Patent Application
20110232601
The present disclosure relates generally to compression ignition engines, and more particularly to injection and combustion of electronically controlled mixture ratios of gasoline and a compression ignition fuel.
Engineers are constantly seeking new ways to reduce undesirable emissions from compression ignition engines. While undesirable constituents in exhaust emissions can be treated with ever more sophisticated aftertreatment systems, burning the fuel in a way that reduces the production of undesirable emissions in the first place has always been a desired alternative. Some of the undesirable emissions currently of concern include NOx, unburned hydrocarbons, and particulate matter. NOx is generally associated with higher combustion temperatures. Unburned hydrocarbons can sometimes be associated with fuel in remote portions of an engine cylinder not burning completely. Particulate matter production can be attributed to a variety of sources known in the art, including fuel composition and other factors. An overall reduction in undesirable emissions from the combustion space can be elusive, as reducing one of the undesirable emissions can often result in a substantial increase in another.
Although compression ignition engines are generally associated with diesel fuel, it is known to burn other less reactive fuels utilizing compression ignited diesel fuel to in turn ignite a less reactive fuel, such as natural gas or gasoline. In one specific engine example that was not motivated by emissions, U.S. Pat. No. 3,308,794 teaches a compression ignition engine that combines a small amount of diesel fuel with a predominantly larger volume of gasoline that is injected directly into the engine as a blend. The gasoline is ignited by the burning diesel fuel, which is compression ignited. Although this reference introduces the concept of igniting gasoline with a small amount of compression ignited diesel, it fails to consider emissions issues, nor does it contemplate or recognize that emissions may be reduced with an ability to vary the mixture ratio of gasoline to diesel independent of engine operating conditions.
The present disclosure is directed toward one or more of the problems set forth above.
In one aspect, a fuel system includes a plurality of fuel injectors, a source of gasoline and a source of compression ignition fuel. An electronically controlled mixing ratio control valve has a first inlet fluidly connected to the source of gasoline, and a second inlet fluidly connected to the source of compression ignition fuel. An outlet of the mixing ratio control valve is fluidly connected to a fuel inlet of at least one of the fuel injectors. The mixing ratio control valve is movable among a plurality of configurations corresponding to different ratios of gasoline to compression ignition fuel in the outlet. An electronic controller is in control communication with the mixing ratio control valve.
In another aspect, a method of operating an engine includes compressing air in an engine cylinder beyond and autoignition condition of a compression ignition fuel. A first mixture of gasoline and compression ignition fuel of a first mixture ratio is injected into the engine cylinder. A change to a second mixture ratio is made responsive to a mixture ratio control signal communicated from an electronic controller to the mixing ratio control valve. The second mixture of gasoline and compression ignition fuel of the second mixture ratio is injected into the engine cylinder.
Referring to
In the fuel system 16 illustrated in
Fuel system 16 includes a source of gasoline 20 that is fluidly connected to a first inlet 25 of a mixing ratio control valve 24 via a transfer pump 21. A source of compression ignition fuel 22 is fluidly connected to a second inlet 26 of mixing ratio control valve 24 via a separate transfer pump 23. An outlet 42 of the mixing ratio control valve 24 is fluidly connected to the fuel inlets 40 of each of the fuel injectors 17 via a mixed fuel supply passage 85. Although the fuel system 16 of
Hydraulic fluid pressure from a common rail 34 supplied to a high pressure inlet 55 of each of the fuel injectors 17 provides the means by which the fuel mixture originating from mixing ratio control valve 24 is pressurized to injection levels in each of the individual fuel injectors 17. In the fuel system 16, pressurized compression ignition fuel is utilized as the hydraulic medium, but other available fluids, such as engine lubricating oil, could also be utilized without departing from the present disclosure. A rail supply pump 36 includes an inlet 37 fluidly connected to the source of compression ignition fuel 22 via transfer pump 23. Thus, a portion of the fuel pumped by transfer pump 23 finds its way to mixing ratio control valve 24, and another portion finds its way to common rail 34 via rail supply pump 36. In particular, an outlet 38 from rail supply pump 36 is fluidly connected to an inlet 33 of common rail 34. Common rail 34 may be equipped with a rail pressure limiting valve 88 that returns overpressurization fluid back to the source of compression ignition fuel 22 via a return line 89. After performing work to pressurize the fuel mixture within the fuel injector 17, the used, now low pressure, actuation fluid (compression ignition fuel from common rail 34) leaves each of the fuel injectors 17 at a low pressure drain 56 to be returned to the source of compression ignition fuel 22 via an actuation fluid return line for recirculation. For clarity, only one of the return lines 86 is shown.
Although it is conceivable that a mechanically controlled engine could fall within the scope of the present disclosure, engine 10 illustrated in
Referring now to
The opening and closing of nozzle outlets 41 are enabled by fuel pressurization chamber 51 being pressurized to injection levels and by movement of a directly operated check 59. Directly operated checks are well known in the art and typically include a needle valve member that is biased into a position to close the nozzle outlets by a spring, but the needle valve member also includes a closing hydraulic surface exposed to fluid pressure in a control chamber. When pressure in the control chamber is high, the direct operated check is held closed and the nozzle outlets remain blocked. When pressure in the needle control chamber is low and fuel pressures are at injection levels, the direct operated check may move to an open position to allow the fuel to spray from nozzle outlets 41 in a known manner. In the illustrated embodiment, a needle control actuator 60, which may include a solenoid or piezo is operably coupled to move a needle control valve 61 between a first position in which a needle control chamber 62 is fluidly connected to low pressure fuel inlet 40 via a passage not shown, and a second position at which needle control chamber 62 fluidly connected to a nozzle supply passage 64. In the illustrated embodiment, the needle control chamber 62 is normally fluidly connected to nozzle supply passage 64 when needle control actuator 60 is deenergized, but the needle control chamber 62 becomes blocked to nozzle supply passage 64 and open to a low pressure passage connected to the fuel inlet 40 when energized. Thus, when both pressure control actuator 45 and needle control actuator 60 are energized, fuel may spray from nozzle outlets 41 into the respective engine cylinders 12 in a known manner. Although the needle control valve 61 is shown as a three way valve, other structures would fall within the scope of the present disclosure. In those alternatives, a so called A and Z orifice strategy are utilized and the needle control valve is a two way valve that opens and closes the low pressure fluid connection, whereas the needle control chamber is always fluidly connected to the nozzle supply passage via a small orifice. Such an alternative would also fall within the scope of the present disclosure. In still another alternative, a fuel injector with no direct control of the nozzle outlets would also fall within the intended scope of the present disclosure. In such a case, the needle check would simply be biased to close the nozzle outlets 41 by a spring with a certain pre-load to define a valve opening pressure. The check would include a opening hydraulic surface exposed to fluid pressure in the nozzle supply passage that would push the needle valve member upward to open the nozzle outlets 41 when fuel pressure exceeded the valve opening pressure defined by the biasing spring, and the needle check would close under the action of the spring when fuel pressure dropped below a valve closing pressure associated with the spring and the hydraulic surface areas of the needle check. Thus, those skilled in the art will appreciate that a wide variety of nozzle assemblies with different working structures would all fall within the intended scope of the present disclosure.
Referring now to
A first check valve 28 is fluidly positioned between first inlet 25 and first seat 27, and acts to prevent the back flow of mixed fuel back toward the source of gasoline 20. A second check valve 30 is fluidly positioned between second inlet 26 and second seat 29, and also prevents the back flow of mixed fuel toward the source of compression ignition fuel 22. The outlet 42 opens into the area 31 between first seat 27 and second seat 29. Thus, depending upon the position of valve member 32, the flow areas past respective seats 27 and 29 is changed, and hence the mixture ratio of fuel in area 31 and outlet 42 is changed. When the valve member 32 is in contact to close first seat 27, pure compression ignition fuel flows through mixing control valve 24. On the otherhand, if valve member 32 were in its upper most position closing seat 29, pure gasoline would flow into area 31 and out of outlet 42. Depending upon the pressures produced by transfer pumps 21 and 23 as well as the flow areas past seats 27 and 29, a continuum of different mixture ratios of gasoline to compression ignition fuel can be produced all the way from pure gasoline to pure compression ignition fuel and anywhere in between.
The present disclosure is generally applicable to any compression ignition engine ranging from simple mechanical control through to the most sophisticated multi-wire electronically controlled engines known in the art. The present disclosure finds particular application in compression ignition engines where there is a desire to alter combustion characteristics by utilizing different mixture ratios of a compression ignition fuel with a less reactive fuel such as gasoline. The present disclosure finds potential application in having the ability to control mixture ratios of gasoline to compression ignition fuel in real time and independent engine operating conditions (i.e., speed and load). Engines according to the present disclosure may potentially reduce undesirable emissions produced as a result of the combustion process, and hence may be utilized to relax demands on exhaust aftertreatment systems.
Through testing and the like, engineers can develop maps for desired mixture ratios based upon any number of sensed or known variables including engine speed, engine load, desired emission profiles and other variables. These maps would be stored or accessible by electronic controller 18 and would be utilized to determine, generate and communicate mixing ratio control signals from electronic controller 18 to the linear actuator 70 of mixing ratio control valve 24. Depending upon engine operating conditions and desired combustion characteristics, electronic controller 18 can at any time change a control signal to mixing ratio control valve 24 and change the ratio of gasoline to compression ignition fuel in the supply line 85 The injection pressure may be controlled by electrical controller 18 via suitable control signals delivered to common rail supply pump 36, which may be driven directly by the engine. Finally, the timing at which fuel is pressurized within the fuel injector 17 may be controlled by energizing pressure control actuator 45 at a desired time. The control of the timing of fuel spray from fuel injector 17 is controlled by the timing at which the needle control actuator 60 is energized.
Those skilled in the art will appreciate that different front end and back end rate shaping and the like can be accomplished by varying the relative timing in the actuation and deactivation of the pressure control valve actuator 45 and the needle control actuator 60. For instance, if a ramp type front end shape were desired, the needle control actuator 60 could be energized before or contemporaneously with the pressure control actuator 45. On the otherhand, if a sort of square front end rate shape were desired, the needle control actuator would be energized well after the pressure control actuator has been energized to bring fuel up to injection pressure levels within the fuel injector 17.
When in operation engine 10 compresses air in each individual cylinder beyond an auto ignition condition of the compression ignition fuel. A first mixture of gasoline and compression ignition fuel of a first mixture ratio may be injected into the engine cylinder 12. Electronic controller may then command a change to a second mixture ratio by communicating a different mixture ratio control signal to the mixing ration control valve, which will respond by altering the respective flow areas past seats 27 and 29 (
It should be understood that the above description is intended for illustrative purposes only, and is not intended to limit the scope of the present disclosure in any way. Thus, those skilled in the art will appreciate that other aspects of the disclosure can be obtained from a study of the drawings, the disclosure and the appended claims.
