Combustion device

Abstract

A combustor (1) has a swirler (22). The swirler has mixing channels (40), the mixing channels having a height/width aspect ratio of less than (2). A secondary fuel inlet (32) is located downstream of mixing channel (40) and may be in a zone (65) of separated flow. Primary fuel admission may be through a threaded or push fit circular movable plug (100). The plug (100) may be conveniently removed for calibration purposes and may have a bell-mouthed entrance.

Description

BACKGROUND OF THE INVENTION [0001] The present invention relates to a combustion device, and more particularly but not exclusively to a combustion device for a gas turbine engine, and furthermore to the assembly of components forming a combustion device. A combustor is commonly used in a gas turbine engine to burn fuel in compressed air to produce exhaust gas for exhaust to a turbine. Recent combustor designs have aimed at reducing emissions of nitrogen oxide (NO) and nitrogen dioxide (NO2)— collectively known as NOx. Running the combustor to produce well-mixed fuel and air in a mixing channel can decrease NOx emissions. However, this level of mixing can create flame instability at low flow rates, leading to flame blow-out. Consequently, it is known to use a secondary or pilot fuel inlet to prevent the blow-out from occurring. One combustor design has a stub tube having several fuel inlets arranged to admit fuel into a mixing channel to increase mixing and reduce NOx emissions. Howe...

AI Technical Summary

Benefits of technology

[0009] Preferably, the mixing channel comprises a bore formed in the body of the apparatus, the bore having an elliptical cross section, which may be circular. The advantage of an elliptic cross section channel is that fuel may be conveniently admitted into the channel from around the channel, so as to increase mixing of the fuel with air entering the channel, and so the channel flow does not suffer from the reduced effect of area that can occur in the corners of rectangular channel flows.

[0010] Preferably, the zone of separated flow is outside of the mixing channel so as to avoid reducing the mixing channel effective area. The secondary fuel inlet is more preferably positioned downstream of the mixing channel. The advantage of this is that air and fuel are well mixed prior to secondary fuel being added, thus minimising NOx emissions, and yet the pilot (or secondary) fuel is available when the mixture is vulnerable to flame blow-out. The body may be a swirler. The mixing channels may be equi-spaced around the circumference of the swirler, and the secondary fuel inlets may be equi-spaced around the center of the swirler to facilitate good mixing of air and fuel. In other cases, the secondary fuel inlets may not be equally spaced. Preferably, the secondary fuel inlets are positioned on axes, each axis being aligned with the longitudinal axis of a mixing channel. Hence, fuel may be admitted into multiple streams of air and the mixture is able to enter the air/fuel chamber from several directions simultaneously, creating a circumferentially uniform influx of the mixture into the air/fuel chamber. In one aspect of the invention, there may be an equal number of secondary fuel inlets and primary fuel inlets, and in another aspect of the invention, there may be fewer secondary fuel inlets than there are primary fuel inlets. Preferably, the mixing channels are oriented so as to impart a swirl component of motion to the air/fuel mixture exiting the mixing channels, such that a vortex is formed in th

Problems solved by technology

However, this level of mixing can create flame instability at low flow rates, leading to flame blow-out.

However, this arrangement is prone to flame instability and potential flame blow-out.

A stub tube creates a wake, which reduces the effective area of the mixing channel and reduces the flow rate of air and fuel through the mixing chan

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