Abstract: The present disclosure refers to a turbocharged internal combustion engine with exhaust gas recycling, comprising an intake manifold, an exhaust manifold, a fresh air turbocharger and an exhaust supercharger, wherein the intake manifold is divided by a separating wall into a fresh air passage and an exhaust passage, one of the passages being connected to inlet openings of cylinders of the engine, the fresh air passage being connected to the outlet of the compressor of the fresh air turbocharger, the exhaust passage being connected to the outlet of the compressor of the exhaust supercharger and the separating wall being formed with orifices connecting the two passages.

Abstract: An energy recovery and cooling system for a hybrid machine is disclosed. The energy recovery and cooling system can include at least one circuit including at least one pump, at least one condenser, and at least one turbine, as well as a first flow path and a second flow path. The first flow path can be connected in fluid communication with the at least one pump, the at least one condenser, and the at least one turbine. The first flow path can additionally be in thermal communication with at least one internal combustion energy system component of the hybrid machine. The second flow path can be connected in fluid communication with the at least one pump, the at least one condenser, and the at least one turbine. The second flow path can additionally be in thermal communication with at least one electrical energy system component of the hybrid machine.

Abstract: An arrangement for injecting a reducing agent into an exhaust line of a combustion engine (1). An exhaust line (3) leads exhaust gases from the engine. A first turbine (4) is in the exhaust line (3). A second turbine (20) in the exhaust line is downstream of the first turbine (4) in the intended direction of flow in the exhaust line. An injector (19) injects reducing agent into the exhaust line (3) so that it is warmed and vaporized by the warm exhaust gases in the exhaust line (3), and an SCR catalyst (29). The injector (19) is in the exhaust line downstream of the first turbine (4) and upstream of the second turbine (20).

Abstract: An engine assembly includes an intake assembly, a spark-ignited internal combustion engine, and an exhaust assembly, and a turbocharger. The internal combustion engine is coupled with the intake assembly and defines a plurality of cylinders that are configured to combust a fuel. A subset of the cylinders are configured to selectively deactivate to stop combusting fuel while others continue combustion. The turbocharger includes a dual-inlet compressor in fluid communication with the intake assembly and a dual-scroll turbine in fluid communication with the exhaust assembly. The dual-inlet compressor and dual-scroll turbine are operatively connected through a shaft.

Abstract: A fresh gas supply device for an internal combustion engine having an exhaust gas turbocharger includes a charge air inlet for letting in compressed charge air from the exhaust gas turbocharger; an outlet connected to the charge air inlet, wherein the connection is closable via at least one backflow flap pivotable about a rotational flap axis; a compressed air inlet for letting compressed air into the outlet; an adjusting unit for adjusting the at least one backflow flap; at least one additional turbocharging unit having an air turbine and a compressor coupled thereto. The air turbine is disposed upstream of the compressed air inlet in the flow direction of the compressed air and compressed air can flow through the air turbine. The compressor is designed to take in and compress additional charge air from the charge air inlet and deliver compressed additional charge air to the outlet.

Abstract: An internal combustion engine includes a plurality of cylinders, an air intake line and an exhaust line collecting exhaust gas. The engine also includes an EGR line for rerouting a part of the exhaust gas from the exhaust line towards the air intake line and at least a first turbocharger comprising a first turbine driven by the exhaust gas flowing towards the atmosphere, linked to a first compressor located on the air intake line. The engine further includes a variable geometry EGR turbine located on the EGR line, driven by the EGR gas flowing in the EGR line. Thus, thanks to the pressure reduction occurring in the turbine, the EGR gas temperature is lowered, and less cooling power from the engine cooling system is required to cool down the EGR.

Abstract: The present invention relates to a multi-stage turbocharger arrangement (1), having a high-pressure turbocharger (20) which has a turbine housing (26A), a bearing housing (27A), a compressor housing (28A); and having a low-pressure turbocharger (21) which has a turbine housing (26B), a bearing housing (27B), a compressor housing (28B); wherein the turbine housings (26A, 26B) are combined to form at least one turbine housing unit (26), and/or wherein the bearing housings (27A, 27B) are combined to form at least one bearing housing unit (27), and/or wherein the compressor housings (28A, 28B) are combined to form at least one compressor housing unit (28).

Abstract: A turbocharger including a turbine wheel having a hub-to-tip ratio of no more than 60% and blades with a high turning angle, a turbine housing forming an inwardly spiraling primary-scroll passageway that significantly converges to produce highly accelerated airflow into the turbine at high circumferential angles, and a two-sided parallel compressor. The compressor and turbine each produce substantially no axial force, allowing the use of minimal axial thrust bearings. The bearing housing forms a shroud for the internal side of the compressor wheel.

Abstract: A two-stage supercharging exhaust turbocharger includes: a high-pressure-stage supercharger having a high-pressure turbine driven by exhaust gas discharged from an exhaust manifold of an engine; a low-pressure-stage supercharger having a low-pressure turbine driven by the exhaust gas used to drive the high-pressure-stage supercharger, the high-pressure-stage supercharger and the low-pressure-stage supercharger being arranged in series in an exhaust gas passageway; and an exhaust gas control valve configured to selectively change flow rates of the exhaust gas passageways of the high-pressure-stage supercharger and the low-pressure-stage supercharger, wherein an exhaust manifold incorporating casing is configured by integrally forming the exhaust manifold, a high-pressure turbine housing of the high-pressure-stage supercharger, and a valve casing accommodating the exhaust gas control valve.

Abstract: A turbine housing includes a wastegate chamber with a wastegate opening; and a wastegate disposed in the wastegate chamber where the wastegate includes a plug configured to plug the wastegate opening and where the plug includes a surface; a shaft configured for receipt by a bore in a wall of the wastegate chamber; and a rotatable arm extending from the shaft where the arm has a surface configured for contacting the surface of the plug for a closed orientation of the plug with respect to the wastegate opening to transmit force from the arm more centrally to the plug. Various other examples of devices, assemblies, systems, methods, etc., are also disclosed.

Abstract: Methods and systems are provided for operating a turbocharged engine. An engine system comprises a turbocharger, a bypass path, and a turbo-compound unit. The turbocharger may include a turbine mechanically coupled to a compressor. The turbo-compound unit may include a turbine mechanically coupled to a load, such as a generator. The turbo-compound unit may be coupled in a bypass path around the turbocharger turbine. In this manner, thermodynamic energy flowing through the bypass path may be harvested to increase the engine-operating efficiency. Further, gas flow through the bypass path may be adjusted to potentially improve the transient response of the turbocharger.

Abstract: A supercharger control device for an internal combustion engine is preferably applied to a system having a first supercharger and a second supercharger. A switching supercharging pressure setting unit sets a switching supercharging pressure used in case of switching a mode for operating the first supercharger and the second supercharger, based on a difference between a target supercharging pressure and an actual supercharging pressure. When the actual supercharging pressure reaches the switching supercharging pressure, a switching control unit performs a control of switching the mode. Therefore, it becomes possible to appropriately prevent the overshoot of the supercharging pressure at the time of switching the mode.

Abstract: The disclosure relates to a method for controlling a turbocharger system of an internal combustion engine. The method comprises controlling a first bypass valve of a high pressure exhaust gas turbine and a second bypass valve of a low pressure gas turbine on the basis of a turbine model, the first and second bypass valves continuously variable. In this way, turbocharger system efficiency may be maximized.

Abstract: A method of boosting air to an intake manifold (20) of an engine (16) having cylinders (C) that emit exhaust gas includes the steps of dividing the exhaust gas emitted from the cylinders into a first exhaust passageway (26A) and a second exhaust passageway (26B), and fluidly communicating at least a portion of the exhaust gas (EG1) from the first exhaust passageway to a divided turbocharger (28). The method also includes the steps of fluidly communicating at least a portion of the exhaust gas (EG1) from the second exhaust passageway (26B) to the divided turbocharger (28), and fluidly communicating the exhaust gas from the divided turbocharger to an undivided turbocharger (42). Further steps in boosting the air include compressing air (CA) at a compressor (48) of the undivided turbocharger (42), and fluidly communicating the compressed air to the intake manifold (20).

Abstract: A natural gas compression system is provided. The system may include a natural gas compressor configured to compress, and thereby pump, natural gas through a pipeline. The system may also include a natural gas burning engine, operatively coupled to the gas compressor, the engine being supplied with air by an induction system. The induction system may include a supercharger driven by the engine and configured to compress intake air and a turbocharger downstream from the supercharger and driven by exhaust gases produced by the engine. The induction system may also include a supercharger compressor bypass configured to selectively recirculate a portion of the compressed output of the supercharger upstream of the supercharger.

Abstract: A system and method for recovering the unused energy of exhaust gas of an internal combustion engine is provided. A charge device for generating compressed intake air for the internal combustion engine is driven by exhaust gas, and an air compressor having at least one compression stage is connected to the charge device to withdraw at least a partial quantity of the compressed intake air, the partial quantity of the compressed intake air of the charge device that can be withdrawn by the air compressor is adjustable.

Abstract: In an internal combustion engine and a method of operation the internal combustion engine which includes a high pressure and a low pressure turbocharger having exhaust gas turbines arranged in series in an engine exhaust line provided with a high pressure exhaust gas recirculation line and a low pressure exhaust gas recirculation line via which exhaust gas can be conducted to an inlet line of the engine, the arrangement is switchable depending on the engine speed between an exhaust gas recirculation by way of the high pressure line and an exhaust gas recirculation by way of both, the high pressure and the low pressure line, to achieve low emissions and low fuel consumption.

Abstract: A system for recovering, engine exhaust energy is provided. The system includes an exhaust system including a first exhaust branch and a second exhaust branch. The system includes a first and a second group of exhaust valves associated with a plurality of engine cylinders. The system also includes an energy recovering assembly. The system further includes a control mechanism configured to control at least one of the first and second groups of exhaust valves according to a determined timing strategy based on at least one engine operating parameter.

Abstract: A device for utilizing the waste heat of an internal combustion includes a single-stage or multi-stage supercharging device, which is designed as an exhaust-gas turbocharger in particular. The single-stage or multi-stage supercharging device is assigned an additional supercharging device including an expansion machine acted upon by an auxiliary circuit, in particular a steam circuit.

Abstract: A duct for connection between an exhaust manifold and a high-pressure turbine inlet include a cylindrical duct body defining a longitudinal axis. A frustoconical outlet nozzle connected at one end of the duct body and extending at about eighty-five degrees from the longitudinal axis. The duct further includes an inlet bell connected at the other end of the duct body and extending at about fifty degrees from the longitudinal axis.

Abstract: A turbocharger system for a vehicle may include a turbocharger, a tank for compressed gas and an exhaust manifold conduit in fluid communication with an inlet of the turbocharger. The tank is in fluid communication with the manifold conduit and is arranged to push compressed gas into the manifold conduit during a predetermined pulse duration time period for initial compressor spin up in the turbocharger.

Abstract: An exhaust casing for use with a turbocharger includes a hollow body that has two mutually opposed large walls, which extend along first and second major dimensions of the hollow body and are spaced apart by a minor dimension of the hollow body, the hollow body defining a plenum and an inlet nozzle opening into the plenum along the minor dimension of the hollow body. The casing further includes an outlet nozzle opening from the plenum along one of the major dimensions of the hollow body.

Abstract: A turbocharger system includes: an engine including a first cylinder head constituting a first bank and a second cylinder head constituting a second bank; a center turbocharger formed between the first bank and the second bank, and connected to exhaust and intake manifolds of the first and second banks; a first turbocharger connected to the other exhaust and intake manifolds of the first bank; and a second turbocharger connected to the other exhaust and intake manifolds of the second bank.

Abstract: A four-cylinder engine has a valve overlap period during which an exhaust valve and an intake valve of each cylinder are both opened. Cylinder pipes for cylinders having adjacent ignition timings of the engine are connected to a turbo charger, and cylinder pipes for cylinders having adjacent ignition timings are connected to another turbo charger. Accordingly, a properly great supercharging pressure can be obtained in a low engine-speed area.

Abstract: In a vehicle, which is provided with: a primary turbo and a secondary turbo, each of which is of an exhaust driven type; an exhaust changeover valve and an intake changeover valve, which are placed in a secondary exhaust passage and a secondary intake passage corresponding to the secondary turbo, respectively; and an intake bypass valve placed in an intake bypass passage, an ECU sets the opening/closing state of each changeover valve to an opening/closing state corresponding to a twin turbo mode at the time of engine stop, and it uses the drive control of each changeover valve which is necessitated in the transition to a single turbo mode at the engine start, thereby performing the sticking detection of the changeover valve at the same time.

Abstract: One embodiment is a method including determining whether an ammonia storage device has a stored quantity of ammonia, predicting an impending ammonia release from the ammonia storage device, determining a NOx increase amount in response to the impending ammonia release, and increasing an amount of NOx provided by an engine based on the NOx increase amount. In certain embodiments, determining the NOx increase amount in response to the impending ammonia release comprises determining a NOx increase schedule based on the stored quantity of ammonia. In certain embodiments, the NOx increase schedule comprises a specified NOx increase time period, and in certain further embodiments, the method further includes decrementing the specified NOx increase time period based on an estimated catalyst degradation value.

Abstract: A damper system for placement between a supercharger and a turbocharger. The damper is located in a plenum placed within the air path from the supercharger to the turbocharger. If the plenum is under positive pressure from the supercharger, the damper seals shut against the plenum, allowing the supercharger to build positive boost pressure to the turbocharger. The damper is designed to stay closed until the plenum experiences a slightly negative pressure. The damper then opens to expose the turbocharger inlet to atmospheric pressure. This allows the turbocharger to intake the airflow from the smaller supercharger, but also to intake additional airflow from the ambient air at atmospheric pressure. The damper allows an engine to take advantage of the low RPM and low load performance and efficiency of smaller superchargers and the performance and efficiency of larger turbochargers under higher load and higher exhaust mass flow rate.

Abstract: A device for cooling charge air, specifically for cooling charge air which is compressed in a compressor of at least one exhaust-gas turbocharger and which is to be supplied to an internal combustion engine, wherein at least two charge-air coolers are arranged in a common housing, specifically in such a way that charge air to be cooled can be supplied separately to the charge-air coolers arranged in the common housing via in each case one separate incoming-air chamber provided by the common housing, and that cooled charge air can be discharged jointly from the charge-air coolers arranged in the common housing via a common outgoing-air chamber provided by the common housing.

Abstract: A two-stage turbocharger assembly for an internal combustion engine is provided. The assembly has a single low pressure turbocharger, and more than two high pressure turbochargers arranged in parallel with each other. The compressor outlet of the single low pressure turbocharger is operatively connected to the compressor inlets of the high pressure turbochargers. The turbine outlets of the high pressure turbochargers are operatively connected to the turbine inlet of the single low pressure turbocharger.

Abstract: A compressor system for a vehicle includes a compressor driven by a drive motor of the vehicle and a suction air conduit for supplying air that has already been precompressed by a turbocharger of the drive motor to the compressor. A mechanism is disposed in the suction air guide for reducing the flow cross-section. The mechanism is able to limit the charging pressure of the already precompressed air supplied to the compressor. A method for controlling a compressor system having a turbocharged compressor limits a charging pressure of the already precompressed air to an adjustable maximum value.

Abstract: An engine system is provided. The system comprises an engine, first and second compressors supplying air to the engine, a first compressor recirculation valve adjustable to two restriction levels, and a second compressor recirculation valve adjustable to three or more restriction levels. In this way, the first and second compressor recirculation valves may be controlled to avoid compressor surge while providing a sufficient amount of boost to meet power demands.

Abstract: A supercharger compressor includes a plurality of rotors rotatably mounted in a housing, a first inlet for air, a second inlet for recirculated exhaust gas, and a flow separator. The flow separator is arranged interior the housing and configured to form a slideable seal with at least one rotor of the plurality of rotors, the slideable seal fluidically isolating the first inlet from the second inlet, at least in part, and retarding pressure equalization therebetween.

Abstract: Methods and systems are provided for an engine including a first turbocharger having a first compressor and a second turbocharger having a second compressor. An EGR differential between the first compressor and the second compressor may be increased under a condensation condition, and decreased under a surge condition. The EGR differential may also be decreased when a compressor outlet temperature exceeds an outlet temperature threshold.

Abstract: A multistage turbocharging system (1) in which the thickness of at least either one of a valve body (51a) that opens and closes a bypass flow passage opening and a washer (51b) that fixes the valve body (51a) to a mounting portion (52) is greater than the minimum width of a flow passage from a valve assembly (51) to a turbine impeller (2d) of the first turbocharger (2).

Abstract: An internal combustion engine having an exhaust gas recirculation device for recirculating exhaust gas of the internal combustion engine to a fresh-air side of the internal combustion engine. For this purpose, it is provided that the exhaust gas recirculation device has at least one compressor for compressing the exhaust gas supplied to the fresh-air side of the internal combustion engine.

Abstract: The disclosure provides a turbo-charging apparatus for a vehicle engine, which includes a first and second turbocharger, an inter-turbine passage connecting a discharging port of a first turbocharger turbine with an introducing port of a second turbocharger turbine, a bypass passage connecting an introducing passage of the first turbocharger turbine with the inter-turbine passage, and a control valve for opening and closing the bypass passage. The inter-turbine passage extends substantially straight from the discharging port of the first turbocharger turbine toward the second turbocharger when viewed from a direction parallel to turbine shafts of the first and second turbochargers, which are arranged substantially parallel to each other, so that the inter-turbine passage connects with an outer circumferential part of the second turbocharger turbine so as to extend in a direction tangent to an outer circumference direction of the second turbocharger turbine.

Abstract: In the case where a low-pressure-side supercharging pressure acquired value corresponding to the pressure of inlet gas at the outlet of a low-pressure compressor operated in a twin supercharging mode is less than a target supercharging pressure in a single supercharging mode, changeover from the twin supercharging mode to the single supercharging mode is prohibited. Meanwhile, in the case where the low-pressure-side supercharging pressure acquired value is equal to or greater than the target supercharging pressure, the changeover from the twin supercharging mode to the single supercharging mode is permitted. Alternatively, in the case where a supercharging pressure during operation in the single supercharging mode is less than a target value of the pressure of supply gas at the outlet of the low-pressure compressor in the twin supercharging mode, changeover from the single supercharging mode to the twin supercharging mode is prohibited.

Abstract: A drive train having an internal combustion engine which includes an output shaft feeding drive power into the drive train. A first turbo charger includes a first exhaust-gas turbine arranged in an exhaust-gas flow and mounted rotatably in a turbine housing that drives a first fresh-air compressor via a first turbine shaft. A turbo-compound system includes a power turbine arranged in the exhaust-gas flow and can be drive connected via a power turbine shaft to the output shaft, with the power turbine shaft mounted rotatably in a power turbine housing and extending parallel to the turbine shaft. The turbine housing and power turbine housing can be supported in or on or integrated into a transmission housing. The first turbocharger is arranged radially outside the turbo-compound system. The first turbocharger and turbo-compound system are arranged on a common side or on different and adjoining or opposite sides of the transmission housing.

Abstract: Disclosed is an apparatus, system, and method to utilize road markers to control vehicle speeds. The road markers may be commanded to emit a light for a pre-determined period of time. Further, the road markers may be controlled such that they are commanded to emit the light based upon a timing sequence associated with a desired speed so that the road markers emit light in a strobe pattern. In this way, if a vehicle is traveling at the desired speed, then the strobe pattern appears static to a driver of the vehicle. Additionally, a message may be transmitted from a traffic authority to increase or decrease the timing sequence of the strobe pattern to increase or decrease the speed to the desired speed.

Abstract: An arrangement for a supercharged combustion engine includes a first compressor compressing air in the engine air inlet line as a first stage and a second compressor compressing the air in the inlet line as a second stage, a first coolant-cooled charge air cooler cooling the air after it has been compressed in the first stage and before it is compressed in the second stage, and an air-cooled charge air cooler cooling the compressed air when it has been compressed by the first stage, a second coolant-cooled charge air cooler cooling the compressed air after it has been compressed in the second stage and before it is compressed in the air-cooled charge air cooler. Exhaust gases in an exhaust line from the engine drive turbines which operate the compressors. A return line from the exhaust line and connected into the inlet line has a cooler for the exhaust gases before mixing the gases with the inlet air.

Abstract: A combustion chamber of an internal combustion engine has at least a first and a second exhaust port, which are decoupled downstream of the combustion chamber. The first exhaust port is opened before the second exhaust port during an expansion stroke of the piston. The first exhaust port is coupled to a high-pressure turbine and the second exhaust port is coupled to a low-pressure turbine. By directing exhaust gases at higher pressure to the high-pressure turbine and gases at lower pressure to the low-pressure turbine, the overall energy recovery from the exhaust gases is greater than a system with one or more exhaust turbines coupled in series with all of the exhaust ports.

Abstract: A butterfly valve for a turbocharger system in which the leak path through the valve is controlled by keeping the clearance between either a shaft of the valve and two bushings small or the clearance between the bushings and the counter bores in the valve element small, and making the other clearance larger.

Abstract: Multi-stage turbocharging, and more particularly, an advanced multi-stage turbocharging system using the variable turbine power of one or more variable turbine geometry (VTG) turbochargers to adjust compressor boost and exhaust back pressure to engine operating demands. The invention further relates to a turbocharged internal combustion engine, in particular a turbocharged internal combustion engine with at least one high-pressure turbine stage and one downstream low-pressure turbine stage, wherein the high-pressure turbine may be a single-flow or double-flow type, wherein the high pressure or low pressure compressor may be variable geometry, wherein the high pressure or low pressure compressor may be variably bypassed, and wherein the high pressure or low pressure turbine may be provided with an active control variable bypass or wastegate.

Abstract: An assembly can include a valve seat for an exhaust bypass valve of a serial turbocharger system where the valve seat includes a base portion and a wall portion that extends axially away from the base portion; and a gasket that includes a planar portion that defines a perimeter and a socket disposed interior to the perimeter, where the socket includes a valve seat surface axially recessed from the planar portion and configured to position the seat. In various examples, the valve seat is positioned in the socket of the gasket and fixed to the gasket. Various other examples of devices, assemblies, systems, methods, etc., are also disclosed.

Abstract: Turbines and compressors, which constitute superchargers, are disposed in series on an exhaust gas passage and an air intake passage, respectively. The supercharger is equipped with a supercharger rotation sensor, which transmits a detection signal obtained according to the rotation of the compressor to a control device, a bypass passage, which bypasses exhaust gas from the upstream side to the downstream side of the turbine, and a bypass valve, which regulates the flow rate of exhaust gas flowing through the bypass passage. Control device regulates the rotational speed of the compressors in a high-efficiency range by producing a control signal based on the detection signal from the supercharger rotation sensor, and sending the control signal to the bypass valve.

Abstract: A turbocharger control system for a high-pressure turbocharger and a low-pressure turbocharger includes a turbo mode determination module and a transition control module. The turbo mode determination module determines a transition from a dual turbo mode to a single turbo mode. The high-pressure turbocharger is active in the dual turbo mode and idle in the single turbo mode. The transition control module determines a turbine efficiency of the high-pressure turbocharger and controls the high-pressure turbocharger during the transition based on a predetermined maximum turbine efficiency equation.

Abstract: A method of controlling an engine includes manipulating a wastegate to maintain the operation of the turbocharger within an optimum operating range. A combustion air bypass valve is manipulated between an open position and a closed position to create a negative pressure differential across a supercharger. The supercharger is sequentially disposed in-line before the turbocharger. The negative pressure differential is converted into a torque by the supercharger and transmitted from the supercharger back to the engine to increase the operating efficiency of the engine.

Abstract: Various systems and methods are provided for routing exhaust from an engine. In one example, a system includes a high pressure turbine and a low pressure turbine. The system further includes a first passage for routing exhaust from a first subset of cylinders, bypassing the high pressure turbine, to upstream of the low pressure turbine in an exhaust passage of the engine, and a second passage for routing exhaust from a second, different, subset of cylinders to upstream of the high pressure turbine.

Abstract: A first turbocharger comprises a first center housing and a first return passage. A second turbocharger comprises a second center housing and a second return passage. The first return passage joins the second return passage at a junction. The length of the second return passage from the second center housing to the junction is longer than that of the first return passage from the first center housing to the junction. A bellows-shaped vibration absorption portion is provided at the second return passage. The first return passage comprises a first upstream return passage and a first downstream return passage, and the first upstream and downstream return passages are connected to each other via the flexible hose.

Abstract: A twin turbo assembly is provided for an automotive vehicle that includes a first and second air intake for, a first and second turbo charger that includes, but is not limited to a first and second compressor connected to the first air intake, a first and second intake duct connecting the first turbo charger to a combustion engine. A first and second bypass valve is provided to connect the first and second air intake, respectively to the first and second intake duct bypassing the first and second compressor. Overpressure inside the intake ducts can be discharged to a volume between the air filter and the respective compressor. The released pressure prevents or at least reduces the risk that compressed air inside the intake ducts may flow against the first compressor and the second compressor, so that the noise emission associated with this backflow is reduced or even prevented.