Final answer:
The statement is true for gasoline engines, which typically use a spark plug to ignite the fuel-air mixture. Diesel engines, however, use compressed hot air to ignite the fuel without a spark plug. Combustion in engines starts with a thermal action leading to an increase in temperature and pressure, performing work by moving the piston.
Step-by-step explanation:
The statement that the mixture of fuel-oil and air is ignited at first by electric ignition is generally true for gasoline engines. These types of engines typically use a spark plug to initiate combustion. The spark plug delivers an electric spark that ignites the fuel-air mixture, leading to the burning of gasoline in the internal combustion engine. A reference to this is seen in the depiction of a gasoline engine where combustion spreads uniformly outward following the spark from the spark plug.
Combustion in an internal combustion engine can be characterized as a thermal action, leading to a rapid increase in temperature and therefore pressure within the engine's cylinder. This pressure then performs work by moving the piston. Similarly, modern rocket fuels can either be liquid or solid mixtures that are carefully measured and ignited to produce thrust, indicating that the ignition method may vary depending on the application and type of engine.