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 simulations 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.

► Unstable operation of a T100 microturbine during steam injection tests was noticed, caused by exhaust gas recirculation.
► Wind tunnel tests were performed to study the effect of the wind direction on the recirculation process.
► Steady-state simulations to investigate the effect of exhaust gas recirculation on thermodynamic performance.
► Dynamic simulations to reveal effects of frequency and amplitude on average performance and stability.
► Wind tunnel tests revealed the necessity to heighten the stack to prevent exhaust recirculation.