Methods and systems for air fuel ratio control

1. A system comprising:

a controller configured for operable coupling with an engine that is configured to drive an electrical power generation system, wherein the controller is further configured to adjust an engine speed of the engine in a closed loop in response to a relationship between oxygen and fuel crossing an air fuel ratio threshold while maintaining a tractive power transmitted to the electrical power generation system, the controller configured to adjust engine speed by adjusting fueling to the engine and torque of the electrical power generation system;

wherein the engine includes a turbocharger arranged between an intake passage and exhaust passage of the engine;

wherein the tractive power is an indication of an identified power setting; and

wherein the relationship between oxygen and fuel includes an exhaust air fuel ratio.

2. The system of claim 1 , wherein the controller is configured to further adjust the engine speed by adjusting generator torque.

3. The system of claim 1 , wherein the controller is configured to adjust the engine fueling by adjusting at least one of injection timing, fuel pulse duration, or fuel injection pressure.

4. The system of claim 1 , wherein the controller is configured to adjust the engine speed in response to the exhaust air fuel ratio by adjusting the engine speed in response to the exhaust air fuel ratio falling below a threshold.

5. The system of claim 1 , wherein the controller is configured to adjust the engine speed in response to the exhaust air fuel ratio by adjusting the engine speed in response to the exhaust air fuel ratio increasing above a threshold.

6. The system of claim 1 , wherein the tractive power transmitted to the electrical power generation system is a selected power level based on a power setting, and wherein the engine is positioned in a rail vehicle and the power setting is a notch setting selected by an operator of the rail vehicle.

7. The system of claim 1 , wherein the engine is positioned in a vehicle, and the electrical power generation system includes a generator mechanically coupled to the engine and a plurality of electric motors electrically coupled to the generator to drive wheels of the vehicle.

8. The system of claim 7 , wherein the plurality of electric motors are configured to provide power to wheels of the vehicle.

9. A system comprising:

a controller configured for operable coupling with a vehicle system having a boosted engine including a turbocharger arranged between an intake passage and an exhaust passage of the engine, a generator configured to be driven by the engine, a plurality of wheels, and a plurality of electric traction motors coupled to the plurality of wheels; wherein:

the controller is configured to identify a power setting, the power setting indicating a tractive power to be transmitted by the plurality of wheels;

the controller is configured to identify a relationship between oxygen and fuel including an exhaust air fuel ratio; and

the controller is configured to continuously adjust an engine speed of the engine in response to the relationship between oxygen and fuel crossing an exhaust air fuel ratio threshold while maintaining the power setting even while adjusting engine speed, the controller configured to adjust the engine speed by adjusting fueling to the engine and a torque of the generator.

10. The system of claim 9 , wherein the exhaust air fuel ratio crossing the threshold includes the exhaust air fuel ratio falling below the threshold.

11. The system of claim 9 , wherein the exhaust air fuel ratio crossing the threshold includes the exhaust air fuel ratio increasing above the threshold.

12. The system of claim 9 , wherein the vehicle system is a rail vehicle system, and the power setting is a notch setting of a notched throttle.

13. The system of claim 9 , wherein the controller is configured to adjust the engine speed based on an exhaust gas recirculation rate from an exhaust gas recirculation system which is configured to route exhaust gas from the exhaust passage to the intake passage of the engine.

14. The system of claim 13 , wherein the controller is configured to adjust the engine speed in response to an increasing exhaust gas recirculation rate.

15. The system of claim 9 , wherein the exhaust air fuel ratio threshold is based on an exhaust level of particulate matter emission and nitrogen oxide emission.

16. A vehicle system, comprising:

a boosted engine including a turbocharger arranged between an intake passage and an exhaust passage of the engine;

a generator mechanically coupled to the engine;

a plurality of electric traction motors electrically coupled to the generator;

a plurality of wheels to which the electric traction motors provide tractive power based on a power setting; and

a controller configured to identify the power setting and an exhaust air fuel ratio, and in response to the exhaust air fuel ratio crossing a threshold, adjusting an engine speed while maintaining the tractive power transmitted to the plurality of wheels, the controller configured to adjust engine speed by adjusting fueling to the engine and generator torque.

17. The vehicle system of claim 16 , wherein adjusting the fueling to the engine includes adjusting at least one of injection timing, fuel pulse duration, and fuel injection pressure.

18. The vehicle system of claim 16 , further comprising an exhaust gas recirculation system, and wherein the controller further adjusts the engine speed based on an exhaust gas recirculation rate and the exhaust air-fuel ratio.

19. The vehicle system of claim 16 , wherein the exhaust air fuel ratio crossing the threshold includes the exhaust air fuel ratio falling below the threshold, and wherein the threshold is based on an exhaust level particulate matter emission.