Discussion of the effects of recirculating exhaust air on performance and efficiency of a typical microturbine

This paper reports on a specific phenomenon, noticed during steam injection experiments on
a microturbine. During the considered experiments, measurements indicated an unsteady inlet air
temperature of the compressor, resulting in unstable operation of the microturbine. Non-continuous
exhaust air recirculation was a possible explanation for the observed behaviour of the microturbine.
The aim of this paper is to investigate and demonstrate the effects of exhaust recirculation on a
microgasturbine. Depending on wind direction, exhaust air re-entered the engine, resulting in changing
inlet conditions which affects the operating regime of the microturbine.
For this paper, a series of experiments were performed in the wind tunnel. These series of experiments
allowed investigation of the effect of the wind direction on flue gasses flow. Next to the experiments,
steady-state simulations of exhaust recirculation were performed in order to study the effect of
exhaust recirculation on thermodynamic performance of the microturbine. Dynamic simulations of the
non-continuous recirculation revealed the effects of frequency and amplitude on average performance
and stability.
Results from simulation supported the important impact of exhaust recirculation. Wind tunnel tests
demonstrated the influence of the wind direction on recirculation and revealed the necessity to
heighten the stack, thus preventing exhaust recirculation.