DEACTIVATION BY AMMONIUM SULFATE/BISULFATE

TECHNICAL FIELD

[0001] The present application relates generally to exhaust aftertreatment systems for use with internal combustion (IC) engines.

BACKGROUND

[0002] Sulfur content in diesel fuel has decreased significantly in most markets due to increasingly stringent environmental regulations. However, certain countries have yet to implement stringent sulfur content limitations across all application segments. Additionally, off- highway and some marine applications typically permit higher sulfur content fuels than on- highway applications.

[0003] During the combustion process in an IC engine (e.g., a diesel-powered engine), sulfur is concurrently formed with carbon monoxide (CO) and hydrocarbons (HC) as various sulfur oxides (SO _x ). Typically, 97-99% of the total amount of SO _x present in exhaust gas comprises sulfur dioxide (S0 ₂ ) and 1-3% comprises sulfur trioxide (S0 ₃ ). Thus, fuel with higher sulfur content tends to produce higher amounts of S0 ₃ . For example, fuel with sulfur content of 1000 ppm may form approximately 1-3 ppm SO ₃ .

[0004] Exhaust aftertreatment systems are used to receive and treat exhaust gas generated by IC engines. Conventional exhaust gas aftertreatment systems include any of several different components to reduce the levels of harmful exhaust emissions present in exhaust gas. For example, certain exhaust aftertreatment systems for diesel-powered IC engines include a selective catalytic reduction (SCR) catalyst to convert NO _x (NO and N0 ₂ in some fraction) into harmless nitrogen gas (N ₂ ) and water vapor (H ₂ 0) in the presence of ammonia (NH3).

[0005] SO ₃ can react with ammonia to produce ammonium sulfate ((NH ₄ ) ₂ S0 ₄ ) and ammonium bisulfate (NH ₄ HSO ₄ ). Certain exhaust aftertreatment components, such as vanadium- based catalysts, are particularly sensitive to contamination from ammonium sulfate and ammonium bisulfate. Contamination from ammonium sulfate and ammonium bisulfate may trigger diagnostic error codes and/or deactivate exhaust aftertreatment components.

SUMMARY

[0006] Various embodiments relate to an exhaust aftertreatment system including an SO ₃ trap. The exhaust aftertreatment system includes an IC engine and an SCR catalyst positioned in an exhaust passage operatively connected to the IC engine. A decomposition tube is positioned in the exhaust passage upstream of the SCR catalyst, and a reductant doser is configured to inject a reductant into the decomposition tube. An SO ₃ trap is positioned in the exhaust passage upstream of the decomposition tube and downstream of the IC engine. The SO ₃ trap is configured to selectively capture S0 ₃ within exhaust gas flowing through the exhaust passage.

[0007] Another example embodiment relates to a method of treating exhaust gas. Exhaust gas is received from an internal combustion engine via an exhaust passage. S03 is selectively captured from the exhaust gas via an S03 trap positioned in the exhaust passage. Reductant is injected into a decomposition tube positioned in the exhaust passage downstream of the S03 trap. The exhaust gas is treated with an SCR catalyst positioned in the exhaust gas downstream of the decomposition tube.

[0008] These and other features, together with the organization and manner of operation thereof, will become apparent from the following detailed description when taken in conjunction with the accompanying drawings, wherein like elements have like numerals throughout the several drawings described below.

BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Fig. 1 is a schematic diagram of an exemplary conventional exhaust aftertreatment system.

[0010] Fig. 2 is a schematic diagram of another example exhaust aftertreatment system including an SO ₃ trap. [0011] Fig. 3 is a schematic diagram of another example exhaust aftertreatment system including an S0 ₃ trap and an aftertreatment control module.

[0012] Fig. 4 is a block diagram of a control system for controlling an exhaust aftertreatment system.

DETAILED DESCRIPTION

[0013] Fig. 1 is a schematic diagram of an exemplary conventional IC engine 100 and an exhaust aftertreatment system 102 fluidly coupled to an exhaust manifold (not shown) of the IC engine 100. According to various embodiments, the IC engine 100 can be a compression-ignited IC engine, such as a diesel or compressed natural gas-fueled engine, or a spark-ignited internal combustion engine, such as a gasoline-fueled engine operating lean. During operation, the IC engine 100 expels exhaust gas, which flows downstream from the IC engine 100 through an exhaust passage 104 including the exhaust gas aftertreatment system 102. Generally, the exhaust gas aftertreatment system 102 is configured to remove various chemical and particulate emissions present in the exhaust gas.

[0014] The exhaust aftertreatment system 102 includes an SCR catalyst 106. The SCR catalyst 106 is configured to reduce NO _x into less harmful emissions, such as N ₂ and H ₂ 0, in the presence of ammonia. Because ammonia is not a natural byproduct of the combustion process, it must be artificially introduced into the exhaust gas prior to the exhaust gas entering the SCR catalyst. Typically, ammonia is not directly injected into the exhaust gas due to safety

considerations associated with storage of liquid ammonia. Accordingly, the exhaust

aftertreatment system 102 includes a doser 108 that is configured to inject diesel exhaust fluid (DEF), which is typically a urea-water solution, into the exhaust gas, where it decomposes into ammonia. In particular, the doser 108 is configured to inject DEF into a decomposition tube 110, which facilitates the decomposition of DEF into ammonia.

[0015] Generally, the urea present in DEF decomposes into gaseous ammonia in three stages. First, the urea evaporates or mixes with exhaust gas. Second, the temperature of the exhaust gas causes a phase change in the urea and decomposition of the urea into isocyanic acid (HNCO) and water. Third, the isocyanic acid reacts with water in a hydrolysis process under specific pressure and temperature concentrations to decompose into ammonia and carbon dioxide (C0 ₂ ). The ammonia is then introduced at the inlet face of the SCR catalyst 106, flows through the catalyst, and is consumed in the NO _x reduction process. Any unconsumed ammonia exiting the SCR catalyst 106 (e.g., "ammonia slip") can be reduced to N ₂ and other less harmful or less noxious components using an ammonia oxidation catalyst (not shown).

[0016] As stated above, the exhaust gas, especially exhaust gas from IC engines 100 running on diesel fuel with high sulfur content, can contain various levels of sulfur oxides, including S0 ₃ . SO ₃ can react with ammonia (e.g., decomposed from DEF) to produce ammonium sulfate ((NH ₄ ) ₂ S0 ₄ ) and ammonium bisulfate (NH ₄ HSO ₄ ) through the following chemical reactions:

2NH ₃ + S0 ₃ + H ₂ 0→ (NH ₄ ) ₂ S0 ₄ (1)

NH3 + S0 ₃ + H ₂ 0→ NH ₄ HSO ₄ (2)

[0017] Certain exhaust aftertreatment components, such as SCR catalysts and diesel oxidation catalysts (DOCs), are particularly sensitive to contamination from ammonium sulfate and ammonium bisulfate, which may trigger diagnostic (e.g., on-board diagnostic (OBD)) error codes and derate engine performance. In particular, vanadium-based SCR catalysts and DOCs are especially sensitive to contamination from ammonium sulfate and ammonium bisulfate. In fact, SCR catalyst deactivation due to the formation of ammonium sulfate and ammonium bisulfate over vanadium-based SCR catalysts is one of the major sources of aftertreatment deactivation issues for diesel engines operating certain markets having high sulfur diesel fuel (e.g., China, Russia, Malaysia, and Indonesia). Because of these reactions mentioned above in which S0 ₃ reacts with ammonia to produce ammonium sulfate and ammonium bisulfate, it is essential to minimize the amount of unreacted ammonia (e.g., ammonia slip) and/or the amount of S0 ₃ in the exhaust gas upstream of the SCR catalyst 106 to minimize the formation of ammonium sulfate and ammonium bisulfate. [0018] The present disclosure is directed towards an SO ₃ trap that is positioned upstream of an SCR catalyst. The S0 ₃ trap is configured to selectively trap and contain S0 ₃ from exhaust gas so as to substantially or completely prevent formation of ammonium sulfate and ammonium bisulfate. The SO ₃ trap is well suited for applications in which diesel fuel tends to contain high levels of sulfur (e.g., 350 ppm or higher). Based on extensive engine test data, it has been determined that fuel with sulfur levels of 350 ppm or higher can cause SCR deactivation due to the formation of ammonium sulfate and ammonium bisulfate.

[0019] Fig. 2 is a schematic diagram of an IC engine 200 and an exhaust aftertreatment system 202 fluidly coupled to the engine 200, according to an example embodiment. Similar to the exhaust aftertreatment system 102 of Fig. 1, the exhaust aftertreatment system 202 includes an SCR catalyst 206 positioned in an exhaust passage 204 and a doser 208 configured to inject DEF into a decomposition tube 210 positioned upstream of the SCR catalyst 206. However, the exhaust aftertreatment system 202 of Fig. 2 further includes an SO ₃ trap 212 positioned downstream of the engine 200 and upstream of each of the doser 208 and the decomposition tube 210. In various embodiments, depending on the application and engine platform, the SO ₃ trap 212 may be installed in the exhaust passage 204 between the turbine output (not shown) and the decomposition tube 210. The SO ₃ trap 212 is configured to be highly selective, such that it selectively traps S0 ₃ in the presence of other compounds, such as S0 ₂ , NO _x , PM, etc.

[0020] By positioning the SO ₃ trap 212 upstream of each of the decomposition tube 210 and the doser 208, any SO ₃ present in the exhaust gas is trapped by the SO ₃ trap 212 before the SO ₃ comes in contact with the ammonia converted from the DEF dispensed into the decomposition tube 210. By preventing the SO ₃ from reacting with the ammonia, the formation of ammonium sulfate and ammonium bisulfate is therefore prevented. Thus, the SO ₃ trap 212 prevents deactivation of the SCR catalyst 206 due to ammonium sulfate and ammonium bisulfate contamination/ formation.

[0021] According to various example embodiments, the SO ₃ trap 212 includes an extruded substrate. In such embodiments, the catalyst may be incorporated throughout the substrate (e.g., homogenous). In other example embodiments, the SO ₃ trap 212 includes a coated substrate. In such embodiments, the catalyst is coated on the substrate (e.g., as a washcoat). According to various examples, the catalyst of the SO ₃ trap 212 can include mixed-oxide materials including at least one of various alkali metals (e.g., Na and K), alkaline earth metals (e.g., Ca, Ba, and Mg), and transition metals (e.g., Co, Mn, Cr, Zr, and Ni).

[0022] In some example embodiments, the SCR catalyst 206 is a first SCR catalyst, and the SO ₃ trap 212 is formed on a second SCR catalyst. According to various examples, the second SCR catalyst includes at least one of a vanadia catalyst, a Cu-zeolite catalyst, a Fe-zeolite catalyst, and a mixed-oxide catalyst. In one example, the SO ₃ trap 212 is formed on the second SCR catalyst by zone-coating a first zone of the second SCR catalyst. In this example, the first zone would operate as an SO ₃ trap and a second zone would operate as an SCR catalyst. In another example, the SO ₃ trap is formed on the second SCR catalyst by layer-coating the second SCR catalyst. In this example, the first layer operates as an SCR catalyst, and a second layer coating the first layer operates as an SO ₃ trap.

[0023] As mentioned above, the amount of SO ₃ in diesel exhaust gas is relatively low compared to other exhaust gas pollutants (e.g., S0 ₂ , NO _x , PM, etc.). Because the SO ₃ trap 212 is configured to selectively trap SO ₃ and to not trap other compounds, such as S0 ₂ , NO _x , PM, etc., the SO ₃ trap 212 may be relatively small in size while having sufficient capacity to last for a significantly long time (e.g., the useful life of the engine 200) before it must be replaced or regenerated. In an example embodiment, the SO ₃ trap 212 is a single-use trap that is replaceably coupled to the exhaust passage 204. In such embodiments, the SO ₃ trap 212 is capable of being removed from the exhaust aftertreatment system 202 (e.g., decoupled from the exhaust passage 204) after operating for a particular operating life. After being removed from the exhaust aftertreatment system 202, the SO ₃ trap 212 may easily be replaced by a new SO ₃ trap 212.

According to various embodiments, the SO ₃ trap 212 may be coupled to the exhaust passage 204 in any number of suitable coupling techniques, such as by bolting together mating flanges on each of the S0 ₃ trap 212 and the exhaust passage 204, or threadedly coupling the S0 ₃ trap to the exhaust passage 204, among other coupling techniques. In some example embodiments, the SO ₃ trap 212 is configured to operate for a relatively long operating life (e.g., 100,000 miles) before requiring replacement. In other example embodiments, the S0 ₃ trap 212 is configured to operate for a relatively shorter operating life (e.g., 5,000 miles), in which case the SO ₃ trap 212 is designed to be relatively low-cost.

[0024] In other example embodiments, the SO ₃ stored in the SO ₃ trap 212 is periodically cleaned out, or in other words, the S0 ₃ trap 212 is "regenerated." According to an example embodiment, the SO ₃ trap 212 is regenerated online by heating the exhaust gas above a particular temperature to release the SO ₃ from the SO ₃ trap 212. Online regeneration refers to regenerating the SO ₃ trap 212 without removing the SO ₃ trap from the exhaust aftertreatment system 202. According to example embodiments, the exhaust gas temperature may be raised to initiate online regeneration by throttling intake air, adapting an exhaust gas recovery (EGR) rate, injecting excess fuel, and by utilizing electric heating systems, among other ways. In some example embodiments, regeneration is performed according to a fixed schedule (e.g., every 5,000 miles). However, other embodiments include an aftertreatment control module that utilizes

measurements from various sensors (e.g., temperature and pressure sensors) to facilitate active regeneration.

[0025] Fig. 3 is a schematic diagram of an IC engine 300 and an exhaust aftertreatment system 302 fluidly coupled to the engine 300, according to an example embodiment. Similar to the exhaust aftertreatment system 202 of Fig. 2, the exhaust aftertreatment system 302 includes an SCR catalyst 306 positioned in an exhaust passage 304, a DEF doser 308 configured to inject DEF into a decomposition tube 310 positioned upstream of the SCR catalyst 306, and an SO ₃ trap 312 positioned downstream of the engine 300 and upstream of each of the DEF doser 308 and the decomposition tube 310. The exhaust aftertreatment system 302 of Fig. 3 further includes an aftertreatment control module 316 operative ly coupled to the IC engine 300 and to various sensors to control the exhaust aftertreatment system 302. In some examples, the aftertreatment control module 316 is configured to control exhaust gas parameters (e.g., exhaust gas

temperature) to initiate online regeneration of the SO ₃ trap 312. For example, the aftertreatment control module 316 can cause exhaust gas temperatures to be raised to initiate online regeneration by throttling intake air, adapting an exhaust gas recovery (EGR) rate, injecting excess fuel, and by utilizing electric heating systems, among other ways. In some examples, the aftertreatment control module 316 is further operatively coupled to the DEF doser 308 to control the dosing rate at which the DEF doser 308 injects DEF into the decomposition tube 310.

According to various example embodiments, the aftertreatment control module 316 may be a stand-alone electronic control module, or may be incorporated into an engine control module (ECM), a transmission control module (TCM), or other electronic control modules.

[0026] According to an example embodiment, the exhaust aftertreatment system 302 further includes various sensors to measure exhaust gas conditions, such as a first temperature sensor 318 positioned to measure a first temperature of exhaust gas flowing through the exhaust passage 304 upstream of the S0 ₃ trap 312, and a second temperature sensor 320 positioned to measure a second temperature of the exhaust gas downstream of the SO ₃ trap 312 and upstream of the decomposition tube 310. The exhaust aftertreatment system 302 further includes a first pressure sensor 322 positioned to measure a first pressure of the exhaust gas upstream of the S0 ₃ trap 312, and a second pressure sensor 324 positioned to measure a second pressure of the exhaust gas downstream of the SO ₃ trap 312 and upstream of the decomposition tube 310. In some embodiments, the aftertreatment control module 316 controls regeneration of the SO ₃ trap 312 based on the first and second temperatures and based on the first and second pressures, among other parameters. For example, a high pressure differential across the SO ₃ trap 312, as measured by the first and second pressure sensors 322, 324, may indicate that the SO ₃ trap 312 is full and must be regenerated.

[0027] Fig. 4 is a block diagram of a control system for controlling an exhaust aftertreatment system in accordance with example embodiments. The exhaust aftertreatment control system includes a controller 400 structured to perform certain operations to control regeneration of an SO ₃ trap (e.g., the SO ₃ trap 312 of Fig. 3). In certain embodiments, the controller 400 forms a portion of a processing subsystem including one or more computing devices having memory, processing, and communication hardware. The controller 400 may be a single device (e.g., the aftertreatment control module 316 of Fig. 3) or a distributed device, and the functions of the controller 400 may be performed by hardware and/or as computer instructions on a non-transient computer readable storage medium.

[0028] The controller 400 may include a microprocessor, an application-specific integrated circuit (ASIC), a field-programmable gate array (FPGA), etc., or combinations thereof. The controller 400 may include memory which may include, but is not limited to, electronic, optical, magnetic, or any other storage or transmission device capable of providing a processor, ASIC, FPGA, etc. with program instructions. The memory may include a memory chip, Electrically Erasable Programmable Read-Only Memory (EEPROM), erasable programmable read only memory (EPROM), flash memory, or any other suitable memory from which the controller 400 can read instructions. The instructions may include code from any suitable programming language.

[0029] In certain embodiments, the controller 400 includes one or more modules structured to functionally execute the operations of the controller. As shown in Fig. 4, the controller 400 may include one or more measurement modules 402 configured to measure various exhaust gas conditions within an exhaust aftertreatment system. In particular embodiments, the one or more measurement modules 402 may be configured to determine exhaust gas conditions, including, but not limited to a first temperature of exhaust gas upstream of an S0 ₃ trap, a second temperature of the exhaust gas downstream of the SO ₃ trap and upstream of a decomposition tube, a first pressure of the exhaust gas upstream of the S0 ₃ trap, and a second pressure of the exhaust gas downstream of the SO ₃ trap and upstream of the decomposition tube.

[0030] In certain embodiments, the controller 400 also includes an exhaust aftertreatment control module 404 communicatively coupled to the at least one measurement module 402. The exhaust aftertreatment control module 404 is configured to precisely control exhaust gas parameters (e.g., temperature) based on the exhaust gas measurement signals, such as the first and second temperatures, and the first and second pressures, among others. For example, the aftertreatment control module 404 can cause exhaust gas temperatures to be raised to initiate online regeneration by throttling intake air, adapting an exhaust gas recovery (EGR) rate, injecting excess fuel, and by utilizing electric heating systems, among other ways.

[0031] It should be noted that the terms "example" and "exemplary" as used herein to describe various embodiments are intended to indicate that such embodiments are possible examples, representations, and/or illustrations of possible embodiments (and such terms are not intended to connote that such embodiments are necessarily extraordinary or superlative examples).

[0032] The description herein including modules emphasizes the structural independence of the aspects of the controller, and illustrates one grouping of operations and responsibilities of the controller. Other groupings that execute similar overall operations are understood within the scope of the present application. Modules may be implemented in hardware and/or as computer instructions on a non-transient computer readable storage medium, and modules may be distributed across various hardware or computer based components. More specific descriptions of certain embodiments of controller operations are included in the section referencing Fig. 3. Example and non-limiting module implementation elements include sensors providing any value determined herein, sensors providing any value that is a precursor to a value determined herein, datalink and/or network hardware including communication chips, oscillating crystals, communication links, cables, twisted pair wiring, coaxial wiring, shielded wiring, transmitters, receivers, and/or transceivers, logic circuits, hard-wired logic circuits, reconfigurable logic circuits in a particular non-transient state configured according to the module specification, any actuator including at least an electrical, hydraulic, or pneumatic actuator, a solenoid, an op-amp, analog control elements (springs, filters, integrators, adders, dividers, gain elements), and/or digital control elements.

[0033] While various embodiments of the disclosure have been shown and described, it is understood that these embodiments are not limited thereto. The embodiments may be changed, modified and further applied by those skilled in the art. Therefore, these embodiments are not limited to the detail shown and described previously, but also include all such changes and modifications.