To move an airplane or a model rocket through the air, we must use a propulsion system to generate thrust. Different types of aircraft use different types of propulsion devices, but all aircraft rely on some type of engine to generate power. Rocket engines, internal combustion, or piston engines, and jet engines all depend on the burning of fuel to produce power. Burning a fuel is called combustion, a chemical process that we study in middle or high school. Because combustion is so important for aircraft and rocket propulsion, we will review the fundamentals.
Combustion is a chemical process in which a substance reacts rapidly with oxygen and gives off heat.
The original substance is called the fuel, and the source of oxygen is called the oxidizer . The fuel can be a solid, liquid, or gas, although for airplane propulsion the fuel is usually a liquid. For model rockets, a solid fuel and oxidizer is used. During combustion, new chemical substances are created from the fuel and the oxidizer. These substances are called exhaust.