In propulsion industry there is an ongoing need to significantly
reduce SFC of jet engines resulting in cost reduction
and lower emissions. Since the design of most of the engine
components is at the limit of today’s technology level further
gain of improvement on short term is to be achieved by implementation
of new system concepts. Especially the stall safety
margin in compression system design holds high potential for
the optimization of the overall engine system. Once a reliable
and effective stall control system becomes available an extension
of present operating range is likely to be achieved by moving the
steady operating line towards the stability limit and to intervene
only in critical situations. At the Institute of Jet Propulsion at the
University of the Federal Armed Forces in Munich, Germany a
Larzac 04 twin-spool turbofan engine has already been equipped
and tested with an adequate active stabilization system of the low
pressure compressor for research purposes.
Those investigations revealed a strong dependency of the achievable
stabilization effect and the amount and momentum of the
injected air mass flow. For flying applications this mass flow
has to be delivered by carried on means. Therefore it always
penalizes the propulsion efficiency. In the given configuration,
redirected air from the last stage of the high pressure compressor
is used for injection. Usage of this bleed air directly influences
the propulsion efficiency of the engine. In order to optimize the
mass flow needed for stabilization, the existing injection system
was redesigned to utilize ejector pumps. With this configuration
a comparable stabilizing effect could be realized with less redirected
air mass flow. In fact the open ejector pump configuration
showed an even higher performance at maximum injection rate
than the closed injection before. Therefore further investigations
with this system focused on the effect of additional flow ports to
the engine intake as they are necessary for an ejector pump and
their basic influence on the operation stability of the low pressure
compressor (LPC). In combination with the already existing stall
detection algorithm of the institute a very promising system for
increasing the available operating range in turbo compressors
could be achieved.
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