Patent GB-1321333-A (GB)
Title: Gas turbine engines having variable pitch guide vanes
IPC: F02C3/10
Filed: 1970-08-21
Abstract: 1321333 Fuel control in gas turbine engines MOTEREN-UND TURBINEN-UNION MUNCHEN GmbH 21 Aug 1970 [4 Sept 1969] 40502/70 Heading F1G [Also in Division G3] Relates to a control system for an automobile gas turbine power unit. The turbine unit comprises a compressor 17, Fig.1, driven by a compressor turbine 19, compressed air flowing through a heat exchanger 23 to a combustion chamber 22 where it serves for combustion of a fuel B and is expanded in the compressor turbine 19. The combustion gases flow via variable pitch guide vanes 25 to the power turbine 26 and are then exhausted to atmosphere via the heat exchanger. The control system A operates to adjust the guide vanes and hence the amount of through flow opening as a function of deviation of gas temperature difference between compressor delivery air and the combustion gases upstream of the compressor turbine from a desired temp difference, and other variable characteristics as described below. In  addition it adjusts a metering device 16 to control the rate of fuel flow to the combustion chamber 22. The fuel is pumped by pump 21 driven by the compressor turbine. The power turbine 26 drives via a gear box 24. In the control system, a signal selector unit 5, Fig.1a, receives a signal E6 significant of deviation in actual speed n 1  of compressor turbine 19 from a desired speed N 1  as demanded by accelerator pedal 1 and controls the fuel B flow rate via the metering device 16 to restore the speed to the desired value. A signal selector unit 8 receives as input signals E 1  to E5. The signal E1 is derived from the sum of first and second signals. The first signal represents the deviation in actual temperature difference between the temperatures (as sensed by thermocouples) at the compressor air intake (t 1 ) and upstream of the compressor turbine (t 4 ) and fed through a unit 10 which compensates for delay in thermocouples response, and a desired temperature difference. The desired temp difference T 4 - T 1  is derived by a function generator 9 which receives as inputs a signal n 1  representing the actual compressor speed and the signal t 1  (compressor intake temp). The said second signal E8 is produced by a function generator 6 from signal inputs received significant of:- actual compressor speed (n 1 ), response time behaviour T w  of the heat-exchanger 23, (i.e. a signal which is a function of the temp variation of compressor air flowing out of the heatexchanger over the time, in response to a sudden change in the temp of the power turbine exhaust gas), and fuel flow rate. The other inputs to the signal selector 8 are:- the signal E 2  which is produced when the actual compressor speed n 1  is below a predetermined speed n 1  e. g. half the desired speed, and this signal helps to maintain a predetermined guide vane opening during the starting period, - the signal E3 representing the deviation of the power turbine speed n 2  from a desired value, N2 and protects against overspeed thereof, the signal E4 representing acceleration and derived from the actual pressure change rate of gases downstream of the compressor and prescribed maximum rate of pressure change, whereby the guide vanes will be operated if the said max. rate of change is exceeded. The signal E5 which is a braking signal and operates the guide vanes to effect braking. The signal selector unit 8 comprises a diode logic gate to which signals E1 to E5 are applied Fig.3 (not shown) and the input signal of maximum magnitude and demanding an increase in guide vane through flow area predominates to control the guide vanes position via a hydraulic servomotor 12 and linkage 13. The output of selector unit 8 is also fed via a switch 16' to the selector unit 5 which is also a diode logic gate Fig. 2 (not shown). There again the highest input signal predominates to control the fuel flow rate.