Research Highlights
Plasma-Assisted Aerospace Technologies
Plasmas in Flames
Nanosecond pulsed discharges are a promising technology to improve the static and dynamic stability of flames. Whereas most works have centered on the impact of the plasma on the flame, fewer studies have focused on the implications of having a strongly inhomogeneous and unsteady environment on the discharge characteristics. In this experimental work we quantify the response of the discharge mode and energy deposition to dynamic combustion environments. The first experimental setup considers a premixed methane/air mesoscale combustor, that allows for 1D laminar flame propagation and provides a simple-to-characterize gaseous background, coupled to nanosecond repetitively pulsed discharges in a dielectric barrier discharge configuration. The study has revealed the strong coupling of the discharge mode and energy deposition with the relative positioning of the flame. The second experiment, in collaboration with RGD Lab and FGC Plasma, considers a burner of more practical interest: a swirl-stabilized combustor of 14kW power under lean conditions and experiencing a 120Hz acoustic instability. The discharge is now generated in a pin-to-ring configuration with the objective of suppressing this instability. In a similar way to the 1D laminar experiment, the discharge evolves over the oscillation cycle of the flame. The results from this work have implications when designing plasma-assisted actuation strategies. Learn more
Models of plasma-assisted combustion for reactor design
We are developing computational models to assess the efficiency and authority of nonthermal plasmas to extend ignition limits and provide flame enhancement. Whereas most efforts in the literature focus either on zero-dimensional detailed kinetic models, or on higher dimensional models with a phenomenological description of the plasma that greatly simplifies its kinetic effects, our work focuses on one-dimensional models that can handle arbitrarily complex chemical kinetic schemes, so that transport effects can be captured while retaining all the relevant chemistry. Our numerical simulation tools include zero-dimensional chemical kinetic solvers that concurrently consider electron-induced chemistry, triggered by plasma, and thermally-induced chemistry, representative of typical combustion reactions; as well as one-dimensional models of flame propagation, ignition and inflammation from filamentary discharges. The objective of these models is to enable engineering design of plasma-assisted combustion technologies through numerical simulation. Learn more
Plasma-assisted CO2 conversion
Plasma-assisted CO2 conversion is a novel technology that could help address climate change by removing greenhouse gasses from the atmosphere and fulfilling the demand for carbon-based products. This technology can also be used for In-Situ Resource Utilization (ISRU) of the Mars atmosphere to create breathable oxygen and rocket fuel for a return mission. Benefits of non-equilibrium plasmas include mild operating conditions, adaptability to different feedstocks, direct-use of electricity, modularity, low investment and operation costs, and tunable reactivity depending on the desired outcome. Project IMPACT, in collaboration with IST Lisbon, is exploring the inverse design and modeling of plasma sources for CO2 conversion, with performance metrics being the conversion rate into value-added chemicals and fuels and the energy efficiency of the reactor, including chemical activation and separation stages. Learn more
Lightning Safety
Aircraft lightning strike risk-mitigation
This project exploits the physics of lightning initiation from aircraft to propose a lightning strike risk-mitigation strategy based on controlling the net electrical charge of the aircraft. The majority of lightning strikes to aircraft are triggered by the aircraft itself, through a bidirectional leader process. Since, under most instances, the positive leader is incepted first, due to lower electric field inception and propagation thresholds, one can envision charging the aircraft to negative charge levels to hinder the process. If done at the correct level, the negative leader might still be avoided, effectively reducing the likelihood of occurrence of the bidirectional discharge. The practical implementation of the strategy would require monitoring the electrical environment, for example, using electric field mills, and actuate accordingly by modifying the net charge of the vehicle, possibly using ion emitting devices, as commanded by an on-board algorithm. In this project we have analyzed the strategy from a theoretical perspective, performed lightning attachment tests in a high voltage laboratory facility, and demonstrated that charge control can be achieved via ion emission, both in the wind tunnel and in flight. Learn more
Unconventional aircraft zoning
The protection of aircraft from lightning strikes is an essential component in the aircraft development and certification process. In the past, lightning strikes to aircraft have caused catastrophic accidents that have promoted extensive studies into the mechanisms behind lightning events and their mitigation strategies. These recommendations have led to protective measures in the form of wire mesh and diverter strips on nonmetallic surfaces, removing sources of spark-triggered ignition in the fuel system, adequate grounding and wire bundle shielding strategies, and route management to avoid thunderstorms. While significant progress has been made in aircraft lighting protection, much of what we know about aircraft triggered lightning comes from historical experience and testing. Next generation aircraft designs may not conform to the same assumptions under which models for existing aircraft are valid. In this project we are developing a general computational tool for the prediction of the first and second attachment points on arbitrary aircraft geometries. The tool couples numerical electrostatics simulation to a predictive attachment model, and uses open source software. Learn more
Fundamentals of Electrical Breakdown
Experimental studies of streamer coronas
Streamer coronas are widely used as a low temperature plasma source in industrial applications, both established (e.g. ozone generation, air cleaning, electrostatic precipitators) and emerging (e.g. CO2 conversion, ignition, combustion, medicine, water treatment, catalysis). They also appear in nature, at largely different scales, during the formation and propagation of lightning leaders (with implications in aviation and wind power), sprites and blue jets. Despite the wide range of interest, streamer coronas remain a poorly understood phenomenon, in particular, aspects related to the collective nature of streamers or their long-timescale behavior.
Recent work by our group has sought to experimentally measure the electric field inside a positive DC streamer corona, using the recently-developed E-FISH laser diagnostic technique. We measured the electric field at different vertical locations in the streamer corona and over the full time period between two sequential pulses. We found some surprising results regarding the time-dependent behavior of the electric field, which challenge the established theory that the pulsation frequency of the streamers is driven by electric field recovery due to removal of space charge from the inter-electrode gap. Learn more
Hierarchical models of streamers
Another aspect of our research into the fundamental physics of streamers is numerical modeling. Our group is developing a hierarchical framework for the modeling of streamer discharges, ranging from 2D axisymmetric fluid models (as shown in the accompanying image), to reduced order models using the 1.5D approximation and description using macroscopic parameters. These reduced order models may serve as building blocks to tackle the more complex problem of a streamer corona in a more computationally-efficient way. Learn more
Streamers in airflow
The behavior of streamer discharges in wind is relevant for several problems related to atmospheric electricity, as components of electrostatic discharge and precursors of lightning in wind turbines and aircraft. Experiments of streamers in wind are lacking in the literature, a gap we are working on addressing through wind tunnel campaigns. The objective of this work is both to elucidate the physics of breakdown in wind, as well as explore electrode structures of practical interest (e.g. p-static wicks, wind turbine blade tips, etc.). Learn more