TECHNICAL FIELD

[0001] The present device relates to an ammonia flow modulator (AFM) used in a NOx reduction system to control ammonia gas flow to an exhaust after-treatment system. Particularly, the device relates to an AFM having features to prevent or reduce moisture buildup in the ammonia flow passages.

BACKGROUND

[0002] Compression ignition engines provide advantages in fuel economy, but produce both Οχ and particulates during normal operation. New and existing regulations continually challenge manufacturers to achieve good fuel economy and reduce the particulates and NO _x emissions. Lean-burning engines achieve the fuel economy objective, but the high concentrations of oxygen in the exhaust of these engines yields significantly high

concentrations of NO _x as well. Accordingly, the use of NO _x reducing exhaust treatment schemes is being employed in a growing number of systems.

[0003] One such system is the direct addition of ammonia gas to the exhaust stream. It is an advantage to deliver ammonia directly in the form of a gas, both for simplicity of the flow control system and for efficient mixing of the reducing agent, ammonia, with the exhaust gas. The ammonia dosing is controlled based on any number of readings taken by the system, including exhaust gas temperature, pressure, etc. In addition, an aqueous urea solution cannot be dosed at a low engine load since the temperature of the exhaust gas line would be too low for complete conversion of urea to ammonia (and CO ₂ ).

[0004] Direct ammonia gas dosing is not, however, without complications. Trapped ammonia in flow passages, particularly passages in a flow modulator, can hold moisture which may freeze in the passage. Further, moisture which pools or becomes trapped in valves or proximate sensors can significantly upset ammonia dosing schemes. This can lead to failed emission testing for a vehicle and potential revenue losses for a vehicle owner.

[0005] Accordingly, the present device operates to reduce, if not eliminate, moisture to prevent pooling in modulator passages. This protects the passages and associated valves and sensors. Alternatively, the device may eliminate the freezing issue to prevent blocking and disruption of ammonia flow. SUMMARY

[0006] There is disclosed herein a device which avoids the disadvantages of prior devices while affording additional structural and operating advantages.

[0007] Generally, a reductant (ammonia) flow modulator comprising a housing, a fluid passage, a first valve, preferably having a precision orifice, positioned within the passage, and an orientation which prevents fluid from pooling in the passage is disclosed and claimed. The passage orientation is preferably substantially vertical to allow gravity to pull fluid from the passage and prevent pooling.

[0008] In an alternate embodiment, a heat source may be positioned within the housing proximate at least one of a fluid inlet, a fluid outlet, or the fluid passage. The heat source prevents freezing of fluid in the passage.

[0009] In an embodiment of the device, the heat source comprises an electric heating element. In a distinct embodiment, the heat source comprises an exhaust gas heat exchanger.

[0010] In either embodiment, the ammonia flow modulator may further comprise a second inlet and a second passage fluidly connecting the second inlet to the outlet. This is preferably accomplished by fluidly linking the second passage to the first passage and including a check valve to prevent backflow. A controller coupled to the first valve is used to control ammonia flow.

[0011] These and other embodiments and their advantages can be more readily understood from a review of the following detailed description and the corresponding appended drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] FIG. 1 is a schematic of an exhaust gas NO _x reduction (EGNR) system incorporating the start-up cartridge and main cartridges of the present system;

[0013] FIG. 2 is a perspective view of the mantel housing containing the main cartridges and the start-up cartridge positioned near but separate from the mantle;

[0014] FIG. 3 is a right side view of the mantle housing;

[0015] FIG. 4 is a left side view of the mantle housing;

[0016] FIG. 5 is a schematic illustrating one embodiment of an AFM device in accordance with the present disclosure; and

[0017] FIG. 6 is a schematic illustrating another embodiment of an AFM device in accordance with the present disclosure. DETAILED DESCRIPTION

[0018] Referring to FIGS. 1-6, there is illustrated a system for storage and delivery of gaseous ammonia for use in the reduction of NO _x in an exhaust gas stream (EGNR). The present flow modulator device, generally designated by the numeral 10, is discussed with respect to ammonia flow control, specifically for controlling the supply of ammonia gas to an after-treatment device 30 (FIG. 1) for use in a compression ignition engine (not shown). As the exhaust system of a vehicle, including that of a diesel engine, is well known, it will not be described in detail.

[0019] A reductant, such as ammonia gas is delivered to the exhaust stream by way of a fluid tubing 50 connected at one end to an ammonia source 40 and at the other end to an injector 60 positioned within the exhaust stream.

[0020] As shown in FIGS. 2-4, the ammonia source 40 used for ammonia dosing in the exhaust stream includes a first or start-up unit 12 and a mantle housing 14 having a main unit 16 containing at least one cartridge or canister. The ammonia-containing material loaded into the cartridges of units 12 and 16— also referred to herein as the start-up cartridge 12 and main cartridge 16— is generally in a solid form, such as a compressed powder or granules, and may include any suitable shape for packing into the cartridges, including disks, balls, granules, or a tightly -packed powder.

[0021] Suitable material for use with the present system include metal-ammine salts, which offer a solid storage medium for ammonia, and represent a safe, practical and compact option for storage and transportation of ammonia. Ammonia may be released from the metal ammine salt by heating the salt to temperatures in the range from 10°C to the melting point to the metal ammine salt complex, for example, to a temperature from 30° to 700°C, and preferably to a temperature of from 100° to 500°C. Generally speaking, metal ammine salts useful in the present device include the general formula M(NH ₃ ) _n X _z , where M is one or more metal ions capable of binding ammonia, such as Li, Mg, Ca, Sr, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, etc., n is the coordination number usually 2-12, and X is one or more anions, depending on the valence of M, where representative examples of X are F, CI, Br, I, S0 ₄ , Mo0 ₄ , P0 ₄ , etc. Preferably, ammonia saturated strontium chloride, Sr(NH ₃ )Ci _2, is used. While embodiments using ammonia as the preferred reductant are disclosed, the invention is not limited to such embodiments, and other reductants may be utilized instead of, or in addition to, ammonia for carrying out the inventions disclosed and claimed herein. Examples of such other, or additional reductants include, but are not limited to, urea, ammonium carbamate, and hydrogen.

[0022] As noted above, in order to use the ammonia gas in the treatment of NO _x in an exhaust system, it is necessary to apply a sufficient amount of heat to the cartridges of units 12 and 16, and thus the ammonia-containing material, in order to release the ammonia into its useful gaseous form. Heating the cartridges of units 12, 16 may be accomplished through use of any suitable heating device, such as heating jacket or mantle (not shown) surrounding the cartridges. In this regard, during the initial start-up of an engine, there is generally insufficient heat generated to activate the ammonia-containing material, especially material stored in the main unit 16 within the mantle housing 14. Therefore, in order to jump-start the release of ammonia gas into the after-treatment device 30 and the exhaust stream, the smaller first or start-up unit 12 is positioned separately from the mantle 14 containing the cartridges of main unit 16. Because of its significantly smaller size than that of the main cartridges 16, the first or start-up cartridge 12 can be heated quickly after receiving the appropriate signals from the vehicle's electronics system including an electronic control module (ECM) 18 and Peripheral Interface Module (PIM) 20, which are transmitted to the heating device (not shown). In this manner, the start-up cartridge 12 can start releasing ammonia gas into an after-treatment device 30 and the exhaust stream practically from the initial start-up of the engine, while the main unit 16 is more slowly readied. The flow of ammonia gas from the start-up unit 12 and the main unit 16 is directed through the ammonia flow modulator 10.

[0023] The flow modulator 10 comprises a housing 42 having an inlet 44 for each of the start-up unit 12 and main unit 16, an outlet 46, passages 48 which connect the inlets 44A,B to the outlet 46, and a control valve 52. As shown in FIG. 5, the passage 48B from the inlet of the main unit intersects the passage 48A from the start-up unit before or upstream of the control valve 52. A check valve 54 may be used to prevent backflow from the start-up unit passage 48A into the main unit passage 48B. Also, a pressure release valve 56 may be positioned to bypass the control valve 52 to prevent damaging the precision orifice of the control valve 52.

[0024] The ammonia flow modulator 10 also contains a plurality of circuits and sensors which are designed to facilitate the flow of a sufficient amount of ammonia gas to the exhaust after-treatment device 30. Each passage 48 may include a pressure sensor 62 and/or a temperature sensor 64 to monitor incoming ammonia gas characteristics. An effluent pressure sensor 65 may be positioned downstream of the control valve 52 as well. A controller 70 is preferably coupled to each of the sensors (pressure and temperature) and valves, including the control valve 52 and pressure release valve 56, to orchestrate proper ammonia delivery from each of the start-up unit 12 and the main unit 16.

[0025] A key aspect of the flow modulator 10 is its ability to prevent blockage due to water freezing in the passages or valves. In a first embodiment, shown in FIG. 5, a heat source 80 is used to maintain the modulator components at a suitable temperature. The heat source 80 may be, for example, an electric heating element, a heat exchanger coupled to the exhaust gas, or any other suitable device for supplying heat to the modulator 10. The heat source 80 is preferably positioned within the housing 42 of the modulator 10, proximate the inlets 44, the passages 48, and the control valve 52. The controller 70 of the modulator 10 can be coupled to the heat source 80 and a temperature sensor to regulate the modulator temperature, as necessary.

[0026] An alternate embodiment of the flow modulator 10 is shown in FIG. 6, where the orientation of the modulator passages 48 prevent moisture from becoming trapped within the modulator 10. The passages 48 are generally vertically oriented and straight to take full advantage of gravity to move ammonia through. The lack of "bends" and horizontal surfaces within the passages 48 prevents moisture pooling and keeps them free of fluid during non-use when freezing is most likely to occur. For added reliability, heat sources may also be employed for such embodiments, if desired.

[0027] Once the ammonia gas is completely released from the ammonia-containing material contained within the start-up unit 12, and the system temperature has reached a sufficient level to activate the main unit 16, the start-up unit 12 can be replenished with ammonia for subsequent use. Positioning the start-up unit 12 outside of the mantle 14 containing the main unit 16, maximizes the heat loss from the start-up unit 12, and also prevents it from being affected by the heat generated from the mantle 14 and main unit 16. Once the cartridge 12 cools to a certain level where the ammonia gas is no longer released from the ammonia-containing material, the material within the unit 12 can be replenished. Replenishing the ammonia-absorbing material can be accomplished in any number of ways, including re-directing a partial flow of ammonia gas released from the main unit 16 due to the drop in temperature to the start-up cartridge, or replenishing by an outside, exterior source of ammonia gas or liquid, or by any other suitable means.

[0028] In addition, by enclosing the main unit 16 within a mantle housing 14, it is possible to control and maintain the activating temperature required to release the ammonia gas from the material contained within the cartridge or cartridges. The housing 14 acts to minimize the loss of heat to the ambient temperature. Minimizing the temperature loss provides a more efficient and consistent release of ammonia gas from the ammonia- containing material within the main cartridge 16 to an after-treatment device 30.

[0029] The start-up cartridge 12 is preferably positioned outside of the mantle housing 14 containing the main cartridge units 16 in such a manner that the start-up cartridge is able to cool down quickly without being influenced by any heat generated from the main cartridge unit. In this manner, the ammonia-containing material in the start-up cartridge 12 can be replenished quickly once the cartridge is cooled below the temperature required for sublimation of the material to ammonia gas.

[0030] Regeneration of the start-up cartridge 12 can be accomplished by directing ammonia gas from the main cartridges 16. Quick regeneration of the start-up cartridge permits it to be ready immediately for the next time the engine is started. The method further comprises a step of maintaining an activating temperature inside the mantle 14 for sufficient release of ammonia gas from the ammonia-containing material within the main cartridge to the after-treatment device 30. In this manner, the method provides for a consistent flow of ammonia into the exhaust stream, and thus, a more efficient and consistent reduction of NO _x .