The main advantages of an internal combustion engine over the external combustion engine are given below :
1. An internal combustion engine (or petrol engine) is smaller and lighter. On the other hand, an external combustion engine (or steam engine) is big and heavy.
A petrol engine is smaller, lighter, and occupies less space because it does not have a furnace or a boiler. The small size of a petrol engine is due to the fact that only a small amount of fuel (that is, petrol) is introduced into the cylinder and burnt at a time. This eliminates the need of having big boilers as in a steam engine. Due to its small size and lightness, a petrol engine can be used to run even small vehicles like cars and scooters which a steam engine cannot do. Thus, the small size of a petrol engine is an important advantage over the steam engine. And being small, a petrol engine also occupies much less space than a steam engine.
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2. An internal combustion engine (or petrol engine) can be started at once at a moment’s notice. On the other hand, an external combustion engine (or steam engine) takes a long time to start.
Since petrol burns at once, so a petrol engine can be started at a moment’s notice. The production of steam by burning coal and boiling water, takes a long time due to which a steam engine takes a long time to be put in action.
3. An internal combustion engine (or petrol engine) is quite safe to use. On the other hand, an external combustion engine (or steam engine) is not very safe to use.
In a petrol engine, the high pressure gases are produced in the cylinder at short intervals and utilized as soon as they are formed. This makes the petrol engine safe from bursting. In a steam engine, however, the high pressure steam is to be maintained in the boiler all the time. So, an excess of steam pressure can lead to the bursting of boiler. This makes a steam engine quite unsafe.
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4. An internal combustion engine (or petrol engine) has higher efficiency. On the other hand an external combustion engine (or steam engine) has a lower efficiency.
The efficiency of an internal combustion engine (or petrol engine) is about 40%, which means that an internal combustion engine can convert 40 per cent of heat energy into work. The efficiency of an external combustion engine (or steam engine) is only about 20%, which means that an external combustion engine can convert 20 per cent of heat energy into work. One of the reasons for the higher efficiency of a petrol engine is that the temperature produced by the burning of petrol in a cylinder is higher than that of steam produced in boilers. Another reason is that because of the small size of petrol engine, the loss of heat from its surface is much less than that from a steam engine, which has a large surface area.