Ultra low NOx burner using distributed direct fuel injection

A water heater, comprising:

• (a) a water tank configured to hold water therein and having a bottom surface and defining a flue passing upwardly therethrough;
• (b) a combustion space surrounded by an outer wall and bound by the bottom surface of the water tank so that the combustion space is disposed beneath the bottom surface of the water tank, the combustion space in fluid communication with the flue, the combustion space having a bottom area configured to allow air to pass upwardly therethrough substantially unimpeded;
• (c) a burner box assembly disposed in the combustion space and including:
• (i) a housing bounded by at least one sidewall, the housing having a top and an opposite bottom, the top and the bottom each open so that the sidewall defines an open passage that is configured to allow substantially unimpeded vertical convective airflow upwardly from the bottom so that 100% of all combustion air flows upwardly from the open bottom;
• and
• (ii) a fuel tube extending into the passage defined by housing, the fuel tube having an inner cavity that is confined by a tube wall and that is in fluid communication with a fuel connection port outside of the housing, the tube wall defining a plurality of spaced apart orifices passing therethrough that are configured to distribute fuel received through the fuel connection into the open passage defined by the sidewall of the housing, the fuel tube disposed at a distance from the top of the housing so that substantially all of the fuel distributed from the fuel tube is entrained by the combustion air before the fuel reaches the top of the housing, thereby forming a substantially homogenous fuel/air mixture;
• and
• (iii) a porous heat dissipating surface disposed across the top of the housing, the porous heat dissipating surface configured to support a flame resulting from combustion of the fuel/air mixture, the porous heat dissipating surface including enough open area so that the fuel/air mixture passes through the porous heat dissipating surface substantially unimpeded, the porous heat dissipating surface configured to dissipate heat from the flame and to prevent flashback of the flame into the housing;
• and
• (d) a plenum disposed within the combustion space and around the burner box assembly, the plenum having at least one outer dimension configured to interfere with acoustic harmonics in the combustion space,
• wherein the burner box assembly is configured to support the flame so as to heat water in the water tank through the bottom surface of the water tank and the flue 14,
• wherein the fuel tube comprises a straight tube that extends from a first side of the housing to an opposite second side of the housing and
• wherein the orifices are evenly spaced apart along two spaced apart rows that run the length of the tube.

A burner box, comprising:

• (a) a housing bounded by at least one sidewall, the housing having a top and an opposite bottom, the top and the bottom each open so that the sidewall defines an open passage that is configured to allow substantially unimpeded vertical convective airflow upwardly from the bottom so that 100% of all combustion air flows upwardly from the open bottom;
• and
• (b) a fuel tube extending into the passage defined by housing, the fuel tube having an inner cavity that is confined by a tube wall and that is in fluid communication with a fuel connection port outside of the housing, the tube wall defining a plurality of spaced apart orifices passing therethrough that are configured to distribute fuel received through the fuel connection into the open passage defined by the sidewall of the housing, the fuel tube disposed at a distance from the top of the housing so that substantially all of the fuel distributed from the fuel tube is entrained by the combustion air before the fuel reaches the top of the housing, thereby forming a substantially homogenous fuel/air mixture;
• and
• (c) a porous heat dissipating surface disposed across the top of the housing, the porous heat dissipating surface configured to support a flame resulting from combustion of the fuel/air mixture, the porous heat dissipating surface including enough open area so that the fuel/air mixture passes through the porous heat dissipating surface substantially unimpeded, the porous heat dissipating surface configured to dissipate heat from the flame and to prevent flashback of the flame into the housing,
• wherein the housing has a rectangular plan shape with a first pair of walls that are separated by a first distance and a second pair of walls that are separated by a second distance, in which the first distance is greater than the second distance and wherein the tube has a length that is substantially the first distance, and
• wherein a first one of the first pair of walls comprise an opening passing therethrough through which the fuel tube extends, an end of the fuel tube affixed to a second one of the first pair of walls so as to hold the fuel tube in an alignment that results in fuel injection in a substantially upward direction.