Zero-knowledge of turboprop engine, read exactly this article first
Modern aircraft with high payload and range require engines that can develop the required thrust with a minimum specific gravity. Turbojet engines meet these requirements. However, they are uneconomical compared to propeller installations at low flight speeds.
In this regard, some types of aircraft designed for relatively low speeds and long distances require the installation of engines that would combine the advantages of a turbojet engine with the advantages of a propeller-driven at low speeds. These engines include turboprop engines.
A turboprop engine is a gas turbine aircraft engine in which the turbine develops more power than is needed to turn the compressor, and this excess power is used to turn the propeller.
The turboprop engine consists of the same components as the turbojet engine. However, unlike the turbojet engine, the propeller and gearbox are additionally mounted on a turboprop engine. To obtain maximum engine power, the turbine must develop high speeds [up to 20,000 rpm]. If the propeller rotates at the same speed, then the efficiency of the latter will be extremely low, as the maximum efficiency of the propeller in the design flight modes reaches 750-1500 rpm.
To reduce the speed of the propeller compared to the speed of the gas turbine, a gearbox is installed in the turboprop engine. In high-power engines, two oppositely rotating propellers are sometimes used, with one gearbox operating both propellers.
In some turboprop engines, the compressor is driven by one turbine and the propeller by another. This creates favorable conditions for regulating the engine. Thrust is created mainly by the propeller [up to 90%] and only slightly due to the reaction of the gas jet.
Multi-stage turbines are used in turboprop engines [the number of stages is from 2 to 6], which is dictated by the need to control large heat droplets on a turboprop turbine than on a turbojet turbine. In addition, the use of a multistage turbine makes it possible to reduce its speed and therefore the size and weight of the gearbox.
The purpose of the main elements in the turboprop engine does not differ from the purpose of the same elements of the turbojet engine. The working process of the turboprop engine is also similar to that of the turbojet engine.
Just like with a turbojet engine, the airflow pre-compressed in the intake manifold is subjected to basic compression in the compressor and then enters the combustion chamber, where the fuel is injected simultaneously through the injectors. The gases formed as a result of the combustion of the air-fuel mixture have high potential energy. They rush to the gas turbine, where, expanding almost completely, they produce work, which is then transferred to the compressor, propeller, and unit drives. Behind the turbine, the gas pressure is almost equal to atmospheric pressure.
In modern turboprop engines, the thrust, obtained only due to the reaction of the gas jet flowing from the engine, is 10-20% of the total thrust.
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