Patent Publication Number: US-8973553-B2

Title: Multi-sensing fuel injection system and method for making the same

Description:
CROSS-REFERENCES TO RELATED APPLICATIONS 
     The present application claims the benefit of priority to PCT Application No. PCT/US2010/042549, filed Jul. 20, 2010, which application claims the benefit of U.S. Provisional Patent Application No. 61/226,920, filed Jul. 20, 2009, the entirety of which is hereby incorporated by reference. 
    
    
     FEDERALLY SPONSORED RESEARCH AND DEVELOPMENT 
     This invention was made with Government support under Contract No. W56HZV-08-C-0627 awarded by the U.S. Army. The Government has certain rights in the invention. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates generally to a sensing apparatus, and more particularly, to an electrically isolated fuel injector for internal combustion engines. 
     BACKGROUND 
     Internal combustion engines such as those used in diesel powered vehicles are typically ignited by a mixture of injected fuel and hot compressed air. While diesel engines provide higher thermal efficiency than spark-ignited gasoline engines, for instance, diesel engines are known to emit undesirable exhaust emissions, such as high levels of nitrogen oxide (NO x ) and black particulate smoke, which are undesirable. Thus, government agencies require diesel engines to meet strict regulations regarding the quantity of exhaust emissions in an effort to reduce pollutants in the environment. The environmental emissions regulations for these engines are becoming more stringent and difficult to meet, particularly for emissions resulting from fossil fuel combustion. 
     There is a need to monitor and control the combustion process, not only to reduce engine-out emissions, but also to produce the exhaust gas composition and temperature necessary to enhance the operation of after treatment-devices used to reduce emissions. 
     SUMMARY 
     There is a need in the art for an improved system for detecting ionization current to control diesel engine combustion. The precise control of the combustion process in combustion engines requires a feedback signal indicative of the combustion process. One commonly considered signal is the cylinder gas pressure, measured by a quartz crystal pressure transducer, or other types of pressure transducers. The use of cylinder pressure transducers, however, is generally limited to laboratory settings and is not favored in practice due to its relatively high cost and limited durability under actual operating conditions. 
     Of the measuring methods known for detecting engine combustion conditions during engine operation, ion current measurement has been considered to be highly useful because it can be used for directly observing the chemical reaction resulting from the engine combustion. As such, an in-cylinder ionization sensor may be employed to sense various engine parameters according to different engine operating conditions. For instance, ionization sensors are operable to detect the combustion process based on the theory that positive and negative ions are generated during the combustion process. Thus, ionization sensors can replace many sensors commonly integrated in diesel engines, particularly the expensive pressure transducers discussed above. 
     In gasoline operated engine, for instance, spark plugs may be used to detect ionization current (e.g., a spark plug with a central electrode and one or more spaced apart side electrodes). In diesel operated engines, on the other hand, a glow plug can be used to sense the ion current. For instance, a glow may be modified so as to be electrically insulated from the engine body, wherein the glow plug and engine body each acts as an electrode. Alternatively, it may be possible to incorporate an ionization sensor into an orifice of a glow plug. By way of example, an electric conductive layer made of platinum may be formed on a surface of a heating element of the glow plug, wherein the layer is electrically insulated from the combustion chamber and a glow plug clamping fixture. The foregoing combination is a feasible technology for production and provides several key benefits. For instance, modifications to the engine may not be required, and the location of the glow plug is well-suited for sensing. Nonetheless, due to thermal and magnetic conditions in or near the glow plug, typical ionization conditioning circuitry has been positioned at substantial protective distances from the glow plug. Unfortunately, these protective distances further degrade a typically weak signal, and thus reduce the signal-to-noise ratio of the detected ionization signal before reaching the ionization conditioning circuitry. In addition, soot deposits formed on surfaces of the glow plug further degrade the integrity of the signal. 
     The present invention provides an improved ion sensing system for detecting ionization current in a combustion chamber of a compression-ignited engine such as, but not limited to, a diesel engine or a homogeneous charge compression ignition (HCCI) engine. The system includes an electrically insulated fuel injector disposed within a combustion chamber of an internal combustion engine. The fuel injector provides fuel to an engine cylinder in response to receiving an injection signal from an electronic controller operatively connected thereto. A first electrically insulated member is provided for electrically isolating the fuel injector from the body of the internal combustion engine. A second electrically insulated member is provided for fixedly positioning the fuel injector within the combustion chamber. 
     The system further includes an ionization detection circuit for sensing ionization current. The ionization detection circuit includes a power source for supplying power to the fuel injector. The power source is electrically connected to the fuel injector via a first terminal having a preset positive potential, and is electrically connected to the engine body via a second terminal. 
     Additional benefits and advantages of the present invention will become apparent to those skilled in the art to which the invention relates from the subsequent description of the preferred embodiment and the appended claims, taken in conjunction with the accompanying drawings. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view of a system for detecting ionization current in accordance with the present invention; 
         FIG. 2  is a schematic view of a system for detecting ionization current in accordance with an alternative embodiment of the present invention; 
         FIG. 3  is an enlarged cross-sectional view of a high pressure coupling depicted in  FIG. 2 ; 
         FIGS. 4A-4D  are waveform diagrams illustrating combustion pressure and ionization current signals versus engine piston crank angle signals; 
         FIG. 5A  is a schematic view of a glow plug integrated with a fuel injector within a combustion chamber; 
         FIG. 5B  is a waveform diagram illustrating a signal transmitted by an ion sensor disposed within an orifice of the glow plug of  FIG. 5A  versus a signal transmitted by the fuel injector of  FIG. 5A ; 
         FIG. 6  is a waveform diagram illustrating the results of implementing a current probe with the system of the present invention; 
         FIG. 7A  is a waveform diagram illustrating the results of a normal operating fuel injector driver; 
         FIG. 7B  is a waveform diagram illustrating the results of an abnormally operating fuel injector driver; 
         FIG. 8A  is a waveform diagram illustrating the results of implementing a current probe with the fuel injector driver employed in  FIG. 7A ; 
         FIG. 8B  is a waveform diagram illustrating the results of implementing a current probe with the fuel injector driver employed in  FIG. 7B ; 
         FIG. 9  is a flowchart illustrating a method of making an ion sensing apparatus in accordance with the present invention; and 
         FIG. 10  is a flowchart illustrating the functional steps of an electronic control unit. 
     
    
    
     DETAILED DESCRIPTION 
     Referring now to  FIG. 1 , a system embodying principles of the present invention is illustrated therein and designated generally by reference numeral  10 . In one embodiment, the system  10  includes a fuel injector  12  for injecting fuel in a combustion chamber  14  formed in an engine body  16  of an engine having at least one cylinder. The engine is preferably an internal combustion engine such as a diesel engine. As used herein, it is to be understood that the term “engine” is to be broadly construed and may refer to typical diesel engines, HCCI engines, dual mode engines, flexible-fuel engines, dual-fuel engines, direct injection gasoline engines, hydrogen engines, etc. 
     In this embodiment, the fuel injector  12  is coupled to a solenoid  15  operable to drive a needle (not shown) for injecting fuel from a nozzle  17 . The solenoid  15  may be a two position on/off valve, a piezoelectric valve, or any suitable valve known to those of ordinary skill in the art. An electronic control unit (ECU)  19  for controlling the engine is electrically connected to the solenoid  15  via solenoid terminals  21 . It is to be understood that the ECU  19  may be any suitable control device known to those of ordinary skill in the art. For instance, the ECU may include a microprocessor having a central processing unit (CPU), storage media such as read-only memory (ROM) and random-access memory (RAM), input/output circuits, etc. The solenoid terminals  21  are electrically insulated from the fuel injector  12  and serve as the electric wiring for carrying an energizing current for driving the needle to inject fuel through the nozzle  17 . As will be understood to those skilled in the art, the injection of fuel assists in the removal of soot deposits formed onto external surfaces of an orifice of the fuel injector. 
     The fuel injector  12  is insulated from the engine body  16  by way of a first electrically insulated member such as a washer  18 . The washer  18  may be composed of an electrically insulating material or may be formed as a metal having an electrically insulating coating. According to one aspect of the invention, a second electrically insulated member may be provided for securely fixing the fuel injector  12  in place. As shown in  FIG. 1 , for example, the second electrically insulating member includes a fork  20  mounted on the engine body  16  and connected to the body  12 A of the fuel injector  12  so as to ensure electrical isolation therefrom. The fork may be composed of an electrically insulating material or may be formed as a metal having an electrically insulating coating. 
     The fuel injector  12  is fluidly connected to a fuel pump  22  via a fuel line  24 . The fuel pump  22  is driven by an output shaft (not shown) and is operable to supply fuel to the fuel injector  12  through the fuel line  24 . According to one embodiment of the invention, the fuel line  24  is electrically insulated from the fuel pump  22  by way of a third electrically insulating member. In  FIG. 1 , for example, the third electrically insulating member includes an insulating member such as a washer or a ferrule  26  disposed between the fuel pump  22  and a proximal end of the fuel line  24 . The ferrule  26  may be composed of an electrically insulating material or may be formed as a metal having an electrically insulating coating. 
     According to an alternative embodiment of the invention, a high pressure coupling  28  is provided for electrically insulating part of the fuel line  24  from the fuel pump  22 . As best shown in  FIG. 2 , the high pressure coupling  28  is disposed between the proximal end of the fuel line  24  and a distal end thereof. Thus, it can be seen that an isolated part  24 A of the fuel line  24  extending from the fuel injector  12  to the high pressure coupling  28  is electrically insulated from the fuel pump  22 , and hence, the engine body  16 . In contrast, a non-isolated part  24 B of the fuel line  24  extending from the high pressure coupling  28  to the fuel pump  22  is not electrically insulated from the engine body  16 . 
     Referring now to  FIG. 3 , the high pressure coupling  28  will be described in greater detail. According to one embodiment, the high pressure coupling  28  includes a cylindrical steel housing  30  encasing a non-metallic body  32 . The non-metallic body  32  is slightly displaced from a first and second non-metallic washer  34 ,  36  disposed at opposite ends thereof, thereby forming a pair of air gaps  38 ,  40  therebetween. The non-metallic body  32  and the first and second non-metallic washers  34 ,  36  may be formed out of any non-conductive material with high tensile strength, such as, but not limited to, Garolite. A threaded metallic cap  42  having an elongated opening  44  for receiving the isolated part  24 A of the fuel line  24  is fixedly mounted on the first non-metallic washer at a distal end of the high pressure coupling  28 . 
     The high pressure coupling  28  further includes a first ferrule  46  fluidly connected to a second ferrule  48  via a relatively thin passageway  50  for transmitting fuel thereto. The isolated part  24 A of the fuel line  24  is connected to the first ferrule  46  via the opening  44  of the threaded cap  42 , whereas the non-isolated part  24 B of the fuel line  24  is connected to the second ferrule  48  via a central opening  52  formed along the housing  30  at a proximal end of the high pressure coupling  28 . As can be seen in  FIG. 3 , the isolated part  24 A of the fuel line  24  has a smaller diameter than that of the opening of the threaded cap. As such, the isolated part  24 A of the fuel line  24  may be connected to the first ferrule  46  without contacting the threaded cap  42 . 
     Referring back to  FIGS. 1 and 2 , the system  2  further includes an ion sensing circuit  54  for measuring the concentration of ions in the combustion chamber  14 . The ion sensing circuit  54  comprises a power supply such as, but not limited to, a DC power supply  56  having a preset voltage. The DC power supply  56  is electrically connected to the fuel injector body  12 A via a positive terminal  58  and is electrically connected to the engine body  16  via a negative terminal  60 . The ion sensing circuit  54  further includes a resistor  62  for sensing an ion current. In addition, since ionization signals tend to be relatively weak, a signal conditioning unit  64  may be provided for filtering or amplification purposes. The signal conditioning unit  64  may be integrated with low pass filters and/or high pass filters to reshape an incoming ion signal. Moreover, while the signal conditioning unit  64  is depicted as forming part of the ion sensing circuit  54 , it is to be understood that the signal conditioning unit  64  may be provided as a separate component, or integrated with the ECU  19 . A voltage measuring device such as, but not limited to, a potentiometer  66  is electrically connected across the resistor  62  to measure the ion current. The potentiometer  66  is also electrically connected to the ECU  19  and is configured to send an ionization signal thereto. 
     In operation, the ECU  19  transmits an injection command to the solenoid  15 , thereby causing an energizing current to pass through the solenoid  15  to drive the needle. In turn, fuel is injected from the nozzle  17  into the combustion chamber  14 . The injected fuel mixes with hot compressed air to bring about fuel combustion. During the combustion process, a plurality of positive and negative ions are formed within the combustion chamber. To detect the ionization content, the DC power supply  56  applies an electric voltage to the fuel injector body  12 A. The application of the voltage enables the plurality of ions to generate an ion current which subsequently flows along a path containing the resistor  62 . The potentiometer  66  measures the voltage drop across the resistor  62 , and outputs a signal representative of the ion current to the ECU  19 . Additionally, the ionization signal may be passed through the signal conditioning unit  64  for filtering or amplification purposes. 
     As will be described in greater detail below, the functional operation of the ECU  19  may be based on spikes observed in the ionization signal.  FIG. 10 , for instance, is a flow chart explaining the steps the ECU  19  may carry out to determine various operating conditions of the engine. In step S 1 , the ECU  19  initially determines whether or not a first spike in the ionization signal has been detected in the ionization signal. If the ECU  19  does not detect a first spike, then the ECU  19  concludes that the fuel injector  12  has not injected fuel into the combustion chamber  14 , as indicated in block B 1 . If the ECU  19  does detect a first spike in the ionization signal, the ECU  19  proceeds to step S 2 . In step S 2 , the ECU  19  determines whether or not a second spike in the ionization signal has been detected. More specifically, the ECU  19  determines whether the amplitude of a second spike (the second spike indicates the end of fuel injection) in the ionization signal is greater than a predetermined value. If not, the ECU  19  concludes that the fuel injector driver is defective (e.g., the fuel injector  12  may be injecting too much fuel), as indicated in block B 2 . If so, the ECU  19  proceeds to step S 3 . 
     In step S 3 , the ECU  19  determines whether a third spike in the ionization signal has been detected. If not, the ECU  19  concludes that combustion has not occurred (e.g., due to the occurrence of a misfire or abnormal burning), as indicated in block B 3 . If the ECU  19  detects a third spike in the ionization signal, the ECU  19  concludes that combustion has occurred. Nonetheless, the ECU  19  proceeds to step B 4  and determines whether or not a fourth spike has been detected in the ionization signal. If so, then the ECU  19  concludes that a leakage of fuel has occurred during the expansion cycle, as indicated in block B 4 . If not, then the ECU  19  concludes that the injection of fuel and the combustion thereof is successful, as indicated in block B 5 . Accordingly, based on the existence or non-existence of a spike in the ionization signal, the engine may be controlled to modify various conditions such as the combustion mode, ignition timing, fuel injection timing, quantity of fuel being injected, etc. 
       FIGS. 4A-4D  illustrate waveforms corresponding to various signals during operation of a diesel engine. In particular, the foregoing figures depict a waveform of a signal indicative of a pressure trace  100 , a needle lift position  102 , a rate of a heat release trace  104 , and an ion current  106  (i.e., the output of the potentiometer  66 ) during a cycle of the engine. The graphs in  FIGS. 4A-4D  are based on engine simulations according to a start-of-injection pulse preset to 8.25 Crank Angle Degrees (CAD) before Top Dead Center (TDC). 
     Referring first to  FIG. 4A , the pressure trace signal  100  indicates the level of compression of an engine cylinder (not shown). It can be seen that since the needle lift signal  102  displays no information, fuel has not been injected into the combustion chamber  14  yet. As such, the heat release trace  104  signal and the ionization signal  106  similarly indicate that no activity is taking place inside the combustion chamber  14 . 
     Referring now to  FIG. 4B , a waveform diagram is shown illustrating the results of an initial firing cycle in the engine during a cold start. In particular, the pressure trace signal  100  indicates a late firing (partial misfiring) and the heat release trace signal  104  indicates a relatively low heat release with respect to the fuel injected into the combustion chamber  14 . The ionization signal  106  peaks at exactly 8.25 CAD before TDC. This peak refers to the start-of-injection pulse and hereinafter will be referred to as the start-of-injection spike  108 , whereas the second peak in the ionization signal  106  refers to the end-of-injection pulse and hereinafter will be referred to as the end-of-injection spike  120 . 
     In  FIG. 4B , the start-of-injection spike  108  primarily indicates interference caused by the energizing current flowing through the solenoid  15 . As previously described, the fuel injector  12  is connected to a preset positive potential  58  and contains the solenoid  15 , which is electrically insulated from the fuel injector  12 . Thus, the energized fuel injector  12  is operable to detect current passing through the solenoid  15  since any current flowing through the fuel injector  12  will cause a disturbance in the voltage of the fuel injector body  12 A. In this manner, the fuel injector  12  is operable to serve as a current probe. 
     For instance, the needle lift signal  102  depicted in  FIG. 4B  indicates a spike  110  almost immediately after the start-of-injection spike  108 . The delay between the spikes  108  and  110  is attributable to the time consumed by the solenoid  15  to drive the needle upon becoming energized. Looking at the overall ionization signal  106  during this cycle, a few notable conclusions can be drawn. First, it can be seen that fuel has been successfully injected into the combustion chamber  14  due to the presence of the start-of-injection spike  108 . Secondly, however, it can be seen that the fuel injector driver is defected since the amplitude of the end-of-injection spike  120  is nearly zero, which indicates that too much fuel (i.e., more fuel than specified by the ECU  19 ) has been injected into the combustion chamber  14 . Furthermore, it can also be seen that abnormal burning or a misfire has occurred due to the absence of an additional spike in the ionization signal  106 . 
     Turning now to  FIG. 4C , a waveform diagram is shown illustrating the results of a successful combustion cycle. In contrast to  FIG. 4B , the heat release trace signal  104  indicates a relatively high release rate, and the amplitude of the end-of-injection spike  120  indicates that the fuel injector  12  is operating normally (i.e., the fuel injector  12  is injecting the quantity of fuel specified by the ECU  19 ). While the start-of-injection spike  108  is similarly observed at 8.25 CAD before TDC, a third peak in the ionization signal  106  occurs at approximately 7 CAD after TDC. The third peak  112  indicates the start of combustion and will hereinafter be referred to as the start-of-combustion spike  112 . The presence of the start-of-injection spike  108  and the start-of-combustion spike  112  in the ionization signal  106  indicates a successful combustion cycle. Additionally, the start-of-injection and start-of-combustion spikes  108  and  112  can be used to calculate the ignition delay, which can subsequently be communicated as feedback information to the ECU  19 . Calculation of the ignition delay may be particularly helpful in the control of HCCI engines. Similarly, information regarding the amplitudes of the start-of-injection and end-of-injection spikes  108  and  120 , as well as the distance between these spikes, can be communicated as feedback to the ECU  19  in order to determine the amount of amount of fuel injected and monitor the integrity of the fuel injection system  10 . 
     Referring now to  FIG. 4D , the results are generally identical to those illustrated in  FIG. 4C  with the exception of a fourth spike  118  in the ionization signal  106  occurring relatively late in the expansion stroke of the engine cycle. The fourth spike  118  indicates fuel droplets that have exited the nozzle  17  and burned locally in the high temperature environment near the body of the fuel injector  12 . Since burning of fuel effectuates the formation of ions, the fuel injector  12 , which is configured as an ion sensor, is operable to detect fuel leaks during the expansion cycle. 
     Based on the foregoing, the ECU  19  can be configured to utilize information obtained from the ionization signal to efficiently control various engine operating conditions. For instance, the ECU  19  can use such information to control the injection of fuel, as well as to control other systems to enhance engine performance, achieve better fuel economy, and lower exhaust emissions. 
     Referring now to  FIG. 5A , a glow plug  68  is shown as being integrated with the fuel injector  12  inside the combustion chamber  14 . The glow plug  68  includes a second ion sensor located in an orifice of the glow plug  68 . The integration of the glow plug  68  with the fuel injector  12  may be implemented to measure an additional ionization signal during the combustion process. As a result, engine performance may be enhanced without the necessity of drilling additional holes in the cylinder head of the engine. It should be understood to those of ordinary skill in the art that a spark plug can similarly be implemented as a second ion sensor in spark-ignited engines. 
     As can best be seen in  FIG. 5B , the ionization signal  106  indicative of the ion current measured by the fuel injector  12  indicates a start-of-injection spike  108  and a start-of-combustion spike  112 . With regard to the start-of-combustion spike  112 , however, it can be seen that the ionization signal  200  indicative of the ion current measured by the second ion sensor located in the glow plug  68  indicates a start-of-combustion spike  202  occurring slightly before the start-of-combustion spike  112 . Accordingly, the foregoing information can be used to conclude that the combustion process began near the glow plug orifice prior to beginning near the body of the fuel injector  12 . 
     As previously discussed, the fuel injector  12  according to the present invention is operable to function as a current probe.  FIG. 6 , for instance, illustrates the results of connecting a current probe (not shown) to the fuel injector  12 . The results are based on a simulation in which an electric pulse signal is sent to the solenoid  15  at 6 CAD before TDC, and wherein fuel is not injected into the combustion chamber  14 . The signal corresponding to the fuel injector  12  is the ionization signal  106 , whereas the signal corresponding to the current probe is denoted by reference numeral  300  and will hereinafter be referred to as the current probe signal  300 . Point  302  of the current probe signal  300  indicates the start-of-injection pulse detected by the current probe, and point  304  indicates the end-of-injection pulse detected by the current probe. Notably, a comparison of the ionization signal  106  and the current probe signal  300  illustrates a near identical correlation between the start-of-injection pulse  108  and end-of-injection pulse  120  detected by the fuel injector  12  and the start-of-injection pulse  302  and end-of-injection pulse  304  detected by the current probe. Accordingly, the results of  FIG. 6  confirm that the fuel injector  12  of the present invention can detect the electric injection pulse signal transmitted from the ECU  19  to the solenoid  15 . 
     Referring now to  FIGS. 7A and 7B , waveform diagrams are shown illustrating the difference between a normal operating fuel injector driver and a defective fuel injector driver.  FIG. 7A  depicts a normal start-of-injection pulse  108  and a normal end-of-injection pulse  120  detected by the fuel injector  12 . The corresponding needle lift signal  102  begins at 7 CAD before TDC and ends at TDC with an amplitude of approximately 0.05 mm.  FIG. 7B  depicts the results of an engine running with the same electric pulse width signal requested by the ECU  19  and the same operating conditions as in  FIG. 7A . While the start-of-injection pulse  108  is similarly observed at about 8.25 CAD before TDC, the amplitude of the end-of-injection pulse  120  is near zero. In addition, although the corresponding needle lift signal  102  similarly begins at 7 CAD before TDC, it ends at 1 CAD after TDC with a higher amplitude of approximately 0.55 mm. Furthermore, it can be seen that the needle lift signal  102  shown in  FIG. 7B  is higher and wider than in  FIG. 7A . The results of  FIG. 7B  therefore indicate a defective fuel injector driver since more fuel has been injected despite the fact that the engine operating conditions are the same as in  FIG. 7A . 
       FIGS. 8A and 8B  illustrate the results of connecting a current probe (not shown) to the fuel injector  12 . The results are based on the same engine operating conditions employed in  FIGS. 7A and 7B .  FIG. 8A  depicts the current probe signal  300  corresponding to  FIG. 7A , which reflects a normal functioning fuel injection driver.  FIG. 8B , on the other hand, depicts the current probe signal corresponding to  FIG. 7B , which reflects an abnormally functioning fuel injector driver. For instance, although the start-of-injection pulse  302  of the current probe signal  300  in  FIG. 8B  is the same as in  FIG. 8A , the end-of-injection pulse  304  of the current probe signal  300  in  FIG. 8B  is different. Specifically, the end-of-injection pulse  304  of the current probe signal  300  in  FIG. 8B  has a slower decaying slope than the end-of-injection pulse  304  in  FIG. 8A , which indicates a defect in the fuel injector driver. 
     Referring now to  FIG. 9 , a method  900  of making an ion sensing apparatus for detecting ionization current in a combustion chamber  14  of an engine starts in step  902 . The components of the ion sensing apparatus which are identical to those corresponding to the ion sensing system  10  discussed above, are denoted by like reference characters and will not be described in detail below. 
     In step  904 , a fuel injector  12  is electrically insulated from an engine body  16  of the engine. This may be accomplished according to various techniques known to those of ordinary skill in the art. For instance, an insulating member such as the aforementioned ceramic washer  18  may be disposed between the fuel injector  12  and the engine body  16 . In step  906 , the fuel injector  12  is fixedly positioned within the combustion chamber  14 . For instance, a retaining device such as the electrically insulated fork  20  discussed above may be provided to secure the fuel injector  12  in place and ensure electrical isolation between the fuel injector  12  and the engine body  16 . 
     In step  908 , a fuel line  24  for supplying fuel to the fuel injector  12  is electrically insulated from the engine body  16 . According to one embodiment, the fuel line  12  may be electrically insulated from the engine body  16  by way of the ceramic ferrule  26 . As previously discussed, the ferrule  26  may be disposed between a proximal end of the fuel line  14  and a fuel pump  22  operable to supply fuel thereto. Alternatively, an isolated part  24 A of the fuel line  24  may be electrically insulated from the engine body  16  by way of an insulating device such as the high pressure coupling  28  discussed above. It should be understood to those of ordinary skill in the art that the isolation between the fuel line  24  and the fuel injector  26  can be done for every fuel injector associated with a given cylinder of an engine. Alternatively, the entire common rail may be insulated by way of an isolating member such as the ferrule  26  or high pressure coupling  28 , such that a single isolating member is necessary. 
     Continuing with step  910 , the fuel injector is electrically connected to a power source via a positive terminal  58  having a preset potential. The power source may be the DC power source  56  discussed above. In step  912 , the engine body  16  is electrically connected to the power source  56  via a negative terminal  60 . The method ends in step  914 . 
     While the above description constitutes the preferred embodiment of the present invention, it will be appreciated that the invention is susceptible to modification, variation and change without departing from the proper scope and fair meaning of the accompanying claims.