The main objective of this paper is development of a simple real-time transient performance model for jet engine control. A jet engine arrives to its most dangerous condition during transient operation that may be triggered by fast changes of the input fuel command signal. Thus, the control system specifications are formulated to specify the maximal variance of the fuel flow command (from idle to maximum power level) during transient maneuver. Linear and piecewise-linear techniques are not always convenient and appropriate for turbine engine controller design. An alternative quasilinear simple/fast engine model is discussed in this paper. This model has maximum accuracy for maximal variance of the fuel flow input command in accordance to the jet engine control system specifications. The fast model is obtained using the Novel Generalized Describing Function, proposed for investigation of nonlinear control systems. The paper presents the Novel Generalized Describing Function definition and then discusses the application of this technique for the development a fast turbine engine simulation suitable for control and real-time applications. Simulation results are compared between the conventional and fast models and found to provide good agreement.
Since its discovery,
the flameless combustion (FC) regime has been
a promising alternative to reduce pollutant emissions of gas turbine
engines. This combustion mode is characterized by well-distributed
reaction zones, which potentially decreases temperature gradients,
acoustic oscillations, and NOx emissions.
Its attainment within gas turbine engines has proved to be challenging
because previous design attempts faced limitations related to operational
range and combustion efficiency. Along with an aircraft conceptual
design, the AHEAD project proposed a novel hybrid engine. One of the
key features of the proposed hybrid engine is the use of two combustion
chambers, with the second combustor operating in the FC mode. This
novel configuration would allow the facilitation of the attainment
of the FC regime. The conceptual design was adapted to a laboratory
scale combustor that was tested at elevated temperature and atmospheric
pressure. In the current work, the emission behavior of this scaled
combustor is analyzed using computational fluid dynamics (CFD) and
chemical reactor network (CRN). The CFD was able to provide information
with the flow field in the combustor, while the CRN was used to model
and predict emissions. The CRN approach allowed the analysis of the
NOx formation pathways, indicating that
the prompt NOx was the dominant pathway
in the combustor. The combustor design can be improved by modifying
the mixing between fuel and oxidizer as well as the split between
combustion and dilution air.
One of the factors which reduces combustion efficiency in a fluidized-bed combustor is the elutriation of fine coal particles from the freeboard above the bed surface. To our knowledge, data about the real local flow behavior of the two-phase flow in the freeboard are lacking in the literature. This paper concerns the measurement of the gas and the elutriated particle velocities in the freeboard of a cold fluidized bed using Laser Doppler Anemometry. A special electronic system has been devised to record simultaneously the gas and particle velocities and to indicate the size of the particles. In this paper the apparatus and some preliminary measurements are reported. The most significant observation is that the gas velocity profiles exhibit minima near the bed center and maxima near the walls.
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