Patent Application
20100038455
This application is entitled to the benefit of British Patent Application No. GB 0814791.0, filed on Aug. 14, 2008.
This invention relates to liquid ejectors in general but particularly to fuel injectors, which may be used in a gas turbine engine.
There is a continuing need, driven by environmental concerns and governmental regulations, for improving the efficiency of and decreasing the emissions from gas turbine engines of the type utilised to power jet aircraft, marine vessels or generate electricity. Particularly there is a continuing drive to reduce nitrous oxide (NOx) emissions.
Advanced gas turbine combustors must meet these requirements for lower NOx emissions under conditions in which the control of NOx generation is very challenging. For example, the goal for the Ultra Efficient Engine Technology (UEET) gas turbine combustor research being done by NASA is a 70 percent reduction in NOx emissions and a 15 percent improvement in fuel efficiency compared to ICAO 1996 standards technology. Realisation of the fuel efficiency objectives will require an overall cycle pressure ratio as high as 60 to 1 and a peak cycle temperature of 1600° C. or greater. The severe combustor pressure and temperature conditions required for improved fuel efficiency make the NOx emissions goal much more difficult to achieve.
Conventional fuel injectors that seek to address this issue have concentrically arranged pilot and main injectors with the main injector surrounding the pilot injector. However, conventional injector arrangements have several operational disadvantages, including for example, flame stability and relight characteristics, the potential for excessive combustor dynamics or pressure fluctuations caused by combustor instability.
Stability and relight are particular requirements for the pilot injector which operates at low power requirements. The pilot sprayer has a very low fuel delta pressure at altitude relight, below that which conventional pressure spray injectors atomise the fuel. Stability is improved through the use of an airspray pilot which has an additional core air swirler and heatshield and which offers an improved atomisation and fuel distribution within the combustor.
In comparison to a pressure-jet atomiser an airspray atomiser is more complex, adding to the development and build cost of the whole injector.
A known fuel injector is known from U.S. Pat. No. 6,986,255 and depicted in the prior art diagram,
It is an object of the present invention to seek to provide an improved ejector.
According to a first aspect of the invention there is provided a pressure jet liquid ejector comprising an axially located passage ending as a nozzle having an internal surface facing radially inwardly towards the axis, extending as an outboard cone about the axis of the bore and terminating at a tip, and an outer surface facing radially outwardly away from the axis and intersecting with the internal surface at the tip, wherein the outer surface has a profile for accelerating a gaseous flow over the outer surface.
Preferably the outer surface has a radius from the axis that varies along the axial length of the outer surface to provide the profile.
The radius along the axial direction may decrease and then increase to provide an annular depression with an axially rearward lead in and an axially forward lead out.
Preferably the outer surface has an axially extending annular portion of constant radius between the end of the axially forward lead out and the tip.
The outboard cone may extend outwardly at an angle between 30° and 70° to the axis but more likely to be between 30° and 40° to the axis. The outboard cone angle preferably replicates the unconstrained trajectory of swirling fuel leaving the passage in use at the highest fuel flow required.
Preferably at least part of the passage is radially inward of an insulating sleeve for providing resistance to the transfer of heat from the gaseous flow to the passage, wherein the outer surface of the insulating sleeve provides at least part of the outer surface.
The supply passage preferably has swirl means for imparting swirl to a liquid which flows through the supply passage in use.
The ejector may have a housing which defines with the outer surface a gaseous flow passage through which, in use, a gas flows. The gas is preferably air.
Preferably the gaseous flow passage has swirling means for imparting swirl to the gas flow.
Preferably the axis of the ejector is the axis of a lean burn fuel injector for a gas turbine and the injector further comprises a further fuel injector arranged concentrically about the axis and located radially outwardly of the outer surface.
Preferably the liquid to be ejected and supplied through the supply passage is fuel which is then injected into the combustor of a gas turbine engine.
For reference, the nozzle 2 is located on the axis of a fuel injector and could replace component 102 of the prior art figures.
The nozzle 2 has an internal surface 4 which faces towards the centreline of the ejector 6 right to its tip 8 where it intersects with an outer surface 10 which faces away from the ejector axis 6.
The nozzle is supplied with fuel from an axially arranged fuel passage 12. An array of swirl vanes 14 or other swirl generating means impart swirl to the fuel which feeds onto the outwardly extending cone of the internal surface 4. The angle of the cone (α) to the axis of the ejector and the profile of the transition from the fuel passage 12 to the cone 4 replicates the unconstrained trajectory of the swirling fuel leaving the outlet of the passage 12 at the highest fuel flow required. This prevents the fuel film from separating from the surface and maximises the fuel film velocity on the surface. The maximised velocity minimises the fuel film thickness which consequently minimises the droplet size when the fuel film is atomised at the tip of the ejector to optimise the relight capability, flame extinction and improve smoke emissions. By blending the internal surface of the cone to the wall of the passage it is possible to avoid the presence of sharp edges which can cause the fuel film to detach.
For the primary application of the ejector, in a gas turbine fuel injector, the angle α is typically between 30° and 70° but is more often within the range 30° and 40°.
The outer surface 10 of the nozzle has a profile which accelerates an airflow towards the tip. The profile has an annular depression around the nozzle axis that has a streamlined lead in and a streamlined lead out. A short, axially extending portion 16 may be provided to link the lead out portion of the depression with the intersection with the internal surface at the internal surface tip S. The acceleration of the air flow minimises the boundary surface on the outer surface and maximises the air velocity at the tip, which is also the location at which the air flow impacts the fuel and atomisation of the fuel is effected.
Air is supplied through a swirl passage 101 and swirl is imparted to the air as it flows through a swirler 104. The outer wall of the swirl passage has a contraction 109 that also helps to maintain the velocity of the air flow through the swirl passage.
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Whilst the invention finds particular application in fuel injectors for gas turbine engines it may also find application in other fields which require atomisation of a liquid. Such technical fields may include, but not be limited to, farming and land vehicles.
| Number | Date | Country | Kind |
|---|---|---|---|
| 0814791.0 | Aug 2008 | GB | national |
