Flame control in the flame-holding region

Abstract

A combustion system includes a fuel nozzle, a charge source, a discharge electrode, and a voltage supply coupled to the charge source and discharge electrode. The charge source is configured to apply a polarized charge to a flame supported by the nozzle, and the discharge electrode is configured to attract a flame-front portion of the flame to hold the flame for flame stability. The discharge electrode can be toroidal in shape, positioned coaxially with the nozzle downstream from the nozzle. The voltage supply is configured to hold the charge source at a charge potential and the discharge electrode at the discharge potential. The nozzle can be configured to apply the polarized charge to a fuel stream emitted by the nozzle, whereafter the charge is passed to the flame upon combustion of the fuel.

What is claimed is: 
     
         1 . A combustion system, comprising:
 a fuel nozzle configured to emit a fuel stream;   a charge source configured to apply a polarized charge to a flame supported by the nozzle; and   a first discharge electrode positioned and configured to attract a flame-front portion of the flame when energized at a discharge potential.   
     
     
         2 . The system of  claim 1 , comprising a voltage source electrically coupled to the charge source and the first discharge electrode, and configured to hold the charge source at a charge potential and the first discharge electrode at the discharge potential. 
     
     
         3 . The system of  claim 2 , wherein the voltage source is configured to hold the first discharge electrode at the discharge potential having a polarity opposite a polarity of the polarized charge. 
     
     
         4 . The system of  claim 1 , comprising a voltage source electrically coupled to the charge source and the first discharge electrode, configured to hold the charge source at a charge potential, and wherein the first discharge electrode is electrically coupled to a circuit ground in common with the voltage source. 
     
     
         5 . The system of  claim 1 , wherein the first discharge electrode is positioned and configured to discharge a portion of the polarized charge when contacted by the flame-front portion of the flame. 
     
     
         6 . The system of  claim 1 , wherein the fuel nozzle comprises a charge electrode, and is configured to apply the polarizing charge to the fuel stream as it is emitted from the nozzle. 
     
     
         7 . The system of  claim 1 , wherein the charge source is configured to generate ions. 
     
     
         8 . The system of  claim 1 , wherein the first discharge electrode has a toroidal shape, and is positioned coaxially with the fuel nozzle and downstream therefrom, with reference to a direction of flow of a stream of fuel emitted by the nozzle. 
     
     
         9 . The system of  claim 8 , wherein the fuel nozzle is configured to emit the fuel stream in a divergent cone, and wherein the toroidally-shaped first discharge electrode is sized and positioned such that an inner diameter of the first discharge electrode is at least equal to a diameter of the divergent cone at a point at which the fuel stream passes the first discharge electrode. 
     
     
         10 . The system of  claim 8 , comprising an actuator coupled to the first discharge electrode and configured to move the electrode relative to the nozzle. 
     
     
         11 . The system of  claim 10 , wherein the actuator is configured to rotate the first discharge electrode about an axis lying perpendicular to a longitudinal axis of the nozzle. 
     
     
         12 . The system of  claim 11 , wherein the actuator is configured to adjust an angular position of the first discharge electrode relative to the longitudinal axis of the nozzle. 
     
     
         13 . The system of  claim 10 , wherein the actuator is configured to translate the first discharge electrode along a line parallel to a longitudinal axis of the nozzle. 
     
     
         14 . The system of  claim 1 , comprising:
 a plurality of discharge electrodes, including the first discharge electrode;   a voltage source electrically coupled to the charge source and to each of the plurality of discharge electrodes.   
     
     
         15 . The system of  claim 14 , wherein the plurality of discharge electrodes are positioned in radial symmetry around a longitudinal axis of the fuel nozzle. 
     
     
         16 . The system of  claim 14 , wherein the voltage source is configured to hold each of the plurality of discharge electrodes at the discharge potential. 
     
     
         17 . The system of  claim 16 , wherein the voltage source is configured to selectively hold some of the plurality of discharge electrodes at the discharge potential, while decoupling others of the plurality of discharge electrodes from a circuit including the voltage source and the charge source. 
     
     
         18 . The system of  claim 15 , wherein each of the plurality of discharge electrodes is positioned at one of a plurality of distances radially from the longitudinal axis of the fuel nozzle. 
     
     
         19 . The system of  claim 15 , wherein each of the plurality of discharge electrodes is positioned at one of a plurality of distances axially from the fuel nozzle. 
     
     
         20 . A method, comprising:
 emitting a fuel stream from a burner nozzle of a combustion system;   applying an electrical charge to a flame supported by the fuel stream;   attracting a flame front of the flame toward a discharge electrode by holding the discharge electrode at a discharge potential, relative to the electrical charge.   
     
     
         21 . The method of  claim 20 , wherein the holding the discharge electrode at a discharge potential includes holding the discharge electrode at a potential having a polarity that is opposite a polarity of the electrical charge. 
     
     
         22 . The method of  claim 20 , wherein the holding the discharge electrode at a discharge potential includes the discharge electrode at a ground potential that is common to a circuit coupled to charge source configured to apply the electrical charge. 
     
     
         23 . The method of  claim 20 , wherein the attracting a flame front of the flame toward a discharge electrode includes discharging a portion of the electrical charge upon contact of the flame front with the discharge electrode. 
     
     
         24 . The method of  claim 20 , wherein the applying an electrical charge to a flame includes applying the electrical charge to the fuel stream as it exits the burner nozzle. 
     
     
         25 . The method of  claim 24 , wherein the applying the electrical charge to the fuel stream includes applying the electrical charge to an electrically conductive portion of the burner nozzle. 
     
     
         26 . The method of  claim 20 , wherein the applying an electrical charge to a flame includes generating ions and introducing the ions to the flame. 
     
     
         27 . The method of  claim 20 , wherein the holding the discharge electrode at a discharge potential includes holding a toroidally-shaped discharge electrode at the discharge potential. 
     
     
         28 . The method of  claim 20 , wherein the holding the discharge electrode at a discharge potential includes holding a plurality of discharge electrodes at the discharge potential.