Strictly speaking, the engines carried on these civil aviation passenger planes should be called "turbofan engines". They are very different from turboprop engines in appearance, but they are quite similar in working principles.
When the turboprop engine starts to work, air will enter from the compressed blade in front of the engine. After becoming compressed air, it will enter the combustion chamber will be fully mixed with the fuel and ignited. At this time, the high-temperature gas will expand rapidly and spray backwards. These gases emitted backwards will push the turbine blades behind the engine. The turbine blades will then transmit kinetic energy to the gearbox in front of the engine through the transmission shaft, so the propeller in front rotates.
Through the working principle of the turboprop engine, can you see what force does the aircraft equipped with this kind of engine rely on to fly forward?
is not a high-temperature gas that is ejected from the rear, but an air that is accelerated by the propeller in the front and quickly pushed backward. This part of the gas is also called "bypass air". Let’s take a look at the turbofan engine. Its working principle is actually similar to that of a propeller engine. The difference is that the propeller exposed outside is replaced with a fan installed inside.
When turbine starts working, the fan in front begins to rotate, and a large amount of air flows in from the front, but these influxes will be divided into two parts.
part becomes compressed air into the combustion chamber, and eventually becomes high-temperature gas discharged from the rear, while the other part is directly pushed back by the fan. The air directly pushed back is the source of power of the turbofan engine, which is what we call "bypass air". Obviously, whether it is a turboprop engine or an turbofan engine , the forward force comes from the bypass air driven by the blades, rather than the high-temperature gas emitted directly from the back, so neither of these engines is a real jet engine.
Real jet engines rely entirely on the high-temperature gas sprayed backwards, and this kind of engine is usually only installed on fighter .
Although the principles are similar, the turboprop engine and turbofan engine have different efficiencies. With the same fuel consumption, the propeller aircraft is obviously more efficient because all the air pushed by the propeller is bypass air that pushes the aircraft forward, and part of the air pushed by the turbofan engine is to become compressed air entering the combustion chamber. In this case, why do civil aviation passenger aircraft use turbofan engines? Because propeller engines have one disadvantage, that is, they cannot fly too fast.
What should we do if the propeller aircraft wants to increase its speed?
has to make the propeller rotate faster, but the speed of the propeller rotates has a limit, because once the propeller rotates at the speed of sound, an shock wave will be generated, that is, a wedge-shaped or conical air wave will appear at the tip of the propeller, which will cause the propeller's efficiency to plummet. But there is no problem with the turbofan engine at all, because the intake channel of the turbofan engine has undergone special treatment. After the airflow enters, the speed will decrease rapidly, and naturally there will be no shock waves in front of the fan. It can be seen that the two engines have their own advantages and disadvantages. The propeller engine is efficient but slow, while the turbofan engine is relatively fuel-consuming, but fast. For civil aviation companies, of course, it is more cost-effective to choose fuel-efficient propeller engines, but if you choose propeller, other companies use turbofan engines, who will take your slow plane? This is also a kind of inverter .
