1 Eng Performance 2

8/3/2019 1 Eng Performance 2

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CLASS ONE ENGINEERING KNOWLEDGE

ENGINE PERFORMANCE

Page

Engine diagnosis 2

Indicator diagrams 3

Computer analysis 11

Load diagrams 14

Engine safety margins 16

ENGINE PERFORMANCE Page 1 of 17


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DIAGNOSIS OF DIESEL ENGINES

The marine engineer must be aware that the engine under his control is performing at itsoptimum level. This will not only reduce the fuel required for a given power or voyage, butalso reduce maintenance requirements and costs.

There are various methods by which this can be achieved, namely:1. Trend analysis 2. Indicator cards 3. Computer analysis

TREND ANALYSIS

Trend analysis is nothing new. Engineers have been taking a log reading for generations,and using these readings to decide whether the engine and auxiliary plant is operatingcorrectly. These readings of system pressures and temperatures differ fundamentallyfrom the indicator cards in that they use data obtained over a much longer period, anduse repeated readings to obtain a trend of events. This will reduce the errors that canoccur from an erroneous single reading.

However trend readings do require that a history or database of readings be obtainedbefore suitable analysis can be carried out. Also the readings taken can not be directlyrelated to the fault/s, and are often an effect of the fault. (Such as the exhausttemperature of a cylinder would change if the piston rings were worn, but this could alsobe caused by a number of other faults, whereas a direct cylinder pressure reading wouldbe a better way of identifying the actual fault).

Hence both indicator cards and trend analysis should be used in tandem due to thedifferent information each are recording. The big advantage of using two methods ofanalysis is that if both methods indicate a similar fault, then the possibility of a correct

analysis is greatly enhanced.

The trend of engine performance has been used for a number of years by engine buildersby measuring the following parameters;

a) Exhaust temps

b) Fuel rack setting, this will equal fuel input when all pumps are in good condition.

c) T/C revs and scavenge pressure obtained

d) Pressure drop across scavenge coolers and T/C air filters

e) Temp & pressure of fuel input

f) Actual measurement of Pmax (combustion pressure), and Pcomp

INDICATOR CARDS



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The taking of indicator cards, allows the engineer to receive more information about thecombustion process (via the draw or out of phase card), measure the cylinder poweroutput of the engine (via the power cards), and check the cleanliness of the scavengingprocess (via the light spring diagram).

Advantages - relatively easy to take, produce a permanent record for future records, andare obtained at very little extra cost. As such they are a valuable addition to the analysis

tools available for the engineer.

Disadvantages - the card is only a "snapshot" of the events which occur; and faults with

the taking and analysis of the cards, can cause the engineer to mal-adjust his engine,

making engine operation even worse than what it was before.

Indicator diagrams can be used to investigate specific faults in the operation of the engine,

especially in the all important combustion sequence. The cards can be taken by either the

traditional mechanical indicator, or using the more modern electronic indicator.

There are five types of indicator cards, which can provide the following information:

Power or in-phase cards

Cylinder power, calculated from the area within the p~V diagram

Indicates afterburning present when card shape enlarged during the

expansion stroke

Draw or out-of-phase cards Measurement of the compression pressure Measurement of the point of fuel ignition

Light/weak spring card

Fouling of exhaust or scavenge gas flows

Compression card

Measurement of the compression pressure

Timing check of the indicator cam

Pressure derivative

Measurement of the point of fuel ignition

Measurement of the maximum rate of pressure rise following initialcombustion



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Late fuel injection.

Later fuel injection is a common problem, and will occur when any wear occurs in the fuel

injection or camshaft drive system.

The results of the late fuel injection can be similar to that of the worn fuel injection pumpor injector, and shows the importance of collecting all the information from the engine

before analysing. In this case the trace of the draw card clearly shows that the fuel isbeing injected later than normal. Thus this fault must be attended to first, before anypossible differences in the cylinder powers or exhaust temperatures are investigated.

In this example the fuel injection has been retarded by 4 degrees on a slow speed engine.Other important parameter changes that were noted were 35o C increase in cylinder exhaust temperature 12% decrease in cylinder power 15 bar decrease in cylinder maximum pressure

If only the exhaust temperature increase had been noted, and this change was adjusted

by decreasing the fuel pump rack position alone, then the imbalance between cylinderpowers would be even greater than before.

The cause of this late fuel injection could be: Incorrect fuel pump timing adjustment Wear in the camshaft drive system (either gears or chain drive) Worn fuel pump plunger, but this would also inject less fuel hence the exhaust

temperature would usually change very slightly Defective fuel injection pump delivery or suction valve/spring



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Worn piston rings or liner.With all indicator cards, the first check of the card should be the compression pressure. Theexample shows the power card, and even this card can be used to indicate the approximatecompression pressure developed by the piston. The best method would be to take a cylinderpressure with no fuel admitted, but this can only be done at low engine speeds, otherwisethe other cylinders may overload.

When the piston rings are worn, then the following indications will be present Lower cylinder power developed Lower cylinder maximum pressure Lower cylinder compression pressure Higher exhaust gas temperatures

The following faults could cause excess wear of the piston rings or liner: Abrasive particles in the fuel oil such as silicon and aluminium from the oil refinery

process Insufficient cylinder oil injection in the slow speed engine

Operating the engine at low temperatures when using residual fuels containing sulphur Neglecting honing of the cylinder liner during overhaul Using low alkalinity cylinder lubricating oils when using residual fuels containing sulphur


Normal curve

Worn piston rings with lowcompression pressure


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Worn fuel injection pump.This produces a lower maximum pressure, a lower power developed, and usually lowerexhaust gas temperatures.

This is caused by the worn fuel pump pressurising the fuel within it at a slower rate thannormal. However not only is the fuel injection retarded, it is also injected at a lower pressure,

causing both less fuel to be admitted, and larger fuel droplets than normal. The combinationof these effects would be: Lower cylinder power Late fuel injection Slightly lower exhaust gas temperatures Increased exhaust gas smoke emitted from that cylinder

Hence it is vital that all changes in parameters are investigated, so that the actual cause canbe more readily identified.

Note that when the fuel pump is adjusted to compensate for this wear by only increasing the

fuel rack setting, the result would produce similar effects to the worn fuel injector, i.e. higherexhaust gas temperatures for the same cylinder power (as the fuel droplets produced will belarger).Hence it is important to advance the fuel timing as well as increase the fuel rack setting tocompensate for this fault.

The following faults could cause excess wear of the fuel pump: Abrasive particles in the fuel oil such as aluminium and silicon catalytic fines No fuel (acts as a lubricant) or insufficient plunger/barrel clearance



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Worn Injector holesThis produces larger fuel droplets that are inherently slower to burn or combust. Thesedroplets produce lower maximum cylinder pressures and higher exhaust gas temperatures.

As there are a number of parameter changes that could cause higher exhaust temperatures,these should be investigated first before the engine is stopped to visually examine the fuel

injector.

The worn injector holes would produce Lower cylinder power Lower maximum cylinder pressure Higher exhaust gas temperatures Darker exhaust gas smoke No change to the fuel timing

The following faults could cause excess wear of the injector holes: Abrasive particles in the fuel oil such as aluminium and silicon catalytic fines

Corrosion



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The power card provides a measurement of the cylinder power, and allows the true specificfuel consumption to be calculated. This will allow comparisons of the fuel efficiency of theengine to be carried out at different load settings. The cylinder power is calculated bymeasuring the area of the pressure~volume graph, and converting this into the meaneffective pressure acting on the piston. By multiplying this pressure by the working volumeand speed of the piston, the power developed by that cylinder can be calculated. Power

measurements are important to ensure that the maximum power of the engine is notexceeded, (causing premature damage), and that engine cylinder power balance is uniform,(which produces higher engine efficiency than a poorly balanced engine, and avoidsoverloading some cylinders when the engine is close to developing full power).

Once all the indicator cards are taken, the following analysis would be required: Measurement of the compression pressures to ensure all cylinder valves, piston rings

and liners are sealing the combustion chamber effectively Check the position of the fuel ignition, to ensure that it is normal for that engine type (if in

doubt, most engines ignite close to the piston top dead centre position) Check the level of cylinder maximum pressure. This pressure is dependant on the point

of fuel ignition and the amount of fuel admitted Check the power developed by the cylinder and engine

Faults should be identified and repaired before adjustments to the cylinder powers areattempted. This power balance is carried out by first ensuring that the fuel ignition is at thecorrect point for each cylinder, then retake all the power cards before balancing the engineusing the individual adjustment of the fuel control shaft at the input to each fuel pump.

However indicator cards have the following limitations:

1. The pressure sensing point of the cylinder relies on pressure waves being

transmitted through a narrow passage. Also the actual place of ignition can occur

randomly in the cylinder, which affects the level of pressure transmitted andreceived. This means that similar `cylinder' pressures can be registered as slightly

different pressures by the indicator unit. Thus readings of power variations may be

due to incorrect readings by the indicator unit.

2. If an indicator diagram is used to adjust the engine parameters, then we must

assume that the single diagram is representative of that cylinder. For an engine

running at 100rpm, then in one month 4.3 million cycles occur. It is unlikely all

cylinders will continue to exhibit the same power balance profile.

3. The calculation of the power of a cylinder can often rely on accuracy of hand traced

planimeter. The accuracy of planimeter and hence power calculations will be poor.

Electronic indicators have an advantage in this respect. These units use inputsfrom cylinder pressure and flywheel position. The pressure sensor can measure

and record the pressure from sequential cycles. This means that rogue readings

will not be used to calculate engine power and hence cause mal-adjustment of the

engine power settings.

4. Friction within the mechanical indicator

5. Uneven load on the engine due to changes in the external load conditions over the

period when indicator cards are taken

6. Uneven temperature of the mechanical and some electronic indicators

To find whether the readings taken are normal or otherwise, analysis is required. This



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may simply be by comparing the results to the test bed results or engine builders model

curves for that engine, or more sophisticated software can be used.

MAN B&W have introduced a CAPA system which when the required data is entered into

the programme over a period of time, provides performance calculations, and indicates

parameter trends. It also lists the adjustments that should be carried out to the engine, to

improve efficiency or reduce possible damage.



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MODEL CURVE FOR MAN B&W ENGINE TYPE L90MCE



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COMPUTER ANALYSIS

The present popularity of computers at sea has allowed the engine manufacturers toproduce software which can assist the engineer analyse his engine. MAN B&W (andothers) have produced Engine Diagnosis Systems such as CAPA that can assist theengineer to;

Detect that the engine is not operating correctly Locate the fault Indicate when certain maintenance is required to be carried out

The latest version of MAN B&W software is the CoCoS system. This system constantlymonitors the engine performance, via the normal data-logging system. Thus every 300seconds (5 mins) the software programme checks the various system pressures andtemperatures of the engine, which are stored for playback and analysis when required bythe engineer.

Advantages - due to the vast number of readings taken by this software, the chance that

an incorrect reading will produce the wrong analysis is greatly reduced. When a reading istaken which differs widely from the expected trend, the software programme highlightsthis, so the engineer, to ensure that a faulty probe is not the cause can carry out a manualcheck.

Cylinder pressure readings (and fuel injection pressures if required) still have to bemanually taken and downloaded into the software programme. Thus even on the presentgeneration of diagnosis software, indicator cards (electronic) are still required.

So should the engineer use these programmes to determine his maintenanceschedules?

It would be more convenient to use direct monitoring (CBM) to control the exactmaintenance schedules, as this would; Maximise component usage Reduce spare part costs (seals always renewed every overhaul) Avoid over-maintenance(i.e. maintenance only when detected as needed)

Disadvantages - The diagnosis software could indicate that the overhaul is required after a convenient

port or vessel lay-up, when the maintenance would obviously be carried out (i.e. a fuel

valve test would always be carried out in port, rather than in the middle of the voyage) The software cannot deal with unknown or future events. You may be aware that the

vessel is to be placed on a valuable charter, which requires no downtime orstoppages, or the vessel may be operating in winter or extreme weather in the nearfuture. Maintenance may be advanced to ensure optimum engine performance duringthis period.

The diagnosis unit may indicate that numerous overhauls are required at one time.Planned maintenance is designed, and should be organised to reduce the highdemands on the available work-force

The trend analysis system of the diagnosis software will mainly use increased rates ofchange as the sole criteria for the need to overhaul certain machinery, but some items

such as T/C ball bearings, piston rings, etc, can fail in service. It is this time to the end



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of the useful life that would be integrated with the planned maintenance system. It is

unlikely that a diagnosis system will be able to give an advanced warning that sudden

catastrophic component failures were about to occur.

To aid the engineer combine all the tools at his disposal, an integrated package would bethe ideal approach, thus use would be made of;

Indicator cards, as only these inform the engineer of the effectiveness of thecombustion process, and indicate the condition of the piston ringsDiagnosis software, these allow the engineer to make the correct decision from thevast array of information which is received from the data-log Plannedmaintenance. The overhaul periods are adjusted for each individual engine and itscircumstances. The engineer should constantly strive to achieve maximum overhaulperiods without producing component failure in service, or downtime. This willminimise running, overhaul and spare gear costs.



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CoCoS-EDS

Engine Diagnostics System

The engine diagnostics systemCoCoS-EDS is a diagnostic tooldedicated for assisting in theperformance evaluation of MANB&W and Pielstick engines.

The diagnostic capabilities ofCoCoS-EDS are based on MANB&Ws and Pielsticks expertiseand experience in the design,manufacture and maintenance ofdiesel engines, accumulated overmore than a century.

Through CoCos-EDS we offer you notonly a dedicated diagnostic tool for yourMAN B&W and Pielstick engines, butalso a tool for logging, monitoring andstoring of engine performance and datatrends.

The main objectives of CoCoS-EDS are:

To assist in decision makingonboard, at the office, or at thepower plant.

To improve availability andreliability of diesel engines.

To reduce operating costs andlosses due to engine failure.

These objectives are achieved through:

Logging, monitoring and storage ofoperating data.

Unambiguous diagnostics of operatingstates.

Timely detection of irregularities.

To obtain the full benefits of the principalfeatures of Co-CoS-EDS, it should have on-line connections to the alarm system andother data acquisition systems. However,manual input facilities make it possible toutilise CoCoS-EDS for off-line equipmenttoo.

CoCoS-MPS

Maintenance Planning System

The maintenance planning systemCoCoS-MPS is a dedicated tool for

assisting in planning and initiatingof preventive maintenance work ondiesel engines and other technicalequipment.

Through CoCoS-MPS we offer you notonly a dedicated planning tool, but alsoa comprehensive preventivemaintenance programme containing ourrecommendations concerningmaintenance of MAN B&W and Pielstick

engines.

The main objectives of Co-CoS-MPSare:

To assist in the decision makingonboard or at the power plant.

To improve availability andreliability of diesel engines.

To reduce maintenance costs andlosses.


Comprehensive maintenanceprogrammes for MAN B&W andPielstick engines.

Dedicated tools for extensive planning

of engine maintenance. Forecasting of the consumption of

spare parts and work hours. Logging of maintenance history and

experience.

CoCoS-MPS can be used as a stand-alonesystem. However, to obtain the full benefitsof the principal features of CoCoS-MPS, itshould have direct access to CoCoS-SPCand SPO.

Co-CoS-SPC

Spare Part Catalogue

The spare part catalogue Co-CoS-SPC is a dedicated tool forassisting in the identification ofspare parts. With CoCoS-SPCyou get access to a number ofcomputerised spare partcatalogues for MAN B&W andPielstick engines.

Through CoCoS-SPC we offer you notonly a spare part identification tool, butalso a tool to build and maintain your own

computerised spare part catalogues forother technical equipment.

The main objectives of Co-CoS-SPCare:

To assist in the identification ofspare parts for diesel engines andother technical equipment, onboardor at the power plant.

To give easy access to spare partinformation.


Multilevel part lists

Graphics Spare part information Extended search

Co-CoS-SPC can be used as a stand-alonesystem. However, to obtain the full benefitsof the features of Co-CoS-SPC, it shouldhave direct access to CoCoS-MPS andCoCoS-SPO.

Co-CoSSPO

Stock handling and spare PartOrdering

The stock handling and spare partordering system Co-CoS-SPO is adedicated tool for assisting inhandling and control of the sparepart stock, and in the procurementof required spare parts.

Through Co-CoS-SPO you also get a toolfor tracing certified components and forlogging their operation and overhaul

history.The main objectives of Co-CoS-SPOare: To assist in the handling of the

spare part stock. To give up-to-date information on

current stock. To forecast spare part availability. To assist in the procurement of

spare parts.

These objectives are achieved through: Stock administration Automatic generation of ordering

proposals. Easy preparation of and follow-up on

orders. Extensive reporting.CoCoS-SPO can be used as a stand-alonesystem. However, to obtain full benefits ofthe integrated stock handling and sparepart ordering and of the other principalfeatures of CoCoS-SPO, it should havedirect access to CoCoS-MPS and CoCoS-SPC.

LOAD DIAGRAMS (MAN B&W)



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A load diagram is a graph showing the relationship between engine speed and power over

the operating range of the engine. The diagram is drawn for a specific engine, and is

dictated by the MCR (maximum continuous rating) required to propel the vessel, at a

certain engine load and speed.

Imposed on this diagram is the propeller curve, which is the relationship between propeller

power and shaft rotational speed (power speed3).

For the diagram shown, the following line notations are used

1) This is the propeller curve which intersects the MCR of 100% power and 100% speed.

2) Propeller curve, fouled hull + heavy weather heavy running.

3) This is the maximum engine speed which can be accepted for continuous operation.The limit is usually 103.5-105% depending on the engine builder, with engine trials just

above (+2%) this level. Running the engine at low load and above 100% speed shouldbe avoided for extended periods.

4) This represents the limit at which an ample supply of air is available for combustion.Operation above this line would create thermal overload, and imposes a limitation onthe maximum combination of torque and speed.

5) This is the limitation of mep which extends from the 100% power/speed point. Thisindicates the mechanical limit of the engine. Some makers extend this line horizontallyfrom the MCR point, thus impose a 100% power limit after the 100% speed limit.

6) As any fouling of the propeller or hull, or adverse weather conditions willincrease the power absorbed by the propeller for the same engine speed. Thiswill move the propeller loading to the left of the propeller `curve'. Thus in orderto compensate for this the engine/propeller is designed with 2-3% `light' orreduced load, so that as it becomes dirty it will operate close to the optimum line1.

7) The line represents the maximum power output of the engine at 100% of the MCR(Maximum Continuous Rating).

8) This dashed line represents the thermal overload limit of the engine.

9) This dashed line represents the mechanical overload (overspeed) of the engine.

MAN B&W have fitted a load-up control system to some of their engines, to prevent

engine overload that could occur during heavy weather, fouled hull, shallow water or too

heavy propeller set-ups. They discuss that without these units most engines would

operate beyond the permissible limit of continuous operation for some period. They state



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that future governors should incorporate such a unit as an integral part.



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SAFETY MARGINS FOR ENGINE OPERATION (NSD)

The maximum continuous rating of the engine (MCR) is the maximum power/speed

combination of a particular engine. The only time this limit is to be exceeded is during

trials, when a 10% overload is permissible for one hour.

To ensure that during `normal' operation the engine power/speed does not exceed thislimit, certain safety margins are introduced which reduce the output power of the engine,

and this new power should produce the contractual speed of the vessel in calm seas, with

a clean hull and propeller, shown as point A on the diagram.

4 safety margins are shown;

1. Sea margin. This is the expected increase in power required to maintain the

vessel's calm weather speed. This margin is dependant upon expected sea routes,

& time between dry-docks. This margin is about 15% power, and is measured

along the propeller curve.

2. Light running margin. This margin compensates for the expected drop in shaft

revolutions between dry-docks for constant power operation. This margin of 5-6%

is made up of;

a) Influence of wind & weather on intake water flow to propeller. An increase of

1.5-2% is the difference between force 2 trial conditions, and average force

4-5.

b) Increase in ship's resistance and wake due to hull rippling, local fouling, and

under-paint roughness, will produce 1.5-2% increase.

c) Increase in propeller frictional losses from 12 m to 40 m will cause a 1%increase.

d) Reduction in engine efficiency due to fouled air coolers, fouled T/C, piston

ring deterioration, poor fuel injection, & increase in EGB fouling will cause a

1% increase.

3. Shaft Generator allowance. If a shaft generator is fitted, then a power allowance

must be made, depending upon the size of the generator.

4. Engine/Operational margin. Most owners will specify the contractual speed at 90%

of the MCR. This margin will allow the vessel to increase above the rated speed, orincrease the time between dry-docks.

To recap: Point A This is the calm weather, clean hull operation position

Point B This is the design point for the propeller

Point D This is the service condition for aged hull and average weather



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