Abstract:
A device that uses electrical discharges/nonthermal plasmas in a gaseous medium to activate a fuel or fuel-oxidizer mixture to promote more effective and efficient combustion, in which a dielectric barrier discharge or silent discharge plasma is used to break up larger organic molecules (the fuel) into smaller ones that are more easily and completely combusted. The discharge also creates free radicals that promote more efficient combustion. The device is a cylindrical, coaxial (cylinder in a cylinder) dielectric barrier discharge/silent discharge plasma reactor. It includes two conducting electrodes, one or both of which are covered by a dielectric material. The electrodes are separated by a thin, gas-containing space. A high voltage is applied to the electrodes to create electric discharge streamers in the gas. The discharges are the source of the nonthermal plasma.

Description:
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT  
       [0001] This invention was made with Government support under Contract No. W-7405-ENG-36, awarded by the Department of Energy. The Government has certain rights in this invention. 
     
    
     
       CROSS-REFERENCE TO RELATED APPLICATIONS  
         [0002]    Not Applicable  
         INCORPORATION-BY-REFERENCE OF MATERIAL SUBMITTED ON A COMPACT DISC  
         [0003]    Not Applicable  
         BACKGROUND OF THE INVENTION  
         [0004]    1. Field of the Invention  
           [0005]    This invention pertains generally to devices for processing combustible gases, and more particularly to non-thermal plasma reactors.  
           [0006]    2. Description of Related Art  
           [0007]    To operate fossil-fueled motor vehicles and other combustion-related engines or machinery under higher efficiency and reduced pollution output conditions in the future, it is desirable to have clean-burning, energy-efficient fuel usage. Higher-order hydrocarbons can be broken up, activated, or exposed to active species to achieve greater combustion efficiency. One example of a particular application is the deployment of a controlled-detonation gas-turbine engine (e.g., an aircraft engine).  
           [0008]    Prior-art plasma combustion-enhancement reactors use thermal arcs or microwave radiation to activate fuel or a fuel-oxidizer mixture. These devices are inefficient, tend to consume copious amounts of energy, and have low active species/free radical yields.  
           [0009]    The present invention has recognized these prior art drawbacks, and has provided the below-disclosed solutions to one or more of the prior art deficiencies.  
         BRIEF SUMMARY OF THE INVENTION  
         [0010]    The present invention is a device that employs electrical discharges/nonthermal plasmas in a gaseous medium to activate or convert a fuel or a fuel-oxidizer mixture to promote more effective and efficient combustion. In nonthermal plasmas, the electrons are “hot”, while the ions and neutral species are “cold”—which results in little waste enthalpy being deposited in a process gas stream. This is in direct contrast to thermal plasmas, where the electron, ion, and neutral-species energies are in thermal equilibrium (or “hot”) and considerable waste heat is deposited in the process gas. The present invention utilizes a type of electrical discharge called a silent discharge plasma (SDP), or a dielectric barrier discharge (DBD), to break up large organic fuel molecules into smaller molecules that are more easily and completely combusted and to create highly reactive free-radical chemical species that can promote more efficient combustion by their strong oxidizing power or by their ability to promote combustion-sustaining chain reactions or chain reactions that further generate active species.  
           [0011]    In the present invention, a SDP/DBD reactor is applied to gas streams containing organic fuels or fuel/oxidizer mixtures.  
           [0012]    In one aspect of the present invention, a device for processing combustible gases includes a high voltage electrode and a ground electrode that is slightly spaced from the high voltage electrode. A dielectric layer is disposed adjacent to the high voltage electrode between the high voltage electrode and the ground electrode. A gas modification passage is established within the housing between the dielectric layer and the ground electrode. Moreover, a process gas supply provides a process gas to the gas modification passage. The high voltage electrode can be energizable to create nonthermal electrical microdischarges between the high voltage electrode and the ground electrode across the dielectric layer.  
           [0013]    In another aspect of the present invention, a device for processing combustible gases includes a gas modification passage. Moreover, the device includes means for supplying a process gas to the gas modification passage and means for creating nonthermal electrical microdischarges along the length of the gas modification passage. The process gas flows through the nonthermal electrical microdischarge.  
           [0014]    In yet another aspect of the present invention, a device for processing combustible gases includes a cylindrical housing. A metal oxidizer gas supply tube is disposed within the housing. The oxidizer gas supply tube is electrically grounded. Moreover, a first dielectric tube is disposed within the housing around the oxidizer gas supply tube and a gas modification passage is established between the oxidizer gas supply tube and the first dielectric tube. A metal high voltage electrode circumscribes the first dielectric tube. The high voltage electrode is energizable to create nonthermal electrical microdischarges between the high voltage electrode and the oxidizer gas supply tube along the length of the gas modification passage.  
           [0015]    In still another aspect of the present invention, a device for processing combustible gases includes a rectangular box-shaped housing in which a metal, rectangular, plate-shaped ground electrode is disposed. A rectangular, plate-shaped dielectric layer is slightly spaced from the ground electrode and a gas modification passage is established between the ground electrode and the dielectric layer. In this aspect, a metal, rectangular, plate-shaped high voltage electrode is disposed within the housing adjacent to the dielectric layer. The high voltage electrode is energizable to create nonthermal electrical microdischarges between the high voltage electrode and the ground electrode along the length of the gas modification passage.  
           [0016]    In yet still another aspect of the present invention, a method for processing combustible gases includes establishing a gas modification passage that defines a length. Nonthermal electrical microdischarge is created along the length of the gas modification passage. Additionally, a process gas is provided to the gas modification passage such that the process gas flows through the nonthermal electrical microdischarge.  
           [0017]    An object of the present invention is to provide a device that can be used to convert or activate either fuel or fuel-air mixtures.  
           [0018]    Another object of the present invention is to provide a device that can be used to convert or activate a relatively larger volume of fuel or fuel-air mixture.  
           [0019]    Another object of the present invention is to provide a device that can be used in supersonic combustion applications, as well as conventional internal-combustion engine applications.  
           [0020]    Another object of the present invention is to provide a device that can be meshed with internal-combustion engine fuel-injector systems in order to provide a higher proportion of optimally-atomized and activated fuel into a combustion chamber.  
           [0021]    Further aspects of the invention will be brought out in the following portions of the specification, wherein the detailed description is for the purpose of fully disclosing preferred embodiments of the invention without placing limitations thereon.  
       
    
    
     BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING(S)  
       [0022]    The invention will be more fully understood by reference to the following drawings which are for illustrative purposes only:  
         [0023]    [0023]FIG. 1 is a side plan view of a first embodiment of a silent discharge plasma reactor.  
         [0024]    [0024]FIG. 2 is an end view of the first embodiment of the SDP reactor.  
         [0025]    [0025]FIG. 3 is a cross-section view of the first embodiment of the SDP reactor taken along line  3 - 3  in FIG. 2.  
         [0026]    [0026]FIG. 4 is a cross-section view of a second embodiment of a SDP reactor.  
         [0027]    [0027]FIG. 5 is a cross-section view of a third embodiment of a SDP/DBD reactor.  
         [0028]    [0028]FIG. 6 is a cross-section view of a fourth embodiment of a SDP/DBD reactor.  
         [0029]    [0029]FIG. 7 is a side plan view of a fifth embodiment of a SDP/DBD reactor.  
         [0030]    [0030]FIG. 8 is a cross-section view of the fifth embodiment of the SDP/DBD reactor taken along line  8 - 8  in FIG. 7.  
         [0031]    [0031]FIG. 9 is a cross-section view of a sixth embodiment of a SDP/DBD reactor.  
         [0032]    [0032]FIG. 10 is a block diagram of a non-limiting, exemplary combustion system. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0033]    Referring more specifically to the drawings, for illustrative purposes the present invention is embodied in the apparatus generally shown in FIG. 1 through FIG. 10. It will be appreciated that each apparatus may vary as to configuration and as to details of the parts, and that the method may vary as to the specific steps and sequence, without departing from the basic concepts as disclosed herein.  
         [0034]    [0034]FIGS. 1, 2, and  3  show a first embodiment of a silent discharge plasma/dielectric-barrier discharge (SDP/DBD) reactor according to the present invention, generally designated  10 . As shown in FIGS. 1 and 2, the reactor  10  includes a generally cylindrical housing  12  disposed between a generally disk-shaped inlet end cap  14  and a generally disk-shaped outlet end cap  16 . FIGS. 1 and 2 show that the end caps  14 ,  16  can be removably engaged with the housing  10  using plural nuts  18  and plural bolts  20 , but it can be appreciated that any other fastening means well known in the art can be used.  
         [0035]    [0035]FIG. 3 shows that the reactor  10  includes a metal, generally cylindrical high-voltage (HV) electrode  22  disposed within the housing  12  between the end caps  14 ,  16 . In a preferred embodiment, the HV electrode  22  is connected to an alternating current (AC) source or a pulsed direct current (DC) source. Moreover, a generally cylindrical, dielectric tube  24  is disposed within the HV electrode  22  such that the HV electrode  22  closely surrounds the dielectric tube  24 . Preferably, the dielectric tube  24  is made from a dielectric material, e.g., glass, ceramic, etc. As shown in FIG. 3, a metal, generally cylindrical oxidizer gas supply tube  26  is disposed within the dielectric tube  24 . It is to be understood that the oxidizer gas supply tube  26  is electrically grounded. It is to be understood that the electrode  22  and the tubes  24 ,  26  are concentric to each other and are centered on a central axis  28  established by the reactor  10 .  
         [0036]    [0036]FIG. 3 shows that a gas modification passage  30  is established between the oxidizer gas supply tube  26  and the dielectric tube  24 . Also, an oxidizer gas supply passage  32  is established within the oxidizer gas supply tube  26 . Moreover, one end of the oxidizer gas supply tube  26  establishes an oxidizer gas inlet  34  and the other end of the oxidizer gas supply tube  26  establishes an oxidizer gas outlet  36 . As shown, a modified process gas outlet  38  is established by the outlet end cap  16  and leads from the gas modification passage  30 . FIG. 3 further shows that a first “O” ring  40  and a second “O” ring  42  can be used to seal the ends of the dielectric tube  24 , e.g., by placing the first “O” ring  40  between the dielectric tube  24  and the inlet end cap  14  and by placing the second “O” ring  42  between the dielectric tube  24  and the outlet end cap  16 .  
         [0037]    [0037]FIG. 3 further shows that a first “O” ring groove  44  is established in the inlet end cap  14  such that it circumscribes the oxidizer gas supply tube  26  and a third “O” ring  46  is inserted therein to seal the inlet end cap  14  and prevent modified gas from escaping from the reactor  10  at the interface between the oxidizer gas supply tube  26  and the inlet end cap  14 .  
         [0038]    It is to be understood that when the HV electrode  22  is energized, nonthermal electrical microdischarges occurs between the dielectric tube  24  and the metal oxidizer gas supply tube  26  which is electrically grounded. The nonthermal electrical microdischarges occur within the gas modification passage  30  and the width of the gas modification passage  30  defines a discharge gap  48 .  
         [0039]    Preferably, the discharge gap  48  is between one and several millimeters (e.g., 1-10 mm).  
         [0040]    It is to be understood that as the process gas, e.g., a fuel or a fuel-air mixture, flows through the gas modification passage  30  within the SDP/DBD reactor  10 , the nonthermal electrical microdischarges between the HV electrode  22  and the grounded oxidizer gas supply tube  26  across the dielectric tube  24 , can generate highly reactive chemical species, e.g., free radicals, in the process gas to yield a modified process gas. The modified process gas can then be fed to an internal combustion engine, furnace, or any other combustion device. The reactive species generated within the gas modification passage  30  can break up large organic fuel molecules into smaller ones that are more easily and completely combusted and can create highly reactive free-radical chemical species that can promote more efficient combustion by their strong oxidizing power or by their ability to promote combustion-sustaining chain reactions or chain reactions that further generate active species.  
         [0041]    Accordingly, the present invention can be used to “convert” combustible fuels. In other words, the present invention can be used to create fragmented, more easily combustible compounds having smaller molecules. Additionally, the present invention can be used to “activate” combustible fuels, i.e., it can be used to create highly reactive free-radical species that are strong oxidizers or combustion chain carriers, which tend to increase combustion efficiency.  
         [0042]    [0042]FIG. 4 shows a second embodiment of a SDP/DBD reactor according to the present invention, generally designated  100 . As shown in FIG. 4, the reactor  100  is similar in every aspect to the reactor shown in FIGS. 1, 2, and  3  except for the following modifications. First, a wire  102  is wound around the dielectric tube  24  to establish a HV electrode instead of using HV electrode  22 . In addition, the oxidizer gas supply tube  104  shown in FIG. 4 is a tube that is formed with at least one oxidizer outlet  106  to allow oxidizer gas to flow through the reactor  100 . As shown, oxidizer gas outlet  106  is formed laterally along the oxidizer gas supply tube  104  and connects the oxidizer gas supply passage  34  to the gas modification passage  30 . Moreover, a plug  108  is installed at the end of the oxidizer gas supply tube  104 .  
         [0043]    [0043]FIG. 5 shows a third embodiment of a SDP/DBD reactor according to the present invention, generally designated  150 . As shown in FIG. 5, the reactor  150  is similar in every aspect to the reactor shown in FIGS. 1, 2, and  3  except for the following modifications. First, the oxidizer gas supply tube  152  shown in FIG. 5 is a tube that is formed with at least one oxidizer outlet  154  to allow oxidizer gas to flow through the reactor  150 . Second, a second dielectric tube  156  circumscribes the oxidizer gas supply tube  152 . Accordingly, a gas modification passage  158  is established between the dielectric tubes  24 ,  156  and nonthermal electrical microdischarges occur between the HV electrode  22  and the grounded oxidizer gas supply tube  152  across the dielectric tubes  24 ,  156 . Moreover, a plug  160  is installed the end of the oxidizer gas supply tube  152 .  
         [0044]    [0044]FIG. 6 shows a fourth embodiment of a SDP/DBD reactor according to the present invention, generally designated  170 . As shown in FIG. 6, the reactor  170  is similar in every aspect to the reactor shown in FIGS. 1, 2, and  3  except for the following modifications. First, a solid cylindrical ground electrode  172  is disposed within the dielectric tube  24  which, in turn, is disposed within the cylindrical HV electrode  22 . The gas modification passage  30  is established between the dielectric tube  24  and the ground electrode  172  and nonthermal electrical microdischarges occur between the HV electrode  22  and the ground electrode  172  across the dielectric tube  24 . Oxidizer gas flows through an oxidizer gas inlet  174 , through the gas modification passage  30 , and exits the reactor  170  through an oxidizer gas outlet  176 . In this embodiment, oxidizer-activated fuel mixing does not take place at the end of the electrode  172 ; instead the activated fuel or fuel-oxidizer mixture simply exits the reactor through passage  176  and enters a combustion chamber.  
         [0045]    [0045]FIGS. 7 and 8 show a fifth embodiment of a SDP/DBD reactor according to the present invention, generally designated  200 . As shown in FIGS. 7 and 8, the reactor  200  includes a generally rectangular housing  202  disposed between a generally flat, rectangular, plate-shaped inlet end cap  204  and a generally flat, rectangular, plate-shaped outlet end cap  206 . FIGS. 7 and 8 show that the end caps  204 ,  206  can be removably engaged with the housing  200  using plural nuts  208  and plural bolts  210 , but it can be appreciated that any other fastening means well known in the art can be used.  
         [0046]    [0046]FIG. 8 shows that the reactor  200  includes a metal, generally flat, rectangular, plate-shaped high-voltage (HV) electrode  212  disposed within the housing  202  between the end caps  204 ,  206 . Preferably, the HV electrode  212  is connected to an alternating current (AC) source or a pulsed direct current (DC) source. Moreover, a generally flat, rectangular dielectric plate  214  is disposed within the reactor  200  immediately adjacent to the HV electrode  212 . Preferably, the dielectric plate  214  is made from a material such as glass, ceramic, etc. As shown in FIG. 8, a metal, generally flat, rectangular, plate-shaped ground electrode  216  is disposed within the reactor  200  such that it is slightly spaced from the dielectric plate  214 . It is to be understood that the ground electrode  216  is electrically grounded.  
         [0047]    As shown in FIG. 8, a gas modification passage  218  is established between the ground electrode  216  and the dielectric plate  214 . FIG. 8 further shows that the inlet end cap  204  is formed with a process gas inlet  220  that leads to the gas modification passage  218 . Also, a modified gas outlet  222  is established by the outlet end cap  206  and leads from the gas modification passage  220 .  
         [0048]    It is to be understood that when the HV electrode  212  is energized, nonthermal electrical microdischarges occur between the HV electrode  212  and the ground electrode  216  across the dielectric plate  214 . These nonthermal electrical microdischarges occur within the gas modification passage  218  and the width of the gas modification passage  218  defines a discharge gap  224 . Preferably, the discharge gap  224  is between one and several millimeters (e.g., 1-10 mm). It can be appreciated that as a process gas flows through the gas modification passage  218 , it is modified by the nonthermal electrical microdischarges within the gas modification passage  218 , as described in detail above.  
         [0049]    Referring now to FIG. 9, a sixth embodiment of a SDP/DBD reactor according to the present invention is shown and is generally designated  300 . The reactor  300  shown in FIG. 9 is essentially identical to the reactor shown in FIGS. 7 and 8 with the one exception that a second dielectric plate  302  is disposed within the reactor  300  between the HV electrode  212  and the ground electrode  216 . As shown, the second dielectric plate  302  is immediately adjacent to the ground electrode  216 .  
         [0050]    Referring now to FIG. 10, a non-limiting, exemplary combustion system is shown and is generally designated  400 . FIG. 10 shows that the system  400  includes an SDP/DBD reactor, e.g., the reactor  10  shown in FIGS. 1, 2, and  3  and described in detail above. A process gas supply  402  can be connected to the SDP/DBD reactor  10  via a process gas fluid line  404 , e.g., by connecting fluid line  404  to the oxidizer gas inlet  36  (FIG. 3). As shown, a flow meter  406  is installed along the process gas fluid line  404  to monitor the flow of gas to the SDP/DBD reactor  10 .  
         [0051]    As further shown in FIG. 10, a power supply  408 , e.g., an AC power supply, is connected to the SDP/DBD reactor  10  via a high voltage (HV) transformer  410 . Moreover, an oscilloscope  412  is also connected to the SDP/DBD reactor  10  and can be used to monitor the current and voltage of the signal applied to the SDP/DBD reactor  10  that is used to create the nonthermal electrical microdischarges within the gas modification passage  30  (FIG. 3).  
         [0052]    [0052]FIG. 10 shows that the SDP/DBD reactor  10  is connected to a combustion chamber  414  by a modified process gas fluid line  416  that provides modified gas to the combustion chamber  414 . An air supply  418  provides air to the combustion chamber  414  via an air fluid line  420  and a flow meter  422  installed along fluid line  420  monitors the flow of air to the combustion chamber  414 . It can be appreciated that the modified gas from the SDP/DBD reactor  10  and the air from the air supply  418  can be combined within the combustion chamber  414  and ignited to produce a flame  424 . It can be appreciated that the air supply  418  can also be connected to the SDP/DBD reactor  10 , as indicated by dashed line  426 , and the air/process gas mixture can be modified as described in detail above as it flows through the gas modification passage  30  (FIG. 3).  
         [0053]    Although the description above contains many details, these should not be construed as limiting the scope of the invention but as merely providing illustrations of some of the presently preferred embodiments of this invention. Therefore, it will be appreciated that the scope of the present invention fully encompasses other embodiments which may become obvious to those skilled in the art, and that the scope of the present invention is accordingly to be limited by nothing other than the appended claims, in which reference to an element in the singular is not intended to mean “one and only one” unless explicitly so stated, but rather “one or more.” All structural, chemical, and functional equivalents to the elements of the above-described preferred embodiment that are known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the present claims. Moreover, it is not necessary for a device or method to address each and every problem sought to be solved by the present invention, for it to be encompassed by the present claims. Furthermore, no element, component, or method step in the present disclosure is intended to be dedicated to the public regardless of whether the element, component, or method step is explicitly recited in the claims. No claim element herein is to be construed under the provisions of 35 U.S.C. 112, sixth paragraph, unless the element is expressly recited using the phrase “means for.”