Daniel Singleton

The role of non-thermal transient plasma for enhanced flame ignition in C2H4-air

Transient plasma ignition, involving short ignition pulses (typically 10?50?ns), has been shown to effectively reduce ignition delays and improve engine performance for a wide range of combustion-driven engines relative to conventional spark ignition. This methodology is therefore potentially useful for many engine applications; however, at present there is limited understanding of the underlying physics. Evidence is presented here for two distinct phases of the plasma-ignition process: an initial non-equilibrium plasma phase, wherein energetic electrons transfer energy into electronically excited species that accelerate reaction rates, and a spatially distributed thermal phase, that produces exothermic fuel oxidation reactions that result in ignition. It is shown that ignition kernels are formed at the ends of the spatially separated streamer channels, at the cathode and/or anode depending on the local electric field strength, and that the temperature in the streamer channel is close to room temperature up to 100?ns after the discharge.

Compact Pulsed-Power System for Transient Plasma Ignition

The use of a compact solid-state pulse generator and compact igniters for transient plasma ignition in a pulse detonation engine (PDE) is reported and compared with previous results using a pseudospark pulse generator and threaded rod electrode. Transient plasma is attractive as a technology for the ignition of PDEs and other engine applications because it results in reductions in ignition delay and has been shown to ignite leaner mixtures which allows for lower specific fuel consumption, high-repetition rates, high-altitude operation, and reduced NOx emissions. It has been applied effectively to the ignition of PDEs as well as internal combustion engines. Nonequilibrium transient plasma discharges are produced by applying high-voltage nanosecond pulses that generate streamers, which generate radicals and other electronically excited species over a volume. The pulse generator used is in this experiment is capable of delivering 180 mJ into a 200-¿ load, in the form of a 60-kV 12-ns pulse. Combined with transient plasma igniters comparable with traditional spark plugs, the system was successfully tested in a PDE, resulting in similar ignition delays to those previously reported while using a smaller electrode geometry and delivering an order of magnitude less energy.

Low energy compact power modulators for transient plasma ignition

In this paper recent studies of compact power modulators, used to produce nonequilibrium plasma in the transient, formative phase of an arc, and applied to ignition of a quiescent fuel-air mixture in a constant-volume reactor, are reported. In this work, ignition delays produced by transient plasma were measured and compared in pre-mixed C2H4-air at atmospheric pressure. Two compact power modulators studied included; 1) a 54 ns pseudospark switched line-type power modulator that delivered 365 mJ per pulse, and 2) a 12 ns SCR-switched magnetic compression based power modulator that delivered 75 mJ per pulse. Despite the difference in energy delivered, both systems achieved similar ignition delays across a broad range of fuel-air equivalence ratios, and produced ignition delays up to two times shorter than those produced using traditional spark ignition. The results indicate that lower energy and therefore more compact power modulators may be used for this application.

Compact solid state high repetition rate variable amplitude pulse generator

Presented is a solid state high repetition-rate pulse generator with adjustable output amplitude, together with a resonant LC charger. This pulse generator was designed for transient plasma production for ignition and other aerospace plasma applications. The design of the pulse-forming network makes use of commercially available insulated gate bipolar transistors (IGBT) switching a capacitor bank into a METGLAS transformer together with a Fitch voltage doubling circuit. The capacitor bank is charged to 1 kV by a resonant LC charger, also switched by a commercial IGBT. The output of the pulse generator is controlled by the gate voltage of the IGBTs. Pulses with a width of 40ns can be generated with repetition rates up to 10 kHz. The amplitude can be controlled from 9 kV to 38 kV into a 500Ω load.

Demonstration of Improved Dilution Tolerance Using a Production-Intent Compact Nanosecond Pulse Ignition System

Transient plasma ignition using nanosecond pulses has demonstrated the potential to enable improved fuel economy and reduced emissions by enabling lean and EGR limit extension in dilute burn engines. Existing spark ignition technology is not adequate because the energy transfer mechanisms between the spark and the fuel-air mixture are not efficient enough to guarantee stable ignition for dilute mixtures at high-load conditions. Additionally, long duration sparks and other advanced ignition solutions that require increased energy delivered accelerate spark plug electrode wear. To date, non-thermal plasma ignition with nanosecond pulses have demonstrated a lean ignition limit beyond an air/fuel ratio of 24 [1], demonstrated high-pressure ignition at densities equivalent to over 100 bar at the time of ignition [2], and demonstrated stable (COV 20 % [3]. While low-energy nanosecond pulses have demonstrated strong performance compared to existing solutions, they currently only exist on the market in laboratory systems, rather than a production ready system in a single rugged, weather-proof, under-the-hood enclosure. Transient Plasma Systems (TPS) has recently demonstrated the potential for a retroffitable solution similar to coil-on-plug architecture that allows a direct replacement of existing ignition technology without any engine modification. The system was run on a gasoline direct injection engine at Argonne National Laboratory and demonstrated the same trends as previously observed with research grade systems, including lean and EGR limit extension and more stable ignition across a range of loads. The system was capable of delivering 30 kV pulses in bursts of up to 20 pulses at 30 kHz, and demonstrated stable combustion at an air/fuel ratio of 23.5, exhaust gas recirculation of 23 %, and ignition at 19.2 bar with COV <3 % using only 20 kV pulses.

Transient Plasma Fuel–Air Ignition

Transient plasma ignition, a method of fuel-air ignition involving streamer discharges produced by nanosecond high-voltage pulses, is attractive, and that it reduces ignition delay, increases the burning rate, and can ignite leaner mixtures compared with the traditional spark ignition. In this paper, images of the transient plasma discharges and subsequent flame development in a C2H4-air mixture were captured using a single-lens reflex camera and a high-speed camera, respectively.

Optimization of compact power modulators for transient plasma ignition

Non-equilibrated (non-thermal) plasma generated by short (ns), high-voltage (kV) pulses has attractive electron characteristics that fundamentally and favorably alter pre-combustion chemistry and physics [1]. This technology has been demonstrated in applications for airborne engines, including pulse detonation engines [2], in collaborative studies with Nissan in applications for internal combustion engines [3], as well as for more fundamental studies [4]. We report recent studies where two compact power modulator systems are used to produce non-equilibrium plasma in the transient, formative phase of an arc, and are applied to ignition and combustion (transient plasma ignition or TPI) in a constant volume reactor. In this work, ignition delays, a key parameter in the application to pulse detonation engines, were measured in transient plasma ignited C2H4-air in a constant volume reactor at atmospheric pressure. Two compact power modulators were used; a 12 ns SCR-switched magnetic compression based pulse generator and an 85 ns pseudospark switched line-type pulse generator. The results show that despite the difference in energy delivered (70 mJ vs. 400 mJ), both systems achieve similar ignition delays across a broad range of equivalence ratios, and produce ignition delays up to two times shorter than with traditional spark ignition, confirming previous results obtained in an flowing system (pulse detonation engine) [5]. The results indicate that lower energy, more compact power modulators may be used for this application.

Study of the volumetric effect of Transient Plasma Ignition in quiescent ethylene-air

Transient Plasma Ignition (TPI) uses short pulse lengths (typically ≪100 ns) and high voltages (10s of kV) to generate a non-equilibrium transient plasma discharge, allowing radicals and other electronically excited species to be produced over a relatively large volume compared to traditional spark ignition. Studies show that nanosecond pulsed power technology can lead to much shorter ignition delay times and pressure rise times than conventional spark ignition, and that ignition occurs along the anode1. We report here studies of different length electrodes for TPI and traditional spark ignition in a combustion reactor with C2H4-air mixtures. The length of the anode and the output voltage of the pulse generator were varied, resulting in a change in the number of ignition kernels. As the length of the anode is decreased, the peak pressure approaches that achieved using a traditional spark plug, however the pressure rise and ignition delay remain shorter. The shape of the pressure curves for the TPI case with short electrodes indicates a more volumetric ignition in comparison to the spark plug, despite similar ignition geometry.

The role of water in transient plasma ignition for combustion

Pulse detonation engines offer the potential for a single, air-breathing, propulsion system that can operate from subsonic speeds (including take-off) to high Mach number flight. Critical to this technology is rapid repetition rate operation. Plasma-based ignition systems based on short pulse, high voltage pulsed power have been shown to decrease the ignition time in experimental system. The presence of water in the fuel-air mixture, however, has been shown to adversely affect the performance of these ignition systems. Herein, we report on simulations of the plasma chemistry from the application of the pulsed power (10s of ns) through the ignition time (100s of microsecond). These simulations suggest a long-lived neutral species created by the transient plasma ignition process that are strongly affected by water, and can play a role in both combustion processes. Comparison with experimental results, potential mitigation schemes for the water effects, and implications for internal combustion engines will be discussed.

Development of high rep-rate pulse detonation engines based on transient plasma ignition technology

Summary form only given. pulse detonation engines (PDE) are a class of air breathing engines that offer propulsion from sub- to supersonic velocities from a single system. Critical to this technology is the robust and reliable operation at high repetition rates. This forces consideration of a variety of science and engineering challenges to develop systems that rapidly detonate the fuel-air mixture while maintaining reliability and high efficiencies. This paper focuses on recent results on a number of fronts: First, we report on the implementation of transient plasma ignition (TPI) system in an operational PDE test-bed at NPS. We discuss the physics of deflagration-to-detonation transition and the engineering challenges associated with the system resonances and shock-to-electrode interactions at high rep-rate operation. Second, we describe preliminary efforts to understand the role of plasma streamers in modification of the plasma chemistry, fuel cracking, and deflagration-to- detonation transition. TPI ignition relies on high voltage (10s of kV) ionization of the fuel-oxidizer mixture, but with sufficiently short pulse lengths (typically <100 ns) to avoid the low efficiencies (thermal energy deposition) of arc formation. The importance of field enhancement, cathode/anode surface physics of the oxidizer, circuit impedance effects, energy coupling, and chemical kinetics on TPI are studied via simulation, and compared with experimental data. Both global models and kinetic particle- in-cell results are discussed.