A characteristic 4 cylinder vehicle traveling along the highway at around the speed of 50 miles per hour, will generate 4000 controlled explosions per minute inside the engine as the spark plugs burn the fuel in every cylinder to drive the vehicle on the road. Obviously, these explosions generate a huge amount of heat and, if not controlled, will destroy an engine in a matter of minutes. To control these great temperatures is the occupation of the cooling system.
The engine runs best at an optimum temperature. If the engine temperature is too low, fuel economy will suffer and emissions will rise. If the temperature is permitted to get very hot for a long time, the engine will self-destruct.
Types of Cooling System
Actually, there are two types of cooling systems found on motor vehicles.
Air Cooling
The heat is transferred to the air present in the atmosphere through the extended surfaces called fins.
Liquid Cooling
The heat is transferred to a coolant and this coolant operates on a closed cycle.
Working of a Cooling System
The main components of a cooling system are given below:
ü Water pump to circulate the coolant
ü Thermostat valve to control the temperature of the coolant
ü Radiator to cool the coolant
ü Radiator cap to control the pressure in the system
ü Coolant
ü Cooling Fan
ü Interconnecting hoses to transfer the coolant from engine to radiator
Cooling cycle refers to the flow of water through the whole system which is driven by the water pump.
The schematic of water flow is given as:
Thermostat valve is placed between radiator and engine. Thermostat valve opens fully at a higher temperature and closes at a lower temperature.
Water Pump
A water pump is a simple device that will keep the coolant moving as long as the engine is running. It is usually mounted on the front of the engine and turns whenever the engine is running. The water pump is driven by the engine through one of the following:
ü A fan belt that will also be responsible for motivating an added component like an alternator or power steering pump
ü The timing belt that is also responsible for driving one or more camshafts
Thermostat Valve
Thermostat valve controls the amount of water going in the radiator to maintain a certain preset temperature of the coolant. The thermostat is simply a valve placed between the engine and the radiator that measures the temperature of the coolant and, if it is hot enough, opens to allow the coolant to
flow through the radiator. Subject to the situation that the coolant is not at a temperature high enough, the flow to the radiator is blocked and fluid is directed to a bypass system that allows the coolant to return directly back to the engine.
The bypass system allows the coolant to keep moving through the engine to balance the temperature and avoid hot spots. As the flow to the radiator is jammed, the engine will reach working temperature earlier and, on a cold day, will let the heater to begin bringing hot air to the interior more rapidly.
Radiator
The radiator has two main types:
Vertical flow Radiator
Crossflow radiator
Vertical Flow Radiator
In this type of radiator, the inlet and outlet valves of the radiator are placed at the top and bottom of the radiator.
Cross Flow Radiator
In this type of radiator, the inlet and outlet valves are placed at right and left sides of the radiator.
Working Principle
A radiator is a type of heat exchanger which is used to cool the water coming from the engine. The hot water travels in the parallel tubes in the radiator and some extended surfaces are attached to those tubes which are called fins to increase the surface area.
A fan is placed in front of the radiator so that forced convection can take place. In this way, heat is transferred by convection from water to the ambient air. If the car has a heating system, the air coming from radiator can be used in heater by the process.
Radiator Cap
Radiator cap performs two important tasks in a radiator:
· To increase the boiling point of the coolant
· To maintain the specific pressure in the radiator
Increasing boiling point of the coolant
When the pressure is increased, the boiling point of any liquid increases as well. The same thing happens in the radiator. The radiator cap increases the pressure which consequently raises the boiling temperature.
Radiator cap has two valves has two valves in it:
o Pressure valve
o Vacuum valve
When the fluid in the radiator has a higher temperature, it tries to expand which ultimately increases the pressure in the radiator. Now the only place where this pressure can be released is radiator cap. So, the spring on pressure valve determines the maximum amount of pressure in the system.
If the pressure is raised above this point the spring will be compressed causing the valve to open and let the fluid escape to the reservoir. When the radiator cools back down, a vacuum is created in the system which opens the vacuum valve and the water comes back to make up the efficiency of coolant.
Cooling Fan
The speed of the cooling fan should be related to the amount of hot water coming in the radiator to save the energy. Its speed should be directly proportional to the amount of cooling required. But usually, in most cars, the fan rotates with a constant speed.
Also, the fan should be kept working when the thermostat valve opens. It should not be directly connected to the electrical system of the car.
Coolant
The coolant must not freeze in the tubes at cold weather and it should not react with the system component. So, in order to achieve that target, following additives are added in water:
· Anti-freeze agents
· Anti-rust agents
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