Turbojet Engine
A turbojet engine consists of a compressor, combustion system, turbine, and nozzle, which is a converging tube placed inside the exhaust pipe. The flow of hot compressed gas coming from the turbine enters the nozzle and is converted into a high-speed gas jet. As a result of the reaction force exerted by the gas jet on the engine, a thrust force is generated that can be used to propel an aircraft. In the simplest designs, the compressor and turbine share a common shaft. In more complex designs, the compressor consists of two parts (a two-stage compressor), with each stage driven by its own turbine via concentric gearing. A third variant involves the presence of a tunnel fan, usually installed at the entrance of the compressor inlet and driven by a third turbine or connected to the first stage of the compressor. This fan operates on the principle of a turbofan engine, where the majority of the air bypasses the compressor and turbine, combining with the jet exhaust to create additional thrust. This configuration is sometimes referred to as a "bypass turbojet engine."
Source: "Explanatory Notes to the Harmonized System of Goods Nomenclature for Foreign Economic Activity of the Russian Federation (HSN FEA Russia)" (prepared by the Federal Customs Service of Russia) (volume 3, sections XII - XVI, groups 64 - 84)