Mitigation of diesel emission fluid (DEF) deposition in exhaust system for engine

1. An exhaust system for an engine comprising:

an exhaust conduit extending between an upstream end structured to receive exhaust produced by the engine, and a downstream end;

a selective catalytic reduction (SCR) device positioned in the exhaust conduit;

a diesel emission fluid (DEF) system including a DEF admission valve connected to the exhaust conduit at a location that is upstream of the SCR, a preheater, a condition sensor, and a DEF delivery controller;

the DEF delivery controller is coupled with the preheater and with the condition sensor, and structured to:

receive a condition signal produced by the condition sensor that is indicative of a DEF deposition risk condition in the exhaust system;

command an increased heat energy output of the preheater based on the condition signal, such that a temperature of DEF to be admitted into the exhaust conduit is increased to a deposition-mitigation temperature; and

determine the deposition-mitigation temperature based on a DEF dosing amount.

2. The exhaust system of claim 1 wherein the condition signal includes an exhaust temperature signal indicative of a reduction in exhaust temperature.

3. The exhaust system of claim 2 wherein:

the DEF delivery controller is further structured to command actuating the DEF admission valve to admit DEF increased in temperature to the deposition-mitigation temperature into the exhaust conduit; and

the reduction in exhaust temperature includes a reduction to an exhaust temperature of about 200° C. or less.

4. The exhaust system of claim 1 wherein:

the condition sensor is one of a plurality of condition sensors structured to produce a plurality of condition signals; and

the DEF delivery controller is further structured to determine the deposition-mitigation temperature based on the plurality of condition signals.

5. The exhaust system of claim 4 wherein the DEF delivery controller is further structured to look up the deposition-mitigation temperature in a map having an exhaust temperature coordinate, an exhaust flow coordinate, and a DEF dosing coordinate.

6. The exhaust system of claim 1 wherein the DEF delivery controller is further structured to:

calculate a preheater control value based on a difference between a present DEF temperature and the deposition-mitigation temperature; and

command the increased heat energy output of the preheater based upon the preheater control value.

7. The exhaust system of claim 6 wherein the DEF delivery controller is further structured to calculate the preheater control value based on an expected ambient heat loss.

8. A diesel emission fluid (DEF) system comprising:

a DEF delivery controller structured to couple with a preheater, for preheating DEF for delivery into an exhaust conduit in the exhaust system, and with a condition sensor, for monitoring a DEF deposition risk condition in the exhaust system;

the DEF delivery controller being further structured to:

receive a condition signal from the condition sensor indicative of a DEF deposition risk condition in the exhaust system;

determine a deposition-mitigation temperature for DEF to be admitted into an exhaust conduit in the exhaust system, based on the condition signal and a DEF dosing amount; and

command an increased heat energy output of the preheater, such that a temperature of the DEF to be admitted into the exhaust conduit is increased to the deposition-mitigation temperature.

9. The DEF system of claim 8 wherein:

the deposition risk condition includes a reduced exhaust temperature condition; and

the DEF delivery controller is further structured to command the increased heat energy output of the preheater by commanding turning on the preheater.

10. The DEF system of claim 8 wherein the DEF delivery system includes the condition sensor, and wherein the condition sensor is an exhaust temperature sensor and the condition signal is an exhaust temperature signal.

11. The DEF system of claim 10 wherein the DEF delivery controller is further structured to:

calculate a preheater control value based on a difference between a present DEF temperature and the deposition-mitigation temperature; and

command the increased heat energy output of the preheater based upon the preheater control value.

12. The DEF system of claim 11 further comprising:

a DEF tank temperature condition sensor structured to produce a DEF tank temperature signal;

an ambient temperature condition sensor structured to produce an ambient temperature signal; and

the DEF delivery controller is further structured to calculate the preheater control value based on the exhaust temperature signal, the DEF tank temperature signal, and the ambient temperature signal.

13. The DEF system of claim 10 wherein the DEF delivery controller is further structured to look up the deposition-mitigation temperature in a map having an exhaust temperature coordinate, an exhaust flow coordinate, and DEF dosing coordinate.

14. A method of operating an exhaust system for an internal combustion engine comprising:

producing a condition signal indicative of a diesel emission fluid (DEF) solids deposition risk in the exhaust system;

increasing a heat energy output of a preheater for DEF in a DEF system of the exhaust system based on the condition signal;

increasing a temperature of DEF in the DEF system to a deposition-mitigation temperature based on the increased heat energy output; and

commanding admission of the DEF increased in temperature to the deposition-mitigation temperature into an exhaust conduit in the exhaust system.

15. The method of claim 14 wherein the producing of a condition signal includes producing an exhaust temperature signal indicative of a reduction in exhaust temperature.

16. The method of claim 15 wherein the increasing of the heat energy output of the preheater includes increasing the heat energy output by turning on the preheater.

17. The method of claim 15 further comprising determining the deposition-mitigation temperature based on exhaust temperature, exhaust flow, and DEF dosing.

18. The method of claim 14 further comprising calculating a preheater control value based on a difference between a present DEF temperature and the deposition-mitigation temperature.

19. The method of claim 18 wherein the calculating of the preheater control value further includes calculating the preheater control value based on an expected ambient heat loss.