Plasma-assisted ignition-stabilized combustion (PAISC): Benefits, limitations, and costs

This work aims to find the benefits, limitations, and costs (in terms of plasma energy and NOx emissions) of plasma-assisted ignition-stabilized combustion (PAISC). The experiments are performed on a custom-made methane-air jet flame burner with two coaxial flow inlets. Dielectric barrier discharge (DBD) configuration is set up in the outer flow channel which acts as four ignition sources. The DBDs are operated by bursts of positive voltage pulses of 10 ns duration and 24 kV amplitude. In this way, four ignition kernels are created in flow simultaneously. The ignited kernels expand while blowing out with the flow which is followed by new ignition kernel initiation during the next burst. This cycle is repeated continuously and complete burning of the fuel is ensured by proper interactions between ignited kernels. The PAISC dynamics are visualized using OH* chemiluminescence images captured at 10 kHz framerate. Along with visualization measurements, we measure CO and NOx emissions using an industrial gas analyzer. The gas analyzer measurements are complemented by two-photon laser-induced fluorescence (TALIF) measurements of CO. We find the optimal plasma parameters to optimize CO, and NOx emissions and the effective flame length. A parametric study for various flow parameters is performed and combustion operation regimes are identified. The main highlight of this work is quasi-complete combustion at flow speeds of up to 4 times the blowout flow speed, which costs less than 10 ppm@3%O2 plasma-produced NOx and has a plasma energy consumption of less than 1% of the combustion heat release. Novelty and Significance Statement Various researchers have demonstrated plasma's ability to enhance combustion at near-lean-blowout limits in the past. This work presents a novel plasma-assisted ignition stabilized combustion (PAISC) strategy to achieve quasi-complete combustion at flow speeds much above blowout flow speeds. Pulsed dielectric barrier discharge plasma is used to ignite methane-air flow as it is a fast, repetitive, and energy-efficient ignition source. We study PAISC dynamics using high-speed visualization along with CO, NOx emissions, and plasma energy for various plasma and flow parameters. From these analyses, we optimize plasma parameters first and then discuss the benefits, limitations, and costs of PAISC at optimal plasma conditions. We believe that the presented strategy will motivate future combustor design with a wider range of operability, especially for high-speed propulsion applications.