STRATEGY FOR PARASITARY LOAD ON ENGINES BY INCREASING FUEL PRESSURE

Abstract

The operation of an engine system (10) includes cold starting an engine (12), closing spill valves (48) to pressurize fuel in a plurality of piston cavities (42), opening injectors (44, 46) in some of a plurality of fuel injectors (36) to inject fuel into firing cylinders (16) in an engine cycle, and opening spill valves (48) in some of the plurality of fuel injectors (36) while injectors (44, 46) remain closed therein to vent fuel into a low-pressure plenum (50) in the engine cycle. Pressurizing the fuel in the fuel injectors remaining closed parasitically loads the engine to increase the amount of fuel burned, which accelerates warm-up and limits misfires. Related devices and control logic are also disclosed.

Description

Technical FieldThe present disclosure relates generally to operation of an engine system, and more particularly to parasitic loading of an engine by fuel pressure without injection during cold start.BackgroundInternal combustion engines are used worldwide for various purposes, from the drive of a drive train in a vehicle to the drive of pumps, compressors and electric generators. For heavy load applications, compression ignition diesel engines are commonly used. Essentially, all internal combustion engines operate after a particular version of a basic cycle of controlled combustion of fuel in a cylinder to produce a rapid temperature and pressure increase that drives a piston coupled to a rotatable crankshaft.When an engine is started to initiate this cycle, it is generally necessary to rotate parts in the engine by an external mechanism such as a starter. In addition to the necessary actuation of the movable parts in the engine, the combustion process must also be started. In many cases, particularly in auto-ignition engines, cold engine fuel cannot be easily directed into the engine and ignited with sufficient reliability. Cold metallic surfaces forming engine cylinders, for example, may tend to quench combustion flames that arise. Over the years, various strategies have been proposed to initiate the ignition of the fuel into the fuel.To achieve the same result and subsequently maintain the combustion. An example of an engine start mode of operation is described in Rockwell et al. Pat. No. 7,201,127 B2. The technique offers numerous opportunities for improvements and / or alternative strategies.SummaryIn one aspect, a method of operating an engine system includes cold starting an engine, moving a plurality of pistons in a plurality of piston cavities between advanced positions and retracted positions, and closing a plurality of spill valves each fluidly disposed between one of the plurality of piston cavities and a low pressure chamber to pressurize fuel in each of the plurality of piston cavities. The method further comprises opening a first injector in a first fuel injector to inject fuel pressurized by a first of the plurality of pistons into a cylinder of the engine in an engine cycle, and opening one of the plurality of spill valves in a second fuel injector while a second injector in the second fuel injector remains closed to bleed fuel pressurized by a second of the plurality of pistons into the low pressure space in the engine cycle. The method further includes parasitically charging the engine by pressurization of fuel by the second of the plurality of pistons.In another aspect, an engine system includes an engine having an engine housing with a plurality of cylinders therein and a fuel system having first and second fuel injectors each including a piston in a piston cavity, an injector, and an electrically actuated spill valve. The fuel system defines a low pressure chamber. The engine system further includes a parasitic load controller configured to command closing of the spill valve in the first fuel injector to pressurize a fuel in the corresponding piston cavity and to command closing of the spill valve in the second fuel injector to pressurize the fuel in the corresponding piston cavity. The parasitic load control unit is further configured to command opening of the injector in the first fuel injector in an engine cycle to inject the pressurized fuel from a corresponding piston cavity into one of the plurality of cylinders in the engine and to command opening of the spill valve in the second fuel injector in the engine cycle while the injector in the second fuel injector remains closed to drain the pressurized fuel from the corresponding piston cavity into the low pressure cavity.A fuel system also includes a parasitic load control unit structured for control communication with each of a plurality of electrically actuated spill valves and a plurality of injectors of a plurality of fuel injectors in a fuel system. The parasitic load control unit is further configured to command closing of the plurality of spill valves to pressurize fuel in a plurality of piston cavities of the plurality of fuel injectors and opening of the injectors of an ignition group of the plurality of fuel injectors to inject the pressurized fuel into a plurality of ignition cylinders in an engine. The parasitic load control unit is further structured to command opening of spill valves of a non-igniting group of the plurality of fuel injectors while the respective injectors remain closed to parasitically load the engine during cold start.Brief Description of the DrawingsFIG. 1 is a schematic view of an engine system according to an embodiment; FIG. 2 is a schematic side view of a fuel system according to an embodiment; FIG. 3 is a diagram of the events and conditions of the fuel system during a crank angle time period; FIG. 4 is a graph of valve displacement and fuel pressure versus time; and FIG. 5 is a flow diagram illustrating an example methodology and logic flow, according to an embodiment.Detailed DescriptionFIG. 1 illustrates an internal combustion engine system 10 according to one embodiment. The engine system 10 includes an engine 12 having an engine housing 14 in which a plurality of combustion cylinders 16 are formed. A plurality of pistons 18 are movable within the cylinders 16 between a top dead center position and a bottom dead center position. The pistons 18 are connected to a crankshaft 20 in a generally conventional manner. The cylinders 16 may include any number greater than one and may be in any suitable arrangement, such as an in-line arrangement, a V-arrangement, or another. The cylinders 16 may be physically and / or functionally arranged in a first cylinder bank and a second cylinder bank. In one embodiment, a first cylinder row and a second cylinder row could be disposed on opposite sides of a V-pattern. The first and second cylinder banks could also include the first and second cylinders, respectively, in an inline configuration, alternating cylinders in an inline configuration, or another arrangement. Engine 12 may comprise a four stroke compression ignition engine operated with a suitable liquid compression ignition fuel, such as a diesel distillate fuel. In other implementations, engine 12 could be spark ignited, pre-chamber ignited, ignited with pilot fuel in a two-fuel strategy, or still other. Motor 12 may be operated to drive a load such as a driveshaft in a vehicle, pump, compressor, or other equipment.The engine system 10 also includes a camshaft 24 having a plurality of cams 26 rotatable at half engine speed via a transmission (not shown) connected to the crankshaft 20 in a generally conventional manner. Engine system 10 also includes a fuel system 28. fuel system 28 may include a pump 30 configured to deliver a fuel, such as diesel fuel, from a fuel supply 32 to a plurality of fuel injectors 36 via a fuel supply line 34. Fuel injectors 36 may be supported in an engine head 22 mounted on an engine housing or cylinder block 14. In one embodiment, the fuel supply line 34 extends through the engine head 22 to provide low pressure fuel supply simultaneously to each of the fuel injector 36. Other embodiments could include top-feeding fuel to individual fuel injectors or another fueling strategy. A drain or return line (not shown) may return drained fuel from engine head 22 to fuel supply 32, in some embodiments. Each of the fuel injectors 36 includes a plunger 38 that is directly contacted by one of the cams 26 or via a rocker arm (not shown) that is directly contacted by one of the cams 26.For purposes of the present description, fuel system 28 may be understood to include a first fuel injector 36 and a second fuel injector 36, which may be any two fuel injectors in fuel system 28, and as further explained herein, a first fuel injector in a first group of fuel injectors 36 and a second fuel injector in a second group of fuel injectors 36. The second group may also be a firing group temporarily and a non-firing group temporarily. The first group may include fuel injectors connected to firing cylinders in a first cylinder bank and the second group may include non-firing cylinders in a second group of fuel injectors. The listed groupings and the ignition or non-ignition function may be switched during operation, for example at cold start, as also explained further herein.Each of the plurality of fuel injectors 36, sometimes referred to in the singular, may be interchangeable for operation in the fuel system 28. Fuel injector 36 includes a piston 40 in a piston cavity 42. piston 40 may be coupled to plunger 38 and moved between an advanced position and a retracted position within the corresponding piston cavity 42 in response to rotation of the associated cam 26. In other embodiments, a piston and piston cavity may be disposed outside of a fuel injector. Furthermore, embodiments are provided where a piston pressurizes fuel for multiple fuel injectors.Fuel injector 36 further includes an injector 44. injector 44 Injector 44 is movable to controllably start, stop, and possibly vary a fuel injection rate into a corresponding one of cylinders 16. Fuel injector 36 also includes injection control valve 46. "An injector" as contemplated herein means a valve that controls fuel injection. Accordingly, either an exhaust valve or a needle valve, such as injector 34 shown in FIG. 1, or an injection control valve that controls a corresponding exhaust valve or needle valve may be considered an injector for purposes of the present description.Fuel injector 36 further includes an electrically actuated spill valve 48, also discussed in greater detail herein. Fuel system 28 further defines a low pressure chamber 50. a low pressure chamber as contemplated herein means a physical cavity, conduit, passage, etc., having at least temporarily a low pressure relative to a higher pressure within a fuel injector. Accordingly, the low pressure chamber 50 may include an internal fuel supply line within the engine head 22, a drain line or other cavity, recess, etc., also within a single fuel injector.The engine system 10 also includes a control system 52. the control system 52 may include a plurality of sensors, electrical actuators, and other electrical or electronic components in or in communication with the fuel system 28. As shown in FIG. 1, the control system 52 includes a crank angle timer 54 operable to generate data indicative of a crank angle timer of the engine 12 used in the control system 52 to perform control aspects of the present disclosure at desired engine crank angle timings, as also discussed further herein. The control system 52 further includes a fueling controller 56. the fueling controller 56 is described below as parasitic load control- 56 configured to selectively parasitic load the engine system 10, for example, to speed up engine warm-up and / or prevent misfire during a cold start. The parasitic load can take place, for example, before and until a low idling speed of the engine system 10 is reached.The parasitic load controller 56 may include any suitable programmable logic unit, such as a microprocessor or microcontroller, and computer readable volatile or non-volatile memory, such as RAM, ROM, flash, or one or more of many others storing executable program instructions, maps, tables, etc. The features and functions of the parasitic load controller 56 are discussed further below.Referring now to FIG. 2, further features of fuel injector 36 are illustrated in more detail. Fuel injector 36 includes an injector housing 60 having a housing 62 positionable within engine head 22 such that fuel injector 36 includes a direct injector that extends into a corresponding cylinder 16 to directly inject fuel. The housing 62 includes at least one fuel inlet 64 formed therein which receives low pressure fuel via a fuel supply line 34. The piston 40 is also shown in the injector housing 60 and, as described above, may be at least partially moved within the piston cavity 42 to a retracted position to draw fuel into the piston cavity 42 via the fuel inlet 64 and an advanced position to pressurize the fuel for injection or to push the fuel back into the low pressure space 50 through the fuel inlet 64. As mentioned above, fuel injector 36 includes an electrically actuated spill valve 48, which spill valve may be located within injector housing 60 or may be externally positioned in some embodiments. Spill valve 48 may be moved between a fully open position, in which fuel is passively communicated to low pressure chamber 50 by reciprocation of plunger 40, and a fully closed position, in which plunger cavity 42 is isolated from low pressure chamber 50 and plunger 40 advances to pressurize fuel and direct it to nozzle outlets 68 via nozzle passage 66.The injection valve 44 is movable to open and close the nozzle outlets 68 to control fuel injection. Fuel injector 36 also includes a control chamber 70 in fluid communication with nozzle passage 66. When high pressure is present in the nozzle passage 66, a closing hydraulic pressure may be applied to the injection valve 44 in the hydraulic control chamber 70 as long as the control valve 46 is closed. When the control valve 46 is opened, the control chamber 70 is connected to the low pressure chamber 50 so that the high pressure from the nozzle passage 66 pressurizes the injection valve 44. Each of spill valves 48, injectors 44, and control valves 46 may be of a known type. A biasing spring 72 is operatively positioned between the spill valve 48 and the control valve 46. Biasing spring 72 may bias control valve 46 toward a closed position and spill valve 48 toward an open position. In some embodiments, separate springs may be used. Energization of an electric solenoid drive for the control valve 46 opens the control valve 46 against the closing bias of the biasing spring 72, and energization of an electric solenoid drive for the spill valve 48 causes the spill valve 48 to close against an opening bias of the biasing spring 72.Also shown in FIG. 2 are features of the control system 52, including normal operating software or control logic 74 and cold start software or control logic 76. the parasitic load control unit 56 may be part of a fuel delivery control unit, as described above, that operates the fuel system 28 under all conditions, including "normal" conditions as well as cold start conditions. Cold start conditions, as described herein, mean a start condition where the engine system 10 transitions from not operating or OFF to operating or ON. Thus, a cold start does not necessarily require the engine system 10 to have a cold temperature, but only to be started after the shutdown by turning the ignition key or operating a start button.As indicated above, cold start of an internal combustion engine and, in a particular case, start of a compression ignition diesel engine may be associated with certain challenges. A challenge has been the likelihood of misfire in at least some of the cylinders for many years. During misfire, the time required for an engine system to warm up and achieve a steady state operation, such as low idle speed, may increase and other combustion control and / or emissions issues may also occur. In many applications, it may be desirable to minimize start time, and therefore it is often desirable to transition an engine to a steady state operating condition, e.g., low idle speed, as quickly as possible. It has been found that parasitic loading of the engine system 10 during cold start may temporarily increase the amount of fuel burned per cylinder by adding load to the engine 12 to increase temperature more quickly and prevent misfire. The control system 52 may generally be structured in consideration of these and other goals.To this end, the parasitic load controller 56 may be structured to command closing of an spill valve 48 in a first fuel injector 36 to pressurize a fuel in the corresponding piston cavity 42 and to command closing of a spill valve 48 in a second fuel injector 36 to pressurize the fuel in the corresponding piston cavity 42. The parasitic load control through 56 may be further structured to control the opening of an injector 44 in the first fuel injector 36 in an engine cycle to inject the pressurized fuel from the corresponding piston cavity 42 into one of the plurality of cylinders 16 in an engine 12. The parasitic load controller 56 may also be configured to command the opening of the spill valve 48 in the second fuel injector 36 in the engine cycle while the injector 44 in the second fuel injector 36 remains closed to drain the pressurized fuel from the corresponding piston cavity 42 into the low pressure chamber 50.The above description focuses on a case where one fuel injector is used to inject fuel into a cylinder in which the fuel is burned to generate an output of the engine 12 by the rotating crankshaft 20, and another fuel injector pressurizes the fuel but releases the fuel pressure or returns it to the low pressure space 50. In this way, the engine 12 may be thought of as having the task of pressurizing the fuel for two fuel injections, but realizing only the combustion energy from one of these fuel pressure increases.As a result, the engine system 10 is parasitically loaded by the non-firing cylinder, such that the firing cylinders must increase the fuel injection amount and the amount of fuel burned to meet the load requirements of the engine 12. In one practical implementation, rather than current practice with only two fuel injectors, control system 52 will typically use multiple firing cylinders supplied with fuel from a plurality of fuel injectors in an ignition group, as well as multiple non-firing cylinders connected to a group of non-firing fuel injectors. Thus, the first injector 44 discussed above may be one of a plurality of injectors 44 in a plurality of fuel injectors 36 that are opened to inject fuel into a plurality of cylinders of the engine 12 in an engine cycle, and the second injector 44 described above may be one of the plurality of injectors 44 that remain closed to discharge fuel pressurized by a plurality of pistons 40 into a low pressure chamber 50 in the same engine cycle. The plurality of injectors 44 opened to inject fuel may be located in a plurality of fuel injectors 36 connected to a plurality of firing cylinders in a first cylinder bank in an engine 12, and the plurality of injectors 44 remaining closed may be located in a plurality of fuel injectors 36 connected to a plurality of non-firing cylinders in a second cylinder bank in an engine 12. The parasitic load control through 56 may be further structured to switch the parasitic load of the engine 12 from the second cylinder bank to the first cylinder bank in a second engine cycle. Similarly, the parasitic load controller 56 may be understood to parasitically load the engine 12 via the second fuel injector in a first engine cycle and via the first fuel injector in a second engine cycle.Referring now to FIG. 3, a diagram 100 is shown illustrating events and conditions of the engine and fuel system in an engine cycle over a range of crank angle degrees shown on the X axis. A cam speed is shown at 102. A cam shift (cam shift) is shown at 104. Numeral 106 shows the piston pressure (piston pressure) and 108 the rocker pressure (rocker pressure). As will be recalled, Figure 1 shows that the cams 26 contact the followers 38. It should be appreciated that the cams 26 may rotate into contact with rocker arms, which in turn are connected to the followers 38.Numerals 110, 112 and 114 show injection currents. The injection currents 110, 112, and 114 may include control electrical currents or commands generated by the parasitic load controller 56 and used to excite a solenoid drive of the spill valve 48. In one embodiment, the parasitic load controller 56 may be configured to command the spill valve 48 to close and open again to discharge pressurized fuel in a plurality of pulses in an engine cycle. In the illustrated embodiment, the plurality of pulses includes three pulses. Other embodiments could include two pulses, one pulse, or more than three pulses. Thus, according to the example shown in FIG. 3, the parasitic load control unit 56 will separately activate the solenoid drive of the spill valve 48 three times. Numerals 120, 122, and 124 indicate the movement of the spill valve responsive to the pulses of the injection stream 110, 112, 114. It will be appreciated that pulses 110, 112 and 114 are not exactly the same. Pulse 110 has a longer duration. A dwell time 118 between pulse 112 and pulse 114 may be longer than a dwell time 116 between pulse 110 and pulse 112.Those skilled in the art will appreciate the possibility that a fuel injector may be pressurized by advancing a piston in a piston cavity to pressurize fuel while an spill valve is closed and an injector remains closed. The parasitic load control unit 56 may operate to prevent overpressurization of the fuel injector in question by controllably opening and then re-closing the spill valve 48 to prevent damage or degradation of performance that may result from overpressurization. The prevention of over-pressurization of the subject fuel injector 36 may be based on at least one of a pulse duration, a pulse number, or a pulse-pulse dwell time of a plurality of pulses. The numeral 126 shows the recoil movement and illustrates that the associated injection valve remains closed. It can also be seen from FIG. 3 that the plurality of pulses occur during a rising portion of the cam displacement profile 104 of a cam coupled to a plunger coupled to the piston of the respective fuel injector.Referring now to FIG. 4, a graph 200 is shown depicting spill valve displacement at 210 and fuel pressure at 225 over time. It can be seen from FIG. 4 that a plurality of pulses 220 in the spill valve displacement 210 and a plurality of pulses 230 in the fuel pressure 225 are recognizable. It is believed that in many cases it would be desirable to incorporate as many pulses of fuel pressure relief as possible into an engine cycle as long as possible to maximize parasitic load while preventing over pressure.Industrial applicabilityReferring now to the drawings in general, but with reference to FIG. 5, a flowchart 300 is shown illustrating an example methodology and logic flow. In a block 310, engine 12 is cold started, i.e., engine 12 is turned on and crankshaft 20 is rotated, for example, by a starter connected to an associated transmission. In a block 320, the camshaft 24 is rotated to move the pistons 42 in each of the fuel injectors 36 between extended and retracted positions. From block 320, the flowchart 300 proceeds to block 330 to control the closing of the spill valves 48 at prescribed times to pressurize fuel in the fuel injector 36. Because each of the cylinders 16 has a different phase of the associated components, the commanded closing of the spill valves 48 will generally occur at different times.From block 330, the flowchart 300 proceeds to a block 340 to command the opening of the injectors 44 of an ignition group of injectors 36 at prescribed times to inject fuel into the associated cylinders 16 for combustion. From block 340, the flowchart 300 proceeds to a block 350 to command the opening of spill valves 48 of the non-igniting group of injectors 36 at prescribed times to parasitically load the engine 12. It should be appreciated that the commanded opening of injectors and the commanded opening of spill valves may have different timings or even overlap in time and therefore do not occur simultaneously.As also discussed herein, once a cylinder bank of the engine 12 has been used to parasitically load the engine for a predefined time, such as a predefined number of engine cycles, the controller may switch to another cylinder bank to parasitically load the engine 12 for a prescribed time, such as a number of engine cycles. Control could also switch from the other cylinder bank back to the first cylinder bank, transition to a third cylinder bank, or transition in any pattern between any number of cylinders and associated fuel injectors to selectively parasitically load engine 12. When the engine system 10 is warmed up, for example, by achieving a low idle speed or even before, the logic executed for the cold start operation may be ended and normal operation continued.The present description is for illustrative purposes only and should not be construed as limiting the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that various changes may be made to the presently disclosed embodiments without departing from the full and fair scope and spirit of the present disclosure. Other aspects, features and advantages will become apparent upon examination of the accompanying drawings and claims. As used herein, the articles "a" and "an" are intended to include one or more elements and may be used interchangeably with "a", one or more". When only one element is provided, the term "a," "an," or similar language is used. Likewise, the terms "comprises," "comprising," "comprising," or the like, as used herein, are intended to be open ended terms. Further, the term "based on" is intended to mean "based at least in part on" unless expressly stated otherwise.References included in the specificationThis list of documents cited by the applicant has been produced in an automated manner and is only included for the better information of the reader. The list is not part of the German patent application or utility model application. The DPMA does not take any adhesion for any faults or omissions.Patent Literature citedU.S. Pat. No. 7,201,127 B2

[0004]

Claims

A method of operating an engine system (10) comprising: cold starting an engine (12); moving a plurality of pistons (40) in a plurality of piston cavities (42) between advanced positions and retracted positions; closing a plurality of spill valves (48) each fluidly disposed between one of the plurality of piston cavities and a low pressure chamber (50) to pressurize fuel in each of the plurality of piston cavities; opening a first injector (44, 46) in a first fuel injector (36) to inject fuel pressurized by a first of the plurality of pistons into a cylinder (16) of the engine in an engine cycle; opening one of the plurality of spill valves in a second fuel injector (36) while a second injector (44, 46) in the second fuel injector remains closed to discharge fuel pressurized by a second of the plurality of pistons into the low pressure space in the engine cycle; and parasitically loading the engine via pressurization of fuel by the second of the plurality of pistons.The method of claim 1, wherein: moving a plurality of pistons comprises moving the plurality of pistons via a plurality of followers (38) coupled to a plurality of cams (26) on a camshaft (24) of the engine; parasitic loading of the engine occurs during cold start of the engine and prior to transition of the engine to a low idle speed of the engine; the first injector is one of the plurality of injectors in a plurality of fuel injectors opened to inject fuel into a plurality of cylinders of the engine in the engine cycle; and the second injector is one of the plurality of injectors that remain closed to discharge fuel pressurized by a plurality of the plurality of pistons into the low pressure space in the engine cycle.The method of claim 2, wherein: the plurality of injectors opened to inject fuel are arranged in a plurality of direct injectors (36) extending into the plurality of firing cylinders in a first cylinder bank in the engine; the plurality of injectors remaining closed are arranged in a plurality of direct injectors (36) extending into a plurality of non-firing cylinders in a second cylinder bank in the engine; and the method further comprises switching the parasitic load of the engine from the second cylinder bank to the first cylinder bank in a second engine cycle.The method of any preceding claim, further comprising re-closing and then re-opening the one of the plurality of spill valves while the second injector remains closed to discharge fuel pressurized by the second of the plurality of pistons in a plurality of pulses.The method of claim 4, wherein the plurality of pulses comprises three pulses.The method of claim 4 or 5, further comprising preventing over-pressurization of the second fuel injector based on at least one of a pulse duration, a pulse number, and a pulse-pulse dwell time of the plurality of pulses.The method of any of claims 4 to 6, wherein closing and re-closing one of the plurality of spill valves comprises activating an electric spill valve actuator.An engine system (10) comprising: an engine (12) having an engine housing (14) in which a plurality of cylinders (16) are located; a fuel system (28) having a first fuel injector (36) and a second fuel injector (36) each having a piston (40) in a piston cavity (42), an injector (44, 46), and an electrically actuated spill valve (48), the fuel system defining a low pressure space (50); a parasitic load control unit (56) configured to: command closure of the spill valve in the first fuel injector to pressurize a fuel in the corresponding piston cavity; command closure of the spill valve in the second fuel injector to pressurize the fuel in the corresponding piston cavity; commanding opening of the injector in the first fuel injector in an engine cycle to inject the pressurized fuel from the corresponding piston cavity into a cylinder of the plurality of cylinders in the engine; and controlling opening of the spill valve in the second fuel injector in the engine cycle while maintaining the injector in the second fuel injector closed to drain the pressurized fuel from the corresponding piston cavity into the low pressure space.The engine system of claim 8, wherein the engine is parasitically loaded via the second fuel injector in the engine cycle and the parasitic load controller is further configured to parasitically load the engine via the first fuel injector in a second engine cycle; and wherein the parasitic load controller is further configured to command the re-closing and re-opening of the spill valve in the second fuel injector in the engine cycle to discharge the pressurized fuel in a plurality of pulses.The engine system of claim 9, wherein: the plurality of pulses comprise three pulses and the plurality of pulses vary with respect to at least one of pulse duration or pulse-pulse dwell time; the plurality of pulses occurs during an increasing portion of a cam displacement profile of a cam (26) coupled to a plunger (38) coupled to the piston of the second fuel injector; and the commanded opening of the spill valve in the second fuel injector comprises a commanded de-excitation of the spill valve and the spill valve is commanded to de-excite a plurality of times to generate the plurality of pulses.A fuel system (28) comprising: a parasitic load control unit (56) structured for control communication with each of a plurality of electrically actuated spill valves (48) and a plurality of injectors (44, 46) of a plurality of fuel injectors (36) in a fuel system (28); the parasitic load control unit is further configured to command closing of the plurality of spill valves to pressurize fuel in a plurality of piston cavities (42) of the plurality of fuel injectors; the parasitic load control unit is further configured to command opening of the injectors of an ignition group of the plurality of fuel injectors to inject the pressurized fuel into a plurality of ignition cylinders (16) in an engine (12); and the parasitic load controller is further configured to command opening of spill valves of a non-igniting group of the plurality of fuel injectors while the respective injectors remain closed to parasitically load the engine during the cold start.The fuel system of claim 11, wherein: the parasitic load controller is further configured to pulse the commanded opening of the spill valves to discharge the pressurized fuel from each of the plurality of piston cavities into a low pressure space in a plurality of pulses; the parasitic load controller is further configured to vary at least one of a duration, a number, and a pulse-pulse dwell time of the plurality of pulses from each of the plurality of piston cavities.The fuel system of claim 11 or 12, further comprising: the plurality of spill valves each comprising an electric actuator and a biasing spring (72), and wherein each of the plurality of spill valves is movable against a biasing force of the biasing spring by energizing the corresponding electric actuator to an intermediate position between a fully open position and a fully closed position to generate the plurality of pulses from the corresponding piston cavity; the plurality of fuel injectors and at least one camshaft (24) having a plurality of cams (26) coupled to the plurality of pistons.

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