Engine bleed air: a primer
Use of Bleed Air in Aircraft Pneumatic Systems: A Primer ( taken from Chapter 6 on Pneumatic Systems from the 3 rd Edition of the book “Aircraft Systems” by Ian Moir and Allan Seabridge ) The use of aircraft engines as a source of high pressure, high temperature air can be understood by examining the characteristics of the turbofan engine. Modern engines “bypass” a significant portion of the mass flow past the engine and increasingly a small portion of the mass flow passes through the engine core or gas generation section. The ratio of bypass air to engine core air is called the bypass ratio and this can easily exceed 10:1 for the very latest civil engines; much higher than the 4 or 5:1 ratio for the previous generation. The characteristics of a modern turbofan engine are shown in figure 6.1. This shows the pressure (in psi) and the temperature (in degree centigrade) at various points throughout the engine for three conditions: ground idle, take off power and
