The basic shape of the turbine jet engine s, also called TL engine or Turbo Engine called, is similar to the turboprop engine, an arrangement of compressors and turbines arranged on a common shaft. The air is compressed in the compressor and then fed into the combustion chamber, which is arranged around the shaft as a coaxial ring or single combustion chamber system. The compressors consist of several alternating arrangements of impellers and guide wheels called stages. The wheel consists of a large number of blades mounted on a circular disc. During rotation, the impeller blades supply mechanical energy to the airflow. One compressor usually has eight stages, with two successive compressors it is ca. 15 steps.
After compression, the air is forced into the combustion chambers. There, the continuous combustion of the fuel adds heat; only now does the gas have enough energy to drive the compressor on the one hand and generate the thrust to move the aircraft on the other hand.
The combustion chamber is made of a high-strength material, because the flame temperature is about 2000 °C. However, intensive air supply prevents the temperature at the outlet of the combustion chamber from rising above 1000 °C, because the turbine materials cannot withstand higher temperatures. The gas expands greatly (while the pressure remains the same) due to the addition of heat. The hot gas now flows through the turbine.
Behind the turbine, there is a short transition section in which the annular cross-section of the gas flow is increased before the flow is directed into the thrust nozzle. In this nozzle, a tapered tube, the gas is strongly accelerated, converting the thermal energy contained in the gas into kinetic energy. Temperature and pressure decrease in the nozzle. The resulting thrust depends on the throughput (i.E., the mass of gas per unit of time), the exit velocity of the gas, which can be several times the speed of sound, and the airspeed (more precisely: the difference between exit and airspeed). The thrust can be increased by up to 50 % if an afterburner is used to impart additional thermal energy to the gases flowing out of the turbine.
Rocket engines
Rocket engines are also jet engines, but they differ from conventional aircraft engines in one important respect: they also operate in a vacuum. Unlike the "air-breathing" jet jet engines, both fuel components (the actual fuel and the oxidizer as an air substitute) have to be carried on board. A distinction is made between liquid-fueled rockets and solid-fueled rockets according to the condition of the components used. The fuels used are alcohols, petroleum products, and liquid hydrogen; oxidizers are essentially liquid oxygen or oxygen-rich compounds such as hydrogen peroxide ( H 2 O 2 ) or nitric acid ( HNO 3 ). In aviation, rocket engines are used exclusively in military applications and for research, z. B. In the case of the U.S. X-15, which can be flown at approx. 15 km altitude from a carrier aircraft. The X-15 reached a maximum speed of about 7300 km/h in 1963. A maximum altitude of about 108 km.
Environmental impact of aircraft engines
In the combustion chambers of modern aircraft engines, much greater quantities of nitrogen oxides are produced than in piston engines because of the higher temperatures involved. This results in considerable environmental pollution. Since emissions also take place in the uppermost layers of the troposphere (at an altitude of about ten to twelve kilometers), nitrogen oxides can easily reach the stratosphere, where they contribute to an increase in the ozone hole, but also to an increase in the ozone content in the lower layers of the troposphere. Both effects are undesirable, since ozone at high altitudes filters out short-wave UV radiation and is a harmful, even toxic gas in the biosphere. But not only nitrogen oxides are formed during the combustion of the fuel, there is also the production of the greenhouse gases carbon dioxide and water vapor. The noise pollution – especially for people on the ground – should also not be underestimated. For supersonic aircraft, beyond the sound barrier, the "sonic boom" is added to the engine noise. Attempts are being made to reduce aircraft noise by banning night flights in densely populated regions and by using steep takeoff and landing runways.