Dual air circuit for exhaust gas treatment

1. An exhaust treatment system for an engine, comprising:

a diesel particulate filter;

a regeneration device to receive exhaust from the engine and being positioned upstream of the diesel particulate filter;

a compressor providing a source of compressed air;

an air/fuel nozzle coupled to the regeneration device, being in receipt of a fuel supply and the compressed air, the fuel and compressed air being forced through an orifice of the nozzle to atomize the fuel;

a bypass line providing compressed air from the compressor to the regeneration device without passing through the orifice of the nozzle; and

a valve operable to allow compressed air to flow through the bypass line when a predetermined condition exists.

2. The exhaust treatment system of claim 1 wherein a load on the compressor is reduced when the valve is open.

3. The exhaust treatment system of claim 2 wherein the valve includes a passive pressure relief valve.

4. The exhaust treatment system of claim 2 wherein the valve includes a solenoid for varying flow through the bypass line.

5. The exhaust treatment system of claim 1 further including a check valve restricting flow in the bypass line from the regeneration device toward the compressor.

6. The exhaust treatment system of claim 1 wherein the predetermined condition includes a compressed air pressure in the bypass line exceeding a predetermined value.

7. The exhaust treatment system of claim 1 wherein the regeneration device includes a primary combustion zone in receipt of the fuel and compressed air flowing through the orifice as well as the compressed air passing through the bypass line.

8. The exhaust treatment system of claim 1 further including an igniter positioned within the primary combustion zone to initiate combustion of the fuel.

9. The exhaust treatment system of claim 1 wherein the compressor is adapted to be driven by the engine.

10. The exhaust treatment system of claim 1 wherein the predetermined condition includes exceeding a 10 kPa pressure in the bypass line.

11. A method of treating exhaust from an engine, comprising:

compressing air using energy from the engine;

positioning a regeneration device upstream from a diesel particulate filter;

passing exhaust through the regeneration device and the diesel particulate filter;

providing a fuel and compressed air from the compressor to an air/fuel nozzle Coupled to regeneration device; and

providing a parallel path for compressed air from the compressor to the regeneration device bypassing the air/fuel nozzle to reduce the load on the compressor.

12. The method of claim 11 further including positioning a normally closed valve within the parallel path and supplying the compressed air to the regeneration device through the valve when a predetermined condition exists.

13. The method of claim 12 wherein the predetermined condition includes a compressed air pressure in the parallel path exceeding a predetermined value.

14. The method of claim 13 wherein the fuel and compressed air provided to the air/fuel nozzle are forced through an orifice of the nozzle to atomize the fuel.

15. The method of claim 14 further including mixing the atomized fuel with the compressed air provided via the parallel path within a primary combustion zone of the regeneration device.

16. The method of claim 15 further including igniting the atomized fuel within the primary combustion zone.

17. The method of claim 13 wherein the predetermined value of pressure within the parallel path includes 10 kPa.