Patent Application
20080295809
The present invention relates generally to a fuel system for combustion engines, and more particularly to an arrangement of a liquid separator and a fuel tank.
Vehicle fuel tanks for volatile hydrocarbon fuels such as gasoline normally contain a volume of liquid fuel and a volume of gas above the liquid fuel. Ambient temperature fluctuations lead to corresponding pressure fluctuations in the fuel tank. Excess pressure buildup in the fuel tank is reduced by a fuel tank venting system that vents fuel vapor out of a vent outlet of the fuel tank, collects and stores the fuel vapor in an activated carbon canister (ACC), and releases the fuel vapor downstream to an operating engine for combustion in the engine.
A liquid separator is placed in fluid communication between the fuel tank and the ACC to prevent carryover of a portion of the liquid fuel from the fuel tank to the ACC. Accordingly, the liquid separator separates and contains some liquid fuel and allows gaseous fuel vapor to pass to the ACC. But, from time to time, the liquid fuel must be transferred from the liquid separator back to the liquid fuel volume of the fuel tank to prevent the liquid separator from filling and blocking flow of gaseous fuel vapor therethrough.
There are three conventional solutions to this problem. First, the liquid separator may be located within the fuel tank and a fuel pump or a jet pump in the fuel tank may be placed in fluid communication with the liquid separator to discharge liquid fuel out of the liquid separator and into the liquid fuel volume of the fuel tank. Second, the liquid separator may be placed in an upper gaseous portion of the fuel tank interior and may include a bottom wall sloped toward a drain opening to discharge liquid fuel by gravity. Third, the liquid separator may be placed above the fuel tank such that a drain port of the liquid separator is higher than the vapor outlet of the fuel tank so that the liquid separator drains liquid fuel to the fuel tank under the force of gravity.
A fuel system according to one implementation includes a fuel tank and a liquid separator. The fuel tank includes an interior in which liquid fuel and fuel vapor are contained, and has at least one vent in fluid communication with a vapor dome in the interior of the fuel tank. The liquid separator is in fluid communication with the at least one vent in the fuel tank, and has a fuel port disposed at a lower elevation than the at least one vent to enable the liquid fuel in the liquid separator to be passively aspirated under negative pressure conditions within the fuel tank.
A method according to one implementation includes emptying a liquid separator. The method includes providing a fuel tank having a vent opening, and providing the liquid separator with a fuel port. The method also includes disposing the liquid separator at an elevation with respect to the fuel tank such that the fuel port is disposed at a lower elevation than the vent opening of the fuel tank to enable the liquid fuel in the liquid separator to be passively aspirated under negative pressure conditions within the fuel tank.
At least some of the objects, features and advantages that may be achieved by at least certain embodiments of the invention include providing a fuel system that does not require a fuel pump or jet to drain liquid fuel from a liquid separator; does not require mounting a liquid separator within an upper interior portion of a fuel tank or above a fuel tank; enables a liquid separator to be mounted inside or outside a fuel tank and to be aspirated under negative pressure conditions within the fuel tank; is of relatively simple design, economical manufacture and assembly, rugged, durable, reliable, and in service has a long useful life.
Of course, other objects, features and advantages will be apparent in view of this disclosure to those skilled in the art. Various other fuel systems embodying the invention may achieve more or less than the noted objects, features or advantages.
These and other objects, features and advantages of the present invention will be apparent from the following detailed description of preferred embodiments and best mode, appended claims, and accompanying drawings in which:
Referring in more detail to the drawings,
The fuel tank 12 may include a fuel filler pipe 18, with a removable closure or cap 19, to admit fuel into an interior 20 of the fuel tank 12, and a vent 22 to permit fuel vapor to be vented out of the interior 20 of the fuel tank 12. The vent 22 may include an opening in a wall of the fuel tank 12, a one-way or two-way check valve in fluid communication with such an opening, or a rollover vent valve in communication with such an opening. In other words, the vent 22 may be any suitable fluid communication feature or device, and includes a vent opening 23. The fuel tank 12 holds liquid fuel 24, which may accumulate up to a predetermined maximum level 26, with a vapor dome 27 above the liquid fuel in the interior of the fuel tank 12. The vapor dome 27 may include a dome-shaped geometric feature but may also include the variable volume gaseous space above the liquid fuel 24. The vent 22 and its vent opening 23 are in fluid communication with the vapor dome 27 and with the conduit 16. An exemplary size of the fuel tank 12 is on the order of about ninety liters.
The liquid separator 14 includes one or more fuel ports 28 to receive incoming fuel vapor and transmit outgoing liquid fuel, and may also include one or more gaseous fuel vapor outlets 30 to transmit outgoing gaseous fuel vapor to a downstream device such as canister 31 with activated carbon. The fuel port(s) 28 may be located at or near a lowermost portion of the liquid separator 14, and the vapor outlet(s) 30 may be located at or near an uppermost portion of the liquid separator 14. The liquid separator 14 defines an interior 32, in which liquid fuel 34 may accumulate up to a predetermined maximum level 36. An exemplary size of the liquid separator 14 is on the order of about 500 ml, with a useable volume on the order of about 250 ml.
In general, the liquid separator 14 may be disposed inside or outside of the fuel tank 12. More specifically, whether disposed inside or outside of the fuel tank 12, the liquid separator 14 is disposed at an elevation with respect to the fuel tank 12 such that the fuel port 28 is disposed at a lower elevation than the vent opening 23 of the fuel tank 12. Even more specifically, the liquid separator 14 may be disposed at an elevation with respect to the fuel tank 12 such that the surface of liquid fuel at its maximum level in the liquid separator 14 is disposed at a lower elevation than the vent opening 23 of the vent 22 in the fuel tank 12. Also, the gaseous fuel vapor outlet 30 may disposed at a higher elevation than the fuel port 28, and is preferably disposed as high as possible for better liquid vapor separation. Also, for example, the fuel port 28 may be disposed within about 5 to 400 mm lower than the vent 22. Furthermore, the fuel port 28 may be disposed at a higher elevation than the maximum liquid fuel level 26 in the fuel tank 12. In an exemplary fuel system, for every 1 mm in height differential between the fuel port 28 and the vent opening 23, about 0.01 kPa in negative fuel tank pressure may be required to aspirate liquid fuel from the liquid separator 14 to the fuel tank 12.
In use, some portion of the liquid fuel 24 in the fuel tank 12 is converted to fuel vapor, which is vented (along with any liquid fuel) through the opening 23 of the vent 22, through the conduit 16, and into the liquid separator 14. Thereafter, some portion of the liquid fuel is separated from the vented fuel vapor and retained in the liquid separator 14 and the fuel vapor is communicated to some useful downstream device such as an ACC and/or an operating engine. According to three exemplary conditions, when pressure in the fuel tank 12 is negative, liquid fuel 34 in the liquid separator 14 is passively aspirated out of the fuel port 28, through the conduit 16, through the opening 23 of the vent 22, and back into the fuel tank 12. Such conditions are discussed below in turn with reference to
In
In any case, the liquid separator 114 may be disposed at an elevation with respect to the fuel tank 112 such that its fuel port 128 is disposed at a lower elevation than a vent opening 123 of the fuel tank 112. Even more specifically, the liquid separator 114 may be disposed at an elevation with respect to the fuel tank 112 such that the surface of liquid fuel at its maximum level in the liquid separator 114 is disposed at a lower elevation than the vent opening 123 of the vent 122 in the fuel tank 112. Furthermore, the fuel port 128 may be disposed at a higher elevation than a maximum liquid fuel level 126 in the fuel tank 112.
One of the conditions occurs when a vehicle is driven downhill, wherein atmospheric pressure increases, thereby creating a relative pressure decrease in a fuel tank. For example, when a vehicle drives from about 2500 meters above sea level to about 500 meters above sea level, atmospheric pressure increases from about 750 mbar (75 kPa) to about 950 mbar (95 kPa). In other words, such vehicle descent results in a pressure increase of about 20 kPa over 2000 meters of descent, or about 0.01 kPa/meter. Again, for every 1 millimeter (mm) in vertical height differential between the surface of liquid fuel at its maximum level in the exemplary liquid separator and the fuel tank vent opening, about 0.01 kPa in negative fuel tank pressure may be required to aspirate liquid fuel from an exemplary liquid separator into its fuel tank. Thus, for a 10 mm height differential, a 10 m vehicle descent is required to aspirate fuel from the exemplary liquid separator into the fuel tank.
Another condition occurs when fuel tank temperature decreases, such as after a vehicle is stopped, shut down, and parked for an extended period. An exemplary reduction in fuel tank temperature ranges from about 40° C. to about 28° C. The ideal gas law may be simplified to P×V/T=constant, wherein P is gas pressure in a vessel, V is gas volume of the vessel, and T is gas temperature ° K in the vessel. Accordingly, P1×V1/T1=P2×V2/T2, wherein V2=V1+ΔV. For a fuel volume ΔV=αv×Vfuel×ΔT, a volume expansion factor for a typical automotive gasoline αv=0.0011 K−1.
An exemplary test involved a height differential of about 25 mm between a surface of liquid fuel at its maximum level in a liquid separator and a fuel tank vent opening. At this height differential, a negative pressure of about 0.25 kPA is required to aspirate the liquid separator. According to the exemplary test, an initial tank pressure P1 was about 107 kPa, the initial vapor volume V1 was about 80 liters (l) and initial liquid fuel volume was about 10 l of a total fuel tank volume of about 90 l , and an initial temperature T1 of about 39° C. (312 K) was noted. After about 6.5 minutes of vehicle shut down, liquid fuel began flowing from the liquid separator into the fuel tank and an interim temperature T2 of about 37° C. (310 K) was noted.
From the equations described above, ΔV=0.0011 K−1 (10 l×2 K)=0.022 l and, thus, an interim volume V2=80 l+0.022 l 80.02 l. Therefore, an interim pressure P2=(P1×V1/T1)/(V2/T2)=(107 kPa×80 l/312 K)/(80.02 l/310 K)=106.3 kPA. The pressure dr about 0.7 kPa between initial and interim pressures P1 and P2 exceeds the 0.25 kPa needed and, thus, aspiration of the liquid separator began. After about 18 minutes, all liquid fuel was aspirated out of the liquid separator and pressure in the fuel tank and liquid separator equalized, such that an end pressure P3 was zero.
A further condition occurs when a vehicle is initially started after the vehicle has been shut down for an extended period. Because the temperature is basically constant, under the simplified ideal gas law, P×V=constant, so that P1×V1=P2×V2. Thus, P2=P1×V1/V2 for the gas volume in a fuel tank. V2=V1+VFC (volume of fuel pumped out of the fuel tank for consumption by the engine).
Parameter values during one exemplary test include 1 liter per hour (lph) fuel consumption, initial gas pressure P1 of about 1 bar atmospheric pressure, and initial gas volume V1 of about 20 l. Under these conditions, about 1.2 minutes after vehicle startup, fuel began flowing from the liquid separator to the fuel tank. Accordingly, an interim gas volume V2=20 l+(1 lph×1.2/60 h)=20.02 l. Thus, interim gas pressure P2=1 bar×20 l/20.02 l=0.99 bar. Thus, the pressure drop in the fuel tank at the start of aspiration was about 0.01 bar or 1 kPa. The 100 ml of fuel in the liquid separator is aspirated at the rate of the fuel consumption of 1 lph. Accordingly, the period over which the liquid separator is aspirated can be calculated as follows: (1000 ml/60 min)/100 ml=6 minutes. Therefore, the liquid separator is aspirated within about 7.2 minutes after vehicle startup in this example.
While the forms of the invention herein disclosed constitute presently preferred embodiments, many others are possible. It is not intended herein to mention all the possible equivalent forms or ramifications of the invention. It is understood that the terms used herein are merely descriptive, rather than limiting, and that various changes may be made without departing from the spirit or scope of the invention.
This application claims the benefit of U.S. Provisional Application Ser. No. 60/941,532 filed Jun. 1, 2007. The content of the above application is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 60941532 | Jun 2007 | US |
