CONVENTIONAL PROPULSION SYSTEMS
Today’s propulsion systems are storing energy in liquid form. This fuel is usually based on oil and is thermally decomposed, i.e. burnt. Technically, with small modifications, these systems are also capable of using gaseous fuels like hydrogen or natural gas. The fuel is burnt in either piston engines or in gas turbines to produce mechanical power. These machines are connected to a shaft which is linked to an aerodynamic propulsion device, either a propeller (piston-propeller or turbo-propeller) or a fan (turbo-fan). All systems accelerate an incoming mass flow of air to produce thrust. An additional part of the thrust may be created by recovering part of the thermodynamic energy in the exhaust, i.e. by passing the hot gases through suitable nozzles. In case of propulsion by propellers it is often necessary to use a gearbox to adapt the performance characteristics of the engine to the characteristics of the propulsion device so that the overall efficiency is maximized. Gearboxes are now also introduced to decouple the fan from the turbine of turbofan engines, thus increasing their total efficiency considerably.
