engine-world

Ⅲ. Engine Fundamental Requirements　(Air, Fuel, Measurement unit)

① Air - Air has properties that should be taken into consideration. It produces shock waves at the speed of sound, which greatly affects the engine. The engine has rotating blades such as propellers, fans, and compressor and turbine blades. Since these are limited in rotational speed (see Graph) to avoid shock waves, the entire blades and cross- sectional shape are being studied daily to delay the generation of shock waves.
The state of the flow path duct shape and sound velocity also changes as shown in the table. (See Table) The engine inlet, compressor diffuser and exhaust ductare designed with this change in mind. Also, when compressed, the temperature rises. As with the main wing of the aircraft, if the angle of attack of the blade is increased, peeling (disturbance) will occur. As the countermeasure against this phenomenon, the compressor employs air bleed and / or variable vane mechanism.
② Fuel The fuel used differs depending on the type of engine. -Piston engine Gasoline is used. The high-power engine required highly anti-knock gasoline containing highly toxic "4-ethyl lead ". This was one factor to replace the jet engine. -Jet engine Kerosene-based jet fuel is mainly used. It has the higher flash point and is safer than gasoline. In the engine, fuel and air are mixed and burned, but when completely burned, the temperature reaches 2000 °C and all metals are melted. Therefore, the engine takes in excess air to lower the temperature. The temperature greatly affects the efficiency, so the materials and design of the turbine section are researched and devised by each company to make it as high as possible. Instead of conventional fossil fuels, the replacement with "Sustainable Aviation Fuel (SAF)" refined from biomass-derived raw materials, waste, waste cooking oil, etc. is in progress. In the future, the use of liquid hydrogen is also being studied.

③ Measurement Unit (Measuring Method) The way to generate "THRUST" is the same, but the measurement units of the engineitselfarenot the same. The measurement method differs as follows depending on whethertheengineitself has the output axis (shaft). Organize and ... "With output shaft""Piston, Turboprop engine, Turboshaft .... ....Shaft-Horsepower(PS) 75 kgf-m/s (See Notes) "With no output shaft" - Turbojet, Turbofan, Propfan....THRUSTkgf, lbf The “PS” is calculated by connecting the load device such as the dynamometer totheoutputshaft, braking and measuring the counter torque. The “THRUST” is measured with the load cell directly by the spring-suspendedenginejumpingforward. This thrust is called Static Thrust.

These two units cannot be converted directly because they have different unit systems,butthefollowing formula is available as Thrust Horsepower. Flying speed (m/s) x Thrust at that time (kg) / 75 = Thrust Horsepower . ... Since actual measurement is difficult, it is a reference value to the last. (Note) Horsepower includes "English horsepower (HP)" and "France horsepower (PS)", and "PS" is used in Japan.