Experimental study of stability and pollutant emissions of turbulent biogas flames under microsecond pulsed plasma

•Investigation the effects of microsecond pulsed plasma on the stabilization and emission characteristics of non-premixed swirling biogas/air flames.•Effects of CO2 with and without plasma are performed.•Generation of many excited species by MPP plasma such as N2*, NO*, O*, and H*•Excited species from the flame (OH*, C2*, CN*, CH*) are amplified with plasma.•The presence of MPP plasma significantly improves flame stabilization.•The activation of MPP leads to a decrease in CO emission, which is enhanced with an increase in pulse repetition frequency.•NOx production becomes more significant with increasing pulse repetition frequency. Biogas is a mixture of methane (50–80%.vol), carbon dioxide (20–45%.vol), and in smaller proportions of N2, O2, H2S, and NH3. For a high rate of CO2 in the biogas, the combustion can generate strong instabilities and the flame can be very lifted from the burner and even blown. To overcome these problems of instabilities and flame extinction, the use of a microsecond pulsed plasma is considered for this study. This study aims to characterize the effects of microsecond pulsed discharges on the stabilization and emission characteristics of non-premixed swirling biogas/air flames at different operating conditions of combustion (CO2 rate, power, and equivalence ratio) and plasma (pulse repetition frequency and input electrical voltage). The plasma is performed above a coaxial burner with a swirler of the oxidizer. It is generated by a DC-pulsed power generator with a high voltage (HV) pulse duration of a few microseconds. The burner consists of two concentric tubes and a central metal rod used as a cathode for the plasma. The outer tube contains a swirler and supplies the oxidant flow, and the inner tube delivers the fuel (methane, biogas) around the central metal rod. High voltage pulses are applied on two anode tungsten wires that are symmetrically arranged from either side of the cathode to obtain two plasma zones in the stabilization region of the flame. The burner is placed in a parallelepiped combustion chamber with a volume of 100x48x48 cm3. Mass flow rates of air and fuel are regulated by thermal mass flow controllers (Brooks SLA5851S). OH* chemiluminescence measurements are done to describe the structure and the flame stability throughout the lift-off heights (Hf) variation. Results showed that plasma generated by microsecond HV pulses can improve flame stability by decreasing its Hf especially at low fuel velocities. In thi