Patent Publication Number: US-8974645-B2

Title: Method and device for plasma reformation of fuel for engine applications

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     The present application is a national phase entry under 35 U.S.C. §371 of International Application No. PCT/DE2008/001862, published in German, which claims the benefit of German Patent Application No. 10 2007 054 967.0, filed Nov. 17, 2007. The disclosures of said applications are incorporated by reference herein. 
     The present invention relates to a method and a device for plasma reformation of fuel, in particular kerosene, for engine applications. 
     In the reformation of hydrocarbons against the background of generating combustion gases rich in hydrogen, at present catalytic systems are used. In this process various reaction control techniques are applied, for example partial oxidation (sub-stoichiometric combustion) or steam reformation. Catalytic reformer systems are inherently comparatively large in design, which is disadvantageous in engine applications. In the engine industry, two-stage combustion comprising “hot pilot combustion” and downstream “colder main combustion” has partly won through in order to significantly reduce NO x  emissions. 
     NO x  production is in particular supported by high combustion temperatures. Attempts are thus being made to find a process which makes it possible to reduce the combustion temperature and in particular temperature peaks during combustion, while at the same time achieving as far as possible complete combustion of the fuel (also in relation to carbon particles). 
     It is thus the objective object of the present invention to provide a method which, while providing complete combustion of the fuel used, reduces the combustion temperature and in particular temperature peaks. Moreover, it is the object of the present invention to provide a device by means of which the present method can be implemented, with the device being sufficiently small for use in engine applications. 
     This objective object is met by the aspects of the present invention that are defined in the independent claims. Advantageous improvements are presented in the dependent claims. 
     In particular, the objective object is met in a first aspect by means of a method for plasma reformation of fuel, in particular kerosene, in which method the fuel is first, in an expansion nozzle ( 3 ), transferred to the plasma state, and subsequently further fuel is injected into the plasma in order to be decomposed, as a result of the heat, into components such as CO, C and H. 
     The method according to the first aspect of the present invention has the advantages that the elementary and/or low-molecular-weight components of the fuel which are generated in the plasma undergo complete combustion even at reduced temperatures of approximately 1000° C. 
     Furthermore, the objective object is met in a second aspect by means of a device ( 1 ) for plasma reformation of fuel, in particular kerosene, which device comprises an expansion nozzle ( 3 ) with a subsequent fuel chamber ( 5 ), wherein the expansion nozzle ( 3 ) is connected to a line ( 7 ), to a hollow waveguide ( 11 ) that connects an energy source ( 9 ), and to nozzles ( 13 ) so that in the expansion nozzle ( 3 ) a plasma flame ( 15 ) can be generated, and wherein the combustion chamber ( 5 ) is connected to air nozzles ( 17 ) so that a combustion flame ( 19 ) can be generated. 
     The device ( 1 ) according to the second aspect of the present invention provides advantages in that as a result of its shape similar to that of a water jet pump, the fuel in the plasma state expands at extremely high speed by way of the expansion nozzle ( 3 ) and consequently attracts the combustion air so that no pumping in the compressor of an engine occurs. Furthermore, the device is comparatively small and well suited to engine applications. 
    
    
     
         FIG. 1  shows an example of a device ( 1 ) according to the invention for plasma reformation of fuel, such as kerosene. 
     
    
    
     In the method according to the invention for plasma reformation of fuel, such as kerosene, the fuel is fed through the line ( 7 ) to the inlet of the expansion nozzle ( 3 ). By way of a hollow waveguide ( 11 ) energy is supplied from an energy source ( 9 ) in order to generate the plasma state. In this arrangement, as a result of the supply of the energy, the fuel, in particular kerosene, (at atomic level) is decomposed into its elementary and/or low-molecular components in a highly ionised manner. 
     Plasma reformation according to the invention preferably requires a thermal high-pressure plasma, for example an arc discharge, or advantageously a microwave plasma. 
     Subsequently, further fuel, in particular kerosene, is injected through nozzles ( 13 ) into the arising plasma flame ( 15 ) in order to be decomposed in the heat into components such as CO, C and H. The elementary and/or low-molecular components in the highly ionised state can also fully combust at temperatures lower than those in conventional engines, preferably at approximately 1000° C. 
     From the expansion nozzle ( 3 ) the plasma flame ( 15 ) is expanded at high speed into the combustion chamber ( 5 ). As a result of this high speed of the highly ionised components in the plasma flame ( 15 ) the combustion chamber ( 5 ), which follows on from the expansion nozzle ( 3 ), can be used in the manner of a water jet pump. Consequently, suction intake of the air, which is necessary for combustion, from the air nozzles ( 17 ) takes place without any additional devices for supplying air. Apart from reduced equipment-related expenditure, this also prevents any undesirable pumping in the compressor from occurring. 
     The combustion that takes place in the combustion chamber ( 5 ), in particular low-temperature combustion or “cold combustion”, takes place completely, even at reduced temperatures of approximately 1000° C. because the plasma state of the fuel (essentially comprising ions and radical hydrocarbon fragments) requires significantly less activation energy for combustion. Preferably, combustion takes place with an extreme excess of air. 
     Regarding the method according to the invention for plasma reformation of fuel, such as kerosene, as a result of the reduction of the combustion temperature to approximately 1000° C., in particular the formation of NO x  is significantly reduced. According to the method of the present invention, in addition only part of the fuel is transferred by the energy from the energy source ( 9 ) to the plasma state. The remaining fuel is decomposed by the generated plasma itself into its elementary and/or low-molecular-weight components. The energy used can therefore be significantly reduced, as can the size of the energy source ( 9 ). 
     Regarding the device ( 1 ) according to the invention for plasma reformation of fuel, such as kerosene, as a result of the reduced equipment-related expenditure (for example the absence of pumps for the combustion air) the device of the present invention can be designed so as to be smaller. The connection of the significantly smaller energy source ( 9 ) by way of a waveguide ( 11 ) to the expansion nozzle ( 3 ) provides a further advantage. The use of the waveguide ( 11 ) makes a decentralised arrangement of the energy source ( 9 ) possible. As a result of these equipment-related advantages the device ( 1 ) according to the invention can easily be used in engine applications. 
     Although the present invention was described with reference to a method and a device for plasma reformation of kerosene in engine applications, it is possible to use propellants and fuels that are known to the person skilled in the art and that are equivalent to kerosene. Furthermore, the method and the device need not be confined to engine applications, but can instead be arranged upstream of various types of turbines, combustion engines or fuel cells.