HIGH PRESSURE INTERCOOLED TURBINE ENGINE

Abstract: High pressure ratios in a Brayton cycle gas turbine engine are achieved in a construction utilizing a low pressure spool (10), an intermediate pressure spool (12) and a high pressure spool (14). Intercoolers (30 and 32) are located between the stages defined by the spools (10, 12 and 14) to densify the air compressed by a low pressure compressor (18) and an intermediate compressor (34) associated with the spools (10 and 12) respectively.

Description: HIGH PRESSURE INTERCOOLED TURBINE ENGINE Field of the Invention This invention relates to turbine engines, and more particularly, to a compound, turbine engine operating under high pressure with intercooling between compression stages. Background of the Invention Since the introduction of Brayton cycle gas turbine engines in the early 1940*s, significant advances have been made in their construction and operating cycles to improve their thermal efficiency and thus, their fuel economy. However, even with those advances, the gas turbine has been unable to approach the thermal efficiency of a diesel engine. A primary limitation has been the inability to attain relatively high cycle pressures, particularly in relatively small engines (those having a horsepower rating of 1000 or less) . Recent applications of small radial flow compressors have demonstrated their capability to deliver very high overall pressure ratios when triple spooled with inter¬ coolers. Thus, the present invention seeks to utilize such compressors to attain a high pressure ratio in a Brayton cycle gas turbine engine to improve thermal efficiency so that such turbines may be competitive with diesel cycle engines. There have been several prior attempts to harvest the benefits of intercooling between turbine stages. Rolls Royce has produced a gas turbine with two intercoolers and three separate rotating shafts. This engine was used in marine applications where the ready availability of cooling water simplified intercooling. Ford Motor Company has developed a gas turbine engine known as the 704/705 with a somewhat similar cycle. In this engine, the intercooler was air cooled, resulting in higher losses and reduced intercooling efficiency. Both of these developments were too complex for the then current state of the art. The present invention is directed to overcoming one or more of the above problems. Summary of the Invention It is the principal object of the invention to provide a new and improved turbine engine. More specifically, it is an object of the invention to provide a multiple stage turbine engine that may operate at very high pressure ratios to achieve good thermal efficiency. An exemplary embodiment of the invention achieves the foregoing object in a compound gas turbine engine including at least three independently rotatable spools. A first of the spools includes a low pressure compressor and a low pressure turbine. A second of the spools includes an intermediate pressure compressor and an intermediate pres¬ sure turbine. Still a third of the spools includes a high pressure compressor and a high pressure turbine. At least two interstage intercoolers are provided and compressed air ducting connects one of the intercoolers between the low and intermediate pressure compressors and further connects the other of the intercoolers between the intermediate and high pressure compressors. There is provided at least one combustor for burning fuel to produce gases of combustion and the same is con¬ nected between the high pressure compressor and the high pressure turbine. The combustor receives compressed air from the high pressure compressor and burns fuel and directs the resulting gases of combustion to the high pressure turbine. Combustion gas ducting connects the high and the intermediate pressure turbines and also connects the inter¬ mediate and low pressure turbines. Power take-off means are provided for the engine. In a design for aeronautical application wherein intercooler effectiveness is necessarily limited for weight reasons to no more than about .75, it is considered that overall compressor pressure ratios in excess of 40 may be achieved to thereby achieve high thermal efficiency. According to a preferred embodiment of the invention, each of the low, intermediate and high pressure compressors is a radial flow compressor. In a preferred embodiment, the low pressure spool includes a shaft and each of the interstage intercoolers includes a cooling air inlet and a cooling air outlet. Alternatively liquid cooling means could be used instead of air. The power take-off is in the form of a separate free power turbine connected to receive combustion gas from the low pressure turbine. A reheater may be selectively opera¬ ted to heat combustion gas passing from the low pressure turbine to the free power turbine and a fan is mounted on the shaft of the first spool to be driven by the low power turbine. Cooling air ducting connects the fan and the cooling air inlets of the intercoolers. In one embodiment of the invention, the spools are generally coplanar and disposed and spaced, side by side, parallel relation. An air inlet is provided in alignment with the low pressure spool on the compressor side thereof and the fan is disposed in such inlet. The compressed air ducting extends generally transverse to the spools on the compressor sides thereof and the cooling air ducting is in heat exchange relation with the compressed air ducting along the length thereof to define the two intercoolers. In another embodiment of the invention, the spools are disposed and spaced, side by side, triangular, parallel relation and there is provided an air inlet with the fan disposed in the inlet as before. The cooling air ducting comprises at least two generally radially disposed ducts terminating at a cooling air inlet of a respective one of the intercoolers. In still another, and highly preferred embodiment, of the invention, the low and intermediate pressure spools in the free power turbine are coaxial. According to this embodiment, the high pressure spool is disposed to one side of the low and intermediate pressure spools and rearwardly thereof. The intercoolers are located forwardly of the high pressure spool and generally in axial alignment therewith and to one side of the low and inter¬ mediate pressure spools. The invention contemplates that, in this embodiment, the low and intermediate turbines in the free power turbines * are axial flow turbines. Other objects and advantages will become apparent from the following specification taken in connection with the accompanying drawings. Description of the Drawing's Fig. 1 is a schematic flow diagram illustrating the organization of the various components of all embodiments of the invention with respect to each other; Fig. 2 is a sectional view of one embodiment of a gas turbine engine made according to the invention; Fig. 3 is a front elevation of the embodiment of Fig. 2; Fig. 4 is a side elevation of the embodiment of Fig. 2 with certain parts shown in section for clarity; Fig. 5 is a sectional view of another embodiment of the invention; Fig. 6 is a front elevation of the embodiment of Fig. 5; Fig. 7 is a sectional view of a highly preferred embodiment of the invention; and Fig. 8 is a rear elevation of the embodiment of Fig. 7. Description of the Preferred Embodiments A schematic flow diagram of a compound gas turbine engine made according to the invention is illustrated in Fig. 1. The invention includes four independently rotatable spools generally designated 10, 12, 14, and 16. The spool 10 is a low pressure spool and includes a radial flow compressor 18 and a turbine wheel 20. The spool 10 also includes a shaft shown schematically at 22 which extends intc an air inlet 24 for the engine. Within the inlet 24, a fan 26 is mounted on the shaft 22. Cooling air ducting 28 extends from the inlet 24 at a location therein just down¬ stream of the fan 26 but upstream of the compressor 18 to first and second intercoolers generally designated 30 and 32. The spool 12 is an intermediate pressure spool and includes a radial flow compressor 34 and interconnected turbine 36. Ducting 38, which includes a passage through the intercooler 30, interconnects the outlet of the " com¬ pressor 18 and the inlet of the compressor 34. The spool 14 is a high pressure spool and includes a radial flow compressor 40 and a turbine 42. Ducting 44 interconnects the outlet of the compressor 34 and the inlet of the compressor 40 via a path through the intercooler 32. It can thus be seen that cooling air taken from the inlet 24 is utilized in the intercoolers 30 and 32 to provide interstage cooling of combustion air, also taken from the inlet 24, after it has been initially compressed by the low pressure compressor 18 and again after it has been further compressed by the intermediate pressure compressor 34. In some instances a separate fan or pump driven by suitable means could be used to provide air or liquid coolant, respectively, to the intercoolers 30 and 32. The outlet of the high pressure compressor 40 is connected to a conventional combustor 46. The combustor 46 receives compressed air from the compressor 40 as well as fuel from a source not shown, burns the same and provides combustion gas to the turbine 42 so that the latter will rotate and drive the compressor 40. Gases of combustion exiting the turbine 42 are conveyed via ducting 48 to the inlet of the turbine 36 to drive the same and thus drive the compressor 34. Additional ducting 50 conducts gases of combustion from the turbine 36 to the low pressure turbine 20 to drive the same. This in turn results in rotation of the low pressure compressor 18 as well as the fan 26. The fourth spool 16 consists of a free power turbine 52 which may be connected through suitable gearing 54 to an output shaft 56. Ducting 58, including a reheat combustor 60, interconnects the low pressure turbine 20 and the free power turbine 52. The reheat combustor 60 may or may not be used as desired and where a given application permits the same to be selectively used, the free power turbine 52 is provided with a variable power turbine nozzle schematically illustrated at 62. It will be appreciated that the use of three stages, given state of the art radial flow compressors, is readily capable of producing a theoretical overall compressor pressure ratio of 64. That is to say, each stage has an individual compressor pressure ratio of 4. In practice, overall pressure ratios in excess of 40 could be achievable. The use of a separate free power turbine is not absol¬ utely necessary but it is generally preferred, particularly when optional reheating is considered. The interstage intercoolers increase the density of the air by reducing the temperature thereof, thereby enabling the attainment of relatively high pressure ratios as is desired. Application of the principals of the invention to particular embodiments will now be described. In this connection, the same reference numerals utilized in the description of Fig. 1 will be employed where applicable in the drawing and those elements will not be redescribed unless material to the construction of the particular embodiment. Addressing now Figs. 2-4, and the embodiment illus¬ trated therein, it will be seen that each of the spools 10, 12, 14 and 16 is independently rotatable on its associated rotational axis 100, 102, 104 and 106. Moreover, it will be seen that each of the turbines 20, 36, 42 and 52 in this embodiment are radial flow turbines. The combustor 46 is an annular combustor disposed about the axis 104 of the spool 14. The power take-off shaft 56 is displaced from the axis of rotation 106 of the free power turbine 52 which, if desired, can be coaxial with the axis 102. It will be observed from Fig. 3 that the various axes are parallel such that the spools are in side by side relation and generally coplanar. As can be seen, a volute 108 surrounds the low pressure compressor 18. The volute 108 opens as at 110 into the interior of a plenum 112 which is in fluid communication with the inlet 114 -to the intermediate pressure compressor 34. A partition 116 (Fig. 3) may divide the plenum 112 into two sections such that a volute 118 surrounding the inter¬ mediate stage compressor 34 may discharge via an opening 120 into the lowermost section which in turn is in fluid com¬ munication with the inlet 122 to the high pressure compres¬ sor 40. The plenum 112 thus forms ducting for the compressed air, which ducting extends generally transverse to the various axes of rotation and across the front of the engine. Within the plenum 112 are suitable means shown schematically at 124 for dividing the same into two separate flow paths in heat exchange relation with one another. This is, of course, to define the intercoolers 30 and 32 and the precise internal configuration is well within the skill of the art. In any event, the partition 124, in addition to defin¬ ing the intercoolers 30 and 32, defines a cooling air duct opening as at 126 to the inlet 24 downstream of the fan 26 and upstream of the low pressure compressor 18. An outlet for the cooling air is shown at 128. Ducting 130 extends from the discharge side of the high pressure turbine 42 to a nozzle 132 surrounding the turbine 36 of the intermediate pressure spool 12. Additional ducting 134 extends from the outlet side of the intermediate pressure turbine 36 to a nozzle 136 surrounding the low pressure turbine 20. The ducting 58 then extends " to a variable nozzle 140 associated with free power turbine 16. The embodiment of Figs. 2-4, inclusive is advantageous in that it allows the use of modular spools and avoids mechani¬ cal complexity that would be associated with concentric shafting. This embodiment is ideally suited for appli¬ cations where engine volume is not of particular concern such as ground power or marine applications. Another embodiment of the invention is illustrated in Figs. 5 and 6. * This embodiment of the invention is very much like that illustrated in Figs. 2-4 but has the added advantage of reduced frontal area. It has a disadvantage of more complicated ducting. In this embodiment, the spools 10, 12, 14 and 16 respectively rotate on axes 200, 202, 204 and 206. As with the embodiment of Figs. 2-4, the inlet 24 is generally coaxial with the axis of rotation of the low pressure spool 10, here the axis 200. In this embodiment, the intercoolers 30 and 32 have inlets 208 and outlets for the compressed air which is received through ducting 212 serving the function of the ducting 38 and 44. In addition, the intercoolers 30 and 32 have cooling air inlets 214 which open radially inwardly and which are connected by ducts that extend radially from the inlet 24 and open thereto at a location intermediate the fan 26 and the low pressure spool 10. Cooling air outlets (not shown) are naturally provided. A highly preferred embodiment is illustrated in Figs. 7 and 8. Though mechanically somewhat more complex than either of the two embodiments heretofore described, it offers the advantage of substantially reduced frontal area and retains relatively simple ducting. In this embodiment, the spools 10, 12 and 16 are rotatable about a single axis 300. The spool 16 is located to the rear of the spools 10 and 12 and the latter include concentric shafts 302 and 304. The shaft 302 drives the fan 26 and thus corresponds to the shaft 22. That is to say, the shaft 302 is associated with the low pressure spool 10. The shaft 304 is a hollow shaft receiving the shaft 302 and is associated with the inter¬ mediate pressure spool 12. In this embodiment, the low pressure turbine 20, the intermediate pressure turbine 36, and the free power turbine 52 are all axial * flow turbines. The compressor 18, 34 and 40 are all radial flow compressors while the high pressure turbine 42 is a radial inflow turbine. According to this embodiment, the high pressure spool 14 is disposed to one side of the spools 10, 12 and 16 and to the rear of the spools 10 and 12. The intercoolers 30 and 32 are generally aligned with the high pressure spool 14, that is, its axis of rotation 306 if projected would extend through the intercoolers 30 and 32. Thus, the intercoolers 30 and 32 are nominally aligned with the spools 10 and 12 from front to rear and displaced to the same side of the axis 300 as is the high pressure spool 14. The intercoolers 30 and 32 may have outlets 308 opening to opposite sides of the axis 306 as illustrated in Fig. 8 and ducting 310 serving the purpose of the ducting 28 extends from a location in the inlet 24 between the fan 36 and the low pressure compressor 18 to inlets (not shown) for the intercoolers 30 and 32. From the foregoing it will be appreciated that a Brayton cycle gas turbine engine made according to the invention is capable of operating at high pressure ratios and may be configured in various ways depending upon the application to which it is to be put. Thus, a Brayton cycle gas turbine engine capable of thermal efficiencies approach¬ ing those obtainable with diesel engines is provided.

Claims: CLAIMS 1. A compound gas turbine engine comprising: at least three independently rotatable spools; a first of said spools including a low pressure com¬ pressor and a lower pressure turbine; a second of said spools including an intermediate pressure compressor and an intermediate pressure turbine; a third of said spools including a high pressure compressor and a high pressure turbine; at least two interstage intercoolers; compressed air ducting connecting one of said inter¬ coolers between said low and intermediate pressure compres¬ sors, and connecting the other of said intercoolers between said intermediate and high pressure compressors; at least one combustor for burning fuel to produce gases of combustion and connected between said high pressure compressor and said high pressure turbine, said combustor receiving compressed air from said high pressure compressor and burning fuel therein and directing the resulting gases of combustion to said high pressure turbine; combustion gas ducting connecting said high and inter¬ mediate pressure turbines, and connecting said intermediate and low pressure turbines; and power take-off means from said engine. 2. The gas turbine of claim 1 wherein said low, intermediate and high pressure compressors are all radial flow compressors. 3. A compound gas turbine engine comprising: at least three independently rotatable spools; a first of said spools including a shaft, a low pres¬ sure compressor and a lower pressure turbine; a second of said spools including an intermediate pressure compressor and an intermediate pressure turbine; a third of said spools including a high pressure compressor and a high pressure turbine; at least two interstage intercoolers each having a cooling air inlet and a cooling air outlet; compressed air ducting connecting one of said inter¬ coolers between said low and intermediate pressure compres¬ sors, and connecting the other of said intercoolers between said intermediate and high pressure compressors; at least one combustor for burning fuel to produce gases of combustion and connected between said high pressure compressor and said high pressure turbine, said combustor receiving compressed air from said high pressure compressor and burning fuel therein and directing the resulting gases of combustion to said high pressure turbine; combustion gas ducting connecting said high and inter¬ mediate pressure turbines, and connecting said intermediate and low pressure turbines; a free power turbine; additional combustion gas ducting connecting said low pressure turbine and free power turbine; means associated with said additional ducting and operable to add heat to combustion gas therein; a fan mounted on said first spool shaft to be driven by said low pressure turbine; and cooling air ducting connecting said fan and said cooling air inlets of said intercoolers. 4. The gas turbine of claim 3 wherein said spools generally coplanar and are disposed in spaced side by side, parallel relation; means defining an air inlet for said engine aligned with said low pressure spool on the compressor side thereof; said fan being disposed in said engine air inlet; said compressed air ducting extending generally trans¬ verse to said spools on the compressor sides thereof; and said cooling air ducting being in heat exchange rela¬ tion with said compressed air ducting along the length thereof to define said intercoolers. 5. The gas turbine of claim 3 wherein said spools are disposed in spaced, side by side, triangular, parallel relation; means defining an air inlet for said engine aligned with said low pressure spool on the compressor side thereof; said fan being disposed in said inlet; said cooling air ducting comprising at least two generally radially disposed ducts terminating in a cooling air inlet of a respective one of said intercoolers. 6. The gas turbine of claim 3 wherein said low and intermediate pressure spools and said free power turbine are coaxial. 7. The gas turbine of claim 3 wherein said low and intermediate pressure spools and said free power turbine are coaxial and said high pressure spool is disposed to one side of said low and intermediate pressure spools and rearwardly thereof. 8. The gas turbine of claim 3 wherein said low and intermediate pressure spools and said free power turbine are coaxial and said high pressure spool is disposed to one side of said low and intermediate pressure spools and rearwardly thereof, said low and intermediate compressors are radial flow compressors and said low and intermediate turbines and said free power turbine are axial flow turbines. 9. The gas turbine of claim 3 wherein said low and intermediate pressure spools and said free power turbine are coaxial and said high pressure spool is disposed to one side of said low and intermediate pressure spools and rearwardly thereof, said intercoolers being located forwardly of said high pressure spool and generally in axial alignment there¬ with, and to one side of said low and intermediate pressure spools. 10. The gas turbine of claim 9 further including means defining an air inlet for said engine forwardly of said low and intermediate pressure spools and in fluid communication with said intermediate pressure compressor generally coaxial therewith, said fan being disposed in said air inlet, said cooling air ducting interconnecting said inlet and said intercoolers and opening to said inlet between said fan and said low pressure compressor.

Inventors: GEISER ROBERT J, ROGERS COLIN, GEISER, ROBERT, J., ROGERS, COLIN
Applicants: SUNDSTRAND CORP, SUNDSTRAND CORPORATION
Application year: 1989
Main classification: F02C3
IPC codes: F02C3, F02C7