On-vehicle nitrogen oxide aftertreatment system

An emissions system for reducing nitrogen oxides in engine exhaust includes an emissions catalyst having an inlet adapted to receive an exhaust from the engine. A fuel tank is adapted to provide fuel for combustion within the engine. A first injector is operable to inject fuel into the exhaust upstream of the catalyst. A second injector is operable to inject supplemental reductant from a supplemental reductant tank into the exhaust upstream of the catalyst. A controller is operable to control the first and second injectors and vary the supply of fuel and supplemental reductant into the exhaust to reduce nitrogen oxides within the exhaust.

BACKGROUND

Selective catalytic reduction technology has been used in conjunction with reducing nitrogen oxides present in the exhaust of internal combustion engines. Many vehicles utilizing internal combustion engines as a prime mover are also equipped with exhaust aftertreatment devices for reducing nitrogen oxide emissions. Some of these systems are constructed using urea-based technology including a separate container mounted to the vehicle for storing the urea, a urea injector and a selective catalytic reduction catalyst. While these systems may have performed well in the past, it may be desirable to provide a selective catalytic reduction system operable without the use of urea or other reductants not typically onboard a vehicle.

SUMMARY

An emissions system for reducing nitrogen oxides in engine exhaust includes an emissions catalyst having an inlet adapted to receive an exhaust from the engine. A fuel tank is adapted to provide fuel for combustion within the engine. A first injector is operable to inject fuel into the exhaust upstream of the catalyst. A second injector is operable to inject supplemental reductant from a supplemental reductant tank into the exhaust upstream of the catalyst. A controller is operable to control the first and second injectors and vary the supply of fuel and supplemental reductant into the exhaust to reduce nitrogen oxides within the exhaust.

An emissions system for reducing nitrogen oxides in engine exhaust includes an emissions catalyst having an inlet adapted to receive an exhaust from the engine. An injector is operable to inject a reductant into the exhaust upstream of the catalyst. A fuel tank is adapted to provide fuel for combustion within the engine. A valve is supplied fuel from the fuel tank. The valve is also in receipt of a reductant from a supplemental reductant tank. The valve is operable to selectively supply one or both of the fuel and the supplemental reductant to the injector to reduce nitrogen oxides within the exhaust.

An emissions system includes an emissions catalyst having an inlet adapted to receive an exhaust from an engine. A first injector is operable to inject fuel from a fuel tank into the exhaust upstream of the catalyst. The fuel tank also provides fuel for combustion in the engine. A second injector is operable to inject supplemental reductant stored in a supplemental reductant tank into the exhaust upstream of the catalyst. A burner is in receipt of the exhaust and positioned upstream from the first and second injectors. A diesel particulate filter is positioned downstream of the burner and upstream of the first and second injectors. A controller is operable to control the burner as well as the first and second injectors to vary the supply of fuel and supplemental reductant into the exhaust to reduce nitrogen oxides within the exhaust.

DETAILED DESCRIPTION

FIG. 1depicts an exhaust treatment system10associated with an exemplary vehicle12. Vehicle12includes an engine14arranged as a prime mover having an exhaust port16in fluid communication with an exhaust pipe18. Engine exhaust flows through pipe18in the direction indicated by the arrow. An injector20is positioned to inject a reductant into the engine exhaust flowing through exhaust pipe18. An emissions catalyst22is positioned downstream of injector20and is in receipt of engine exhaust flowing through pipe18.

A fuel tank26is mounted to vehicle12to store fuel. Fuel tank26is in communication with engine14via a fuel supply line27such that fuel may be selectively supplied to combustion chambers of engine14. It is contemplated that engine14may be a gasoline fueled spark ignition engine or may be a diesel fueled compression engine. Fuels for the gasoline engine may include gasoline, E85, E95 or other similar fuels. Fuels for the diesel engine may include diesel fuel, biofuel B5, B10, B20 or other similar fuels. A supplemental reductant tank28is also mounted to vehicle12. It is contemplated that tank28may store a readily available reductant such as E85, E95, B5, B10, B20 or the like.

A valve30selectively interconnects injector20with one or both of fuel tank26and supplemental reductant tank28. More particularly, a first supply line32extends from fuel tank26to a first inlet port34of valve30. In similar fashion, a second supply line36interconnects tank28and a second inlet port38of valve30.

A controller40, such as an electronic control unit, is operable to control valve30to selectively supply reductant to injector20. Controller40may cause valve30to solely provide fuel from tank26to injector20. Depending on the conditions present, fuel may act as a suitable reductant. Controller40may also control valve30to solely supply the reductant stored within supplemental reductant tank28to injector20. Controller40may simultaneously provide fuel and a supplemental reductant to injector20at one of any number of mixing ratios between 0-100%.

A plurality of sensors42may be in communication with controller40such that the signal provided to control valve30is based on an evaluation of vehicle data. Sensors42may provide signals indicative of, but not limited to, engine speed, engine operating temperature, exhaust temperature, mass air flow, diesel fuel volume within tank26, reductant volume within tank28, NOxconcentration, HC concentration, O2concentration, H2concentration, ammonia concentration and other data that may be available from a CAN bus or dedicated sensors mounted to vehicle12. Based on the input provided from sensors42, controller40selectively operates injector20by injecting the reductant flowing through valve30.

FIG. 2depicts NOxconversion versus temperature having E85 as a reductant used in cooperation with two different catalysts. Catalyst A and catalyst B represent two known catalysts used for selective catalytic reduction in urea-based systems. It should be noted that relatively high NOxconversion is depicted while using E85 as the reductant with either catalyst. The graph depicts a merely exemplary and non-limiting example of E85 concentration where the hydrocarbon to NOxratio is five.

FIG. 3depicts NOxreduction percent versus a ratio of hydrocarbon to NOxwhile using diesel fuel as a reductant. NOxreduction ranges from approximately 38% to 56% as the ratio of hydrocarbon to NOxranges from 4-8 at an operating temperature of approximately 350° C. NOxreduction ranges from approximately 28-47% as the ratio of hydrocarbon to NOxvaries from 4-6 at an operating temperature of approximately 400° C. Based on the dual reductant source and valve arrangement shown inFIG. 1, it should be appreciated that effective NOxreduction may be achieved solely through the use of E85 as a reductant. NOxreduction may also be achieved through the use of engine fuel as a reductant.

It is also contemplated that two or more different reductants may be simultaneously injected into the exhaust stream to effectively convert NOxin the exhaust stream to N2.FIG. 4depicts NOxreduction at various reductive ratios where a first reductant includes E100 and a second reductant includes ultra-low sulfur diesel (ULSD). Percentage NOxreduction was determined for several different reductant ratios where E100 and ULSD were simultaneously injected into an exhaust stream. A first NOxreduction percentage was determined using E100 at a carbon to nitrogen ratio of 1 being simultaneously injected with ULSD having a carbon to nitrogen ratio of 5. A second NOxreduction percentage was determined using the reductant ratio of E100 having a carbon to nitrogen ratio of 3 being simultaneously injected with ULSD having a carbon to nitrogen ratio of 3. At the far right of the chart shown inFIG. 4, a different reduction ratio was evaluated for NOxreduction effectiveness. E100 at a carbon to nitrogen ratio of 3 was simultaneously injected with ULSD having a carbon to nitrogen ratio of 6. The second data point from the right shown inFIG. 4corresponds to 100% E85 being injected at a carbon to nitrogen ratio of 5.

FIGS. 2,3and4illustrate that it may beneficial to determine a ratio of primary and secondary reductant dynamically in response to engine operating conditions. In particular, it may be desirable to monitor an engine exhaust temperature at one or more locations relative to a catalyst. Furthermore, controller40may be programmed to estimate a carbon to nitrogen ratio of one or more reductants stored on board vehicle12. Based on the NOxreduction percentages obtained during various reductant ratios and exhaust temperatures, controller40may optimize the use of reductant stored within tank28. Controller40may also evaluate other vehicle operating conditions including throttle position, engine speed and vehicle speed to set a target NOxreduction percentage and subsequently determine a desired reductant injection ratio.

FIG. 5depicts an alternate exhaust treatment system100. Exhaust treatment system100is substantially similar to exhaust treatment system10. Accordingly, like elements will retain their previously introduced reference numerals. Exhaust treatment system100includes fuel tank26and supplemental reductant tank28. A fuel supply line102interconnects fuel tank26and a first injector104. First injector104is operable to selectively supply fuel as a reductant to the engine exhaust flow in pipe18. The supply of fuel into the exhaust stream is controlled by controller40.

Another supply line106interconnects reductant tank28with a second injector108. Second injector108is selectively operable to inject the reductant contained within tank28into the exhaust stream passing through exhaust pipe18. It should be appreciated that while first injector104is depicted as being upstream of second injector108inFIG. 4, this relative position may be reversed or first injector104may be positioned at substantially the same distance from emissions catalyst22as second injector108. To achieve this arrangement, the injectors may be positioned at different rotational clocking orientations about exhaust pipe18. Controller40is also in communication with second injector108to define and control when reductant stored within tank28is to be supplied to the exhaust flowing through exhaust pipe18.

FIG. 6depicts another alternate exhaust treatment system identified at reference numeral200. Exhaust treatment system200is substantially similar to exhaust treatment system100. Accordingly, like elements will retain their previously introduced reference numerals. Exhaust treatment system200includes each of the elements of exhaust treatment system100as well as a thermal management device202positioned upstream from first injector104and second injector108. Thermal management device202may include a burner204for increasing the temperature of exhaust flowing through exhaust pipe18. Thermal management device202may also include a diesel particulate filter206. Thermal management device202may include both burner204and diesel particulate filter206.

Burner204may include an injector208operable to supply an ignitable fuel to the exhaust stream. An additional source of oxygen may be provided by a pressurized air source209. An igniter210may also be provided as part of burner204to selectively ignite fuel that may be within the exhaust flowing through exhaust pipe18with or without additional fuel being supplied via injector208. When burner204is used in combination with diesel particulate filter206, the filter may be actively regenerated by energizing burner204to burn soot previously collected by diesel particulate filter206. Controller40is operable to control igniter210and injector208to define when burner204heats the exhaust.

FIG. 7illustrates another alternate exhaust treatment system identified at reference numeral300. Exhaust treatment system300is substantially similar to exhaust treatment system200. Accordingly, like elements will retain their previously introduced reference numerals. Exhaust treatment system300includes each of the elements of exhaust treatment system200as well as an additional catalyst302positioned in series with and downstream from catalyst22. Reductant tank26provides reductant to first injector104upstream of catalyst22. Reductant tank28provides reductant to second injector108downstream of catalyst22and upstream of catalyst302. It is contemplated that catalyst22and catalyst302are substantially similar to one another. The use of two catalysts in series may provide an increased NOxreduction percentage and longer catalyst life for each of catalyst22and catalyst302.

The use of diesel fuel as a reductant may increase the likelihood of coking within the catalyst immediately downstream from the diesel fuel reductant injector.FIG. 7depicts diesel fuel as the reductant stored within tank26and provided to first injector104. Thermal management device202is positioned closest to catalyst22in receipt of diesel fuel as the reductant. The increased temperature of the exhaust may minimize the coking and assist with catalyst regeneration, if desired. During operation, first injector104and second injector108may be individually operated or simultaneous reductant injection may occur depending on the engine operating conditions, as previously discussed.

In an alternate arrangement, an optional valve304may be operable to supply the reductant within fuel tank26to second injector108and provide the reductant within tank28to first injector104. A switching of the reductant supply may facilitate regeneration of catalyst22and/or catalyst302. A switching of reductants may increase the life of both catalyst22and catalyst302. It should also be appreciated that the concepts of the present disclosure may be utilized in conjunction with engines outputting large volumes of exhaust per unit time. Some exhaust systems include multiple parallel conduits in communication with the engine. It is within the scope of the present disclosure to use multiple sets of injectors and/or valves to duplicate the previously described exhaust gas treatment systems along more than one of the parallel exhaust conduits.