The main difference between an external combustion engine and an internal combustion engine lies in the location where the actual combustion takes place.
External Combustion Engine: In an external combustion engine, such as a steam engine or a Stirling engine, the combustion occurs outside the engine itself. Fuel is burned in a separate furnace or boiler, which generates heat. This heat is then transferred to a working fluid (e.g., water or gas) that undergoes expansion in the engine, driving a piston or a turbine to produce mechanical energy.
Internal Combustion Engine: In an internal combustion engine, such as a gasoline or diesel engine, the combustion of fuel occurs inside the engine itself. A mixture of fuel and air is ignited within the combustion chamber, resulting in a rapid release of energy. This energy drives the piston, which converts the expanding gases into mechanical work.
In terms of efficiency, internal combustion engines are generally more efficient at converting heat energy into mechanical energy compared to external combustion engines. The reasons are as follows:
Higher Thermal Efficiency: Internal combustion engines can achieve higher thermal efficiencies due to their ability to operate at higher compression ratios. This allows for more complete combustion of the fuel-air mixture and reduces energy losses.
Direct Conversion: In internal combustion engines, the heat energy is directly converted into mechanical energy by the piston, without the need for intermediate steps like heating a working fluid. This direct conversion results in fewer energy losses.
Compact and Lightweight: Internal combustion engines are typically more compact and lightweight than external combustion engines, making them more suitable for various applications such as automobiles and portable devices. The compact design helps reduce heat loss and improve efficiency.
It's worth noting that the efficiency of internal combustion engines can vary depending on factors such as engine design, operating conditions, and the specific fuel being used. Ongoing advancements in engine technology, such as hybrid systems and improved combustion techniques, aim to further enhance the efficiency of internal combustion engines.