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A method includes the step of extinguishing a flame fired from a burner in a reaction zone upon determining that a sensed combustion chamber temperature is at or above the auto-ignition temperature of a fuel. A subsequent step is performed before the sensed combustion chamber temperature drops below

A method includes the step of extinguishing a flame fired from a burner in a reaction zone upon determining that a sensed combustion chamber temperature is at or above the auto-ignition temperature of a fuel. A subsequent step is performed before the sensed combustion chamber temperature drops below the auto-ignition temperature. The subsequent step provides a flow of the fuel through the burner and into the combustion chamber through a reaction zone outlet. This initiates diffuse combustion of the fuel by auto-ignition in the combustion chamber in the absence of a flame fired from the burner in the reaction zone.

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1. A method of operating an apparatus comprising a furnace structure defining a combustion chamber, a reaction zone having an outlet communicating with the combustion chamber, a burner oriented to fire a flame into the reaction zone in a direction extending into the combustion chamber through the re

1. A method of operating an apparatus comprising a furnace structure defining a combustion chamber, a reaction zone having an outlet communicating with the combustion chamber, a burner oriented to fire a flame into the reaction zone in a direction extending into the combustion chamber through the reaction zone outlet, and a temperature sensor in the combustion chamber, said method comprising:a) extinguishing a flame fired from the burner in the reaction zone upon determining that a sensed combustion chamber temperature is not below a predetermined auto-ignition temperature of a fuel; andb) subsequently, but before the sensed combustion chamber temperature drops below the auto-ignition temperature, providing a flow of the fuel through the burner and into the combustion chamber through the reaction zone outlet to initiate diffuse combustion of the fuel by auto-ignition in the combustion chamber in the absence of a flame fired from the burner in the reaction zone. 2. A method as defined in claim 1 wherein a delay is imposed to ensure that the flame is fully extinguished before the flow of fuel is provided through the burner for auto-ignition in the combustion chamber, and the combustion chamber temperature is monitored with reference to the auto-ignition temperature during the delay to ensure that the flow of fuel is provided through the burner before the combustion chamber temperature drops below the auto-ignition temperature. 3. A method as defined in claim 1 wherein the flame is extinguished upon determining that the sensed combustion chamber temperature is not below a specified temperature that is predetermined to be above the auto-ignition temperature. 4. A method as defined in claim 1 wherein the flame is extinguished as recited in claim 1 by interrupting a flow of fuel to the burner. 5. A method as defined in claim 1 wherein the flame is extinguished as recited in claim 1 by applying a gas pulse. 6. A method as defined in claim 1 wherein the flame is extinguished as recited in claim 1 by providing reactants to the burner in a fuel/oxidant ratio that does not sustain the flame. 7. A method as defined in claim 6 wherein the reactants include recirculated flue gas. 8. A method of modifying an apparatus comprising a furnace structure defining a combustion chamber, a reaction zone having an outlet communicating with the combustion chamber, a burner oriented to fire a flame into the reaction zone in a direction extending into the combustion chamber through the reaction zone outlet, a control system, and a reactant supply system operative in response to the control system to provide flows of fuel and oxidant to the reaction zone through the burner for a flame to be fired from the burner, said method comprising:rendering the control system operative to direct the reactant supply system to extinguish a flame fired from the burner in the reaction zone upon determining that a sensed combustion chamber temperature is not below a predetermined auto-ignition temperature of a fuel and subsequently, but before the combustion chamber temperature drops below the auto-ignition temperature, to provide a flow of the fuel through the burner and into the combustion chamber through the reaction zone outlet to initiate diffuse combustion of the fuel by auto-ignition in the combustion chamber in the absence of a flame fired from the burner in the reaction zone. 9. A method as defined in claim 8 wherein the control system is rendered operative to direct the reactant supply system as recited in claim 8 automatically without input from an operator of the apparatus. 10. A method as defined in claim 8 wherein the control system is rendered operative to direct the reactant supply system as recited in claim 8 only if an operator of the apparatus provides corresponding input instructions. 11. A method as defined in claim 8 wherein the control system is rendered operative to impose a delay to ensure that the flame is fully extinguished before the reactant supply system provides the flow of the fuel through the burner for auto-ignition in the combustion chamber, and also to monitor the combustion chamber temperature with reference to the auto-ignition temperature during the delay to ensure that the flow of the fuel is provided through the burner before the combustion chamber temperature drops below the auto-ignition temperature. 12. A method as defined in claim 8 wherein the control system is rendered operative to direct the reactant supply system as recited in claim 8 upon determining that the sensed combustion chamber temperature is not below a specified temperature that is predetermined to be above the auto-ignition temperature. 13. A method as defined in claim 12 wherein the control system is rendered operative to direct the reactant supply system to extinguish the flame as recited in claim 8 by applying a gas pulse. 14. A method as defined in claim 8 wherein the control system is rendered operative to direct the reactant supply system to extinguish the flame as recited in claim 8 by providing reactants to the burner in a fuel/oxidant ratio that does not sustain the flame. 15. A method as defined in claim 14 wherein the reactants include recirculated flue gas. 16. An apparatus for use with a furnace structure defining a combustion chamber, a reaction zone having an outlet communicating with the combustion chamber, a burner oriented to fire a flame into the reaction zone in a direction extending into the combustion chamber through the reaction zone outlet, and a reactant supply system operative to provide flows of fuel and oxidant to the reaction zone through the burner for a flame to be fired from the burner, said apparatus comprising:a control system which is operative to determine whether or not a combustion chamber temperature is below a predetermined auto-ignition temperature of a fuel, to direct the reactant supply system to extinguish a flame fired from the burner upon determining that the combustion chamber temperature is not below the auto-ignition temperature and subsequently, but before the combustion chamber temperature drops below the auto-ignition temperature, to provide a flow of the fuel through the burner and into the combustion chamber through the reaction zone outlet to initiate diffuse combustion of the fuel by auto-ignition in the combustion chamber in the absence of a flame fired from the burner in the reaction zone. 17. An apparatus as defined in claim 16 wherein said control system is operative to direct the reactant supply system to extinguish the flame as recited in claim 16 automatically without input from an operator of the apparatus. 18. An apparatus as defined in claim 16 wherein said control system is operative to direct the reactant supply system to extinguish the flame as recited in claim 16 only if an operator of the apparatus provides corresponding input instructions. 19. An apparatus as defined in claim 16 wherein the control system is operative to impose a delay to ensure that the flame is fully extinguished before the reactant supply system provides the flow of the fuel through the burner for auto-ignition in the combustion chamber, and also to monitor the combustion chamber temperature with reference to the auto-ignition temperature during the delay to ensure that the flow of the fuel is provided through the burner before the combustion chamber temperature drops below the auto-ignition temperature. 20. An apparatus as defined in claim 16 wherein said control system is operative to direct the reactant supply system to extinguish the flame as recited in claim 16 upon determining that the combustion chamber temperature is not below a specified temperature that is predetermined to be above the auto-ignition temperature. 21. An apparatus as defined in claim 16 wherein said control system is operative to direct the reactant supply system to extinguish the flame as recited in claim 16 by applying a gas pulse. 22. An apparatus as defined in clai m 16 wherein said control system is operative to direct the reactant supply system to extinguish the flame as recited in claim 16 by providing reactants to the burner in a fuel/oxidant ratio that does not sustain the flame. 23. An apparatus as defined in claim 22 wherein the reactants include recirculated flue gas. 24. An apparatus comprising:a furnace structure defining a combustion chamber and a reaction zone having an outlet communicating with said combustion chamber;a burner oriented to fire a flame into said reaction zone in a direction extending into said combustion chamber through said reaction zone outlet;a reactant supply system operative to provide flows of fuel and oxidant to said reaction zone through said burner for a flame to be fired from said burner; anda control system operative to determine whether or not a combustion chamber temperature is below a predetermined auto-ignition temperature of a fuel, to direct said reactant supply system to extinguish a flame fired from said burner upon determining that the combustion chamber temperature is not below the auto-ignition temperature and subsequently, but before the combustion chamber temperature drops below the auto-ignition temperature, to provide a flow of the fuel through said burner and into said combustion chamber through said reaction zone outlet to initiate diffuse combustion of the fuel by auto-ignition in said combustion chamber in the absence of a flame fired from said burner in said reaction zone. 25. An apparatus as defined in claim 24 wherein said control system is operative to direct said reactant supply system as recited in claim 24 automatically without input from an operator of the apparatus. 26. An apparatus as defined in claim 24 wherein said control system is operative to direct said reactant supply system as recited in claim 24 only if an operator of the apparatus provides corresponding input instructions. 27. An apparatus as defined in claim 24 wherein said control system is operative to impose a delay to ensure that the flame is fully extinguished before the reactant supply system provides the flow of the fuel through the burner for auto-ignition in the combustion chamber, and also to monitor the combustion chamber temperature with reference to the auto-ignition temperature during the delay to ensure that the flow of the fuel is provided through the burner before the combustion chamber temperature drops below the auto-ignition temperature. 28. An apparatus as defined in claim 24 wherein said control system is operative to direct said reactant supply system as recited in claim 24 upon determining that the combustion chamber temperature is not below a specified temperature that is predetermined to be above the auto-ignition temperature. 29. An apparatus as defined in claim 24 wherein said control system is operative to direct said reactant supply system to extinguish the flame as recited in claim 24 by applying a gas pulse. 30. An apparatus as defined in claim 24 wherein said control system is operative to direct said reactant supply system to extinguish the flame as recited in claim 24 by providing reactants to said burner in a fuel/oxidant ratio that does not sustain the flame. 31. An apparatus as defined in claim 30 wherein the reactants include recirculated flue gas. 32. An apparatus as defined in claim 24 wherein said reaction zone outlet is constricted relative to the configuration of said reaction zone between said burner and said outlet.