Method and apparatus for extending flammability and stability limits in a combustion reaction

Abstract

A method and apparatus for controlling a combustion reaction includes steps and structures for applying an electric field across a combustion reaction. Application of the electric field results in broadening the flammability and stability limits of the fuel.

What is claimed is: 
     
         1 . A method, comprising:
 introducing fuel and air into a combustion volume in a first ratio that is within a first range defined by an upper stability limit and a lower stability limit of the fuel;   igniting the fuel to start a combustion reaction;   producing a modified range defined by a modified upper stability limit higher than the upper stability limit and a modified lower stability limit lower than the lower stability limit of the fuel by applying an electric field across the combustion reaction; and   after igniting the fuel and after producing the modified range, adjusting a flow rate of the fuel or air to produce a second ratio within the modified range and outside the first range.   
     
     
         2 . The method of  claim 1 , further comprising:
 prior to producing the modified range, monitoring one or more characteristics of the combustion reaction; and   detecting values of the one or more monitored characteristics that indicate a requirement that the ratio of fuel and air be adjusted from the first ratio to the second ratio, wherein producing the modified range is performed in response to detecting values of the one or more monitored characteristics.   
     
     
         3 . The method of  claim 1 , wherein applying the electric field modifies an upper flammability limit and a lower flammability limit of the fuel. 
     
     
         4 . A combustion system, comprising:
 a burner configured to support a combustion reaction by emitting fuel and oxidizer;   first and second electrodes positioned to apply an electric field across the combustion reaction; and   a voltage supply operatively coupled to the first and second electrodes, and configured to supply voltage signals to the first and second electrodes sufficient to cause the electric field to produce a modified upper stability limit higher than a normal upper stability limit of the fuel and a modified lower stability limit lower than a normal lower stability limit of the fuel.   
     
     
         5 . The system of  claim 4 , wherein the first electrode comprises a fuel nozzle portion of the burner. 
     
     
         6 . The system of  claim 4 , wherein the second electrode comprises a mesh electrode positioned above the burner. 
     
     
         7 . The system of  claim 4 , further comprising:
 a controller configured to detect operation of the burner and to control the voltage supply to supply voltage signals to the first and second electrodes sufficient to produce the modified upper stability limit and the modified lower stability limit of the fuel.   
     
     
         8 . A method for controlling a combustion reaction, comprising:
 receiving, via a data interface, a command to establish a particular fuel stability limit;   reading data corresponding to a fuel parameter;   determining, as a function of the data, a particular voltage to be applied to a physical electrode operatively coupled to a combustion reaction;   applying the particular voltage to the physical electrode; and   causing the fuel to combust at a mixture within the particular stability limit responsive to an electric field generated by application of the particular voltage to the physical electrode.   
     
     
         9 . The method for controlling a combustion reaction of  claim 8 , wherein determining the particular voltage includes determining second data corresponding to the particular voltage. 
     
     
         10 . The method for controlling a combustion reaction of  claim 9  wherein determining the particular voltage includes:
 converting the second data into a signal; 
 driving a voltage amplifier with the signal; and 
 outputting the particular voltage from the voltage amplifier to the electrode. 
 
     
     
         11 . The method for controlling a combustion reaction of  claim 9 , wherein determining the second data includes algorithmically calculating the second data. 
     
     
         12 . The method for controlling a combustion reaction of  claim 9 , wherein determining the second data includes looking up the second data. 
     
     
         13 . The method for controlling a combustion reaction of  claim 8 , wherein the fuel parameter includes ambient pressure. 
     
     
         14 . The method for controlling a combustion reaction of  claim 8 , wherein the fuel parameter includes ignition temperature. 
     
     
         15 . A low NOx burner, comprising:
 a physical flame holder configured to receive a fuel and oxidant mixture at a particular condition; and   a first and second electrode configured to apply an electric field to the fuel and oxidant mixture, wherein the fuel and oxidant are characterized by a leaner mixture than would stably combust at the particular condition without being exposed to the electric field.   
     
     
         16 . The burner of  claim 15 , wherein the particular condition includes a temperature proximate to the physical flame holder. 
     
     
         17 . The burner of  claim 15 , wherein the particular condition includes atmospheric pressure proximate to the physical flame holder. 
     
     
         18 . A method, comprising:
 introducing fuel and air into a combustion volume in a first ratio that is outside a range defined by an upper stability limit and a lower stability limit of the fuel;   producing a modified range defined by a modified upper stability limit and a modified lower stability limit of the fuel by applying an electric field across the fuel and air, the first ratio falling within the modified range; and   after producing the modified range, igniting the fuel.   
     
     
         19 . The method of  claim 18 , further comprising:
 prior to producing the modified range, monitoring one or more characteristics of the fuel and air;   prior to producing the modified range, detecting values of the one or more monitored characteristics that indicate that the first ratio of the fuel and air is at or above the upper stability limit or the lower stability limit; and   producing the modified range after the monitoring and the detecting.   
     
     
         20 . The method of  claim 18 , wherein producing a modified range includes:
 determining a magnitude of the electric field to be applied, based at least in part on a value of the first ratio and a value of one of the upper stability limit or the lower stability limit; and   applying the electric field at the determined magnitude.   
     
     
         21 . The method of  claim 19 , wherein the producing a modified range includes:
 applying the electric field at a preselected magnitude;   repeating the monitoring and the detecting; and   increasing the magnitude of the applied electric field by a preselected increment.