Final answer:
Combustion in an internal combustion engine is maintained by the heat retained within the combustion chamber or cylinder, which ignites the air-fuel mixture and drives the piston.
Step-by-step explanation:
The correct answer is option 'the combustion chamber or cylinder'. After ignition of the fuel-oil and air, combustion is maintained by retained heat in the combustion chamber or cylinder. In the context of an internal combustion engine, the combustion process begins when the air-fuel mixture is ignited, leading to a rapid increase in temperature.
This temperature rise is so quick that the cylinder volume does not change appreciably during the process, leading to a sharp increase in pressure. This pressure then drives the piston down, which in turn, rotates the crankshaft and provides power to the vehicle.
The heat retained in the combustion chamber's walls is crucial in keeping the combustion process ongoing. It ensures that in subsequent cycles, the temperature remains high enough to ignite the new air-fuel mixture without needing external heat sources.
In other words, the engine is self-sustaining after initial ignition, as long as it receives a continuous supply of fuel and air, and the mechanical parts operate correctly.