In an I.C. engine, fuel is inside the cylinder.

An internal combustion (I.C.) engine is a type of engine that converts the chemical energy stored in fuel into mechanical energy. It operates by burning the fuel inside the combustion chamber, which is typically a cylinder. The fuel is the substance that is ignited to produce the necessary energy for the engine to function.

Explanation:
- Fuel: Fuel is a substance or material that is used to produce energy through combustion. In the context of an I.C. engine, the fuel is typically a hydrocarbon-based liquid or gas, such as gasoline or diesel.
- Combustion Chamber: The combustion chamber is the space inside the cylinder where the fuel is burned. It is designed to facilitate the controlled combustion process and maximize the efficiency of energy conversion.
- Fuel Injection: In modern I.C. engines, the fuel is injected into the combustion chamber in a precise manner. This injection process is controlled by the engine's fuel injection system, which ensures the proper fuel-air mixture for combustion.
- Ignition: Once the fuel is injected into the combustion chamber, it needs to be ignited to start the combustion process. This is typically achieved using spark plugs in gasoline engines or compression ignition in diesel engines.
- Combustion Process: When the fuel is ignited, it undergoes a combustion process where it reacts with oxygen in the air. This reaction releases energy in the form of heat, which causes an increase in pressure inside the combustion chamber.
- Expanding Gases: The heat and pressure generated by the combustion process cause the gases inside the combustion chamber to expand rapidly. This expansion forces the piston to move, which in turn drives the crankshaft and ultimately produces mechanical energy.
- Exhaust: After the combustion process is complete, the burned fuel and the by-products of combustion, such as carbon dioxide and water vapor, are expelled from the combustion chamber through the exhaust system.

In summary, the fuel in an I.C. engine is located inside the cylinder, where it undergoes combustion to produce the energy required for the engine to operate.