Air cooling engine:

It’s also known as “Direct cooling system” because of direct contact of air with the engine cylinder head and engine cylinder i,e air flows across the external surfaces of engine cylinder and engine cylinder head to remove the necessary heat. This is how the heat dissipates from the engine.

We know that the more heat transfer area the more heat transfer rate. So we have to increase the surface area of the cylinder and cylinder head. How we do achieve this is by providing metallic fins on the cylinder and cylinder head. These metallic fins are produced by machining. It should be noted that an arrangement of seperate cylinders will be use in this cooling system so that air flows right around each cylinder increasing the contact area for air.

The amount of heat dissipated depends upon:

1. Area of cooling surface in contact with the air.                                                                   2. Mass flow rate of air.                                     3. Temperature difference between cylinder and area.                                               4. Conductivity of metal.

Advantages of Air Cooled Engines:

1. Its design of air-cooled engine is simple because of absence of other parts that we need in liquid cooling system. 
2. It is lighter in weight than water-cooled engines due to the absence of water jackets, radiator, circulating pump and the weight of the cooling water. 

3. It is cheaper to manufacture. 

4. It needs less care and maintenance. 

5. This system of cooling is particularly advantageous where there are extreme climatic conditions in the arctic ( where liquid gets freeze ) or where there is scarcity of water as in deserts. 

6. No risk of damage from frost, such as cracking of cylinder jackets or radiator water tubes.

7. No danger of coolant leakage, coolant freezing, etc.

Disadvantages of Air Cooled Engine:

1. Relatively large amount of power is 

used to drive the cooling fan.

2. Engines give low power output.

3. Cooling fins under certain conditions 

may vibrate and amplify the noise level.

4. Cooling is not uniform.

5. Engines are subjected to high 

working temperature.