Effects of H2/CO/CH4 syngas composition variation on the NOx and CO emission characteristics in a partially-premixed gas turbine combustor

This paper reports the effects of variations in the fuel composition of H-2/CO/CH4 syngas on the characteristics of NOx and CO emissions in a partially-premixed gas turbine combustor. Combustion tests were conducted on a full range of fuel compositions by varying each component gas from 0% to 100% at heat inputs of 40 and 50 kW(th). Flame temperature, combustor liner temperature, ignition delay time, and flame structure were investigated computationally and experimentally to judge whether they are significant indicators of NOx and CO formation. The characteristics of and reasons for NOx and CO emissions were investigated by analyzing the emission mechanisms and relationships among fuel property, equivalence ratio, flame temperature, liner temperature, flame shape. The flame structures were investigated using the following flame visualization methods: (1) time-averaged OH* chemiluminescence and its Abel-deconvolution; (2) direct photography; and (3) instantaneous OH-PLIF. The flame structures were greatly changed by the fuel composition and heat input, and they were subjected to key affecting parameters of the temperatures of the flames and the liners. NOx and CO emissions also largely varied according to fuel composition and heat input, showing neither linearly nor exponentially clear proportional trends toward the syngas compositions because of the singular conditions. For example, only the 100% CO flame at low load emitted lots of CO, whereas complete combustion was observed in other cases. However, the qualitative observations showed that the root causes of NOx emission behaviors were flame temperature and flame structure, which were directly related to the residence time in the flame. Various sets of practical test results were obtained, and these results could contribute to the optimal selection of the fuel-feeding condition when fuel is changed from natural gas to syngas in order to minimize NOx and CO emissions with stable combustion.