Multi-stage turbocharged engine

1. An engine comprising:

an exhaust manifold and an intake manifold; and

a turbocharger apparatus connected between the exhaust manifold and the intake manifold, the turbocharger apparatus comprising:

a high pressure turbocharger including a turbine configured to receive high pressure exhaust gas from the exhaust manifold and including a compressor configured to discharge high pressure intake air to the intake manifold; and

first and second low pressure turbochargers, each including a compressor configured to receive ambient air and to discharge low pressure air into the high pressure turbocharger via a compressor interstage duct, and each including a turbine configured to receive low pressure exhaust gas from the high pressure turbocharger via a turbine interstage duct and to release exhaust gas to a respective exhaust casing;

wherein each exhaust casing includes:

a hollow body that has two mutually opposed walls, which extend along first and second major dimensions of the hollow body in respective first and second planes, and which and are spaced apart along a minor dimension of the hollow body, the hollow body defining a plenum;

an inlet nozzle opening into the plenum along the minor dimension of the hollow body, an opening of the inlet nozzle defining a third plane; and

an outlet nozzle opening from the plenum along one of the major dimensions of the hollow body;

wherein the third plane defined by the inlet nozzle opening is parallel to at least one of the first plane and the second plane; and

wherein the compressor interstage duct comprises:

a body defining an outlet chamber;

a first leg defining a first passage opening into the outlet chamber from a first inlet; and

a second leg defining a second passage opening into the outlet chamber from a second inlet,

wherein the first and second inlets have a combined flow area that is greater than a flow area of the outlet chamber, the first and second legs having flow areas that gradually diminish from the first inlet and the second inlet, respectively, to where the legs open into the outlet chamber.

2. The engine of claim 1 , wherein the inlet nozzle of each exhaust casing respectively includes a throat of constant diameter, and including a diverging portion that opens from the throat into the plenum.

3. The engine of claim 1 , further comprising a respective collar clamping the inlet nozzle of each exhaust casing to the hollow body.

4. The engine of claim 1 , wherein a center axis of the inlet nozzle of each exhaust casing is perpendicular to a center axis of the outlet nozzle.

5. The engine of claim 4 , wherein an egress of the outlet nozzle is circular, in a plane defined by the egress that is perpendicular to the center axis of the outlet nozzle.

6. The engine of claim 4 , wherein along a line in an interior of the plenum that is perpendicular to the center axis of the outlet nozzle and coaxial with the center axis of the inlet nozzle, a distance between the two mutually opposed walls is shorter than a distance transverse to the line that is between peripheral walls of the hollow body that interconnect the mutually opposed walls.

7. The engine of claim 1 , wherein the legs of the compressor interstage duct have the same flow area as one another at each of a plurality of stations along the legs.

8. The engine of claim 7 , wherein each of the legs of the compressor interstage duct extends from its respective inlet in a plane of the compressor interstage duct parallel to the other of the first or the second leg, curves toward the other of the first or the second leg in the plane of the compressor interstage duct, then bends away from the plane of the compressor interstage duct and joins with the other of the first or the second leg to form the body defining the outlet chamber.

9. The engine of claim 7 , wherein the legs and the body of the compressor interstage duct are formed as an integral piece.

10. The engine of claim 7 , wherein each of the legs of the compressor interstage duct includes a first portion that extends in a first direction along the central axis of its respective inlet, a second portion that extends orthogonally from the first portion toward the second portion of the other of the first or the second leg, and a third portion that merges with the third portion of the other of the first or the second leg.

11. The engine of claim 1 , wherein a rotational axis of the high pressure turbocharger extends parallel to a crankshaft axis of the engine, while rotational axes of the first and second low pressure turbochargers are angled at at least one non-zero angle toward the rotational axis of the high pressure turbocharger in a plane parallel the crankshaft axis of the engine.

12. The engine of claim 1 , wherein each of the legs extends from its respective inlet in a first horizontal direction, curves toward the other of the first or the second leg in a horizontal plane, and bends upward to open into the outlet chamber adjacent the other of the first or the second leg.

13. An engine comprising:

an exhaust manifold and an intake manifold; and

a turbocharger apparatus connected between the exhaust manifold and the intake manifold, the turbocharger apparatus comprising:

a high pressure turbocharger including a turbine configured to receive high pressure exhaust gas from the exhaust manifold and including a compressor configured to discharge high pressure intake air to the intake manifold; and

first and second low pressure turbochargers, each including a compressor configured to receive ambient air and to discharge low pressure air into the high pressure turbocharger via a compressor interstage duct, and each including a turbine configured to receive low pressure exhaust gas from the high pressure turbocharger via a turbine interstage duct and to release exhaust gas to a respective exhaust casing;

wherein each exhaust casing includes:

a hollow body that has two mutually opposed walls, which extend along first and second major dimensions of the hollow body in respective first and second planes, and which and are spaced apart along a minor dimension of the hollow body, the hollow body defining a plenum;

an inlet nozzle opening into the plenum along the minor dimension of the hollow body, an opening of the inlet nozzle defining a third plane; and

an outlet nozzle opening from the plenum along one of the major dimensions of the hollow body;

wherein the third plane defined by the inlet nozzle opening is parallel to at least one of the first plane and the second plane; and

wherein the turbine interstage duct comprises:

a cruciform tube having mutually opposed first and second inlet legs and mutually opposed first and second outlet legs that extend outward from a common junction to separate openings, the outlet legs extending orthogonal to the inlet legs, the opening of the first inlet leg connected to an outlet of the high pressure turbocharger turbine, the second inlet leg being coaxial with the first inlet leg, the opening of the first outlet leg connected to an inlet of the first low pressure turbocharger turbine, and the opening of the second outlet leg connected to an inlet of the second low pressure turbocharger turbine.

14. The engine of claim 13 , wherein a rotational axis of the high pressure turbocharger extends parallel to a crankshaft axis of the engine, while rotational axes of the first and second low pressure turbochargers are angled at at least one non-zero angle toward the rotational axis of the high pressure turbocharger in a plane parallel the crankshaft axis of the engine.

15. The engine of claim 13 , wherein the inlet nozzle of each exhaust casing respectively includes a throat of constant diameter, and including a diverging portion that opens from the throat into the plenum.

16. The engine of claim 13 , further comprising a respective collar clamping the inlet nozzle of each exhaust casing to the hollow body.

17. The engine of claim 13 , wherein a center axis of the inlet nozzle of each exhaust casing is perpendicular to a center axis of the outlet nozzle.

18. An engine comprising:

an exhaust manifold and an intake manifold; and

a turbocharger apparatus connected between the exhaust manifold and the intake manifold, the turbocharger apparatus comprising:

a high pressure turbocharger including a turbine configured to receive high pressure exhaust gas from the exhaust manifold and including a compressor configured to discharge high pressure intake air to the intake manifold; and

first and second low pressure turbochargers, each including a compressor configured to receive ambient air and to discharge low pressure air into the high pressure turbocharger via a compressor interstage duct, and each including a turbine configured to receive low pressure exhaust gas from the high pressure turbocharger via a turbine interstage duct and to release exhaust gas to a respective exhaust casing;

wherein the turbine interstage duct comprises:

a cruciform tube having mutually opposed first and second inlet legs and mutually opposed first and second outlet legs that extend outward from a common junction to separate openings, the outlet legs extending orthogonal to the inlet legs, the opening of the first inlet leg connected to an outlet of the high pressure turbocharger turbine, the second inlet leg being coaxial with the first inlet leg, the opening of the first outlet leg connected to an inlet of the first low pressure turbocharger turbine, and the opening of the second outlet leg connected to an inlet of the second low pressure turbocharger turbine; and

a flow splitter positioned in the opening of the second inlet leg of the cruciform tube, coaxial with the first inlet leg, the flow splitter including a napiform body protruding from the second inlet leg into the common junction of the cruciform tube, with a hyperboloid tip of the napiform body pointing along the axis of the first inlet leg for splitting a first gas flow from the first inlet leg into first and second portions respectively directed toward the first and second outlet legs.

19. An engine comprising:

an exhaust manifold and an intake manifold; and

a turbocharger apparatus connected between the exhaust manifold and the intake manifold, the turbocharger apparatus comprising:

a high pressure turbocharger including a turbine configured to receive high pressure exhaust gas from the exhaust manifold and including a compressor configured to discharge high pressure intake air to the intake manifold; and

first and second low pressure turbochargers, each including a compressor configured to receive ambient air and to discharge low pressure air into the high pressure turbocharger via a compressor interstage duct, and each including a turbine configured to receive low pressure exhaust gas from the high pressure turbocharger via a turbine interstage duct and to release exhaust gas to a respective exhaust casing;

wherein each exhaust casing comprises:

a hollow body that has two mutually opposed large walls, which extend along first and second major dimensions of the hollow body in respective first and second planes and are spaced apart by a minor dimension of the hollow body, the hollow body defining a plenum;

an inlet nozzle opening into the plenum along the minor dimension of the hollow body, an opening of the inlet nozzle defining a third plane, wherein the third plane defined by the inlet nozzle opening is parallel to at least one of the first plane and the second plane; and

an outlet nozzle opening from the plenum along one of the major dimensions of the hollow body;

wherein the compressor interstage duct comprises:

a body defining an outlet chamber;

a first leg defining a first passage opening into the outlet chamber from a first inlet; and

a second leg defining a second passage opening into the outlet chamber from a second inlet,

the first and second inlets having a combined flow area that is greater than a flow area of the outlet chamber, the first and second legs having flow areas that gradually diminish from the first inlet and the second inlet, respectively, to where the legs open into the outlet chamber; and

wherein the turbine interstage duct comprises:

a cruciform tube having mutually opposed first and second inlet legs and mutually opposed first and second outlet legs that extend outward from a common junction to separate openings, the outlet legs extending orthogonal to the inlet legs, the opening of the first inlet leg connected to an outlet of the high pressure turbocharger turbine, the second inlet leg being coaxial with the first inlet leg, the opening of the first outlet leg connected to an inlet of the first low pressure turbocharger turbine, and the opening of the second outlet leg connected to an inlet of the second low pressure turbocharger turbine.