Water injection exhaust treatment system

1. An exhaust treatment system comprising:

a gas supply conduit in fluid communication with a source of compressed gas and including a first valve controlling a flow of compressed gas through the gas supply conduit;

a reductant supply conduit in fluid communication with a reductant source;

a water supply conduit in fluid communication with a water source and including a second valve controlling a flow of water through the water supply conduit;

a nozzle in fluid communication with the gas supply conduit, the reductant supply conduit and the water supply conduit; and

a pump disposed between the nozzle and the second valve and in fluid communication with the reductant supply conduit and the water supply conduit, the pump being operable in a first pumping direction to pump reductant from the reductant source to the nozzle and in a second pumping direction to pump reductant away from the nozzle and toward the reductant source, wherein the pump is operable in the first pumping direction to pump water from the water source to the nozzle and the PUMP is operable in the second pumping direction to pump water away from the nozzle and toward the water source.

2. The exhaust treatment system of claim 1 , wherein the reductant supply conduit includes a third valve movable between open and closed positions to control a flow of reductant between the reductant source and the pump.

3. The exhaust treatment system of claim 1 , further comprising a filter disposed between the pump and the second valve and in fluid communication with the reductant supply conduit and the water supply conduit.

4. The exhaust treatment system of claim 1 , wherein the source of compressed gas includes a source of compressed air.

5. The exhaust treatment system of claim 1 , wherein the gas supply conduit is in fluid communication with parallel first and second gas flow paths.

6. The exhaust treatment system of claim 5 , wherein the first gas flow path includes a third valve that is movable between a first position allowing gas flow through the first gas flow path and a second position restricting gas flow through the first gas flow path.

7. The exhaust treatment system of claim 6 , wherein the first gas flow path fluidly couples the gas supply conduit with a conduit extending between the pump and a first inlet of the nozzle.

8. The exhaust treatment system of claim 7 , wherein the second gas flow path bypasses the third valve and couples the gas supply conduit with a second inlet of the nozzle disposed between the first inlet and an outlet of the nozzle.

9. The exhaust treatment system of claim 8 , wherein the second gas flow path includes a restrictor.

10. The exhaust treatment system of claim 8 , wherein the reductant supply conduit includes a fourth valve movable between open and closed positions to control a flow of reductant between the reductant source and the pump.

11. The exhaust treatment system of claim 10 , comprising:

the exhaust treatment system being operable in a first purge mode in which the pump is operating in the second pumping direction, the fourth valve is open and the first, second and third valves are closed;

the exhaust treatment system being operable in a second purge mode in which the pump stops operating, the second valve is closed and the first, third and fourth valves are open;

the exhaust treatment system being operable in a third purge mode in which the pump is operating in the first pumping direction, the second valve is open and the first, third and fourth valves are closed;

the exhaust treatment system being operable in a fourth purge mode in which the pump is operating in the second pumping direction, the second valve is open and the first, third and fourth valves are closed; and

the exhaust treatment system being operable in a fifth purge mode in which the fourth valve is closed and the first, second and third valves are open.

12. The exhaust treatment system of claim 11 , wherein the second purge mode is performed after the first purge mode; the third purge mode is performed after the second purge mode; the fourth purge mode is performed after the third purge mode; and the fifth purge mode is performed after the fourth purge mode.

13. An exhaust treatment system comprising:

a gas supply conduit in fluid communication with a source of compressed gas and including a first valve controlling a flow of compressed gas through the gas supply conduit;

a reductant supply conduit in fluid communication with a reductant source;

a water supply conduit in fluid communication with a water source and including a second valve controlling a flow of water through the water supply conduit;

a nozzle in fluid communication with the gas supply conduit, the reductant supply conduit and the water supply conduit;

a pump disposed between the nozzle and the second valve and in fluid communication with the reductant supply conduit and the water supply conduit;

a filter disposed between the pump and the second valve and in fluid communication with the reductant supply conduit and the water supply conduit; and

first and second gas flow paths extending between and in fluid communication with the gas supply conduit and the nozzle,

wherein the reductant supply conduit includes a third valve disposed between the pump and the reductant source, the third valve being movable between open and closed positions to control a flow of reductant between the reductant source and the pump.

14. The exhaust treatment system of claim 13 , wherein the first gas flow path includes a fourth valve that is movable between a first position allowing gas flow through the first gas flow path and a second position restricting gas flow through the first gas flow path.

15. The exhaust treatment system of claim 14 , wherein the second gas flow path includes a restrictor.

16. The exhaust treatment system of claim 14 , wherein the first gas flow path fluidly couples the gas supply conduit with a conduit extending between the pump and a first inlet of the nozzle.

17. The exhaust treatment system of claim 16 , wherein the second gas flow path bypasses the fourth valve and couples the gas supply conduit with a second inlet of the nozzle disposed between the first inlet and an outlet of the nozzle.

18. The exhaust treatment system of claim 13 , wherein the pump is operable in a first pumping direction to pump reductant from the reductant source to the nozzle and in a second pumping direction to pump reductant away from the nozzle and toward the reductant source.

19. The exhaust treatment system of claim 18 , wherein the pump is operable in the first pumping direction to pump water from the water source to the nozzle.

20. The exhaust treatment system of claim 19 , wherein the pump is operable in the second pumping direction to pump water away from the nozzle and toward the water source.

21. The exhaust treatment system of claim 13 , wherein the source of compressed gas includes a source of compressed air.

22. A method of operating an exhaust treatment system, the method comprising:

operating a pump in a first direction to pump reductant from a reductant source to a nozzle;

operating the pump in a second direction opposite the first direction to pump reductant toward the reductant source;

operating the pump in the first direction to pump water from a water source to the nozzle; and

shutting down the pump and forcing compressed air through the pump in the second direction.

23. The method of claim 22 , further comprising providing compressed air to the nozzle simultaneously with operating the pump in the first direction to pump reductant from the reductant source to the nozzle.

24. The method of claim 22 , wherein a valve is closed to restrict communication between the reductant source and the pump while operating the pump in the first direction to pump water from the water source to the nozzle.

25. The method of claim 24 , further comprising operating the pump in the second direction to pump water toward the water source.

26. A method of operating an exhaust treatment system, the method comprising:

pumping reductant through a conduit in a first direction from a reductant source to a nozzle and simultaneously supplying compressed air to the nozzle;

forcing one or more of reductant, air and water through the conduit in a second direction toward the reductant source; and

providing a flow of water through the conduit in the first direction, wherein forcing one or more of reductant, air and water through the conduit in the second direction toward the reductant source includes forcing reductant through the conduit in the second direction toward the reductant source and forcing air through the conduit in the second direction.

27. The method of claim 26 , further comprising providing water to the nozzle simultaneously with supplying compressed air to the nozzle and simultaneously with pumping reductant through the conduit in the first direction from the reductant source to the nozzle.

28. The method of claim 26 , further comprising forcing water through the conduit in the second direction.

29. A method of operating an exhaust treatment system, the method comprising:

pumping reductant through a conduit in a first direction from a reductant source to a nozzle and simultaneously supplying compressed air to the nozzle;

forcing one or more of reductant, air and water through the conduit in a second direction toward the reductant source;

providing a flow of water through the conduit in the first direction; and

injecting water into an exhaust stream upstream of the nozzle.