Ignition characteristics in spatially zero-, one- and two-dimensional laminar ethylene flames

Abstract

In the continual effort to reduce emissions and improve efficiency, moderate or intense low-oxygen dilution combustion has been suggested for aeroengine applications. This new application of moderate or intense low-oxygen dilution combustion requires further insight in applying the knowledge from conventional analyses of well-mixed systems to non-premixed flames. The ignition of ethylene, a key species in hydrocarbon oxidation, is simulated in simplified combustion systems with three different hot oxidants using detailed chemical kinetics. Zero-dimensional batch reactors, one-dimensional opposed-flow flame simulations, and planar two-dimensional laminar coflowing slot flame simulations are used to compare different ignition metrics across the autoignitive and moderate or intense lowoxygen dilution combustion regimes. It is found that the autoignition of ethylene with hot air may be described in two dimensions as the intersection of a critical hydroxyl fraction and the most reactive mixture fraction. Although this provides a reasonable prediction of the flame base for ignition with hot air, this becomes less reliable in the approach to the moderate or intense low-oxygen dilution combustion regime. For the cases in, and in the transition to, the moderate or intense low-oxygen dilution combustion regime, a good agreement is seen between a 10 K rise above the oxidant temperature and the onset of strong chemiluminescence seen experimentally.