Aviation and the Global Atmosphere

Aviation and the Global Atmosphere
Figure 7-11: Combustor exit temperature trend with time.
This brief review of theoretical considerations summarizes thermodynamic and aerodynamic constraints for engine designers in the continuing drive toward more
efficient engines for current and future requirements. Although today's most advanced engines have bypass ratios in the range 5 to 9, there will be efforts to continue
to try to increase them. Despite their attractions, however, bypass ratios much in excess of 9 are likely to require a gear box between the power turbine and the fan, or
a novel configuration (a topic taken up further in Section 7.4.3), as well as imposing installation and weight problems.
7.4.2. Historical Trends
The foregoing discussion briefly reviewed the ways in which basic engine cycle considerations
can influence design trends of gas turbines. Practical confirmation of such trends may be
obtained by looking at historical trends of principal parameters affecting the performance of gas
turbines since they were first introduced. Economic and aircraft range considerations have been
uppermost in engine designers' minds. Figure 7-9 clearly shows the impressive progress made
in reducing thrust-specific fuel consumption (mass flow rate of fuel burned per unit of thrust) with
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