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ENGIN

ESYSTEMSOPERATIO

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DESEL ENGINEFUNDAMENTALS

D I E S E L E N G I N E S & F U E L S Y S T E M S E - T E X T


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2LUBRICATION SYSTEMS

Overview

System Operation

Lubricating oil pumps

Gear and rotor

Oil coolers

Oil filters

Full flow, bypass, centrifugal

Lubricating oil

Oil additives

Engine oil classification

Engine service classifications

Contamination and degradation of engine oil

Oil condition monitoring

Oil sampling

Engine oil pressure

Oil pump overhaul

Oil pressure relief valve

Oil cooler leakage test

Revision questions

Industry updates

Related web sites

Additional diagrams/photos

ENGINE SYSTEMS OPERATION




SECTION CONTENTS

2011 DEFS 2.1 LUBRICATION SYSTEMS 3

MODULE CONTENTS
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Lubricat ing Oil Pumps

Gear type pump

The gear type pump consist of two gears placedin an air tight housing. The gears are in mesh withone another. When they rotate a vacuum is formedon the inlet side drawing oil into the pump. The oilis then carried in the gaps between the gear teethfrom the suction side to the discharge side as shownin Fig 2. The line of contact between the close gearmesh and the tight gear fit in the pump housingprovides a seal between the suction and pressuresides preventing oil from flowing back to the suctionside.

Rotor type pump

The rotor type pump consists of an inner and outerrotor placed eccentrically in relation to each other.The inner rotor has always one tooth less than theouter one. Pump operation is based on the variable

chamber principle, that is the space betweenthe outer and inner rotor teeth increasing anddecreasing. During the first part of the rotation ofthe inner rotor, the volume increases and vacuumcauses oil to be drawn through the inlet port asshown in Fig 3. Halfway through the pump rotationthe space between the gear teeth diminishescausing the oil to be discharged from the pumpoutlet port.

Oil Coolers

As engines are designed and built to produce morepower, operating temperatures are becominghigher. One of the functions of the engine oil isto conduct heat away from local hot spots in theengine; in so doing, the oil becomes hot.

The function of an oil cooler is to stop the engine oilfrom becoming excessively hot under heavy loadconditions. The hotter the oil becomes, the greaterthe danger of lubrication failure and oil oxidation.

The operation of an oil cooler is similar to that ofan engine radiator, particularly an air-cooled unit,where the oil is passed through the core, which is

cooled by ambient airflow.

Fig 2. Gear type oil pump operationCourtesy of MAN Nutzfahrzeuge

Fig 3. Rotor type oil pump operationCourtesy of MAN Nutzfahrzeuge

Fig 4. Engine oil cooler showing oil and coolantfows

Courtesy of DAF Trucks




SECTION CONTENTS

2011 DEFS 2.1 LUBRICATION SYSTEMS 6

MODULE CONTENTS

CoolantOil

Suction side Discharge side

Suction side

Discharge side
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SECTION CONTENTS

2011 DEFS 2.2 COOLING SYSTEMS

MODULE CONTENTS

22.2 COOLING SYSTEMS

Overview

Types of cooling systems

Liquid and air cooled

Cooling system operation

Radiator

Coolant

Thermostat

Coolant pump

Fan

Viscous and clutch type

Marine cooling systems

Cooling system temperature

Heat from other sources

Air cooling system operation

Faultfinding the cooling system

Overheating and overcooling

Cavitation

Stray current damage

Fan belt

Revision questions

Industry updates

Related web sitesAdditional diagrams/photos

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Overview

In the course of the work cycle of the internalcombustion engine, a lot of heat is created. Duringthe combustion phase of the engine operation, thetemperature of the burning fuel may reach 1900C.With modern engine design, a greater percentageof this heat generated during combustion isconverted into useful work at the engines flywheel.Out of the total heat produced by a modernengine, up to 43 per cent is converted into usablepower, 27 per cent is lost out the exhaust, 7 per centis lost in radiation and the remaining 23 per cent isdissipated out into the atmosphere via the coolingsystem.

The cooling systems of many diesel engines arenot only called upon to remove heat generatedby combustion, but also to remove heat from anumber of other components associated withengine operation. These components, whichtransfer heat to the engine cooling system, are:

Transmission and torque converter oil cooler

Hydraulic oil cooler

Vehicle retarder oil cooler

Air to water aftercooler Water cooled exhaust manifolds

Marine gearbox oil cooler

The operation and service life of a diesel engineis directly affected by the cooling system. If the

cooling system is of an inadequate size, is poorlymaintained or does not function correctly, theresult can be overheating or overcooling. Boththese extreme conditions can cause excessive andunnecessary internal engine wear, with a resultant

decreased in engine performance, Therefore, it isvery important that the cause of any problem in thecooling system be rectified as soon as possible.

Types of Cool ing Systems

There are two types of cooling systems used inmodern engines:

1. Liquid cooled systems. These use a coolantto remove the heat from the engine and

air or another fluid to cool the coolant.

2. Air cooled systems. These use air flowingaround the engine surfaces to remove heat.

Fig 1. Percentages of heat dissipation from a dieselengine

Fig 2. Liquid cooled engine cooling system

Courtesy of Man Nutzfahrzeuge

Fig 3. Air cooled engine cooling system




SECTION CONTENTS

2011 DEFS 2.2 COOLING SYSTEMS

MODULE CONTENTS

43

27

23

7

Temperaturegauge

Coolant pump

ThermostatExpansiontank

RadiatorCoolantpassages
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Intercooling is the process of cooling the heatedcompressed air before it enters the enginecylinders. In so doing, the air charge becomes

denser, allowing additional fuel to be efficientlyburned, resulting in increased engine power andtorque above that possible with a non intercooledturbocharged engine.

There are two types of intercooler in currentuse, namely the air-to-air and the air-to-waterintercooler. Both are heat exchangers, devices thatbring a hot medium (in this case, the boost air) intoclose contact with a cooler medium (either wateror air), allowing heat to be conducted from the hotto the cold.

Air-to-air IntercoolerWith air-to-air intercooling, the boost air is passedthrough a finned heat exchanger (like water inan engine radiator), and the vehicles forwardmovement causes air to flow across the fins ofthe heat exchanger, thus cooling the boost air. Atypical system is shown in Fig 8.

An air-to-air intercooler can reduce boost airtemperature to as low as 15C above ambient airtemperature. With boost air temperatures as low as

this and under pressure between 175 and 189 kPa,it is possible to provide three times as much air forcombustion as is possible in a naturally aspiratedengine.

Air-to-air intercoolers are used on trucks and mobilevehicles and are mounted in front of the engineradiator.

Air-to-water IntercoolerThis type of intercooler operates by passing theboost air through a water cooled heat exchangermounted in the intake manifold beside the cylinderhead, as shown in Fig 9. Because the boost air ishotter than the engine cooling water, which runsthrough the intercooler, some heat transfer will takeplace. This transfer of heat reduces the charge airtemperature to a (possible) 85C (engine operatingtemperature), if the cooling system is operatingefficiently.

Alt i tude Compensat ion

When an non turbocharged or naturally aspiratedengineis operated at a higher altitude where theair is less dense than at sea level, the quantityof air (and oxygen) entering the engine cylinderon the induction st roke is insufficient for efficientcombustion of the normal fuel charge. As aresult, the performance of the engine diminishesin proportion to the altitude at which it is beingoperated.

On the other hand, turbocharged engines are notaffected to the same degree. As the air becomesless dense with altitude, the turbocharger spins

Fig 8. Schematic diagram of a turbocharged engine tted with an air-to-air intercooler positioned in front ofthe radiator

Courtesy of Scania




SECTION CONTENTS

2011 DEFS 2.3 AIR INTAKE & TURBOCHARGER STSTEMS 49

MODULE CONTENTS

Air-to-air intercooler

Hot air in Cooler air out
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manifold pressure. This in turn increases the gasvelocity through the nozzle ring on to the turbineincreasing its speed and subsequent turbochargerboost pressure. Alternatively, as the nozzle ringopens up, the exhaust manifold pressure decreasesand consequently the gas velocity to the turbinedecreases with a reduction in boost pressure.

On electronic controlled diesel engines theturbocharger operation is monitored by theelectronic control system via a turbocharger speedsensor and an intake boost pressure senor. Whenthe electronic control system senses a turbochargerover speed condition it will command the slidingnozzle ring to open thereby reducing turbine shaftspeed. As turbine speed and subsequent boostpressure is controlled by the positioning of thenozzle ring there is no need for a turbocharger

wastegate to prevent the turbocharger from overspeeding.

In operation, the infinite positioning of nozzle ringon a variable geometry turbocharger is controlledby an electric actuator which in response to engine

operating conditions moves the nozzle ring tothe most appropriate position for efficient engineoperation. Some variable geometry turbochargersuse a pneumatic actuator to move the nozzle ring,however the electric actuator has more infinite andsensitive control of the nozzle ring and is thereforemore widely used.

Variable Geometry Turbocharger(Moveable nozzle vane type)

The principle of operation of this type of variablegeometry turbocharger and the performanceoutcomes are similar to that of the sliding nozzlering type VGT discussed previously. The physicaldifference being that the turbocharger shown in Fig14 uses a set of moveable nozzle vanes (insteadof a sliding ring) in the exhaust turbine housing todirect the flow of exhaust gases on to the turbinewheel.

At low engine speed the nozzle vanes areslightly open restricting the gas flow area therebyincreasing the velocity of the exhaust on to theturbine wheel as shown in Fig 15. Furthermore, thehigh speed velocity of the gas contacts the bladesat right angles thereby maximising the driving forceof the gas on to the rotating turbine. Consequently,the combination of the gas velocity and the angleof gas contact quickly spin the turbine to high rpm.

Fig 13. Nozzle ring positioning on a variablegeometry turbocharger to show how boostpressure can be controlled

Courtesy of Cummins Inc

Fig 14. Photo of the turbine end of a variablegeometry turbocharger with movable nozzlevanes




SECTION CONTENTS

2011 DEFS 2 3 AIR INTAKE & TURBOCHARGER STSTEMS 52

MODULE CONTENTS

Nozzle ring fully closed

Minimum turbine voluteexit area

Maximum exhaust mani-fold pressure

Maximum turbine speed

Maximum turbo boost

Nozzle ring fully open

Maximum turbine voluteexit are

Minimum exhaust mani-fold pressure

Minimum turbine speed

Minimum turbo boost
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