COMBUSTION ENGINE EXHAUST AFTER-TREATMENT SYSTEM INCORPORATING SYNGAS GENERATOR
A combustion engine exhaust after-treatment system includes a syngas generator for producing a syngas stream. The syngas stream is supplied to one or more parts of the engine system resulting in reduced emissions and/or reduced fuel consumption. The syngas generator produces a syngas stream via chemical reaction of the engine exhaust stream with a fuel stream.
The present application is a continuation-in-part of U.S. patent application Ser. No. 11/193,930 entitled “Integrated System for Reducing Fuel Consumption and Emissions in an Internal Combustion Engine” filed on Jul. 29, 2005, which claims priority benefits from U.S. Provisional Patent Application No. 60/592,050 and filed on Jul. 29, 2004 and U.S. Provisional Patent Application No. 60/640,936 filed on Dec. 30, 2004. The '930, '050 and '936 applications are each hereby incorporated by reference herein in their entirety.
FIELD OF THE INVENTIONThe present invention relates to the after-treatment of combustion engine exhaust streams to reduce the amount of deleterious constituents in the exhaust streams. More particularly, the present invention relates to a combustion engine exhaust after-treatment system that incorporates a reducing agent generator for supplying a hydrogen-containing stream to one or more parts of the engine system resulting in reduced emissions and/or reduced fuel consumption.
BACKGROUND OF THE INVENTIONOver the past decades, government-imposed diesel engine emission regulations have been met by various component design modifications and engine control techniques. In general, these changes have resulted in increasing both the capital and operating costs.
The two primary techniques that have been deployed to reduce emissions are:
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- (1) retarding fuel injection timing to reduce engine exhaust NOx levels; and
- (2) employing exhaust gas recirculation (EGR) to lower the in-cylinder combustion temperatures and thus reduce engine exhaust NOx levels.
Each of these techniques also has the undesirable effect of increasing fuel consumption.
Examples of other component design modifications and engine control techniques that have been used to reduce emissions include:
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- (a) redesign of engine cylinders to promote more effective fuel/air mixing;
- (b) improved fuel injector spray patterns to provide more effective air/fuel mixing;
- (c) more efficient turbo-compressor designs; and
- (d) more precise control of fuel injection quantities based on engine speed and torque.
Some of these examples have an additional desirable effect of reducing fuel consumption. These and other approaches are detailed in the open literature (see, for example, www.dieselnet.com).
The diesel engine industry is now in general agreement that meeting upcoming diesel engine emission regulations will be virtually impossible using the conventional approaches of component design modifications and control techniques. Moreover, the industry generally agrees that the incorporation of exhaust after-treatment systems will be required to meet upcoming emission regulations. Thus, while the diesel engine industry continues to develop so-called “in-cylinder” solutions in efforts to comply with emission regulations, significant efforts are now being devoted to the development of exhaust “after-treatment” solutions, including the development of after-treatment equipment and operating techniques for remediating harmful exhaust emissions.
Diesel engines have two different types of emissions that are of primary concern: (1) particulate matter (PM), which is the soot and carbon particles emitted from a diesel engine exhaust pipe in the form of a black cloud (PM has been linked to cancer and other diseases), and (2) nitrogen oxides (NOx), which are linked to respiratory problems, as well as being strong greenhouse gas pollutants.
To meet the upcoming government-imposed particulate matter (PM) emission regulations, the diesel engine industry is generally planning to employ filtering devices that trap the PM present in engine exhaust streams. These filters are periodically regenerated in-situ during operation, either passively or by using specific active control techniques, some of which employ diesel fuel to assist in oxidizing the carbon collected on the filter. Some other filter designs are designed to be cleaned during scheduled maintenance to ensure the continued trapping of PM and adherence to PM emission regulations. If the filtering device contains catalytic material it is referred to as a catalyzed diesel particulate filter (CDPF) and if not, it is simply referred to as a diesel particulate filter (DPF).
The removal of NOx generally takes place with the use of a catalyst bed. One technique being proposed as a method of reducing NOx emissions from diesel engines is called urea selective catalytic reduction (UREA-SCR). In this technique, aqueous urea is sprayed into a catalytic bed in an amount that essentially matches the amount of NOx to be reduced. The urea breaks down into ammonia components and then chemically reduces the NOx into nitrogen gas (N2) and water. As with most technologies, UREA-SCR has advantages and disadvantages. Presently UREA-SCR has attracted significant interest in Europe. North American companies are also considering using UREA-SCR to remediate their engine exhaust streams, but appear to be favoring a system that utilizes a catalyst and adsorbent bed to trap the NOx, and then periodically regenerates these beds to restore their effectiveness to remove NOx from the engine exhaust stream.
Typically, the NOx trapping is performed by passing the entire engine exhaust stream through the catalyst and adsorbent bed. Oxygen present in the exhaust stream reacts over a platinum catalyst with NO in the exhaust stream, yielding NO2 (see Equation (1) below). The NO2 then adsorbs onto the bed adsorbent. A typical adsorbent material is barium oxide, in which case barium nitrate is formed in the adsorption reaction (see Equation (2) below). This type of catalytic/adsorbent bed is often referred to as a “lean NOx trap” (LNT), since NOx is trapped while the bed is in a lean (excess oxygen) environment. When the capacity of the LNT to adsorb NOx from the engine exhaust stream has been met, or prior to this point, the bed is regenerated. Under fuel rich and/or higher temperature conditions the nitrate species become thermodynamically unstable and decompose, producing NO or NO2, according to Equations (3a) and (3b). These nitrogen oxides are subsequently reduced (e.g. by carbon monoxide, hydrogen and/or hydrocarbons) to nitrogen (N2) over the reduction catalyst (Reaction (4) below). Small quantities of ammonia (NH3) and N2O may also be formed during the regeneration mode.
Thus, the following chemical reactions occur in a typical LNT:
Oxidation: NO+½O2→NO2 (1)
Adsorption: NO2+BaO+½O2→Ba(NO3)2 (2)
Desorption of NO3:
Ba(NO3)2═BaO+2NO+ 3/2O2 (3a)
Ba(NO3)2═BaO+2NO2+½O2 (3b)
Reduction of NOx to N2, H2O and CO2 (4)
Besides dealing with PM and NOx, the quantity of unburned hydrocarbons (HC) and carbon monoxide (CO) present in a diesel engine exhaust stream can be reduced by passing the exhaust stream through a catalytic bed. This is typically referred to as a diesel oxidation catalyst (DOC) technique. The HC and CO are oxidized with oxygen present in the exhaust stream over a platinum catalyst that is typically wash-coated onto a cordierite monolith. The DOC has similarities to the catalytic converter employed in connection with gasoline-fueled combustion engines for passenger cars.
In the approach described herein, a combustion engine system incorporates a reducing agent generator, such as a syngas generator, for supplying a hydrogen-containing stream to one or more parts of the engine system including the engine exhaust after-treatment system, resulting in reduced emissions and/or reduced fuel consumption.
SUMMARY OF THE INVENTIONIn various embodiments, a method for operating an engine system comprising an exhaust after-treatment system and a syngas generator comprises directing a fuel stream from a fuel supply to the engine, and directing an air stream to the engine via an air intake line, and operating the engine to produce an engine exhaust stream. The syngas generator is operated to produce a syngas stream. Some or all of the engine exhaust stream is at least periodically directed to one or more exhaust after-treatment devices in the exhaust after-treatment system, for reducing regulated emissions from the engine system. Some or all of the syngas stream is at least periodically directed to one or more of the exhaust after-treatment devices for heating or regenerating the device. The syngas stream exiting such devices is referred to as a depleted syngas stream. This depleted syngas stream and/or additional syngas produced by the syngas generator is directed back to the engine via the air intake line.
In various embodiments a combustion engine and after-treatment system includes a fuel tank and fuel supply subsystem for directing fuel to the engine, and an air supply subsystem for directing an air stream to the engine via an air intake line. An engine exhaust stream line is connected to receive an exhaust stream from the engine. One or more exhaust after-treatment devices are connected to separately receive engine exhaust stream and/or syngas from a syngas generator. For example devices such as a DPF and DOC may be connected to receive syngas, and a LNT may be connected to receive both engine exhaust and syngas at different times. The engine air intake line is fluidly connected receive syngas from the syngas generator or depleted syngas exiting an exhaust after-treatment device or both.
In various systems and methods for reducing NOx levels in a combustion engine exhaust stream the system includes one or more catalytic lean NOx traps. A reducing agent (such as syngas) is produced in a reducing agent generator (such as a syngas generator). In a trapping mode, at least a portion of the engine exhaust stream is introduced into a catalytic lean NOx trap. In a regeneration mode syngas is introduced into the catalytic lean NOx trap to regenerate its capacity to trap NOx. Preferably the duration of the trapping mode is less than about 20 seconds. In preferred embodiments the duration of the regeneration mode is about the same as the duration of the trapping mode. For example, they can both be about 10 seconds. Preferably there is a pair of catalytic lean NOx traps in the system, and when one is in trapping mode the other is in regeneration mode.
The present systems that include a syngas generator (or other reducing agent generator) and one or more exhaust after-treatment devices permit operation of an engine system with improved fuel economy. Instead of being selected to reduce emissions, the timing of the fuel injection into the engine can be selected for improved fuel economy, but so that the level of regulated emissions in said engine exhaust stream might at least periodically exceeds regulation levels. For example, the NOx level in the exhaust stream from the engine may exceed regulation levels. However the exhaust stream is then directed to at least one exhaust after-treatment device in the engine exhaust after-treatment system, for reducing emissions from the engine below the regulated levels. The syngas stream is used to regenerate or heat the exhaust after-treatment devices as needed.
In the system and methods described above, the syngas generator is conveniently operated using a portion of the engine exhaust stream (as oxidant) and the same fuel that is used in the combustion engine as the fuel stream. These streams are converted to syngas in the syngas generated. In preferred embodiments the syngas generator is non-catalytic.
In the system and methods described above, an engine exhaust gas recirculation (EGR) system can be omitted. In other words, the system can be operated so that engine exhaust gas is not recirculated to the engine.
In preferred embodiments the system and methods described above the exhaust after-treatment system includes one or more lean NOx traps. It can instead, or in addition, comprise other after-treatment devices such as, for example, diesel particulate filters (DPFs or CDPFs), diesel oxidation catalysts (DOCs), and selective catalytic reduction (SCR) devices. The system design and method of operation of the SGG and associated components can be used to provide syngas for improved operation such devices. This is especially true during regeneration and when the device or engine is cold.
BRIEF DESCRIPTION OF THE DRAWING(S)
In preferred embodiments of the present approach, a combustion engine system incorporates a syngas generator (SGG), and syngas, is supplied to one or more parts of the engine system including the engine exhaust after-treatment system, resulting in reduced emissions and/or reduced fuel consumption. Preferred embodiments of the present system and method have at least several of the following features:
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- (a) A syngas generator (SGG) that receives diesel fuel and a portion of the engine exhaust stream to produce a syngas stream that contains H2 and CO. The SGG can have a non-catalytic design that employs a portion of the syngas sensible heat to preheat the reactants (although the SGG can also operate without performing this function).
- (b) Passive control of the supply of oxidant (engine exhaust gas stream) to the SGG.
- (c) A metering pump to deliver diesel fuel from the primary diesel fuel tank to the SGG. The metering pump supplies a relatively low pressure stream that is sufficient, in combination with other SGG components, to promote atomization and then vaporization of the diesel fuel within the SGG. The metering pump receives flow control signals from the engine control module.
- (d) One or more flow diverters to direct the syngas stream and the engine exhaust stream to the appropriate emission control device at the appropriate point of time in the engine operating cycle. Syngas can be directed to some or all of the after-treatment devices employed in the system.
- (e) A lean NOx trap (LNT) system that employs two or more LNT catalyst beds and that cycles quickly between the beds to achieve greater adsorption and desorption rates than those achievable with conventional, prior art systems.
- (f) A catalyzed diesel particulate filter (CDPF) that can optionally employ the syngas stream from the SGG. A CDPF traps PM (soot or coke) in the exhaust stream and oxidizes the carbon into CO or CO2. The following chemical reactions occur in a typical CDPF:
C+O2═CO2 (1)
C+½O2═CO (2) - The CDPF catalyst must generally be above a minimum temperature for the oxidation process to occur. The higher the oxygen concentration present the lower the temperature can be. During various points in the engine operating cycle, the engine exhaust may not be hot enough to heat the catalyst to the required temperature. Syngas from the SGG can be introduced into the CDPF, to react with the catalyst and raise the catalyst temperature to the level required to oxidize the soot or coke. In this regard, syngas does not directly promote the regeneration of the CDPF. The primary purpose of using syngas in the CDPF is as a fuel that can be burned to increase the temperature of the CDPF to the point where oxidation of the trapped carbon can take place. This is also the case with a non-catalyzed DPF because, at high enough temperatures, the syngas fuel will burn without a catalyst.
- (g) A diesel oxidation catalyst device (DOC) for reducing the level of CO and unburned hydrocarbon (HC) in the exhaust stream, which can optionally employ syngas from the SGG to enhance the effectiveness of the DOC during various points of time in the engine operating cycle. In this regard, syngas can assist in bringing the DOC quickly to proper operating temperature when the engine is started, and thereby achieve greater exhaust after-treatment efficiencies than those achievable with conventional, prior art systems.
- (h) Local and/or distributed engine control module hardware and software for controlling the SGG and flow diverter operation based on various engine operating parameters to achieve greater exhaust after-treatment efficiencies, using less diesel fuel, and in a more compact after-treatment module volume, than those achievable with conventional, prior art systems.
- (i) Engine control module software for adjusting (advancing) fuel injection timing, thereby permitting improved engine fuel economy and reduced PM levels, but increasing NOx content in the engine exhaust stream which is then mitigated in the after-treatment system.
(j) Directing the depleted syngas stream from the LNT regeneration step back to the engine air intake stream to make use of residual heating value remaining in the depleted syngas stream.
(k) Directing excess syngas (that is not needed for heating or regeneration of the exhaust after-treatment devices) back to the engine air intake stream, thereby allowing the syngas generator to operate continuously and at the same time making use of the heating value of the syngas stream produced.
In preferred embodiments of the system and method, conventional exhaust gas recirculation (EGR) components can be omitted, thereby reducing radiator heat load and also reducing costs. The resultant increase in NOx from the omission of EGR is remediated by the after-treatment system incorporating syngas generation.
In most countries there are emissions regulations in place that specify acceptable levels for specific constituents of engine exhaust streams that are harmful to human health or to the environment. The specific regulations and acceptable levels for each type of emission constituent vary depending upon the type of engine system involved, and also geographically depending on national or regional regulations. The regulations are also adjusted over time, generally becoming more and more stringent in global efforts to protect the environment.
Regulations related to emissions and air quality may generally be divided into two classes:
(A) “tailpipe” emission regulations;
(B) ambient air quality standards.
Diesel engines for highway applications and some for off-road use are subject to the “tailpipe” emission regulations. These regulations specify the maximum amount of pollutants allowed in exhaust gases from a diesel engine. The emissions are measured over an engine test cycle which is also specified in the regulations. The duty to comply is typically on the equipment (engine) manufacturer. The authorities regulating engine tailpipe emissions include the US EPA (Environmental Protection Agency) and California ARB (Air Resources Board). Many applications of diesel engines in confined spaces are regulated through ambient air quality standards rather than by tailpipe regulations. The ambient air quality standards specify the maximum concentrations of air contaminants which are allowed in the workplace. These regulations are set and enforced by occupational health and safety authorities such as OSHA (Occupational Health and Safety Administration) or MSHA (Mining Safety and Health Administration). The duty to comply is on the end-user who has to make sure that the emission control measures which have been employed are adequate.
As used herein, references to “regulated emissions” refer to pollutants that occur in engine exhaust streams that are typically regulated. These include NOx, CO, hydrocarbons, SO2 and particulate matter (PM).
As used herein, references to improving fuel economy generally mean reducing the “brake specific fuel consumption” (BSFC) of the engine system. Fuel consumption mass per unit time is normally recorded during engine testing. One way to evaluate engine system efficiency is to look at the ratio of fuel consumption to useful power. This ratio is the BSFC which, in essence, is a measure of how much fuel an engine system consumes in the process of producing a specific horsepower output.
Turning now to
a fuel intake module 14;
an air intake module 16;
an exhaust module 18; and
an engine control module 19.
As further shown in
As further shown in
As further shown in
From valve 53 in
As further shown in
Turning now to
a fuel intake module 114;
an air intake module 116;
an exhaust after-treatment module 118; and
an engine control module 119.
Fuel intake module 114 of
Air intake module 116 of
As further shown in
Hydrocarbons+O2═CO2+H2O (1)
CO+½O2═CO2 (2)
thereby converting hydrocarbons (HC) and CO present in exhaust stream 178 to CO2 and H2O. The DOC employs catalysts such as platinum to promote the oxidation of unburned HCs and CO with O2 in the exhaust stream. Exhaust stream 182 exiting DOC 180 is exhausted from exhaust after-treatment module 118 to the external atmosphere through muffler and tail pipe assembly 194.
From valve 153 in
As further shown in
In system 110 of
Turning now to
a fuel intake module 214;
an air intake module 216;
an exhaust after-treatment module 218, incorporating a syngas generator 263; and
an engine control module 219.
Fuel intake module 214 of
Air intake module 216 of
As further shown in
Exhaust slip stream 252a is directed to a syngas generator (SGG) 263. A diesel fuel stream 273 is drawn from fuel tank 220 via metering pump 223 and is also directed to SGG 263. SGG 263 includes a mixing zone, an oxidizing zone and a reforming zone (as described in more detail below in connection with
As further shown in
Exhaust stream 256 exiting turbine portion 240b is directed to CDPF 270, where particulate matter (including soot and carbon particles) is removed from exhaust stream 256 to produce a filtered exhaust stream 274. A branch syngas stream 286 is directed from syngas diverter 284 to CDPF 270 to promote operation of the CDPF 270, as described above.
Filtered exhaust stream 274 is directed to NOx reduction device 276 (which can be an LNT) to convert at least some of the NOx compounds present in exhaust stream 274 to benign constituents, primarily N2, H2O and CO2. A branch syngas stream 290 is directed from syngas diverter 284 to LNT 276 to promote regeneration of adsorbent within LNT 276, as described above.
As further shown in
Exhaust stream 282 exiting DOC 280 is exhausted from exhaust after-treatment module 218 to the external atmosphere through tail pipe 294.
Excess syngas stream 288 (that is not directed to the various after-treatment module components) is directed from syngas diverter 284 back to engine air intake module 216. Rather than being directed to the engine air intake module 216 via the EGR loop, in the illustrated embodiment syngas stream 288 is directed to a venturi 239 located upstream of compressor portion 240a, where it is drawn into and merged with air stream 238 exiting air flow sensor 236. Excess syngas stream 288 can be directed through one or more filters or traps such as particulate filters or sulfur traps, (not shown in
From valve 253 in
As further shown in
Engine control module 219 includes a microprocessor 296 that receives electronic signals from engine 212, fuel tank 220, air flow sensor 236 and local control module 298. Microprocessor 296 directs signals to engine 212, fuel injector assembly 224, compressor portion 240a, turbine portion 240b, SGG 263 and EGR valve 266.
In prior art system 110 of
Turning now to
-
- a fuel intake module 314;
- an air intake module 316;
- an exhaust after-treatment module 318 incorporating a syngas generator 363; and
- an engine control module 319.
Fuel intake module 314 of
Air intake module 316 of
Exhaust after-treatment module 318 includes an engine exhaust stream 352, which exits engine 312 at exhaust outlet 351. Exhaust stream 352 is directed to a two-way valve 355 through which at least a portion of exhaust stream 352 exits as exhaust slip stream 352a, and the remaining portion of exhaust stream 352 exits valve 355 as exhaust stream 352b. Exhaust stream 352b exiting two-way valve 355 is directed to turbine portion 340b of the turbocompressor, the compressor portion of which is shown in
Referring now to
In a first mode, upstream flow diverter 367 directs exhaust stream 374 to a first upstream conduit 369a, which is connected at its distal end to the inlet of a first lean NOx trap (LNT) 371a. While in the first mode, upstream flow diverter 367 also directs syngas stream 365 to a second upstream conduit 369b, which is connected at its distal end to the inlet of a second LNT 371b. In the first mode, LNT 371a is in trapping (lean) mode, while LNT 371b is in regeneration (rich) mode (see
In a second mode (which is the mode illustrated in
As directed by control software, upstream flow diverter 367 periodically redirects these two streams to the opposing LNTs such that each of LNT 371a and 371b cycles between a trapping mode and a regeneration mode. Upstream flow diverter 367 is thus employed to simultaneously direct the engine exhaust stream and the syngas stream. This dual functionality of the flow diverter reduces system cost and size/volume.
As further shown in
When LNT 371a is in trapping mode, downstream flow diverter 375 directs the treated exhaust stream exiting LNT 371a to an exhaust outlet conduit 378, which is fluidly connected at its distal end to a DOC device 380. When LNT 371a is in regeneration mode, downstream flow diverter 375 directs the syngas stream exiting LNT 371a to a depleted syngas conduit 388, which is fluidly connected at its distal end to venturi 339, where depleted syngas stream 388 is merged with air stream 338.
When LNT 371b is in trapping mode, downstream flow diverter 375 directs the treated exhaust stream exiting LNT 371b to exhaust outlet conduit 378. When LNT 371b is in regeneration mode, downstream flow diverter 375 directs the syngas stream exiting LNT 371b to depleted syngas conduit 388.
The depleted syngas stream that flows to intake valve (venturi) 339 passes through a sulfur trapping bed 377. Sulfur components from the engine exhaust stream tend to accumulate in the LNTs, particularly near the inlet. In the regeneration of the LNTs, these sulfur components are released, primarily as hydrogen sulfide (H2S). Sulfur trapping bed 377 removes at least some of the sulfur components from the depleted syngas stream, and thereby inhibits sulfur from accumulating due to the recycling of syngas. The depleted syngas stream may also be directed through one or more particulate filters or other types of traps or filters that could be part of bed 377 or could be separate devices.
As further shown in
As further shown in
In the embodiment illustrated in
Omission of the EGR components from system 310 in
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- (a) Engine system cost is reduced.
- (b) Engine system complexity and weight is reduced.
- (c) Particulate matter (PM) levels in the engine exhaust are reduced, thereby imposing less of a burden on the PM reduction system (for example, the DPF requires regeneration less frequently).
- (d) Reduction of cooling load on the radiator, which represents an especially valuable benefit in view of the reduced frontage size of the hood and associated radiator cooling capacity of over-the-road diesel engine trucks and tractors.
- (e) The reduction in the engine system operating temperature caused by the elimination of the EGR can improve system reliability and durability, by increasing the operating life of various system components.
In a preferred system, the engine combustion process can be tailored for high fuel economy rather than making a compromise that yields lower NOx levels. An increase in the NOx levels as a result of removing the EGR system can be compensated for in the NOx removal system (for example, the LNT system), which is designed specifically for removing NOx. The presence of the NOx removal system in the present design avoids the traditional compromise between engine design parameters when seeking both production of motive power efficiently and reduction of engine exhaust pollutants.
In preferred embodiments of the present system, the SGG receives diesel fuel and a portion of the engine exhaust stream to produce a syngas stream that contains H2 and CO. In preferred embodiments, a small portion of the engine exhaust stream is drawn at a point between the engine exhaust manifold and the turbine inlet, and then directed to a SGG via a process line. The high temperature and pressure of the exhaust stream drawn at this point is desirable for the operation of the downstream SGG. The syngas process line is designed to discourage heat loss, discourage pressure drop, reduce cost and facilitate packaging. Keeping the syngas process line short in length and large in diameter mitigates pressure drop and heat loss and eases packaging. The syngas process line is insulated to further mitigate heat loss. Again, this is done because high temperature and pressure benefit the downstream SGG. The syngas process line preferably does not include control devices, as they act as heat sinks, make packaging more difficult and add cost.
A portion of the engine exhaust stream is employed as a reactant feed for the SGG primarily because of the oxygen, water, and carbon dioxide content of the stream, which are all useful in the production of syngas. A secondary benefit of employing the engine exhaust gas stream is for its sensible heat content. Employing a portion of the engine exhaust stream as a reactant avoids the need for an oxygen or water supply subsystem that would add cost, volume, weight and complexity to the overall engine and vehicle product.
Diesel fuel is drawn from the on-board diesel fuel tank by a metering pump. This may involve typical equipment such as fuel filters. The metering pump typically has an accuracy of better than ±20% of flow, as this accuracy balances a trade-off between cost and stability, as well as ability to meet requirements of the after-treatment system. The discharge flow rate of the pump is commanded by the engine control module and its software, based on algorithms specific to the application. The metering pump discharge pressure is typically between 3 and 50 psig. This pressure is suitable for the downstream mixing of the two streams in the SGG.
The diesel fuel metering pump is preferably placed in a position so that the diesel fuel temperature range due to ambient temperature fluctuations is minimized or reduced. The pump could be positioned directly next to the diesel fuel tank. A minimal or reduced diesel fuel temperature swing permits more accurate metering of the diesel fuel.
In preferred embodiments, the downstream flow diverter simultaneously directs the depleted syngas stream exiting the LNT in the regenerating mode to the engine air intake line to capture and combust in the engine the fuel value remaining in the depleted syngas stream. The depleted syngas stream conduit is preferably positioned to join the air intake line at a point directly upstream of the compressor (as shown in
-
- (a) The syngas flow rate to the LNT during regeneration can be increased so that the regeneration is faster and more complete, yet additional syngas is not directed to the tailpipe but is directed back to the engine to capture its fuel value.
- (b) Ability to reduce the required turndown ratio of the SGG by keeping the SGG operating even when syngas is not required, or when only small quantities are required.
- (c) Ability to increase engine output power on demand by producing syngas for the express purpose of increasing engine power and directing the syngas to the engine via the air intake stream.
In order to illustrate the processes typical in a syngas generator, in which both partial oxidation and reforming reactions take place,
Mode of Operation
Diesel engine embodiments of the present system are operated in a manner similar to that of conventional diesel engines. Each diesel engine has its own characteristics for the various engine system parameters over the engine application duty cycle. For example, the engine exhaust pressure and temperature will change depending on engine speed, torque, the engine control module calibration being used and to a lesser degree also with the engine life. Table 1 below provides an example of performance data for a specific engine, engine control module, engine control module calibration and application duty cycle. The after-treatment system is then designed and operated based on this data to achieve reduced exhaust emissions and improved fuel economy.
A significant aspect of the control and operation of the present diesel engine exhaust after-treatment system is the advancing of the fuel injection timing on the order of 3 crank angle degrees to 6 crank angle degrees compared to what is conventionally employed. These figures apply to the specific engine and engine configuration described here, and could vary in other engine configurations and end-uses. In the past, the fuel injection timing has generally been set so as to decrease NOx levels in the engine exhaust stream for the purpose of meeting NOx regulations. An undesirable side effect of this conventional timing protocol has been decreased fuel economy. While engine manufacturers constantly attempt to increase fuel economy, the need to meet ever more stringent NOx emission regulations has resulted in fuel injection timing that significantly reduces fuel economy. When fuel injection timing is advanced, the NOx levels in the exhaust stream are increased by approximately 10% to 50%. The additional NOx levels can be handled in the LNT portion of the present after-treatment system, and although diesel fuel is required to produce syngas for the LNT portion, this fuel penalty is more than off-set by the fuel savings due to advancing the fuel injection timing, so that the net result is a 3-10% reduction in total fuel consumption.
Significant aspects of preferred operating mode and control system embodiments are as follows:
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- (a) There is no active control of the oxidant supply (a small portion of the engine exhaust stream) to the SGG. The SGG oxidant flow is passively controlled and the turndown ratio is limited due to a critical flow venturi that is part of the SGG, and through which the fuel and exhaust gas are directed into the SGG. As the engine exhaust pressure and temperature changes with the engine duty cycle there will be changing mass flow through the critical flow venturi, but the flow range will be smaller than if a non-critical flow device was used. This method reduces the cost of the system.
- (b) The critical flow venturi is sized so as to give an appropriate amount of oxidant, taking into account the changing composition of the oxidant over the duty cycle, that will allow production of syngas in the quantity required to reduce engine exhaust NOx to regulated levels given the after-treatment system used. This method of control is less expensive than methods previously used.
- (c) Diesel fuel flow to the SGG is controlled by the engine control module commanding the metering pump to rotate at a speed so as to give an appropriate fuel-oxidant ratio. Thus the diesel fuel flow is controlled so that when it reacts in the SGG with the oxidant flowing through the critical flow venturi it will yield an appropriate amount of syngas to reduce engine exhaust NOx to regulated levels given the after-treatment system used, and keep the SGG internal temperatures at appropriate temperatures (for example, 1000° C. to 1200° C.).
Thus, the syngas generator preferably uses a portion of the engine exhaust stream as an oxidant. The quantity of oxidant required by the syngas generator typically depends on the following parameters:
-
- (a) The O2, H2O and CO2 content.
- (b) The rate at which the various after-treatment devices are regenerated using the syngas, for example, the rate at which NOx is removed from the LNTs during regeneration.
- (c) The quantity of regulated emissions (for example, NOx) in the engine exhaust, and the capacity of the after-treatment system to trap such emissions.
- (d) Aspects of the syngas generator design and operation such as operating temperature and internal heat exchange.
In some embodiments of a system with dual LNTs, the control system monitors the duration that a LNT has been in trapping mode and then compares that to a predication/estimate of the NOx on the bed based on monitoring the duty cycle of the vehicle. Based on this comparison, the controller actuates the two flow diverters and thus changes the operating mode of each trap.
In the present approach, the LNT beds are in trapping mode preferably for only about 20 seconds or less, which is shorter than conventional trapping (adsorption) times. Furthermore, they are preferably regenerated for a period in the range of 5 to 20 seconds. The duration of this regeneration step is longer than is typical, and promotes the removal of sulfur compounds that accumulate in the bed (see below for more description of the sulfation problem). It can reduce or eliminate the need for a specific longer duration desulfating cycle. Thus, in the present approach the duration of the regeneration mode and the trapping mode are preferably about the same, thus the beds are preferably cycled at a rate in the order of once every 5 to 20 seconds. This cycling frequency is significantly greater than conventional. The faster cycling rate limits the amounts of NOx and sulfur adsorbed and allows for smaller and thus less expensive LNTs. Conventionally most LNT beds are operated in a regenerating mode for only a few seconds, with the trapping mode being substantially longer (often more than an order of magnitude longer than the regenerating mode).
Sulfur compounds tend to accumulate in LNTs particularly in the region near where the engine exhaust stream enters the trap. Sulfation of the trap over time tends to reduce its capacity to trap NOx, but desulfation of the trap generally requires high temperature treatment which can also be detrimental to the trap. Furthermore, during regeneration of the trap the sulfur compounds are converted to H2S which absorbs preferentially over NO2, and can further reduce the capacity of the trap. The present approaches described above, namely (a) using syngas, rather than diesel fuel, to regenerate the LNTs, and/or (b) using a shorter than conventional trapping times, and/or (c) using longer than conventional regeneration times, all facilitate desulfation. Nonetheless sulfation can still be a concern. One or more of following approaches can be used to further mitigate the problem:
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- (a) Three LNTs could be arranged in parallel, where two of them are cycling quickly (for example, 5-20 seconds per trapping and regeneration cycle) and these two are in opposite phase to each other. The third LNT would be in a longer-duration desulfating cycle (for example, in the range of 1 to 10 minutes). This would allow two beds to operate normally while one bed can take the time to be desulfated without disturbing the operation of the two beds that are reducing engine exhaust stream NOx levels.
- (b) During the regeneration step, the syngas could be directed to flow in reverse (opposite to the direction that the engine exhaust stream flowed) through the LNT. In this way, the sulfur components which accumulated and are now liberated nearer to the engine exhaust inlet, are removed directly from the bed, rather than flowing through the length of the bed. This can reduce sulfur poisoning of the major portion of the LNT.
- (c) During the regeneration step, the syngas could be directed to flow in reverse through the LNT as described above, but could enter the trap at some point in the LNT bed beyond the location at which the significant sulfur accumulation has occurred.
- (d) The “front” portion of the LNT (near the engine exhaust stream inlet) could have a different catalyst/adsorbent formulation to assist in promoting desulfation.
- (e) An electrical heater could be placed around the front portion of the LNT and activated to increase bed temperature during desulfation.
- (f) Fuel could be burned to heat the front portion of the bed just prior to supplying syngas in reverse flow for regeneration or desulfation.
- (g) Syngas and engine exhaust could be combusted in the bed itself to provide heat for desulfating.) This could be done with a slow switch-over of the diverter valves alone where the slow movement of the valve allows mixing of the syngas with the exhaust stream over the catalyst, thereby producing heat.
Some conventional after-treatment systems that employ catalyst beds to remove NOx and other emissions, do so by passing the engine exhaust through a bed, and when the bed requires regeneration the engine operating point is changed and the flow through the LNT is bypassed to some degree. The problem with such conventional systems and methods is that there still exists a significant amount of oxygen in the LNT. This oxygen must be removed to allow proper regeneration of the LNT. The present system uses a flow diverter to direct the exhaust gas flow away from the bed about to be regenerated and to a second bed that is then in trapping mode.
Alternative Designs and Modes of Operation
Fuels such as natural gas, CH4, gasoline, methanol, propane, butane or other hydrocarbons could be used rather an diesel fuel.
The fuel used in the SGG could be the same as the primary fuel for the engine, or it could be a different fuel.
If the fuel supplied to the syngas generator is the same as the primary fuel for the engine, the same tank can supply both the engine and the syngas generator, or separate tanks can be used—whichever is more desirable for packaging and vehicle integration reasons.
The syngas generator can be a catalytic reactor.
An electrical heater could be used to assist in vaporizing diesel fuel during start-up of the SGG, especially cold start-up.
The pressure difference between the engine exhaust stream and the syngas gas stream could be deliberately reduced. Because the engine exhaust pressure is typically higher than the pressure of the syngas from the SGG, in some cases there can be leakage of engine exhaust gas into the exhaust after-treatment devices when they are being regenerated with syngas. For example, engine exhaust may leak across the upstream flow diverter to the syngas side in
Various fluid transfer devices could be used to control the mass flow of diesel fuel to the SGG instead of the diesel metering pump described above. These include:
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- (a) “Siphoning” the diesel fuel from the supply tank using the ejector type effect created by using an ‘air assist’ spray nozzle in the SGG.
- (b) Using a centrifugal pump to create a substantially constant pressure of diesel fuel, at a pressure that is matched to the equipment, to admit the diesel fuel into the mixing portion of the SGG. A proportional flow control valve could then be used to control the mass flow of diesel fuel into the SGG.
- (c) Tapping into a point in the fuel common rail. This relatively high pressure point could then be attached to a proportional valve that would receive a control signal from the engine control module.
Also the diesel fuel could be pre-heated prior to mixing in the SGG. Heat can be drawn from the product syngas, from the engine exhaust, the engine coolant stream or another hot stream in the system or a combination of them using an appropriate heat exchanger. This could simplify the design of the SGG.
Potential alternatives or enhancements to the illustrated LNT configuration include:
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- (a) Placing two or more LNTs in series for trapping and then, during regeneration, directing the engine exhaust stream to bypass the regenerating bed(s).
- (b) A small amount of syngas could be introduced into the LNT while in trapping mode to maintain the LNT temperature at a desired level.
- (c) A separate and independent combustor could be employed to create heat to keep the LNT beds at a desired temperature, which could be controlled in turn by controlling amount of diesel fuel directed to the combustor.
- (d) Electrical heaters could be used to quickly heat the LNT to the temperature at which NOx trapping and regeneration are best carried out.
- (e) The same electrical heaters could be used to keep the beds at a desired trapping and regeneration temperature during all modes of operation.
- (f) The LNTs could be incorporated into a heat exchanger to allow control of bed temperature to the desired temperature for trapping and regeneration.
- (g) Syngas could be used to keep the LNTs at the desired temperature.
- (h) The LNT portion could be combined or replaced with a selective catalytic reduction (SCR) system.
- (i) The SCR system could be either UREA- or HC-based. Either could serve as the gross clean-up device and the other as the fine clean-up device. The HC-SCR would preferably perform the gross clean-up continuously and then the LNTs would be used to perform the fine clean-up.
There may be some advantages to incorporating an SCR system in combination with one or more LNTs as mentioned above. Small quantities of ammonia (NH3) can be a by-product formed during regeneration of LNTs. In SCR systems ammonia is used to chemically reduce NOx to nitrogen gas (N2) and water, so it may be possible to use the ammonia by-product formed during regeneration of the LNTs as the reacting agent for the SCR.
A potential alternative to the techniques discussed above for controlling cycle timing is:
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- (a) Employing a closed loop having a NOx sensor, temperature sensor, O2 sensor, HC sensor or other constituent sensor, so switching between regeneration and trapping modes is done based on the sensing of actual values, instead of using a fixed cycle time or algorithm for determining when to switch modes.
Potential alternatives or enhancements to the illustrated LNT structure include:
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- (a) A cylindrical bed or valve system where the LNT absorbent bed, or gas distribution system is divided and sealed in a radial pattern. Engine exhaust is allowed to flow through a portion of the bed, allowing NOx from the exhaust to be trapped, while syngas is allowed to flow through the remaining portions, regenerating those portions of the bed. The bed or the gas distribution system is rotated to switch the portions of the bed from trapping mode to regeneration mode. This reduces the overall size and complexity of the LNT bed and gas distribution configuration.
- (b) Use of sintered metal in the LNT as the substrate and depositing catalyst on that substrate, thereby resulting in lower pressure drops and greater flow rate and permitting the use of smaller bed size.
Potential End-Uses for the Present After-Treatment System
The present systems can be applied to on-road vehicles, off-road vehicles, stationary power generation, and marine applications.
The applications above could be diesel-fueled or fueled by gasoline, natural gas, propane, butane or similar fuels.
A similar design and method of operation of the SGG and associated components can be used to introduce syngas into the air intake of lean burn engines, for example lean burn gasoline engines. This will extend the lean burn limit of the in-cylinder combustion and allow higher air/fuel ratios leading to reduced emissions and improved fuel economy.
The addition of syngas to the air intake stream changes the combustion properties of the combustion charge. This may allow further modifications to the engine, for example air/fuel ratios, fuel injection properties (timing, pressure, spray pattern), compression properties (compression ratios, compression chamber profile). Thus, integration of the SGG with the engine can allow modification of the combustion charge and its properties to allow lower emissions and increased fuel economy.
The SGG could also be integrated with a fuel cell power generator to produce auxiliary power for a vehicle. This allows for increased electrification of the vehicle and thus to lower costs and increased efficiency especially for reduction of idling time. The fuel cell power generation system could be a hybrid system that allows the fuel cell to stay on continuously and charge an energy storage device. The fuel cell could be, for example, a solid oxide fuel cell or a proton exchange membrane fuel cell.
The SGG could be used to create heat to warm the engine, engine oil, thermal-electric generating device or operator compartment of a vehicle when the engine is turned off.
The syngas produced in the system could be used for homogeneous charge compression ignition (HCCI) where addition of syngas to the air intake stream may enhance the combustion process.
While particular elements, embodiments and applications of the present invention have been shown and described, it will be understood, of course, that the invention is not limited thereto since modifications can be made by those skilled in the art without departing from the scope of the present disclosure, particularly in light of the foregoing teachings.
Claims
1. A method of operating an engine system comprising an exhaust after-treatment system and a syngas generator, the method comprising:
- (a) directing a fuel stream from a fuel supply to said engine, and directing an air stream to said engine via an air intake line, and operating said engine to produce an engine exhaust stream;
- (b) operating said syngas generator to produce a syngas stream;
- (c) at least periodically directing at least a portion of said engine exhaust stream to at least one exhaust after-treatment device in said exhaust after-treatment system, for reducing regulated emissions from said engine system;
- (d) at least periodically directing at least a portion of said syngas stream to said at least one exhaust after-treatment device for heating or regenerating said device, thereby producing a depleted syngas stream;
- (e) directing a surplus syngas stream to said engine via said air intake line.
2. The method of claim 1 wherein said surplus syngas stream comprises said depleted syngas stream.
3. The method of claim 1 wherein said surplus syngas stream comprises the portion of said syngas stream that is not directed to said at least one exhaust after-treatment device.
4. The method of claim 1 wherein said surplus syngas stream is directed to said engine via a venturi or ejector in said air intake line.
5. The method of claim 1 wherein said surplus syngas stream is directed to said engine via a particulate filter.
6. The method of claim 1 wherein said surplus syngas stream is directed to said engine via a sulfur trapping bed.
7. The method of claim 1 wherein said surplus syngas stream is introduced into said air intake line upstream of an engine intake air compressor.
8. The method of claim 1 wherein at least a portion of said engine exhaust stream is recirculated to said engine via an exhaust gas recirculation line.
9. The method of claim 1 wherein the quantity of surplus syngas directed to said engine via said air intake line is adjusted in accordance with an operating parameter indicative of the engine power output demand.
10. The method of claim 9 wherein the operating parameter is the accelerator position, or air intake mass flow or the engine speed.
11. The method of claim 9 wherein the rate of production of syngas is adjusted in accordance with an operating parameter indicative of at least one of: the level of regulated emissions in said engine exhaust stream, oxygen content in the engine exhaust stream, air intake mass flow, engine speed and engine power output demand.
12. The method of claim 11 wherein the rate of production of syngas, and the quantity of surplus syngas directed to said engine via said air intake line, are both increased in response to an increase in at least one of the level of regulated emissions in said engine exhaust stream and the engine power output demand.
13. The method of claim 1 wherein fuel from said fuel supply and at least a portion of said engine exhaust stream are directed to said syngas generator and reacted therein to produce said syngas.
14. The method of claim 13 wherein the flow rate of said engine exhaust stream to said syngas generator is passively controlled.
15. The method of claim 1 wherein said syngas generator is operated whenever said engine is operated.
16. The method of claim 1 wherein said regulated emissions comprise NOx, particulate matter and hydrocarbons.
17. The method of claim 1 wherein said exhaust after-treatment system comprises at least one lean NOx trap.
18. The method of claim 1 wherein said exhaust after-treatment system comprises a pair of lean NOx traps.
19. The method of claim 18 wherein an engine exhaust gas flow diverter, located upstream of said pair of lean NOx traps, alternates between directing at least a portion of said engine exhaust stream to a first and then a second one of said pair of traps at the same time as a syngas gas flow diverter, located upstream of said pair of lean NOx traps, alternates between directing at least a portion of said syngas stream to the second and first of said pair of traps respectively, for regenerating said traps.
20. The method of claim 19 wherein at least one downstream flow diverter located downstream of said pair of lean NOx traps alternately directs said depleted syngas stream from whichever one of said pair of traps is being regenerated to said engine via said air intake line.
21. The method of claim 18 wherein a combined upstream flow diverter located upstream of said pair of lean NOx traps directs at least a portion of said engine exhaust stream to a first one of said pair of traps and at the same time directs at least a portion of said syngas stream to the second of said pair of traps for regenerating said second trap, alternately with directing at least a portion of said engine exhaust stream to the second one of said pair of traps at the same time as directing at least a portion of said syngas stream to the first of said pair of traps for regenerating said first trap.
22. The method of claim 20 wherein at least one downstream flow diverter located downstream of said pair of lean NOx traps alternately directs said depleted syngas stream from whichever one of said pair of traps is being regenerated to said engine via said air intake line.
23. The method of claim 18 wherein each of said pair of lean NOx traps is switched between operating in a regenerating mode and in a trapping mode, so that when one is in a regenerating mode the other is in a trapping mode.
24. The method of claim 23 wherein said switching of said traps between a regenerating mode and a trapping mode is performed based on a fixed cycle time or algorithm.
25. The method of claim 22 wherein said switching of said traps between a regenerating mode and a trapping mode is performed and adjusted based on a monitored operating parameter.
26. The method of claim 25 wherein said operating parameter is an operating parameter determined by at least one of a NOx sensor, a temperature sensor, and oxygen sensor, a hydrocarbon sensor.
27. The method of claim 23 wherein the duration of each said trapping mode less than about 20 seconds.
28. The method of claim 27 wherein the duration of each said regeneration mode is about the same as the duration of each said trapping mode.
29. The method of claim 28 wherein the duration of each said regeneration mode and of each said trapping mode is about 10 seconds.
30. The method of claim 1 wherein the syngas generator is a non-catalytic reactor.
31. A combustion engine and after-treatment system comprising:
- (a) a fuel tank and fuel supply subsystem for directing fuel to said engine;
- (b) an air supply subsystem for directing air to said engine stream via an air intake line;
- (c) an engine exhaust stream line connected to receive an exhaust stream from said engine;
- (d) at least one exhaust after-treatment device actuatably fluidly connected to said engine exhaust stream line;
- (e) a syngas generator comprising a syngas output line actuatably fluidly connected to said at least one exhaust after-treatment device;
- wherein said air intake line is fluidly connected receive surplus syngas from at least one of said exhaust after-treatment device and said syngas output line.
32. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive surplus syngas from said exhaust after-treatment device and from said syngas output line.
33. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive said surplus syngas via a venturi or ejector located in said air intake line.
34. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive said surplus syngas via a particulate filter.
35. The combustion engine and after-treatment system of claim 31 wherein said air intake line is fluidly connected receive said surplus syngas via a sulfur trapping bed.
36. The combustion engine and after-treatment system of claim 31 wherein said air supply subsystem comprises a compressor and wherein said air intake line is fluidly connected to receive said surplus syngas upstream of said compressor.
37. The combustion engine and after-treatment system of claim 31 further comprising a controller for adjusting the quantity of surplus syngas directed to said engine via said air intake line in accordance with an operating parameter indicative of the engine power output demand.
38. The combustion engine and after-treatment system of claim 31 wherein said controller is also for adjusting the rate of production of syngas in accordance with an operating parameter indicative of at least one of: the level of regulated emissions in said engine exhaust stream, oxygen content in the engine exhaust stream, air intake mass flow, engine speed and engine power output.
39. The combustion engine and after-treatment system of claim 31 wherein said syngas generator is fluidly connected to said engine exhaust stream line for receiving at least a portion of said engine exhaust stream.
40. The combustion engine and after-treatment system of claim 31 wherein said syngas generator is fluidly connected to said fuel tank and fuel supply subsystem for receiving said fuel.
41. The combustion engine and after-treatment system of claim 31 wherein said exhaust after-treatment system comprises at least one lean NOx trap.
42. The combustion engine and after-treatment system of claim 31 wherein said exhaust after-treatment system comprises a pair of lean NOx traps.
43. The combustion engine and after-treatment system of claim 42 wherein each one of said pair of lean NOx traps is alternatingly fluidly connected to said engine exhaust stream line and to said a syngas generator via a flow diverter located upstream of said pair of traps.
44. The combustion engine and after-treatment system of claim 42 wherein said air intake line is fluidly connected receive depleted syngas alternately from each one of said pair of lean NOx traps via a flow diverter located downstream of said pair of traps.
45. The combustion engine and after-treatment system of claim 31 wherein said syngas generator is a non-catalytic reactor.
46. The combustion engine and after-treatment system claim 31 further comprising an exhaust gas recirculation line fluidly connecting said engine exhaust stream line to said air intake line.
47. A method of mitigating a combustion engine exhaust stream comprising nitrogen oxides, the method comprising:
- (a) operating a reducing agent generator to produce a reducing agent stream;
- (b) in a trapping mode, introducing at least a portion of said engine exhaust stream into at least one catalytic lean NOx trap;
- (e) in a regeneration mode, introducing at least a portion of said reducing agent stream said at least one lean NOx trap,
- wherein the duration of each said trapping mode is less than about 20 seconds.
48. The method of claim 47 wherein the duration of each said regeneration mode is about the same as the duration of each said trapping mode.
49. The method of claim 48 wherein the duration of each said regeneration mode and of each said trapping mode is about 10 seconds.
50. The method of claim 47 wherein said reducing agent generator is a syngas generator and said reducing agent is syngas.
51. The method of claim 50 wherein a fuel stream and at least a portion of said engine exhaust stream are directed to said syngas generator to produce said syngas stream.
52. The method of claim 47 wherein in said trapping mode said engine exhaust stream flows through said catalytic lean NOx trap in a direction substantially opposite to the direction that said reducing agent stream flows through said catalytic lean NOx trap in said regeneration mode.
53. The method of claim 47 wherein said after-treatment module comprises a first lean NOx trap and a second lean NOx trap, said method further comprising alternatingly directing said engine exhaust stream and said reducing agent stream via said upstream flow diverter such that when said first lean NOx trap is in said trapping mode, said second lean NOx trap is in said regeneration mode, and when said first lean NOx trap is in said regeneration mode, said second lean NOx trap is in said trapping mode.
54. A method of operating an engine system with improved fuel economy, the engine system comprising an exhaust after-treatment system and a syngas generator, the method comprising:
- (a) injecting a fuel stream from a fuel supply to said engine, and directing an air stream to said engine via an air intake line, and operating said engine to produce an engine exhaust stream, wherein the timing of the fuel injection is selected for improved fuel economy but so that the level of regulated emissions in said engine exhaust stream, upstream of said exhaust after-treatment system, at least periodically exceeds regulation levels;
- (b) operating said syngas generator to produce a syngas stream;
- (c) at least periodically directing at least a portion of said engine exhaust stream to at least one exhaust after-treatment device in said exhaust after-treatment system, for reducing regulated emissions from said engine system below said regulated levels;
- (d) at least periodically directing at least a portion of said syngas stream to said at least one exhaust after-treatment device for heating or regenerating said device;
55. The method of claim 54 wherein engine exhaust gas is not recirculated to the engine.
Type: Application
Filed: Feb 19, 2007
Publication Date: Aug 23, 2007
Inventor: Erik Johannes (Vancouver)
Application Number: 11/676,499
International Classification: F01N 3/00 (20060101); F01N 3/10 (20060101);