What's the difference between turbojet engine, turbofan engine and rocket engine? How do they work?

Turbofan engine is a kind of aircraft engine, which is developed from turbojet engine. Compared with turbojet, the main feature is that the area of the first-stage compressor is much larger, and it also acts as an air propeller (fan) to push back a part of the sucked air through the periphery of the jet engine. The part of the engine core through which air passes is called the internal duct, and the part outside the engine core through which only fan air passes is called the external duct. The turbofan engine is most suitable for the flight speed of 400 to 1000 km, so most aircraft engines now use turbofans as power sources. Turbojet engine is a kind of turbine engine. It is characterized by completely relying on airflow to generate thrust. Usually used as power for high-speed aircraft. Fuel consumption is higher than that of turbofan engine. There are two types of turbojet engines: centrifugal and axial. Centrifugal type was patented by British Sir Frank Whittle in 1930, but it was not until 194 1 that an airplane equipped with this engine went to heaven for the first time. It did not participate in World War II, but was born in Germany, and participated in 1945 as the first practical jet fighter Me-262. Compared with centrifugal turbojet engine, axial flow has the advantages of small cross section and high compression ratio. Today's turbojet engines are all axial flow. Difference: Compared with turbojet engine, turbofan engine has higher thermal efficiency and lower fuel consumption, so it can obtain a larger thrust-to-weight ratio. These are difficult for turbojet engines to achieve in any case. In fact, the core engines of turbojet engine and turbofan engine are basically the same, the difference is that turbofan engine adds several stages of turbines on the basis of turbojet engine. These turbines drive one or several rows of fans, and part of the airflow behind the fans enters the compressor (inner duct), which is sprayed from the nozzle after combustion, and the other part is directly discharged into the air through the outer duct without combustion. Therefore, the thrust of turbofan engine is the principle of the sum of fan resistance and nozzle thrust: turbojet engine adopts jet propulsion, which avoids the inherent weakness of rocket and ramjet engine. Because the turbine-driven compressor is used, the engine also has enough pressure to generate strong thrust at low speed. The turbojet engine works according to the "duty cycle". It sucks air from the atmosphere, and after compression and heating, the air with energy and momentum is discharged from the propulsion nozzle at a speed as high as 2000 ft/s (6 10 m/s) or about 1400 mph (2253 km/h). When the high-speed jet flows out of the engine, it drives the compressor and turbine to continue to rotate at the same time, maintaining the "working cycle". The mechanical layout of turbine engine is relatively simple, because it only contains two main rotating parts, namely compressor and turbine, and one or several combustion chambers. However, not all aspects of this engine have this simplicity, because thermal and aerodynamic problems are more complicated. These problems are caused by the high working temperature of the combustion chamber and turbine, the changing airflow through the compressor and turbine blades, and the design of the exhaust system that exhausts the gas and forms a propulsion jet. Rocket engine: Chemical rocket engine is the most mature and widely used engine at present. Chemical rocket engine is mainly composed of combustion chamber and nozzle. Chemical propellant is both energy and working medium. It converts chemical energy into heat energy in the combustion chamber, and generates high-temperature gas, which expands and accelerates through the nozzle, converts heat energy into kinetic energy of airflow, and is discharged from the nozzle at high speed (1500 ~ 5000m/s) to generate thrust. Chemical rocket engines are divided into liquid rocket engines, solid rocket engines and hybrid propellant rocket engine according to the state of propellant. Liquid rocket engine adopts liquid storable propellant at room temperature and liquid propellant at low temperature, which has the characteristics of strong adaptability and multiple starting, and can meet the requirements of different launch vehicles and spacecraft. The propellant of solid rocket motor is an organic colloidal solid solution (double-base propellant) containing fuel and oxidant in its molecule or a mixture of several propellant components (composite propellant), which is directly installed in the combustion chamber. It is simple in structure and convenient to use, and can be stored for a long time in the launching state, and is suitable for various strategic and tactical missiles. It is rarely used in hybrid propellant rocket engine.