WO2002036952A2

WO2002036952A2 - Minimum fuel flow schedule adjustment method for turbine engine control

Info

Publication number: WO2002036952A2
Application number: PCT/US2001/048228
Authority: WO
Inventors: Mohamad Hanif Vhora
Original assignee: Honeywell International Inc.
Priority date: 2000-10-31
Filing date: 2001-10-29
Publication date: 2002-05-10
Also published as: AU2002220278A1; TW534949B; WO2002036952A3

Abstract

A control and method is provided that continuously adjusts minimum fuel flow schedules in the electronic control unit of a gas turbine engine. The control and method includes the steps of generating a fuel command signal; a sensed fuel flow signal and a minimum fuel flow schedule. The minimum fuel flow schedule is then multiplied by the ratio of the fuel command signal to the sensed fuel flow signal to provide an adjusted minimum fuel flow schedule.

Description

MINIMUM FUEL FLOW SCHEDULE ADJUSTMENT METHOD FOR TURBINE ENGINE CONTROL TECHNICAL FIELD

This invention relates generally to gas turbine engine controls, and in particular to fuel control systems and methods for gas turbine engines.

BACKGROUND OF THE INVENTION

The operation of gas turbine engines, whether used on the ground for power generation or in flight for propulsion or secondary power, is controlled by an electronic control unit commonly referred to as an ECU.

Incorporated in the ECU are engine start control schedules and steady state control schedules for the engine. An example of a start control schedule can be found in LaCroix, U.S. Patent No. 4,337,615. These control schedules generate a fuel command signal which is sent to the engine's fuel control unit and tells the system how much fuel to deliver to the engine's combustor. It is common practice to program into the ECU minimum fuel schedules below which the fuel command signal is not allowed to go. For example, deceleration as the engine spools down from full operating speed down to idle and further down to engine shutdown, the engine will operate along a minimum fuel schedule. These control schedules and minimum fuel schedules are programmed into the ECU and are based on nominal estimates of the accuracy of the fuel control unit.

Once in the field, the accuracy of the fuel control unit can deviate from the nominal estimates programmed into the ECU. These deviations can result from a number of causes, the two most common being the aging in the fuel control components and unit-to-unit variation in fuel control units. These deviations from nominal can cause a number of problems. For example, if the engine is decelerating and the ECU is commanding minimum fuel, the particular fuel control unit may actually be supplying a greater amount of fuel. As the fuel command signal is already at the minimum, there is no way to bring the actual fuel flow rate down and decelerate the engine. The result can be a runaway engine. Under the same operating circumstances on a different engine, the fuel control unit may actually be supplying a fuel flow below the minimum commanded flow. As there is no way to* increase the minimum fuel schedule, the engine may experience a blow out.

Accordingly, there is a need for an engine control system and method that adjusts the minimum fuel schedules in the electronic control unit of a gas turbine engine. SUMMARY OF THE INVENTION

An object of the present invention is to provide a control and method that adjusts minimum fuel flow schedule in the electronic control unit of a gas turbine engine. The present invention achieves this object by providing a control and method programmed into the electronic control unit of a gas turbine engine. The control and method include the steps of generating a fuel command signal; a sensed fuel flow signal and a minimum fuel flow schedule. The minimum fuel flow schedule is then multiplied by the ratio of the fuel command signal to the sensed fuel flow signal to provide an adjusted minimum fuel flow schedule which is then used by the electronic control unit.

These and other objects, features and advantages of the present invention, are specifically set forth in, or will become apparent from, the following detailed description of a preferred embodiment of the invention when read in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic representation of a gas turbine engine. FIG. 2 is a block diagram of the minimum fuel schedule adjustment control and method contemplated by the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring to FIG. 1 , shows a gas turbine engine 1 having a compressor 2, and a turbine 4 mounted on a shaft 5. A fuel control unit 6 is controlled by an electronic control unit, (ECU) 7. Disposed between the compressor 2 and the turbine 4 is a combustor 10.

In operation, the compressor 2 ingest ambient air, compresses the air and delivers the compressed air to the combustor 10. At the same time, the fuel control unit 6 controls the flow of fuel from a source, (not shown), to the combustor 10 through a fuel line 12. The amount of fuel in the fuel line 12 is determined by the fuel control unit 6 in response to

WFCMD signal from the electronic control unit 7. The fuel control unit 6 also measures the actual fuel flow and sends signal WFSENS to the

ECU 7. In the combustor 10, the air and fuel are mixed and ignited to form a hot gas that is expanded across the turbine 4. The turbine 4 extracts energy from this gas and converts it into shaft power for driving the shaft 5 which in turn drives the compressor 2 and an electric generator not shown in the diagram.

Though the foregoing description of gas turbine engine has been made with respect to a single shaft engine having a single compressor and a single turbine, it should be appreciated that the present invention is applicable to gas turbine shafts having multiple shafts with multiple compressors and turbines. Referring to FIG. 2, in manner familiar to those skilled in the art the ECU 7 generates from predetermined schedules a minimum fuel flow schedule WFMINS for start mode operation and a minimum fuel flow schedule WFMINR for run mode operation. Start mode is the acceleration of the engine from 0% to idle speed. Run mode is the running of.lthe engine after it , has reached the idle speed and also shut down _ ofjiitfee engine. The ECU 7 also contains fuel control logic 14 that generates ajfeel command signal, WFCMDS, for start mode and fuel control logic d.6ϊth^~a* generates a fuel command signal, WFCMDR, for run mode. ThecE6Ui7* also has a mode selector 18 which depending on the operating mόde!^"of, the engine selects the appropriate fuel command signal, WFCMD, -:by; controlling a switch 38.

Also, programmed into the ECU 7, is a minimum fuel schedule- adjustment routine 20. The routine 20 includes a function block 2 .^^ receives the fuel command signal WFCMD from switch 38,ι the sensed-:, fuel flow signal WFSENS from the fuel control unit 6 and calculates anv adjustment factor ADJ by dividing WFCMD by WFSENS. A second - function block 24 receives the WFSENS signal and compares it to a predetermined low limit and a predetermined high limit. If the WFSENS signal falls between these two limits, then function block 24 causes switch

26 to move to the down position as shown in FIG. 2. If the WFSENS signal falls above or below these limits then it is presumed that the fuel control unit 6 is not working properly and switch 26 is moved to the up position disabling the minimum fuel signal adjustment routine 20. With switch 26 in the down position, a function block 28 receives the ADJ signal and limits it on the high side and on the low side. These limits are used to prevent over correction of the minimum fuel. schedules. That is the limits are selected based; upon the expected variability of the fuel control unit 6 plus! margin. tlfjthe ADJi sjgnal is outside iόf these limits;- this', indicates ra problem, with the 'hardware which is ^;beyond the scope^; of ^th'e roιlιtiηe<20fto try to correct. In the preferred embodiment, the high side limit is 1. ιand the low side limit is 0 A . These limits are empirically deterrr ihedi based upon the characterization.: data for the fuel valves and mass flow sensors that are part of the fuel control unit 6.

A multiplier 30 multiples WFM1NR by ADJ to arrive at an adjusted minimum fuel flow schedule for run mode, WFMINRA. Function block 36 receives both the WFMINRA and WFCMDR signals and passes the larger of the two signals to switch 38. Similarly, a. multiplier 32 multiples WFMINS by ADJ to arrive at an adjusted minimum fuel flow signal for start mode, WFMINSA and function block 34 receives both the WFMINSA and WFCMDS signals and passes the larger of the two signals to switch 38. In the preferred embodiment, a low pass filter is used to eliminate noise in the WFSENS signal before the signal reaches function blocks.

This filter develops a phase shift between the WFSENS signal and the WFCMD signal which if not corrected would result in an inaccurate ratio calculation. To avoid this situation, the WFCMD is passed through a similar low pass filter prior to reaching function block 22.

With the present invention, the minimum fuel flow schedules are constantly adjusted by the ratio of commanded fuel flow to actual fuel flow. If the actual fuel flow is lower than commanded, then the adjustment factor will be 'greater: than 1.0 increasing the minimum fuel flow schedule. This prevents the -commanded fuel flow from going all the way down to the unadjusted minimum fuel flow and hence the actual fuel flow from going below the unadjusted minimum fuel flow. Thus, the combustor is protected from a potential flame blowout.

If the actual fuel flow is greater than the commanded fuel flow, then the adjustment factor will be less that 1.0 decreasing the minimum fuel flow schedule. This allows the commanded fuel flow to go below the unadjusted minimum fuel flow schedule thus avoiding a potential speed run away problem.

Various modifications and alterations to the above-described preferred embodiment will be apparent to those skilled in the art. For example, the present invention can be used with other gas turbine engine configurations. It can also be used with fuel schedules other that those for run mode and start mode operation. Accordingly, these descriptions of the invention should be considered exemplary and not as limiting the scope and spirit of the invention as set forth in the following claims.

Claims

WHAT IS CLAIMED IS: 1. A method for adjusting a minimum fuel flow schedule in an electronic control unit for a gas turbine engine comprising the steps of: a) generating a fuel command signal; b) generating the minimum fuel flow schedule; c) sensing the actual fuel flow and generating a signal thereof; d) generating a signal indicative of the ratio of the fuel command signal to the fuel sensed signal; and e) adjusting the minimum fuel flow schedule by the ratio signal. 2. The method of claim 1 further comprising after step (c) the step of comparing the sensed fuel flow signal with a first predetermined high value and a first predetermined low value and proceeding with the method only if the sensed fuel flow signal is between these high and low values. 3. The method of claim 1 further comprising the step of limiting the ratio signal by a second predetermined high value and a second predetermined low value. 4. The method of claim 1 wherein step (a) includes generating a fuel command signal for a first mode of operation and a fuel command signal for a second mode of operation; step (b) includes generating a minimum fuel flow schedule for said first mode of operation and a minimum fuel flow schedule for said second mode of operation; and step (e) includes adjusting the first mode minimum fuel flow schedule and adjusting the second mode minimum fuel flow schedule. 5. The method of claim 4 wherein said first mode is run mode and said second mode is start mode.