Plasma assisted MILD combustion

A new test platform for plasma assisted MILD combustion is developed. The burner consists of three coaxial channels: a center fuel jet, a coflowing dielectric barrier discharge (DBD) reactor, and a vitiated air section. The preheating burner upstream of the vitiated air section enables an increase of the oxidizer temperature up to 1300 K near the exit of the fuel jet nozzle. A nanosecond repetitively pulsed (NRP) DBD is formed surrounding the exit of the fuel jet nozzle, and the effect of the plasma discharge on the MILD combustion regime is investigated in a highly diluted CH4/air mixture. We successfully observe an extension of the MILD combustion regime by applying the plasma discharge at a significantly low preheating temperature of 1050 K. The changes of flame shapes and species distributions with/without plasma discharge are also investigated. A gas chromatography system is used to evaluate the effect of the plasma discharge on the species distribution after the plasma reactor section. Computational fluid dynamics (CFD) simulations are also carried out to understand and gain an insight into the mixing layer interactions with and without the plasma. Based on the species profile data and supported by the CFD simulations, we find that the reforming of a portion of the methane/air mixture at the exit of the fuel jet into intermediate species can have a significant impact on the ignition time scale. In addition, flow perturbations owing to the large density gradient induced by prompt gas heating in the plasma has a significant impact on the mixing process in the fuel jet. Thus, we demonstrate the potential of the newly developed experimental apparatus to advance our understanding of plasma assisted MILD combustion.