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 approximately 50 μm SMD (Sauter mean diameter) 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 divisional 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 NOx emissi...

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.

[0014] In addition, the present invention provides further improvements over the injector of the '603 patent, including increased magnetic pull strength of the metering plug over a wide temperature range, prolonged life of the injector valve and associated actuating components, and cooling with the urea throughout the injector. Additionally, the present invention incorporates adjustable spray quality characteristics on line, and interchangeability of orifice plates for multiple size applications. The ribbed injector body provides additional cooling capability.

[0015] The present invention may be further adapted to provide an injector for injecting hydrocarbons particularly for the purpose of particulate reduction in a diesel exhaust. The combination of pulse width modulation providing instantaneous timing control and mechanical atomization techniques is appropriate for providing small quantities of hydrocarbons with precise timing. The cooling aspects provided by the present invention allow the injector to survive the hot exhaust conditions as well as prevent pre-ignition of the hydrocarbon.

[0016] In an example embodiment of the present invention, methods and apparatus for injecting atomized fluid are provided. An injector is provided, which comprises an injector body, and a whirl chamber arranged on the injector body. The whirl chamber has an exit orifice. A plurality of whirl slots may be provided in the whirl chamber for imparting a rotational velocity to fluid introduced into the whirl chamber. A valve seat positioned within the whirl chamber surrounds the exit orifice. A metering plug may be arranged within the injector body. An actuator may also be mounted on the injector body and connected to the metering plug for moving the metering plug between closed and open positions. The actuator may be located in the injector body and connected to the metering plug for enabling movement of the metering plug from the closed position to the open position.

[0018] The injector may further comprise a fluid inlet extending into the injector and a fluid outlet extending out of the injector. The fluid inlet and fluid outlet may communicate with the whirl chamber via a hollow portion of the metering plug. The fluid inlet, the fluid outlet, and the hollow portion of the metering plug may provide a flow path for fluid through the injector, thereby enabling cooling of the injector. The flow path for the fluid through the injector may be provided independently of the position of the metering plug.

[0019] A metering orifice located in the injector body may control the flowrate of cooling fluid flowing through the injector at a given inlet pressure. The fluid may be a urea solution or a hydrocarbon.

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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