Patent Application
20130067890
Emissions regulations relating to internal combustion engines, including diesel engines, are increasingly stringent. This trend is expected to continue. These stringent regulations often impart expenses on engine manufacturers to find new methods and systems to satisfy the obligations. Additionally, manufacturers must reconsider how to correctly analyze the operating costs of an engine that has been modified with a new method or system. For example, when an aftertreatment device such as selective catalytic reduction (SCR) is used with a diesel engine, one of the cost considerations relates to the fluctuation in price of diesel fuel relative to diesel exhaust fluid (DEF). In addition, the fuel used to heat the Diesel Particulate Filter (DPF) and fuel consumed during regeneration must be considered. It is known that increased temperatures necessary to effect regeneration of the DPF have a deleterious effect on the useful life of the DPF. Accordingly, the effect of the increased exhaust temperatures on the DPF must also be considered. Thus, it is well understood that operating costs relate not just to the consumption of fuel, but also to the consumption of DEF.
The present disclosure relates to methods and controllers for engines that are adapted to be used with one ore more aftertreatment devices to achieve lower operational costs when diesel fuel and DEF are used.
Many approaches have been used to reduce emissions to satisfy government regulations. This includes modifications to engines as well as to aftertreatment devices.
One common engine modification for NOx reduction is exhaust gas recirculation (EGR). EGR diverts a portion of an engine's exhaust gas into the engine cylinders. The exhaust gas is inert and its presence prevents more combustible material (e.g., oxygen) from being in the cylinders by displacing the combustible material. As a result, when combustion occurs, it does not reach temperatures as high as it would in the absence of the recirculated exhaust gas. Because the burned gas temperature of EGR combustion is lower, less NOx is formed in engines using EGR. One exemplary EGR system is disclosed in U.S. Pat. No. 7,213,553 assigned to Detroit Diesel Corporation, which is incorporated by reference herein in its entirety. Whether or not EGR is used, the exhaust that leaves the engine contains a certain amount of what is referred to herein as “engine-out NOx.” The greater the EGR usage, the lower the engine-out NOx.
Aftertreatment devices are frequently used in exhaust systems with diesel engines to reduce emissions. Aftertreatment devices can be used in combination with EGR, but one does not require the other. Aftertreatment devices in the exhaust system are generally used to treat exhaust streams from engines containing engine-out NOx. When the exhaust stream has made it through all of the aftertreatment devices, the remaining exhaust gas runs through the tailpipe to the atmosphere. Government standards are concerned with tailpipe emissions.
One aftertreatment device is an SCR. In exhaust systems so equipped, engine exhaust gas flow containing engine-out NOx runs through an SCR canister, which contains urea and catalyst. Currently, in diesel engines, the grade of urea that is commonly used is also referred to DEF. A commonly used DEF is an organic, non-toxic compound made of about 32.5% urea and about 67.5% deionized water. Additional reducing agents may optionally be included. When NOx in the reacts with DEF, NOx is chemically reduced to nitrogen and water and a small amount of carbon dioxide. One exemplary SCR system is disclosed in U.S. Pat. No. 6,901,748 assigned to Detroit Diesel Corporation, which is incorporated by reference herein in its entirety.
Another commonly used aftertreatment device is a diesel oxidation catalyst (DOC) system. DOC can be used in combination with an SCR. As exhaust gas flows through a DOC canister having interior walls coated with a catalyst containing metals such as platinum or palladium, it contacts the catalyst layer, which causes a chemical oxidation reaction with the constituent gasses in the exhaust stream wherein carbon monoxide and other hydrocarbons are catalyzed to give products of carbon dioxide and water. A DOC is included in the description of U.S. Pat. No. 7,343,736 assigned to Detroit Diesel Corporation, which is incorporated by reference herein in its entirety.
Another commonly used aftertreatment device is a diesel particulate filter (DPF) system. DPF systems are commonly used together with one or both of SCR and DOC. DPFs are filters through which exhaust runs and through which particulates, hydrocarbons and soot cannot readily pass. There are single-use disposable DPFs and reusable DPFs. In some reusable DPFs, a filter may be cleaned or regenerated. Regeneration can occur through increasing engine speed or load, or both, during engine operation so that the temperature of the exhaust gas is increased. The increased exhaust gas temperature may be used in conjunction with a hydrocarbon (HC) doser that injects fuel into the DPF. During a DPF regeneration event, the elevated exhaust temperature causes the HC injected fuel to ignite and combust the soot and HC to regenerate the DPF. A suitable DPF (along with at least one DPF maintenance procedure) is described in U.S. Pat. No. 7,650,781 assigned to Detroit Diesel Corporation, which is incorporated by reference herein in its entirety.
An SCR, DOC and DPF may be arranged in the exhaust system in multiple manners, with one or more of the devices excluded. A typical arrangement is for an engine to recirculate a portion of the exhaust via EGR and to send the remaining portion of the exhaust out of a pipe where it is only periodically dosed with hydrocarbons (HCs), but always sent through a DOC canister, then sent through a DPF, then the exhaust is dosed with DEF and sent through an SCR canister for the reduction reaction to occur. The products of the SCR canister are then released to atmosphere.
It is desired to use one or more aftertreatment devices to achieve emissions standards in the most cost-efficient manner, and to accommodate for variations in price both for diesel fuel and for DEF when at least one of the aftertreatment devices is an SCR.
It has been discovered that the cost effectiveness of a diesel engine operation that uses an SCR aftertreatment device is sensitive to the price ratio of diesel fuel to DEF. Thus, methods and controllers have been developed relating to optimizing the cost effectiveness of NOx reduction based at least in part upon the price ratio of diesel fuel to DEF, hereinafter referred to as “cost ratio” or “CR.”
A method of using a controller to optimize operation of a diesel engine for lowest possible costs is provided. One such method includes receiving input data regarding diesel fuel cost and regarding cost of DEF. The method also includes determining a target engine-out NOx emission level based upon at least the diesel fuel cost input and the DEF cost input using an electronic engine control module. The method then calls for the use of the engine-out NOx emission target level to determine a quantity of DEF to be injected into an aftertreatment device such that all applicable exhaust emissions regulations are satisfied or exceeded. The method also calls for, in fact, causing the determined quantity of DEF to be injected.
An electronic control unit (ECU) is also provided. The ECU includes means for receiving input data regarding diesel fuel cost and cost data for DEF. The ECU also includes means for determining an optimal desired engine-out NOx emission level based upon at least the diesel fuel cost input, the DEF cost input, the net change in diesel fuel required by the HC doser and the overall balance of energy consumed by the engine to deliver the expected output power. The overall balance of energy consumed by the engine is related but not limited to air volume requirements for an air assisted DEF dosing system, the change in engine heat rejection caused by the shift in NOx emissions levels and the effects on other parasitic devices that are driven by the engine. The ECU also includes means for determining a quantity of DEF to be injected into the aftertreatment device to achieve the target engine-out NOx emission level.
The figures herein are used to describe exemplary embodiments of the claimed subject matter and are not intended to be limiting to the scope and sprit of the invention as set forth in the appended claims.
The remainder of the exhaust 21 that is not introduced to pipe 20 is exposed to a hydrocarbon (HC) doser 30. The HC doser is used to periodically inject a predetermined amount of fuel 31 into the exhaust 21. The period can be based on selection of a predetermined time, and/or it can be determined using a controller based on any number of factors including inputs from pressure sensors. If a controller determines that it is necessary to burn accumulated HC and soot out of a DPF 40 (also known as regenerating DPF 40), the controller can cause the HC doser to dose the exhaust 21 with diesel fuel. Generally, when it is desired to initate a regernation event, the engine speed or load, or both, are increased and the temperature of the exhaust gas stream produced is thereby increased. The engine speed is controlled by fueling strategies that vary the quantity and timing of the fuel injected into the combustion chambers of the engine. The resultant exhaust has an elevated temperature into which the HC doser introduces a quantity of fuel, such that the exhaust stream in dosed. The increased temperature exhaust gas/HC dosed exhaust gas mixture (the mixture) passes through a DOC 35 to burn off HC and soot in DPF 40. The reason HC and soot accumulate in DPF 40 is that DPF 40 typically has honeycomb porous walls (not shown) through which non-particulate matter is designed to flow. Particulate matter, then, accumulates in the walls. When too much HC or soot accumulates such that engine performance and/or emissions are impacted, then DPF 40 needs to be regenerated as described.
The filtered mixture is then exposed to a DEF doser 45 where DEF 46 is added to react with and reduce NOx in the filtered mixture in the SCR catalyst canister 50. The chemical reduction reaction occurs in the SCR catalyst canister 50, and the products of the reaction, including nitrogen and water, are released into the atmosphere.
In step 52, the ECU 75 receives signals corresponding to the fuel cost and the DEF cost. Additionally, the ECU 75 may receive many other signals relating to various engine/vehicle sensors and executes control logic embedded in hardware and/or software to control various aspects of the engine 10. The computer readable storage media may, for example, include instructions stored thereon that are executable by the ECU 75 to perform methods of controlling all features and sub-systems in the engine 10. The program instructions may be executed by the ECU, and in the embodiment, specifically by the Motor Processing Unit (MPU) of the Electronic Control Unit (ECU) to control the various systems and subsystems of the engine and/or vehicle through the input/output ports. Furthermore, it is appreciated that any number of sensors and features may be associated with each feature in the system for monitoring and controlling the operation thereof
In step 53, using at least input fuel cost from engine operation, the DPF doser, or both, and input DEF cost and knowledge of the regulatory requirement for tailpipe NOx, a target engine-out NOx emissions value is determined. This means, given the government regulations, for cost purposes, it is determined what percentage of NOx reduction should be handled within the engine (for example, by EGR) and what percentage should be handled via aftertreatments (for example, by SCR).
Once the optimal engine-out NOx emission level is determined step 53, the controller 75 directs step 61 by sending a signal, directly or indirectly, to the engine 10 to adjust the operating setpoints to generate the target engine-out NOx level. Step 61 can be performed because, as shown in
As seen in
The relationship of the cost ratio (CR) of diesel fuel to DEF at target engine-out NOx levels is depicted in
If the CR is greater than 1, then the engine and SCR based aftertreatment system are operated with increased NOx engine output levels. This causes the engine controller to increase utilization of SCR based ATS system, and decrease time interval between regeneration intervals of DPF based ATS system to meet or exceed emissions regulations at requested engine power output level.
If the CR is less than 1, then the controller operates the engine with decreased NOx engine output levels, decrease utilization of SCR based ATS system and increase time between regeneration intervals of DPF based ATS system to meet or exceed emissions regulations at requested engine power output level.
As seen in
When the cost ratio (CR) of diesel fuel to DEF is 0.5 (CR=0.5) as seen at 76, the optimum engine-out NOx 80 is substantially lower than when the cost ratio of diesel fuel to DEF is 2.0 (CR=2.0) as seen at 78. It can also be seen that when the CR is 1.0, the optimum engine out NOx 82 is intermediate the optimum engine out NOx when CR is 0.5 and 2.0. The shift in optimum engine-out NOx from CR 0.5 to CR 2.0 may be more than 50%.
Note also that when the CR is higher, the NOx to particulate matter (PM) ratio is lower. This means there is less particulate matter to burn off of a DPF, resulting is less frequent regenerations which will inherently lower the diesel fuel consumption through an HC doser. The controller further accounts for the difference in engine output particulate matter accumulation on the DPF depending on the CR utilized.
The words used in this application are understood to be words of description, and are not words of limitation. While at least one method and system have been discussed, those skilled in the art recognize that many variations and modifications may be made without departing from the scope and spirit of the invention as set forth in the appended claims.
