Abstract: A pressure exchanger for hydraulic fracking includes a rotor that is configured to rotate about an axis and includes a plurality of rotor ducts extending parallel to the axis, where each rotor duct extends between a first side and a second side of the rotor that are spaced apart from each other. The pressure exchanger further includes a first end cover that is disposed at the first side of the rotor and defines a first pair of apertures configured to communicate a first fluid including fracking particles, and a second end cover that is disposed at the second side of the rotor and defines a second pair of apertures configured to communicate a second fluid. The first end cover further defines a flush port configured to supply the second fluid into the first side of the rotor in a state in which the first pair of apertures communicate the first fluid with the first side of the rotor.

Abstract: A rotary isobaric pressure exchanger (IPX) configured to exchange pressure between a first fluid and a second fluid. The rotary IPX includes a low-pressure port designed to output the first fluid under a first pressure. The rotary IPX further includes a rotor that is connected via a fluid flow path from the low-pressure port. The rotary IPX further includes a shaft routed through a centerbore formed by the rotary IPX. The rotary IPX forms a low-pressure passageway from the low-pressure port to the rotor. The rotary IPX further forms a fluid passageway between the low-pressure passageway and the centerbore. The rotary IPX further includes a motor connected to the shaft, the motor designed to rotate the shaft to drive the rotor.

Abstract: There is disclosed a gas turbine engine including a bearing housing having at least two bearings axially spaced from one another relative to a central axis. The bearing housing includes an axially deformable bellows between the bearings configured to permit axial relative movement of the bearings. A method of operating a bearing assembly is also disclosed.

Abstract: A system includes a hydraulic energy transfer system configured to exchange pressures between a first fluid and a second fluid, wherein pressure of the first fluid is greater than pressure of the second fluid. The system also includes a lubrication system coupled to the hydraulic energy transfer system and configured to pump or direct a lubrication fluid into the hydraulic energy transfer system.

Abstract: The invention relates to a turbine engine combustion module (10), in particular for an aircraft turbine engine, designed to carry out constant-volume combustion, comprising: at least two combustion chambers (12A, 12B) arranged about an axis, each chamber (12A, 12B, 12C) comprising a compressed gas intake port (16) and a burnt gas exhaust port (18); and an ignition means that triggers combustion in the combustion chambers (12A, 12B, 12C). The module (10) comprises at least one duct (80) which establishes a communication between a first combustion chamber (12A) and at least one second combustion chamber (12B) in order to inject burnt gases from the first combustion chamber (12A) into the second combustion chamber (12B) so as to trigger combustion in the second combustion chamber (12B).

Abstract: A system includes an isobaric pressure exchanger (IPX) configured to couple to a manifold. The IPX is also configured to exchange pressure within the IPX between a first fluid at a first pressure and a second fluid at a second pressure. The IPX also includes a housing and at least one manifold connector disposed within the housing that is configured to couple the IPX to the manifold.

Abstract: A hybrid propulsion system includes a wave rotor combustion engine operating in parallel with an electrical motor-generator element. The motor-generator element is coupled to the turbine shaft to selectively drive or be driven by the turbine shaft. In one mode of operation, the motor of the motor generator element is powered by a battery to provide rotational energy to the turbine shaft. In another mode of operation, the wave rotor combustion engine drives the generator to recharge the battery. The wave rotor combustion engine may be further directly coupled to auxiliary components without a gearbox to drive the components at substantially the same speed as the turbine shaft. The turbine rotor of the combustion engine includes a plurality of chambers defined by circumferentially spaced curved vanes that improves specific fuel consumption for the engine.

Abstract: A gas turbine engine comprises a fan, a compressor, a combustor, and a fan drive turbine rotor. The fan drive turbine drives the fan through a gear reduction. The gear reduction includes at least two double helical gears in meshed engagement. Each of the at least two double helical gears are disposed to rotate about respective axes, and each have a first plurality of gear teeth axially spaced from a second plurality of gear teeth by a spacer. Each of the first plurality of gear teeth has a first end facing the spacer and each of the second plurality of gear teeth has a first end facing the spacer. Each first end of the first plurality of gear teeth is circumferentially offset from each first end of the second plurality of gear teeth. A method is also disclosed.

Abstract: Apparatus and methods for combustion of fuel includes, in some embodiments, a fuel nozzle which injects fuel into a combustion channel of a wave rotor combustor or a pulse detonation combustor. In some embodiments the combustion process includes a backward-propagating detonation wave within a substantially closed channel which compresses discrete quantities of combustible and noncombustible mixture. Yet other embodiments include a precombustion chamber integrated into the wave rotor, the outlet stator or both.

Abstract: Disclosed herein are screw shaft turbine compressors having (i) a compressor section, (ii) a turbine section, (iii) a combustion section coupling to the compressor section and the turbine section, and (iv) a grooved shaft. The grooved shaft can include one or more grooves for providing fuel from the compressor section to the combustion section and for allowing exhaust to leave the combustion section and exit the turbine section. A method for generating different speed to torque ratios on the shaft and a system for generating torque on the shaft are further disclosed.

Abstract: A booster assembly for a gas turbine engine having a first rotor assembly comprising a low pressure turbine drivingly connected to a fan via a first shaft and a second rotor assembly comprising a second turbine drivingly connected to a high pressure compressor via a second shaft. The booster assembly comprises a further compressor arranged to be disposed about said common axis between the fan and high-pressure compressor in a direction of flow and a gearing having first and second input rotors and an output rotor. The first input rotor is arranged to be driven by the first rotor assembly and the second input rotor is arranged to be driven by the second rotor assembly such that the output rotor drives the further compressor in dependence upon the difference in rotational speed between the first and second rotor assemblies.

Abstract: Disclosed herein are screw shaft turbine compressors having (i) a compressor section, (ii) a turbine section, (iii) a combustion section coupling to the compressor section and the turbine section, and (iv) a grooved shaft. The grooved shaft can include one or more grooves for providing fuel from the compressor section to the combustion section and for allowing exhaust to leave the combustion section and exit the turbine section. A method for generating different speed to torque ratios on the shaft and a system for generating torque on the shaft are further disclosed.

Abstract: An example method of allocating power within a gas turbine engine includes driving an off-take power delivery assembly using a first amount of power from a spool, the first amount of power corresponding to an off-take power requirement of a gas turbine engine; and driving the spool of the gas turbine engine using a second amount of power, wherein a ratio of the first amount of power to the second amount of power is greater than or equal to 0.009.

Abstract: A pressure vessel provided with a first port acting as a high pressure inlet of a first stream and a second port acting as a high pressure outlet. A rotatable valve element is located in the center of the machine. In operation, a fluid stream is introduced to the machine at high pressure where it then passes through the open ports of the valve element and into flow distributor causing upward displacement of a first duct piston, resulting in pressurization and flow of a second fluid. At the same time the second fluid is introduced to the machine at low pressure and flows into the pressure exchange duct, causing downward displacement of a second duct piston and resulting in flow of the first fluid below the duct piston, which then flows into the lower flow distributor, into the valve element, and then out of the pressure vessel.

Abstract: A gas turbine engine has a fan, a compressor section having a low pressure portion and a high pressure portion, a combustor section, and a turbine having a low pressure portion. The low pressure turbine portion drives the low pressure compressor portion and the fan. A gear reduction effects a reduction in the speed of the fan relative to a speed of the low pressure turbine and the low pressure compressor portion. At least one of the low pressure turbine portion and low pressure compressor portion has a number of blades in each of a plurality of rows. The blades operate at least some of the time at a rotational speed. The number of blades and the rotational speed are such that the following formula holds true for at least one of the blade rows of the at least one of the low pressure turbine portion and/or the low pressure compressor sections: (number of blades×rotational speed)/60?5500. The rotational speed is an approach speed in revolutions per minute.

Abstract: A combustion engine, which is highly efficient, noiseless and lightweight, includes a combustion chamber without pistons. The combusted and expanded air exiting the combustion chamber flows into a displacement pump, such as a gear pump or radial vane pump. The displacement pump drives the load, and, in addition, another smaller displacement pump, which pressurizes fresh air and introduces same, via a feedback loop, into the combustion chamber. Gas or other burnable fuels are introduced in the combustion chamber, so that a continuous fuel burning will occur, after being ignited. The ratio of bigger to the smaller pump is influenced by the percentage of expansion of the air in the combustion chamber.

Abstract: A constant volume combustor device includes, in one form, a detonative combustion. The apparatus includes inlet and outlet ports that interface with a plurality of fluid flow passageways on a rotor. A buffer gas is routed through some of the inlet and outlet ports and into and out of the plurality of fluid flow passageways. One of the inlet ports is a buffer gas inlet port that when placed in registry with a fluid flow passageway allows the flow of buffer gas into the respective passageway. Fuel is delivered into the buffer gas proximate the buffer gas inlet port so that only a portion of the buffer gas inlet port receives any fuel. In one form the wave rotor of the constant volume combustor is supported by magnetic bearings.

Abstract: Apparatus and methods for combustion of fuel. Some embodiments of the inventions include a fuel nozzle which injects fuel into a combustion channel of a wave rotor combustor or a pulse detonation combustor In some embodiments the combustion process includes a backward-propagating detonation wave within a substantially closed channel which compresses discrete quantities of combustible and noncombustible mixture. Yet other embodiments include a precombustion chamber integrated into the wave rotor, the outlet stator or both.

Abstract: A counter-rotatable fan turbine engine includes a counter-rotatable fan section, a worm gas generator, and a low pressure turbine to power the counter-rotatable fan section. The low pressure turbine maybe counter-rotatable or have a single direction of rotation in which case it powers the counter-rotatable fan section through a gearbox. The gas generator has inner and outer bodies having offset inner and outer axes extending through first, second, and third sections of a core assembly. At least one of the bodies is rotatable about its axis. The inner and outer bodies have intermeshed inner and outer helical blades wound about the inner and outer axes and extending radially outwardly and inwardly respectively. The helical blades have first, second, and third twist slopes in the first, second, and third sections respectively. A combustor section extends through at least a portion of the second section.

Abstract: A supercharging system for an internal combustion engine comprising a turbocharger including a compressor and a turbine, and a pressure wave supercharger performing supercharging of the internal combustion engine by increasing a pressure of gas led into each of cells from an intake gas inlet port using a pressure wave of exhaust gas led into the cell from an exhaust gas inlet port and discharging from an intake gas outlet port to an intake passage the gas pressurized, wherein a case of the pressure wave supercharger is connected to the intake passage upstream of the compressor via the intake gas inlet port, and is connected to the intake passage downstream of the compressor via the intake gas outlet port, and is connected to an exhaust passage downstream of the turbine via the exhaust gas inlet port and an exhaust gas outlet port.

Abstract: A Brayton cycle internal combustion engine of the open, or constant pressure type, in which rotary power is produced by the pressure of hot gasses against confined, rotor protrusions.

Abstract: In an internal combustion engine, fresh air is compressed by a pressure-wave supercharger. At least one operating parameter of the pressure-wave supercharger is controlled or regulated as a function of at least one actual operating variable of the internal combustion engine.

Abstract: The present invention provides an ultra micro gas turbine engine which includes a wave rotor. In various embodiments, the ultra micro gas turbine engine of the present invention includes a rotating disk which has a compressor, a wave rotor and a turbine, a first stationary member which includes an inlet and a first wave rotor port end plate, a second stationary member which includes an outlet and a second wave rotor port end plate and a combustion chamber which includes a fuel inlet and an igniter.

Abstract: The exhaust within an exhaust gas recirculation (EGR) system should be purged to allow for access to the components of the EGR system. A system and method for purging the EGR system is provided. The system and method may incorporate a purge gas supply that may include: at least one pressurized cylinder, a storage tank, a compressor, or a benign fluid source. The system and method may drive the exhaust out of the EGR system.

Abstract: The exhaust within an exhaust gas recirculation (EGR) system should be purged to allow for access to the components of the EGR system. A system and method for purging the EGR system is provided. The system and method may incorporate an: EGR purge fan, an EGR purge blower, or a turbomachine. The system and method may draw the exhaust out of the EGR system. The system and method may drive the exhaust out of the EGR system.

Abstract: The exhaust within an exhaust gas recirculation (EGR) system should be purged to allow for access to the components of the EGR system. A method and system for controlling an EGR purge system is provided. The method and system may control the operation of drawing the exhaust out of the EGR system. The method may also control the operation of diving the exhaust out of the EGR system.

Abstract: An axial flow positive displacement turbine includes inner and outer bodies having offset inner and outer axes respectively extending between a relatively high pressure inlet and a relatively low pressure outlet. At least one of the bodies is rotatable about its axis. The inner and outer bodies have intermeshed inner and outer helical blades wound about the inner and outer axes respectively. The inner and outer helical blades extend radially outwardly and inwardly respectively. Each of the bodies has at least two blades. There is one more or one less outer helical blades than inner helical blades. The inner and outer bodies may both be rotatable about inner and outer axes and geared together in a fixed gear ratio. The turbine may have first and second sections with a first twist slope greater than a second twist slope respectively of the inner and outer helical blades.

Abstract: A screw shaft turbine compressor comprising (i) a compressor section, (ii) a turbine section, (iii) a combustion section coupling to the compressor section and the turbine section, and (iv) a grooved shaft. The grooved shaft in one embodiment extends from a portion of the compressor section, through the combustion section, and to a portion of the turbine section.

Abstract: A pulse detonation combustor (PDC) assembly includes an upstream chamber forming an inlet plenum, a downstream chamber including a downstream portion of at least one PDC tube, and an integrated PDC head coupled to the upstream chamber and the downstream chamber. The integrated PDC head is configured to facilitate fuel injection and ignition within the PDC tube. The PDC tube includes an inner seal surface and an outer seal surface configured to mate with the inner seal surface, wherein the inner seal surface includes an elevated section thereon that engages with the outer seal surface such that the PDC tube is free to partially pivot about a longitudinal axis thereof.

Abstract: An axial flow positive displacement compressor has an inlet axially spaced apart and upstream from an outlet. Inner and outer bodies have offset inner and outer axes extend from the inlet to the outlet through first and second sections of a compressor assembly in serial downstream flow relationship. At least one of the bodies is rotatable about its axis. The inner and outer bodies have intermeshed inner and outer helical blades wound about the inner and outer axes respectively. The inner and outer helical blades extend radially outwardly and inwardly respectively. The helical blades have first and second twist slopes in the first and second sections respectively. The first twist slopes are less than the second twist slopes. An engine including the compressor has in downstream serial flow relationship from the compressor a combustor and a high pressure turbine drivingly connected to the compressor by a high pressure shaft.

Abstract: An axial flow positive displacement engine has an inlet axially spaced apart and upstream from an outlet. Inner and outer bodies have offset inner and outer axes extend from the inlet to the outlet through first, second, and third sections of a core assembly in serial downstream flow relationship. At least one of the bodies is rotatable about its axis. The inner and outer bodies have intermeshed inner and outer helical blades wound about the inner and outer axes respectively. The inner and outer helical blades extend radially outwardly and inwardly respectively. The helical blades have first, second, and third twist slopes in the first, second, and third sections respectively. The first twist slopes are less than the second twist slopes and the third twist slopes are less than the second twist slopes. A combustor section extends axially downstream through at least a portion of the second section.

Abstract: A Brayton-cycle rotary ramjet engine (10) operated within the confines of a helically elongated pass-through duct formed between a preferably stationary radially outward surface (14) and an outer rotating flow channel (36). The flow channel (36) is contoured between its inlet (34) and outlet (38) to include a supersonic diffuser (40), a combustor (42) and an expansion nozzle (44). Gaseous fuel, or liquid fuel atomized by a fuel slinger (58) within a housing (46), or solid fuel in the form of fine particulates, is inter-mixed with an oxidizer prior to being directed to the flow channel inlets (34). The air and fuel are combusted in the flow channels (36) and exhausted through the rear of the housing (46). A generator (22) can be coupled to a power shaft (18) to convert net shaft power into electricity. Preferably, the rotor (24) and stator (12) are fabricated from a ceramic or other high-temperature material so that combustor exit temperatures (T3) can be operated at highly efficient levels.

Abstract: In an internal combustion engine, fresh air is compressed by a pressure-wave supercharger. At least one operating parameter of the pressure-wave supercharger is controlled or regulated as a function of at least one actual operating variable of the internal combustion engine.

Abstract: A gas turbine engine has components including a compressor, a combustor, and a turbine. At least one component is radially bladed having at least one row of radially extending rotatable blades and at least another is a worm component having an inner body disposed within an outer body. The inner and outer bodies have offset inner and outer axes, intermeshed inner and outer helical blades wound about the inner and outer axes respectively, and at least one of the inner and outer bodies being rotatable about a corresponding one of the inner and outer axes. An aircraft gas turbine engine has components in serial downstream flow relationship including a fan, a low pressure compressor, a high pressure compressor, a combustor, a high pressure turbine, and a low pressure turbine. At least one of the components is radially bladed and at least one of the components is a worm component.

Abstract: A wave rotor apparatus is provided. In another aspect of the present invention, a radial wave rotor includes fluid passageways oriented in a direction offset from its rotational axis. A further aspect of the present invention employs stacked layers of generally radial channels in a wave rotor. Moreover, turbomachinery is located internal to a wave rotor in yet another aspect of the present invention. In yet another aspect of the present invention, a radial wave rotor has an igniter and fuel injector. Correctional passages are employed in still another aspect of the present invention wave rotor.

Abstract: An axial flow positive displacement engine has an inlet axially spaced apart and upstream from an outlet. Inner and outer bodies have offset inner and outer axes extend from the inlet to the outlet through first, second, and third sections of a core assembly in serial downstream flow relationship. At least one of the bodies is rotatable about its axis. The inner and outer bodies have intermeshed inner and outer helical blades wound about the inner and outer axes respectively. The inner and outer helical blades extend radially outwardly and inwardly respectively and have first, second, and third twist slopes in the first, second, and third sections respectively. The first twist slopes are less than the second twist slopes and the third twist slopes are less than the second twist slopes. A combustion section extends axially downstream from the second section through at least a portion of the third section.

Abstract: The present invention provides a natural gas compression system, comprising a gas inlet component for the entrance of natural gas into the system, a booster component for increasing the pressure of the natural gas, a drying component for drying the natural gas, a compressor component including a reciprocating compressor for further increasing the pressure of the natural gas, a valve control panel and storage component, and a dispensing component.

Abstract: A pressure exchanger for transferring pressure energy from a high-pressure fluid stream to low-pressure fluid stream. A ducted rotor is positioned on a central axle between two end covers inside the vessel with a coaxial inlet and outlet pair that is in communication with a pair of low pressure ports having inclination forming an inlet tangential velocity vector in the direction of rotor rotation and an outlet tangential velocity vector in opposite direction imparting a rotational momentum on rotor. A pair of high-pressure ports is adapted for flow without inclination and imparts no momentum to the rotor. The end covers have a sloped surface following a flat sealing area that increases the clearance in the direction of rotation causing increased outflow during depressurization and lower duct pressure. This also causes increased inflow during the pressurization phase which will dissipate pressure energy as opposed to producing cavitation or pressure waves.

Abstract: The present invention comprises a highly supercharged, regenerative gas-turbine system. The gas turbine comprises a compressor, a regenerator, a combustor, and an expander. A pre-compressor pressurizes air going into the compressor section of the gas turbine. A cooler lowers the temperature of the air going into the compressor. The compressor pressurizes air, which then flows through the regenerator, which heats the air before it enters the combustor. The combustor further heats the air which then flows through the expander and then the regenerator. A post-expander is preferably located downstream of the regenerator. The post-expander is a second expander that receives high-pressure gas exiting the regenerator. The post-expander preferably drives the pre-compressor. The preferred pre-compressor and post-expander are toroidal intersecting vane machines (TIVMs), which are positive-displacement rotary devices. Numerous alternated embodiments of this basic system are described.

Abstract: A rotary ejector enhanced wave rotor pulsed detonation (WRPDE) engine and method are provided. The rotary-ejector-WRPDE includes a housing, one or more inlet ports in the housing, and a rotor mounted within the housing. The rotor includes a plurality of shrouded forward combustion passages in which detonative combustion occurs. Each forward combustion passage has an inlet end for communication with the inlet port. The rotor also includes a plurality of rear combustion passages which are in gaseous communication with the forward combustion passages. The rotor further includes a plurality of transitional combustion passages which join the forward combustion passages to the rear combustion passages and communicate with a source of bypass gas to provide a rotary ejector.

Abstract: A gas turbine system comprises a compressor that takes in suction air on the inlet side and compresses it to compressor end air that is available on the outlet side, a combustor in which a fuel is burned by using the compressor end air while resulting in the formation of hot gas, as well as a turbine in which the hot gas is expanded while providing work output. In a method for cooling this gas turbine system, compressed air is removed from the compressor, is fed as cooling air for cooling inside an internal cooling channel through thermally loaded components of the combustor and/or the turbine, is then compressed and added to the compressor end air. An improved cooling without disadvantage for the efficiency of the system is achieved in that, in the manner of a targeted leakage, a small part of the cooling air is fed for film cooling into the turbine stream through drilled film cooling openings provided on the components.

Abstract: The engine has an input system formed with a fluid displacement pump that enables substantially continuous pumping from a low-pressure side to a high-pressure side substantially without any backflow or backpressure pulsations. The output system has a first output device which provides for the mechanical work output of the engine and a second output device which feeds back to drive the input system. Any increase in the load to be driven by the first output device translates into a proportional increase in the drive energy fed back to the input system.

Abstract: A constant volume combustor device includes detonative combustion. In one form the wave rotor of the constant volume combustor is supported by magnetic bearings.

Abstract: The engine has an input system formed with a fluid displacement pump that enables substantially continuous pumping from a low-pressure side to a high-pressure side substantially without any backflow or backpressure pulsations. The output system, in one embodiment, is an output system having a turbine rotation about an axis that is substantially orthogonal to the pressure flow originating from the prime mover. The output system may include a first turbine which provides for the mechanical work output of the engine and a second turbine which feeds back to drive the input system. Any increase in the load to be driven by the first turbine translates into a proportional increase in the drive energy fed back to the input system. In an alternative embodiment, a differential may be used to distribute the output power to a load or back to the input compressor.

Abstract: The present invention provides for a pressurizer for pressurizing a fluid, comprising a pressurant entrance for the introduction of a pressurant, a fluid entrance for the fluid, a fluid exit for the fluid, and a transfer chamber movable in a cycle with respect to the fluid exit, where for a portion of a cycle the pressurant exerts a force on the fluid inside the transfer chamber. In a preferred aspect of the present invention, the pressurizer further comprises a spindle housing more than one transfer chamber, rotatable about an axis between the fluid entrance and the fluid exit. In another preferred aspect, the transfer chamber comprises either a flexible membrane or a movable piston to separate the pressurant and the fluid.

Abstract: A turbomachine is operated in a manner to improve the degree of efficiency of a machine of this type. To this end, fresh air that has been drawn in by suction is isochorically heated in individual, closed off conveying and heating chambers, which are arranged in succession in the conveying direction, and then supplied to a working machine in which the air is expanded and behind which the air is burned after being mixed with fuel. The resulting combustion gases are then guided past the conveying and heating chambers in the opposite direction to the conveying direction of the same, in such a way that the fresh air that is drawn in by suction is successively isochorically heated in said chambers.

Abstract: A wave rotor detonation engine and method are provided. The wave rotor detonation engine includes a rotor rotatably mounted within a housing, an inlet port, an exhaust port, and an igniter for igniting the gases within the rotor. The rotor includes a plurality of circumferentially spaced longitudinally extending combustion chambers in which detonative combustion occurs. The inlet port has a plurality of separate inlet zones for supplying fuel and air mixtures to the inlet end of the rotor. The inlet zones are circumferentially spaced about the perimeter of the rotor so that the combustion chambers interact with these inlet zones sequentially. Each inlet zone is capable of introducing a different combustible mixture sequentially to a given combustion chamber as it rotates past the inlet zones. This results in the stratification of differing concentrations of combustible material within the combustion chambers which is particularly suited to create detonative combustion within the wave rotor.

Abstract: A pulsed detonation engine wave rotor apparatus and method of using a pressure wave to compress a buffer gas disposed within the engine flow passages. The high pressure buffer gas is routed out of the wave rotor and subsequently reintroduced to the wave rotor to discharge and scavenge the latter stages of the combustion gas remaining under the engine flow passages.

Abstract: A wave rotor apparatus is provided. In another aspect of the present invention, a radial wave rotor includes fluid passageways oriented in a direction offset from its rotational axis. A further aspect of the present invention employs stacked layers of generally radial channels in a wave rotor. Moreover, turbomachinery is located internal to a wave rotor in yet another aspect of the present invention. In yet another aspect of the present invention, a radial wave rotor has an igniter and fuel injector. Correctional passages are employed in still another aspect of the present invention wave rotor.

Abstract: A Brayton cycle internal combustion engine of the open, or constant pressure type, in which rotary power is produced by the pressure of hot gasses against confined, rotor protrusions.