Low temperature emission system having turbocharger bypass

1. An exhaust system for an engine, comprising:

a NOx reducer located to receive exhaust from the engine;

a bypass circuit configured to selectively pass supercharged air to the NOx reducer;

a valve disposed within the bypass circuit to regulate the flow of supercharged air; and

a controller in communication with the valve, the controller being configured to:

move the valve to pass the supercharged air and cool the exhaust received by the NOx reducer; and

move the valve to reduce the passing of the supercharged air and remove sulfur compounds from the NOx reducer.

2. The exhaust system of claim 1 , wherein the supercharged air cools the exhaust below about 400° C.

3. The exhaust system of claim 1 , wherein the passing of the supercharged air is completely stopped to initiate removal of the sulfur compounds.

4. The exhaust system of claim 1 , wherein the supercharged air is directed from downstream of a compressor to the NOx reducer.

5. The exhaust system of claim 1 , further including a temperature sensor configured to indicate a temperature of the NOx reducer, wherein the controller moves the valve to cool the exhaust in response to the temperature of the NOx reducer.

6. The exhaust system of claim 1 , wherein the controller moves the valve to cool the exhaust in response to an estimated temperature.

7. The exhaust system of claim 1 , wherein the controller moves the valve to remove the sulfur compounds in response to an elapsed period of time.

8. The exhaust system of claim 1 , wherein reducing the passing of the supercharged air increases the exhaust temperature.

9. The exhaust system of claim 8 , wherein the exhaust temperature is increased above about 450° C.

10. A method of treating an exhaust flow, comprising:

passing supercharged air to the exhaust flow; and

initiating a desulfation process by reducing the passing of supercharged air to the exhaust flow.

11. The method of claim 10 , wherein the supercharged air cools the exhaust below about 400° C.

12. The method of claim 10 , wherein reducing the passing of the supercharged air increases the exhaust temperature above about 450° C.

13. The method of claim 10 , wherein initiating a desulfation process includes completely stopping the passing of the supercharged air.

14. The method of claim 10 , further including sensing a temperature of the exhaust flow, wherein the passing of supercharged air is in response to the sensed temperature.

15. The method of claim 10 , further including estimating a temperature of the exhaust flow, wherein the passing of supercharged air is in response to the estimated temperature.

16. The method of claim 10 , wherein initiating a desulfation process is in response to an elapsed period of time.

17. The method of claim 10 , further including removing NOx from the exhaust flow, wherein the passing of supercharged air improves the NOx removal ability.

18. The method of claim 17 , wherein the desulfation process improves the NOx removal capacity.

19. A power unit, comprising:

an engine configured to combust a fuel/air mixture and produce a flow of exhaust;

a turbocharger configured to receive the flow of exhaust and compress air directed into the engine;

a catalytic device situated downstream of the turbocharger to remove NOx from the exhaust;

a bypass circuit configured to selectively pass a portion of the compressed air from the turbocharger to cool the catalytic device; and

a controller configured to reduce the passing of compressed air to remove sulfur compounds from the catalytic device.

20. The power unit of claim 19 , wherein:

the compressed air cools the catalytic device below about 400° C.; and

the reduced passing of the compressed air increases the exhaust temperature above about 450° C.