Post on 06-Mar-2018
COOLING SYSTEMCOOLING SYSTEM
I t d tiIntroductionI.C Engines at best can transform about 25-30 % ofthe chemical energy from the fuel in to mechanicalenergy.About 35 % of the heat generated is lost to the coolingAbout 35 % of the heat generated is lost to the coolingmedium remainder being dissipated through exhaustand lubricating oil.
1/3 Heat to Useful Work1/3 Heat to cooling System1/3 Heat to cooling System1/3 Heat to exhaust system
The Purpose of Cooling System
Prevent OverheatingExcess Heat generated in engine
P k t t d lti i t f Peak temperatures exceed melting point of metal
Regulate the most efficient TemperatureRegulate TemperatureRegulate Temperature
Allow engine to warm up in cool weather
Maintain engine in optimum range.
Consequence of engine running too hot:
Pre-ignition Detonation/KnockPre ignition, Detonation/Knock– All result in very high pressure rise and possible damage to engine
fHeat Fatigue of componentsBurnt PistonsBurnt Valves
Failure of lubrication systemOil breakdownOil fil t li d d t d t 200COil film at cylinder destroyed at 200C
Scoring of piston & sleeves
Warping & fracture of components
Consequence of Engine Running Too Cold
Unnecessary WearUnnecessary WearPoor Fuel Economy
Incomplete CombustionLower coolant Temperature
More energy transferred out of cylinderEnergy from is wasted & not available for work (Power)
Promotes corrosive conditions in engineWater of combustion reacts with sulfur oxides in exhaust
Forms acidsForms acids
Allows water & sludge to accumulate in crankcaseOver time, fuel diluting the oil will accumulate
Normally lighter volatile fuel will evaporate as temp. rises
Piston Temperature DistributionVariation of Gas Temperature
H t T fAs a result of combustion, high temperature are
Heat Transferg p
produced, inside the engine cylinder
Considerable heat flow from the gases to thedi t l llsurrounding metal walls
Shearing of the oil film
Heat transfer from gases to the cylinder walls mayoccur predominantly by Convection & Radiation
Heat transfer through the cylinder wall occurs only byHeat transfer through the cylinder wall occurs only byconduction
The temperature profiles across the cylinder barrel wallp p y
For water cooled engine
Air cooled engine
Cylinder Wall Temperature Profile
Parameters Affecting Engine TransferEngine heat transfer depends upon many parameters,unless the effect of these parameters is known, thedesign of a proper cooling system will be difficult.
Fuel-Air Ratio:Fuel-Air Ratio:
A change in fuel-air ratio will change the temperatureof the cylinder gases and affect the flame speed.y g pMaximum gas temperature occurs at equivalenceratio of 1.12. But maximum heat loss occurs atslightly lean air fuel ratioslightly lean air fuel ratio.
Spark Advance:
More or less spark advance from the optimum valueMore or less spark advance from the optimum valuewill result in increased heat rejection to the coolingsystem
i i i d k kiPre-ignition and knocking:
Negligible effect on overall heat transfer
Engine output:Engine output:
Engines which are designed for high M.E.P orhigh piston speeds, heat rejection will behigh piston speeds, heat rejection will beless
Cylinder wall temperature:
Increase in gas temperature has very littleeffect on wall temperature difference and onheat rejectionheat rejection
Characteristics of an efficient cooling system
The two main characteristics desired of an efficient coolingThe two main characteristics desired of an efficient coolingsystem are:
It should capable of removing about 30 % of the heatgenerated in the combustion chamber while maintainingthe optimum temperature of the engine under alloperating conditions of the engineoperating conditions of the engine
It should remove heat at a faster rate when engine ishot. However during starting of the engine the coolingshould be minimum, so that the working parts of theengine reach their operating temperatures in a shorttime
Types of cooling SystemThere are two types of system in generalyp y g
Liquid or indirect cooling systemAir or direct cooling system
Liquid Cooling SystemMainly water/coolant is used and made to circulate throughMainly water/coolant is used and made to circulate throughthe jackets provided around the cylinder, cylinder head,valve ports and seats where it extracts most of the heat
The heat transferred from the cylinder wall and other partsby convection and conduction
The heat from liquid in turn is transferred to air Hence it isThe heat from liquid in turn is transferred to air. Hence it iscalled the indirect cooling system
Methods of Water-cooling System
Water cooling can be carried out by any one ofthe following five methods
Direct or non return system
Thermosyphon system
Forced circulation cooling system
Evaporation cooling system
Pressure cooling system
Direct or Non return System
This system is useful for large installations whereThis system is useful for large installations whereplenty of water is available.
The water from a storage tank is directly suppliedthrough an inlet valve to the engine cooling waterj kjacket
The hot water is not cooled for reuse but simplyThe hot water is not cooled for reuse but simplydischarged.
Th h S tThermosyphon SystemHeat is supplied to the fluid in the tank AppDue to relatively lower density, the hot fluid travels upIts place being taken up by comparatively cold fluid fromth T k B th h th ithe Tank B through the pipe p2
The hot fluid flows through the pipe P1 to the tank Bwhere it gets cooledThe fluid circulates through the system in the form ofconvection current
Tank A –represents the cylinder jacketsp y j
Tank-B- represents a radiator and
water acts as the circulating fluid.water acts as the circulating fluid.
The advantages are
Its simplicityIts simplicity
Automatic circulation of cooling water
The man limitation of the s stem is its inabilit toThe man limitation of the system is its inability tomeet the requirement of large flow rate of water,particularly for high output engines.
Forced circulation Cooling SystemThis system is used in a large number of Automobiles.y gHere the flow of water from radiators to water jacketsis by convection assisted by a pump
Water or coolant is circulated with through jackets aroundthe parts of the engine to be cooled is kept in motion by acentrifugal pump which is driven by the engineThe water is passed through the radiator where it is cooledby the forward motion of the vehicleA thermostat is used to control the water temperaturerequired for coolingrequired for coolingThis system consists of 4 components
Radiatorwater pumpFanthermostatthermostat
Basic Schematic Layout
Cab heatexchanger
Thermo-stat
Heater Control
RadiatorEngine Block & Fan
WaterPump
Engine Block &Cylinder head Water Jacket
Pump
Parts of Engine Cooling System
Cooling System Construction
Radiator
RadiatorTop Hose
Radiator Cap
FanThermostat
Water Pump
Thermostat
Engine Block PumpEngine Block & Water Jacket
C ld E iCold Engine
When an engine iscold, the thermostat iscold.
Coolant flow is throughthe bypass hose andthe bypass hose andthe water jackets.
This allows the enginegto warm up evenly.
The thermostat shouldt t t t 77 oCstart to open at 77 oC
and fully open at 85 oC
Warm Engine
The thermostat opensThe thermostat openswhen the engine warmsup.
This allows coolant tocirculate through the
di t d th tradiator and the waterjackets.
Water JacketsDefined as the open space within in the cylinderp p yblock and cylinder head where coolant flowsWater jackets are designed to allow coolant flowt th i ht t fl t th i ht t th tto the right spots flow to the right spots so thatmaximum cooling can be obtained
Water PumpIt purpose is to circulate the water through the cooling system
Located on the front part of the engine
In most of the vehicles it is driven by a belt is attached to the crankshaftcrankshaft
As the crankshaft turns the fan belt turns
Thermostat
One of the most important parts of the cooling systemOne of the most important parts of the cooling system
Its purpose is to keep the engine coolant at most p p p gefficient temperature
The thermostat is used to bring the coolanttemperature up to operating as quickly as possible
It is designed to sense the temperature of the coolant
Th t tThermostat
Fig. Engine Thermostats
Bellows type with short sealed Bellows type with short sealed tube containing ether. Ether expands when heated causing the thermostat to open. thermostat to open.
Bimetallic strip uncoils when pheated causing the thermostat to open.
RadiatorIts purpose is to allow fresh air reduce thep ptemperature of the coolant.
As the coolant passes through the tubes air is forcedaround the tube
This causes a transfer of heat from the hot coolant toth l ithe cooler air.
In this case, heat is exchanged from the liquidcoolant to air This is called a liquid-to air heatcoolant to air. This is called a liquid to air heatexchanger
Coolant flows through the air fins
The fins and tubes are cooled core
Radiator Parts
Radiator Pressure Cap
Pressure caps are designed toPressure caps are designed to
Increase the pressure on the cooling system
Reduce cavitationsReduce cavitations
Protecting the radiator hose
Prevent or reduce surging
It is important to put pressure on the cooling system.Radiator pressure caps are typically near 15 psi
As the pressure increases the boiling point of thecoolant also increases (about 3 degrees for each 1psi increase)psi increase)
P CPressure Cap
PPressure cap
PPressure cap
E i t kExpansion tank
E i t kExpansion tank
FFan
Coolant Temperature Indicator
C l t T t I di tCoolant Temperature Indicator
C l tCoolant
C l tCoolant
C l tCoolant
C l tCoolantsEthylene Glycol (C2H6O2) is the primary coolant Ethylene Glycol (C2H6O2) is the primary coolant utilized in engines today.
Typical mixtures are 50% water and 50% ethylene l lglycol.
Chemical inhibitors, that are alkaline, are added to the coolant to eliminate acid formation.
Ethylene glycol raises the boiling point and lower the freezing point.
Additives reduce cavitation – a major source of cylinder wall pitting.
Other additive inhibit rust and corrosionOther additive inhibit rust and corrosion.
Ai C l d S tAir-Cooled System
I i l d t t f i i d t In an air cooled system a current of air is made to blow past the outside of the cylinder barrel whose outer surface area has been considerably i d b idi li fiincreased by providing cooling fins.This method will increase the rate of cooling
This method is mainly applicable toengines in motor cycles small carsengines in motor cycles, small cars,airplanes and combat tanks where themotion of vehicle gives velocity to cool theengineg