MARINE DIESEL ENGINE

Introduction

When a ship is being constructed in a shipyard, the most important machinery that is to be selected is the main propulsion machinery.

The marine diesel engines are those which are used in marine vehicles namely boats, ships, submarines.

Both 2 stroke and 4 stroke engines are widely available in the marine industry, but for large ocean going merchant vessel, a 2 -stroke engine is more commonly used as main engine and has much better market.

The engines used for the main propulsion or turning the propeller/s of the normal ships are usually slow speed 2-stroke engines while those used for providing auxiliary power are usually 4-stroke high speed diesel engines.

A Marine Diesel Engines are basically reciprocating C.I. Engines by its unique combustion feature.

Internal combustion engines are those where the combustion of the fuel-air mixture takes place within a closed chamber known as the combustion chamber.

Rudolf Diesel, a Germen Engineer ,developed successfully engine on this principle and obtained a patent in 1893.

You can see both these types of engines in the pictures below, the first figure being that of a 2 stroke main propulsion plant while the second is of a 4 stroke generator.

Just keep in mind that these images are just for giving you a rough idea otherwise they come in a variety of sizes and flavors.

2 & 4 Stroke Marine Diesel Engines

2-Stroke and 4-Stroke engines

2 & 4 Stroke Marine Diesel Engines

• From 1879 to date, Sulzer is one of the largest manufactures of marine diesel engines used for the main propulsion for merchant ships of both four stroke and two stroke design. Sulzer has its own history. Rudolf Diesel as a young engineer followed up his studies by working as an unpaid workshop trainee at Sulzer Brothers in Winterthur, Switzerland.

• Sulzer built its first marine diesel engine in 1898. In 1950 the company built its first two stroke marine diesel engine that was directly reversible, and five years later it introduced valve-less two stroke engines after-charging systems and spray cooled pistons. In 1954, it introduced the concept of turbo charging in its engines.

• In later years it manufactured different series of marine diesel engines, namely the RD, RND, RND-M, RLA and RLB series. In 1981, in a change from the traditional manufacturing of marine diesel engines, Sulzer introduced a more efficient system of scavenging called “uni-flow scavenging.”

• As the latest models of two stroke marine diesel engine use uni-flow scavenging, the constant pressure turbocharged RTA series with a single poppet exhaust valve was developed. Later the new Sulzer diesel became part of the Wärtsilä Corporation, and the more advance automated engine of Wartsila is the RT-flex series.

Selection of 2-Stroke Engine

Even with wide variety of advantages that 4 stroke engine offers like compact size of plant, much more RPM or speed etc, a 2 stroke engine outshines with few but vital advantages.

Some of the important reasons why 2 stroke engines are more popular than 4 stroke engines as main propulsion engine on ships.

Fuel Selection: The fuel prices have gone sky high and better grade fuel is adding higher costs to vessel operation. A two stroke engine can burn low grade fuel oil and hence reduce running cost of the ship.

Efficiency: The thermal and engine efficiency of 2 stroke engine is much better than that of a 4 stroke engine.

Power: Most of the 2 stroke engines are now large stroke engines that produce more power. Hence they have high power to weight ratio as compare to 4 stroke engine.

Reliability: Two stroke engines are more reliable in operation as compare to 4 stroke engine.

Less Maintenance: The maintenance requirement of two stroke engine is much lesser than 4 stroke engine.

Direction control: Direct starting and reversing is easier with two stroke engine.

Classification of Engines

Marine Diesel Engines may be classified according to their speeds i.e. low, medium or high speeds.

Low speed-50-300 rpm, Medium Speed-300-750 rpm, High Speed-750-7500 rpm, 2-stroke engines are of crosshead type ,where guides

shoes slides over the crosshead guides. 4-stroke engines are trunk type engines, where piston has

and extended skirt which acts as guide. 2-sroke engine are reversible engines, where as 4-stroke

engines Uni-directional

Basic Theory

• Isothermal Operation (PV=Constant): An ideal reversible process at constant temperature. Follows Boyle’s law, requiring heat addition during expansion and heat rejection during compression. Impractical due to requirement of very slow piston speeds.

• Adiabatic Operation (PV= Constant):An ideal reversible process with no heat addition or extraction. Work done is equivalent to the change of internal energy.

• Polytrophic Operation ( PVⁿ =Constant): More nearly practical process. The value index n usually lies between unity and gamma.

• The specific heat of a substance is a measure of its ability to absorb a certain amount of heat without increasing temperature.

Basic Theory

Theoretical Cycles:

I.C Engines work on the basis of three fundamental thermodynamic cycles.

1)Otto cycles (constant volume) 2)Diesel cycles (constant pressure)and 3)Dual combustion cycles But modern diesel engines operates on duel combustion

cycle. The Dual or Mixed combustion cycle is a combination of constant volume(Otto cycle) and the constant pressure (Diesel) cycle.

Otto Cycle

P- V Diagram T-S Diagram

The Otto Cycle ( Constant Volume )• This cycle is also known by the name of constant volume cycle and it

consists of the following four steps. • Please take a thorough look at the P-V and T-S diagrams depicting these

processes along with reading the description and you will understand it in a better way. – 1-2 process is that of isentropic compression of air which means that

the entropy of the air remains constant during this transition and can be seen from figure 2 (T-S diagram). It can also be seen from the same diagram that temperature of the air rises during this process, while the volume decreases significantly and pressures rises (figure 1).

– 2-3 process represents addition of heat to the air at a constant volume which results in increase of entropy, temperature and pressure of the air

– 3-4 is the isentropic expansion of air which corresponds to the power stroke of the engine where the pressure generated during combustion is used to drive the piston upwards and hence deliver motion to the piston. The temperature of the air falls in this process and so does the pressure, and volume returns to the original volume to what it was at point 1.

– 4-1 is the process of heat rejection at constant volume which ultimately brings the working substance or air back to the initial condition. In an actual cycle there is the exhaust cycle at this stage but here no expulsion of the working substance is assumed.

Since thermal efficiency of a cycle represents the heat converted into work per unit of heat added.

The thermal efficiency of an Otto cycle is given by Thermal Efficiency = 1-(T4 – T1)/(T3 – T2) Using the relationships of perfect Gas laws which I am

omitting here to avoid complexity the thermal efficiency can also be written as

Thermal Efficiency = 1 – (1/r)^(k-1) Where r is compression ratio and k is a constant depending on

the properties of the working substance.

Diesel Cycle ( Constant Pressure ) :

• P- V Diagram T-S Diagram

The Diesel Cycle:

The four processes of this cycle as explained as follows with the accompanying P-V and T-S diagrams for clarity.

• 1-2 represents the isentropic compression of air leading to rise in temperature and pressure and significant reduction in volume. This reduction in volume or the ratio of reduction is known as compression ratio. This corresponds to the suction stroke of the real engine.

• 2-3 is the addition of heat at a constant pressure corresponding to ignition in the real engine, leading to rise in temperature and entropy and in volume as well. Just remember from your previous study of the Otto cycle that this head addition was at a constant volume over there, hence the difference

• 3-4 is the isentropic expansion of air corresponding to power stroke and leads to reduction in temperature, pressure and volume.

• 4-1 is the rejection of heat at a constant volume (same as the Otto) and at the end of this process the working substances reaches the same point from where it started thus completing one full cycle of four strokes.

• The thermal efficiency is calculated like before by dividing the amount of heat converted into work by the total amount of heat supplied and it gives

• Thermal Efficiency = 1 – 1/k (T4 – T1/T3 – T2)• It is also calculated using the gas laws and can be written in the following

format as well• Thermal Efficiency = 1 – (1/r)^(k-1) * {((rc^k) – 1)/k(rc - 1)}• Where r is the compression ratio between points 2 and 1, and rc is the

compression ratio between the points 3 and 2, k being dependent on the working substance and is a constant

• The diesel cycle on other hand has less thermal efficiency, less specific output, but practicable at high compression ratios. Accordingly, the advantages of both the cycles are combined in what is called a mixed or dual cycle.

• As we saw in the previous two types of cycles namely the Otto cycle and the diesel cycle that they differ in the manner in which heat is added to the cycle either at constant volume or at constant pressure.

• In Diesel engines operating at slow speeds, there is enough time for the combustion to take place at more or less constant speed.

• The behavior of many slow speed engines is more correctly represented by mixed cycle in which the part of heat is added at constant volume and partially at constant pressure, The constant volume has higher thermal efficiency and specific output, but is impractical at compression ratios because of very high peak pressure.

Duel Cycle

– 1-2 is the isentropic compression which results in temperature rise, volume decrease and pressure rise of the working substance i.e. air

– 2-3 is the process where heat is added at a constant volume to the cycle just like in the Otto cycle

– 3-4 is the process where part of the heat added in the previous process is continued to be added but now at a constant pressure instead of a constant volume (thus the name dual mode) like in the case of diesel cycle

– 4-5 represents the isentropic expansion of air– 5-1 is the heat rejection at constant volume thus bringing the

full cycle to a completion and ready for the next cycle

Actual Cycle

The Actual Cycle: The actual cycle is different from the theoretical cycle in the following, From 1-2 the curve is similar in the compression stroke. From 2-3, compression is not strictly adiabatic as there is heat transfer

through the cylinder liner. From 3-4, during expansion stroke, there is heat transfer. From 4-1, heat is rejected with mass flow, specific heat, lower

pressures and temperatures. In actual cycle, there are unavoidable thermal, hydraulic and

mechanical losses. All these factors leading to a much lower the thermal efficiency in the

actual engines.

Stroke: Stroke is distance covered by the piston between top dead centre (TDC) and the bottom dead centre (BDC).

Compression Ratio: The ratio of the volume of air at the start of compression stroke to the volume of air at the end of this stroke. Usual value for a compression ratio for I.C. Engine is about 12.5 to 13.5 i.e. clearance volume is 8% of the stroke volume.

Mean piston speed: is a parameter in the power equation which suggests that power can simply be increased by increasing the m.p.s.

• D=Bore of the cylinder, S=Stroke of the piston• Vc =Volume of compression chamber,• Va =Volume of the cylinder,• Vc =Volume of compression chamber.• Swept Volume=Volume swept by the piston from TDC to BDC. • Vs=Area x Length. Since, Va= Vc + Vs, • Hence, Compression Ratio=Va/Vc = Vc + Vs/ Vc = 1 + Vs /Vc • Mean Piston Speed=Piston distance in one rev. X rpm =2Sn/60

= Sn/30 , Power=Pmx 2Sn x A X n x Constant • Hence Power depends on Mean Piston Speed

Working cycle: The actual engines requires 4- strokes or 2-strokes such as compression, expansion, exhaust and induction.

Accordingly engines are distinguished as 4- strokes or 2-strokes engines.

The working cycle of a 4- stroke engine is described w.r.t. indicator and valve diagram.

4 -Stroke P-V and Valve Timing Diagram

• 1-2 Induction Stroke: Air is drawn into the cylinder at the pressure existing in the intake manifold. The inlet valve closes after the end of stroke.

• 2-3 Compression Stroke: With both inlet and exhaust valve closed, the air is compressed by the piston in the clearance space. The injection of fuel begins at a few degree before the TDC. The is ignited at high temperature produced at the end of compression and most of the heat released at constant volume.

• 3-4 Expansion or Working Stroke: The gases expand until at the end of stroke when the exhaust valve opens. The exhaust is blown down in exhaust manifold and pressure in the cylinder drops.

• 4-1 Exhaust Stroke: The remaining gases in the cylinder are forced out by the displacement of the piston extending over full stroke.

2-Stroke Cycle

1 -2 Compression2 - 3 Fuel Injection3 - 4 Power4 - 5 Exhaust Blowdown5 - 6 Scavenging6 - 1 Post Scavenging

1. approx 110º BTDC2. approx 10º BTDC3. approx 12º ATDC4. approx 110º ATDC5. approx 140º ATDC6. approx 140º BTDC

• The working of a 2-stroke cycle engine differs from that of a four stroke cycle engine because of complete absence of two distinct strokes of induction and exhaust.

• Apart of each of compression and expansion strokes in two stroke is utilized for the process of induction and exhaust.

• Sir, Duglad Clerk, born in GlaSgow, invented the two stroke cycle engine which was first exhibited in 1881.

• Engine Weight: The weight of an engine is a function of cylinder displacement volume, the number of cylinders and a constant.

• The constant part accounts for weight of camshaft, exhaust manifold, gear train etc., which becomes small in proportion of total weight as the no cylinder increases. The weight of an engine for a certain power can be reduced by manipulating the parameters in the following equation.

• Power α Pm x Vd x n• Where Pm= Mean cylinder pressure,• Vd=Piston displacement volume• n= number of revolutions per second.

• Criterion for performance:• The specific fuel consumption is frequently used in Diesel engine as a

criterion for performance.• It is defined as the fuel consumed by the engine in generating 1 KW

brake power per hour and it is expressed gm/Kw hour.

• Mechanical Efficiency: Apart of the power developed in the engine cylinder by burning fuel with air does not appear in the output shaft but is used to overcoming friction in the bearings, pistons and other moving parts, of the engine.

• The power absorbed in performing these duties called friction power. • The brake power is less than the indicated power by the amount of

power consumed by the engine in overcoming mechanical friction.

• I.P.=B.P. +F.P.• The ratio of the power delivered by the engine to the total

power generated within the engine is known as mechanical efficiency.

• Mean Effective Pressure: It is theoretical pressure which may be assumed to act on the piston during its power stroke. There is a great variation of pressure in a diesel cylinder during a cycle of operation. But the power is calculated from average mean effective pressure. The mean effective pressure is determined from a P-V diagram or indicator diagram,

Various power ratings

• The overall operation of the ship is highly dependent on the performance of its main propulsion engine, measured in terms of its power rating.

• There are several terminologies for “Power” rating used for Marine Propulsion engine and each of these give different value of engine performance under various parameters and situations.

• Following is the list of “Power” Terminologies used for a Marine Propulsion Engine on board ship

• Effective Power: The Power available at the output side of the engine i.e. at crankshaft flange of the engine which connects it with the flywheel and rest of the intermediate shaft

• Rated Power: It is the continuous effective power provided by the manufacturer of the engine for a desired or rated RPM of the crankshaft. Rated power includes the loads which acts on the engine due to auxiliary system running from the engine power

• Indicated Horse Power: It is a theoretical power calculated with a formula = PxLxAxN

4500• Where P- Mean indicated pressure of the cylinder• L- Stroke of the engine• A- Cross Sectional Area of the engine cylinder• N- Speed of the engine in RPM• 4500 is a constant for conversion.• In this calculation, the frictional losses are not considered. Since it is

calculated from indicated pressure of the engine, it is called Indicated Horse Power or IHP and used for calculating mechanical efficiency of the engine

• Shaft Horse Power: The power delivered by the engine to the propeller shaft is measured by an instrument known as torsion meter which is available on board.

• Break Horse Power: This is the power measured at the crankshaft with the brake dynamometer and is always higher than the shaft horse power. This is because the power available at shaft accounts for frictional and mechanical losses.

• Gross Power: Continuous effective power provided by the manufacturer for a given RPM using defined number of auxiliaries at normal service running condition without any overloading of the engine.

• Continuous Power: It is the BHP measured at the power take off end when the engine is running at continuous safe operation range outside any time limit. This is provided by the supplier.

• Overload Power or rating: It is the power excess of effective power than the rated power for a short period of time, when the same auxiliaries are used under similar service condition for limited period.

• Minimum Power: The guaranteed minimum or lower most power value by the manufacturer for an approximate crankshaft RPM is the minimum power of the engine.

• Astern Output Power: The maximum power engine can generate when running in the astern direction at safe condition.

• Maximum Continuous Rating or MCR: It is the maximum power output engine can produce while running continuously at safe limits and conditions.

• Normal or Standard Rating: This is the power output of the engine at normal service speed which gives the highest economical efficiency, thermal and mechanical efficiency. At this speed, the wear down of the engine is at the minimum rate.

•

• Compatibility of Engine output when coupled with propeller:• An engine is designed for certain power rating. The engine power will depend on

propeller characteristics. The relation between the engine and propeller is called the propeller law.

• Power α ∆ 2/3 V³ • Where ∆ = Ship displacement• V=Ship speed• At constant displacement,• Power α 2/3 V³ , but V α (P X N),• Where P=Pitch of the propeller,• N= Rev per minute,• But for the same propeller i.e. P Remaining constant,• Then, Power α N³, • Also Power α Pm.L.A.N.• α Pm.N. ( L and A Being basic dimensions of engine and are constant) • Combating pm α N²

Performance Testing

• For testing the performance of the diesel engine b.h.p. is measured accurately by coupling the engine with the dynamometer at the test bed and pb, brake mean effective pressure is calculated from the relation.

• BP= pb x L x A x n/1000 kw.• It is an accepted practice to use the b.m.e.p. to indicate the power rating in

the cylinder as this value can be accurately calculated from the dynamometer test.

• The engine in the test bed is loaded according to the propeller curve so that it represents the actual working condition when coupled to a propeller.

• The selection of propeller should be such that when coupled to engine in a ship the propeller absorbs the less power under fully laden condition, assuming the hull is clean.

• If the propeller curve is to be theoretical loading limit, a reserve of power should be provided for increase of ships resistance.

Propulsive characteristics

Performance Curves

Engine Testing

• Bed Test: Is carried out to ascertain that the performance characteristics are up to the prescribed standards.

• Sea Trial: Is carried out to confirm the machinery and ships performances as per contractual agreement.

• Comparative Test: To ensure manitainence of the standard.• Prototype model Test: After design and for improvement.• Mooring Trial: Carried out at quey in moored conditions in

order to test normal operating condition of all parts of the main engine and associated auxiliaries prior to sea trial.

• Running-in test: Is carried out with controlled output before operation of main engine for a long period.

• Official Trial: In order to confirm the reliability and performance characteristics of the propulsion plant when coupled to the propeller in open sea.

• Guarantee speed test is carried out by go-and-return between fixed mile posts. The test shall be carried out after raising the speed progressively at ¼, 2/4 , ¾ and corresponding to max. rated continuous output.

• Overload Test –A ten percent overload test is carried out.• Astern Test is carried out when the main Engine is running ahead at MCR,

the engine should be stopped and reversed at quickest possible time and engine should run at highest possible rpm in the astern direction corresponding to 75% to 85% of continuous rated power.

• Minimum revolution test is carried out to confirm a minimum revolution at which the engine can run smoothly and steadily with all cylinders firing.

• Endurance test shall be carried out at least for the maximum continuous output. The speed test, starting test and circle test may be performed during this time.

• Starting test :The air reservoirs are pressed to max. press. And engine is started in ahead and astern direction alternately without replenishing the reservoir until the engine can no longer be started. The no of starts should be as follows;

• For reversible engines- 12 starts or more,• For non –reversible engines -6 starts or more ,• The pressure drop in air reservoir at each start is noted.• Other test such as vibration, Noise, cylinder cut-off carried out.

• Over-speed or Governor Test: The test is carried out to check the response of the governor at different load. The stabilization period shall not exceed 4 secs in case of sudden change from no load to 25 % of rated full load and vice versa.

• Over speed governors shall come into action on reaching 15% above the continuous rating.

• Some of the features of the tests are,• a. Max speed control of governor and over speed trip.• b. Speed variation at controlled speed.• c. The speed changes from extreme value to settle to a steady value.• d. The speed range of the governor is likely to cover over the range

of its adjustment.

• Heat Balance: A diesel engine working on the basis of an air standard cycle is liberated in the engine cylinder. There is the cycle efficiency and various other losses in a practical engine.

• Heat balance chart is a useful method of computing thermodynamic losses in the engine. Attempts are made to recover some of these losses from engine waste to improve thermal efficiency of the engine.

• These are three main thermodynamic losses,• a. Loss due to incomplete combustion,• b. loss through the cooling water and • c. Loss of heat with the exhaust gases.• The loss due to imperfect combustion will appear as a loss in power

generation in the engine.

• Thermodynamics: The branch of science (physics) that studies conversion of energy from one form to the other is called as thermodynamics. Thermodynamics is a very important subject studied under the branch of Mechanical Engineering. Various conversions of energy are possible, like chemical to heat, heat to mechanical, hydraulic to electrical or mechanical, etc. Almost all the energies can be converted from one form to the other form.

• First law of thermodynamics: It is very simple and simply says that energy can neither be created nor it can be destroyed, however, it can be converted from one form to the other.

• Second law of thermodynamics : States that heat energy can be transferred only from body at high temperature to the body at lower temperature. Since heat is directly proportional to temperature, this law can also be understood as: heat flows from body at high temperature to the body at low temperature. If you want to transfer heat from low temperature to high temperature body, external work has to be done.

• In refrigeration and air-conditioning system, heat moves from low temperature to high temperature reservoir, hence they need power (electricity) to work.

• The third law of thermodynamics: says that “entropy of the pure crystal at absolute zero temperature is zero and entropy can never be negative.”

• To understand this law clearly we should know what absolute zero temperature and entropy are.

• Absolute Zero Temperature:• We know zero degree Celsius temperature, it is the temperature at which water

gets converted into ice, and hence it is also called freezing point temperature of water. There are many gases like helium, hydrogen that can be cooled to temperatures much below zero degrees Celsius and at certain level they get liquefied. The lowest temperature, to which all the substances or gases can be cooled to, is called as absolute zero temperature. There cannot be any temperature below this point and at this temperature all the movements of all the molecules within the substance stop.

• Zeroth’s Law of Thermodynamics: which states that if two bodies are in thermal equilibrium with third body, then they are in thermal equilibrium with each other. For example, if temperature of body A is equal to temperature of body C and temperature of body B is also equal to temperature of body C, then temperature of body A is equal to that of B.

• What is Entropy:• Entropy is the total energy inside the substance, which

is not available for work during thermodynamic process. It can be considered as the internal energy of the substance, which depends on the movement of molecules inside the substance. The more the movement of the molecules, the more the entropy. As the temperature of the substance increases, the movement of the molecules inside the substance also increases and with it the entropy of the substance also increases.

Protection system for Main Engine

• To avoid any major loss or damage to the marine engine, several protective devices are fitted to safeguard the engine from major damages and breakdown.

• Different Types of Protections on a Ship’s Marine Engine• Basically there are four main types of protection systems used to safeguard propulsion

engine:• 1. Alarm: In case of deviation of engine parameters from a set value, an audible and

visual alarm will sound which will give an early warning of the problem.• 2. Slow down: It is the next stage of protection when actions taken are not sufficient to

control the ongoing problem; hence engine slow down is done to counter the disturbed parameter.

• 3. Shut down: When there is a higher fluctuation in the engine parameters which can harm other systems of the engine, the shut down protective devices cut off the fuel supply and the engine stops.

• 4. Starting Interlock: This will not allow the engine to start from the stand-still condition if some important system within the engine has not been operated or arranged properly.

• Different Engine Slow Down Situations• In this situation the main engine will come to dead slow RPM i.e. below 30 RPM as the

slow down protection gets activated. Following are different slow down situation for main engine:

• Lube oil pressure falls to 1.5 bar• Cam shaft pressure falls below 2 bar• There is no flow of piston cooling media (water or oil)• Oil mist detector or Main bearing sensors has been activated• Lube oil temperature at the inlet of engine is high > 60 deg C• Piston Cooling temperature is high > 75 deg C• Jacket water Temperature is high > 88 deg c• Engine cylinder exhaust temperature is high > 450 deg C• Scavenge air temperature is high > 65 deg C• Thrust block temperature is high > 75 deg C• Low flow of Cylinder lube oil• Control air pressure is low < 5.5 bar

• Different Shut down Situations:

• Lube oil inlet pressure to engine is very low <1 bar• Cam shaft Lube oil pressure is very low < 1.5 bar• Very high Jacket cooling water temperature >95 deg C• Low Jacket cooling water pressure < 0.1 bar• No flow of Cylinder lube oil• Thrust block temperature very high > 90 deg C• Lube oil inlet pressure for turbocharger is low < 0.8 bar• Over speed of the engine which activates shut down at 107 %

of Max. continuous rating MCR

• Different Starting Interlocks are:• Turning gear engage interlock• Auxiliary blower off interlock• Lube oil and other important pump not running

interlock. • Apart from safety protections on a ship’s

engine, various other systems to ensure that various other operations are not affected.

•

Performance of the Engine

• On ship, it is important to check the performance of the engine from time to time so as to ascertain working condition and fault finding.

• In earlier days, the performance of diesel engine was taken manually, but with the advancement of technology, automatic monitoring systems are being used.

• Types of Diesel Engine Monitoring Systems• With the help of monitoring systems, the diesel performance of the engine can

be taken easily and within no time. The new technology provides two types of monitoring systems.

• In the first system, the diesel performance is monitored continuously and is thus known as online monitoring.

• Whereas in the second system, the engineer has to manually put the instrument on the cylinder head, connecting the wire to rpm sensor and taking the readings manually and later transferring to the computer.

• Generally on ships, the main engine has an online diesel performance system whereas for diesel generators have a manual system.

• Understanding Indication Diagram

• Indicator diagrams are indicative of the power generated within engines and are a useful tool for marine engineers to know how well their engines are performing

• Indicator diagrams are used to assess the performance of each unit of the main engine on a ship.

• It is based on the indicator diagram that the overall performance of the main engine is found out.

• Indicator diagrams are taken at regular intervals of time and matched with that of the ship’s sea trial diagrams to check if there is any major difference in performance.

• If there is any difference, it is important that the problem is rectified before starting the engine.

• Generally there are two types of indicator diagrams – one is power card and other is draw card. With the help of these two diagrams we can determine the compression pressure, peak pressure and the engine power.

• High loading is to be prevented on main engine’s units or else it can lead to several problems such as bearing damage, cracking etc.

• It is therefore for this reason very important to read these diagrams properly as they provide several details about the cylinder working pressures and load.

• In earlier days, the indicator diagram was taken with the help of mechanical indicator which was to be fitted on top of the indicator cocks.

• Bur nowadays a pressure transducer is fitted on the indicator cocks with the help of which the indicator diagram can be taken at any moment and displayed in the computer.

• Engine Indicator• Just take a look at the figure to see what an engine indicator looks

like. • As the name suggests it is used to draw the indicator diagram for

an actual engine while it is firing (working). The black coloured handle you see at the bottom of the instrument helps to fit this instrument in the appropriate slot in the cylinder head known as the indicator cock.

• Once the arrangement is in place the piston inside the instrument is exposed to the pressure variations happening inside the cylinder and these are them transferred on to a paper through the stylus which moves in proportion to the movement of the piston and the spring on top which opposes the instrument piston movement.

• Preparation for the Diagram• There are certain points which need to be kept in mind before plotting an

indicator diagram in order to ensure that it gives a fairly true indication of the power generated.

These points are listed in the bullet format as follows.• The propeller of the ship should be fully immersed in water• The ship should be at even keel and preferably fully laden• There are no strong winds present either against or in favour of the direction of

motion of the ship. If winds are present the engine will either produce more power or will produce lesser power for the given speed because of the wind resistance or aid, as the case may be

• The underside of the ship is pretty clean and is not fouled with underwater growth, otherwise the engine would develop more power for the given speed

• The engine indicator is clean and properly lubricated so that friction does not cause an error in the reading

• The writing pressure of the stylus against the inserted sheet of paper should neither be too low nor too strong. If it is strong it might tear the paper, while if it is too low it will not leave a strong impression

• The cock should be clean so that all the pressure is made available to the piston of the engine indicator

• Recording the Diagram• The engine indicator should be fastened to the cock and the cord on the

instrument should be kept taut• While the cock is still in the shut position, the atmospheric pressure line should

be traced• The indicator cock should be opened and the stylus should be pressed against

the paper till the cycle gets imprinted after which the cock should be safely shut• The cord now needs to be removed and the indicator cock opened again and to

be pulled with hand, the timing being such that the piston is at the top dead center at that time

• The indicator diagram shown below is a normal diagram (Diagrams taken before the use of the engine) and the diagrams that are taken from the engine are taken and compared for deficiency.

Types of Deficiencies

• Deficiency type 1

• When the above diagram is compared with the normal diagram it can be seen that the compression pressure is normal and the maximum firing pressure is too high.

• This can be due to early injection, a result of incorrect fuel timing of the cams, incorrect VIT setting, or leaking fuel injector

• Deficiency Type 2• When the above diagram is compared with the normal

diagram it can be seen that the compression pressure is normal and the maximum firing pressure is too high.

• This can be due to early injection, a result of incorrect fuel timing of the cams, incorrect VIT setting, or leaking fuel injector

• Deficiency Type 3• This diagram shows that the compression pressure is

low, and the peak pressure is also too low.• This can be due to the• Leaking exhaust valve.• Leak through piston rings i.e broken or worn out piston

rings.• High Liner wear. • Burnt piston crown.• Low scavenge pressure.

• Deficiency Type 4• This diagram shows high compression pressure together with

high peak pressure.• This can be as a result of the following:• Exhaust valve opening too late i.e incorrect exhaust valve

timing.• Overload of the engine.

• This effect can be a result of following factors:-• Bad quality of fuel.• Fuel injector nozzle blocked.• Fuel pumps leaking.• Low fuel pressure.• Injector seized.• Advantages of Diesel Performance System• 1) Efficient and reliable operation of the engine.

2) Helps in saving fuel and optimizing SFOC( Specific Fuel Oil Consumption.3) Helps in predicting the necessary repairs and preventing engine failure.4) Helps in reducing spare parts cost and increasing time between overhauls.

POWER BALANCING

• The efficiency of the overall ship depends a lot on the efficiency of the engine running in its engine room. One of the important factors to ensure efficiency of marine engines is to control the power produced from each of its cylinder.

• The process of making fine adjustments to achieve equal power from all engine cylinders is known as power balancing.

• Power balancing of engines is carried out by making minor adjustment to fuel pumps of individual cylinders. The quantity of fuel injected in the cylinder plays the most important role in power balancing.

• The small adjustments made to the fuel pumps should be such that the units are not overloaded and the exhaust temperature doesn’t go beyond the safe limits.

• It is therefore necessary to be extremely careful while carrying out adjustments for power balancing.

• Important Points While Carrying out Power Balancing of Marine Engines

• Power balancing should be done in such a way that:

• Individual units are not overloaded• Exhaust temperature of the units do not rise

above the acceptable levels• Fuel pumps are able to cut off when engine is

stopped

• Things to check while making Adjustments for Power Balancing of Marine Engines

• Fuel pump rack position• Exhaust and cooling water return

temperatures for each cylinder of marine engine

• Measurements from indicator diagram• VIT adjustment

• It is to note that not all cylinder units show equal exhaust temperatures. However, for each engine the figures follow a certain path which can help in accessing a situation. Peak or maximum pressure of the cylinders should also be checked along with cylinder temperatures.

• If proper care is not taken during power balancing, the marine engine can become unbalanced, leading to other serious problems.

• Unbalanced situation of the engine might lead to• Overloading of bearings and running gears• Overheating or bearing failure• Piston blow past• Overheated or piston seizure• Vibration followed by fatigue• Fatigue cracking in bearings, studs, or bolts• Cracking in crankshaft• Failure of holding down bolts

• If you are the watching keeping officer, you must check the following things to ensure smooth power balancing of marine engines:

• Check relevant temperature and pressures (exhaust and cooling return temperatures)

• Check lubricating oil and turbo charger pressures• Check for any unusual noise or vibration• Keep an eye on the exhaust for any kind of smoke• Check if the turbocharger is running smoothly without

surging .• Check fuel pump settings

• Measure clearances and timings of fuel pumps when engine is not working

• Ensure that fuel injectors are changed at regular intervals of time after cleaning and testing. A faulty injector would not only cause loss in power but would also lead to overloading of other cylinders as the governor would try to maintain the normal total power output

• Carry out maintenance of the marine engine at regular interval of time and note down any deviation from the normal running speed

• Any error found should be rectified at the earliest.