APPARATUS FOR STARTING A GAS TURBINE ENGINE

Abstract: In a gas turbine engine the engine turbine (30) and rotary compressor (12) are coupled for dependent rotation. A compressor plate diffuser (36) with an integral, floating plate one-way valve (60) is mounted in a housing (52) receiving diffused compressed air for channeling to a combustor (24). A source (54) of pressurized air supplies the housing (52) during startup at a point upstream of combustor (24) and downstream of one-way valve (60) for initiating rotation of the turbine (30) and coupled compressor (12).

Description: APPARATUS AND METHOD FOR STARTING A GAS TURBINE ENGINE This invention relates to apparatus and method for starting a gas turbine engine of the type having a rotary compressor for compressing air, a combustor for combusting the compressed air with fuel to produce combustion gases under pressure, and a turbine for expanding the combustion gases to produce mechanical work, the turbine and the compressor being coupled for dependent rotation. Conventional gas turbine engines starting systems require the use of an auxiliary motor with associated gearing and clutch mechanisms to start the engine. Typically, the auxiliary motor is made to turn a rotary compressor component of the gas turbine engine to initiate the flow of compressed air through the combustor and then through the turbine component in order to initiate rotation of the latter element. Once the necessary speed of rotation in the turbine component is established, fuel is introduced into the combustor and normal operation of the gas turbine engine is established. The necessity for a separate auxiliary starting motor, together with ancillary clutch and mechanical drive systems, increases the bulk, weight and cost of the overall engine, and contributes to the probability for failure of a component and the resultant need for expensive maintenance. SUMMARY OF THE INVENTION The present invention utilizes the turbine component of a gas turbine engine with a rotary compressor component coupled to the turbine for dependent rotation therewith, in place of the auxiliary motor conventionally used during the startup mode. Because the weight, bulk and complications attendant to the use of an auxiliary startup motor are eliminated by the present invention, cost savings can be achieved, and the overall system can be significantly simplified, leading to a higher reliability. By using a larger part of the turbine working capacity, a very rapid start and acceleration can be achieved which would not be practical using a conventional starting system. Moreover, the reduction in engine weight and bulk can be expected to result in a corresponding and important weight reduction for certain applications such as vehicle propulsion power plants. In accordance with the purpose of the invention as embodied and broadly described herein, apparatus for starting a gas turbine engine of the type having a rotary compressor for compressing air, a combustor for combusting the compressed air with fuel to produce combustion gases under pressure, and a turbine for expanding the combustion gases to produce mechanical work, the turbine and the compressor being coupled for dependent rotation, comprises diffuser means operatively connected to the rotary compressor to receive and convert the high velocity, high pressure air to low velocity, higher pressure air; means operatively connected to the diffuser means for receiving and collect- ing the low velocity, higher pressure compressed air and channeling the higher pressure air to the combustor, the collecting means including a housing, a high pressure gas flow path being defined through the diffuser means and the housing, and to the combustor; means for supplying pressurized gas to the housing at a point upstream of the combustor and downstream of the diffuser means in the flow path during engine startup; and valve means integral with the diffuser means for preventing reverse flow of the pressurized gas through the compressor, the pressurized gas flowing through the combustor and being expanded in the turbine to cause rotation of the turbine and the compressor and to establish a flow of pressurized air to the combustor. Preferably, the diffuser means includes a plate-type radial diffuser and the housing means receives higher pressure air from the plate diffuser, and the valve means is associated with the plate diffuser, and wherein said plate diffuser includes an annular nozzle portion having an inner edge defining an axially directed plate diffuser inlet, and a radially directed flared outer edge, a planar member oriented perpendicular to the plate diffuser inlet axis and spaced from the nozzle, a plate member positioned between the nozzle and the planar member, the radially outer portion of the plate member together with the spaced adjacent outer nozzle edge forming a radially directed plate diffuser exit when the plate member abuts the planar member, and plate securing means for providing unrestricted axial movement of the plate member between a sealing position against the planar member and an unsealing position against the nozzle, the introduction of said pressurized gas during startup causing a net pressure force on the plate to move said plate member to the sealing position, and the impact force of high velocity air from the compressor during subsequent normal operation causing movement of the plate member to the unsealing position. It is further preferred that the apparatus include means for bleeding the pressurized gas to the back surface of the plate member facing the planar member during startup, the bleeding means by-passing the portion of the flow path through the plate diffuser exit, and that the pressurized gas is pressurized air. Further in accordance with the purpose of the present invention as broadly described herein, the method for starting a gas turbine engine having a rotary compressor and diffuser for providing high pressure air, a combustor for combusting fuel with the compressed air to produce combustion gases, and a turbine for expanding the combustion gases to produce mechanical work, the turbine and the compressor being mechanically coupled for dependent rotation, comprises the steps of introducing pressurized gas into the compressed air flow path between the diffuser and the combustor; preventing back flow of pressurized gas through the diffuser and compressor using one way valve means associated with the diffuser; expanding the pressurized gas through the turbine to cause rotation of the turbine and the compressor; and returning the one way valve to normal open position under the influence of the flow of compressed air from the rotating compressor Preferably, the pressurized gas is air, and the method includes the further step of combusting fuel with the pressurized air to increase gas energy prior to the expanding step. The accompanying drawings illustrate one embodiment of the invention and, together with the description, serve to explain the principles of the invention. In the drawings: Fig. 1 is a schematic cross-sectional view of a plate diffuser showing the non-return valve of the present invention being utilized in a gas turbine engine: and Fig. 2 is a sectional view taken of a portion of the apparatus shown in Fig. 1, at the location 2-2. In Fig. 1 of the drawings there is shown schematically a gas turbine engine 10 embodying the present invention. Engine 10 includes a rotary compressor 12 having an inlet 14 for the air to be compressed and an outlet 16 for the compressed air, which is typically delivered at a relatively high velocity. Engine 10 further includes a means 18 for diffusing the high velocity air to convert the kinetic energy of the high velocity gas into increased gas pressure. Engine 10 further includes means 20 for collecting the diffused air from diffusing means 18 and channeling it to the remainder of the engine for utilization. Specific components for achieving the diffusing and collecting functions as they relate to the present invention will be discussed hereinafter. The high pressure air flows from the collecting means 20 via ducting 22 to a combustor 24 where it is mixed with fuel from a fuel source 26 and combusted to yield high pressure combustion gases. These combustion gases are, in turn, channeled via ducting 28 to a turbine 30 where they are expanded to produce rotary mechanical power. Expanded combustion gases exiting turbine 30 via turbine outlet 32 are then either discharged to the atmosphere or processed further to recover heat values such as in a recuperated gas turbine cycle. One of ordinary skill in the art in designing gas turbine engine systems would readily understand the foregoing and be able to adapt the present invention to a recuperated gas turbine engine application. The above-described components of engine 10, except for the components constituting the diffusing and collecting means, can be readily selected from any conventional apparatus. For instance, the rotary compressor 12 can be a pure radial or pure axial rotary compressor or a mixed axial-radial machine. Similarly, the rotation of compressor 12 can be directly or indirectly connected to turbine 30. Such a connection is depicted schematically by a broken line 34 between compressor 12 and turbine 30 in Fig. 1. In accordance with the present invention there is provided diffuser means operatively connected to the rotary compressor to receive and convert the high velocity, high pressure air to relatively low velocity, higher pressure air. As embodied herein and as shown in Fig. 1, diffuser means 18 includes a plate-type radial diffuser 36 which receives high velocity gas through an axial inlet portion 38 and delivers high pressure, low velocity gas through a radial outlet portion 40. In the embodiment shown in Fig. 1, plate diffuser 36 includes an annular nozzle part 42 having an inner edge 44 defining the axial inlet and a flared outer edge 46 defining in part the radial exit 40. Plate diffuser 36 further includes planar wall member 48 positioned parallel to, and spaced from, nozzle edge 46 by a plurality of spacer studs 50. Three equally spaced spacer studs are shown in Fig.2 positioned around the circumference of the flared edge 46. The precise dimensions of plate diffuser 36 will depend on the flow capacity of the compressor 12 and one of ordinary skill in the art will be able to make the necessary calculations. Also, more than a single plate diffuser unit may be utilized, and the multiple units may be arranged symmetrically about the periphery of compressor 12. Further in accordance with the present invention, means are provided for receiving and collecting the diffused air from the plate diffuser 36. As embodied herein, collecting means 20 includes a housing 52 completely surrounding exit 40 of plate diffuser 36 and operatively connected to channel the diffused air to ducting 22 for flow to combustor 24. A flow path is thus defined for the compressed air during normal operation of the gas turbine engine 10, namely through plate diffuser 36 and housing 52 to ducting 22, and this path is shown by the arrows in Fig.1. The precise shape of housing 52 will depend in general on the shape and orientation of the other components of the engine 10 and on the relative location of ducting 22, as well as on the actual number of individual diffuser units. Still further in accordance with the present invention, there is provided means for supplying pressurized gas during engine startup to the compressed air flow path downstream of the diffuser means 18 and upstream of the combustor 24. As embodied herein, a high pressure gas source 54 is connected to housing 52 via a valved conduit 56. Thus, upon activation of the valved conduit 56 during startup, the pressurized gas can be admitted to the flow path at a point downstream of plate diffuser 36 and upstream of combustor 24. Upon admission, the pressurized gas flows through the combustor 24 to the turbine 30, thereby causing rotation of that component together with compressor 12 coupled for dependent rotation. The rotation of the turbine 30 and compressor 12 components results in the initiation of flow of pressurized air through engine 10, which air can be mixed with fuel in combustor 24 and the engine 10 started and brought to normal operating conditions. Preferably, the compressed gas admitted from gas source 54 is compressed air which can be combusted with fuel in combustor 24 to increase the enthalpy and thus the energy deliverable to turbine 30 during startup. However, the present invention is intended to utilize any suitable source of pressurized gas, including a non-oxidizing gas, such as can be delivered from solid fuel gas generator units, and the present invention is not intended to be limited by the particular type of pressurized gas source 54. Still further in accordance with the present invention, there is provided valve means integral with the diffuser means for preventing reverse flow of the pressurized gas through the compressor through startup. As embodied herein, valve means includes a plate member 60 positioned between the flared edge 46 and the planar wall member 48 of plate diffuser 36. As can be appreciated from Fig. 1, plate member 60 when positioned against wall member 48 provides essentially unrestricted flow through the plate diffuser 36 along the normal flow path, while when positioned against edge 46 (shown in Fig. 1 by the dotted lines) plate member 48 effectively seals off plate diffuser 36 from reverse flow. As can be best seen in Fig. 2 plate member 60 is provided with relief notches 62 corresponding to the location of spacer studs 52 and of a size to permit unrestricted sliding clearance. Plate member 60 thus is constrained for essentially unrestricted axial movement between edge 46 and wall member 48. During startup operation, valve conduit 56 is activated to allow a quantity of pressurized gas from gas source 54 to be admitted to housing 52. The charge of pressurized gas initially begins to flow into plate diffuser exit 40, as well as through ducting 22. The momentary back flow of pressurized gas through plate diffuser 36 creates a decrease in pressure on the face of plate member 60 adjacent the flared edge 46 relative to the other face of plate member 60, as a consequence of the Bernoulli effect. The net pressure force on plate member 60 is then such to translate it axially into the sealing position where thereafter it is held by the static force of the pressurized gas. After turbine 30 and compressor 12 have started rotation, the flow of compressed air from compressor 12 into the plate diffuser inlet 38 will impact against plate member 60 and translate it axially in the opposite direction against wall member 48 where it will be held during normal operation of engine by the impact force of the turning compressed air stream. Preferably, wall member 48 is provided with a plurality of through-holes 64 (three are shown in Fig. 2) to allow the pressurized gas access to the back surface of plate member 60, that is, the surface opposite the flared edge 46. Holes 64 serve to decrease the time for plate member 60 to respond to the introduction of pressurized gas from source 54 during startup and consequently to minimize the loss of pressurized gas back through the compressor 12. During a normal operation, the position of holes 64 is such that plate member 60 acts to seal off holes 64 and force the turning compressed air to exit plate diffuser 36 through the normal exit 40. It will be apparent to those skilled in the art that various modifications and variations could be made in the compressor pipe diffuser non-return valve for use in gas turbine engine starting systems of the present invention without departing from the scope or spirit of the invention.

Claims: CLAIMS: 1. Apparatus for starting a gas turbine engine of the type having a rotary compressor (12) for compressing air, a combustor (24) for combusting the compressed air with fuel to produce combustion gases under pressure, and a turbine (30) for expanding the combustion gases to produce mechanical work, the turbine and the compressor being coupled (34) for dependent rotation, characterized by (a) diffuser means (18) operatively connected to the rotary compressor (12) to receive and convert the high velocity, high pressure air to low velocity, higher pressure air; ; (b) means (20) operatively connected to said diffuser means (18) for receiving and collecting the low velocity, higher pressure compressed air and channeling said higher pressure air to said combustor (24), said collecting means (20) including a housing (52), a high pressure gas flow path being defined through said diffuser means (18) and said housing (52), and to the combustor (24); (c) means (54, 56) for supplying pressurized gas to said housing (52) at a point upstream of the combustor (24) and downstream of said diffuser means (18) in said flow path during engine startup; and (d) valve means (60) integral with said diffuser means (18) for preventing reverse flow of said pressurized gas through the compressor (12), the pressurized gas flowing through the combustor (24) and being expanded in the turbine (30) to cause rotation of the turbine (30) and the compressor (12) and to establish a flow of pressurized air to the combustor (20). 2. Apparatus according to claim 1, characterized in that the said pressurized gas is air for combustion with fuel in the combustor (24) to further increase gas energy during the engine startup. 3. Apparatus according to claim 1, characterized in that said diffuser means (18) includes a plate-type radial diffuser (36) and said housing means (52) receives higher pressure air from said plate diffuser (36), and wherein said valve means (60) is associated with said plate diffuser (36). 4. Apparatus according to claim 3, characterized in that said plate diffuser (36) includes (a) an annular nozzle portion (42) having an inner edge (44) defining an axially directed plate diffuser inlet (38), and a radially directed flared outer edge (46), (b) a planar member (48) oriented perpendicular to the axis of said plate diffuser inlet (38) and spaced from said nozzle portion (42); ; (c) a plate member (60) positioned between said nozzle portion (42) and said planar member (48), the radially outer portion of said plate member (60) together with the spaced adjacent outer nozzle edge (46) forming a radially directed plate diffuser exit (40) when said plate member (60) abuts said planar member (48), and (d) plate securing means (50) for providing unrestricted axial movement of said plate member (60) between a sealing position against said planar member (48) and an unsealing position against said nozzle portion (42), the introduction of said pressurized gas during startup causing a net pressure force on said plate member (60) to move said plate member (60) to said sealing position, and the impact force of high velocity air from the compressor (12) during subsequent normal operation causing movement of said plate member (60) to said unsealing position. 5. Apparatus according to claim 4, characterized in that said plate securing means (50) includes a plurality of spacer studs (50) connecting said nozzle portion (42) and said planar member (48) and corresponding number of relief notches (62) in said plate member (60), said plate member (60) being captured by said studs (50). 6. Apparatus according to claim 4, characterized by means (64) for bleeding said pressurized gas to the back surface of said plate member (60) facing said planar member (48) during startup, said bleeding means (6A) by-passing the portion of the flow path through the plate diffuser exit (40). 7. Apparatus according to claim 6, characterized in that said bleeding-means (64) includes a plurality of vent holes (64) through said planar member (48), flow through said vent holes (64) being obstructed by said plate member (60) when in said unsealing position during normal operation. 8. Method for starting a gas turbine engine having a rotary compressor for compressing air, a combustor for combusting the compressed air with fuel to produce combustion gases under pressure, and a turbine for expanding the combustion gases to produce mechanical work, the turbine and the compressor being coupled for dependent rotation, characterized by the steps of (a) providing a diffuser for increasing pressure between the compressor and the combustor; (b) introducing pressurized gas into the compressed air flow path between the diffuser and the combustor; (c) preventing back flow of pressurized gas through the diffuser and compressor using one way valve means associated with the diffuser; (d) expanding the pressurized gas through the turbine to cause rotation of the turbine and the compressor; and (e) returning the one way valve to normal open position under the influence of the flow of compressed air from the rotating compressor. 9. Method according to claim 8, characterized in that the pressurized gas is air, and the method includes the further step of combusting fuel with the pressurized air to increase gas energy prior to the expanding step. 10. Method according to claim 8, characterized in that the diffuser includes a plate type diffuser stage and the valve means includes an axially floating plate member mounted in the plate diffuser, and wherein said preventing step includes the step of translating said plate member into a sealing position under the force of the pressurized gas. 11. Method according to claim 10, characterized in that said translation step includes the substep of preferentially bleeding pressurized air to the back-side of the plate member to initiate movement towards the sealing position.

Inventors: KLAEBO, PER
Applicants: A/S KONGSBERG VAPENFABRIKK
Application year: 1983
Main classification: F02C7
IPC codes: F02C7