Chapter 2 – Cooling SystemPrepared by MUHAMMAD HILMI BIN ZAID

SUMMARY The topic covers basic theoretical

knowledge on engine cooling systems. Areas involving type, function and working principles of cooling systems and its components. Coolant or anti-freeze is also discussed in this topic.

SYLLABUS Understand function, construction and operation of

cooling system and its components Describe types of cooling system:

Air-cooled Water-cooled

Explain the function, construction and operation of water cooling system and its components: Radiator Water pump Thermostat Radiator pressure cap Radiator fan Water temperature indicator Expansion tank

Understand different types of coolants/anti-freeze Explain various types of coolants/anti-

freeze: Ethylene glycol Propylene glycol Organic Acid Technology Hybrid Organic Acid Technology

INTRODUCTION

Today’s engines create a

tremendous amount of heat.

Most of this heat is generated

during combustion.

Metal temperatures

around the combustion

chamber can run as high as 1,000°F

(537.7°C).

This heat can destroy the

engine and must be removed.

Purpose of Cooling System Purpose - To remove the

excessive heat from the engine to avoid components in the engine damaged.

Too much cooling is also not desirable because it reduces the thermal efficiency.

The engine will perform best in the desired operating temperature.

TYPES OF COOLING SYSTEM Air-cooled system Water-cooled system

Air-cooled System Air cooled system is generally used in small

engines such as 15-20 kW and in aero plane engines.

In this system fins or extended surfaces are provided on the cylinder walls, cylinder head, etc.

Heat generated due to combustion in the engine cylinder will be conducted to the fins and when the air flows over the fins, heat will be dissipated to air.

Factors affect cooling efficiency The amount of heat

dissipated to air depends upon :1) Amount of air flowing

through the fins.2) Fin surface area.3) Thermal conductivity of

metal used for fins

Advantages System is light because radiator/pump

is absent. There are no leakages. Coolant and antifreeze solutions are not

required. Can be used in cold climates, where if

water is used it may freeze.

Disadvantages Comparatively it is less efficient. It is used in aero planes and motorcycle

engines where the engines are exposed to air directly.

Water-cooled System In this method, cooling water jackets are

provided around the cylinder, cylinder head, valve seats etc.

The water when circulated through the jackets, it absorbs heat of combustion.

This hot water will then be cooling in the radiator partially by a fan and partially by the flow developed by the forward motion of the vehicle.

The cooled water is again recirculated through the water jackets.

Types of water-cooled system Thermo Siphon System

In this system the circulation of water is due to difference in temperature (i.e. difference in densities) of water. So in this system pump is not required but water is circulated because of density difference only.

Pump Circulation System In this system circulation of water is

obtained by a pump. This pump is driven by engine output shaft through belts.

Thermo Siphon System

Pump Circulation System

Working principle of water-cooled system.

Heat is removed from around the

combustion chambers by a

coolant circulating inside the engine.

A pump moves the coolant through the engine block

and then through the

cylinder head.

The coolant flows to the top of the radiator and loses heat

as it flows down through the

radiator.

Ram air and the airflow from the

cooling fan move through

the radiator and cool the coolant.

The cooled coolant leaves

the radiator and enters the

water pump then its sent back through the engine.

Working principle of water-cooled system.

Components Radiator Water pump Thermostat Radiator pressure cap Expansion tank Radiator fan Water temperature indicator

Radiator The radiator is basically a heat

exchanger, transferring heat from the engine to the air passing through it.

The radiator itself is a series of tubes and fins (collectively called the core) that expose the coolant’s heat to as much surface area as possible.

Attached to the sides or top and bottom of the core are plastic or aluminum tanks.

One tank holds hot coolant and the other holds the cooled coolant.

Cores are normally comprised of flattened aluminum tubes surrounded by thin aluminum fins.

The fins conduct the heat from the tubes to the air flowing through the radiator.

Most radiators have draincock or plugs near the bottom.

Coolant is added at the radiator cap or the recovery tank.

Design of radiators Radiators are normally based on one of

two designs: cross flow or down flow. In a cross-flow radiator, coolant enters

on one side, travels through tubes, and collects on the opposite side.

In a down-flow radiator, coolant enters the top of the radiator and is drawn downward by gravity.

Water Pump The heart of the cooling

system is the water pump. Its job is to move the coolant

through the system. Typically the water pump is

driven by the crankshaft through pulleys and a drive belt

The pumps are centrifugal-type pumps with a rotating impeller to move the coolant.

The shaft is mounted in the water pump housing and rotates on bearings.

The pump has a seal to keep the coolant from passing through it.

The inlet of the pump connects to the lower radiator hose, and its outlet connects to the engine block.

Thermostat A thermostat is a temperature-

responsive coolant flow control valve. It controls the temperature and amount

of coolant entering the radiator. Most thermostats are located on the top

and front of an engine.

How it works? While the engine is cold, the thermostat

remains closed, allowing coolant to only circulate in the engine.

This allows the engine to uniformly warm up. When the coolant reaches a specified

temperature, the thermostat begins to open and allows coolant to flow to the radiator.

The hotter the coolant gets, the more the thermostat opens, sending more coolant to the radiator.

Thermostat Closed Thermostat Open

When engine is cold When engine reaches the specified temperature

The thermostat permits fast engine warm-up.

Slow warm-up causes condensation in the crankcase, which can cause the formation of sludge.

Radiator Pressure Cap Radiator caps keep the coolant from

splashing out of the radiator. They also keep the coolant’s temperature

within a desired range by keeping the coolant pressurized to a specified level.

The pressure raises the boiling point of the coolant.

This allows the coolant to reach higher-than-normal temperatures without boiling.

This also allows the coolant to absorb more heat from the engine and more heat to transfer from the radiator core to outside air.

This is due to a basic law of nature that states that the greater the heat difference is between two objects, the faster the heat of the hotter object will move to the cooler object.

The pressure in the system is regulated by a pressure relief or vent valve in the radiator cap.

When the pressure reaches the pressure rating of the cap, it pushes up on the spring in the pressure relief

valve.

This opens the valve and allows excess pressure to exit the radiator.

When enough pressure has been released, to drop system pressure below the cap’s rating, the spring

will close the pressure relief valve.

Expansion tank All late-model cooling systems have an

expansion or recovery tank. Cooling systems with expansion tanks are

called closed-cooling systems. They are designed to catch and hold any

coolant that passes through the pressure cap.

How it works?

The vacuum release valve

inside the pressure cap

opens and the coolant in the

expansion tank is drawn back into

the cooling system.

The coolant passes to an

expansion tank. When the engine is shut down, the coolant begins to

shrink.

As the engine warms up, the

coolant expands. This eventually

causes the pressure cap to

release.

Radiator Fan The efficiency of the cooling system

depends on the amount of heat that can be removed from the system and transferred to the air.

At high speeds, the ram air through the radiator should be sufficient/enough to maintain proper cooling.

At low speeds and idle, the system needs additional air. This air is delivered by a fan.

The fan may be driven by the engine, via a belt, or driven by an electric motor.

A belt-driven fan is bolted to a pulley on the water pump and turns constantly with the engine.

Thus, belt-driven fans always draw air through the radiator from the rear.

Problem of belt-driven fan Fan air is usually only necessary at idle

and low-speed operation. Horsepower is required to turn the fan.

The operation of a cooling fan reduces the available horsepower to the drive wheels and the fuel economy of the vehicle.

Fans are also very noisy at high speeds, adding to driver fatigue and total vehicle noise.

Solution? To eliminate this power waste during times

when fan operation is not needed, many of today’s belt-driven fans operate only when the engine and radiator heat up.

This is accomplished by a fan clutch. When the engine and fan clutch are cold, the

fan moves independently from the clutch and moves little air.

In most cases, the clutch slips at high speeds; therefore, it is not turning at full engine speed

Water Temperature Indicator Coolant temperature indicators alert the

driver of an overheating condition. These indicators are a temperature

gauge and/or a warning light. A temperature sensor is threaded into a

bore in a water jacket.

Coolant/Anti-freeze Engine coolant is a mixture of water and

antifreeze/coolant. Water alone has a boiling point of 100°C and a

freezing point of 0°C at sea level. Engine coolant has a higher boiling temperature

and a lower freezing point than water. The exact boiling or freezing temperatures

depend on the mixture. The typical recommended mixture is a 50/50

solution of water and antifreeze/coolant.

Types of Coolant/Anti-freeze Ethylene glycol Propylene glycol Organic acid technology (OAT) Hybrid organic acid technology (HOAT)

Ethylene glycol This is the most commonly used

antifreeze/coolant. It is green in color and provides good

protection regardless of climate, but it is poisonous.

Should be handled carefully and disposed of properly.

Sweet tasting (accidental ingestion or as a murder weapon)

Propylene glycol This type has the same basic characteristics

as ethylene glycol-based coolant but is not sweet tasting.

Less harmful to animals and children. (non-toxic antifreeze)

Used when ethylene-glycol is inappropriate such as in food processing system or water pipes system in homes.

Propylene glycol-based coolants should not be mixed with ethylene glycol.

Organic acid technology (OAT) This coolant is also environmentally

friendly and contains zero phosphates or silicones.

This orange coolant is often referred to by a brand name “DEX-COOL” and is used in all late-model GM vehicles.

Extended service life of 240 000 km.

Hybrid organic acid technology (HOAT) This is similar to OAT coolant but has

been enhanced with additives (silicates or phosphates) that make the coolant less abrasive to water pumps

Advantages of Water-Cooled System Uniform cooling of cylinder, cylinder head

and valves. Specific fuel consumption of engine improves

by using water cooling system. If we employ water cooling system, then

engine need not be provided at the front end of moving vehicle.

Engine is less noisy as compared with air cooled engines, as it has water for damping noise.

Disadvantages of Water-Cooled System It depends upon the supply of water. The water pump which circulates water

absorbs considerable power. If the water cooling system fails then it

will result in severe damage of engine. The water cooling system is high cost as

it has more number of parts. Also it requires more maintenance and

care for its parts.

Exercise Why is cooling necessary for IC engine? Explain in brief the methods of cooling

of IC engine. Differentiate between air cooling system

and water cooling system. What is the purpose of the fins in an air-

cooled system? Explain the function of thermostat?

Thank You