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The Potential of Sequential Combustion for High Bypass Jet Engines FREE

[+] Author Affiliations
Konrad Vogeler

ABB Power Generation Ltd, Baden, Switzerland

Paper No. 98-GT-311, pp. V002T02A006; 10 pages
doi:10.1115/98-GT-311
From:
  • ASME 1998 International Gas Turbine and Aeroengine Congress and Exhibition
  • Volume 2: Aircraft Engine; Marine; Microturbines and Small Turbomachinery
  • Stockholm, Sweden, June 2–5, 1998
  • Conference Sponsors: International Gas Turbine Institute
  • ISBN: 978-0-7918-7863-7
  • Copyright © 1998 by ASME

abstract

ABB has designed a new family of industrial gasturbines for power generation using a Sequential Combustion Cycle (SCC) on a large single shaft engine. This concept allows considerable increase in power density and efficiency by only increasing pressure without raising the maximum hot gas temperature of the cycle. Instead a second combustion after an HP-turbine is used to reheat the gas before the final expansion in an LP-turbine.

This concept is applied to the analysis of a high bypass ratio jet engine. In an engine with a single combustor, thrust is a function of bypass ratio and the combination of maximum pressure and temperature in the cycle. The proposed SCC allows increased thrust without pushing technology on materials and cooling. A modern twin spool engine is taken as reference. When total inlet massflow is kept constant, increasing bypass ratio decreases core mass flow. This limits the fuel flow for the HP-spool and hence total energy input to the engine. Introduction of the SCC gives another parameter of freedom to the cycle design. However the twin spool concept is now a disadvantage. The low fuel flow for the HP-spool due to high bypass ratio means there is not enough energy available to build up the necessary pressure for an economical expansion in the LP-turbine after the second combustion. Specific fuel consumption will be unacceptable.

It is proposed to apply the SCC concept in a single spool engine with a geared fan. Both turbines can now support the compression. The fan is operated as a constant speed propeller with variable blade pitch. This engine concept allows for a given inlet massflow a substantially higher bypass ratio and hence decreases specific fuel consumption while specific thrust can be kept on a level which will be considerably higher than it would be in todays engines with comparable bypass ratio.

Copyright © 1998 by ASME
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