Patent Application
20130151125
The subject matter disclosed herein relates to emissions control in internal combustion engine and more particularly to the control of CO and NOx emissions in an internal combustion engine.
Internal combustion engines are ideally operated in a way that the combustion mixture contains air and fuel in the exact relative proportions required for a stoichiometric combustion reaction. A rich burn engine may operate with a stoichiometric amount of fuel or a slight excess fuel, while a lean-burn engine operates with excess oxygen (O2) compared to the amount required for stoichiometric combustion. The operation of an internal combustion engine in lean mode may reduce throttling losses and can take advantage of higher compression ratios thereby providing improvements in performance and efficiency. Rich burn engines, on the other hand are relatively simple, reliable and stable, and adapt well to changing loads.
In order to comply with emissions standards, many rich burn internal combustion engines utilize non-selective catalytic reduction (NSCR) subsystems also known as 3-way catalyst. These subsystems reduce emissions of nitrogen oxides NO and NO2 (collectively NOx), carbon monoxide (CO) and volatile organic compounds (VOC), along with other regulated emissions. 3-way catalysts have high reduction efficiencies and are economical but require tight control of the air fuel ratio of the engine in order to meet emissions standards. These standards are sometimes stated in terms of grams of emissions per brake horsepower hour (g/bhp-hr).
Previously, rich burn emissions control with a catalyst was only possible using O2 sensing at both the input and output locations of the catalyst subsystem. In those systems a control subsystem adjusted the air fuel ratio continuously to maintain a constant O2 content in the exhaust. The target value for the constant O2 content (the O2 voltage setpoint) was static. Occasionally, these control systems allowed greater variation of emissions than is optimal over varying operating and environmental conditions as well as shifts in the catalyst operating window. The reason is that to reach low NOx and CO emissions levels one cannot simply set the O2 voltage setpoint to a single value. The optimal O2 voltage setpoint for emissions compliance varies depending on load, speed, ambient conditions, among other conditions.
According to one aspect of the invention, a method of operating an internal combustion engine over a range of operating conditions, the internal combustion engine having at least one O2 sensor is provided. The method of this aspect includes operating the engine at an initial O2 voltage setpoint and automatically adjusting the O2 voltage setpoint to a new O2 voltage setpoint to reduce emissions.
According to another aspect of the present invention a system for improving emission performance of an internal combustion engine over a range of operating conditions is provided. The system of this aspect includes a catalyst subsystem for treating exhaust from the internal combustion engine; an O2 sensor disposed upstream from the catalyst subsystem; and a NOx sensor disposed in the exhaust. The system of this aspect also includes a control subsystem that receives data from the O2 sensor and the NOx sensor, and automatically adjusts an O2 voltage setpoint to a new voltage setpoint to reduce emissions.
According to another aspect of the present invention, a control system for controlling emissions in an internal combustion engine exhaust is provided. The control system of this aspect includes at least one subsystem that controls an O2 voltage setpoint; at least one subsystem that measures NOx emissions in the engine exhaust; and at least one subsystem that initiates a lambda sweep to determine an optimal O2 voltage setpoint.
According to another aspect of the present invention, a method for controlling emissions in an internal combustion engine exhaust is provided. The method of this aspect includes measuring NOx emissions; initiating a lambda sweep to determine an O2 voltage setpoint at which NOx emissions at the new operating condition comply with NOx emissions standards; and operating the internal combustion engine at the new O2 voltage setpoint.
According to another aspect of the present invention, computer-readable media is provided. The computer readable media of this aspect provides instructions that, when executed by a control module that controls emissions in an internal combustion engine exhaust, cause the control module to measure NOx emissions; initiate a lambda sweep to determine an O2 voltage setpoint at which NOx emissions at the new operating condition comply with NOx emissions standards; and operate the internal combustion engine at the new O2 voltage setpoint.
The following description of the Figures is not intended to be, and should not be interpreted to be, limiting in any way.
Illustrated in
The internal combustion engine system 1 also includes a right regulator 33 associated with the right cylinder bank 5, and a left regulator 35 associated with the left cylinder bank 3. The right regulator 33 controls the flow of air and fuel to the right cylinder bank 5, and the left regulator 35 controls the flow of air and fuel to the left cylinder bank 3. A regulator is a device that determines and maintains the operating parameters of a system, usually within certain prescribed or preset limits. The right regulator 33 and left regulator 35 adjust the air fuel ratio in the right cylinder bank 5 and the left cylinder bank 3 respectively. Although the embodiment illustrated in
Associated with the right cylinder bank 5 and the left cylinder bank 3 is a manifold 37 that conveys the exhaust gases from internal combustion engine system 1. The manifold 37 includes a left manifold tube 38 into which is placed at least one left O2 sensor 39, and a right manifold tube 40 into which is placed at least one right O2 sensor 41. The left O2 sensor 39 and right O2 sensor 41 (also known as lambda sensors) are electronic devices that measure the proportion of O2 in the exhaust inside the manifolds 38, 40 and determine, in real time, if the air fuel ratio of a combustion engine is rich or lean. Information from the left O2 sensor 39 and the right O2 sensor 41 may be used to indirectly determine the air fuel ratio. In some embodiments only one O2 sensor may be used. Among the types of O2 sensors available are concentration cell (zirconia sensors), oxide semiconductor (TiO2 sensors) and electrochemical O2 sensors (limiting current sensors). The sensors do not typically measure O2 concentration directly, but rather the difference between the amount of O2 in the exhaust gas and the amount of O2 in a reference sample. Rich mixtures cause an O2 demand. This demand results in a build-up of voltage due to transportation of O2 ions through a sensor layer. Lean mixture result in low voltage, since there is an O2 excess.
Exhaust gases from the internal combustion engine system 1 are conveyed through the right manifold tube 40 and the left manifold tube 38 into a catalytic chamber 43 that contains a catalyst for the reduction of NOx and CO emissions. In a preferred embodiment the catalyst may be a 3-way catalyst commonly used for internal combustion engine applications. The catalyst converts CO, NOx and VOC emissions through reduction and oxidation to produce carbon dioxide, nitrogen, and water. Three-way catalysts are effective when the engine is operated within a narrow band of air-fuel ratios near stoichiometry. The conversion efficiency of the catalyst declines significantly when the engine is operated outside of that band of air-fuel ratios. Under lean engine operation, there is excess O2 and the reduction of NOx is not favored. Under rich conditions, excess fuel consumes all of the available O2 in the exhaust prior to the catalyst, thereby making oxidation reactions less likely.
A NOx sensor 45 is disposed downstream from the catalytic chamber 43. In alternative embodiments, the NOx sensor may be located upstream of the catalytic chamber 43 (if a catalyst is used), or multiple NOx sensors may be used. NOx sensors are devices that detect nitrogen oxides in combustion environments such as internal combustion engine system 1. A variety of different sensors are available for adaptation to use in an internal combustion engine system 1. For example, there are a variety of solid-state electrochemical sensors including solid electrolyte (potentiometric and amperometric) and semiconducting types.
The NOx sensor 45, right O2 sensor 41 and left O2 sensor 39, right regulator 33 and left regulator 35 are all coupled to an emission control module 47. The emission control module 47 may be provided as a microprocessor and a memory, or as software otherwise provided or embedded within other processors or electronic systems associated with the internal combustion engine system 1 or in any other known forms. Emissions control module 47 in various embodiments may include instructions executable by one or more computing devices. Such instructions may be compiled or interpreted from computer programs created using a variety of known programming languages and/or technologies, including, without limitation, and either alone or in combination, Java™, C, C++, Visual Basic, Java Script, Perl, etc. In general, a processor (e.g., a microprocessor) receives instructions, e.g., from a memory, a computer-readable medium, etc., and executes these instructions, thereby performing one or more processes, including one or more of the processes described herein. Such instructions and other data may be stored and transmitted using a variety of known computer readable media.
A computer-readable medium includes any medium that participates in providing data (e.g., instructions), which may be read by a computer. Such a medium may take many forms, including, but not limited to, non-volatile media, volatile media, and transmission media. Non-volatile media include, for example, optical or magnetic disks and other persistent memory. Volatile media include dynamic random access memory (DRAM), which typically constitutes a main memory. Transmission media include coaxial cables, copper wire and fiber optics, including the wires that comprise a system bus coupled to the processor. Transmission media may include or convey acoustic waves, light waves and electromagnetic emissions, such as those generated during radio frequency (RF) and infrared (IR) data communications. Common forms of computer-readable media include, for example, a floppy disk, a flexible disk, hard disk, magnetic tape, any other magnetic medium, a CD-ROM, DVD, any other optical medium, punch cards, paper tape, any other physical medium with patterns of holes, a RAM, a PROM, an EPROM, a FLASH-EEPROM, any other memory chip or cartridge, a carrier wave as described hereinafter, or any other medium from which a computer can read.
The internal combustion engine system 1 with improved emissions control capabilities may be operated over a range of operating conditions by automatically adjusting a setpoint of one or more O2 sensors, such as left O2 sensor 30, right O2 sensor 41, or both. An O2 voltage setpoint is the target value for O2 that the emission control module 47 will aim to reach by controlling the amount of fuel that enters the engine relative to the amount of air. The amount of fuel that enters the engine relative to air is called the air fuel ratio (AFR), and sometimes expressed as Lambda (λ) which is the engine's AFR relative to a stoichiometric AFR. The internal combustion engine system 1 accomplishes an improved emissions performance by adjusting the pre-catalyst O2 voltage setpoints from a calibrated high setpoint at a calibrated sweep rate downwards to a low O2 voltage setpoint until NOx measurements become unstable or spike (i.e. stability level threshold is breached). In one embodiment, stability may be determined by measuring NOx concentration over a given period of time.” The sweep rate may be in milli-volts per second and may be specifically calibrated for each engine. Once the stability threshold is breached the O2 voltage setpoint is adjusted upward at a calibrated sweep rate until the stability level is achieved (NOx readings NOX sensor 45 become stable again).
The principles behind the process for automatically adjusting the setpoints is best understood with reference to
On the right-hand side of the chart in
When, for example, engine load, fuel quality, or engine ambient conditions change, conditions C1 may shift as shown in C2, C3, or shift in other ways. When conditions change from conditions C1 to conditions C2 the area between the NOx curve (shown as dashed double lines on the right hand side of the chart) and the CO curve (shown as solid double lines on the left hand side of the chart) narrows. When conditions change from conditions C1 to conditions C3 the area between the NOx curve and the CO curve widens. Additionally, with changing conditions the NOx and CO curves may be shifted left or right. This phenomenon makes it very difficult to control emissions with a static O2 voltage setpoint.
The principle behind the method for setting a new O2 voltage setpoint for NOx compliance 50. is best illustrated with reference to
The internal combustion engine system 1 may be used for operating an engine at an optimum O2 voltage setpoint for NOx and CO compliance. NOx sensor 45 may be used to provide an indication of CO concentration that is represented as an increase in the NOx ppm output as the rich knee of the lambda curve is approached. The CO concentration in on the rich side appear to create stable interference in the NOx sensor 45resulting in a NOx reading. This anomaly is caused by ammonia creation at extreme rich levels which is reported as NOx concentration by the NOx sensor 45.
Using both a lean and rich stability detection algorithm with this anomaly, it is possible to develop a method for setting a new O2 voltage setpoint for NOx and CO compliance. This is accomplished by performing a lambda sweep (i.e. sweeping the O2 voltage setpoint))to verify both locations of the lean and rich knees on the lambda curve. The O2 voltage setpoint may then be readjusted to a value at a point between the lean and rich knees to achieve lower NOx and CO catalyst out emissions in the optimal part of the emissions curve.
The principle of a method for setting a new O2 voltage setpoint for NOx and CO compliance 80 is best illustrated with reference to
If at any time the lambda sweep routine is not able to detect the knee(s) on the curve(s), a new sweep may be performed to retry the setpoint optimization. Reasons for not detecting optimal setpoints could include; changes in fuel composition, large changes in humidity, other environmental conditions, or degrading of catalyst performance. Optionally emission control module 47 may be programmed to periodically re-establish the optimum setpoint to the left of the knee. This is done as these optimum points will shift due to changes in operating and/or environmental conditions.
The internal combustion engine system 1 provides NOx and CO compliance over a wider range of operating conditions, including environmental and catalyst window shift conditions by providing periodic automatic resetting of the O2 setpoints. Additionally, because of the continuous measurements taken over time, emission control module 47 may log emissions performance and emissions compliance status. Another option that may be added to the emission control module 47 would include the addition of shut down instructions if the internal combustion engine system 1 is not in compliance with emission regulations.
While the methods and apparatus described above and/or claimed herein are described above with reference to an exemplary embodiment, it will be understood by those skilled in the art that various changes may be made and equivalence may be substituted for elements thereof without departing from the scope of the methods and apparatus described above and/or claimed herein. In addition, many modifications may be made to the teachings of above to adapt to a particular situation without departing from the scope thereof. Therefore, it is intended that the methods and apparatus described above and/or claimed herein not be limited to the embodiment disclosed for carrying out this invention, but that the invention includes all embodiments falling with the scope of the intended claims. Moreover, the use of the term's first, second, etc. does not denote any order of importance, but rather the term's first, second, etc. are used to distinguish one element from another. Furthermore, it should be emphasized that a variety of computer platforms and control modules and operating systems are contemplated.
