GB2134184A

GB2134184A - Liquid fuel supply pressure compensator

Info

Publication number: GB2134184A
Application number: GB08301967A
Authority: GB
Inventors: John Ronald Tilston
Original assignee: UK Secretary of State for Defence
Current assignee: UK Secretary of State for Defence
Priority date: 1983-01-25
Filing date: 1983-01-25
Publication date: 1984-08-08
Also published as: GB8301967D0

Abstract

The fuel distribution system of a gas turbine engine, 71, comprises a fuel pump 76 connected via pipes 74 to the combustion chamber fuel atomisers 73. At idle or low power running the fuel supply pressure is of the same order as the static head in the pipes and combustion at the top of the engine may be starved of fuel, a condition which can damage the turbine blades. To overcome this problem, float operated pressure compensators 75 equalise the fuel pressure at each atomiser by generating a pressure reduction in the supply pressure equal to the static head at each atomiser, the pressure reduction being independent of fuel flow rate. There is also automatic adjustment for acceleration generated increases in the static head. Several different float operated pressure compensators are described. <IMAGE>

Description

SPECIFICATION Liquid supply pressure compensator The present invention relates to liquid distribution systems wherein a pressurised source of liquid feeds a plurality of outlets disposed along a pressure gradient, ie disposed vertically if a pressure gradient is generated by gravitational head in a fluid.

An example of such a liquid distribution system is the fuel supply system in a gas turbine engine.

Conventionally, a gas turbine engine is operated with the longitudinal axis of symmetry substantially horizontal and such an engine includes a fuel distribution system to a plurality offuel atomisers in the combustion region of the engine. Each atomiser is fed from either a manifold surrounding the engine axis or a separate supply pipe from a fuel distributor.

In both cases the fuel supply to each atomiser must provide an adequate differential between the fuel pressure at each atomiser and the pressure within the combustion region associated with each atomiser. At high engine power the pressure differential is sufficiently large to render negligible any gravitational effectonthefuel system. However, when an engine is idling, low or cruise poweroperation,thedifferential pressure required to maintain the necessary fuel supply rate is of the same order as the static pressure head of fuel in the manifold or supply pipes and consequently gravitational effect is not negligible.As a result, combustion at the top ofthe engine tends to be starved of fuel while combustion atthe bottom of the engine tends to be glutted with fuel and in an extreme case the fuel supply to the top of the engine may cease. In consequence, the engine runs unevenly and also the turbine blades are subjected to high frequency thermal cycling which can seriously affect their life. These effects are made worse when the engine is in an environment, such as a marine vehicle or a manoeuvring aircraft,where additional acceleration effects are encountered.

Many valve systems have been proposed to overcome this problem, butthese have proved to be too complicated for reliability, oversensitive to acceleration effects, or both.

At idle, low or cruise power operation in a gas turbine engine, a pressure compensator is required to provide a pressure differential between the supply and an atomiser or atomisers, if more than one in a horizontal plane, equal to the static head of fuel between that atomiser in the engine. Ideally at such idle, low and cruise power operation, the pressure differential acrossthe compensator will be indepen dent ofthefuel flow rate and at high power operation should offerthe minimum resistance to fuel flow. In addition,the compensatorshould be insensitiveto acceleration effects and especially for aircraft use should be small and of lightweight.

According to the present invention a liquid distribution system having a pressurised source of liquid and a plurality ofvertically separated outlets wherein the static head of a liquid acting between the highest outlet and each lower outlet is opposed by the action of a flow operated pressure compensator connected to each lower outlet which generates a pressure differential equal to the static head, the pressure differential under equilibrium conditions being proportional to the mass ofthefloat in the compensator and independent of liquid flow rate through the compensator so as to provide an equal liquid supply pressure at each outlet.

The liquid distribution system may also have a pressure compensator connected to a plurality of outlets, each outlet having the same requirement for static head compensation.

The liquid distribution system may also be installed in an environment in which it is subject to a component of acceleration paralleltothe axis of the pressure compensators such thatthe acceleration induced increase in the static head is equal to the increased pressure differential generated by the pressure compensator due to the effect of the component of acceleration parallel to the axis of the compensator on the mass ofthe float in the compensator.

The liquid distribution system may also be ofthe type which becomes partially or completely empty when not in use and a further benefit ofthe invention is that the higher parts ofthe system are more rapidly filled asthe pressure differential generated byeach compensator as a period of increasing flow begins is greaterthan that generated during equilibrium conditions buy a pressure proportional to the force required to displace the float in the compensator from an equilibrium position.

Embodiments ofthe invention will now be described in detail with reference to the accompanying drawings, in which Figure 1 shows schematically a liquid distribution system with a plurality of vertically disposed outlets.

Figure 2 shows schematically the effect of static head compensation in the liquid distribution system of Figure 1 by pressure compensators ofthe type shown in Figure 2.

Figure 3 shows schematically a pressure compensator suitable for use in the liquid distribution system of Figure 1.

Figures 4 and 5 show schematically alternative embodiments of pressure compensators.

Figure 6 shows schematically a pressure compensator arranged to provide emergency shut off in the event of excessive flow.

Figure 7 shows schematically pressure compensators in the fuel distribution system of a gasturbine engine.

In Figure 1 a pressurised source of liquid 1 feeds a supply pipe 2 connected to a series of outlets, 3, 4, 5, and 6, outlet3 being the lowest and outlet6the highest. The outlets are respectively at height, h3, for outlet 3, h4 for outlet 4, h5 for outlet 5 and he for outlet 6 above the height ofthe source 1, and in this embodiment h3 is equal to zero.The source of liquid provides liquid at a pressure P0 and as there is no static head acting to reduce the pressure available at outlet3, the supply pressure atoutlet3, neglecting frictional losses in the transmission of liquid through the supply pipe 2, is also PO Due to the action ofthe static head, the supply pressureatthe successively higher outlets 4,5 and 6 will be P0-pgh4atoutlet4 P0- pghs at outlet5 P0-pgh6 at outlet 6 where p is the density ofthe liquid and g is the acceleration due to gravity, 13, 14, 15 and 16 showthe path of liquid flowing from the outlets 3,4,5 and 6 respectively.

In Figure 2 compensation for static head has been achieved bythe attachment offlow operated press ure compensators 23, 24, 25 respectively to the outlets 3,4,5 of the liquid distribution system such thatthe available pressure at all the outlets is equal to the pressure available at outlet 6that is Po-pgh6. The pressure compensators 23, 24, 25 must produce pressure differentials of pg(h6-h3), pg(h6-h4) and pg(h6-h5) respectively to equalise the pressure at each outlet, where h3, h4, h5 and h5 are the vertical displacements ofthe outlets 3,4,5 and 6 from the source 1 and in this embodiment h3 is equal to zero, p isthedensityofthe liquid andg isthe acceleration due to gravity.The flow, 26, from each ofthe outlets 3, 4, 5 and 6 is now equal .

In Figure 3 a flow operated pressure compensator 31 suitable for use to achieve the static head compensation shown in Figure 2 has a substantially vertical tapered tube, 32, with a liquid inlet 33 atthe bottom and outlet 34 at the top. Within the tapered tube is a float 35 of mass M and cross sectional area A.

Flow of liquid of density through the compensator, shown byarrows F, is directed through the passage, 36, between the float and the tapered tube and the area of the passage varies with the position of the float in the tapered tube. When equilibrium is established with the float having no vertical motion in the tapered tube, the weight ofthe float must be equal to the upthrust on the float due to the passage of liquid through the pressure compensator. At equilib rium, V2A Mg=p 2 1 where g is the acceleration due to gravity and V is the - mean velocity of liquid passing the float.The pressure difference, Pd, across the float is equal to the upthrust on the float divided by the area A, that is V2 Pd=p 2 2 and combining 1 and 2 and rearranging gives Pd= Mg 3 A Thus for a float of given mass, M, and cross sectional area, A, the equilibrium pressure differen tial generated by the pressure compensator is independent of the flow rate through the compen sator.

In use, the pressure differential can be arranged to be equal to the static head requiring compensation by selection ofthe mass and effective area ofthefloat.

When the static head is generated by a vertical height H of liquid, the static head pressure Ps is given by Ps=pgH 4 therefore combining equations 3 and 4 gives Pd M 5 P5 AHp and for exact compensation ofthe static head Pd 1 M 6 P5 AHp and hence M M 7 The ratio of Pd to Ps is independent of the acceleration term g, and the compensator can provide not only Pd equal to P5 and within the limit of the supply pressure, Pd equal to anyfraction or multiple of P5 under normal gravity but also compensates automatically for any acceleration induced increase in the static head.

Afurtherembodimentofa pressure compensator is shown in section across a diameter in Figure 4. In this form the flow operated pressure compensator, 41, has a substantially vertical cylindrical tube 42, with an inlet43 atthe bottom and outlet 44 atthetop.

Within the cylindrical float 45 which is a sliding fit in the cylinder. The float has a tapered bore 46 to cooperate with a tapered needle 47 positioned on the axis ofthe cylinder42, with the end of greatest diameter downward. Flowthrough the compensator, shown by arrows F, passes through the passage 48, between float and needle. The area of passage 48 varies with the position ofthe float.

In Figure 5 a diametrical cross section of a flow operated pressure compensator 51, is shown. The pressure compensator has a spherical float, 52, which is a sliding fitwithin an inner perforated cylinder 53.

An outertube 54 having an outlet 55 encloses the cylinder such that flow th rough the compensater shown by arrows F passes from the inlet 56 at the bottom ofthe innercylinderto the outletviathe uncovered perforations 57 ofthe inner cylinder. The area of uncovered perforations and hence the area of the flow passage through the compensator varies with the position ofthefloat 52.

In Figure 6 a diametrical cross section of a flow operated pressure compensator, 61, is shown. The pressure compensator has a hollow cylindrical float, 62, that is a sliding fit between the follow perforated inner cylinder 63 and the concentric outer cylinder 64.

Flowpassesthrough the compensator as shown by arrows F. Under normal maximum flow conditions through the compensator, the float rests against the bottom ofthe coil spring 65. If the flow rate increases beyond the normal maximum, the float crushes the spring and excludesflowtothe outlet 66.

Figure 7 shows schematically a cross section of a gas turbine engine 71 in the region ofthe combustion chamners 72 ofthe engine. There is an atomiser 73 in each combustion chamberfed by a fuel pipes 74,the atomisers being supplied from a pressure compensator assembly 75 which is in turn supplied with pressurised fuel by a pump assembly, 76, which pumpsfuelfrom afuel store which is not shown.

Compensation forthe static head and acceleration induced static head present between the atomisers is achieved by pressure compensators ofthe type described above working on the principle detailed in the description of Figure 3 above.

The combustion region ofthe engine is surrounded by a pressure casing 77 and the fuel pipes 74, must penetrate this casing. To ensurethefuel pipes feeding the upper atomisers have the shortest possible length within the casing it will be seen that parts of the fuel lines run above the atomisers before penetrating the pressure casing, which results in part ofthe fuel distribution system becoming empty when the engine ceases to run. The increased pressure differential generated by the pressure compensators atthe beginning of a period of increasing flow ensures the rapid refilling of the drained sections of fuelpipe.

Further, it will be appreciated that in any liquid distribution system a flow operated pressure compensator may be used as a flow independent pressure reducer.

Each embodiment of the flow operated pressure compensator may also be modified such that the presence ofaflowthrough the compensator above a predetermined value movesthefloat in the compan satorto a position where the compensator presents a fixed resistance to flow and the pressure drop across the compensator depends on the flow rate through the compensator.

The area ofthe flow passage through each embodimentofthecompensatormaybevaried by shaping ofthetaperedtube, Figure3, needle, Figure 4, or size and shape of perforations Figures 5 and 6 such that the position ofthe float and increased pressure differentials atthe beginning of periods of increased flow aretailored to the required pressure demands ofthe liquid outlets.

Further, an embodiment ofthe invention may include a pressurised liquid source feeding a plurality of horizontal outlets, requiring a different pressure to be available at each outletwhen flow is present provided by a flow operated pressure compensator at eaçi outlet.

CLAIMS (filed on 24.1.84) t. A liquid fuel distribution system for use in a vehicle, the system including a pressurised source of liquid fuel, a plurality ofvertically separated fuel outlets, and float operated pressure compensator means connected between the source and thefuel outlets andarrangedto oppose static head pressure ofthefuelwherebyin use under steady flow conditions the compensator means provides pressure reduction which is independent oftheflow rate through the outlet.

2 Aliquidfuel distribution system for use in a vehicle as claimed in claim 1, wherein the system is subject two a component of acceleration so as to increase static head pressure in the system, the component of acceleration being parallel to the freely moveable direction of the floatwithin the compensator means, such that in use the pressure compensator meansprovidesa pressure reduction equaltothe acceleration increased static head pressure by virtue of the effect of the component of acceleration on the float.

3. A liquid fuel distribution system for use in a vehicle as claimed in claim 1, wherein the pressure reduction generated by the pressure compensator means is largerthan the steadyflow pressure reduction during a period of increasing flow and is smallerthanthesteadyflow pressure reduction during a period of decreasing flow by virtue of the inertia of the float in the compensator.

4. A liquid fuel distribution system for use in a vehicle as claimed in claim 1 or claim 2 or claim 3, wherein the liquid fuel distribution system is the fuel system of a gas turbine engine.

5. A liquid fuel distribution system as herein before described, with particular reference to Figures 3,4,5and6.

6. A liquid fuel distribution system as herein before described, with particular reference to Figure 7.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **.

atomisers being supplied from a pressure compensator assembly 75 which is in turn supplied with pressurised fuel by a pump assembly, 76, which pumpsfuelfrom afuel store which is not shown.

Compensation forthe static head and acceleration induced static head present between the atomisers is achieved by pressure compensators ofthe type described above working on the principle detailed in the description of Figure 3 above.

The combustion region ofthe engine is surrounded by a pressure casing 77 and the fuel pipes 74, must penetrate this casing. To ensurethefuel pipes feeding the upper atomisers have the shortest possible length within the casing it will be seen that parts of the fuel lines run above the atomisers before penetrating the pressure casing, which results in part ofthe fuel distribution system becoming empty when the engine ceases to run. The increased pressure differential generated by the pressure compensators atthe beginning of a period of increasing flow ensures the rapid refilling of the drained sections of fuelpipe.

Further, it will be appreciated that in any liquid distribution system a flow operated pressure compensator may be used as a flow independent pressure reducer.

Each embodiment of the flow operated pressure compensator may also be modified such that the presence ofaflowthrough the compensator above a predetermined value movesthefloat in the compan satorto a position where the compensator presents a fixed resistance to flow and the pressure drop across the compensator depends on the flow rate through the compensator.

The area ofthe flow passage through each embodimentofthecompensatormaybevaried by shaping ofthetaperedtube, Figure3, needle, Figure 4, or size and shape of perforations Figures 5 and 6 such that the position ofthe float and increased pressure differentials atthe beginning of periods of increased flow aretailored to the required pressure demands ofthe liquid outlets.

Further, an embodiment ofthe invention may include a pressurised liquid source feeding a plurality of horizontal outlets, requiring a different pressure to be available at each outletwhen flow is present provided by a flow operated pressure compensator at eaçi outlet.

CLAIMS (filed on 24.1.84) t. A liquid fuel distribution system for use in a vehicle, the system including a pressurised source of liquid fuel, a plurality ofvertically separated fuel outlets, and float operated pressure compensator means connected between the source and thefuel outlets andarrangedto oppose static head pressure ofthefuelwherebyin use under steady flow conditions the compensator means provides pressure reduction which is independent oftheflow rate through the outlet.
2 Aliquidfuel distribution system for use in a vehicle as claimed in claim 1, wherein the system is subject two a component of acceleration so as to increase static head pressure in the system, the component of acceleration being parallel to the freely moveable direction of the floatwithin the compensator means, such that in use the pressure compensator meansprovidesa pressure reduction equaltothe acceleration increased static head pressure by virtue of the effect of the component of acceleration on the float.
3. A liquid fuel distribution system for use in a vehicle as claimed in claim 1, wherein the pressure reduction generated by the pressure compensator means is largerthan the steadyflow pressure reduction during a period of increasing flow and is smallerthanthesteadyflow pressure reduction during a period of decreasing flow by virtue of the inertia of the float in the compensator.
4. A liquid fuel distribution system for use in a vehicle as claimed in claim 1 or claim 2 or claim 3, wherein the liquid fuel distribution system is the fuel system of a gas turbine engine.
5. A liquid fuel distribution system as herein before described, with particular reference to Figures 3,4,5and6.
6. A liquid fuel distribution system as herein before described, with particular reference to Figure
7.