Turboprop engine: device, circuit, principle of operation. Manufacture of turboprop engines in Russia

The turboprop engine looks like a piston engine: both have an air screw. But in all other respects they are different. Consider what this unit represents, how it works, what are its pros and cons.

general characteristics

The turboprop engine belongs to the class of gas turbines, which were developed as universal power converters and became widely used in aviation. They consist of a heat engine where the expanded gases rotate the turbine and form a torque, and other units are attached to its shaft. The turboprop engine is supplied with an air screw.

It is a cross between piston and turbojet aggregates. First, piston engines were installed in the aircraft, consisting of cylinders in the form of a star with a shaft located inside. But due to the fact that they had too large dimensions and weight, as well as a low speed capability, they were no longer used, giving preference to the emerging turbojet plants. But even these engines were not devoid of shortcomings. They could develop supersonic speed, but they consumed a lot of fuel. Therefore, their operation was too expensive for passenger transportation.

The turboprop engine had to cope with such a disadvantage. And this problem was solved. The design and principle of operation were taken from the mechanism of the turbojet engine, and from the piston engine - the propellers. Thus, it became possible to combine small dimensions, economy and high efficiency.

The engines were invented and built in the thirties of the last century under the Soviet Union, and two decades later began their mass production. The power varied from 1880 to 11000 kW. For a long period of time they were used in military and civil aviation. However, they were not suitable for supersonic speed. Therefore, with the advent of such capacities in military aviation, they were refused. But civilian aircraft are mainly supplied by them.

Turboprop engine design and operation principle

The motor design is very simple. It includes:

• Reducer;
• air propeller;
• the combustion chamber;
• compressor;
• nozzle.

Scheme turboprop engine is as follows: after injection and compression of the compressor air enters the combustion chamber. Fuel is also injected there. The resulting mixture ignites and creates gases, which when expanded enter the turbine and rotate it, and it, in turn, rotates the compressor and screw. Unallocated energy exits through the nozzle, creating a reactive thrust. Since its magnitude is not significant (only ten percent), it is not considered a turbojet turboprop engine.

The principle of operation and design, however, are similar to it, but the energy here does not completely exit through the nozzle, creating reactive thrust, but only partially, since the useful energy also rotates the screw.

Working shaft

There are engines with one or two shafts. In the single-shaft version, a compressor, a turbine, and a screw are located on one shaft. In the two-shaft - on one of them installed a turbine and a compressor, and on the other - a screw through the reducer. There are also two turbines connected to each other by a gas-dynamic method. One of them is designed for the screw, and the other is for the compressor. This option is most common, since the energy can be used without starting the screws. And this is especially convenient when the aircraft is on the ground.

Compressor

This part consists of two to six steps, allowing you to perceive significant changes in temperature and pressure, as well as reduce the speed. Thanks to this design, it is possible to reduce the weight and dimensions, which is very important for aircraft engines. Compressor includes impellers and directing device. The latter may or may not provide for regulation.

Air propeller

Due to this part, draft is formed, but the speed is limited. The best indicator is the level from 750 to 1500 rpm, as with the increase in efficiency will start to fall, and the screw instead of acceleration will turn into a brake. The phenomenon is called the "locking effect". It is caused by the propeller blades, which start to function incorrectly at high speeds during rotation, exceeding the speed of sound . The same effect will be observed with an increase in their diameter.

Turbine

The turbine can reach speeds of up to twenty thousand revolutions per minute, but the screw can not match it, so there is a reduction gear, reducing the speed and increasing the torque. Reducers can be different, but their main task, regardless of the type, is to reduce speed and increase torque.

It is this characteristic that limits the use of a turboprop engine in military aircraft. However, the development of a supersonic engine does not stop, although they are not yet successful. To increase traction, a turboprop engine is sometimes supplied with two screws. The principle of operation in this case they are realized due to rotation in opposite directions, but with the help of a single reducer.

As an example, we can consider the engine D-27 (turbo-rotor-type), which has two screw fans attached to the free turbine by a reducer. This is the only model of this design used in civil aviation. But its successful application is considered a great leap forward in improving the performance of the engine in question.

Advantages and disadvantages

We will highlight the minuses and pluses that characterize the work of a turboprop engine. Advantages are:

• Low weight compared to piston units;
• Efficiency compared to turbojet engines (thanks to an air screw, the efficiency reaches eighty-six percent).

However, despite such undeniable advantages, jet engines are in some cases a more preferable option. The speed limit of the turboprop engine is seven hundred and fifty kilometers per hour. However, this is not enough for modern aviation . In addition, the noise is very high, exceeding the permissible values of the International Civil Aviation Organization.

Therefore, the production of turboprop engines in Russia is limited. They are mainly installed in airplanes that fly over long distances and at low speed. Then the application is justified.

However, in military aviation, where the main characteristics that aircraft should have are high maneuverability and silent operation, and not economy, these engines do not meet the necessary requirements and turbojet engines are used here.

At the same time, the development of supersonic propellers is constantly being carried out in order to overcome the "blocking effect" and reach a new level. Perhaps, when the invention becomes a reality, jet engines will be rejected in favor of turboprops and military aircraft. But at the present time they can only be called "workhorses", not the most powerful, but stably functioning.