Patent Application
20080006333
The present invention will be better understood from the description as set forth hereinafter, with reference to the accompanying drawings, in which:
An embodiment of the invention will now be explained with reference to the accompanying drawings.
In
In the multi-fuel system of this embodiment, commercially available regular gasoline is separated through the fuel separator 7 into a high-octane fuel containing much of those components having high octane values and a low-octane fuel containing much of those components having low octane values, and these fuels are fed into an internal combustion engine of a vehicle in accordance with the operating conditions of the vehicle.
Commercially available regular gasoline is supplied into the material fuel tank 5 at, for example, a gas station, and is separated into high-octane fuel and low-octane fuel through the fuel separator 7 while the vehicle is in operation. The high-octane fuel that is separated is stored in the high-octane fuel tank 1, and the low-octane fuel is stored in the low-octane fuel tank 3, respectively, which are then fed into the internal combustion engine (not shown) in the vehicle from the tanks 1 and 3, depending upon the operating conditions.
As the fuel separator 7 in this embodiment, for example, a pervaporation membrane type separator, or a fractional distillation type separator utilizing a difference in boiling point between the high-octane component and the low-octane component, or any type of separator capable of separating commercially available gasoline into high-octane fuel and low-octane fuel can be used.
In the case of the multi-fuel system as shown in
In general, high-octane components in the gasoline have boiling points higher than those of low-octane components, and have lower saturated vapor pressures than those of the low-octane components at the same temperature.
Therefore, the high-octane fuel after being separated has a lower saturated vapor pressure than that of the regular gasoline while, conversely, the low-octane fuel has a higher saturated vapor pressure than that of the regular gasoline.
As described above, regular gasoline has a relatively high saturated vapor pressure. In a normal temperature range experienced by a vehicle, therefore, a mixture having a high fuel concentration is formed in space above the liquid level (vapor space) in the fuel tank 5, and the fuel concentration of the mixture becomes higher than the upper-limit of an ignitable concentration. Therefore, there is no probability that the mixture will catch fire in the vapor space in the tank 5.
However, the high-octane fuel separated from the material fuel through the fuel separator 7 has a saturated vapor pressure lower than that of the regular gasoline. In the vapor space in the high-octane fuel tank 1, therefore, the fuel concentration of the mixture becomes lower than that of the mixture in the material fuel tank 5, and a mixture of a fuel concentration that can catch fire at normal temperature is often formed in the high-octane fuel tank 1.
In the case of commercially available high-octane gasoline as described earlier, the blended components can be adjusted in advance so as to increase the saturated vapor pressure without lowering the octane value. However, when high-octane fuel is formed by separating commercially available regular gasoline by the onboard fuel separating system as in the multi-fuel system of
Therefore, the multi-fuel system shown in
According to this embodiment, it is attempted to prevent the formation of a mixture of air and fuel vapor of an ignitable concentration in the high-octane fuel tank 1 by any one or more of the methods of the following embodiments.
The description of the following embodiments does not indicate the portions that are not directly related to the invention, such as the material fuel tank 5 and the fuel separator 7 in the constitution shown in
In the drawings, further, the same reference numerals denote the same elements.
In this embodiment, a communication pipe 11 is provided for connecting a vapor space above the liquid level in the high-octane fuel tank 1 to the vapor space in the low-octane fuel tank 3. The vapor space in the high-octane fuel tank 1 is further connected to a canister 15 through a vapor pipe 13.
The canister 15 is equipped with an adsorbent such as activated carbon which adsorbs the fuel vapor that flows in from the high-octane fuel tank 1 through the vapor pipe 13 and prevents it from being emitted to the atmosphere.
The fuel vapor adsorbed by the canister 15 is fed, through a purge pipe that is not shown, to an intake passage of the internal combustion engine of the vehicle, and burns in the combustion chambers of the internal combustion engine.
By providing the communication pipe 11 and the vapor pipe 13 as shown in
Therefore, the vapor space in the high-octane fuel tank 1 is filled with fuel vapor having a high saturated vapor pressure from the low-octane fuel tank 3. The saturated vapor pressure of fuel in the low-octane fuel tank 3 is higher than the saturated vapor pressure of the material regular gasoline. Therefore, the fuel concentration of a mixture in the vapor space in the high-octane fuel tank 1 becomes higher than the upper-limit of ignitable concentration, and hence the mixture is prevented from catching fire in the vapor space in the high-octane fuel tank 1.
When the pressure decreases in the tanks 1 and 3 due to variation in the atmospheric temperature, air may flow into the high-octane fuel tank 1 from the canister 15 through the vapor pipe 13, and a mixture that can catch fire may be formed in the vapor space. As shown in
In this case as shown in
In the modification in
In the embodiments of
In the embodiment of
Therefore, the vapor spaces of the high-octane fuel tank 1 and the low-octane fuel tank 3 are connected to each other, and fuel vapor of a high saturated vapor pressure in the vapor space in the low-octane fuel tank 3 flows into the vapor space of the high-octane fuel tank 1. Thus, the formation of a mixture of a concentration in the ignitable range in the high-octane fuel tank 1 does not occur.
Since the high-octane fuel tank 1 is accommodated within the low-octane fuel tank 3 in this embodiment, the space required for installing the fuel tanks, as well as the amounts of pipe works and number of parts, can be reduced compared to the case where separate tanks are used.
In the embodiments of
This embodiment differs from the embodiments of
In
The heater of any kind, such as an electric heater or a heater that uses a hot medium such as hot water, can be used as the heater of this embodiment, provided it is capable of raising the temperature in the high-octane fuel tank 1 up to a predetermined temperature that will be described later.
In this embodiment, the fuel temperature in the tank 1 is raised by the heater 65 in order to increase the saturated vapor pressure of fuel so that the formation of a mixture of an ignitable concentration in the tank 1 does not occur.
A mixture of air and fuel vapor is always formed in the vapor space in the tank 1. When the pressure remains constant in the tank, the fuel concentration in the mixture increases in proportion to the partial pressure of the fuel vapor in the vapor space, i.e., in proportion to the saturated vapor pressure of the fuel vapor.
As can be seen in
In this embodiment, further, the vapor space of the high-octane fuel tank 1 does not communicate with the low-octane fuel tank 3. Therefore, it is possible to completely prevent the fuel in either tank from entering into the other tank through the communication pipe, for whatever reason.
The fuel temperature required for preventing the formation of a mixture of ignitable concentration range varies, depending upon the components of the high-octane fuel after being separated. It is therefore preferable that the set point temperature of the heater 65 be determined through experiments using actual high-octane fuels.
In this embodiment, too, the formation of a mixture of an ignitable concentration in the fuel tank 1 is avoided without introducing fuel vapor in the low-octane fuel tank 3 into the vapor space in the high-octane fuel tank 1.
The embodiment of
This embodiment, however, is different from the embodiment of
In this embodiment, the formation of a mixture of an ignitable concentration in the vapor space in the tank 1 is avoided by lowering the pressure in the high-octane fuel tank 1 by using the vacuum pump 75.
As described earlier, the partial pressure of fuel vapor in the tank 1 becomes equal to the saturated vapor pressure of fuel, irrespective of the pressure in the tank, and hence becomes nearly constant if the fuel temperature is constant. The fuel concentration of the mixture in the vapor space increases in proportion to the ratio of the partial pressure of fuel vapor and the pressure in the tank 1.
In this embodiment, the total pressure in the tank is lowered by the vacuum pump 75 instead of elevating the partial pressure of fuel vapor, and the pressure in the tank is lowered so as to increase the fuel concentration of the mixture in the vapor space in the tank 1.
Therefore, this embodiment makes it possible to obtain the same effect as that of the embodiment of
This embodiment is different from the embodiments explained above in that no vapor space is formed above the liquid fuel level in the tank 1.
In this embodiment as shown in
Further, a vapor pipe 83 is connected to the top of the bladder 81 for connecting the interior of the bladder 81 to the canister 15 through the check valve 17. In this embodiment, the vapor pipe 83 is used for venting air in case air has entered into the bladder. Further, in the case where the fuel temperature in the bladder 81 rises and the saturated vapor pressure becomes higher than atmospheric pressure, fuel vapor is formed in the upper part of the bladder 81. However, this fuel vapor is guided into the canister 15 through the vapor pipe 83 in this embodiment.
The bladder 81 expands and contracts to meet an increase or decrease of fuel therein, and hence the fuel always fills the entire volume of the bladder 81 without vapor space being formed therein.
In this embodiment, therefore, since no mixture of air and fuel vapor is formed in the tank 1, there is no possibility of the mixture catching fire, irrespective of the saturated vapor pressure of the fuel.
Though this embodiment uses a diaphragm or the bladder as variable volume means for varying the tank volume, depending upon an increase or a decrease in the fuel in the tank, any other means may be used, such as a moving separator wall as variable volume means.
