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Adaptive jet engines work analysis and control

Kowalski M.

Journal of KONES

2011

Vol. 18, No. 2

225-234

The paper describes major designs of adaptive jet engines as well as their structural and operational advantages. Attention is paid to actual thermodynamic cycles of such engines and energy balance of flows. Particular attention paid to a double-rotor engine designed by Pratt & Whitney, where a portion of air is bled from downstream of the compressor and then supplied to the area downstream the turbine when the engine is operated at its maximum performance (turbine bypass engine). Then attention is paid to actual thermodynamic cycles of such engines and energy balance of flows. It was shown that real working cycles of these engines represent figures with variable surface areas, which is the reason for the second name of these units - engines with variable thermodynamic cycle. It is explained how basic parameters of such engines affect sensitiveness of operating cycles and controllability. The analysis has been conducted separately for internal and external channel. The sensitivity analysis for the working cycle makes it possible to select parameters that are potentially controllable and adjustable. To sum up the foregoing deliberations one has to state that operation of turbojet adaptive engines is the topic that needs much more investigation. Even the design solution of the engine itself, although being really exciting and promising, is troublesome in the aspects of the design and process engineering, and will lead to a series of operation and maintenance problems.

Adaptive jet engines, advantages and application opportunities

Kowalski M.

Journal of KONES

2011

Vol. 18, No. 3

161-168

The paper has been intended to shortly describe the design of an adaptive jet engine, commonly termed 'the bypass engine'. Examples have been presented of how the bleeding of air affects the most essential engine performance characteristics, i.e. thrust, specific fuel consumption, and efficiency. Pointed out are economic advantages (only slight) of the application of this design as compared to the one-pass turbojet engine with no bleed. Furthermore, considered are capabilities to adapt an engine design of the bypass type for a one-pass turbojet engine K-15 as one of several upgrade opportunities. Simulation-based computations have proved, however, that there are some limitations on the bleed air amount and initial engine operational range for the accomplishment of the idea from the standpoint of capabilities to maintain conditions for the compressor-turbine matching. Also, the effect of this type of air bleeding upon the engine running-up process and the change in the running-up time for this type of the upgraded engine has been shown. In the Recapitulation and Conclusions section a mention has been made on the amount of bleed air to be passed through external channels from behind the compressor to behind the turbine: the bleed air amount increases as the total rate of the air flow along the engine flow path increases. It means that better effects of applying this type of air bleeding processes are gained in large engines. Presented are also capabilities of further developments and applications.