Abstract:
The present disclosure is directed to a method of operating an engine. The method may include determining an injection characteristic based on usage of a primary fuel and determining a need for a secondary fuel. The method may further include determining a first engine characteristic and modifying the injection characteristic based on the need for the secondary fuel and the first engine characteristic. The method may still further include injecting the primary fuel based on the modified injection characteristic and introducing the secondary fuel.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates generally to a fuel control system and, more particularly, to a fuel control system having a cold start strategy. 
       BACKGROUND 
       [0002]    Engines use injectors to introduce fuel into the combustion chambers of the engine. The injectors may be hydraulically or mechanically actuated with mechanical, hydraulic, or electrical control of fuel delivery. Machines that use these engines may be operated in less than ideal atmospheric conditions such as at high altitudes or in cold weather. Under these conditions, particularly cold conditions, an engine may have trouble maintaining the temperature required to sustain combustion. Repeated failed attempts to start an engine in cold conditions may result in excessive wear of the engine. 
         [0003]    One way to improve starting and/or operation in cold conditions is to introduce a starting fluid, in addition to normal fuel, into the engine to assist in starting the engine. This starting fluid is a highly flammable liquid that may allow for a higher combustion temperature during cold start conditions and may facilitate operation of an engine that might not otherwise start. 
         [0004]    One system for introducing starting fluid into an engine is described in U.S. Pat. No. 5,388,553 (the &#39;553 patent), issued to Burke et al. on Feb. 14, 1995. Specifically, the &#39;533 patent describes a system that introduces an ether mixture into an engine when an engine coolant temperature is below a predetermined temperature and when an engine speed is within a predetermined speed range. Specifically, the system of the &#39;533 patent begins to introduce ether into the engine only when the engine coolant temperature is below 40° F. and when the engine speed is greater than 80 RPM and less than 1800 RPM. The system of the &#39;553 patent stops introducing ether when the engine speed exceeds 1800 RPM regardless of engine coolant temperature. The system of the &#39;553 patent does not introduce ether into the engine if the engine coolant temperature is initially greater than 40° F. 
         [0005]    While prior art systems may assist the starting of an engine in cold conditions, inefficiencies may occur throughout engine start up and during engine operation when the engine is being fueled by the starting fluid. Due to the different chemical properties of the starting fluid, the engine injection timing characteristics that may be ideal for the injection of only the normal fuel may not be ideal for use with the starting fluid. Prior art systems may not account for these differences. 
         [0006]    The disclosed fuel control system is directed to improving prior art systems. 
       SUMMARY 
       [0007]    In one aspect, the present disclosure is directed to a method of operating an engine. The method may include determining an injection characteristic based on usage of a primary fuel. The method may also include determining a need for a secondary fuel during starting of the engine and modifying the injection characteristic based on the need for the secondary fuel. The method may still further include injecting the primary fuel based on the modified injection characteristic and introducing the secondary fuel. 
         [0008]    In another aspect, the present disclosure is directed to a fuel control system for operating an engine. The fuel control system may include a sensor configured to generate a signal indicative of an engine characteristic. The fuel control system may also include a controller in communication with the sensor and configured to determine an injection characteristic based on usage of a primary fuel. The controller may also be configured to receive the signal indicative of the engine characteristic and determine a need for a secondary fuel. The controller may still further be configured to modify the injection characteristic based on the need for the secondary fuel and the signal, affect the injection of the primary fuel based on the modified injection characteristic, and affect the introduction of the secondary fuel. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is a diagrammatic illustration of an exemplary disclosed power system; 
           [0010]      FIG. 2  is a schematic illustration of an exemplary disclosed fuel control system that may be used with the power system of  FIG. 1 ; and 
           [0011]      FIG. 3  is a flow diagram illustrating an exemplary disclosed method of operating the fuel control system of  FIG. 2 . 
       
    
    
     DETAILED DESCRIPTION 
       [0012]      FIG. 1  illustrates an exemplary power system  12 . Power system  12  is described herein as a diesel-fueled, internal combustion engine. However, it is contemplated that power system  12  may embody any other type of internal combustion engine, such as, for example, a gasoline or gaseous fuel-powered engine. Power system  12  may include an engine block  14  at least partially defining a plurality of cylinders  16 , and a plurality of piston assemblies  18  disposed within cylinders  16 . It is contemplated that power system  12  may include any number of cylinders  16  and that cylinders  16  may be disposed in an “in-line” configuration, a “V” configuration, or in any other conventional configuration. 
         [0013]    Each piston assembly  18  may be configured to reciprocate between a bottom-dead-center (BDC) position, or lower-most position within cylinder  16 , and a top-dead-center (TDC) position, or upper-most position, within cylinder  16 . In particular, piston assembly  18  may be pivotally coupled to a crankshaft  20  by way of a connecting rod (not shown). Crankshaft  20  of power system  12  may be rotatably disposed within engine block  14 , and each piston assembly  18  coupled to crankshaft  20  such that a sliding motion of each piston assembly  18  within each cylinder  16  results in a rotation of crankshaft  20 . Similarly, a rotation of crankshaft  20  may result in a sliding motion of piston assemblies  18 . As crankshaft  20  rotates through about 180 degrees, piston assembly  18  may move through one full stroke between BDC and TDC. In one embodiment, power system  12  may be a four stroke (e.g., four cycle) engine, wherein a complete cycle includes an intake stroke (TDC to BDC), a compression stroke (BDC to TDC), a power stroke (TDC to BDC), and an exhaust stroke (BDC to TDC). It is also contemplated that power system  12  may alternatively embody a two stroke (e.g., two cycle) engine, wherein a complete cycle includes a compression/exhaust stroke (BDC to TDC) and a power/exhaust/intake stroke (TDC to BDC). 
         [0014]    An intake valve  22  may be associated with each cylinder  16  to selectively restrict fluid flow through a respective intake port  24 . Each intake valve  22  may be actuated to move or “lift” to thereby open the respective intake port  24 . In a cylinder  16  having a pair of intake ports  24  and a pair of intake valves  22 , the pair of intake valves  22  may be actuated by a single valve actuator (not shown) or by a pair of valve actuators (not shown). Of the four piston strokes described above, each intake valve  22  may open during a portion of the intake stroke to allow air or an air and fuel mixture to enter each respective cylinder  16 . 
         [0015]    An exhaust valve  26  may also be associated with each cylinder  16 , and configured to selectively block a respective exhaust port  28 . Each exhaust valve  26  may be actuated to move or “lift” to thereby open the respective exhaust port  28 . In a cylinder  16  having a pair of exhaust ports  28  and a pair of exhaust valves  26 , the pair of exhaust valves  26  may be actuated by a single valve actuator (not shown) or by a pair of valve actuators (not shown). Of the four piston strokes described above, each exhaust valve  26  may open during a portion of the exhaust stroke to allow exhaust to be pushed from each respective cylinder  16  by the motion of piston assemblies  18 . 
         [0016]    Each of intake and exhaust valves  22 ,  26  may be operated in any conventional manner to move from the closed or flow blocking position to an open or flow passing position in a cyclical manner. For example, intake and exhaust valves  22 ,  26  may be lifted by way of a cam (not shown) that is rotatingly driven by crankshaft  20 , by way of a hydraulic actuator (not shown), by way of an electronic actuator (not shown), or in any other manner. During normal operation of power system  12 , intake and exhaust valves  22 ,  26  may be lifted in a predefined cycle related to the motion of piston assemblies  18 . It is contemplated, however, that a variable valve actuator (not shown) may be associated with any one or more of intake and/or exhaust valves  22 ,  26  to selectively interrupt the cyclical motion thereof during alternative modes of operation. In particular, one or more of intake and/or exhaust valves  22 ,  26  may be selectively opened, held open, closed, or held closed to implement a compression braking mode of operation, an exhaust gas recirculation mode of operation, a low-NOx mode of operation, an homogenous combustion compression ignition (HCCI) mode of operation, a starting mode of operation, a cold mode of operation, or any other known mode of operation, if desired. 
         [0017]    An air induction system  32  may be associated with power system  12  and include components that condition and introduce compressed air into cylinders  16  by way of intake ports  24  and intake valves  22 . For example, air induction system  32  may include an air filter  34 , an air cooler  36  located down stream of air filter  34 , and a compressor  38  connected to draw inlet air through filter  34  and cooler  36 . It is contemplated that air induction system  32  may include different or additional components than described above such as, for example, inlet bypass components, a throttle valve, and other known components. It is further contemplated that compressor  38  may be omitted if a naturally aspirated engine is desired. 
         [0018]    Air filter  34  may be configured to remove or trap debris from air flowing into power system  12 . For example, air filter  34  may include a full-flow filter, a self-cleaning filter, a centrifuge filter, an electro-static precipitator, or any other type of air filtering device known in the art. It is contemplated that more than one air filter  34  may be included within air induction system  32  and disposed in a series or parallel arrangement, if desired. Air filter  34  may be connected to inlet ports  24  via a fluid passageway  40 . 
         [0019]    Air cooler  36  may embody an air-to-air heat exchanger or an air-to-liquid heat exchanger disposed within fluid passageway  40  and configured to facilitate the transfer of heat to or from the air directed into cylinders  16 . For example, air cooler  36  may include a tube-and-shell type heat exchanger, a plate type heat exchanger, a tube-and-fin type heat exchanger, or any other type of heat exchanger known in the art. By cooling the air directed into cylinders  16 , a greater amount of air may be drawn into and combusted by power system  12  during any one combustion cycle. The flow of air directed through air cooler  36  may be regulated by an induction valve (not shown) such that a desired flow rate, pressure, and/or temperature at the inlet of power system  12  may be achieved. Although illustrated as being located upstream of compressor  38 , it is contemplated that air cooler  36  may alternatively or additionally be located downstream of compressor  38 , if desired. It is also contemplated that air cooler  36  may be omitted if desired. 
         [0020]    Compressor  38  may also be disposed within fluid passageway  40  and located downstream of air filter  34  to compress the air flowing into power system  12 . Compressor  38  may embody a fixed geometry type compressor, a variable geometry type compressor, or any other type of compressor known in the art. It is contemplated that more than one compressor  38  may be included within air induction system  32  and disposed in parallel or in series relationship, if desired. 
         [0021]    An exhaust system  42  may also be associated with power system  12 , and include components that condition and direct exhaust from cylinders  16  by way of exhaust ports  28  and exhaust valves  26 . For example, exhaust system  42  may include a turbine  44  disposed within a passageway  46  and driven by the exiting exhaust before it is directed to the atmosphere. It is contemplated that exhaust system  42  may include different or additional components than described above such as, for example, exhaust bypass components, an exhaust gas recirculation circuit, an exhaust brake, and other known components. 
         [0022]    Turbine  44  may also be disposed within fluid passageway  46  and located to receive exhaust leaving power system  12  via exhaust ports  28 . Turbine  44  may be connected to one or more compressors  38  of air induction system  32  by way of a common shaft  48  to form a turbocharger  54 . As the hot exhaust gases exiting power system  12  move through passageway  46  to turbine  44  and expand against vanes (not shown) thereof, turbine  44  may rotate and drive the connected compressor  38  to pressurize inlet air. It is contemplated that more than one turbine  44  may be included within exhaust system  42  and disposed in parallel or in series relationship, if desired. 
         [0023]    A plurality of fuel injectors  30  may be associated with cylinders  16  to selectively inject pressurized fuel into corresponding combustion chambers (not shown). Fuel injectors  30  may be configured to inject fuel at a timing relative to the angle of crankshaft  20 . For example, fuel may be injected as piston  18  nears a top-dead-center position (about 360° of crankshaft rotation) in a compression stroke to allow for compression-ignited-combustion of the injected fuel. Alternatively, fuel may be injected as piston  18  begins the compression stroke (about 180° of crankshaft rotation) heading towards a top-dead-center position for homogenous charge compression ignition operation. Fuel may also be injected as piston  18  is moving from a top-dead-center position towards a bottom-dead-center position during an expansion stroke (approximately 360-540° of crankshaft rotation) for a late post injection to create a reducing atmosphere for after treatment regeneration. The timing, quantity, and/or pressure of each injection may correspond with a particular mode of engine operation; a performance parameter of power system  12  such as engine speed, engine loading, engine temperature, and engine boost pressure; an ambient condition such as temperature; and/or other factors known in the art. In order to accomplish these specific injection events, power system  12  may request an injection of fuel from a controller  62  at a specific start of injection (SOI) pressure or timing and a specific end of injection (EOI) timing or pressure or a specific injection duration. One or more of sensors  92 ,  94 , and  98  may be associated with power system  12  to generate a signal indicative of these parameters 
         [0024]    While fuel injectors  30  may inject a primary fuel, for example diesel fuel, directly into the combustion chambers of power system  12 , a secondary fuel may be introduced into the combustion chambers by way of induction system  32 . The secondary fuel may be introduced instead of or in addition to the primary fuel. In one example, the secondary fuel may include a starting fluid such as diethyl ether, dimethyl ether, or a mixture of diethyl and dimethyl ether, which may be stored in a container  50 . The starting fluid may flow or be sprayed into fluid passageway  40  through a line  58 . A valve  52  may be disposed in line  58  between container  50  and fluid passageway  40  to selectively restrict the flow of starting fluid into fluid passageway  40 . A sensor (not shown) may be able to sense an extent to which valve  52  is open and send a signal indicative thereof to controller  62 . Starting fluid that flows into fluid passageway  40  may pass through an atomizer  56 . Atomizer  56  may be located to reduce the starting fluid into fine particles as it enters fluid passageway  40  such that it may mix uniformly with the compressed air in fluid passageway  40 . 
         [0025]    An operator interface device  60  may be associated with power system  12  for manual regulation of the starting fluid. Operator interface device  60  may be configured to receive an input from an operator indicative of a desire to start power system  12 . Alternatively it is contemplated that the input could be a computer generated command from an automated system that assists the operator, or a command from an autonomous system that operates in place of the operator. Operator interface device  60  may include a wheel, a knob, a push-pull device, a switch, and other operator interface device known in the art. Operator interface device may be in communication with controller  62 . 
         [0026]    Controller  62  may be configured to adjust the operation of power system  12  based on the input from operator interface device  60 , one or more sensed performance parameters or modes of operation of power system  12 , an ambient condition, the sensed position of valve  52 , and/or information contained in one or more of electronic maps  64  and  66 . Electronic maps  64  and  66  may contain tabulated values indicative of SOI timing modifications, EOI timing modifications, and/or injection duration modifications, and a required movement of valve  52  based on the various inputs. Controller  62  may adjust the SOI timing or pressure, EOI timing or pressure, injection durations of fuel injectors  30 , and/or the position of valve  52  based on received signals generated by sensors  92 ,  94 , and  98  and the sensor associated with valve  52 . 
         [0027]    By way of example, controller  62  may receive a signal from sensor  98  indicating that the ambient temperature may be too low for efficient starting of power system  12 , and in response thereto, controller  62  may open valve  52  to utilize a secondary fuel. In another example, controller  62  may receive a signal indicating the rotational speed of power system  12  from sensor  92  being within a starting speed range and the engine coolant temperature from sensor  94  being too low for optimum engine operation. Based on these received signals, controller  62  may then look up a modification, if any, to the SOI timing and pressure, EOI timing and pressure, and/or injection duration. Controller  62  may then modify the injection characteristic accordingly to facilitate starting and/or operation of power system  12  with the use of the secondary fuel. 
         [0028]    Controller  62  may embody a single microprocessor or multiple microprocessors that include a means for controlling an operation of power system  12 . Numerous commercially available microprocessors can be configured to perform the functions of controller  62 . It should be appreciated that controller  204  could readily embody a general microprocessor capable of controlling numerous functions. Controller  62  may include a memory, a secondary storage device, a processor, and any other components for running an application. Various other circuits may be associated with controller  62  such as power supply circuitry, signal conditioning circuitry, solenoid driver circuitry, and other types of circuitry. 
         [0029]      FIG. 3  shows a flow-diagram illustrating a method of controlling fuel injection and starting fluid introduction.  FIG. 3  will be discussed in detail in the following section. 
       INDUSTRIAL APPLICABILITY 
       [0030]    The disclosed fuel control system may be used in connection with any engine where it is desirable to assist starting and/or operation in cold weather. The disclosed fuel control system may adjust fuel injection characteristics based on engine rotational speed and a coolant or ambient temperature when a starting fluid is utilized. By adjusting the injection characteristics, the engine may start more consistently and operate more efficiently. In this manner, the disclosed fuel control system may reduce wear and tear on an engine. 
         [0031]      FIG. 3  is a flow diagram illustrating an exemplary disclosed method of operating the fuel control system. An operator may input a command to start power system  12  via operator input device  60 . When starting power system  12  in the presence of diesel fuel only, controller  62  may start an injection of diesel fuel into power system  12  via fuel injector  30  at a conventional start of injection (SOI) timing and pressure and a conventional end of injection (EOI) timing and pressure. Additionally, under normal conditions, the flow of the secondary fuel into fluid passageway  40  may be inhibited during starting. However, under cold conditions, fluid passageway  40  may introduce compressed air and the secondary fuel into power system  12 . Controller  62  may determine whether to start power system  12  under normal conditions or cold conditions, based on a signal indicative of an ambient temperature received from sensor  98 . Controller  62  may open valve  52  if valve  52  is closed and the ambient temperature is below a predetermined threshold. 
         [0032]    In block  70 , controller  62  may then attempt to start power system  12 . Power system  12  may request a conventional SOI timing. In block  72 , controller  62  may receive signals indicative of the rotational speed of power system  12  and the engine coolant temperature. In block  76 , controller  62  may determine a modification to the conventional SOI timing based on the received signals. The modification may be referred to as an offset, may be a number of degrees to advance or retard the SOI timing, and may be found by referring to offset map  66 . In block  82 , controller  62  may modify the initial SOI timing or pressure, EOI timing or pressure, and/or injection duration requested by power system  12 , and fuel injectors  30  may inject the primary fuel into the combustion chambers based on the modified injection characteristic while the secondary fuel is being introduced into power system  12  via air induction system  32 . 
         [0033]    In block  74 , controller  62  may determine if the rotational speed of power system  12  is below a predetermined idle speed. If power system  12  is below the idle speed, controller  62  may repeat the above mentioned operations at specified intervals or continuously until the sensed rotational speed of power system  12  meets or exceeds the predetermined idle speed. In block  84 , once power system  12  meets or exceeds the idle speed, controller  62  may determine a predetermined amount of time to continue introducing the secondary fuel into power system  12  based on the sensed engine coolant temperature. This amount of time may be referred to as post duration time and may be found by referring to post duration map  64 . In block  86 , the secondary fuel may continue to be introduced into power system  12  for the post duration time. In block  90 , after the post duration time has passed, controller  62  may close valve  52 . After this point, valve  52  may remain closed and power system  12  may revert to operation under normal conditions (i.e. the flow of secondary fuel is inhibited, and the continued injection of diesel fuel into power system  12  through fuel injector  30 .) 
         [0034]    For example, the predetermined threshold for power system  12  to begin a cold mode of operation may be an ambient temperature below 32° F. and the predetermined idle speed may be greater than 700 RPM. If the ambient temperature is −10° F., controller  62  may open valve  52  to allow the secondary fuel to be introduced into power system  12 . Furthermore, the speed of power system  12  may initially be 0 RPM and the engine coolant temperature may be 0° F. Power system  12  may request a conventional SOI timing of 20° before top-dead-center. Controller  62  may then reference map  64  and determine that the SOI timing should be modified, specifically that the SOI timing may be retarded by 10° such that the final SOI timing may be 10° before top-dead-center. The speed of power system  12  may next be 500 RPM and the engine coolant temperature may be 0° F. Power system  12  may request a SOI timing of 20° before top-dead-center. Controller  62  may reference map  64  and determine that the SOI timing should be retarded by 7° such that the modified SOI timing may be 13° before top-dead-center. The speed of the power system may next be greater than 700 RPM and the engine coolant temperature may be 0° F. Controller  62  may determine that the speed of power system  12  is greater than the predetermined idle speed. Controller  62  may then reference map  62  and may determine a post duration time of 5 seconds. After 5 seconds, controller  62  may then close valve  52 . 
         [0035]    Several advantages of the disclosed fuel control system may be realized. In particular the disclosed fuel control system may be used in conjunction with any engine where it is desirable to assist starting and/or operation in cold weather. The disclosed fuel control system may adjust injection characteristics based on engine rotational speed and coolant temperature when a secondary fuel is utilized. Furthermore, the disclosed fuel control system may adjust the injection characteristics at multiple times at intervals or continuously. By adjusting the injection characteristics, an engine may start more consistently and operate more efficiently. In this manner, the disclosed control system may reduce wear on an engine. 
         [0036]    It will be apparent to those skilled in the art that various modifications and variations can be made to the fuel control system of the present disclosure. Other embodiments of the fuel control system will be apparent to those skilled in the art from consideration of the specification and practice of the injection system disclosed herein. By way of example, it would be apparent to those skilled in the art that variations of starting fluid or fluids not containing ether mixtures may be used as a starting aid. It is intended that the specification and examples be considered as exemplary only, with a true scope being indicated by the following claims and their equivalents.