Question

what is the main difference between an internal combustion engine and an external combustion engine

Answer 1

What is Internal Combustion Engine:-

In an internal combustion engine, the working fluid consists of a combustible fluid placed inside a cylinder these engines, the fluid undergoes combustion inside the cylinder and expands.

What is External Combustion Engine:-

In an external combustion engine, the combustion takes place outside the cylinder. Heat then needs to be transferred to the cylinder where work is done. Steam engines are an example of external combustion 
engine.

Answer 2

Difference between IC engine and External combustion engine
1. External combustion engine run smoothly and silently where of internal combustion engines are very noisy. Noise produce from continuous explosions inside the cylinder of IC engine.

2. Working pressure and temperature in external combustion is low whereas in I.C engines working pressure and temperature is high.

3. External combustion engines have 15-20% efficiency whereas Internal combustion engine have 35-60%.

4. An external combustion engine requires a boiler and other components to transfer energy.Thus it is a heavy engine whereas in an I.C engine parts are light and compact.
hope it helps!!!!!