专利汇可以提供Fuel injector专利检索,专利查询,专利分析的服务。并且A fuel injector for a fuel spray nozzle of a gas turbine engine combustor is provided. The fuel injector has an annular flow passage which conveys fuel to a prefilming lip at an end of the flow passage. The fuel injector also has plurality of fuel distributor slots which are circumferentially spaced around and in fluid communication with the other end of the flow passage to deliver respective fuel streams into the flow passage. The slots are configured so that the fuel streams enter the flow passage at a swirl angle of at least 80° relative to the axis of the flow passage.,下面是Fuel injector专利的具体信息内容。
The present invention relates to a fuel injector for a fuel spray nozzle of a gas turbine engine combustor
Fuel injection systems deliver fuel to the combustion chamber of an engine, where the fuel is mixed with air before combustion. One form of fuel injection system known in the art is a fuel spray nozzle. Fuel spray nozzles atomise the fuel to ensure its rapid evaporation and burning when mixed with air.
An airblast atomiser nozzle is a type of fuel spray nozzle in which fuel delivered to the combustion chamber by a fuel injector is aerated by swirlers to ensure rapid mixing of fuel and air, and to create a finely atomised fuel spray.
Efficient mixing of air and fuel results in higher combustion rates. It also reduces unburnt hydrocarbons and exhaust smoke (which result from incompletely combusted fuel) emitted from the combustion chamber.
Additionally, "lean burn combustion" is being developed as a way of operating at relatively low flame temperatures. The lower temperatures significantly reduce NOx emissions, but can necessitate the use of a pilot and mains fuel nozzle to avoid lean extinction at low engine powers.
The fuel injection nozzle 10 has a central axis 11, and is in general circularly symmetrical about this axis. A pilot fuel injector 12 is centred on the axis, and is surrounded by a pilot swirler 13. A mains airblast fuel injector 14 is concentrically located about the pilot fuel injector 12, with inner and outer mains swirlers 15 and 16 positioned radially inward and outward thereof.
The mains airblast fuel injector has an annular flow passage or gallery 17. Circumferentially spaced fuel distributor slots 19 deliver fuel to the fore end of the gallery. The fuel is then conveyed along the gallery to a prefilming lip 18 formed at the aft end of the gallery. An annular film of liquid fuel forms on the lip, and is entrained in and atomised by the much more rapidly moving and swirling air streams produced by inner mains swirler 15 and outer mains swirler 16.
To achieve lean burn, the system not only incorporates pilot and mains fuel injectors, but also requires a relatively large amount of combustion air. To realise the low combustion temperatures the fuel must be well mixed with the air prior to combustion, hence creating uniform low flame temperatures. Non-uniform mixing prior to combustion can result in locally high combustion temperatures, and hence no reduction in NOx emissions. Low combustion efficiency in the lower temperature areas increases the engine's specific fuel consumption, and emissions of carbon monoxide and unburnt fuel.
Thus it is desirable to improve the design of fuel injectors to achieve more uniform fuel-air mixing.
A first aspect of the invention provides a fuel injector for a fuel spray nozzle of a gas turbine engine combustor, the fuel injector having:
wherein the slots are configured so that the fuel streams enter the flow passage at a swirl angle of at least 80° relative to the axis of the flow passage.
By "swirl angle" is meant the angle between the axis of the flow passage (which is typically coincident with the central axis of a fuel spray nozzle, of which the fuel injector is an element) and the direction of flow of a fuel stream as it enters the flow passage.
Advantageously, by swirling the fuel streams at a high swirl angle, the fuel streams can be merged earlier in the flow passage, producing a more circumferentially uniform fuel mass flow rate from the passage onto the prefilming lip. Indeed, preferably, the flow passage is configured so that the fuel streams merge in the flow passage to provide a circumferentially substantially uniform fuel mass flow at the prefilming lip.
A further advantage of the high swirl angle is that a shortened flow passage can be adopted, allowing a more compact and lighter fuel injector to be produced.
Preferably, in the circumferential direction, the ratio of the slot pitch (i.e. the distance between the centres of neighbouring slots) to the slot width at the narrowest point of a slot is at most 40. Preferably the ratio is at least 5, and more preferably at least 20.
Preferably, the ratio of the annular flow passage length in the axial direction to the slot width in the circumferential direction at the narrowest point of a slot is at most 20, and more preferably at most 10 or 3.
Preferably, the fuel distributor slots open to an upstream wall of the annular flow passage, the slots being further configured so that on entry into the flow passage the fuel streams retain contact with the upstream wall. Typically, the upstream wall is perpendicular to the axis of the flow passage. In this case, by retaining contact with the wall, at least the edges of the fuel streams have 90° swirl angles. However, other arrangements are possible. For example, the upstream wall may have a serrated, rippled or saw-tooth profile in the circumferential direction such that portions of the wall at the exits of the slots are at an angle of less than 90° (but at least 80°) to the axis of the flow passage, whereby the fuel streams can enter the flow passage at a corresponding swirl angle and still retain contact with the wall.
By keeping the fuel streams in contact with the upstream wall of the flow passage, rapid merging of the flow streams can be achieved. Further, two phase flow in the passage can be reduced or eliminated.
To retain contact between the fuel streams and the upstream wall of the flow passage, each slot may have:
The predetermined angle may be at least 70°. The predetermined angle may be at most 85°.
Preferably, the pressure surface is absent from the second section. This can help to discourage expansion of the fuel stream, which might otherwise tend to counter the Coand effect.
The flow passage may be a cylindrical annulus. Alternatively, the flow passage may be a frustoconical annulus which expands from the fuel distributor slots to the prefilming lip. Configuring the fuel distributor slots, so that the fuel streams merge early in the flow passage, allows relatively simple passage geometries to be adopted. Advantageously, such geometries can allow fuel to drain fully from the passage when the flow of fuel is stopped. This helps to prevent trapped fuel coking in and blocking the passage when the main fuel is stopped (staged) below full engine power and the engine operates with pilot fuel only.
Preferably the fuel injector is an airblast fuel injector.
A further aspect of the invention provides a fuel spray nozzle having the fuel injector according to the previous aspect. For example, the fuel injector may be a mains fuel injector, with the nozzle further having a radially inwards pilot fuel injector.
A further aspect of the invention provides a gas turbine engine combustor having the fuel spray nozzle of the previous aspect.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings in which:
Before discussing the invention it is helpful to provide more detail of other fuel injector arrangements.
The mains fuel injector of a pilot and mains fuel nozzle passes typically 85% of the fuel and air, and is thus the dominant emissions source. In a fuel injection nozzle such as that shown in
One option is to modify the shape of the gallery to encourage better circumferential spread of the fuel streams.
Possible further modifications to achieve uniform circumferential mass flow are (a) to lengthen the gallery between the fuel distributor slots and the prefilming lip and (b) to adopt a more complicated gallery geometry. However, these add cost, size and weight.
Further, as a result of engine staging operations the mains fuel is not always flowing. That is, to achieve high combustion efficiencies, the nozzle sometimes flows fuel through the pilot injector only. In this case, the fuel in the mains gallery should drain away completely to prevent stagnant fuel thermally degrading in the gallery and forming coke. Successive mains staging events (which can occur many times per flight) can cause such coke deposits to grow, until eventually the gallery may become partially or completely blocked. As incomplete mains fuel draining tends to occur in more complicated gallery geometries, this mitigates against the adoption of such geometries. Stagnant mains fuel upstream of the gallery remains cooler due to the closer proximity of pilot fuel passages, and coking is therefore not such a problem in these locations.
The two phase flow in the mains gallery illustrated in
Thus, according to the present invention, a different approach is taken to encourage the fuel streams in the mains gallery to provide a uniform circumferential mass flow rate at the gallery exit. Trigonometric calculations using a typical fuel gallery geometry show that, for a gallery and fuel slot arrangement as shown in
Although, generating a higher swirl angle can cause the fuel streams to meet in the gallery, which is an improvement over the fuel flows illustrated in
90° swirl allows the individual streams to merge early and flow together for a significant distance in the gallery, allowing the fuel mass flow rate to become circumferentially uniform by the time it reaches the gallery exit, and hence to provide a circumferentially uniform mass flow onto the prefilming lip. 90° swirl can also eliminate two phase flow and hence the hot walls that can cause fuel coking. It also does not require a complex geometry for the gallery. Indeed, only a relatively short gallery may be needed, as shown in
A fuel distributor slot 29 having a geometry for producing 90° swirl is shown in
The following section of the slot 29 provides an outlet to the gallery 30 at the upstream wall 33 of the gallery. At the outlet, the pressure surface 31 has a relatively small radius R2. The suction surface 32, on the other hand, has a radius R3 which blends to the upstream wall over a significantly longer distance. The uniform flow velocity produced by the central section of the slot encourages adherence of the flow to the radius R3 of the suction surface. Further, the flow adheres to the radius R3 by the Coanda effect, and hence as the suction surface blends to the upstream wall the edge of the fuel stream contacting the wall achieves 90° of swirl.
To encourage the fuel stream to retain contact with the upstream wall 33, the pressure surface 31 does not extend to oppose R3. Further R3 should be sufficiently large. Thus the pressure surface has a relatively small blend radius R2 to the upstream wall. Indeed, the radius R2 could be replaced by a square end that achieves a similar length reduction in the pressure surface. Preferably, R3 starts on the suction surface 32 at at least 0.5 slot widths downstream of the end of the pressure surface to ensure that the fuel flow is not diffusing (expanding) when it starts to flow around R3, as such diffusion would oppose the flow adhering to R3.
With at least the edge of the fuel stream exhibiting 90° of swirl into the gallery, there is rapid convergence of the fuel streams and a relatively uniform circumferential fuel flow rate at the gallery exit to the prefilming lip. Indeed, it may be possible to reduce the length of the gallery while maintaining the uniform flow. This simplifies manufacture of the injector, and promotes complete drainage of the gallery when the flow of mains fuel is staged.
effect and thence to the upstream wall 33.
Thus the edge of the fuel stream exhibits less 90 of swirl into the gallery. However the spreading of the stream can still cause it to converge with adjacent streams to provide relatively uniform circumferential fuel flow.
To summarise, the 90° of swirl at the fuel distributor slot exit can achieve the following:
While the invention has been described in conjunction with the exemplary embodiments described above, many equivalent modifications and variations will be apparent to those skilled in the art when given this disclosure. Accordingly, the exemplary embodiments of the invention set forth above are considered to be illustrative and not limiting. Various changes to the described embodiments may be made without departing from the spirit and scope of the invention as claimed.
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