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