A microturbine operating with variable heat output

The concept of variable heat output using a recuperator bypass has been studied on a microturbine. The target of this research is to quantify to which extent variable heat output is possible using an existing microturbine design. In the paper we compare the predicted and measured performance of the system as well as present and discuss the change of NO_x emissions resulting from overfiring the microturbine combustor when reducing the air preheating temperature in bypass mode. We clarify which choice of bypass is suitable considering in particular the recuperator thermo-mechanical loading. We show that the performance of the system in variable heat output can be well extrapolated with a thermodynamic model calibrated with the normal operation mode data and how experimental or theoretical data can be used to predict the change of NO_x emission. It is shown that the full benefit of variable heat output can only be gained with a modified combustor design. As an example for this a lean-lean staged combutor concept is proposed.