A burner having an air intake, a premix manifold, a blast tube, a rich fuel manifold, and a pilot. The blast tube includes a diffuser, an auxiliary passage, and a shutter. The shutter has at least an open position allowing air and fuel mixtures to flow through the auxiliary passage and the diffuser, and a closed position allowing flow through only the diffuser. Air moves from the air intake to the premix manifold where it mixes with a first fuel. The mixture moves through the blast tube and is ignited by the pilot, forming a lean center flame. A second fuel moves through the rich fuel manifold and ignites via the lean center flame, forming a rich secondary flame. The lean center flame and rich secondary flame combine to form a first flame.

A liquid fuel or hybrid fuel burner and method of operating the burner are described. The combustion air and/or NOx reducing medium are introduced at more than one location in the burner. A portion of the combustion air and the NOx reducing medium can be injected into the primary combustion zone through the NOx reducing medium conduit which surrounds the fuel injector which injects atomized liquid fuel or fuel gas into the primary combustion zone. Another portion of the combustion air and the NOx reducing medium can be introduced into the primary combustion zone through a passage in the burner tile surrounding the NOx reducing medium conduit. A third portion of NOx reducing medium can be injected outside the burner tile. NOx reducing medium can be introduced into any combination of the three locations.