimal and maximum cylinder number per line or vee configuration is now reduced.

Recalling the equations for the brake cylinder power:

3 P ₃₂sr pm, cm k.232

nt

2stroke stroke ' . 500 1000 1500 2000 2500 rotational speed [rpm] 32 k3 2 / P 3 3 17 v

g pm,

Equation 8,1

Chart 6 7 (mar 6 d

or with D:

Pe

m -cm 2

8 k

Chart 6.7 and Chart 6.8 display the data of the brake cylinder power plot versus the rotational speed or the bore.

7000 5000 g' 5000 4000 3000 .g" 2000 1000 1Y% 2 stroke stroke 1 of 500 1000 1500 bore minm]

Verifying the data in Chart 5.7 and 6.8 shows the same deviation as for the engine brake power. Because there is only compensated for the number of cylinders which is proportional with the engine brake power. This results in a zerro deviation.

Because the theory suits the practice exactly, this verification has not been plotted.

6.4 Stroke volume

Besides the engine brake power and the brake cylinder power there is an other indicator for the engine performance; the specific stroke volume (Vs.) or stroke volume specific power

(SVSP).

6.4.1

specific stroke volume

The specific stroke volume gives an insight in the amount of stroke volume needed to produce a certain power.

The equation for the specific stroke volume (Ve) is the following one:

Vs* = 2

k25

D

pm. C,

DATA INQUIRY OF THE S TA 7E-OF-THE-ART MARINE DIESEL ENGINES 29

01