Method for injecting reductant into an exhaust gas of an engine using an oscillating supply pressures

1. A method for injecting a reductant into an exhaust gas of a power system, the method comprising:

injecting the reductant at a commanded flow rate;

calculating a baseline supply pressure of the reductant;

calculating a higher supply pressure based on the baseline supply pressure, the higher supply pressure being higher than the baseline supply pressure;

calculating a lower supply pressure based on the baseline supply pressure, the lower supply pressure being lower than the baseline supply pressure;

oscillating a supply pressure of the reductant between the higher supply pressure and the lower supply pressure; and

increasing a difference between the higher supply pressure and the baseline supply pressure when a space velocity decreases.

2. The method of claim 1 , wherein the injecting comprises compensating for oscillations in the supply pressure so as to maintain a constant flow rate of the reductant being injected.

3. The method of claim 1 , further comprising calculating the commanded flow rate based on one or more physical states of the power system.

4. The method of claim 1 , further comprising calculating the higher and lower supply pressure based on one or more physical states of the power system.

5. The method of claim 1 , further comprising calculating the higher and lower supply pressures based on an exhaust temperature.

6. The method of claim 1 , further comprising calculating the higher and lower supply pressures based on a space velocity.

7. The method of claim 1 , wherein the oscillating comprises oscillating the supply pressure of the reductant between the higher supply pressure for a single injection of the reductant and the lower supply pressure for a next single injection of the reductant.

8. The method of claim 1 , wherein a difference between the baseline supply pressure and the lower supply pressure is greater in magnitude than a difference between the higher supply pressure and the baseline supply pressure.

9. The method of claim 1 , further comprising increasing a difference between the baseline supply pressure and the lower supply pressure when a space velocity decreases.

10. The method of claim 1 , further comprising decreasing a difference between the higher supply pressure and the baseline supply pressure when a space velocity increases.

11. The method of claim 1 , further comprising decreasing a difference between the baseline supply pressure and the lower supply pressure when a space velocity increases.

12. The method of claim 1 , further comprising increasing a difference between the higher supply pressure and the baseline supply pressure when an exhaust temperature decreases.

13. The method of claim 1 , further comprising increasing a difference between the baseline supply pressure and the lower supply pressure when an exhaust temperature decreases.

14. The method of claim 1 , further comprising decreasing a difference between the higher supply pressure and the baseline supply pressure when an exhaust temperature increases.

15. The method of claim 1 , further comprising decreasing a difference between the baseline supply pressure and the lower supply pressure when and exhaust temperature increases.

16. The method of claim 1 , further comprising:

calculating a first time period for injecting at the higher supply pressure; and

calculating a second time period for injecting at the lower supply pressure.

17. The method of claim 16 , further comprising:

decreasing the first and second time periods when an exhaust temperature increases; and

increasing the first and second time periods when an exhaust temperature decreases.

18. The method of claim 16 , further comprising:

decreasing the first and second time periods when a space velocity increases; and

increasing the first and second time periods when a space velocity decreases.

19. The method of claim 16 , further comprising:

decreasing an opening time period when the supply pressure oscillates to the higher supply pressure; and

increasing an opening time period when the supply pressure oscillates to the lower supply pressure.

20. The method of claim 1 , wherein the oscillating comprises oscillating the supply pressure of the reductant between the higher supply pressure for a plurality of injections of the reductant and the lower supply pressure for a next plurality of injections of the reductant, the pluralities being in immediate sequence.

21. The method of claim 20 , the higher supply pressure being one of a plurality of higher supply pressures, the lower supply pressure being one of a plurality of lower supply pressures, and the method further comprising:

calculating the higher supply pressures based on the baseline supply pressure, the higher supply pressures being higher than the baseline supply pressure; and

calculating the lower supply pressures based on the baseline supply pressure, the lower supply pressures being lower than the baseline supply pressure.

22. The method of claim 21 , wherein an average difference between the baseline supply pressure and the lower supply pressures is greater in magnitude than an average difference between the higher supply pressures and the baseline supply pressure.

23. The method of claim 1 , wherein the injecting and the oscillating occur simultaneously.

24. A method for injecting a reductant into an exhaust gas of a power system, the method comprising:

injecting the reductant at a commanded flow rate;

calculating a baseline supply pressure of the reductant;

calculating a higher supply pressure based on the baseline supply pressure, the higher supply pressure being higher than the baseline supply pressure;

calculating a lower supply pressure based on the baseline supply pressure, the lower supply pressure being lower than the baseline supply pressure;

oscillating a supply pressure of the reductant between the higher supply pressure and the lower supply pressure; and

increasing a difference between the higher supply pressure and the baseline supply pressure when an exhaust temperature decreases.