GB2176535A - A degrader for antimisting fuel - Google Patents

Abstract

The degrader (10) for antimisting fuels used in gas turbine engines comprises a cylindrical housing (12) which has a fuel inlet and a fuel outlet (14) at opposite axial ends thereof. A rotor (20) is rotatably mounted coaxially within the housing, and the rotor is spaced from the inner surface (18) of the housing. The rotor has at least one lobe (28) which extends radially towards the inner surface of the housing to form a venturi-shaped gap. As the rotor rotates a velocity difference is formed between the fuel and the rotor due to drag forces on the inner surface of the housing. This causes the fuel to flow through the venturi-shaped gap, and if the velocity difference is great enough cavitation occurs which degrades the fuel. The inner surface of the housing may be roughened to increase drag forces, and the downstream surface of the lobe may be roughened to increase cavitation. <IMAGE>

Description

SPECIFICATION A degrader for fuel The present invention relates to degraders for fuels, particularly antimisting fuels for use in aero gas turbine engines.

In recent years a lot of work has been carried out on the development of antimisting fuels, ie., antimisting kerosene or AMK in short, for the use of aero gas turbine engines. The development of AMK will reduce the possibility of an aircraft fuel fire or explosion in the event of an accident. Antimisting fuels have an antimisting additive, which is a long molecular chain polymer, to render the fuel less volatile and therefore less likely to ignite.

While it is desireable to reduce the possibilities of fire in the event of an accident, the use of the antimisting additives in the fuel are undesireable in the gas turbine engine, as they prevent ignition of the fuel by preventing vapourisation. The antimisting additives must therefore be removed or degraded before the fuel is supplied into the combustion chamber of the gas turbine engine so that the fuel will be vapourised.

The fuel degraders used at present are relatively heavy, and complex, and require high energy consumption. Such fuel degeaders may comprise multi-stage high pressure pumps with venturi or meshes after each pump.

The present invention seeks to provide a fuel degrader which is relatively light, simple and requires reduced energy consumption.

Accordingly the present invention provides a fuel degrader comprising a housing having a rotor rotatably mounted therein and adapted to be driven by driving means, the housing having an inlet for fuel at one axial end and an outlet for fuel at the opposite axial end, the rotor being spaced radially from the inner surface of the housing, the rotor being spaced radially from the inner surface fo the housing, the rotor having at least one lobe extending radially from the circumference of the rotor and forming a venturi-shaped gap with the inner surface of the housing, in operation rotation of the rotor and drag forces on the inner surface of the housing producing a velocity difference between the fuel and the rotor, the velocity difference between the fuel and the rotor causing the fuel to flow through the venturi-shaped gap, the fuel being degraded by cavitation due to the high velocity difference as it flows through the venturi-shaped gap.

The inner surface of the housing may be roughened to increase drag forces acting on the fuel in order to increase the velocity difference between the fuel and the rotor.

The at least one lobe and rotor may have roughened surfaces downstream of the tip of the lobe to increase cavitation of the fuel, as it flows through the venturi-shaped gap.

The rotor may have a plurality of lobes arranged equi-spaced circumferentially on the rotor to minimise vibration of the rotor.

The rotor may have two lobes arranged diammetrically opposite each other on the rotor.

The present invention will be more fully described by way of reference to the accompanying drawings in which: Figure 1 is an axial section through a fuel degrader according to the present invention.

Figure 2 is a sectional view through the fuel degrader in Fig. 1 looking in the direction of arrows X.

Figure 3 is an axial section through a second embodiments of a fuel degrader according to the present invention.

Figure 4 is a sectional view through the fuel degrader in Fig. 3 looking in the direction of arrows Y.

Figure 5 is an enlarged view of part of the fuel degrader shown in Fig. 2. and Figure 6 is a partially cut away view of a gas turbine engine showing a combustion chamber supplied with fuel from a fuel degrader according to the present invention.

Referring to Figs. 1 and 2, there is shown a fuel degrader 10 comprising a cylindrical housing 12 having an inlet 16 for fuel at one axial end, and an outlet 14 for fuel at the opposite axial end. A rotor 20 is positioned coaxially within the cylindrical housing 12 and the rotor 20 is rotatably mounted in the cylindrical housing by means of a shaft 22 extending coaxially through an aperture 26 on the axis of the cylindrical housing, and a stub shaft 24 extending into a recess 30 on the axis of the cylindrical housing at the opposite axial end.

The rotor 20 is spaced radially from the inner surface 18 of the cylindrical housing 12, and has a lobe 28 extending radially from its circumference towards the inner surface of the cylindrical housing, to form a venturi-shaped gap 32 with the inner surface of the housing, as shown in Fig. 5. The shaft 22 being driven by a driving means (not shown), ie., a power off take shaft from a gas turbine engine In operation the shaft 22 driven by the driving means, and the rotor 20 rotates anticlockwise, for example, in the direction of Arrow A, as shown in Fig. 2. Fuel is supplied from a fuel system on the aircraft or gas turbine engine into the cylindrical housing 12 through the inlet 16.As the rotor 20 revolves around its axis of rotation it pushes the fuel ahead of the lobe 28 in the direction of rotation, but drag forces at the inner surface 18 of the cylindrical housing produce a velocity difference between the rotor and the fuel, which forces the fuel through the venturishaped gap 32 between the lobe 28 and the inner surface 18 of the housing 12.

If the velocity difference between the fuel and the rotor is sufficiently great cavitation will occur at or near the tip 29 of the lobe 28 and the flow will be highly separated in the venturi-shaped gap downstream of the tip 29 causing degradation of the fuel.

Referring to Fig. 5 which shows an enlarged portion of Fig. 2, the inner surface 18 of the cylindrical housing is roughened, for example toothed, so as to increase the drag forces acting on the fuel and to decrease the induced flow of fuel, in order to create an increased velocity difference between the fuel and the rotor.

The surface 34 of the lobe 28 and rotor 22 downstream of the tip 29 of the lobe 28 may be roughened, so as to increase cavitation of the fuel as it flows through the venturi-shaped gap, in order to increase turbulence and degradation of the fuel.

The degraded fuel then flows through the outlet 14 to the combustion chamber of the gas turbine engine where the degraded fuel can now be vapourised and burnt.

Referring to Figs. 3 and 4, a similar fuel degrader is shown, and similar parts as in Figs. 1 and 2 have been given the same reference numerals, and their precise construction and operation will not be discussed again. The rotor 20 in this embodiment is provided with two lobes 28 diammetrically opposite each other on the rotor, so as to minimise the vibration loads on the rotor. It would of course be possible to provide a fuel degrader with more than two lobes on the rotor, but it would be preferable that they are equi-spaced and balanced to minimise vibration loads.

A fuel degrader as described is a relatively simple device, and is relatively light. The rotor of the fuel degrader will have to rotate at high speeds in order to degrade the fuel, but will require reduced amounts of energy as compared to the prior art. This fuel degrader will be less sensitive to contaminants in the fuel because there are no small clearances in the device.

Fig. 6 shows a gas turbine engine 60 which comprises in flow series an inlet 52, a fan and intermediate compressor 54, a fan duct outlet 56, a high pressure compressor 58, a combustion system 60, a turbine 62 and an exhaust nozzle 64. The gas turbine engine operates conventionally and this will not be discussed. The combustion system comprises an annular combustion chamber 66 which has a plurality of equi-spaced circumferentially arranged fuel burners 68 adapted to supply fuel into the combustion chamber to be burnt. The fuel burners are supplied with fuel from a fuel manifold 70 extending coaxially around the combustion system, and the fuel manifold is supplied with fuel from the fuel degrader 10 which degrades the antimisting fuel supplied by the fuel system 72. The fuel system 72 will comprise low and high pressure pumps, a fuel flow regulator and a spill valve. The fuel degrader may be positioned so that the outlet 14 supplies fuel to the fuel flow regulator which then supplies fuel to the fuel manifold.

The fuel degrader may equally well be used for degrading fuel for use in other types of engines.

The pressure in the fuel degrader may be depressed by means of a restrictor at the fuel inlet, and/or by a suction pump at the fuel outlet so as to increase cavitation further.

The roughened inner surface of the housing, and the roughened surfaces of the lobe and rotor downstream of the tip of the lobe, may be any suitable form of surface discontinuity ie., cavities, teeth or other surface interruptions.

Claims (7)

1. A fuel degrader comprising a housing having a rotor rotatably mounted therein and adapted to be driven by driving means, the housing having an inlet for fuel at one axial end and an outlet for fuel at the opposite axial end, the rotor being spaced radially from the inner surface of the housing, the rotor having at least one lobe extending radially from the circumference of the rotor and forming a venturi- shaped gap with the inner surface of the housing, in operation rotation of the rotor and drag forces on the inner surface of the housing producing a velocity difference between the fuel and the rotor, the velocity difference between the fuel and the rotor causing the fuel to flow through the venturi-shaped gap, the fuel being degraded by cavitation due to the high velocity difference as it flows through the venturi-shaped gap.

2. A fuel degrader as claimed in claim 1 in which the inner surface of the housing is roughened to increase drag forces acting on the fuel in order to increase the velocity difference between the fuel and the rotor.

3. A fuel degrader as claimed in claim 1 or claim 2 in which the at least one lobe and the rotor have roughened surfaces downstream of the tip of the lobe to increase cavitation of the fuel as it flows through the venturi-shaped gap.

4. A fuel degrader as claimed in any of claims 1 to 3 in which the rotor has a plurality of lobes arranged equi-spaced circumferentially on the rotor.

5. A fuel degrader as claimed in claim 4 in which the rotor has two lobes arranged diammetrically opposite each other on the rotor.

6. A fuel degrader substantially as herein before described with reference to and as shown in the accompanying drawings.

7. A gas turbine engine having a fuel system comprising a fuel degrader as claimed in any of claims 1 to 6.