AU2014200324A1 - Turbocharger, system, and method for draining fluid from a turbocharger - Google Patents

Abstract

Various methods and systems are provided for removing fluid from a turbocharger turbine. In one example, a turbocharger comprises a turbine including a casing housing a rotor, a drain passage coupled to the casing, and an air jet coupled to the drain passage, the air jet supplying intake air from a high-pressure compressor outlet to the drain passage. 20 Atmosphere - e 208 238 24A0 -236 From HP compressor Atmosphere

Description

TURBOCHARGER, SYSTEM, AND METHOD FOR DRAINING FLUID FROM A TURBOCHARGER [0001] This application claims priority from United States of America Application No. 13/749,893 filed on 25 January 2013, the contents of which are to be taken as incorporated herewith by this reference. FIELD [0002] Embodiments of the subject matter disclosed herein relate to a turbocharger for an internal combustion engine. BACKGROUND [0003] Turbochargers are devices used to increase the power output of an engine by compressing air into the engine with a compressor driven by a turbine that harvests energy from the hot engine exhaust gases. Over time, as turbocharged engines operate, some of the additives in the lubricating oil are deposited on the turbocharger turbine nozzle ring and turbine wheel blades. These deposits tend to be readily dissolved in rainwater. Many turbocharged engines, such as those used in locomotives, are designed with a simple stack or relatively open muffler directly above the turbocharger turbine. Thus, if the engine is shut down and no gas is flowing through the turbine, rainwater can accumulate around the stationary turbine parts. If the water level is high enough and the water is undisturbed for a period of time, the deposits on the turbine blades partially or completely submerged in the water can be locally dissolved, leading to a significant rotor imbalance once the engine is restarted. 1 [0004] The discussion of documents, acts, materials, devices, articles and the like is included in this specification solely for the purpose of providing a context for the present invention. It is not suggested or represented that any or all of these matters formed part of the prior art base or were common general knowledge in the field relevant to the present invention as it existed before the priority date of each claim of this application. BRIEF DESCRIPTION [0005] According to an aspect of the invention, a turbocharger comprises a turbine including a casing housing a rotor, a drain passage coupled to the casing, and an air jet coupled to the drain passage. The air jet is configured to supply intake air from a high pressure compressor outlet to the drain passage. [0006] In this way, according to one aspect of the invention, water that has accumulated in the turbine casing may be passively drained via the drain passage. To prevent leakage of exhaust gas out of the drain passage, compressed intake air may be routed to the drain passage, sealing the drain passage when the pressure of the compressed intake air is greater than the pressure of the exhaust in the turbine. This may occur, for example, during engine operation when intake air is directed through the high pressure compressor. Then, when compressed intake air is not available (such as when the engine is off), the water may drain out of the turbine. [0007] According to another aspect of the present invention, there is provided a system, comprising: an engine; a first turbocharger including a first turbine mechanically coupled to a first compressor; a second turbocharger including a second turbine located downstream of the first turbine in an exhaust flow path, the second turbine mechanically coupled to a second compressor, the second compressor located upstream of the first 2 compressor in an intake flow path; a drain passage coupling the second turbine to atmosphere; and a compressed air line coupling the drain passage to an outlet of the first compressor. [0008] According to yet another aspect of the present invention, there is provided a method, comprising: when a pressure of intake air at a high-pressure compressor outlet is greater than a pressure of exhaust gas downstream of a low-pressure turbine, sealing a flow of exhaust gas from the low-pressure turbine through a drain passage to atmosphere; and when the pressure of intake air at the high-pressure compressor outlet is not greater than the pressure of exhaust gas downstream of the low-pressure turbine, draining fluid from the low-pressure turbine through the drain passage. [0009] It should be understood that the brief description above is provided to introduce in simplified form a selection of concepts that are further described in the detailed description. It is not meant to identify key or essential features of the claimed subject matter, the scope of which is defined uniquely by the claims that follow the detailed description. Furthermore, the claimed subject matter is not limited to implementations that solve any disadvantages noted above or in any part of this disclosure. BRIEF DESCRIPTION OF THE DRAWINGS [0010] The present invention will be better understood from reading the following description of non-limiting embodiments, with reference to the attached drawings, wherein below: [0011] FIG. 1 shows a schematic diagram of a rail vehicle with an engine according to an embodiment of the invention. 3 [0012] FIG. 2 shows a cross-sectional view of a turbocharger according to an embodiment of the invention. [0013] FIG. 3 shows a flow chart illustrating a method for removing accumulated fluid from a turbocharger according to an embodiment of the invention. DETAILED DESCRIPTION [0014] The following description relates to various embodiments of a turbocharger including a drain passage coupled to the casing of the turbocharger. The drain passage may passively drain accumulated water out of the turbine when the engine is not operating. However, during engine operation, to prevent the drain passage from providing a path for exhaust gas to leak out of the turbine and to the vehicle cabin (for example), the drain passage may be coupled to the outlet of a compressor. During engine operation, the compressor may generate air of higher pressure than the exhaust downstream of the turbine. This high pressure air flows to the drain passage and prevents flow of exhaust gas out of the turbine casing. The drain passage may be coupled to the turbine of a low-pressure turbocharger and the compressed intake air may be directed to the drain passage from a compressor outlet of a high-pressure turbocharger. The intake air from the outlet of the high-pressure compressor may be of pressure greater than atmospheric at substantially all engine operating conditions. For example, the intake air at the high-pressure compressor outlet may greater than atmospheric at each throttle position (e.g., for some rail vehicles, notched throttle position), including idle. [0015] The approach described herein may be employed in a variety of engine types, and a variety of engine-driven systems. Some of these systems may be stationary, while others may be on semi-mobile or mobile platforms. Semi-mobile platforms may be 4 relocated between operational periods, such as mounted on flatbed trailers. Mobile platforms include self-propelled vehicles. Such vehicles can include on-road transportation vehicles and off-highway vehicles (OHV), the latter of which include mining equipment, marine vessels, and locomotives and other rail vehicles. For clarity of illustration, a locomotive is provided as an example of a mobile platform supporting a system incorporating an embodiment of the invention. [0016] Before further discussion of the approach for draining fluid from a turbocharger turbine, an example of a platform is disclosed in which the engine system may be installed in a vehicle, such as a rail vehicle. For example, FIG. 1 shows a block diagram of an embodiment of a vehicle system 100 (e.g., a locomotive system), herein depicted as a rail vehicle 106, configured to run on a rail 102 via a plurality of wheels 110. As depicted, the rail vehicle 106 includes an engine 104. In other non-limiting embodiments, the engine 104 may be a stationary engine, such as in a power-plant application, or an engine in a marine vessel or off-highway vehicle propulsion system as noted above. [0017] The engine 104 receives intake air for combustion from an intake, such as an intake manifold 115. The intake may be any suitable conduit or conduits through which gases flow to enter the engine. For example, the intake may include the intake manifold 115, the intake passage 114, and the like. The intake passage 114 receives ambient air from an air filter (not shown) that filters air from outside of a vehicle in which the engine 104 may be positioned. Exhaust gas resulting from combustion in the engine 104 is supplied to an exhaust, such as exhaust passage 116. The exhaust may be any suitable conduit through which gases flow from the engine. For example, the exhaust may 5 include an exhaust manifold 117, the exhaust passage 116, and the like. Exhaust gas flows through the exhaust passage 116, and out of an exhaust stack of the rail vehicle 106. In one example, the engine 104 is a diesel engine that combusts air and diesel fuel through compression ignition. In other non-limiting embodiments, the engine 104 may combust fuel including gasoline, kerosene, biodiesel, or other petroleum distillates of similar density through compression ignition (and/or spark ignition). [0018] In one embodiment, the rail vehicle 106 is a diesel-electric vehicle. As depicted in FIG. 1, the engine 104 is coupled to an electric power generation system, which includes an alternator/generator 140 and electric traction motors 112. For example, the engine 104 is a diesel engine that generates a torque output that is transmitted to the alternator/generator 140 which is mechanically coupled to the engine 104. The alternator/generator 140 produces electrical power that may be stored and applied for subsequent propagation to a variety of downstream electrical components. As an example, the alternator/generator 140 may be electrically coupled to a plurality of traction motors 112 and the alternator/generator 140 may provide electrical power to the plurality of traction motors 112. As depicted, the plurality of traction motors 112 are each connected to one of a plurality of wheels 110 to provide tractive power to propel the rail vehicle 106. One example configuration includes one traction motor per wheel. As depicted herein, six pairs of traction motors correspond to each of six pairs of wheels of the rail vehicle. In another example, alternator/generator 140 may be coupled to one or more resistive grids 142. The resistive grids 142 may be configured to dissipate excess engine torque via heat produced by the grids from electricity generated by alternator/generator 140. 6 [0019] In the embodiment depicted in FIG. 1, the engine 104 is a V-12 engine having twelve cylinders. In other examples, the engine may be a V-6, V-8, V-10, V-16, 1-4, 1-6, 1-8, opposed 4, or another engine type. As depicted, the engine 104 includes a subset of cylinders 105, which includes six cylinders that supply exhaust gas exclusively to a first exhaust manifold 117, and a subset of cylinders 107, which includes six cylinders that supply exhaust gas exclusively to a second exhaust manifold 119. In other embodiments, all cylinders may supply exhaust gas to a single exhaust manifold. [0020] As depicted in FIG. 1, the cylinders 105 and cylinders 107 are coupled to the exhaust passage 116 to route exhaust gas from the engine to atmosphere (after it passes through a muffler 130 and first and second turbochargers 120 and 124). [0021] As depicted in FIG. 1, the vehicle system 100 further includes a two-stage turbocharger with the first turbocharger 120 and the second turbocharger 124 arranged in series, each of the turbochargers 120 and 124 arranged between the intake passage 114 and the exhaust passage 116. The two-stage turbocharger increases air charge of ambient air drawn into the intake passage 114 in order to provide greater charge density during combustion to increase power output and/or engine-operating efficiency. The first turbocharger 120 operates at a relatively lower pressure, and includes a first turbine 121 which drives a first compressor 122. The first turbine 121 and the first compressor 122 are mechanically coupled via a first shaft 123. The first turbocharger may be referred to the "low-pressure stage" of the turbocharger. The second turbocharger 124 operates at a relatively higher pressure, and includes a second turbine 125 which drives a second compressor 126. The second turbocharger may be referred to the "high-pressure stage" 7 of the turbocharger. The second turbine and the second compressor are mechanically coupled via a second shaft 127. [0022] As explained above, the terms "high pressure" and "low pressure" are relative, meaning that "high" pressure is a pressure higher than a "low" pressure. Conversely, a "low" pressure is a pressure lower than a "high" pressure. [0023] As used herein, "two-stage turbocharger" may generally refer to a multi-stage turbocharger configuration that includes two or more turbochargers. For example, a two stage turbocharger may include a high-pressure turbocharger and a low-pressure turbocharger arranged in series, three turbocharger arranged in series, two low pressure turbochargers feeding a high pressure turbocharger, one low pressure turbocharger feeding two high pressure turbochargers, etc. In one example, three turbochargers are used in series. In another example, only two turbochargers are used in series. [0024] While a high-pressure turbocharger including a high-pressure turbine coupled to a high-pressure compressor is illustrated, in some embodiments the high-pressure compressor may not be coupled to a high-pressure compressor but may instead be driven by an alternate mechanism, such as via a coupling to the engine, via a motor, etc. [0025] In the embodiment shown in FIG. 1, the second turbocharger 124 is provided with a turbine bypass valve 128 which allows exhaust gas to bypass the second turbocharger 124. The turbine bypass valve 128 may be opened, for example, to divert the exhaust gas flow away from the second turbine 125. In this manner, the rotating speed of the compressor 126, and thus the boost provided by the turbochargers 120, 124 to the engine 104 may be regulated during steady state conditions. Additionally, the first turbocharger 120 may also be provided with a turbine bypass valve. In other 8 embodiments, only the first turbocharger 120 may be provided with a turbine bypass valve, or only the second turbocharger 124 may be provided with a turbine bypass valve. Additionally, the second turbocharger may be provided with a compressor bypass valve (not shown), which allows gas to bypass the second compressor 126 to avoid compressor surge, for example. In some embodiments, first turbocharger 120 may also be provided with a compressor bypass valve, while in other embodiments, only first turbocharger 120 may be provided with a compressor bypass valve. [0026] A compressed air line 129 may couple the outlet of high-pressure compressor 126 to low-pressure turbine 121. As will be explained in more detail below with respect to FIG. 2, compressed air line 129 may provide air of higher pressure than the exhaust downstream of low-pressure turbine 121 in order to prevent leakage of exhaust out of turbine 121 during engine operation. In some embodiments, compressed air line 129 may couple the outlet of a compressor of a supercharger (not shown in FIG. 1) driven by the engine. [0027] The vehicle system 100 further includes a muffler 130 or other silencer. Muffler 130 may be open to atmosphere via one or more exhaust stacks (not shown). Exhaust gas exiting first turbine 121 may travel through muffler 130 before being expelled to atmosphere. [0028] The vehicle system 100 further includes the control unit 180, which is provided and configured to control various components related to the vehicle system 100. In one example, the control unit 180 includes a computer control system. The control unit 180 further includes non-transitory, computer readable storage media (not shown) including code for enabling on-board monitoring and control of engine operation. The 9 control unit 180, while overseeing control and management of the vehicle system 100, may be configured to receive signals from a variety of engine sensors, as further elaborated herein, in order to determine operating parameters and operating conditions, and correspondingly adjust various engine actuators to control operation of the vehicle system 100. For example, the control unit 180 may receive signals from various engine sensors including, but not limited to, engine speed, engine load, boost pressure, ambient pressure, exhaust temperature, exhaust pressure, etc. Correspondingly, the control unit 180 may control the vehicle system 100 by sending commands to various components such as traction motors, alternator, cylinder valves, throttle, heat exchangers, wastegates or other valves or flow control elements, etc. [0029] FIG. 2 shows a cross-section of an embodiment of a turbocharger 200 that may be coupled to an engine. Turbocharger 200 may be one stage of a multi-stage turbocharger. In one example, turbocharger 200 may be a low-pressure turbocharger, such as turbocharger 120 described above with reference to FIG. 1. In one example, the turbocharger may be bolted to the engine. In another example, the turbocharger 200 may be coupled between the exhaust passage and the intake passage of the engine. In other examples, the turbocharger may be coupled to the engine by any other suitable manner. [0030] The turbocharger 200 includes a turbine stage 202 and a compressor 204. Exhaust gases from the engine pass through the turbine stage 202, and energy from the exhaust gases is converted into rotational kinetic energy to rotate a shaft 206 which, in turn, drives the compressor 204. Ambient intake air is compressed (e.g., pressure of the air is increased) as it is drawn through the rotating compressor 204 such that a greater mass of air may be delivered to the cylinders of the engine. 10 [0031] The turbocharger includes a casing 210. In some embodiments, the turbine stage 202 and the compressor 204 may have separate casings which are bolted together, for example, such that a single unit (e.g., turbocharger 200) is formed. As an example, the turbocharger may have a casing made of cast iron and the compressor may have a casing made of an aluminum alloy. [0032] The turbocharger 200 further includes bearings 208 to support the shaft 206, such that the shaft may rotate at a high speed with reduced friction. As depicted in FIG. 2, the turbocharger 200 further includes two non-contact seals (e.g., labyrinth seals), a turbine labyrinth seal 214 positioned between an oil cavity 212 and the turbine 202 and a compressor labyrinth seal 216 positioned between the oil cavity 212 and the compressor 204. [0033] Exhaust gas may enter through an inlet, such as gas inlet transition region 220, and pass over a nose piece 222. A nozzle ring 224 may include airfoil-shaped vanes arranged circumferentially to form a complete 3600 assembly. The nozzle ring 224 may act to optimally direct the exhaust gas to a turbine disc/blade assembly, including blades 226 and a turbine disc 228, coupled to the shaft 206. In some embodiments, the turbine disc and blades may be an integral component, known as a turbine blisk. The rotating assembly of the turbine, including the turbine disc, blades, and shaft, may collectively be referred to as the turbine rotor. [0034] The blades 226 may be airfoil-shaped blades extending outwardly from the turbine disc 228, which rotates about the centerline axis of the engine. An annular shroud 230 is coupled to the casing at a shroud mounting flange 232 and arranged so as to closely surround the blades 226 and thereby define the flowpath boundary for the exhaust 11 stream flowing through the turbine stage 202. Cavity 234 may be an open space under shroud 230 that may be configured to receive exhaust gas that has passed over the turbine rotor. Cavity 234 may be open to atmosphere, in that turbine casing 210 at the top of the turbine stage may open to atmosphere and lead down to cavity 234. As such, water passing through the exhaust stack and muffler (e.g., rain water) may enter turbine casing 210 and collect in cavity 234. Cavity 234 may be the vertically lowest point of the turbine casing that is open to atmosphere, relative to the vehicle ground. For example, the vertical low point may be a lowest point when the turbocharger is installed in a vehicle and the vehicle is on a level surface for motive operation. [0035] As explained previously, if water is allowed to accumulate in the turbine casing while the engine is shut down, the build-up of various particulates on the turbine disc and blades may dissolve when exposed to the accumulated water. This may result in an unbalanced turbine rotor, leading to turbocharger degradation. To drain any accumulated water, a drain passage 236 may be coupled to turbine casing 210 in cavity 234. The drain passage 236 may comprise an opening at the bottom of cavity 234 and/or other suitable fluid drainage configuration, such as a straw, nipple, etc. Drain passage 236 may lead out of turbine casing 210 and to atmosphere (e.g., external to the vehicle/system in which the turbocharger is installed). In this way, fluid such as water may passively drain out of turbine stage 202. [0036] However, drain passage 236 may provide a path for the exhaust gas flowing through the turbocharger. In some examples, the exhaust gas may leak out of turbine stage 202 to the vehicle cabin or other vehicle compartment via the drain passage 236. To prevent the leak of exhaust gas via drain passage 236, drain passage 236 may be 12 supplied with pressurized air during engine operation. In the example depicted in FIG. 2, compressed intake air from downstream of a high-pressure compressor (such as second compressor 126 of FIG. 1) may be directed to drain passage 236 via compressed air line 238, similar to the compressed air line 129 illustrated in FIG. 1. [0037] In an example, compressed air line 238 may include an air jet 240 or ejector, venturi, nozzle, etc., that creates an increase in velocity of the air moving through compressed air line 238. Air jet 240 may include a restricted throat or other configuration that creates vacuum when compressed air is drawn through compressed air line 238. This vacuum may act to also drawn in air from atmosphere and/or otherwise block leakage of exhaust from drain passage 236. As such, to prevent leakage of exhaust from drain passage 236, air at greater than atmospheric pressure is supplied to the compressed air line during all engine operating conditions. [0038] The turbine stage 202 is an axial turbine, as the exhaust flow impels on the turbine blades in an axial direction relative to the center axis of the engine. However, in some embodiments, turbine stage 202 may be a radial turbine. [0039] FIG. 3 is a flow chart illustrating a method 300 for removing accumulated fluid from a turbine casing. At 302, method 300 includes sealing a flow of exhaust gas from a low-pressure turbine to atmosphere through a drain passage during engine operation. As explained above, the drain passage may be coupled to a cavity of the low pressure turbine that may accumulate water. The drain passage may be open to atmosphere in order to passively drain water out of the turbine. However, to ensure exhaust gas flowing through the turbocharger during engine operation does not leak out of the turbine, the drain passage may be sealed. This includes, at 304, directing air from 13 a high-pressure compressor outlet to the drain passage. The air from the high-pressure compressor may be of higher pressure than the exhaust in the turbine. [0040] At 306, method 300 includes draining fluid from the low-pressure turbine to atmosphere through the drain passage during engine off conditions. When the engine is not operating, exhaust is not produced and thus no exhaust is present in the turbine to leak out of the drain passage. Thus, compressed air is not supplied to the drain passage, and any accumulated fluid (e.g., water) is allowed to passively drain via the drain passage. [0041] An embodiment relates to turbocharger. The turbocharger comprises a turbine including a casing that houses a rotor, a drain passage coupled to the casing, and an air jet coupled to the drain passage. The air jet is configured to supply intake air from a high-pressure compressor outlet to the drain passage. Another embodiment relates to a vehicle having such a turbocharger installed as part of the vehicle. For example, in embodiments, the vehicle is a locomotive or other rail vehicle. [0042] Another embodiment relates to a system. The system comprises an engine, a first turbocharger including a first turbine mechanically coupled to a first compressor, and a second turbocharger including a second turbine located downstream of the first turbine in an exhaust flow path. The second turbine is mechanically coupled to a second compressor. The second compressor is located upstream of the first compressor in an intake flow path. The system further comprises a drain passage coupling the second turbine to atmosphere, and a compressed air line coupling the drain passage to an outlet of the first compressor. An air jet may be coupled to the compressed air line. In operation, in embodiments, the drain passage is configured to passively drain fluid from 14 the second turbine when the engine is not operating, and the drain passage is configured to seal a flow of exhaust gas from the second turbine to atmosphere when the engine is operating (e.g., when the engine is operating, compressed intake air flows from the outlet of the first compressor through the compressed air line to the drain passage in order to seal the flow of exhaust gas). Another embodiment relates to a vehicle comprising a vehicle platform, and such a system attached to the vehicle platform. In embodiments, the vehicle is a locomotive or other rail vehicle. [0043] As used herein, an element or step recited in the singular and proceeded with the word "a" or "an" should be understood as not excluding plural of said elements or steps, unless such exclusion is explicitly stated. Furthermore, references to "one embodiment" of the present invention are not intended to be interpreted as excluding the existence of additional embodiments that also incorporate the recited features. Moreover, unless explicitly stated to the contrary, embodiments "comprising," "including," or "having" an element or a plurality of elements having a particular property may include additional such elements not having that property. The terms "including" and "in which" are used as the plain-language equivalents of the respective terms "comprising" and "wherein." Moreover, the terms "first," "second," and "third," etc. are used merely as labels, and are not intended to impose numerical requirements or a particular positional order on their objects. [0044] This written description uses examples to disclose the invention, including the best mode, and also to enable a person of ordinary skill in the relevant art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, 15 and may include other examples that occur to those of ordinary skill in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims. 16

Claims (20)

1. A turbocharger, comprising: a turbine including a casing housing a rotor; a drain passage coupled to the casing; and an air jet coupled to the drain passage, the air jet configured to supply intake air from a high-pressure compressor outlet to the drain passage.

2. The turbocharger of claim 1, wherein the turbine is a low-pressure turbine located downstream of a high-pressure turbine in an exhaust flow path.

3. The turbocharger of claim 1 or 2, wherein the turbine is mechanically coupled to a low-pressure compressor located upstream of the high-pressure compressor in an intake air flow path.

4. The turbocharger of any one of claims 1 to 3, wherein the turbine casing is open to atmosphere in at least one location.

5. The turbocharger of any one of claims 1 to 4, wherein the drain passage is coupled to atmosphere.

6. The turbocharger of claim 1 to 5, wherein the drain passage is coupled to a vertical low point of the casing. 17

7. The turbocharger of any one of claims 1 to 6, wherein the turbine is located downstream of an engine, and wherein the drain passage is configured to passively drain fluid from the casing when the engine is not operating.

8. The turbocharger of claim 7, wherein the drain passage is configured to seal a flow of exhaust gas from the casing to atmosphere when the engine is operating.

9. The turbocharger of any one of claims 1 to 8, wherein the turbocharger is installed in a vehicle, and wherein a pressure of the intake air from the high-pressure compressor outlet is greater than atmospheric pressure during engine operation.

10. A system, comprising: an engine; a first turbocharger including a first turbine mechanically coupled to a first compressor; a second turbocharger including a second turbine located downstream of the first turbine in an exhaust flow path, the second turbine mechanically coupled to a second compressor, the second compressor located upstream of the first compressor in an intake flow path; a drain passage coupling the second turbine to atmosphere; and a compressed air line coupling the drain passage to an outlet of the first compressor. 18

11. The system of claim 10, wherein the drain passage is configured to passively drain fluid from the second turbine when the engine is not operating.

12. The system of claim 10, wherein the drain passage is configured to seal a flow of exhaust gas from the second turbine to atmosphere when the engine is operating.

13. The system of claim 12, wherein, when the engine is operating, compressed intake air flows from the outlet of the first compressor to the drain passage through the compressed air line in order to seal the flow of exhaust gas.

14. A vehicle comprising: a vehicle platform; and the system of claim 10 attached to the vehicle platform.

15. A method, comprising: when a pressure of intake air at a high-pressure compressor outlet is greater than a pressure of exhaust gas downstream of a low-pressure turbine, sealing a flow of exhaust gas from the low-pressure turbine through a drain passage to atmosphere; and when the pressure of intake air at the high-pressure compressor outlet is not greater than the pressure of exhaust gas downstream of the low-pressure turbine, draining fluid from the low-pressure turbine through the drain passage. 19

16. The method of claim 15, wherein sealing the flow of exhaust gas from the low pressure turbine through the drain passage to atmosphere further comprises directing air from the high-pressure compressor outlet to the drain passage.

17. The method of claim 15, wherein the pressure of intake air at the high-pressure compressor outlet being greater than the pressure of exhaust gas downstream of the low pressure turbine occurs during engine operation.

18. The method of claim 15, wherein the pressure of intake air at the high-pressure compressor outlet being no greater than the pressure of exhaust gas downstream of the low-pressure turbine occurs during engine off conditions.

19. The method of claim 15, further comprising compressing the intake air with the high-pressure compressor, the high-pressure compressor driven by a high-pressure turbine.

20. The method of claim 15, further comprising compressing the intake air with the high-pressure compressor, the high-pressure compressor driven by at least one of a motor or an engine. 20