Patent Application
20140000566
The present device relates to a fuel-injection system using high-efficiency (HE) injection nozzles. Particularly, the present device relates to an a HE fuel-injection nozzle coking compensation strategy.
Fuel systems typically employ multiple closed-nozzle fuel injectors to inject high pressure fuel into the combustion chambers of an engine. Each of these fuel injectors includes a nozzle assembly having a cylindrical bore with a nozzle supply passageway and a nozzle outlet. The efficiency of the nozzle outlet or orifice is a measure of how effectively the energy stored in the fuel as pressure is converted into kinetic energy. The greater the kinetic energy, the more the fuel is broken apart (atomized), improving combustion completeness and lowering soot. High-efficiency (HE) nozzles, i.e., those with the highest orifice efficiency, are desirable for emissions.
Unfortunately, HE nozzles also have a greater propensity to exhibit coking, or injector spray hole fouling, which is the deposition of coked fuel layers on the orifice wall (internal) and on the outside surface of the nozzle tip (external). The flow rate of a coked nozzle is reduced because of the added restriction to the flow. As rated injection pressures of new injection systems increase to further provide emission benefits, it has become increasingly difficult to design HE nozzles without coking.
Coking is when the byproducts of combustion accumulate on or near the injector nozzle openings. As the deposits build up, they can clog the injector nozzle orifices and adversely affect the performance of the fuel injectors. This can lead to reduced fuel economy and can increase the amount of pollutants released into the atmosphere through exhaust.
To date, the problem of coking has been addressed by engine manufactures seeking nozzle designs that avoid flow rate losses, deemed unacceptable when the loss is more than about three percent. One method for maintaining high nozzle efficiency without coking has been to minimize the spray hole aspect ratio (L/D)—the ratio of the spray hole length (L) to the spray hole exit diameter (D). The ability to further decrease spray hole length (L) is constrained by the allowable stresses in the nozzle metal as injection pressure increases. The ability to further increase spray hole exit diameter (D) is constrained by the nozzle flow rate and the number of holes that are best for emissions for a given engine application. Other methods, such as increasing spray hole internal roughness or making subtle changes in spray hole geometry, provide only marginal improvements to reduce coking.
The device of the present disclosure is directed to overcoming the problems set forth above, but in a way previously unappreciated by those skilled in the art. The present device provides a unique operation strategy which makes use of HE nozzles and requires few additional components over those currently used in fuel injection systems. The device and methods of the present invention recognize and take advantage of two previously unappreciated facts: (1) flow rate loss due to coking will eventually stabilize after sufficient service time, and (2) good emission performance can be maintained even with coked nozzles.
There is disclosed herein an improved fuel injection nozzle system and control strategy which avoids the disadvantages of prior devices while affording additional structural and operating advantages. The disclosed device and methods compensate for nozzle coking in a fuel injection system, particularly where high-efficiency nozzles are used.
In an embodiment of the disclosed method for compensating for nozzle coking in a fuel injection system, the method includes the steps of creating an expected fuel flow rate formula for a selected fuel injection nozzle, operating the selected fuel injection nozzle for a period of time, measuring fuel pressure and injector control valve on-time of the fuel injection nozzle during operation, determining the expected fuel flow rate for the measured fuel pressure and injector control valve on-time, measuring an actual fuel flow rate of the fuel injection nozzle, determining a coking condition of the fuel injection nozzle, and automatically altering the injector control valve on-time to compensate.
The expected fuel flow rate formula is empirically determined as a function of fuel pressure and injector control valve on-time, while the actual fuel flow rate is measured by a flow rate sensor attached to the fuel injection system. Accordingly, for the disclosed embodiment, determination of a coking condition is based on a difference between the actual fuel flow rate and the expected fuel flow rate. Compensation in the control valve on-time is as a result of the deterioration in the actual fuel flow rate.
In an embodiment of the invention, the disclosed compensation method using the expected fuel flow rate formula is integrated in an engine control strategy. Likewise, the altering of the injector control valve on-time may also be made part of the engine control strategy.
Generally speaking, the disclosed fuel injection system includes a fuel source, a fuel injection nozzle fed by the fuel source, a control valve connected between the fuel source and the injection nozzle, a fuel flow rate sensor, a fuel pressure sensor, a control valve on-time sensor, and a control circuit electronically connected to each of the fuel flow sensor, pressure sensor, the control valve on-time sensor and the control valve.
In an embodiment of the disclosed device the control circuit alters the control valve on-time when the actual fuel flow rate is different than an expected fuel flow rate based on the measured fuel pressure and measured control valve on-time. This difference is also an indication of the coking status of the particular injection nozzle. As such, high-efficiency nozzles are particularly useful in embodiments of the present system.
Methods for creating a fuel injection nozzle control strategy are also disclosed where, in select embodiments, a specific fuel injection nozzle configuration is to be controlled. The method includes determining expected fuel flow rate for the selected fuel injection nozzle, operating the selected fuel injection nozzle for a period of time, measuring fuel pressure and injector control valve on-time of the fuel injection nozzle, measuring the actual fuel flow rate of the fuel injection nozzle during operation, determining a coked nozzle condition of the fuel injection nozzle, and altering the injector control valve on-time to compensate for the coked nozzle.
In an embodiment of the disclosed method, the calculating of any difference and the altering of the injector control valve on-time are performed by an engine control circuit. The step of determining a coked nozzle condition may include the step of calculating any difference, typically a deficit, between the actual fuel flow rate and the expected fuel flow rate corresponding to the measured fuel pressure and injector control valve on-time for the fuel injection nozzle.
These and other aspects of the invention may be understood more readily from the following description of certain embodiments.
For the purpose of facilitating an understanding of the subject matter sought to be protected, there are illustrated in the accompanying drawings embodiments thereof, from an inspection of which, when considered in connection with the following description, the subject matter sought to be protected, its construction and operation, and many of its advantages should be readily understood and appreciated.
While this invention is susceptible of embodiments in many different forms, there is shown in the drawings and will herein be described in detail a preferred embodiment of the invention with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention and is not intended to limit the broad aspect of the invention to embodiments illustrated.
Referring to
Generally speaking, with reference to the drawing of
The injection nozzle 12 may be most any suitable nozzle type. However, the high-efficiency nozzles are particularly useful for most engines, yet they are also particularly prone to coking. This coking tendency actually makes the high-efficiency nozzles also particularly appropriate for use with the present compensation system and methods.
To determine the fuel pressure and control valve on-time variables for the present system embodiment, sensors already employed in most engines are useful. The fuel pressure sensor 18 and control valve on-time sensor 20 are electronically connected to an engine system control circuit 30. The engine control strategy, e.g., see
The addition of a fuel flow rate sensor 16 to the system is used to measure the actual fuel flow into the engine cylinder 32. The fuel flow sensor 16 is also electronically connected to the control circuit 30. When the control circuit 30 determines that the actual fuel flow rate is different than the expected fuel flow rate, as determined from the measured control valve on-time and fuel pressure, the control valve on-time can be altered or adjusted to compensate. A comparator may be used as part of the control circuit 30 to compare the expected and actual fuel flow for the injection system. A deficit in the actual fuel flow (as compared to the expected fuel flow) represents a condition of the fuel system, particularly the condition of the injection nozzle due to coking.
Referring now to the flow chart of
Once the fuel flow rate formula is created, it may be made part of the engine control strategy. Then, as the engine operates with the selected fuel injection nozzle for a period of time, measurements of fuel pressure and injector control valve on-time of the fuel injection nozzle can be made. Such a process step would not require additional components, as both variables are already monitored in all current engines using standard pressure sensors and timing sensors, as necessary. From the measured fuel pressure and injector control valve on-time, an expected fuel flow rate can be determined for the selected injection nozzle based on the created fuel flow rate formula.
Whether performed simultaneous to other system variable measurements or sequentially (i.e., before or after), the actual fuel flow rate of the fuel injection nozzle can be measured. A commercially available fuel flow rate sensor may be added to the system, as described above. The actual and expected fuel flow rates are then compared to determine a difference, if any. Of course, a standard for the difference can be set to be sure any calculated difference is significant. Further, redundant measures can also be made to minimize the possibility of anomalies in the measured variables. If no difference exists between the actual and expected fuel flow rates, then engine operation continues unchanged and the monitoring steps are repeated. However, a gradual change (i.e., a deterioration) in the actual flow rate relative to the expected flow rate is considered to represent the condition of the fuel injection system, especially the condition of the injection nozzle due to coking. As the flow rate diminishes, the amount of fuel being delivered to the engine cylinder is likewise reduced, resulting in power and efficiency losses.
However, instead of eliminating the coking condition of the injection nozzle, the system of the present embodiment automatically alters the duration of the injector control valve on-time to compensate for deterioration in the actual fuel flow rate. That is, as the nozzle becomes coked and the flow of fuel is reduced as a result, the control valve is opened for a longer period to maintain the necessary amount of fuel being delivered to the engine cylinder. Eventually, the nozzle coking condition stabilizes and additional adjustments of the control valve on-time are unnecessary.
One embodiment of this strategy is illustrated in the chart of
The matter set forth in the foregoing description and accompanying drawings is offered by way of illustration only and not as a limitation. While particular embodiments have been shown and described, it will be apparent to those skilled in the art that changes and modifications may be made without departing from the broader aspects of applicants' contribution. The actual scope of the protection sought is intended to be defined in the following claims when viewed in their proper perspective based on the prior art.
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/US11/28968 | 3/18/2011 | WO | 00 | 9/14/2013 |
