Cross-Reference to Related Applications

[0001] This application claims the benefit of benefit of priority to U.S. Provisional Application Number 62/424,914 filed on November 21, 2016, the disclosure of which is incorporated by reference herein.

Background of the Invention

[0002] The first portion of the background relates to the challenges of engine aftertreatment system operation at low exhaust temperatures. One of the findings from the blended aftertreatment system (BATS) program in North Carolina was that exhaust gas temperatures where the Urea is injected and vaporized needs to be 220°C for early stage dissociation, but the overall SCR system and bulk exhaust gas temps could be cooler in the 165°C range and the SCR system still had good NOx reduction efficiency at low loads and air flows.

[0003] While the BATS solution was good for passenger locomotives that had both a large prime mover and a smaller generator that ran at higher loads and exhaust temperatures, it did not offer a solution to the majority of locomotives that only had a single large prime mover. These large medium speed engines were very efficient and spent considerable times at idle and low loads, where exhaust temperatures would be below the 220°C needed to vaporize and process a mixture of UREA liquid and exhaust gas.

[0004] For locomotive engines operating with natural gas as the primary fuel, this low temperature operation also hinders the use of an oxidizing catalyst (OC) which is needed to reduce carbon monoxide (CO) emissions and help reduce non-methane hydrocarbon (NMHC) emissions, two of the EPA-mandated criteria emissions that are generated in higher quantities when a diesel engine is converted to natural gas. The temperature range for making an OC efficiently reduce CO and start reducing NMHC is the same 200+ Celsius that is needed for effective SCR operation.

[0005] A similar problem but at a different range of temperatures is becoming apparent with the introduction of heavy duty natural gas engines that operate at very lean air fuel ratios in order to both increase thermal efficiency and lower NOx emissions. In the emissions regulations for on-road applications, there is not an exception for methane emissions and therefor total hydrocarbons (HC) need to be reduced. Methane has a very high ignition temperature over 500°C and therefore an OC needs to be at a temperature greater than 400°C before it is effectively oxidizing methane, which makes up a majority of the challenging HC emissions from a high efficiency lean burn engine.

[0006] What would help solve the above problems is an effective solution to increase engine out exhaust temperatures on these engines with a minimal penally in extra fuel consumption and complexity.

Brief Summary of the invention

[0007] Instead of second engine operating at a higher exhaust temperature to make up for the low main engine exhaust temperature as in the first BATS system, there could be a separate exhaust gas heating loop where urea is mixed with a portion of the main engine exhaust. In this loop, the urea is vaporized if needed and the dissociation process is started. If the hot exhaust gasses in this loop are not hot enough at some operating conditions, they could be locally heated with the injection of fuel that is burned across a small oxidizing catalyst. Typical aftertreatment systems on heavy duty engines dose all of the exhaust gases with raw fuel and or UREA. What is novel in this case is that a portion of the total exhaust gas flow is removed and locally heated to the appropriate temperature before dosing with fuel or UREA. This separate external exhaust gas loop will be called the heating loop.

[0008] This system is not specific to just SCR systems that require UREA dosing. It would work for any exhaust aftertreatment system that is challenged to reduce emissions at low exhaust temperatures, including an OC by itself or in series with an SCR.

[0009] The first challenge of a heating loop would be to induce the correct portion of the total exhaust gas mass to go through the separate loop. The simplest technique would be to use the main exhaust gasses kinetic energy to drive the portion of exhaust gas through the loop. In the main exhaust pipe, an inlet could be facing into the exhaust flow using ram air pressure to drive exhaust into the loop. Where the heated loop gasses are reintroduced back into the main exhaust flow, the outlet could be directed in the direction of the main exhaust gas flow causing a low pressure region at the loop exit and further increasing the flow of exhaust gases drawn into and through the heating loop.

[0010] In a preferred embodiment, the ram inlet and lower exit pressure would generate all of the heating loop flow that is required. Any additional flow that is not moved by these pressure differences that is needed could be generated in a simple fashion using an air amplifier similar to that disclosed in US4046492. Compressed air is a readily available source to drive an air amplifier. Trucks, locomotives, busses and many other heavy-duty engine applications typically have compressed air supplies to operate the air brakes on the vehicle. Air amplifiers (a type of jet pump) are simple and low maintenance. The only moving part would be an air flow control mechanism, typically a solenoid that is controlling reasonably low pressure (likely 100-150psi) and near ambient temperature air. Further, the pressurized air flow to the air amplifier can be manipulated by using more than one solenoid to control the pressurized air flow or pulsing one or more solenoids at varying duty cycles to vary the amount of additional exhaust gases that the air amplifier draws into the heating loop.

[0011] On turbo engines, the exhaust back pressure upstream of the turbine can be used as a source of pressurized air to drive the air amplifier operating at the near ambient pressure that the exhaust gasses going through the aftertreatment are operating at. As most turbochargers operate with a wastegate slightly open at higher loads, bypassing the turbine with some exhaust gas to drive a air amplifier in the heating loop should have no or very little effect on engine efficiency. Compressed air from the turbine would be at a lower pressure than typical compressed air from and air brake compressor so it will operate at a lower mass amplification ratio. Also turbine back pressure varies with engine load and is negligible at idle. The turbo pressure variation with engine load will vary in the same direction as the requirement for the air amplifier to induce exhaust gas flow. Like the airbrake compressed air supply system, the preturbine pressurized exhaust gas supply flow or pressure could be manipulated with a valve that controls flow rate. Because valves that operate at these high temperatures can be problematic, in a preferred embodiment the pressurized exhaust gas supply would be controlled by a fixed orifice with no moving parts.

[00010] If there is a benefit to having the orifice larger at lower exhaust temperatures, one variation could be an orifice that varies with temperature using the premise of thermal expansion. This could be with a bimetallic spring that when heated moves into position to restrict the orifice. While technically a moving part, a bimetallic spring system could be designed that had no rubbing parts such as a bearing that over time would wear and change its characteristics. The preferred embodiment would have the flow control orifice be the actual jet nozzle where the compressed exhaust gas is mixed with the heating loop exhaust gases.

[0012] In some air amplifiers, the fixed orifice is actually a continuous radial gap between two radial faces of almost touching parts. In the case of the Nex Flow Air Products Corp part number 30003TS this gap is set to .004 inch and is adjustable by turning the threaded body parts in relation to each other. These two parts could be designed in such a way that this gap was closed up at higher temperatures that would correspond to higher engine loads and higher turbine boost pressure. If one part was made from stainless steel and one from carbon steel, the stainless part would grow in length 1.5 times that of the steel part thereby changing the gap distance.

[0013] In a natural gas fueled engine using a heating loop, if natural gas fuel is being injected into the heating loop to add temperature, the natural gas injector could also be used to drive an air amplifier. This would have the secondary benefit of also helping to evenly mix the air and fuel if the air amplifier has a continuous radial gap for an orifice like the Nex Flow PN 30003TS.

[0014] A natural gas-powered air amplifier would both improve mixing and get the benefit of recycling the energy used to compress the natural gas, it likely will still need an additional compressed air powered air amplifier to both increase and control the amount of exhaust gas flowing through the heating loop.

[0015] Now that there is an adequate and controlled amount of exhaust gas flowing through the heating loop, a system needs to be implemented to raise its temperature. This additional heat will typically be provided by combusting injected fuel and excess oxygen in the exhaust gases across an OC mounted inside the dosing loop flow path. Compared to an open flame burner, combusting the fuel across a catalyst will minimize the amount of criteria emissions added to the total exhaust flow when this extra fuel combusted.

[0016] If or when the exhaust temperature entering the dosing loop is not hot enough to ignite the injected fuel when it reaches the dosing loop OC, an additional system will be needed to temporarily provide extra heat to the exhaust gas flow until the OC is at a high enough temperature to light off and insure continuous catalytic combustion of the injected fuel. A simple way of doing this is with an electric exhaust heater similar to a Watlow ECO Heat unit. This electric heater could be used for both diesel injection or natural gas injection. The electric heater is more likely to be effective with diesel fuel injection because of diesel fuels much lower light off temperature at the OC.

[0017] Instead of an electric heater when using natural gas, a conventional burner with a flame holder and ignition system could be used to drive the OC temperature up to that needed for light off and continuous catalytic combustion. The supply pressure of natural gas to the natural gas injector could be manipulated to control the heat rate of both the preheater and the catalytic combustion system. The flame holder system should only need an ignition source to start combustions. One method to switch from combustion at the flame holder to combustion at the catalyst system is to temporarily turn off the natural gas supply to the heating loop and keep it off long enough to extinguish the flame at the flame holder but then turn the natural gas fuel back on soon enough that the OC is still hot enough to light off and maintain continuous catalytic combustion.

[0018] Various embodiments of the above described system will be effective for engines that only need an OC. For systems that will use an SCR the system is the same up to the OC that combusts the added fuel for heating up the exhaust gases. After the OC is where the UREA would be injected and then there would need to be a length of straight and well insulated ducting to give the UREA time to mix with the hot exhaust gases and start decomposing into ammonia before the mixture of ammonia and exhaust gas from the heating loop mixes with the bulk of the exhaust gases in the main exhaust system on its way to the SCR unit.

[0019] For an aftertreatment system that only has an OC, the heating loop system should not need to increase flow capacity at higher loads as the main engine exhaust temperature should become high enough to keep the after treatment operating, in this case the air amplifiers and fuel injection for the heating loop can be turned off.

[0020] On the other hand, for an SCR system, the systems exhaust gas mass flow and heating capacity will need to increase as the required amount of UREA increases. This makes the turbocharged engine slightly easier for an SCR application as the exhaust back pressure being used to drive an air amplifier requires less energy than suppling compressed air from an engine driven compressor to drive the increasing amounts of exhaust gas through the heating loop.

[0021] Exhaust gas heating can also be used in the main exhaust system. As high efficiency engines are able to operate at lower and lower exhaust temperatures, two problems are becoming apparent. First the exhaust temperatures are getting so low that at moderate loads it is not high enough to oxidize any of the methane that isn't burned in the main chamber. Also these lower temperatures make it a challenge to drive the turbo charger. Putting an OC upstream of the turbocharger has been investigated in prior art but at the time found not practical. What would be an improvement over a heating loop as proposed above could be a pre-turbine and after treatment system. The preferred embodiment would be a natural gas engine with a pre turbine after treatment system that has both OC substrates and SCR substrates. This could have a heating system in front of the first OC substrate, then a UREA injection system, then a second heater, then a final OC before the exhaust gases reach the turbocharger. In this case the extra fuel needed to increase the exhaust temperature enough to burn off the methane and the oxidized methane that originally left the engine cylinder without being burned would now provide energy to the turbo charger turbine. The reason that a heater after the SCR is needed is that the light off temperature for methane in the final OC is higher than the temperature that the SCR should be operating at.

[0022] To add further benefit to this system, the turbocharger could be electrified. This will greatly accelerate engine response and increase engine efficiency by eliminating the need for a waste gate and capturing as much energy as possible with the exhaust turbine. For more efficiency a second electrically driven compressor can be used in series with the turbocharger.

[0023] For gaseous fuels the heaters in this system could use a burner at first until the OC substrates reach light off temperature and then turn off the gas supply momentarily to extinguish the burner flame so that the combustion then starts up again and continues in the OC downstream of that burner.

Description of the Drawings

[0024] Fig. 1 is a side view of a turbocharged engine with an aftertreatment system including a heating loop. [0025] Fig. 2 is a side view of a normally aspirated engine with an aftertreatment system including a heating loop.

[0026] Fig. 3 is a preferred embodiment for a turbocharged diesel engine with an SCR aftertreatment system.

[0027] Fig. 4 is a block diagram of a control system with its sensors and valves.

Detailed Description

[0028] To facilitate an understanding of the present disclosure, a number of terms and phrases are defined below:

[0029] Blended Aftertreatment System (BATS): As described in US 9,752,481, incorporated herein by reference, a BATS system reduces the NOx emissions from the mixed exhaust of two engines in a single larger SCR assembly using only one UREA injection point into the exhaust of the smaller engine.

[0030] Gaseous Fuel: The predominant gaseous fuel used in internal combustion engines is natural gas consisting mostly of methane, but with minor modifications these engines could consume any gaseous fuel including but not limited to propane, natural gas and hydrogen. In this document the term natural gas and gaseous fuel are used interchangeably.

[0031] Hydrocarbon (HC): Emissions resulting from incomplete combustion of fuel and engine lube oil.

[0032] Main Charge: The air fuel mixture in the main combustion chamber space between the piston top and the cylinder head. If an opposed piston engine, this would be the space between the opposed piston faces.

[0033] Particulate Matter (PM): Particulate matter is a criteria pollution emitted from many sources. In this document we will commonly refer to it simply as PM. It could include both diesel soot PM that is considered toxic in California or the type of PM created by the consumption and combustion of lube oil from an engine. While still considered PM as a criteria emission, the PM from lube oil consumption is considered less toxic than diesel soot.

[0034] Reductant: In active NOx reductions systems like a Selective Catalytic Reduction (SCR) system, a reductant is mixed with the hot exhaust gases and is chemically processed by the catalyst system along with the exhaust gasses to reduce NOx emissions to N2 and water. Diesel Exhaust Fluid (DEF) is currently the most common reductant for SCR systems in mobile applications. DEF is actually a mixture of 32.5% UREA and 67.5% water. Once injected into the engine the DEF is first vaporized, and then the UREA crystals are decomposed into ammonia and C02 molecules. It is the ammonia particles that the SCR catalyst uses to reduce NOx into N2 and water. SCR systems can be used on heat engines burning any kind of fuel so the DEF term can be misleading, in Germany DEF falls under the trademark AdBlue. DEF is also frequently called UREA for short. In some instances ammonia gas is extracted from some other system and injected directly into the exhaust flow as a gas before the exhaust and ammonia mixture reaches the SCR catalysts.

Throughout this document the reductant injected into any aftertreatment device that actively reduces NOx will typically be referred to as UREA. In addition the term SCR will be used to identify any active NOx reduction system that uses a reductant.

[0035] FIG. 1 is a side view of a turbocharged medium speed engine with a heating loop. Exhaust Manifold 3 is on top of engine 1 and routes pressurized exhaust gases into turbocharger 2. Main exhaust duct 4 routes the exhaust gases from turbocharger 2 into aftertreatement 5. After the exhaust gases are treated in aftertreatment 5 they exit the engine system through main exhaust outlet 20. Aftertreatment 5 may contain OC substrates, SCR substrates or a combination of both. If an aftertreatment 5 system contains both types of substrates it is controlled in the same manner as a system with only SCR substrates.

[0036] Heating loop inlet 6 extracts a portion of exhaust gases from main exhaust duct 4 and directs it through heater loop 7. Once the portion of exhaust gases have been processed through all the devices along heater loop piping 7 they are then injected back into the main exhaust duct 4 through heater loop exit 8. Air amplifier EP 10 will be fed pressurized exhaust gas sourced from exhaust manifold 3 to assist drawing more exhaust gas into heater loop piping 7. Air Amplifier CA 11 is driven by compressed air from an external source somewhere in the vehicle. This could be supplied by an engine driven air compressor that supplies air to the air brake system. If the vehicle doesn't already have an air compressor is could be supplied by the compressor in turbo 3, although this would be less efficient as turbo 3 boost pressure is likely ¼ that of the air brake system and will require 4 times as much air mass to be as effective and all of this air will need to be heated by adding more heat energy into the heating loop 7. Electric preheater 12 is used to increase the temperature of the portion of exhaust gases to a point that the OC 15 will light off and burn the fuel and lean exhaust gas mixture. Electric preheater 12 would typically only be used with a fuel other than methane that has a lower ignition temperature, diesel fuel would be the most appropriate fuel for use with electric preheater 12. Fuel injector 13 is used to inject fuel into the heating loop 7. This is most likely the same fuel used to power engine 1, it could be a liquid hydrocarbon fuel such as diesel or any gaseous fuel. In the case of pressurized gaseous fuels, fuel injector 13 may also act as an air amplifier that is powered by the pressurized gaseous fuel. Fuel burner 14 is used typically for gaseous fuels like methane that have very high ignition temperatures that are not reasonable for use of an electric preheater 12. Fuel burner 14 will likely incorporate a flame holder and ignition system to start combustion. OC 15 is where flameless combustion will occur once the heating loop 7 is at operating temperature. Temperature sensor 16 is the parameter that a control system will monitor to determine the system status and determine when to inject fuel, how much fuel to inject and when to transition from fuel burner 14 to OC 15 to catalytically burn the injected fuel at the highest efficiency at lowest emissions. Gaseous fuel can be injected at any time, but diesel fuel should only be injected after the portion of exhaust gas flow has been preheated by electric preheater 12 to a threshold temperature that will cause light off of OC 15. After light off, the temperature sensor 16 will monitor the exit temperature of OC 15 and that temperature will be used to determine if more or less fuel should be injected by fuel injector 13 to achieve the target temperature in the heating loop 7.

[0037] For an aftertreatment 5 unit that only has an OC substrate, the temperature sensor 16 will be the last device that heating loop 7 is equipped with and the now heated portion of exhaust gases would be then injected through heating loop exit 8 back into the main exhaust duct 4.

[0038] For an aftertreatment 5 unit that does have an SCR substrate, additional components will be added to heating loop 7. UREA injector 17 is used to inject UREA into heating loop 7. Temperature sensor 19 will be used to measure the temperature of the portion of exhaust gas that was first heated and then cooled by injecting UREA into it. With an SCR function temperature sensor 19 becomes the parameter that is used to determine fuel flow through fuel injector 13 to maintain a target temperature at the exit of heating loop 7. In some embodiments, if a temperature sensor 19 is installed, the temperature sensor 16 after OC 15 can be eliminated.

[0039] Recent research has indicated that decomposition of UREA is assisted by being passed through a catalyst at high temperature. In a conventional SCR system, when the air and UREA mixture gets to the SCR substrates, the UREA is typically only 50% of the way through the decomposition process and the remaining decomposition to ammonia occurs as the exhaust gas and decomposing UREA move along the flow length of the substrate. This lowers the overall effectiveness of the substrate. If all of the UREA had been decomposed to ammonia before the exhaust gases started passing through the SCR substrate, it would have a higher NOx reduction efficiency and would be able to operate at lower temperatures. OC 18 is used to increase the amount of decomposition of the mixture of UREA and heated exhaust gases before they exit the heating loop 7 on their way to the SCR substrates inside of aftertreatment 5.

[0040] Fig. 2 is a side view of a normally aspirated medium speed engine with a heating loop. Figure 2 has all the same components and functionality as Figure 1 except that turbo main exhaust duct 4' connects exhaust manifold 3 directly to aftertreatment 5 and turbo 3 and the exhaust pressure driven air amplifier EP 10 have been deleted. Because air amplifier EP 10 has been deleted, the compressed air driven air amplifier CA 11 may have to provide more motive force to induce enough exhaust gas flow through heating loop 7 [0041] Fig. 3 is the preferred embodiment of a medium speed turbocharged diesel engine with and SCR aftertreatment system and simplified heating loop. Exhaust Manifold 3 is on top of engine 1 and routes pressurized exhaust gases into turbocharger 2. Main exhaust duct 4 routes the exhaust gases from turbocharger 2 into aftertreatement 5. After the exhaust gases are treated in aftertreatment 5 they exit the engine system through main exhaust outlet 20.

[0042] Heating loop inlet 6 extracts a portion of exhaust gases from main exhaust duct 4 and directs it through heater loop 7. Once the portion of exhaust gases have been processed through all the devices along heater loop piping 7 they are then injected back into the main exhaust duct 4 through heater loop exit 8. Air amplifier EP 10 will be fed pressurized exhaust gas sourced from exhaust manifold 3 to assist drawing more exhaust gas into heater loop piping 7. Electric preheater 12 is used to increase the temperature of the portion of exhaust gases to a point that the OC 15 will light off and burn the diesel fuel and lean exhaust gas mixture. Fuel injector 13 is used to inject diesel fuel into the heating loop 7. OC 15 is where flameless combustion will occur once the heating loop 7 is at operating temperature. Temperature sensor 19 is the parameter that a control system will monitor to determine the system status and determine when to inject fuel and how much fuel to inject. Diesel fuel should only be injected after the portion of exhaust gas flow has been preheated by electric preheater 12 to a threshold temperature that will cause light off of OC 15. After light off temperature sensor 19 will monitor the exit temperature of OC 15 and that temperature will be used to determine if more or less fuel should be injected by fuel injectorl3 to achieve the target temperature in the heating loop 7. Once OC 15 is at temperature and catalytically combusting the injected fuel, electric preheater 12 can be turned down or off.

[0043] After temperature sensor 19 has determined that the heating loop 7 temperature is hot enough, UREA injector 17 is used to inject UREA into heating loop 7. As more UREA is injected through injector 17, temperature sensor 19 will detect a dropping temperature in heating loop 7 and the control system will command more fuel be injected through injector 13 to bring the heating loop exhaust gas exit temperature back up to its target temperature.

[0044] Fig. 4 is a bock diagram of a simplified control system for a heating loop 7.

Controller unit 30 is electrically connected to various sensors and control valves. Temp sensor 31 will read the exhaust exit temperature from heating loop 7 and depending on its control mode with control the amount of fuel flowing through injector 3. This fuel flow can be controlled by valve 32 which could be an on or off solenoid valve that is modulated to control the flow rate of fuel to injector 13 or this control valve 32 could be an integral part of injector 13. Control solenoide 33 will control the flow of electricity to electric preheater 12 if the system is so equipped. This electric current flow could be controlled by several different electrical devices ranging from a simple switch to a PWM controlled transistor module.

[0045] Control valve 34 regulates the supply of compressed air to an air amplifier CA 11 if the system is so equipped. It may be a simple on off valve with one setting , it can also be PWM controlled to linearly regulate flow.

[0046] Control valve 35 will control UREA flow to UREA injector 17. This could be a solenoid valve that modulates flow or a pumping system of some sort that provides a metered amount of UREA.

[0047] Controller 30 may have its own table of engine operating parameters, but it most likely will be in communication with a master controller that will send it engine load information and updated operating parameters such as heating loop 7 target exhaust temperature. Any of these control valves or solenoids could be physically integrated into control 30 without changing its functionality. Controller unit 30 itself could be integrated into another controller that controls other devices and even the entire engine system or vehicle.

[0048] It should be noted that various changes and modifications to the presently preferred embodiments described herein will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the present invention and without diminishing its attendant advantages.