The University of Michigan
Department of Aerospace Engineering
| Plasmadynamics & Electric Propulsion Laboratory |
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PEPL Research Projects
Environmental Plasmas
project personnel: Laura Spencer and Alec Gallimore
previous personnel: Kristina Lemmer and Sonca Nguyen
project sponsors:

Figure 1. Schematic of helicon plamsa source (a) and of the separately pumped RGA chamber (b).

Figure 2. RGA spectrum of the water plasma indicating the presence of molecular hydrogen and oxygen, hydroxyl, and water. An argon peak is observed because a small amount of argon was added to the gas line for calibration purposes. (From ref. 2).

Figure 3. Measurements of the energy efficiency of carbon dioxide dissociation in the plasma source.

Motivation:

Current dependence on fossil fuels to satisfy increasing energy needs has had a nontrivial effect on the overall carbon dioxide (CO2) content in the atmosphere. Similar to other greenhouse gases, CO2 molecules absorb infrared radiation emitted from the Earth's surface in asymmetric vibrationally excited modes, inhibiting radiation from leaving the atmosphere. These molecules release the radiation in all directions when they de-excite, thus heating the planet by re-directing outward bound radiation back to the Earth's surface. The 2009 U.S. Greenhouse Gas Inventory Report has stated that CO2 emissions account for 85% of all greenhouse gas emissions with the majority of these emissions created as the result of fossil fuel combustion. Given that the atmospheric concentrations of CO2 have risen about 36% since the industrial revolution, the earth's carbon cycle has become unbalanced and unable to compensate for the extra anthropogenic CO2 emissions, resulting in climate change.

Method:

PEPL has chosen to address the energy and climate change challenges via an rf plasma source by experimentally studying the production of hydrogen from water vapor and the destruction of carbon dioxide. Both projects were performed in the Cathode Test Facility (CTF) at PEPL, consisting of a cylindrical vacuum chamber measuring 0.61 m in diameter and 2.44 m in length. CTF is operated in conjunction with an Edwards XDS 35i dry pump for chamber evacuation reaching a base pressure of less than 3x10-3 torr. The rf plasma source is mounted on the side of the chamber, and gas is injected into the chamber via a 15-cm-diameter by 50-cm-long quartz tube vacuum sealed to the side of the chamber by a rubber O-ring. The plasma source consists of a 13.56-MHz, 1-kW rf power supply connected to a double helix antenna via a pi-style matching network. The antenna is wrapped around the quartz gas injection tube and is surrounded by three electromagnetic coils that provide an external peak magnetic field of 415 G along the centerline. The electromagnetic coils are powered by a Lambda DC power supply capable of outputting a maximum current of 60 A. Species identification is performed by a Stanford Research Systems RGA100 residual gas analyzer. To accommodate the pressure requirements of the RGA, a differentially pumped subchamber was attached to the top of CTF in which the RGA was housed. Figure 1 shows a diagram of the plasma source and the separate RGA chamber.

Results:

The rf plasma source was shown to dissociate the water vapor plasma to produce hydrogen as well as break down carbon dioxide to produce carbon monoxide. Figure 2 shows a sample of the raw RGA data clearly indicating a strong peak at the mass per charge ratio of hydrogen. There were also traces of the OH radical and oxygen. Figure 3 shows the energy efficiency of carbon dioxide dissociation in the plasma source. The energy efficiencies of both processes to produce hydrogen and to destruct carbon dioxide were only a few percent. Therefore it has been determined that this particular plasma source will not be useful for this application. Currently, PEPL is developing an atmospheric pressure microwave plasma source to continue to investigate the capabilities of plasma-assisted carbon dioxide dissociation.

 

Selected Relevant Publications

  1. Lemmer, K. M., "Use of a Helicon Source for Development of a Re-Entry Blackout Amelioration System," Ph.D. Dissertation, University of Michigan, 2009.
  2. Nguyen, S. V. T., "Hydrogen Production in a Radio-Frequency Plasma Source Operating on Water Vapor," Ph.D. Dissertation, University of Michigan, 2009.
  3. Spencer, L. and .Gallimore, A., "Mass Spectrometric Analysis of CO2/Ar and CO/Ar Plasma in a Radio Frequency Discharge," 37th International Conference on Plasma Science, Norfolk, VCA, June 20 - June 24, 2010.
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