Patent Description:
Split flow control for modem turbine engines is typically used to control the fuel flow to two or more combustion zones in the engine that are fed via a number of fuel nozzles supplied from primary and second manifolds. While numerous control architectures are available, many such systems use a simple flow divider value for this purpose. One such simply split flow control valve is shown in <FIG> in an operating (full fuel flow), primary flow only (reduced fuel flow), and shutdown mode of operation (no fuel flow) from the left to the right. Such simple valves operate to equalize the pressure related to total fuel flow in order to control the fuel flow of two flow circuits that feed a plurality of fuel nozzles through the independent primary and secondary manifolds.

As the fuel pressure from the fuel control system is reduced from the primary operating condition shown on the left of <FIG>, the reduced fuel pressure allows the main split flow control piston to move upward under force of the main control spring. This movement serves to reduce, and then eliminate, secondary flow to the secondary manifold as shown in the middle illustration of <FIG>. As the pressure is reduced still further, the primary flow is reduced as the piston continues to move upward to balance the fuel pressure with the spring force, until even the primary fuel flow is stopped in the shutdown mode shown on the rightmost illustration of <FIG>.

While not present in all split flow systems, the valve of <FIG> illustrates the presence of an ecology piston that is held on an ecology valve seat by a secondary spring during the operating modes. However, once the shutdown mode is achieved by full stroke of the main split flow control piston, the ecology piston is lifted from its seat to drain the primary and secondary manifolds to prevent coking of the fuel that might otherwise remain therein. The fuel from these manifolds may flow into an ecology valve for ready supply back to the manifolds to ensure that they are primed for controlled flow from the fuel control system once engine operation is again commanded.

As will now be apparent, such systems control the flow split by metering a portion of the total flow in one of the fuel manifolds. The remainder of the total flow is passed down to the other manifold. This method of fuel flow split control is insensitive to manifold pressures, thus fuel flow split accuracy is not impacted by downstream manifold and nozzle variation. Thus, the total engine fuel flow split can be accurately maintained over a wide range of operating conditions.

While perfectly suitable in many turbine engine installations, in some applications it is necessary to operate at low power for an extended period of time. Unlike in the valve shown in <FIG> that only opens the ecology valve to purge both manifolds during shutdown, in this low power mode it is desired to purge the secondary manifold while continuing to operate from the primary manifold. This is desired in order to enrich the primary circuit, to improve flame out margin, and to ensure the secondary nozzles do not coke up due to continued presence of fuel during periods of continuing operation in the low power mode.

The problem is, however, that while the low power mode of operation only needs fuel to be supplied by the primary manifold, in a commanded second key operating mode this same fuel flow rate is required to be supplied to the engine from both primary and the secondary manifold. In other words, the two modes of operation, to wit the extended operating low power mode and the commanded second key operating mode, each use essentially the same fuel flow to the engine, but use different split ratios depending on whether the engine is coming from a low power condition or a high power condition. Furthermore in the extended operating condition the secondary manifold must be purged whereas in the commanded second key operating mode the secondary manifold must remain primed with fuel.

In a fuel system technical implementation, this requirement for an intentional hysteresis loop creates an issue for a passive flow divider valve, without adding additional features to enable the two different modes at a single flow rate. In one such implementation a hysteresis can be built into the valve logic, and software can be written into the computer logic to enable the desired conditions. However, such active computer driven control increases the complexity and cost of the fuel flow control system.

In view of the above, what is needed is a passive split flow divider valve solution that, in a first condition, is capable of flowing fuel to both manifolds when an idle condition is commanded from a high power operating condition, but that, in a second condition, flows fuel only to the primary manifold when the idle condition is commanded from low power operating condition. That is, the second condition provides the same idle condition flow rate as the first condition but with the secondary manifold closed and purged. Such a passive split flow valve solution offers better metrics for system cost, weight, and reliability compared to a solution that requires electronics to provide the different split ratios dependent on ascending or descending combustion fuel flow.

Embodiments of the present invention provide such a passive solution. These and other advantages of the invention, as well as additional inventive features, will be apparent from the description of the invention provided herein.

<CIT> describes a fuel divider system that includes a housing assembly and a flow passage network having an inlet, a primary outlet, and a secondary outlet. A fuel divider piston is slidably disposed within the housing assembly and movable between a flow biasing position and a flow equalizing position. A control chamber is fluidly coupled to the flow passage network and fluidly communicates with the piston. An inlet chamber, at least partially defined by the piston and the housing assembly, is fluidly coupled to the inlet.

<CIT> describes a fuel control system for a gas turbine engine having a staged combustor includes apparatus and methods to operate the combustor during pilot operation, staged operation, and transition between the two modes of operation.

<CIT> describes a gas turbine engine fuel system that has an ecology valve for withdrawing residual fuel from primary and secondary fuel manifolds upon engine shutdown. The ecology valve has primary and secondary reservoirs respectively connected in fluid flow communication with the primary and secondary fuel manifolds and a reciprocating piston movable from a retracted position when engine start-up is initiated to an extended position under normal engine running conditions. The movement of the reciprocating piston between the retracted and extended positions controls the flow of fuel from and to the primary and secondary reservoirs.

<CIT> describes a fuel control system for supplying metered quantities of fuel from a fuel supply, through a fuel pump, a metering valve and a pressurizing valve to a plurality of engine fuel manifolds includes an ecology valve for withdrawing fuel from the engine fuel manifolds during cessation of engine operation and for returning fuel to the engine fuel manifolds to be burned during normal engine operation. The ecology valve includes a valve housing having a plurality of ecology ports adapted to be coupled to corresponding ones of the engine fuel manifolds and a control port adapted to be connected to a corresponding control port of the fuel pressurizing valve. BRIEF SUMMARY OF THE.

Embodiments of the present invention provide a passive flow splitting system are defined in claims <NUM>, <NUM> and their dependencies. In particular embodiments such passive flow splitting system is utilized in a turbine engine control system to provide split fuel flow to two fuel manifolds to supply primary and secondary fuel injectors for the particular combustion zones. Preferably, embodiments provide the ability to split fuel to the primary and secondary manifolds to supply the injectors at an intentionally different split ratio dependent on ascending or descending combustion fuel flow.

A passive fuel divider valve (FDV) can be utilized that includes a primary piston and a secondary piston. The primary piston is moveable independently from the secondary piston to meter fuel flow to the primary manifold of the engine fuel supply system in one embodiment, and is biased away from the secondary piston. The secondary piston meters fuel flow to the secondary manifold of the engine fuel supply system in one embodiment, and is biased to prohibit such flow. The primary piston strokes with increasing fuel pressure to meter such flow to the primary manifold, and contacts the secondary piston with increasing fuel pressure to cause it to meter flow to the secondary manifold. Preferably, the primary piston and the secondary piston are hydro-locked during such metering.

An ecology valve can be provided to purge the fuel and ecology it from the primary and/or secondary manifolds. The control for such ecology valve is provided in one embodiment by a transfer valve. This transfer valve senses fuel pressure supplied to the secondary manifold by the FDV in order to alternatively supply inlet pressure or fuel pump operating pressure to the control side of the ecology piston of the ecology valve.

An FDV can be configured to provide a low power mode of operation that only supplies fuel to the primary manifold. The FDV is also configured to provide the same fuel flow rate as in the low power mode in a commanded second key operating mode that supplies fuel to the engine from both the primary and the secondary manifolds. With such configuration of the FDV, the two modes of operation, to wit the low power mode and the commanded second key operating mode, each use essentially the same fuel flow to the engine, but use different split ratios depending on whether the engine is coming from a low power condition or a high power condition, such differences defining a flow rate hysteresis loop enabling such operations in the different modes.

The secondary manifold can be purged while continuing to operate from the primary manifold in the low power mode in order to enrich the primary circuit, to improve flame out margin, and to ensure the secondary nozzles do not coke up due to continued presence of fuel during periods of continuing operation in the low power mode.

On the contrary, the intent is to cover all alternatives, modifications and equivalents as included within the scope of the appended claims.

Turning now to the drawings, there is illustrated in <FIG> a passive split flow fuel control system constructed in accordance with an embodiment of the present invention. Such a system is capable of providing different split ratios to the primary and the second fuel manifolds of a multi-zone turbine engine dependent on ascending or descending combustion fuel flow. As will be discussed in detail hereinbelow, use of the split fuel flow divider valve provides an intentional hysteresis loop that, in a first condition, is capable of flowing fuel to both manifolds when an idle condition is commanded from a high power operating condition, but that, in a second condition, flows fuel only to the primary manifold when the idle condition is commanded from low power operating condition. That is, the second condition provides the same overall idle flow rate as the first condition but with the secondary manifold closed and purged.

However, it should be noted that while the following will describe various features and advantages provided by embodiments of the present invention in the context of fuel flow to a turbine engine with different combustion zones supplied by primary and secondary manifolds, such embodiments and operating environments should be taken by way of example and not by way of limitation.

As illustrated in each of <FIG>, an embodiment of the split flow fuel control system <NUM> of the present invention includes a flow dividing valve (FDV) <NUM>, which schedules both the primary <NUM> and secondary <NUM> manifold port openings as a function of total flow. A transfer valve <NUM> is included in the illustrated embodiment, which controls the charge/discharge of the double diameter ecology piston <NUM> of ecology valve <NUM>. This ecology valve <NUM> is fluidly connected to, and therefore is capable of reservoiring the fuel in, both the primary and secondary manifolds (not shown). This reservoiring is accomplished by fluidly connecting the primary manifold via flow line <NUM> to purge volume <NUM> of the ecology valve <NUM>, and by fluidly connecting the secondary manifold via flow line <NUM> to purge volume <NUM> of the ecology valve <NUM>.

The FDV <NUM> includes a primary piston <NUM> and a secondary piston <NUM>. The primary piston <NUM> is biased upward and against a first seal <NUM> by a first spring <NUM>, and the secondary piston <NUM> is biased upward and against a second seal <NUM> and a third seal <NUM> by a second spring <NUM>. In relative terms, the force of spring <NUM> is lighter than that of spring <NUM>. As will be discussed more fully below with reference to <FIG>, as the inlet fuel pressure is increased at the inlet <NUM> of the FDV <NUM>, the primary piston <NUM> is forced downward against the force of spring <NUM> to meter a flow of fuel to the primary manifold from primary manifold port opening <NUM> via flow line <NUM>. This primary manifold fuel pressure is also provided through a restriction <NUM> to the back side of the secondary piston <NUM>.

As the fuel pressure continues to increase at the inlet <NUM>, the primary piston <NUM> will continue to move downwardly and will eventually contact the secondary piston <NUM>. At such point the force of the spring <NUM> will need to be overcome in order to continue to stroke the, now hydro-locked, combined, primary piston <NUM> and secondary piston <NUM>. Such movement will first unseat the secondary piston <NUM> from the second <NUM> and third <NUM> seals. Continued movement of the secondary piston <NUM> will result in the fuel pressure being provided through restriction <NUM> to the transfer valve <NUM>, and the metering of fuel flow to the secondary manifold from secondary manifold port opening <NUM> via flow line <NUM> as shown in <FIG>.

The capability to run the engine for extended durations with fuel flow only supplied to the primary manifold requires the system to purge the secondary manifold while fuel flow to the primary is maintained. This is accomplished in the illustrated embodiment through operation of the switching transfer valve <NUM>. This transfer valve <NUM> senses inlet pressure to the secondary piston <NUM> through restriction <NUM> in order to control the position of its piston <NUM> against the force of spring <NUM> (and the inlet pressure of the fuel control system's fuel pump, i.e. low pressure). The positioning of piston <NUM> operates to control the dual purge volume ecology piston <NUM> by connecting it through restriction <NUM> either to the fuel control system inlet pressure (Pinlet) as shown in <FIG> or to the fuel control system's pressure as shown in <FIG>. If the fuel pressure provided is less than the force of spring <NUM> acting on the other side of piston <NUM>, the ecology valve <NUM> will be as shown in <FIG>, and if greater as shown in <FIG>. The ecology piston <NUM> is in the charged position in <FIG> when secondary flow via line <NUM> is on, and in the purge position in <FIG> when secondary flow is off. Drop tight sealing between the primary and secondary manifolds is provided to prevent coking in the secondary manifold. This is accomplished with a dual face seal configuration discussed above integral to the FDV <NUM> and a single face seal <NUM> in the transfer valve <NUM>.

Having now discussed the components of an embodiment of the system <NUM> of the present invention, attention is now directed back to <FIG> illustrating the shutdown mode. In this mode, the FDV <NUM> is closed, providing a drop tight seal to the secondary manifold from either the primary manifold or upstream pressure. The transfer valve <NUM> is positioned to provide Pinlet pressure to the inlet of the double diameter ecology piston <NUM>, which pressure is less than the force of spring <NUM> keeping the piston <NUM> biased in the un-charged state. This uncharged state provides ecology of both the primary and secondary manifolds, i.e. it purges the fuel that would otherwise remain in these two manifolds and stores it in each of the two ecology volumes of the ecology valve <NUM>. The ecology piston <NUM> provides dual dynamic sealing via seals <NUM>, <NUM> bracketing overboard drain <NUM> which seals the secondary manifold line from primary pressure.

With quick reference to <FIG> and <FIG>, this shutdown mode is shown as region <NUM> in the graphical illustration of mass flow rate to the primary manifold (Wf Pprime) and to the secondary manifold (Wf Psec) versus primary piston (<NUM>) stroke.

Once the engine control system commands operation of the engine, and with reference now to <FIG>, the fuel pump (not shown) begins to increase the fuel pressure to the inlet <NUM> of the FDV <NUM>. This increasing pressure begins to overcome the force of spring <NUM> and stroke the primary piston <NUM> such that fuel is now capable of flowing to the primary manifold.

This initial increase of the fuel flow rate to the primary manifold (Wf Pprim) as the primary manifold port opening <NUM> is being metered is shown in <FIG> and <FIG> as line segment <NUM>.

However, once this primary manifold port opening <NUM> is fully opened (the condition depicted in <FIG>), the Wf Pprim remains relatively steady, i.e. does not appreciably increase at nearly the same rate as during segment <NUM> with increased fuel pressure (P22) or primary piston <NUM> stroke (beyond the position shown in <FIG> and before the position shown in <FIG>). This generally plateaued region is shown in <FIG> and <FIG> as the generally horizontal segment <NUM> during which Wf Pprime may only increase <NUM>-<NUM> pph over the stroke distance of the primary piston <NUM> during this time.

This occurs as the increased fuel pressure resulting in further stroke of the primary piston <NUM> during this period is fed back via flow path <NUM> shown in <FIG>. That is, flow path <NUM> initially is used to provide fuel flow to the primary manifold as it begins to open as the primary piston <NUM> strokes downwardly to the position shown in <FIG> (forming region <NUM> of <FIG> and <FIG>). However, further stroking of the primary piston <NUM> opens the flow path <NUM> on the opposite side of the FDV <NUM> shown in <FIG>. Based on the relative sizing and metering of the two flow paths <NUM>, <NUM> as the primary piston <NUM> continues to stroke downwardly, flow path <NUM> begins to act to feed back the fuel pressure such that the generally horizontal segment <NUM> of <FIG> and <FIG> is formed despite the increasing stroke of primary piston <NUM>. In other words, the increasing inlet pressure that results in increased stroke of primary piston <NUM> is mostly fed back to the inlet via flow path <NUM> instead of resulting in a equal increased pressure flowing to the primarily manifold via <NUM>.

During the primary piston <NUM> stroke along line <NUM> (and until point <NUM> of <FIG> and <FIG> is reached, to be discussed more fully below), the FDV <NUM> regulates to provide total flow to the primary manifold as the secondary piston <NUM> remains on the dual soft seals <NUM>, <NUM> providing drop tight sealing between primary and secondary manifolds. This prevents coking in the secondary nozzles. During this time the transfer valve <NUM> control pressure (through restriction <NUM>) is equal to Psec pressure and provides Pinlet pressure as the control pressure to the back side of the ecology piston <NUM> (through restriction <NUM>), keeping the ecology valve <NUM> in the un-charged state.

However, at point <NUM> shown best in <FIG>, the primary piston <NUM> has contacted and begins to move the secondary piston <NUM> off seals <NUM>, <NUM>. Continued stroking of the primary piston <NUM> and secondary piston <NUM> will first provide P22 pressure through restriction <NUM> to the transfer valve <NUM>. However, the configuration of the secondary piston <NUM> does not allow, i.e. does not begin metering, fuel flow to the secondary manifold until point <NUM> best shown in <FIG> is reached.

After this point <NUM>, the Wf Pprime begins to decrease and Wf Psec begins to increase as the total fuel flow is divided between the two manifolds. During this time the transfer valve <NUM> control pressure is becoming equal to P22 pressure through restriction <NUM> to begin to move piston <NUM> to the right. This ultimately provides P22 pressure as the control pressure to the ecology piston <NUM> to transition it to the charged state. The movement of piston <NUM> provides the inlet pressure Pinlet to the back side of the ecology piston <NUM> to stroke it to the right. This movement of the ecology piston <NUM> provides the fuel in ecology volume <NUM> to the secondary manifold (and from volume <NUM> to the primary manifold) as shown in <FIG> during full operation mode.

In transitioning to the full operation mode, the inlet flow to the FDV <NUM> increases to initiate secondary flow. The force capability of the primary piston <NUM> is overcome and the first piston <NUM> becomes hydraulically locked to the secondary piston <NUM>. When locked the two pistons <NUM>/<NUM> travel together as one and function very similar to a typical flow divider valve dividing flow between the two manifolds as a function of inlet flow. As mentioned briefly in the preceding description, upon cracking, i.e. movement of the secondary piston <NUM> off seals <NUM>, <NUM>, Pprim pressure is ported to the transfer valve <NUM>, which moves the piston <NUM> to provide P22 pressure to the control pressure side of the ecology piston <NUM> returning it to the charged position as shown in <FIG>. The FDV <NUM> provides full manifold equalization at higher total flows.

Upon re-entering either the shutdown (<FIG>) or the primary/low power (<FIG>) mode of operation, i.e. when reducing fuel flow from the full operation mode of <FIG>, the transfer valve <NUM> again provides Pinlet control pressure to the ecology piston <NUM>. This is because the secondary manifold pressure drops when the secondary piston <NUM> reseats against seals <NUM>, <NUM> cutting off its fuel flow. The control pressure to the transfer valve <NUM> drops back through restriction <NUM> causing the transfer piston <NUM> to move back to the left. However, the rate of discharge for the ecology piston <NUM>, i.e. movement to the left under force of spring <NUM>, is restricted by restriction <NUM> to provide an amount of dampening needed meet the engine's needs and ultimately purging the secondary manifold fuel into ecology volume <NUM>.

As may be seen most clearly in <FIG>, the advanced two piston (<NUM>/<NUM>) FDV <NUM> of an embodiment of the present invention provides a consistent hysteresis loop depending on whether the fuel flow is increasing (as discussed above primarily with respect to line <NUM>) or decreasing (discussion to follow with regard to dashed line <NUM>). The hysteresis allows for two different engine operating modes, to wit, a second key operating mode between points <NUM> and <NUM> along dashed line <NUM> and the primary/low power mode to the left of point <NUM> along solid line <NUM> (until transition to line <NUM> where flow rate decreases with decreasing P22), to be commanded at the same overall fuel flow. That is, during the two modes the overall fuel flow rate (Wf Pprim alone to the left of point <NUM> along line <NUM> during increasing flow from shutdown, or Wf Pprim along dashed line <NUM> + Wf Psec between points <NUM> and <NUM> during decreasing flow from full operation) is the same. The second key operating mode provides flow to the secondary manifold, and the primary/low power mode provides drip tight sealing and ecology of the secondary manifold. This is accomplished by approaching the second key operating mode from a higher flow (><NUM> pph), and entering primary/low power mode from a lower inlet flow (<<NUM> pph).

With this understanding reference is again made to <FIG>, which shows the full nominal primary (Wf Pprim) and secondary (Wf Psec) flows schedule versus FDV <NUM> primary piston <NUM> stroke. The hysteresis loop enabling the two modes of operation is shown in solid line when entering it during increasing flow, i.e. from left to right, and in dashed line when entering it during decreasing flow, i.e. from right to left.

Also as discussed above, <FIG> is provided to focus on the region of the operating envelope associated with startup, transition to idle, and transition to primary/low power mode. The arrows on <FIG> pointing to the right highlight the direction of increasing flow as flow is increased through the primary only operating zone (to the left of point <NUM>) then through the transition zone until point <NUM> to bring on secondary flow. As the FDV <NUM> translates through the transition zone, the primary piston <NUM> contacts the secondary piston <NUM> and pushes the secondary piston <NUM> off its sealed stop at point <NUM> and thereafter initiates secondary flow beginning at point <NUM>. The primary and secondary pistons <NUM>/<NUM> travel together as one for all valve positions beyond point <NUM> and supply fuel to both the primary and secondary manifolds in the region that begins at point <NUM> and to the right.

The arrows that point to the left highlight the direction of decreasing flow as the FDV <NUM> pistons <NUM> and <NUM> travel back to primary/low power mode on a distinctly different schedule (dashed line <NUM>) versus the increasing direction. As the hydro-locked pistons <NUM>/<NUM> travel back across secondary piston stop at point <NUM>, the secondary piston <NUM> is seated and secondary manifold is again sealed from the primary manifold. As flow is further reduced, the primary piston <NUM> translates through the transition zone completing the hysteresis loop.

As will now be apparent, in the second key operating mode a metered flow is commanded that is equivalent to the primary/low power mode. However, because the direction of stroke is from high power, the FDV <NUM> does not close the secondary manifold. In the primary/low power mode, engine control system initially commands a very low fuel flow. This allows the secondary port opening <NUM> to close, and be drop tight sealed from the primary port opening <NUM>, and the transfer valve inlet pressure is equal to Psec (or P3). This provides Pinlet to the ecology piston <NUM> inlet, and charges the ecology piston <NUM> to purge the secondary manifold via line <NUM> into volume <NUM>.

At shutdown when the engine is commanded off, the FDV <NUM> slews shut, and the ecology piston <NUM> purges both manifolds.

Claim 1:
A passive flow splitting system (<NUM>) for use in a turbine engine fuel control system to provide split fuel flow to a primary fuel manifold and a secondary fuel manifold to supply primary fuel injectors and secondary fuel injectors, respectively, for particular combustion zones thereof, comprising:
a passive fuel divider valve (<NUM>) configured to provide intentionally different split ratios dependent on ascending or descending fuel mass flow rate, the fuel divider valve including a primary piston (<NUM>) and a secondary piston (<NUM>), fuel divider valve (<NUM>) comprising a housing having an inlet (<NUM>), a primary manifold port (<NUM>), a secondary manifold port (<NUM>), and a plurality of flow paths (<NUM>, <NUM>) defined therein,
wherein the primary piston is moveable independently of the secondary piston to meter fuel flow to the primary manifold of an engine fuel supply system, and being biased away from the secondary piston,
wherein the secondary piston (<NUM>) is configured to meter fuel flow to the secondary manifold of the engine fuel supply system, and being biased to prohibit such flow, and
wherein the primary piston (<NUM>) strokes with increasing fuel pressure to meter the fuel flow to the primary manifold, and contacts the secondary piston with increasing fuel pressure to cause the secondary piston to meter flow to the secondary manifold, the primary piston (<NUM>) and the secondary piston being hydro-locked during such metering;
an ecology valve (<NUM>) configured to reservoir fuel at least from the secondary manifold when the secondary piston of the fuel divider valve is positioned to prohibit fuel flow thereto; and
a transfer valve (<NUM>) configured to control a state of the ecology valve (<NUM>) based on fuel pressure supplied to the secondary manifold by the fuel divider valve.