engine-world

�V. Engine Fundamental Requirements　

(Air, Fuel, Rotation, Temp., Maintenance, Measurement unit)   

�@ Air - Air has properties that should be taken into consideration. This generates shock waves at the speed of sound, and an aircraft can avoid them by adjusting its flying speed, but engines have rotating blades such as propellers, fans, and compressor/turbine blades, and the peripheral speed of their tips can reach the speed of sound and generate shock waves regardless of the flying speed. As a result, research into the overall shape of wings and their cross-sectional shapes is being conducted on a daily basis in order to delay the generation of shock waves. Please refer to the  Graph that shows the relationship between the diameter of a rotating part and the  Rotation   Speed at which the speed of sound is reached under standard conditions.
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 duct are designed with this change in mind.
Compression also causes the temperature to rise. In particular, with axial compressors, increasing the angle of attack of the blades can cause  separation (turbulence), just like with the main wings of an aircraft. To address this phenomenon, compressors use bleed and/or variable vane mechanisms.
�A Fuel (Type) - As a measure against future global warming, efforts are underway to develop and commercialize new fuels.

�B Rotation Measures From idle to maximum output, the engine's rotation speed changes while adjusting the fuel  supply  according to atmospheric conditions. The rotating assembly is made up of many connected parts, so vibration control is important. A highly rigid structure is used that prevents the rotating axis from shifting due to centrifugal  force or thermal expansion. Representative examples are introduced below as basic components. 　　　　　　　　Bearing, 　　　　　　　Curvic(R) Coupling,　　　　Involute Spline

�C Temperature Control In an engine, fuel and air are mixed and burned, but at the perfect combustion, the temperature  will reach 2000℃, and all metals will melt. Here is a table summarizing high temperaturecountermeasures for each type of engine.

�D Maintenance (LCF, EHM) Aircraft and engines are significantly lighter than general consumer products, and are used for  an overwhelmingly long time. This makes maintenance very important. There are inspections at airports for each flight, regular inspections in hangars, and overhaul  maintenance at specialized factories. Piston engines and private jet engines are managed based on "hours of use." Jet engines used by airlines are managed based on "cycles" in addition to "hours of use." A "Cycle" is counted from start to stop as one cycle. The reason for this is that repeated large temperature changes from normal temperature to high-power temperature cause unavoidable metal fatigue. This is called "Low Cycle Fatigue (LCF),"and turbine disks are particularly affected. A "cycle limit" is set for them, and they are replaced  before reaching that cycle. In the past, a method called "overhaul" was used, but with the advancement of maintenance  technology such as monitoring, maintenance methods that reflect the actual performance of  each airline, engine, and module are adopted. This is called "Engine Heavy Maintenance (EHM)  method."

�E Measurement Unit (Measuring Method) The way to generate "THRUST" is the same, but the measurement units of the engine  itself  are not the same. The measurement method differs as follows depending on whether  the  engine itself 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 to the outputshaft, braking and measuring the counter torque. The “THRUST” is measured with the load cell directly by the spring-suspended engine moving  forward. This thrust is called Static Thrust.
These two units cannot be converted directly because they have different unit systems,  but  the following 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.