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ENGINE COOLING SYSTEMS IN CARS

Department of Engineering and Technology

Date-15/10/2014

TERM PAPER REPORT ON

Submitted By: Yajurvendra Singh Tomar

B.Tech (Mechanical Engineering) 3rd Year

Roll No. : 120106287

System I.D: 2012011612

Submitted To: Mr Gomish Sharma

ContentsABSTRACT …II

1. INTRODUCTION …3

2. WORKING OF A COOLING SYSTEM …4

3. COMPONENTS OF COOLING SYSTEM …6

3.1. WATER JACKET …6

3.2. WATER PUMP …6

3.3. ENGINE FAN …6

3.4. VARIABLE SPEED FAN …7

3.5. FLEXIBLE BLADE FAN …7

3.6. ELECTRIC FAN …7

3.7. RADIATOR …8

3.8. EXPANSION TANK …8

3.9. THERMOSTAT …9

3.10. COOLING BYPASS PASSAGE …9

3.11. RADIATOR CAP …10

4. ANTIFREEZE AND COOLANT …11

4.1 ANTIFREEZE …11

4.2 TYPES OF ANTIFREEZE …12

List of FiguresFig 1: Engine Cooling System …3

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ABSTRACT

The following paper deals with the topic of Engine Cooling System in Cars, these systems are used in the cooling of the engines of the cars, was introduced around the early 1870s.It is mandatory in every engine to have its own cooling mechanism or system. The operation of the cooling system is to remove the excess heat from the engine. The removal of heat prevents the damage to parts and also keeps the engine at its normal pressure. The radiator is the main part of the cooling system. The paper begins with a brief introduction of cooling mechanism. The next part is about its components and its working. Then we study about its various components in details and their uses. In the last part we discuss about the fluids or coolant used in the system. Then finally we sum up to the Conclusion.

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1. Introduction

The burning air-fuel mixture in the engine cylinders may reach 4000°F [2200 °C] or higher. This means engine parts get hot. However, cylinder walls must not reach hotter than about 500°F [260°C], higher temperatures causes lubricating oil to break down and lose its lubricating ability. Other engine parts are also damaged. To prevent overheating, the cooling system removes the excess heat. The cooling system keeps the engine at its most efficient temperature at all speeds and operating conditions. It also helps bring the engine up to normal operating temperature as quickly as possible. In addition, the cooling system provides a source of heat for the passenger-compartment heater-and-air- conditioner.

Fig 1: Engine Cooling System

Cooling system uses five basic parts:-

1. Water Jacket2. Water Pump3. Thermostat4. Radiator5. Fan

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2. Working of a Cooling System

The cooling system is a system of parts and fluid that work together to control an engine’s operating temperature for optimal performance. The system is made up of passages inside the engine block and heads, a water pump and drive belt to circulate the coolant, a thermostat to control the temperature of the coolant, a radiator to cool the coolant, a radiator cap to control the pressure in the system, and hoses to transfer the coolant from the engine to the radiator.

The liquid that flows through a cooling system, antifreeze, or commonly referred to as coolant, withstands extreme hot and cold temperatures and contains rust inhibitors and lubricants to keep the system running smoothly.

Coolant follows a circulation path that begins with the water pump. The water pump’s impeller uses centrifugal force to draw coolant from the radiator and push it into the engine block. Pumps are usually fan, serpentine timing belt, or timing chain driven. Nowadays, they may even be driven electrically. If the water pump experiences a leak from the seal, a cracked housing, broken impeller or a bearing malfunction, it can compromise the entire cooling system, causing the vehicle to overheat.

As coolant flows through the system, it picks up heat from the engine before arriving at the thermostat. The thermostat is a valve that measures the temperature of the coolant and opens to allow hot fluid to travel to the radiator. If the thermostat becomes ‘stuck’ and quits working, it will affect the entire cooling system.

Once released by the thermostat, hot coolant travels through a hose to be cooled by the radiator. The antifreeze passes through thin tubes in the radiator. It is cooled as air flow is passed over the outside of the tubes. Depending upon the speed of the vehicle, airflow is provided by the vehicle’s movement down the road (ram air effect) and/or cooling fans. Radiator restrictions can compromise its ability to transfer heat. These can be either external air flow or internal coolant flow restrictions. A malfunctioning electric cooling fan or fan clutch can limit air flow across the radiator. Check/replace the fan clutch…the life expectancy of water pumps and fan clutches are about the same and share a common shaft. A failed fan clutch can cause severe damage to the water pump.

As coolant temperature increases, so does the pressure in the cooling system. This pressure is regulated by the radiator cap. Correct system pressure is

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required for proper water pump seal lubrication. Increasing the cooling system pressure raises the boiling point of the coolant. Each one pound of increased pressure raises the boiling point by 3˚F. If the pressure builds up higher than the set pressure point, a spring-loaded valve in the cap will release the pressure. If an engine has overheated, the radiator cap and thermostat should be replaced.

It is important to regularly inspect the condition of your cooling system’s belts and hoses. Soft hoses, oil soaked belts or cracked belts and hoses can have dire effects on the entire cooling system. Proper belt tension is also important.

Always refer to your manufacturer’s manual to determine the recommended coolant type for your vehicle. This and the proper mixture of coolant and distilled water are the lifeblood towards keeping your system running cool. Most parts retailers now offer a solution of premixed coolant and distilled water. While it may seem like an unnecessary added expense, the cleanliness of the premixed solution will pay off over time.

Mineral deposits and sediments from corroded or malfunctioning parts accumulate in the cooling system. Before performing a cooling system repair, it is recommended to flush the cooling system prior to installing any new parts. This is a task made even easier by using a flush-fill kit. Failure to flush the system will contaminate the new parts being installed and could lead to premature component failure.

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3. Components of cooling System

3.1. Water Jacket

The water jackets are open spaces between the cylinder walls and the outside shell of the block and head. Coolant from the water pump flows first through the block water jackets. Then the coolant flows up through the cylinder-head water jackets and back to the radiator.

3.2. Water Pump

Water pumps are impeller pumps. They attach to the front of the engine and are driven by a belt from the crankshaft pulley. The pump circulates as much as 7500 gallons (28,390 L) of coolant an hour. As the impeller rotates, the curved blades draw coolant from the bottom of the radiator. They force the coolant through the pump outlet to the water jackets.

The impeller shaft is supported on sealed bearings which never need lubrication. Seals prevent the coolant from leaking past the bearings. The water pump is driven by the fan belt. The water pump may also be driven by a single serpentine belt that also drives other components.

3.3. Engine Fan

The radiator sometimes needs additional airflow through it to prevent the engine from overheating. This usually occurs at idle and slow speed. At higher vehicle speeds, the air rammed through the radiator by the forward motion of the vehicle provides all the cooling that is needed. An engine fan or cooling fan pulls the additional air through the radiator. The fan may be either a mechanical fan or an electric fan.

Engines mounted longitudinally in rear-drive vehicles usually have a mechanical fan that mounts to the water-pump shaft. The fan is made of sheet steel or molded plastic. It has four to seven blades and turns with the water-pump impeller. A fan shroud around the fan directs the airflow. This increases the efficiency of the fan.

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3.4. Variable Speed Fan

Many longitudinal engines use a variable-speed fan driven through a fan clutch. The fan clutch is a temperature-controlled fluid coupling that mounts between the water-pump pulley and the fan. The air passing through the radiator strikes a thermostatic blade or spring on the front of the clutch. The temperature of the air causes the thermostatic device to bend. This operates a valve that allows silicone oil to enter or leave the fluid coupling.

When the engine is cold, the fluid coupling slips so the fan is not driven. This reduces noise and saves engine power. As the engine warms up, the thermostatic device causes more oil to enter the fluid coupling. Then the fan clutch begins to drive the fan.

3.5. Flexible Blade Fan

Another way to reduce the power needed to drive the fan and reduce fan noise is to use flexible blades on the fan. In operation, the blades slant or pitch of the blades decreases as fan speed increases. Centrifugal force flattens the blades so they take a smaller bite of air. This reduces noise and airflow, and the power needed to turn the fan.

3.6. Electric Fan

Transverse engines in front-drive vehicles usually have an electric fan. An electric motor turns the blades. A thermostatic switch turns on the fan only when needed. For example, in one engine, the switch turns on the fan when the coolant reaches 200°F [93°C]. It turns off the fan if the coolant drops below this temperature. On vehicles with air conditioning, turning on the air conditioning bypasses the thermostatic switch. The fan runs all the time when the air conditioner is on. The fan is turned on and off by the electronic control module (ECM) in many vehicles with an electronic engine control system.

Most fans, mechanical and electric, are pull-type fans. They mount behind the radiator and pull air through it.

Some cars also have a push-type fan. It mounts in front of the radiator and pushes air through it.

An electric fan drains less power from the engine and creates less noise than a mechanical fan. Also, there is no fan belt to inspect, adjust, or replace.

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3.7. Radiator

The radiator is a heat exchanger that removes heat from engine coolant passing through it. The heat transfers from the hot coolant to the cooler outside air.

An automotive radiator has three main parts. These are a radiator core, and inlet and outlet tanks. The cores are usually made of aluminium. The tanks may be made of plastic or metal. The core has two sets of passages, a set of tubes, and a set of fins attached to the tubes. The tubes run from the inlet tank to the outlet tank. Coolant flows through the tubes and air flows between the fins. The hot coolant sends heat through the tubes to the fins. The outside air passing between the fins picks up and carries away the heat. This lowers the temperature of the coolant.

The coolant flows from the upper tank down through the tubes to the lower tank. Most cars use a cross-flow radiator. The tubes are horizontal so the coolant flows from the inlet tank horizontally to the outlet tank. The cross-flow radiator takes up less space from top to bottom. A car with a cross- flow radiator can have a lower hood line.

A typical radiator in a car with factory-installed air conditioning has seven fins per inch [25.4 mm]. Heavy-duty radiators may have more fins and more rows of tubes. These provide greater cooling capacity to handle additional heat loads such as those caused by the air conditioner or turbocharger.

On vehicles with an automatic transaxle or transmission, the outlet tank has a transmission oil cooler. Many radiators have a drain valve in the bottom. Radiators with filler neck in the top seal the opening with a radiator pressure cap.

3.8. Expansion Tank

Most cooling systems have a separate plastic reservoir or expansion tank. It is partly filled with coolant and connected by an overflow or transfer tube to the radiator filler neck. As the engine heats up, the coolant expands and flows through the transfer tube into the expansion tank. When the engine is turned off and cools, the coolant contracts. This creates a partial vacuum in the cooling system. Then the vacuum siphons coolant from the expansion tank back through the transfer tube and into the radiator.

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The cooling system with an expansion tank is a closed system. Coolant can flow back and forth between the radiator and the expansion .tank as the engine heats and cools, this keeps the cooling system filled for maximum cooling efficiency. The expansion tank also eliminates air bubbles from the coolant. Coolant without air bubbles can handle more heat.

3.9. Thermostat

The thermostat is a heat-operated valve that regulates coolant temperature. It does this by controlling coolant flow from the engine to the radiator. The thermostat is in the coolant passage between the cylinder head and the radiator. The valve in the thermostat opens anti doses as coolant temperature changes. When the engine is cold, the thermostat closes. As the engine warms up, the thermostat opens. This prevents or allows coolant to flow through the radiator.

By closing the passage to the radiator when the engine, is cold, the engine warms up more quickly. Engine heat stays in the engine instead of being carried to the radiator. This shortens warmup time, wastes less fuel, and reduces exhaust emissions. After warmup, the thermostat keeps the engine running at a higher temperature than it would without a thermostat. The higher operating temperature improves engine efficiency and reduces exhaust emissions.

There are several types of automotive thermostats. A heat-sensitive wax pellet operates most thermostats; it expands with increasing temperature to open the valve.

The thermostat opens at a specific temperature or thermostat rating. This number is usually stamped on the thermostat. Two common ratings are 185°F [85°C] and 195°F |91°C], most thermostats begin to open at their rated tem-perature. They are fully open about 20°F [11°C] higher. For example, a 195°F [91°C] starts to open at that temperature. It is fully open about 215°F [102°C].

3.10. Cooling Bypass Passage

Most engines have a small coolant bypass passage. The bypass may be an external bypass hose on the top of the water pump, or an internal passage. It permits some coolant to circulate within the cylinder block and head when the engine is cold and the thermostat closed. This provides equal warming of the cylinders and prevents hot spots.

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Some engines use a blocking-bypass thermostat. It has a bypass valve that restricts or closes the bypass passage as the thermostat opens after engine warmup. This prevents coolant from continuing to flow through the bypass.

3.12. Radiator Cap

Cooling systems are sealed and pressurized by a radiator pressure cup. Sealing reduces coolant loss from evaporation and allows the use of an expansion tank. Pressurizing raises the boiling temperature of the coolant, thereby increasing cooling efficiency.

At normal atmospheric pressure, water boils at 212°F [100°C], if air pressure increases, the boiling point also increases. For example, if the pressure is raised by 15 psi [103 kPa) over atmospheric pressure, the boiling point is raised to about 260°F | I27°C], Every I psi [7 kPa| increase in pressure raises the boiling point of water about 3 1/4°F [ 1,8°CJ. This is the principle on which the pres-surized cooling system works.

As the pressure in the cooling system goes up, the boiling point of the coolant goes higher than 212 F |100°C|. There is a greater difference between coolant temperature and outside air temperature. The hotter the coolant, the faster heat moves from the radiator to the cooler passing air. Pressurizing the cooling system also increases water-pump efficiency.

Normal pressure in the cooling system is determined by the vehicle manufacturer. Less than normal pressure allows coolant to be lost and may cause boiling. Too much pressure can damage the radiator and blow off hoses. The radiator cap has a pressure-relief valve (Fig. 25-20) to prevent excessive pressure. When the pressure goes too high, it raises the valve. Excess pressure and coolant then escape into the expansion tank.

The radiator cap also has a vacuum-relief valve. It protects the system from developing a vacuum that could collapse the radiator. When the engine is shut off and begins to cool, the coolant contracts. Cold coolant takes up less space than hot coolant. As the volume of coolant decreases, a vacuum develops in the cooling system. This pulls open the vacuum valve. Coolant from the expansion tank then flows back into the cooling system.

The radiator pressure cap must seal tightly if the pressurized cooling system is to work properly. When the cap is put on the filler neck, the locking lugs on the

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cap fit under the filler-neck flange. The cam locking surface of the flange tightens the cap as it is turned clockwise. This also preloads the pressure-relief valve spring.

4. Antifreeze and Coolant

4.1. Antifreeze

Antifreeze is a chemical additive which lowers the freezing point of a water-based liquid. An antifreeze mixture is used to achieve freezing-point depression for cold environments and also achieves boiling-point elevation ("anti-boil") to allow higher coolant temperature

Most automotive engines are "water"-cooled to remove waste heat, although the "water" is actually antifreeze/water mixture and not plain water. The term engine coolant is widely used in the automotive industry, which covers its primary function of convective heat transfer for internal combustion engines. When used in an automotive context, corrosion inhibitors are added to help protect vehicles' radiators, which often contain a range of electrochemically incompatible metals (aluminium, cast iron, copper, brass, solder, et cetera). Water pump seal lubricant is also added.

Antifreeze was developed to overcome the shortcomings of water as a heat transfer fluid. In some engines freeze plugs (engine block expansion plugs) are placed in areas of the engine block where coolant flows in order to protect the engine from freeze damage if the ambient temperature drops below the freezing point of the antifreeze/water mixture. These should not be confused with core plugs, whose purpose is to allow removal of sand used in the casting process of engine blocks (core plugs will be pushed out if the coolant freezes, though, assuming that they adjoin the coolant passages, which is not always the case).

On the other hand, if the engine coolant gets too hot, it might boil while inside the engine, causing voids (pockets of steam), and leading to localized hot spots and the catastrophic failure of the engine. If plain water were to be used as an engine coolant, it would promote galvanic corrosion. Proper engine coolant and a pressurized coolant system can help obviate the problems which make plain water incompatible with automotive engines. With proper antifreeze, a wide temperature range can be tolerated by the engine coolant, such as −34 °F (−37 °C) to +265 °F (129 °C) for 50% (by volume) propylene glycol diluted with water and a 15 psi pressurized coolant system.

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Early engine coolant antifreeze was methanol (methyl alcohol), still used in windshield washer fluid. As radiator caps were vented, not sealed, the methanol was lost to evaporation, requiring frequent replenishment to avoid freezing of the coolant. Methanol also accelerates corrosion of the metals, especially aluminium, used in the engine and cooling systems. Ethylene glycol was developed, and soon replaced methanol as an engine cooling system antifreeze. It has a very low volatility compared to methanol and to water.

Fluid - Freezing Point - Boiling Point

Pure Water: 0 C / 32 F - 100 C / 212 F

50/50 mix of C2H6O2/Water: -37 C / -35 F - 106 C / 223 F

70/30 mix of C2H6O2/Water: -55 C / -67 F - 113 C / 235 F

4.2. Types of Antifreeze

There are two types of ethylene-glycol antifreeze, high silicate and low silicate. This refers to the amount of silicone silicate inhibitor added to the ethylene glycol. Most automotive engines use high-silicate antifreeze. It protects aluminium parts. Without this protection, aluminium flakes from the water jackets of an aluminium cylinder head may clog the radiator.

Low-silicate antifreeze is used in diesel or gasoline engines with cast-iron cylinder block and heads. The recommended antifreeze is listed in the vehicle owner’s manual.

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CONCLUSIONCooling system is one of the most important parts of the automobile; it

dissipates the extra heat out of the engine which can damage the various

components of the engine. The temperature of the engine reaches high

enough to weld the piston with the cylinder which can damages the engine.

So there is a provision of cooling system which keeps the various

components of the engine cool and safe. Cooling system is of two type : Air

cooling and Liquid cooling system. Air cooling system is mostly used in old

cars and bikes. It is not suitable for the engines which dissipates large

amount of heat whereas liquid cooling is the most reliable cooling system

used mostly in modern cars. The mixture of water and ethylene glycol is

used in the system. Ethylene glycol is mixed in water because water freezes

in winters or in the region having temperature below freezing point, so

ethylene glycol increases the freezing point of the water.

So cooling system plays a vital role as a part of an automobile to keep it

working with full efficiency.

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BIBLIOGRAPHY

Cooling Systems in Automobiles & Cars(IJEAT)-ISSN: 2249 – 8958, Volume-2, Issue-4, April 2013

Automotive Mechanics William by H Crouse and Donald L Anglin www.howacarworks.com/basics/how-an-engine-cooling-system-works http://westislandgarage.com

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