Gas turbine engines are known to include a compressor for compressing air, a combustor for producing a hot gas by burning fuel in the presence of the compressed air produced by the compressor, and a turbine for expanding the hot gas to extract shaft power. Staging is the delivery of fuel to burners of the gas turbine engine through at least two separately controllable fuel supply systems or stages. Staging is known as a method to control combustion in the combustor. For example, gas turbine engine may use two stages for starting, such as a pilot stage and a main burner, or “A,” stage.
Historically, a starting process for gas turbine engines has required that fuel pressure and temperature be confined to respective predetermined ranges for reducing a variation in fuel mass flow to the engine to achieve consistent ignition. Fuel mass flows outside a predetermined range would result in a failed starting attempt. To achieve a pressure of the fuel within its predetermined range, a fuel gas regulator is typically disposed in the main fuel supply path to maintain a desired pressure downstream of the regulator. Although fuel pressure may be controlled in this manner, the fuel gas temperature may not be as easily controlled to ensure the temperature of the fuel is within its required predetermined range for starting. Only when the fuel is within its predetermined range is starting attempted. Consequently, gas turbine ignition settings are required to be modified if there are any changes to the upstream fuel conditions such as temperature, pressure, gas composition.
Gas turbine combustors may be started using a “pop” and “glide” technique for providing an initially richer fuel flow during a pop portion of a starting procedure until the fuel is ignited in the combustor. After ignition is achieved, the pop portion is followed by a leaner fuel flow during a glide portion of the starting procedure until the turbine is ramped up to a desired speed. The pop portion provides a richer fuel condition ensuring successful ignition, while the glide portion provides a slightly leaner fuel condition to avoid higher blade path temperatures during the initial acceleration. The transition from pop to glide is typically accomplished relatively gradual to avoid a flame out condition.
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