GB2199083A

GB2199083A - Gas turbine engine

Info

Publication number: GB2199083A
Application number: GB08630334A
Authority: GB
Inventors: Albert Jubb; Eric William Stansbury; Graham Alfred Reynolds; Robert George Ward
Original assignee: Rolls Royce PLC
Current assignee: Rolls Royce PLC
Priority date: 1986-12-19
Filing date: 1986-12-19
Publication date: 1988-06-29
Also published as: GB8630334D0

Abstract

A gas turbine engine (e.g. for use in a land vehicle) (10) capable of operating in two modes comprising in flow series a low pressure compressor (13), a high pressure compressor (15) a heat exchanger (16), combustion equipment (17), a high pressure turbine (18), and a free power turbine (20). In the first mode of engine operation, the efflux from the power turbine (20) is directed through the heat exchanger (16) to be in heat exchange relationship with the high pressure compressor (15) efflux. However in the second mode of operation when a power boost is required (e.g. for powering ancillary equipment), the heat exchanger (16) is by-passed by the free power turbine (20) efflux and the efflux is ducted directly to a low pressure compressor (24) which drives the low pressure compressor (13) to boost the air delivered to the high pressure compressor (15). <IMAGE>

Description

GAS TURBINE ENGINE This invention relates to a gas turbine engine and has particular reference to a gas turbine which is adapted for use in powering a land based vehicle.

Gas turbine engine have been used as power units for land based vehicles. Their high power output and comparatively low weight and small size make them attractive alternatives to other, more conventional power units such as reciprocating diesel engines, in heavyweight vehicles such as tanks. However if the vehicle carries equipment with high power consumption characteristics, the vehicle gas turbine engine power unit may not have sufficient capacity to meet those power requirements. In such circumstances, it becomes necessary to provide the vehicle with an ancilliary power unit in order to meet the additional power requirements as and when they arise. The drawback with such an approach is of course that the main gas turbine engine power unit has the task of propelling the additional weight incurred by the presence of the ancilliary power unit.

It is an object of the present invention to provide a gas turbine power unit suitable for powering a vehicle which is capable of operating in two modes: a first mode in which the power unit has a power output sufficient to propel the vehicle, and a second mode in which the power unit has a boosted power output sufficient to power ancilliary equipment provided on the vehicle.

According to the present invention, a gas turbine engine comprises, in flow series, a low pressure compressor, a high pressure compressor, a heat exchanger, combustion equipment and a high pressure turbine adapted to receive the efflux of said combustion equipment and which is drivingly connected to said high pressure compressor, the efflux from said free power turbine being ducted to a low pressure turbine drivingly connected to said low pressure compressor which efflux is ducted to said low pressure turbine via said heat exchanger in a first mode of operation of said engine to place said free power turbine efflux and said high pressure compressor efflux in heat exchange relationship, and which is ducted directly to said low pressure turbine in a second mode of operation of said engine in which the resultant efflux from said low pressure compressor facilitates a boost in the power output of said engine.

The invention will now be described, by way of example, with reference to the accompanying drawing, which is a diagrammatic representation of a gas turbine engine in accordance with the present invention.

With reference to the drawing, a gas turbine engine generally indicated at 10 is adapted to power a land based vehicle, such as a tank, provided with ancilliary equipment, such as a weapon system of the type described in our co-pending patent application no 8606394, which has a high power consumption and which the gas turbine engine 10 is also required to power.

The engine 10 comprises an air inlet 11 which directs air into an inertial particle separator 12, which is of conventional construction and operation, to remove any coarse dust or other debris from the air. Such dust or other debris may be encountered if, for instance, the engine 10 is required to operate in desert conditions.

The air is then directed into a low pressure compressor 13, the operation of which will be discussed later, before being directed into a solid media type filter 14 which separates from the air any fine dust which was not separated from the air by the inertial separator 12. The air is then directed into a high pressure compressor 15, which is of the centrifugal type, which serves to compress the air before it is passed through a heat exchanger 16.

The heat exchanger 16 is a small, efficient, lightweight unit which is capable of withstanding thermal shock without resultant cyclic fatigue and may conveniently have a corrugated metal sheet matrix so as to achieve this end.

From the heat exchanger 16, the air is directed into a combustion system 17 of conventional construction where it is mixed with a suitable fuel and the mixture combusted. The resultant combustion products then expand through a high pressure radial flow turbine 18 which drives the high pressure compressor 15 by means of a shaft 19, before being directed into a free power turbine 20. The free power turbine 20 has a power output shaft 21 and. is of the axial type with three stages. Since the free power turbine 20 is required to power high power consumption ancilliary equipment, it must be of appropriate construction to withstand the shock of rapid deceleration when such equipment is brought into operation. To this end, the power turbine 20 is preferably provided with short turbine blades and its power output shaft 21 is as short as possible with a diameter which is as large as possible.

The efflux from the power turbine 20 is ducted to a valve 22. In a first mode of operation of the engine 10, in which it functions solely as a propulsive unit for the vehicle on which it is mounted, the valve 22 is arranged so that the free power turbine 20 efflux passes through the heat exchanger 16 where it is placed in heat exchange relationship with air exhausted from the high pressure compressor 15. This has the effects firstly of reducing the temperature, and therefore the infra-red radiation signature of the free -power turbine efflux and secondly improving the thermodynamic efficiency of the engine 10.

A low infra-red signature is of course desirable if the vehicle powered by the engine 10 could be attacked by heat-seeking missiles.

The cooled power turbine 20 efflux is then directed to atmosphere via secondary combustion equipment 23 which is not operational in this mdde of engine operation and which will be described later, and a low pressure pressure turbine 24. Since, however the power turbine 20 efflux is cool by the time it reaches the low pressure turbine 24, it does not cause any significant operation of the low pressure turbine 24.

When the engine 10 is required to power high power consumption ancilliary equipment, it is caused to operate in a second mode of operation in which the power output of the engine 10 is boosted. This boost in power output is brought about by switching the valve 22 so that the efflux from the power turbine 20 flows through ducting 25, thereby by-passing the heat exchanger 16. A one-way valve 26 prevents the efflux from flowing into the heat exchanger 16 via its outlet. The hot efflux passes through the secondary combustion equipment 23 before expanding through the low pressure turbine 24 and being exhausted to atmosphere.

The low pressure turbine 24 is interconnected with the low pressure compressor 13 by a shaft 25 so that operation of the low pressure turbine 24 in this mode of engine operation causes the low pressure compressor 13 to boost the amount of air supplied to the combustion equipment 17. This in turn brings about a large increase in the power output of the engine 10 so that it is capable of providing sufficient power for the ancilliary equipment. The low pressure turbine 24 and low pressure compressor 13 thus act in effect as a turbo-blower.

It is envisaged that switching the engine 10 from its first mode of operation to its second mode of operation could bring about a four-fold increase in its power output. If, however, such an increase in power output is not sufficient to power the ancilliary equipment, the secondary combustion equipment 23 may be brought into operation. Thus fuel is mixed with the hot free power turbine 20 efflux in the secondary combustion equipment 23 and the mixture combusted to increase the temperature of the free power turbine 20 efflux and hence the power output of the low pressure turbine 24/compressor 13 assembly.

Claims

Claims:

1. A gas turbine engine comprising, in flow series, a low pressure compressor, a high pressure compressor, a heat exchanger, combustion equipment and a high pressure turbine adapted to receive the efflux of said combustion equipment and which is drivingly connected to said high pressure compressor, the efflux from said free power turbine being ducted to a low pressure turbine drivingly connected to said low pressure compressor which efflux is ducted to said low pressure turbine via said heat exchanger in a first mode of operation of said engine to place said free power turbine efflux and said high pressure compressor efflux in heat exchange relationship, and which is ducted directly to said low pressure turbine in a second mode of operation of said engine in which the resultant efflux from said low pressure compressor facilitates a boost in the power output of said engine.

2. A gas turbine engine as claimed in claim 1 wherein secondary combustion means are interposed between said free power turbine and said low pressure turbine, said secondary combustion means being operational when said engine is operating in said second mode of operation.

3. A gas turbine engine as claimed in claim 1 or claim 2 wherein particle separation means are provided upstream of said low pressure compressor.

4. A gas turbine engine as claimed in claim 3 wherein filtration means are provided upstream of said high pressure compressor.

5. A gas turbine engine as claimed in any one preceding claim wherein valve means are interposed between said free power turbine and said heat exchanger, said valve means being switchable between two positions, a first position in which the efflux of said free power turbine is directed to said heat exchanger and a second position in which the efflux of said free power turbine is directed to ducting which by-passes said heat exchanger.

6. A gas turbine engine substantially as hereinbefore described with reference to and as shown in the accompanying drawings.