Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
7.5.2. The Gas Turbine Combustion System
and all existing combustion products, showing
In the cross-sectional drawing of a modern civil aircraft engine (Figure 7-13), the combustor is shown in its central position between the compressor and turbine. Highpressure
air enters the combustor at a relatively high velocity. The air is first carefully decelerated to minimize pressure losses, then forced into the combustion
chamber, where fuel is added. The combustion chamber is designed to allow time and space for the fuel and air to mix thoroughly and burn efficiently before entering
the turbine stages. Detailed design features of the combustor control the complex burning processes, thus the completeness of the chemical reactions involved and the
nature and scale of individual emissions from the engine. Therefore, the combustor has a key role in determining the impact of aircraft on climate.
7.5.2.1. Combustor Features and Requirements
Aircraft engine combustors must meet the special requirements of operations over a very wide range of pressures and temperatures. The combustor must be able to
ignite and accelerate the engine over a wide operational envelope. For instance, it must be able to ignite at high altitude (up to 9 km) after an unscheduled shutdown
when the air is very cold (e.g., 220 K) and pressure is low (e.g., 0.03 MPa). It must also be able to maintain stable burning over a very wide range of air velocities and
fuel/air ratios to prevent "flameout" during engine deceleration. At the other end of the power range, when pressures and temperatures are very high, the combustor
must be able to burn fuel so that turbine components are presented with a smooth temperature profile, to minimize damage to the blades and vanes and thereby
maximize service life. Together, these requirements present a major engineering challenge because the simplest solutions to meet requirements at one end of the
operational envelope often conflict with those required at the other. Relatively recent emissions requirements have added considerably to the time and cost of
developing combustors that fully satisfy the operational and environmental requirements placed on today's aircraft.
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