Porous flame holder for low NOx combustion

A burner, comprising:

• a fuel nozzle assembly configured to output at least one jet of substantially pure fuel configured to entrain oxidant to provide a gaseous mixture including the fuel and the oxidant;
• and
• a porous flame holder defining gas passages each having a minimum lateral dimension equal to or greater than a fuel quenching distance, the gas passages being aligned to receive the gaseous mixture from the fuel nozzle assembly, the gas passages being configured to pass a combustion reaction supported by the gaseous mixture;
• wherein the gas passages each include respective walls arranged and configured to receive heat from a reacting portion of the gaseous mixture, radiate or conduct the heat toward an upstream portion of the wall adjacent to an unreacted portion of the gaseous mixture, and transfer the heat to the unreacted portion of the gaseous mixture within the gas passage;
• wherein the fuel nozzle assembly is configured to, as the gaseous mixture approaches the porous flame holder, mix the gaseous mixture sufficiently to substantially destroy Taylor layers between the substantially pure fuel and air carrying the oxidant in a structurally uninterrupted space between the fuel nozzle assembly and the porous flame holder;
• and
• wherein the gas passages are formed at a pitch of 4 per inch or more than 4 per inch across two dimensions of the porous flame holder.

A method of lowering combustion NOx, comprising:

• outputting, from a fuel nozzle assembly, at least one jet of substantially pure fuel and entrained oxidant toward a porous flame holder;
• then
• allowing time for a mixture of the fuel and oxidant to evolve to a better-mixed state while the fuel and the oxidant traverse a structurally uninterrupted dilution distance between the fuel nozzle assembly and the porous flame holder, the dilution distance selected to permit said allowing of time;
• and then
• combusting the mixture inside the porous flame holder;
• wherein walls of gas passages of the porous flame holder are each configured to radiate or conduct heat, received from the combusting of the mixture at a heat receiving region of the respective wall, to an upstream region of the wall adjacent to an unreacted portion of the mixture, and transfer the heat to the unreacted portion of the mixture sufficiently to cause the combustion to be supported inside the porous flame holder, and
• wherein the dilution distance between the fuel nozzle assembly and the porous flame holder is selected to permit substantial destruction of Taylor layers between the substantially pure fuel and air carrying the oxidant as the mixture reaches the porous flame holder.

A method of lowering combustion NOx, comprising:

• outputting, from a fuel nozzle assembly, at least one jet of substantially pure fuel and entrained oxidant toward a porous flame holder;
• then
• allowing time for a mixture of the fuel and the oxidant to evolve to a better-mixed state while the fuel and the oxidant traverse a structurally uninterrupted dilution distance between the fuel nozzle assembly and the porous flame holder, the dilution distance selected to permit said allowing of time;
• and then
• combusting the mixture inside the porous flame holder;
• wherein walls of gas passages of the porous flame holder are each configured to radiate or conduct heat, received from the combusting of the mixture, to a portion of the mixture in another portion of the gas passage sufficiently to cause the combustion to be supported inside the porous flame holder,
• wherein the dilution distance between the fuel nozzle assembly and the porous flame holder is selected to permit substantial destruction of Taylor layers between the substantially pure fuel and air carrying the oxidant as the mixture reaches the porous flame holder,
• wherein the step of combusting the mixture comprises passing the mixture through the gas passages of the porous flame holder, the gas passages having a minimum lateral dimension equal to or greater than a fuel quenching distance of the mixture;
• and
• wherein the gas passages are formed at a pitch of 4 per inch or more across two dimensions of the porous flame holder.

A diluted fuel burner, comprising:

• a fuel nozzle assembly configured to output at least one jet of substantially pure fuel and to entrain oxidant to produce a gaseous mixture including the fuel and the oxidant;
• a porous flame holder defining gas passages aligned to receive the gaseous mixture from the fuel nozzle assembly, the gas passages being configured to carry a combustion reaction supported by the gaseous mixture;
• and
• a porous flame holder support structure configured to hold the porous flame holder away from the fuel nozzle assembly at a structurally uninterrupted dilution distance selected to allow dilution of the gaseous mixture;
• wherein the dilution distance is selected to permit substantial destruction of Taylor layers between the substantially pure fuel and air carrying the oxidant as the mixture approaches the porous flame holder.