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Combustion Modeling Lab at UC Berkeley

Current Research

Ignition by non-thermal plasma: Nanosecond pulsed discharge


Daniel Pineda, Tiernan Casey (CML)

In conjuction with Transient Plasma Systems, Inc


Introduction

Spark plugs have been used to ignite combustible mixtures like those found in automotive engines for over a century, and the principles of the ignition by sparks (thermal plasma) have remained relatively unchanged during that time. By utilizing a transient non-thermal plasma, more effective combustion can be realized.

TPS System TestingTPS CEO Dan Singleton elaborates on the physics behind nanosecond pulsed discharge ignition to Profs. Chen and Dibble and graduate students in the Combustion Analysis Laboratory in Hesse Hall.

Preliminary experiments on lean methane-air mixtures in a constant volume combustion chamber have determined that utilizing a pulsed (10 kHz) nonthermal plasma generated by a rapid (12 ns) voltage rise (~15 kV) across ignition electrodes can decrease flame development time and increase the rate of pressure rise and advance the time of peak heat release. The relative contributions of compounding chemical kinetic and hydrodynamic effects to this combustion enhancement remain to be identified and present an ongoing research project for the Combustion Modeling Laboratory.


Nanosecond Pulsed Discharge in a Lean Methane-Air Mixture

Abstract: High-speed schlieren imaging of nanosecond pulsed discharges in a near-atmospheric lean methane/air mixture reveals enhanced ignition over traditional inductive spark. The chamber pressure history also indicates faster flame development time.

Schlieren Images, phi = 0.70Schlieren images taken at 50,000 fps for spark-ignited (a) and nanosecond pulsed discharge ignition modes using 5 pulses (b) and 20 pulses (c).


Nanosecond pulse plasma assisted ignition simulations at atmospheric pressure

Abstract: Ignition assistance by a pulsed applied voltage is investigated in a canonical one-dimensional configuration. An incipient ignition kernel, formed by localized energy deposition into a lean mixture of methane and air at atmospheric pressure, is subjected to sub-breakdown electric fields by a DC potential applied across the domain, resulting in non-thermal behavior of the electron sub-fluid formed during the discharge. A two-fluid approach is employed to couple thermal neutrals and ions to the non-thermal electrons, and a two-temperature plasma mechanism describing gas phase combustion, excitation of neutral species, and high-energy electron kinetics is employed to account for non-thermal chemical effects. Charged species transported from the ignition zone drift rapidly through the domain, augmenting the magnitude of the electric field in the fresh gas during the pulse through a dynamic-electrode effect, which results in an increase in the energy of the electrons in the fresh mixture with increasing time. Enhanced fuel and oxidizer decomposition due to electron impact dissociation and interaction with excited neutrals generate a pool of radicals, mostly O and H, in the fresh gas ahead of the flame's preheat zone. The effect of the nanosecond pulse is to increase the mass of fuel burned at equivalent times relative to the unsupported ignition through enhanced radical generation, resulting in an increased heat release rate in the immediate aftermath of the pulse.