Flame enhancement of ethylene/methane mixtures by ozone addition

Abstract

As one of the longest lasting species in plasma-assisted combustion, ozone has a pronounced effect on ignition and flame propagation. Many previous studies, however, have only investigated the combustion enhancement by ozone for single-component fuels. In the present study, the impact of ozone addition on multi-component fuel mixtures is examined through one-dimensional laminar flame simulations across a range of temperatures, pressures, residence times, and mixture compositions. Due to the presence of an alkene (ethylene), ozone is consumed through pre-flame ozonolysis reactions even at room temperature. The flame speed is shown to be dependent on the domain length (residence time), and a new reference flame speed is defined for ozonolysis-assisted flame propagation. It is also found that the flame speed enhancement by ozone is highly nonlinear, as a small amount of ethylene produces a disproportionate boost in the laminar flame speed. Finally, the competition between ozonolysis, ozone decomposition, and other ozone reactions in a mixture of alkenes and alkanes is examined in detail. Increases in the pressure, temperature, and equivalence ratio (for rich mixtures) favor ozonolysis reactions over other ozone reactions. The results of this study provide important insights into the timescales, length scales, and reaction pathways that govern ozone-assisted combustion of multi-component fuels in real combustors.