Development and application of a reactor network approach for estimating NOx emissions of an aero engine with lean combustion during cruise

Kurzfassung

Lean combustors as introduced by General Electric in their latest GEnx engine require a new approach for the estimation of in-flight NOx emissions. The approach presented in this paper is implemented as a reactor network model in DLR’s existing combustor pre-design and analysis tool ComDAT. In a reactor network the combustor volume is divided into a number of reactors in which the combustion is calculated with chemical kinetics. The advantage of this approach in comparison to a correlation is that the effect of modifications in the combustor architecture (e. g. cooling concepts) or air-fuel homogenization on the NOx emissions can be investigated. To classify the presented method, alternative methods regarding in-flight emission calculation are initially reviewed and assessed. To enhance the reliability of the emission prediction the reactor networks need to be calibrated. This means that the air and fuel flow distribution within the reactor networks as well as the dimensions of the reactors are adjusted such that the sum of the squared deviations between calculated and reference emissions is minimized for a given set of cruise operating conditions. For modeling the reference (or target) emissions during cruise, publicly available emissions and associated information of the GEnx were used, as this engine type is the only engine in service incorporating lean low-NOx combustion technology. The necessary combustor entry and exit conditions for the different flight states are obtained from an engine model using DLR’s engine performance code VarCycle. The development of the reactor networks, the modeling of the reference emissions as well as the process of calibration is described in this paper. Finally the calibrated reactor networks will be used to estimate and compare the NOx emissions of a generic lean burn engine at three different flight altitudes within cruise.