Stability enhancement of ozone-assisted laminar premixed Bunsen flames in nitrogen co-flow

摘要

Ozone (O_3) is known as one of the strongest oxidizers and therefore is widely used in many applications. Typically in the combustion field, a combination of non-thermal plasma and combustion systems have been studied focusing on the effects of ozone on flame propagation speeds and ignition characteristics. Here, we experimentally investigated the effects of ozone on blowoff of premixed methane/air and propane/air flames over a full range of equivalence ratios at room temperature and atmospheric pressure by using a co-flow burner and a dielectric barrier discharge. The results with ozone showed that a nozzle exit jet velocity at the moment of flame blowoff (blowoff velocity) significantly increased, and flammability limits for both fuel-lean and rich mixtures were also extended. Ozone had stronger effects of percent enhancement in the blowoff velocity for off-stoichiometric mixtures, while minimum enhancements could be observed around stoichiometric conditions for both fuels showing linear positive dependence on a tested range of ozone concentration up to 3810 ppm. Through chemical kinetic simulations, the experimentally observed trends of the enhancement in blowoff velocity were identified as a result of the modification of the laminar burning velocity. Two ozone decomposition pathways of O_3 + N_2 → O + O_2 + N_2 and O_3 + H → O_2 + OH were identified as the most controlling steps. These reactions, coupled with fuel consumption characteristics of each fuel determined the degree of promotion in laminar burning velocities, supporting experimental observations on blowoff velocities with ozone addition.