2023 Author: Bryan Walter | [email protected]. Last modified: 2023-05-21 22:24
On April 22, 1941, the Soviet designer Arkhip Lyulka filed an application with the USSR State Patent for the invention of a turbojet bypass engine. Work on the creation of this power plant was carried out under the direction of Lyulka since 1937. As a result of these works, the designer created a prototype of a turbojet engine with an axial compressor. Subsequently, the scheme proposed by Lyulka became the basis for the jet power plants existing today.
Before the invention of the Cradle, all turbojet engines developed in the world were single-circuit. In them, in flight, the incoming air was decelerated in a special inlet chamber, after which it entered the compressor - a set of rotating screws compressing the incoming gases up to 40 times. Then the compressed air entered the combustion chamber, where it was mixed with fuel. Compression of air is necessary in order to ensure a more complete combustion of the fuel. The gases expanding during combustion flowed out of the combustion chamber, rotating the turbine blades, which spun the compressor through a common shaft. After the turbine, the gases flowed out through the nozzle, creating thrust.
Turbojet engine. 1 - inlet device, 2 - compressor, 3 - combustion chamber, 4 - turbine, 5 - nozzle
Cradle suggested adding a second - external - air circuit to the turbojet engine, through which the incoming air, practically without undergoing any changes, entered the nozzle zone, where it mixed with the hot exhaust gases and was thrown out. At the same time, it was possible to reduce the total fuel consumption of the power plant (there is no combustion chamber in the external circuit) and to increase the total thrust. Almost all modern turbojet engines are dual-circuit.
Diagram of the Lyulka's by-pass turbojet engine. 1 - diffuser (distributes air to the external and internal circuits), 2 - low pressure compressor, 3 - high pressure compressor, 4 - combustion chamber, 5 - turbine, 6 - nozzle
Today, jet propulsion systems are distinguished by the degree of bypass. This is the name of the ratio of the volume of air passing through the outer loop to the volume of air passing through the inner one. Engines for military aircraft are distinguished by a low degree of bypass, which require high thrust, but fuel consumption is not important. Engines for civil aircraft are distinguished by a large by-pass ratio, in which the outer contour makes the greatest contribution to thrust - up to 70-80 percent. They are highly efficient, consuming several times less fuel than power plants with a low bypass ratio.