Abstract:
A method of reducing emissions from a large, medium speed fuel injected diesel engine of the type used on locomotives subject to transient modes of engine operation in which the engine is accelerated or increased loads are applied. The method comprises: monitor at least one operating parameter of the diesel engine; determining, based on such operating parameter, whether the diesel engine is in a transient mode; and controlling a timing of fuel injection to cylinders of the engine, to retard the timing when the diesel engine is in a transient mode relative to the timing of fuel injection when the diesel engine is not in a transient mode of operation.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     The invention relates generally to the suppression of emissions generation from internal combustion engines and, more particularly, to a fuel injection control system that suppresses emission generation.  
         [0002]     Internal combustion engines, such as compression ignition engines are well known for producing black smoke or heavy particulate emissions during acceleration or load ascending transients. One cause of this phenomenon is incomplete fuel-air mixing during the injection and combustion of the fuel injected in compression cylinders during these acceleration and load ascending transient engine operating modes.  
         [0003]     A basic combustion process for compression ignitions involves a diffusion type combustion of liquid fuel. As liquid fuel is injected into compressed hot cylinder air, it evaporates and mixes with the surrounding air to form a flammable mixture. This is a continuing process that happens over time as the fuel is injected into the cylinder. The mixture formed initially will combust and raise the local temperature before the later evaporated fuel has time to fully mix with air. As a result, the later burned fuel is subjected to high temperatures with insufficient air to support complete combustion of the fuel. Under such conditions, high temperature pyrolysis of fuel will take place and thus form soot. As the combustion proceeds in the cylinder, a substantial portion of this soot will be burned-up as a result of later exposure to available air in the cylinder. The soot will continue to be burned up in the engine until the power stroke volume expansion sufficiently lowers the cylinder temperature, thereby ceasing the chemical reaction. Any non-combusted soot remaining in the cylinder at this point exits the engine as smoke or particulate emission when the exhaust valve is opened.  
         [0004]     In compression ignition engines, therefore, the above-noted soot formation is tempered by soot burn-up. In typical compression ignition engines under typical operating conditions the soot burn-up mechanism sufficiently reduces emissions caused by soot formation. However, in certain engines operating under accelerating or load ascending transient conditions, the soot burn-up mechanism is insufficient for reducing the generation of soot emissions, as is discussed more fully herein below. Engines operating under acceleration or load ascending transient conditions, hereafter referred to as a “transient mode”, will often “late burn” injected fuel. During the late burn of injected fuel, adequate time is not provided for the occurrence of the soot burn-up process prior to opening of the exhaust valve. There often is a significant expulsion of smoke and particulate emission in a large compression ignition operating in a transient mode.  
         [0005]     Compression ignition engines known in the prior art typically have fixed injection timing via a governor and mechanical linkages which actuate a series of fuel delivery devices simultaneously. Fuel injection start timing is generally predetermined for any given engine operating point and typically cannot be modified for varying conditions. Fuel delivery systems may include pump-line-nozzle configurations or unit injection configurations. An electronic fuel injection system for large cylinder volume displacement compression ignitions is disclosed in U.S. Pat. No. 5,394,851. The referenced fuel injection system is employed in conjunction with a typical compression ignition engine shown generally at  10  in  FIG. 1 . The engine  10  may be any large compression ignition. Such an engine may include a turbo charger  12  and a series of unitized power assemblies  14 . For example, a twelve-cylinder engine has twelve such power assemblies while a sixteen-cylinder engine has sixteen such power assemblies. The engine  10  further includes an air intake manifold  16 , a fuel supply line  18  for supplying fuel to each of the power assemblies  14 , a water inlet manifold  20  used in cooling the engine, a lube oil pump  22  and a water pump  24 , all as known in the art. An intercooler  26  connected to the turbo charger  12  facilitates cooling of the turbo charged air before it enters a respective combustion chamber inside one of the power assemblies  14 . The engine may be a Vee-style type, also as known in the art.  
         [0006]     Although well suited for its application, the system of  FIG. 1  neither distinguishes nor does it accommodate for accelerating and load ascending transient operating modes and the effect of these operating modes upon the generation of emissions due to late combustion as discussed herein. In such systems, the fuel injection timing of a compression ignition is usually prescribed for each operating condition (speed and load) at its optimum for steady state operation. When the engine is in a transient mode, the injection timing will still be set at its instantaneous value called for by the steady state condition. Operating in a steady state mode, there is usually enough time in the combustion cylinder to control particulate or smoke emissions via the soot burn-up process described above. During a transient mode however, the engine calls for more fuel thus the fuel injection duration becomes longer. The combustion of the added fuel, which enters the cylinder at the end of the injection duration, does not have enough time for soot burn-up before the exhaust valve opens. The result is the increased emission of heavy smoke or particulate matter during the exhaust stage of the engine cycle.  
         [0007]     Normal acceleration of a compression ignition (such as a medium speed engine for locomotive applications) puts the engine in a transient mode which varies from a steady state mode and increases the production of soot and particulate emissions. Such engines also encounter radical load changes due to the switching of large auxiliary loads such as compressor loads or fan loads in locomotive applications and “hotel” power loads (an alternator for generating 110 V at 60 hz) for passenger train applications. Driving such loads or turning off such loads can result in load transients on the order of 500 horsepower at any instant. Late burning of injected fuel, as discussed above, is prevalent in such acceleration and load ascending transient compression ignition operating modes. The late burning prevents proper combustion of generated soot and results in increased engine expulsion of smoke and particulate emissions.  
       BRIEF DESCRIPTION OF THE INVENTION  
       [0008]     The disclosed method relates a method of reducing emissions from an internal combustion engine, the method comprising: retarding a fuel injection timing in at least one piston cylinder when the internal combustion engine is in a transient mode.  
         [0009]     The disclosed apparatus relates to an apparatus for reducing emissions from a internal combustion engine, the apparatus comprising: an internal combustion engine; an engine monitor for monitoring operating parameters of the internal combustion engine to detect transient modes of operation; and an electronic fuel injection system in communication with the engine monitor and operatively coupled to the internal combustion engine and having a controller to adjust fuel injection timing so as to retard fuel injection to the internal combustion engine when the internal combustion engine is in a transient mode.  
         [0010]     The disclosed apparatus also relates to an electronic fuel injection system comprising: an engine transient sensing device; and a control device for retarding fuel injection timing during a transient condition and communicatively coupled to the engine transient sensing device.  
         [0011]     Additionally, the disclosed apparatus relates to a storage medium encoded with machine-readable computer program code for electronically controlling a fuel injection, the storage medium including instructions for causing a computer to implement a method comprising: retarding a fuel injection timing in at least one piston cylinder when an internal combustion engine is in a transient mode. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0012]      FIG. 1  is a perspective view of a common Vee-style compression ignition engine;  
         [0013]      FIG. 2  is a schematic view of the disclosed apparatus;  
         [0014]      FIG. 3  is a plot showing the Effect on Heat Release Rate;  
         [0015]      FIG. 4  is a plot showing Plunger Velocity vs. Start of Injection;  
         [0016]      FIG. 5  is a plot showing the Effect on Engine Load Rate;  
         [0017]      FIG. 6  is a flowchart illustrating an embodiment of the disclosed method;  
         [0018]      FIG. 7  is a schematic view of another embodiment of the disclosed apparatus; and  
         [0019]      FIG. 8  is a schematic view of another embodiment of the disclosed apparatus. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0020]      FIG. 2  is a schematic of one embodiment of the disclosed apparatus for suppressing internal combustion engine emissions. Many of the embodiments are discussed here below with respect to large, medium speed compression ignition engines of the type used on railroad locomotives subject to transient modes of operation, such as arising from changes in engine throttle notch position, differences between commanded and actual engine speed, and the imposition of loads on the engine over short periods of time. A compression ignition engine  10  is shown operatively coupled to an electronic fuel injection system  34 . Communicably coupled to the engine  10  and electronic fuel injection system  34  is an engine monitor  30 . In this embodiment, the engine monitor  14  monitors the engine, and determines when the engine is in a transient mode. In another embodiment, the electronic fuel injection system  34  may incorporate the engine monitor  30 . When in a transient mode, the monitor  30  communicates this information to the electronic fuel injection system  34 , and the electronic fuel injection system  34  retards the fuel injection timing of at least one piston cylinder. The fuel injection may be retarded to a point after top dead center (“TDC”). In one embodiment the fuel injection timing may be retarded to a range between about 10 degrees after TDC. This retarding of the fuel injection timing reduces the amount of smoke emissions from compression ignition engines during transient mode operation.  
         [0021]      FIG. 3  shows an Effect on Heat Release Rate plot. The X-axis of  FIG. 3  is the crank angle of the piston relative to TDC in degrees, with points to the left of TDC line being “before TDC” and points to the right of TDC being “after TDC”. The Y-axis of the effect of Heat Release Rate plot represents the amount of heat release from the combustion of fuel in the cylinder. The advanced fuel injection line is a plot of points for a typical advanced fuel injection in a piston cylinder, where the fuel is injected at about 3 degrees before TDC. There is a spike on the advanced line which is the pre-mix burn. This corresponds to a relatively clean burning of the fuel due to a well-mixed air/fuel combination. Following the pre-mix burn spike is a large extended diffusion burn of the fuel. The diffusion burn corresponds to a relatively dirty burning of the fuel, and is associated with a lack of good mixing between the fuel and air. It has been recently discovered that during transient engine operating conditions, retarding the fuel injection to about 3 to 10 degrees after TDC (as opposed to the commonly accepted wisdom of setting timing to be about 3 degrees before TDC), results in the fuel burning cleaner. The retarded fuel injection line shows a larger pre-mix burn spike than the advanced line. This is due to the fact that since fuel is being injected into the cylinder after TDC, that is, as the cylinder is expanding and pressure is decreasing, it takes more time for the fuel to auto-ignite. This extra time allows for a better mixing of the fuel and air in the piston cylinder, which therefore results in a greater pre-mix burn. Since more of the fuel is burned in a pre-mix state, less fuel is available for the dirtier diffusion burn, hence the diffusion burn under the retarded fuel injection line is smaller and ends more quickly than the diffusion burn of the advanced fuel injection line, which leads to cleaner burning as compared to engines with advanced fuel injection during a transient mode.  
         [0022]      FIG. 4  is a plot of plunger velocity versus crank angle relative to TDC for an exemplary compression ignition engine. For steady state operation, shown by the Steady State Operation point, in a typical compression ignition engine, fuel may be typically injected at around 5 degrees before TDC. At that point, the plunger velocity is relatively high. Plunger velocity is directly proportional to fuel injection pressure, thus fuel injection pressure is also relatively high. High fuel injection pressure leads to better mixing between the fuel and the air in the cylinder and thereby produces a cleaner burn. This is one of the reasons why a compression ignition engine burns cleaner during a steady state operation. During transients, it is known to advance the fuel injection to the transient advance point on  FIG. 4 . The Transient Advance Operating point may be about 15 degrees before TDC in a typical compression ignition engine. The purpose of advancing the injection point for a transient mode is to give the fuel and air more time to mix before auto-ignition, in the hopes of reducing the diffusion burn and producing a cleaner burn. However, at about 15 degrees before TDC the plunger velocity is about 30% less than the plunger velocity at the steady state operating point. Therefore, there is a proportional reduction in injection pressure. With a lower injection pressure, there is less mixing of the fuel and air in the cylinder. Thus, there are at least two competing processes when the fuel injection is advanced: (1) more mixing time is provided, providing a cleaner burn; and (2) less fuel injection pressure is generated, thus reducing the mixing of the fuel and air and providing a less clean burn. If a retarded fuel injection is employed, using about a 3 to 10 degree after TDC injection, as shown with the Transient Retard Operating point in  FIG. 4 , then there is only about a 10 percent reduction in plunger velocity with respect to the Steady State Operating point. This corresponds to a proportional reduction in fuel injection pressure, which is much smaller than the reduction seen at the typical Transient Advance Operating point, thereby producing a cleaner burn than is achieved by advancing the fuel injection.  
         [0023]      FIG. 5  shows the Effect on Engine Load Rate on an exemplary compression ignition engine that is required to keep engine emissions at or below a certain specified level. The advanced fuel injection line shows that it takes about 80 to 90 seconds for a compression ignition engine that uses an advanced fuel injection for its transient mode to achieve full load while keeping engine emissions at or below the specified level. On the other hand, when a retarded fuel injection is used for its transient mode, then as the retarded fuel injection line shows, it takes only about 40 to 45 seconds for the engine to achieve full load while keeping engine emissions at or below the certain specified level.  
         [0024]      FIG. 6  shows one embodiment of the disclosed method. At process block  40 , the engine monitor  30  monitors the engine. At decision block  44 , it is determined whether the engine is in a transient mode. To determine whether the engine is in a transient mode at decision block  44 , the engine monitor  30  may analyze data such as, but not limited to: throttle position, engine speed, power from an alternator field controller, crankshaft speed, engine acceleration, alternator frequency, cylinder firing frequency, alternator power, fueling level, intake manifold pressure, exhaust manifold pressure, exhaust manifold temperature, turbocharger speed, fuel pressure, water pressure, oil pressure, horsepower. At process block  48 , the electronic fuel injection system retards the fuel injection, that is, it delays the fuel injection until about 3 to 10 degrees after TDC. At decision block  52 , the engine monitor determines whether the engine is out of the transient mode. To determine whether the engine is out of the transient mode at decision block  52 , the engine monitor  30  may analyze data such as, but not limited to: throttle position, engine speed, power from an alternator field controller, crankshaft speed, engine acceleration, alternator frequency, cylinder firing frequency, alternator power, fueling level, intake manifold pressure, exhaust manifold pressure, exhaust manifold temperature, turbocharger speed, fuel pressure, water pressure, oil pressure, horsepower. The acts described in  FIG. 6  may be implemented mechanically.  
         [0025]     Referring to  FIG. 7 , the method disclosed in  FIG. 6  may be embodied in the form of computer-implemented processes and apparatuses for practicing those processes. The disclosed method may also be embodied in the form of a computer program code containing instructions embodied in tangible media, such as floppy diskettes, CD-ROMs, hard drives, or any other computer-readable storage medium  60 , wherein, when the computer program code is loaded into and executed by a computer  64 , the computer becomes an apparatus for practicing the invention. The present method may also be embodied in the form of computer program code, for example, whether stored in a storage medium  60 , loaded into and/or executed by a computer  64 , or transmitted via a data signal  68  over some transmission medium, such as over electrical wiring or cabling, through fiber optics, or via electromagnetic radiation, wherein, when the computer program code is loaded into and executed by a computer, the computer becomes an apparatus for practicing the invention. When implemented on a general-purpose microprocessor, the computer program code segments configure the microprocessor to create specific logic circuits.  
         [0026]      FIG. 8  shows a schematic of another embodiment of the disclosed apparatus. An engine  10  is in operable communication with an engine monitor  30  and an engine controller  70 . The engine monitor  30  and engine controller  70  are also in operable communication with each other. In this embodiment, the acts described in  FIG. 6  may be configured to implemented mechanically or they may be configured to be implemented electronically.  
         [0027]     A technical contribution of the disclosed method and apparatus is that it provides for a computer controlled fuel injection system which reduces the emissions from an internal combustion ignition engine by retarding the fuel injection during transient operation.  
         [0028]     While the invention has been described with reference to exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope of the invention. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the invention without departing from the essential scope thereof. Therefore, it is intended that the invention not be limited to the particular embodiments disclosed for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.