VARIABLE EXHAUST MIXING DEVICE

Abstract

A system and method for variable exhaust mixing is provided. A variable exhaust mixing device including a butterfly valve is positioned in an exhaust stream and the butterfly valve is opened more to decrease mixing and closed more to increase mixing. The increased mixing provided by the variable exhaust mixing device allows the injection of dosed fuel into the exhaust stream at a lower exhaust flow rate.

Description

BACKGROUND

A Diesel Oxidation Catalyst (DOC) uses a chemical process to break down pollutants from diesel engines in the exhaust stream, turning them into less harmful components. The DOC is normally a honeycomb shaped configuration coated in a catalyst designed to trigger a chemical reaction to reduce particulate matter. More specifically, a DOC is an exhaust aftertreatment device for diesel engines and contains palladium and platinum which serve as catalysts to oxidize hydrocarbons and carbon monoxide into carbon dioxide and water.

Additionally, dosed fuel may be provided to the DOC to improve DOC performance. However, there are limitations on how much fuel can be dosed depending on exhaust flow and temperature

SUMMARY

A variable exhaust mixing system is provided that includes a butterfly valve positioned in an exhaust stream. The butterfly valve is opened more to decrease mixing and closed more to increase mixing. The increased mixing provided by the variable exhaust mixing device allows the injection of dosed fuel into the exhaust stream at a lower exhaust flow rate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a variable exhaust mixing system.

FIG. 2 illustrates the DOC inlet temperature, the Pre-DOC out temperature, the Pre-DOC in temperature, and the engine speed in rpm.

DETAILED DESCRIPTION

FIG. 1 illustrates a variable exhaust mixing system 100. FIG. 1 includes a turbocharger 110, an exhaust stream 120, a variable exhaust mixing device 130, a device controller 140, a dosing valve 150, dosed fuel 160, and a Diesel Oxidation Catalyst (DOC) 170.

In operation, the exhaust stream 120 downstream of the turbocharger 110 passes through a variable exhaust mixing device 130 that is controlled by a device control 140. The exhaust stream 120 continues to a dosing valve 150 where dosed fuel 160 is provided to the exhaust stream 120 before the exhaust stream 120 enters the DOC 170.

During operation, the variable exhaust mixing device 130 provides better mixing of the dosed fuel into the exhaust flow, which allows significantly improved conversion in the DOC 170. As shown in FIG. 1, the variable exhaust mixing device is a piece of hardware placed in the exhaust system, downstream of the turbocharger and upstream of the dosing valve, which creates swirl in the exhaust.

In one embodiment, the variable exhaust mixing device 130 is a butterfly valve placed in the exhaust stream, which may be commanded to open and close to different positions. This valve improves the mixing of the fuel into the exhaust stream and provides a wider range of engine operation where fuel may be injected. Additionally, the valve is controlled in an embodiment by software provided by the device controller 140.

Additionally, the variable exhaust mixing device allows the injection of fuel at low flow.

FIG. 2 illustrates the DOC inlet temperature 210, the Pre-DOC out temperature 220, the Pre-DOC in temperature 230, and the engine speed in rpm 240. The improved conversion due to the variable exhaust mixing device is shown in FIG. 2. More specifically, an approximately 90 C additional temperature out of the DOC was achieved under the same conditions when using a mixing device.

With regard to the software control of the valve, in an embodiment, the valve changes orientation based on engine operation. For example, low exhaust flow is provided with more aggressive mixing (the butterfly valve is closed more) which may not be possible at higher flows due to backpressure, for example. Consequently, based on exhaust flow, the valve is controlled to change its orientation to produce greater or lesser mixing.

Additionally, the ability to produce variable mixing increases the exhaust flow range in which fuel may be injected. For example, the fuel may now be injected over the entire exhaust flow operating range as opposed to not being able to be injected at flows below about 300 kg/hr, for example.

Additionally, although a butterfly valve has been discussed above, other types of valves may be employed such as a gate valve or disc valve. Additionally, multiple types of valves may be employed.

Claims

1. A variable exhaust mixing system including:

a variable exhaust mixing device positioned in an exhaust stream;

wherein said variable exhaust mixing device is controlled to decrease the amount of mixing of said exhaust stream with increasing exhaust flow.

2. The system of claim 1 wherein a device control controls said variable exhaust mixing device.

3. The system of claim 1 wherein a dosing valve is present in the exhaust stream downstream of said variable exhaust mixing device.

4. The system of claim 3 wherein said dosing valve provides dosed fuel into the exhaust stream.

5. The system of claim 1 wherein said variable exhaust mixing device is a butterfly valve.

6. The system of claim 5 wherein said butterfly valve is opened more to decrease mixing

7. The system of claim 5 wherein said butterfly valve is closed more to increase mixing.

8. The system of claim 1 wherein said variable exhaust mixing device is located downstream from a turbocharger.

9. The system of claim 1 wherein said variable exhaust mixing device is located upstream of a Diesel Oxidation Catalyst (DOC).

10. A method for producing variable mixing of an exhaust stream, said method including:

positioning a variable exhaust mixing device in an exhaust stream, wherein said variable exhaust mixing device is a butterfly valve.

11. The method of claim 10 wherein said butterfly valve is opened more to decrease mixing

12. The method of claim 10 wherein said butterfly valve is closed more to increase mixing.