Patent Publication Number: US-2005140341-A1

Title: Microcombustion electricity generator

Description:
DESCRIPTION  
      The present invention relates to a microcombustion electricity generator, which allows the kinetic energy of a plasma generated by combustion to be transformed into an electric current in a utiliser device or external load.  
      The electricity generator according to the invention is characterised in that it comprises  
      a microcombustor provided with at least one electrically controlled fuel injector, and operable to produce, at an exhaust outlet, a flow of exhaust gas in plasma state, comprising positive ions and electrons separated from one another; and  
      a conversion device coupled to the said exhaust outlet of the microcombustor, and comprising  
      a duct of electrically insulating material coupled to the said exhaust outlet of the microcombustor and provided in its initial portion with means for separation and capture of the negative charges (electrons) of the plasma, in such a way that  
      downstream of the said initial portion of the duct the plasma comprises substantially only positive ions;  
      downstream of the said initial portion the duct has an intermediate portion provided with an external cladding of electrically conductive material insulated from the said plasma, the ends of which are connectable to a load or electric utiliser device;  
      the arrangement being such that in operation the flow of positive ions in the said intermediate portion of the duct induces, electrostatically in the said conductive cladding, a negative charge which propagates in the said cladding substantially in the direction of flow of the plasma in the said intermediate portion of the duct thereby generating a flow of electrical current in the load. 
    
    
      Further characteristics and advantages of the invention will become apparent from the following detailed description, given purely by way of non-limitative example, with reference to the attached drawings, in which:  
       FIG. 1  is a partially sectioned schematic representation of a microcombustion electricity generator according to the invention; and  
       FIG. 2  is a partial illustration of a variant embodiment. 
    
    
      An electricity generator according to the invention is generally indicated  1  in  FIG. 1 .  
      This generator comprises a microcombustor  2  of type known per se, provided with at least one electrically controlled fuel injector  3  and a device  4  for feeding a flow of combustion supporter.  
      The microcombustor  2  has an exhaust outlet  5  to which is coupled the inlet of a conversion device generally indicated  6 .  
      The conversion device  6  comprises a duct  7  of electrically insulating material, for example a ceramic material.  
      The duct  7  has an inlet end  7   a  coupled to the exhaust  5  of the microcombustor  2 . This portion  7   a  of the duct  7  has two facing metal electrodes  8  and  9  on its walls, separated from one another and parallel to the direction of flow of the exhaust gas.  
      One of the two electrodes, indicated  8 , is connected to the positive pole of an external voltage generator  13 . The other electrode  9 , on the side facing the flow, is covered with a thin layer of dielectric material  10  in such a way that the plasma constituted by the exhaust gas from the microcombustor does not come into direct contact with it, and is connected to the negative pole of the said voltage generator  13 .  
      Downstream of the electrodes  8  and  9  the duct  7  forms a restriction defining a nozzle  11  for the purpose of increasing the speed of flow of the positive charges.  
      The intermediate portion  7   b  of the duct  7  downstream of the nozzle  11 , has an external metal cladding layer indicated  12 . The opposite ends of this metal cladding are connected by means of conductors, such as wires or suitable electrical contacts, to a utiliser device or external load L.  
      Within the section  7   b  of the duct  7  is disposed a shaped body  14  of electrically insulating material, for example ceramic, acting to define a duct with a circular annular section for the plasma flow.  
      Finally, the duct  7  has an outlet end for escape of the exhaust gas, indicated  7   c;  this end is provided with an essentially transverse metal grille  15  connected to the negative pole of the voltage generator  13 .  
      In operation the microcombustor  2  emits into the duct  7  of the conversion device  6  a stream of exhaust gas in plasma state comprising positive ions and electrons separated from one another.  
      In  FIG. 1  these ions and the electrons of the plasma have been indicated as I and e respectively, and have been symbolically represented by means of small circles containing the conventional sign for their electrical charge.  
      The electrodes  8  and  9  connected to the voltage supply  13  generate within the duct  7   a  an electric field perpendicular to the direction of flow of charges. Because of the said electric field the electrical charges forming part of the plasma are diverted towards the electrodes of opposite sign: the electrons e are “captured” by the electrode  8  connected to the positive pole of the generator  13 , the positive ions I cannot on the other hand come into contact with the negative electrode  9  by virtue of the presence of the insulating layer  10 , and therefore proceed in their motion towards the outlet end of the duct  7 . Therefore the plasma becomes a stream of essentially only positive charges.  
      The nozzle  11  has the function of further accelerating the stream of ions I.  
      In the subsequent section  7   b  of the duct  7  the positive ions I cause the appearance of negative electric charges on the external metal cladding  12  (by electrostatic induction): the positive ions I yield part of their kinetic energy to these negative charges by “dragging them” in the metal conductor along the direction of movement of the plasma.  
      The ends of the conductive cladding  12  are connected to a utiliser device L which closes an electric circuit in which current is caused to circulate.  
      To increase the interface surface and interaction between the plasma of ions I and the conductive cladding  12  in the duct  7  a separator  14  is conveniently introduced in such a way as to permit the plasma to distribute itself through a section in the form of a circular ring.  
      It can be observed that the outer metal layer  12  is conveniently insulated from the flow of plasma so that the positive ions I are not neutralised in contact with it.  
      The outlet grille  15  is electrically insulated from the outer metal layer  12  of the duct  7 , and neutralises the positive ions of the plasma which pass through it. The terminal section or outlet  7   c  of the duct  7  represents the exhaust of neutralised gas.  
      In relation to the duct  7  it can be seen that its minimum dimension is tied to the condition that it must exist in the plasma state, which requires that the Debye ratio of the trajectory which one electron describes about an ion must be largely less than the minimum dimension d of the container in which the plasma is confined, according to the relation 
 
 d&gt;&gt;{square root}{square root over (kT/4πe     2     n)} 
 
 where k is the Boltzmann constant, T is the (absolute) temperature, e is the electron charge, and n is the plasma density. 
 
      The separation of the positive and negative charges of the plasma in the duct  7  can take place, not only by way of the two electrodes  8  and  9  described, but also by two metal grilles  18  and  19  connected to the positive and negative poles of an external voltage generator  13  and located axially spaced from one another transversely of the direction of flow of the plasma. This configuration is represented in  FIG. 2  which schematically reproduces in section the initial part  7   a  of the duct  7 .  
      Naturally, the principle of the invention remaining the same, the embodiments and details of construction can be widely varied with respect to what has been described and illustrated purely by way of non-limitative example without by this departing from the ambient of the invention as defined in the annexed claims.