Fuel nozzle for gas turbines

Abstract

A fuel nozzle for use with gas turbines includes a centrally disposed orifice for discharging fuel into a combustion chamber. A first annular passage surrounds the fuel orifice and discharges primary air adjacent the exit of the fuel orifice for effecting atomization of the fuel and mixture of the air with the fuel to provide a fuel/air spray having a predetermined spray angle. A second annular passage for supplying secondary air is provided surrounding the first passage. This second passage is formed to supply air in a manner which creates a relatively low pressure substantially at the base of the fuel/air spray. When operating at the low fuel flow rates corresponding to low loads, air is supplied only through the first air passage and a relatively narrow spray angle, with a substantial concentration of fuel, is achieved. In a specific embodiment, as the load increases secondary air is supplied with a swirling motion through the second or outer annular passage and creates a vortex of rotating air flow, resulting in a reduction in static pressure at the base of the spray formed by the mixture of fuel and primary air. The reduction in pressure at the base of the spray causes the spray angle to be increased and enhances fuel and air mixing. This improves combustion and reduces smoke emission. In other embodiments, if desired, secondary air may be supplied at any fuel flow rate to provide the optimum spray angle for any given condition. The spray angle is controllable independently of the fuel flow rate.