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A combustion apparatus (10) incorporating a dry low NOx (DLN) combustor (20) that uses two different fuels (30, 40) simultaneously. One fuel (30) is premixed with air (22) for a primary combustion zone (25), and a second fuel (40) supplies a diffusion pilot flame (29). Each fuel may be selected for

A combustion apparatus (10) incorporating a dry low NOx (DLN) combustor (20) that uses two different fuels (30, 40) simultaneously. One fuel (30) is premixed with air (22) for a primary combustion zone (25), and a second fuel (40) supplies a diffusion pilot flame (29). Each fuel may be selected for its specialized role, maximizing overall combustion efficiency while lowering emissions. A primary fuel (30) such as natural gas (NG) may be chosen for its economy and combustion characteristics in a lean premix. A pilot fuel (40) may be chosen for having a low diffusion flame temperature and a clean burn. An oxygenated pilot fuel such as dimethyl ether (DME) has a lower flame temperature than natural gas, thereby reducing NOx from the pilot flame. The pilot fuel (40) may be produced from the primary fuel (30) by a reformer (50) associated with the combustion apparatus.

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1. A method of combusting fuel, the method comprising: premixing a primary fuel with air in a premixing stage to produce an air/fuel premix;burning the air/fuel premix in a primary combustion zone of a combustor;diffusing a second fuel into a pilot combustion zone of the combustor, wherein the secon

1. A method of combusting fuel, the method comprising: premixing a primary fuel with air in a premixing stage to produce an air/fuel premix;burning the air/fuel premix in a primary combustion zone of a combustor;diffusing a second fuel into a pilot combustion zone of the combustor, wherein the second fuel is a fuel different from the primary fuel and is selected to produce a lower emission in a diffusion burn than would be achieved in a diffusion burn of the primary fuel in the pilot combustion zone; andburning the diffused second fuel in a diffusion flame in the pilot combustion zone simultaneously with the burning of the air/fuel premix in the primary combustion zone. 2. The method of claim 1, wherein the second fuel is selected to have a lower diffusion burning temperature than the primary fuel. 3. The method of claim 1, wherein the first fuel is non-oxygenated and the second fuel is a fuel oxygenate. 4. The method of claim 3, wherein the second fuel is produced by reforming a portion of the first fuel. 5. The method of claim 1, wherein the second fuel is a fuel oxygenate. 6. The method of claim 1, wherein the second fuel is dimethyl ether. 7. The method of claim 1, wherein the first fuel comprises natural gas and the second fuel comprises dimethyl ether. 8. The method of claim 1, wherein the first fuel comprises natural gas and the second fuel comprises a fuel oxygenate, and further comprising controlling the method to limit production of NOx to less than 5 ppm without the need for post-combustion catalytic treatment. 9. The method of claim 8, wherein the second fuel is selected to comprise dimethyl ether. 10. A combustion apparatus designed to practice the method of claim 1. 11. A combustion apparatus comprising: a primary combustion zone and an associated pilot combustion zone;a pre-mixing stage directing a pre-mix of air and a non-oxygenated primary fuel into the primary combustion zone; anda pilot stage directing a diffusion of a pilot fuel oxygenate into the pilot combustion zone;wherein the combustion apparatus burns the primary fuel and the pilot fuel oxygenate simultaneously to produce a combustion product exhibiting a reduced emission when compared to a combustion product that would be produced by the burning of the pre-mix of primary fuel with a diffusion pilot stage of the primary fuel. 12. The combustion apparatus of claim 11, wherein the pilot fuel oxygenate is selected to have a lower diffusion flame temperature than that of the primary fuel to produce a reduced NOx emission. 13. The combustion apparatus of claim 11, wherein the primary fuel comprises natural gas and the pilot fuel oxygenate comprises dimethyl ether. 14. The combustion apparatus of claim 11, further comprising a reformer converting a portion of the primary fuel into the pilot fuel oxygenate. 15. A gas turbine engine comprising the combustion apparatus of claim 11. 16. A combustion apparatus comprising: a primary combustion zone;a primary fuel element in fluid communication with an air/fuel premixer for delivering a primary fuel premix into the primary combustion zone;a pilot combustion zone associated with the primary combustion zone;a pilot fuel element in fluid communication with a diffusion nozzle for delivering a pilot fuel diffusion into the pilot combustion zone; anda reformer connected between the primary fuel element and the pilot fuel element for converting a portion of primary fuel into pilot fuel. 17. The combustion apparatus of claim 16, further comprising the reformer converting a portion of a natural gas primary fuel into a dimethyl ether pilot fuel. 18. The combustion apparatus of claim 16, wherein the pilot fuel element delivers an oxygenated pilot fuel diffusion. 19. The combustion apparatus of claim 16, wherein the reformer converts the portion of primary fuel into a pilot fuel oxygenate having a lower diffusion flame temperature than that of the primary fuel. 20. The combustion apparatus of claim 19, wherein the reformer converts the portion of primary fuel into dimethyl ether.