Internal-combustion engines – Charge forming device – Liquid fuel evaporating by extended fuel film
Reexamination Certificate
2000-01-19
2001-02-20
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Liquid fuel evaporating by extended fuel film
C123S514000, C123S516000, C123S557000
Reexamination Certificate
active
06189516
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a fuel vapour extraction system for an internal combustion engine supplied with a volatile liquid fuel from a fuel storage tank, the engine having an air intake system and a liquid fuel injection system for dispensing fuel to mix with air to be burnt in the engine.
BACKGROUND OF THE INVENTION
There are known, in particular from marine applications, fuel vapour extraction systems for an internal combustion engine that is supplied with a volatile liquid fuel from a fuel storage tank and that has an air intake system and a liquid fuel injection system for dispensing fuel to mix with air to be burnt in the engine. The fuel vapour extraction system includes a volatising chamber connected to the fuel storage tank by a valve serving to maintain a constant liquid level of fuel in the chamber and a vapour space above the liquid level in the chamber, and means for drawing vapour from the vapour space in order to maintain a reduced pressure in the volatising chamber. The fuel injection system includes a fuel circulation pump for drawing liquid fuel from the volatising chamber and supplying the fuel under pressure to a fuel rail, fuel injectors for dispensing metered quantities of fuel from the fuel rail to the engine cylinders, a relief valve for maintaining a constant fuel pressure in the fuel rail and a fuel return pipe for returning unused fuel from the fuel rail to the volatising chamber. Examples of such systems are to be found in U.S. Pat. Nos. 5,647,331, 5,115,784 and 5,579,740 and in WO89/06312.
Such systems are employed in marine applications because safety regulations relating to marine vessels in some countries forbid the return of fuel from the injection system to the main fuel storage tank. Instead the fuel is returned to a separate chamber and steps are taken to extract vapour from the latter chamber to avoid vapour lock in the fuel. These systems do not intentionally fraction the fuel to enable the engine management system to make the best use of the different fractions.
U.S. Pat. No. 5,373,825 discloses a fuel vapour extraction system intended for an engine burning a heavy oil that comprises a volatising chamber separate from the fuel tank for intentionally volatising the lighter fraction of the oil. Within the volatising chamber, the oil is heated by a heating element and the lighter fraction of the oil is driven out by the applied heat at substantially ambient air pressure, ambient air being admitted into the chamber to mix with the gasified fuel-and transport it to the air supply of the engine. The remaining liquid fraction that is not gasified is also drawn from the volatising chamber by a fuel injection system and injected into the combustion chamber of the engine. Only a small quantity of surplus oil, that is not injected into the engine, is recycled to the volatising chamber.
This vapour extraction system has the advantage of achieving a continuous supply of fuel vapour, the availability of which can be used to advantage by a suitably designed engine operating with vaporised fuel. However, to achieve a continuous vapour supply, heating energy must be applied continuously to heat the oil which is a drain on the fuel consumption of the engine. The heating element raises the temperature of the oil to a point where the lighter fraction begins to boil and further heating then provides the latent of heat of vaporisation for maintaining a steady gasifying rate.
If the invention is applied to gasoline fuel instead of a heavy oil, the remaining liquid fraction that is drawn from the volatising chamber will be too hot and will need to be cooled before it is delivered to the fuel injection system in order to avoid vapour lock in the fuel injection system. If the bulk of the fuel is recirculated, as occurs in gasoline engines under idle and low load conditions, the system becomes very wasteful of energy as the same fuel is repeatedly heated and then cooled, which is reflected in high fuel consumption.
There are several other disadvantages associated with the application of external heat to the fuel in the volatising chamber. For example, during cold start, there will not be available an adequate supply of vapour until the temperature of the fuel has been raised sufficiently. Furthermore, because of the slow response of the heating element, it will not be possible to increase the vapour flow rapidly when there is sudden increase in the demand for vapour. Also, because of the limited rate at which the heated fuel can be cooled, it will not then be possible to cool the increased flow of the hot liquid fuel sufficiently rapidly before it enters the fuel injection system, thereby risking vapour lock.
OBJECT OF THE INVENTION
The present invention therefore seeks to provide a continuous supply of fuel vapour that does not rely on the use of an externally powered heating element to heat the fuel to promote its vaporisation.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a fuel vapour extraction system for an internal combustion engine supplied with a volatile liquid fuel from a fuel storage tank, the engine having an air intake system and a liquid fuel injection system for dispensing fuel to mix with air to be burnt in the engine, the fuel vapour extraction system including a volatising chamber connected to the fuel storage tank by a valve serving to maintain a constant liquid level of fuel in the chamber and a vapour space above the liquid level in the chamber, and means for drawing vapour from the vapour space in order to maintain a reduced pressure in the volatising chamber, the fuel injection system including a fuel circulation pump for drawing liquid fuel from the volatising chamber and supplying the fuel under pressure to a fuel rail, fuel injectors for dispensing metered quantities of fuel from the fuel rail to the engine cylinders, a relief valve for maintaining a constant fuel pressure in the fuel rail and a fuel return pipe for returning unused fuel from the fuel rail to the volatising chamber, characterised by means within the vapour space of the volatising chamber for promoting evaporation of the return fuel by significantly increasing the surface area to volume ratio of the return fuel.
The means for promoting evaporation can be means for atomising the fuel into fine droplets or the fuel may be allowed to fall on an evaporator of large surface area.
In use, fuel evaporates off the evaporator or from the droplets by virtue of the reduced pressure biasing the vapour equilibrium in the volatising chamber, and in the process cools the remaining fuel by drawing heat from it to supply the latent heat of vaporisation. This heat is replenished by transfer of heat contained in the fuel returning to the volatising chamber after circulating through the fuel rail and picking up waste heat from the fuel pump, the engine block and the engine compartment.
Although the transfer of heat from the fuel is relatively small for each pass of the fuel through the volatising chamber, sufficient heat can still be extracted to support the vapour equilibrium and maintain a steady evaporation rate if the fuel is circulated at a high flow rate.
The volatile liquid fuel in the fuel storage tank may be a single component fuel like methanol, or it may be a blend of hydrocarbon fuels like gasoline having a range of boiling points.
The means for drawing the fuel vapour and maintaining a reduced pressure in the vapour space of the volatising chamber may be a venturi section in the air intake passage leading to the intake system of the engine, or it may be a low pressure region in the intake system of the engine downstream of the engine main throttle. Alternatively these means may be a vacuum pump driven directly or indirectly by the engine.
In contrast with the prior art discussed earlier, the present invention relies on controlling the vapour equilibrium in the volatising chamber to regulate the availability of the vapour. This process is reversible and the exchange of vapour with the liquid may be in either direction
Drouillard Jerome R.
Ford Global Technologies Inc.
Huynh Hai
Wolfe Willis R.
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