Engine Cooling System

Construction & Working About Cooling System

Introduction:

Cooling system is used in the engine to run the engine by keeping cool, and working it without getting over heat.

Type of cooling systems:

·         According to air cooling

·         According to water cooling

Air cooling:

Most modern internal combustion engines are cooled by a closed circuit carrying liquid coolant through channels in the engine block and cylinder head, where the coolant absorbs heat, to a heat exchanger or radiator where the coolant releases heat into the air. Thus, while they are ultimately cooled by air, because of the liquid-coolant circuit they are known as water-cooled. In contrast, heat generated by an air-cooled engine is released directly into the air. Typically this is facilitated with metal fins covering the outside of the cylinders which increase the surface area that air can act on.

In all combustion engines, a great percentage of the heat generated (around 44%) escapes through the exhaust, not through either a liquid cooling system nor through the metal fins of an air-cooled engine (12%). About 8% of the heat energy finds its way into the oil, which although primarily meant for lubrication, also plays a role in heat dissipation via a cooler.

Advantage
It keeps your engine cold.
Air cooling is a method of dissipating.

It works by making the object to be cooled have a larger surface area or have an increased flow of air over its surface, or both

In the case of the latter it is done by using a fan blowing into or onto the object one wants to cool. In many cases the addition of fins adds to the total surface area making that makes for greater efficiency in cooling.

Disadvantage
It does not work sometimes.

It is not very efficient as it require atmosphere air.

Water cooling:

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 Cooling System

There are two types of water cooling system:

 1. 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.

2. Pump Circulation System

In this system circulation of water is obtained by a pump. This pump is driven by means of engine output shaft through V-belts. Engine

Components consist in water cooling system:

1. Source of heat

2. Radiator

3. Water pump

4. Thermostat

5. Fan

6. Expansion tank

                                   

Construction and Working of Thermostat

Thermostat

The thermostat's main job is to allow the engine to heat up quickly, and then to keep the engine at a constant temperature. It does this by regulating the amount of water that goes through the

radiator. At low temperatures, the outlet to the radiator is completely blocked - all of the coolant is recirculated back through the engine.Once the temperature of the coolant rises to between 82 - 91 C (180 and 195 F), the thermostat starts to open, allowing fluid to flowthrough the radiator.By the time the coolant reaches 93 - 103 C (200 to 218 F), the thermostat is open all the way. If you ever have the chance to test one, a thermostat is an amazing thing to watch because what it does seems impossible. You can put one in a pot of boiling water on the stove. As it heats up, its The open and closed positions of a thermostat© NSW DET 2008 Page 21 of 33valve opens about an inch, apparently by magic! If you'd like to try this yourself, go to a car parts store and buy one for a couple of bucks. The secret of the thermostat lies in the small cylinder located on the engine-side of the device. This cylinder is filled with a wax that begins to melt at around 180 F (different thermostats open at different temperatures, but 180 F is a common one). A rod connected to the valve presses into this wax. When the wax melts, it expands significantly, pushing the rod out of the cylinder and opening the valve. This same technique is used in automatic openers for greenhouse vents and skylights. In these devices, the wax melts at a lower temperature.

Water pump:

The size ofthe impelleris not critical, norisit criticalthatthe impeller have an anti‐cavitationscavitations plate on the backside of the impeller.Each ofthe pumps pictured will work well.The new water pumps have a small, stamped steel impeller and they also work well

Radiator cap:

1. Filler cap to access the cooling sytem.

2. Closure cap to keep coolant in the radiator.

3. Pressure cap to prevent overheating by pressurizing the systemto raise the boiling temperature of coolant and allow the automobile's engine to operate atmore efficient higher temp, eratures,

4. Pressure relief valve to safely and harmlessly vent excess pressure into the overflow jug, and

5. Vacuum relief/siphon relief/siphon valve to draw coolant from the overflow jug back into the radiator to prevent air from entering the system and allowing the coolant to performits function more efficiently.

Water Jackets:

Cooling water jackets are provided around the cylinder, cylinder head, valve seats and any hot parts which are to be cooled. Heat generated in the engine cylinder, conducted through the cylinder walls to the jackets. The water flowing through the jackets absorbs this heat and gets hot. This hot water will then be cooled in the radiator.

Advantages

(a) Uniform cooling of cylinder, cylinder head and valves.

(b) Specific fuel consumption of engine improves by using water cooling system.

(c) If we employ water cooling system, then engine need not be provided at the front end of moving vehicle.

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

Disadvantages

(a) It depends upon the supply of water.

(b) The water pump which circulates water absorbs considerable power.

(c) If the water cooling system fails then it will result in severe damage of engine.

(d) The water cooling system is costlier as it has more number of parts. Also it requires more maintenance and care for its parts.