Engine system with exhaust gas recirculation, and method of operating the same

1. An engine system with exhaust gas recirculation, comprising:

a combustion engine having an intake manifold and an exhaust manifold;

a turbocharger including an exhaust turbine and an air compressor coupled to the exhaust turbine;

an exhaust flow path extending between the exhaust manifold and an inlet of the exhaust turbine;

a first flow mixer having a first inlet, a second inlet, and an outlet;

a charge air flow path extending between an outlet of the air compressor and the first inlet of the first flow mixer;

a first heat exchanger located along the charge air flow path to transfer heat from compressed charge air traveling along the charge air flow path from the air compressor to the first flow mixer;

a first exhaust gas recirculation flow path extending between the exhaust manifold and the second inlet of the flow mixer, wherein the first exhaust gas recirculation flow path does not extend through any heat exchangers;

a mixed gas flow path extending between the outlet of the first flow mixer and the intake manifold;

a first mixed gas heat exchanger located along the mixed gas flow path,

a second flow mixer having a first inlet, a second inlet, and an outlet, the first inlet and the outlet of the second flow mixer being located along the mixed gas flow path between the first mixed gas heat exchanger and the intake manifold;

a second exhaust gas recirculation flow path extending between the exhaust manifold and the second inlet of the second flow mixer, wherein the second exhaust gas recirculation flow path does not extend through any heat exchangers; and

a second mixed gas heat exchanger located along the mixed gas flow path between the outlet of the second flow mixer and the intake manifold.

2. The engine system of claim 1 , wherein mixed gas flowing through the first mixed gas heat exchanger is cooled by a first coolant flow passing through the first mixed gas heat exchanger and wherein mixed gas flowing through the second mixed gas heat exchanger is cooled by a second coolant flow passing through the second mixed gas heat exchanger, the second coolant flow being different than the first coolant flow.

3. The engine system of claim 1 , further comprising a valve located along both the first and the second exhaust gas recirculation flow paths to proportion recirculated exhaust gas between the second inlet of the first flow mixer and the second inlet of the second flow mixer.

4. The engine system of claim 3 , wherein the valve operates in response to a mixed gas temperature between the outlet of the first flow mixer and the first mixed gas heat exchanger.

5. An engine system with exhaust gas recirculation, comprising:

a combustion engine having an intake manifold and an exhaust manifold;

a turbocharger including an exhaust turbine and an air compressor coupled to the exhaust turbine;

an exhaust flow path extending between the exhaust manifold and an inlet of the exhaust turbine;

a flow mixer having a first inlet, a second inlet, and an outlet;

a charge air flow path extending between an outlet of the air compressor and the first inlet of the flow mixer;

a first heat exchanger located along the charge air flow path to transfer heat from compressed charge air traveling along the charge air flow path from the air compressor to the flow mixer;

an exhaust gas recirculation flow path extending between the exhaust manifold and the second inlet of the flow mixer, wherein the exhaust gas recirculation flow path does not extend through any heat exchangers;

a mixed gas flow path extending between the outlet of the flow mixer and the intake manifold; and

a mixed gas heat exchanger located along the mixed gas flow path to transfer heat from a mixed gas traveling along the mixed gas flow path,

wherein the mixed gas heat exchanger is one of a plurality of mixed gas heat exchangers located along the mixed gas flow path.

6. The engine system of claim 5 , wherein at least some of the plurality of mixed gas heat exchangers are additionally located along a portion of a common heat receiving fluid circuit, the common heat receiving fluid circuit being part of a waste heat recovery bottoming cycle of the engine system.

7. The engine system of claim 6 , wherein the plurality of mixed gas heat exchangers includes a first mixed gas heat exchanger and a second mixed gas heat exchanger, wherein the first mixed gas heat exchanger is arranged upstream of the second mixed gas heat exchanger along the mixed gas flow path and wherein the first mixed gas heat exchanger is arranged downstream of the second mixed gas heat exchanger along the common heat receiving fluid circuit.

8. The engine system of claim 7 , further comprising an additional waste heat recovery heat exchanger arranged along the common heat receiving fluid circuit between the first mixed gas heat exchanger and the second mixed gas heat exchanger.

9. A method of operating an engine system comprising:

receiving a flow of uncooled exhaust gas from an exhaust manifold of the engine system;

splitting the flow of uncooled exhaust gas into an un-recirculated portion and a recirculated portion;

recovering energy from the un-recirculated portion to pressurize a flow of charge air;

rejecting heat from the pressurized flow of charge air to cool the charge air;

combining the cooled charge air with at least some of the recirculated portion of uncooled exhaust gas to form a mixed gas;

rejecting heat from the mixed gas to cool the mixed gas by passing the mixed gas through a mixed gas heat exchanger, by passing a flow of ambient air through the mixed gas heat exchanger, and by transferring heat from the mixed gas to the flow of ambient air within the mixed gas heat exchanger; and

delivering the cooled mixed gas to an intake manifold of the engine system,

wherein the mixed gas heat exchanger is a terminal one of a plurality of mixed gas heat exchangers through which the mixed gas passes before being delivered to the intake manifold.

10. A method of operating an engine system comprising:

receiving a flow of uncooled exhaust gas from an exhaust manifold of the engine system;

splitting the flow of uncooled exhaust gas into an un-recirculated portion and a recirculated portion;

recovering energy from the un-recirculated portion to pressurize a flow of charge air;

rejecting heat from the pressurized flow of charge air to cool the charge air;

combining the cooled charge air with at least some of the recirculated portion of uncooled exhaust gas to form a mixed gas;

measuring a temperature of the mixed gas after combining the cooled charge air with at least some of the recirculated portion of uncooled exhaust gas to form the mixed gas;

adjusting the amount of the recirculated portion of uncooled exhaust gas being combined with the cooled charge air in order to regulate the measured temperature of the mixed gas;

rejecting heat from the mixed gas to cool the mixed gas after adjusting the amount of the recirculated portion of uncooled exhaust gas being combined with the cooled charge air;

combining any remaining recirculated portion of uncooled exhaust gas with the mixed gas after rejecting heat from the mixed gas; and

delivering the cooled mixed gas to an intake manifold of the engine system.

11. The method of claim 10 , further comprising rejecting additional heat from the charge air and recirculated portion of uncooled exhaust gas after the step of combining any remaining recirculated portion of uncooled exhaust gas with the mixed gas.

12. The method of claim 10 , further comprising:

pressurizing a flow of working fluid;

heating the flow of working fluid to form a superheated vapor working fluid;

expanding the superheated vapor working fluid to recover energy therefrom; and

condensing the expanded working fluid to return it to a liquid state, wherein a least a portion of the heat used to form the superheated vapor working fluid is heat rejected from the mixed gas to cool the mixed gas.

13. The method of claim 12 , wherein the step of rejecting heat from the mixed gas to cool the mixed gas includes flowing the mixed gas through a plurality of heat exchangers and wherein the step of heating the flow of working fluid to form a superheated vapor working fluid includes flowing the working fluid through at least one of the plurality of heat exchangers.

14. The method of claim 13 :

wherein flowing the mixed gas through the plurality of heat exchangers comprises passing the mixed gas successively through a first and then a second heat exchanger, and

wherein flowing the working fluid through at least one of the plurality of heat exchangers comprises,

passing the working fluid into the second heat exchanger in order to heat the working fluid and cool the mixed gas;

receiving the working fluid from the second heat exchanger in a partially heated condition;

passing the working fluid into the first heat exchanger;

fully heating the working fluid in the first heat exchanger using heat from the mixed gas; and

receiving the working fluid from the first heat exchanger in a superheated vapor state.

15. The method of claim 14 , wherein flowing the working fluid through at least one of the plurality of heat exchangers further comprises passing the working fluid through a third heat exchanger after passing the working fluid through the second heat exchanger but before passing the working fluid through the first heat exchanger in order to heat the working fluid, wherein the working fluid is heated in the third heat exchanger using un-recirculated exhaust gas or engine coolant.

16. The engine system of claim 5 , wherein the first heat exchanger is a liquid-cooled heat exchanger and is additionally located along a portion of an engine coolant circuit of the engine system.

17. The engine system of claim 5 , wherein the mixed gas heat exchanger is an air-cooled heat exchanger.

18. The method of claim 9 , wherein rejecting heat from the mixed gas includes cooling the mixed gas to an intake manifold temperature differential of no more than fifteen degrees Celsius.

19. The method of claim 10 , wherein rejecting heat from the mixed gas includes cooling the mixed gas to an intake manifold temperature differential of no more than fifteen degrees Celsius.