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Various methods and systems are provided for estimating a wall temperature in a heat exchanger and reducing the risk of boiling on a coolant side of the heat exchanger. In one embodiment, a method for an engine comprises estimating a wall temperature at a location in a heat exchanger and adjusting a

Various methods and systems are provided for estimating a wall temperature in a heat exchanger and reducing the risk of boiling on a coolant side of the heat exchanger. In one embodiment, a method for an engine comprises estimating a wall temperature at a location in a heat exchanger and adjusting an engine operating parameter of an engine coupled to the heat exchanger based on the wall temperature.

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1. A method, comprising: increasing an engine speed of an engine coupled to a heat exchanger based on a wall temperature at a location in the heat exchanger while maintaining motor traction power of a traction motor, the engine speed increased up to a maximum rated speed of the engine, the wall temp

1. A method, comprising: increasing an engine speed of an engine coupled to a heat exchanger based on a wall temperature at a location in the heat exchanger while maintaining motor traction power of a traction motor, the engine speed increased up to a maximum rated speed of the engine, the wall temperature including a temperature of a wall in fluid contact with an engine coolant; andresponsive to the engine speed increasing to the maximum rated speed of the engine, de-rating engine power. 2. The method of claim 1, further comprising increasing the engine speed from a first engine speed to a second engine speed when the wall temperature is greater than an upper threshold temperature, the upper threshold temperature based on an engine coolant pressure. 3. The method of claim 2, wherein the engine coolant pressure is a pressure downstream of a coolant pump and upstream of the heat exchanger. 4. The method of claim 2, wherein the engine coolant pressure is one or more of a sensed or modeled pressure at the location in the heat exchanger. 5. A method, comprising: adjusting an engine operating parameter of an engine coupled to a heat exchanger based on a wall temperature at a location in the heat exchanger, wherein adjusting the engine operating parameter includes increasing an engine speed of the engine, the wall temperature including a temperature of a wall in fluid contact with an engine coolant;increasing the engine speed from a first engine speed to a second engine speed when the wall temperature is greater than an upper threshold temperature, the upper threshold temperature based on an engine coolant pressure; andde-rating engine power of the engine when the wall temperature remains greater than the upper threshold temperature after increasing the engine speed. 6. The method of claim 1, further comprising estimating the wall temperature by estimating heat transfer at the location in the heat exchanger, based on a temperature difference between the engine coolant and a second heat transfer fluid, and further based on one or more thermal resistances across the heat exchanger. 7. The method of claim 6, wherein estimating the heat transfer includes determining a first convection coefficient based on a temperature and flow rate of the engine coolant and a second convection coefficient based on a temperature and flow rate of the second heat transfer fluid. 8. The method of claim 7, wherein estimating the heat transfer further includes determining the one or more thermal resistances across the heat exchanger based on the first convection coefficient, the second convection coefficient, one or more heat exchanger material properties, and one or more fouling coefficients. 9. The method of claim 1, wherein the heat exchanger is an exhaust gas recirculation cooler, wherein the location is a selected location on an outlet side of a coolant passage in the exhaust gas recirculation cooler, and wherein the engine is coupled to an alternator that generates electric power, the electric power driving the traction motor coupled to motive wheels of a rail vehicle. 10. A method, comprising: sensing bulk boiling of a heat transfer fluid in a heat exchanger via a heat transfer fluid temperature measured by a heat exchanger temperature sensor;estimating local boiling of the heat transfer fluid via a wall temperature of the heat exchanger; andadjusting an engine operating parameter including one or more of increasing engine speed or de-rating power of an engine responsive to the wall temperature in the heat exchanger being greater than an upper threshold temperature to reduce wall temperature before bulk boiling occurs, the wall temperature including a temperature of a wall in fluid contact with the heat transfer fluid. 11. The method of claim 10, further comprising not adjusting the engine operating parameter when the wall temperature is less than the upper threshold temperature. 12. The method of claim 10, wherein the heat exchanger is an exhaust gas recirculation cooler, wherein heat is transferred between the heat transfer fluid and a second heat transfer fluid in the exhaust gas recirculation cooler, the second heat transfer fluid including an exhaust gas and the heat transfer fluid including an engine coolant. 13. The method of claim 10, further comprising estimating the wall temperature in the heat exchanger based on a temperature difference between the heat transfer fluid and a second heat transfer fluid in the heat exchanger and one or more thermal resistances across the heat exchanger. 14. The method of claim 13, further comprising determining the one or more thermal resistances across the heat exchanger based on a first convection coefficient and a second convection coefficient, the first convection coefficient based on a temperature and flow rate of the heat transfer fluid and the second convection coefficient based on a temperature and flow rate of the second heat transfer fluid. 15. The method of claim 14, wherein determining the one or more thermal resistances is further based on fouling coefficients and a thickness and thermal conductivity of a material separating the heat transfer fluid and the second heat transfer fluid, wherein the fouling coefficients are determined based on estimated cooler fouling, the estimated cooler fouling based on one or more of an engine run time, a run time in different modes of engine operation, and an estimated amount of fouling material present in an exhaust gas. 16. The method of claim 10, wherein the upper threshold temperature increases with increasing engine coolant pressure. 17. A method, comprising: estimating a wall temperature in a heat exchanger based on a temperature difference between a first heat transfer fluid and a second heat transfer fluid in the heat exchanger and further based on one or more thermal resistances across the heat exchanger, the wall temperature including a temperature of a wall in fluid contact with the first heat transfer fluid and in fluid contact with the second heat transfer fluid;during a first condition, when the wall temperature is greater than an upper threshold temperature, increasing engine speed of an engine; andduring a second condition, different from the first condition, de-rating power of the engine. 18. The method of claim 17, wherein the second condition includes when the wall temperature in the heat exchanger is greater than the upper threshold temperature and the engine speed is at a maximum threshold speed.