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In one embodiment, a system includes a fuel nozzle that includes a fuel injector configured to output a fuel flow and a premixer tube disposed about the fuel flow output from the fuel injector. The premixer tube includes a perforated portion and a non-perforated portion, and the non-perforated porti

In one embodiment, a system includes a fuel nozzle that includes a fuel injector configured to output a fuel flow and a premixer tube disposed about the fuel flow output from the fuel injector. The premixer tube includes a perforated portion and a non-perforated portion, and the non-perforated portion is downstream of the perforated portion.

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1. A system, comprising: a fuel nozzle, comprising: a fuel injector configured to output a fuel flow;a premixer tube disposed about the fuel flow output from the fuel injector, wherein the premixer tube comprises a perforated portion and a non-perforated portion, and the non-perforated portion is do

1. A system, comprising: a fuel nozzle, comprising: a fuel injector configured to output a fuel flow;a premixer tube disposed about the fuel flow output from the fuel injector, wherein the premixer tube comprises a perforated portion and a non-perforated portion, and the non-perforated portion is downstream of the perforated portion; anda cap enclosing the fuel injector and the premixer tube, wherein the cap is configured to receive air, to direct the air to a downstream portion of the cap to facilitate cooling of a downstream portion of the fuel nozzle, and to direct the air used for cooling into an upstream portion of the premixer tube, and wherein the cap is configured to be disposed within a combustor casing. 2. The system of claim 1, wherein perforations of the perforated portion are configured to swirl air entering the premixer tube. 3. The system of claim 2, wherein a degree of swirl varies with axial position along the length of the premixer tube. 4. The system of claim 1, wherein the fuel injector is configured to inject a gas and an atomized liquid substantially simultaneously. 5. The system of claim 1, wherein the fuel nozzle comprises a plurality of fuel injectors and a plurality of premixer tubes. 6. The system of claim 1, comprising a combustor having the fuel nozzle. 7. The system of claim 6, comprising a turbine engine comprising a plurality of combustors. 8. The system of claim 1, wherein the cap comprises a plurality of windows positioned around a circumference of the cap to receive the air. 9. A system, comprising: a fuel nozzle, comprising: a fuel injector configured to output a fuel flow;a perforated premixer tube comprising perforations disposed about the fuel flow downstream of the fuel injector, wherein the perforations are angled to facilitate airflow into the perforated premixer tube in a swirling motion, and a degree of swirl varies based on an axial position of the perforations along a length of the perforated premixer tube; anda cap enclosing the fuel injector and the perforated premixer tube, wherein the cap is configured to receive air, to direct the air to a downstream portion of the cap to facilitate cooling of a downstream portion of the fuel nozzle, and to direct the air used for cooling into an upstream portion of the perforated premixer tube, and wherein the cap is configured to be disposed within a combustor casing. 10. The system of claim 9, wherein a first set of perforations at a first axial position is configured to swirl air in a substantially opposite direction from a second set of perforations at a second axial position along the length of the perforated premixer tube. 11. The system of claim 9, wherein perforations of the perforated premixer tube are oriented at an angle in an axial direction along a longitudinal axis of the perforated premixer tube. 12. The system of claim 9, wherein the fuel injector is configured to inject a gas, an atomized liquid, or a combination thereof. 13. The system of claim 9, wherein the perforated premixer tube comprises a perforated portion and a non-perforated portion, wherein the perforated portion is upstream of the non-perforated portion. 14. The system of claim 9, comprising a plurality of fuel injectors and a plurality of perforated premixer tubes. 15. The system of claim 9, wherein the cap comprises a plurality of windows positioned around a circumference of the cap to receive the air. 16. A system, comprising: a fuel nozzle, comprising: a plurality of fuel injectors;a plurality of perforated premixer tubes, wherein each fuel injector outputs a flow of fuel in a downstream direction into a perforated premixer tube at an upstream portion of the perforated premixer tube; anda cap comprising a plurality of air windows positioned around a circumference of the cap and leading to an internal cavity, wherein the plurality of perforated premixer tubes are disposed in the internal cavity, and the cap is configured to route air through the air windows to a downstream portion of the cap, through the internal cavity around the perforated premixer tubes at least partially in an upstream direction from a downstream portion to the upstream portion of the perforated premixer tubes, and into the premixer tubes at the upstream portion, wherein the upstream direction is generally opposite from the downstream direction of the flow of fuel, and wherein the cap is configured to be disposed within a combustor casing. 17. The system of claim 16, wherein the plurality of perforated premixer tubes comprise a perforated portion and a non-perforated portion, wherein the perforated portion is upstream of the non-perforated portion. 18. The system of claim 16, wherein each perforated premixer tube comprises perforations angled to swirl the air. 19. The system of claim 18, wherein a degree of the swirl varies with axial position along a length of each perforated premixer tube. 20. The system of claim 16, wherein the plurality of fuel injectors are configured to inject a gas and an atomized liquid substantially simultaneously.