The present invention relates generally to tailoring the composition of an engine fuel to meet the engine's drive cycle conditions by utilizing exhaust heat from the engine to provide a plurality of fuel components for engine operation. More specifically the invention is concerned with controlling the temperature of a fuel being fed to a separation device incorporated in an internal combustion engine fuel supply system for separation into a plurality of fuel compositions therein.
The on-board separation of gasoline into a high octane and a low octane fraction for injection into an internal combustion engine at different parts of the drive cycle has been the subject of numerous investigations in recent years and various separation devices have been proposed. To facilitate an understanding of the problems associated with such separations, specific reference is made to the use of a membrane separator in an engine fuel supply system to effect the separation. Such a system is disclosed in U.S. Pat. No. 6,622,663, which is incorporated herein by reference.
In the on-board octane segregation, gasoline is heated to 80-160° C., preferably to about 140° C. before it is fed to a membrane module for separation into high-octane and low-octane fractions. Heating the gasoline using the waste heat in the auto exhaust is an energy efficient approach and conventional heat exchangers have been envisioned as accomplishing such heating. Unfortunately space limitations make use of conventional heat exchangers difficult. Also carefully designed control schemes and equipment are required to assure that the heated gasoline does not exceed 160° C. otherwise reactive components in the gasoline, such as diolefins can react and foul the equipment.
Thus one object of the invention is to provide a novel and effective means of controlling the temperature of a gasoline stream to be fed into a separator incorporated in a fuel system of an internal combustion engine.
Another object is to provide means for heating a gasoline stream to be fed into a separator incorporated in the fuel supply system of an internal combustion engine that can be readily configured to meet space and orientation requirements of the system.
Accordingly, in an internal combustion engine fuel system having a separator for separating a primary fuel into a high octane fuel and a low octane fuel, and wherein the primary fuel is heated for separation in the separator, the improvement comprising a heat pipe having an evaporator section positioned to be in the heat exchange relationship with exhaust gas from the internal combustion engine under conditions of use; and a heat output area in heat exchange relationship with a primary fuel as it is fed into the separator whereby the primary fuel is heated.
In one embodiment the heat pipe is a variable conductance heat pipe having a top operating temperature not greater than about 160° C.
The present invention is particularly suitable for use with a fuel system such as that claimed in U.S. Pat. No. 6,622,663 which is incorporated herein by reference. As can be seen from
In the present invention hot exhaust gases from engine 18 are used to heat the primary fuel supplied to separator 12. This heating is accomplished by means of a heat pipe. As is known a heat pipe comprises a closed, evacuated chamber that contains a thermodynamic working fluid. In operation the working fluid absorbs its latent heat of vaporization in an evaporation section of the pipe and moves the heat to a heat output area where condensation takes place. Condensate returns to the evaporation section by gravity. Alternatively a wick also can be used to return the condensate by capillary forces such as when the heat pipe is oriented substantially horizontally and gravitational forces would not effect return of condensate to the evaporation section.
Thus in the present invention the heat pipe is positioned to have an evaporation section in communication with exhaust gas to transfer heat to the working fluid causing it to be vaporized and flow to the condensation section of the heat pipe. The condensation section of the heat pipe is positioned in heat transfer communication with the primary fuel being fed to the membrane separator. This is shown in
In one embodiment of the invention shown in
One embodiment of a suitable heat pipe configuration is shown in a cross section in
As will be appreciated the heat pipe preferably is one which will limit the temperature of the stream being heated to a value below a threshold. Such heat pipes are referred to as variable conductance heat pipes. Such variable conductance can be achieved for example by selection of an appropriate working fluid. In the practice of the present invention water is the preferred working fluid for heating gasoline to the 140° C. to 160° C. range. Hence, when total vaporization of the water occurs heat transfer in the evaporation section essentially stops and the fuel is not heated above about 160° C. An alternate method is to add a non-condensable inert gas with a working fluid. Of course water-glycol and similar mixtures may be used especially where freezing of the working fluid may be of concern. The wick structure itself may be used to prevent problems associated with freezing. Water frozen inside a wick will exist in small crystals and not cause the mechanical stressed from freezing that can cause the heat pipe to burst when frozen.
Among the advantages of the present invention is that the gasoline feed temperature can be automatically regulated without the need for external controls, valving and the like. The heat will be provided by waste heat, and use of the heat pipe permits various configurations that can be accommodated in the limited spaces on board a vehicle.
Although the present invention has been described with particular reference to a membrane separator other separators may be used. Thus heat may be supplied to effect separation of fuel by distillation. In another embodiment an adsorption type separator may be employed and heat may be supplied in accordance with the invention to desorb from the adsorbent.
This application claims the benefit of U.S. Provisional Application No. 60/602,218 filed Aug. 17, 2004.
Number | Date | Country | |
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60602218 | Aug 2004 | US |