Transient Plasma Ignition -- Non-thermal plasma Actuator

Transient Plasma Ignition

a) Transient plasma discharge with threaded rod electrode

b) Side view of pulsed corona discharge, central electrode diameter: .25”, energy: 356mJ/pulse

c) Transient plasma and arc discharges with 4-needle electrodeTransient Plasma Ignition

Transient plasma discharge, sometimes called pulsed corona discharge, is the transient phase of spark discharge before arc formation. The transient phase lasts 10-100 nanoseconds while the remainder of the spark discharge (arc and glow discharge) takes microseconds or even milliseconds. In conventional commercial flame spark ignition, only a very small portion of the discharge energy (<1 mJ/pulse) goes to the transient phase; most of the energy (typically 30-100 mJ/pulse) goes to the arc and glow discharges. But experiments show that, for flame ignition, the transient plasma phase is more efficient than the arc and glow discharge phases. 94% of the transient phase discharge energy goes to plasma, which leads to flame ignition. In the arc and glow discharge phases, only 50% (arc) or 30% (glow) of the energy goes to plasma --- 45% (arc) or 70% (glow) of the energy is dissipated in electrode heating. For our transient plasma discharge, the electric field in a streamer wave front can be so high that there exist energetic electrons. Although the parameters of a streamer are difficult to characterize because of their strong spatial and temporal inhomogeneity, it has been demonstrated that non-equilibrium electrons can exist in the head of streamer for a transient (tens of ns) time with electron energies greater than 10eV. Energetic electrons with high kinetic energies can effectively generate reactive species such as O atom, H atom, the flame front marker CH and the chain branching oxidizer OH, which can then rapidly initiate chain reactions.

Transient plasma discharge can readily ignite flame at many points (tens to hundreds) simultaneously. Conventional spark ignition has only one discharge channel. Multi-site ignition can greatly increase the burning rate and decrease heat loss to the chamber walls, boosting thermal efficiency and facilitating lean fuel burning. Transient plasma ignition has a higher thermal efficiency as a result of the higher electron energy, which provides a better match with the ionization and dissociation energy of many molecules, with less radiative and conductive heat loss.

Non-thermal plasma Actuator

Experimental Setup

Non-thermal plasma has been studied as a potential way for oxides of nitrogen (NOx) reduction in exhaust of lean-burn diesel engines by using plasma-catalyst system1. More efficiently, transient non-thermal plasma has also been applied in reducing pollutions of gas, liquid and solid, especially for NOx reduction. In these transient plasma systems, high energy intensity plasma corona lasts only for tens of nanoseconds but can significantly remove NOx emissions with energy cost at 10~20 eV per NO molecule.

Since the transient non-thermal plasma can direct generate tremendous amount of ions, atoms, and most importantly, reactive radials, including oxygen atom (O), CH* and OH*, it is proposed to be an effective approach to influence gas turbine combustion, such as NOx, and carbon monoxide (CO) emissions, combustion instability and lean blow off limit. In this pioneer investigation of the generator of transient plasma caused by pulsed corona as a potential control actuator for gas turbine combustion, its application to effectively change the combustion radial fields is demonstrated. This demonstration was performed in a multiple swirl-dump spray combustor that features typical modern gas turbine combustor design.