Methods and apparatus for injecting atomized fluid

Abstract

The present invention provides methods and apparatus for injecting fluid, such as an aqueous urea solution, into an exhaust stream in order to reduce oxides of nitrogen (NOx) emissions from diesel engine exhaust. The present invention uses mechanical spill return atomization techniques to produce droplets having an average size of approximately 50 μm SMD or smaller. This size range is appropriate to allow urea to react into ammonia within the residence time associated with an on-road diesel engine. This effect is achieved through the use of a whirl plate having a plurality of whirl slots surrounding an exit orifice of the injector, which produce a high velocity rotating flow in the whirl chamber. When the rotating flow of fluid is passed through the exit orifice into an exhaust stream, atomization occurs from a combination of centrifugal force and shearing of the fluid by air as it jets into the exhaust stream.

Description

[0001] This application is a continuation-in-part of co-pending, commonly assigned U.S. patent application Ser. No. 11 / 112,039 filed on Apr. 22, 2005, which claims the benefit of U.S. Provisional Application No. 60 / 565,356, filed Apr. 26, 2004.BACKGROUND OF THE INVENTION [0002] The present invention relates generally to the reduction of emissions produced by lean burn engines. In particular, the present invention provides methods and apparatus for injecting fluid, such as an aqueous urea solution, into an exhaust stream in order to reduce oxides of nitrogen (NOx) emissions from diesel engine exhaust. [0003] Lean burn engines provide improved fuel efficiency by operating with an excess of oxygen over the amount necessary for complete combustion of the fuel. Such engines are said to run “lean” or on a “lean mixture.” However, this increase in fuel economy is offset by undesired pollution emissions, specifically in the form of oxides of nitrogen (NOx). [0004] One method used to reduce ...

AI Technical Summary

Benefits of technology

[0011] The present invention provides improved methods and apparatus for injecting fluid, such as an aqueous urea solution, into an exhaust stream in order to reduce oxides of nitrogen (NOx) emissions from diesel engine exhaust. In particular, the injector of the present invention is an enhanced performance atomizer for use with any diesel or natural gas engine.

Problems solved by technology

Such engines are said to run “lean” or on a “lean mixture.” However, this increase in fuel economy is offset by undesired pollution emissions, specifically in the form of oxides of nitrogen (NOx).

However, use of such an aqueous urea solution involves many disadvantages.

Urea is highly corrosive and attacks mechanical components of the SCR system, such as the injectors used to inject the urea mixture into the exhaust gas stream.

Solidified urea may foul moving parts of the injector and clog any openings, rendering the injector unusable.

In addition, if the urea mixture is not finely atomized, urea deposits will form in the catalytic reactor, inhibiting the action of the catalyst and thereby reducing the SCR system effectiveness.

However, high injection pressures often result in over-penetration of the injector spray plume into the exhaust stream, causing the plume to impinge on the inner surface of the exhaust pipe opposite the injector.

Over-penetration leads to inefficient use of the urea mixture and reduces the range over which the vehicle can operate with reduced NOx emissions.

Further, aqueous urea is a poor lubricant.

This characteristic adversely affects moving parts within the injector and requires that special fits, clearances and tolerances be employed between relatively moving parts within an injector.

This characteristic adversely affects mating surfaces requiring enhanced sealing resources in many locations.

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