Internal-combustion engines – Charge forming device – Heating of combustible mixture
Reexamination Certificate
1998-10-02
2001-04-10
Wolfe, Willis R. (Department: 3747)
Internal-combustion engines
Charge forming device
Heating of combustible mixture
C123S0270GE
Reexamination Certificate
active
06213104
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a method and a device for supplying fuel to an internal combustion engine. More specifically, the invention relates to a method and a device in which a liquid fuel supplied to the engine is in a supercritical state.
2. Description of the Related Art
In general, a fuel supply system for an internal combustion engine is required to supply liquid fuel to combustion chambers of the engine in the form of a very fine mist. Especially, in a direct cylinder injection system for injecting fuel into the combustion chamber directly, such as the injection system of a diesel engine, the size of particles of the injected fuel largely affects the performance of the engine. In the direct cylinder injection system, the combustion of the fuel in the combustion chamber, and thus the performance of the engine can be largely improved by reducing the size of the particles of the injected fuel.
It is thought that high pressure fuel injection, in which fuel is injected from the fuel injection valve at a very high pressure, is effective in order to reduce the size of the particles of the injected fuel. Therefore, in recent fuel injection systems, the fuel injection pressure is set at a very high value in order to satisfy the requirement for low exhaust gas emission and low fuel consumption. For example, some of the fuel injection systems for diesel engines use a fuel injection pressure as high as more than 50 MPa (500 atm) to generate very fine particles of injected fuel in the combustion chamber.
However, in the high pressure fuel injection system a fuel pump which is capable of pressurizing the fuel to a very high pressure is required. Since the high pressure fuel pump is very expensive, this increases the cost of whole fuel injection system. Further, in the high pressure fuel pump, the clearances between the sliding parts must be small in order to prevent the high pressure fuel from leaking. This tends to cause wear of the sliding parts and lowers the reliability of the pump.
SUMMARY OF THE INVENTION
In view of the problems in the related art as set forth above, the object of the present invention is to provide a method and a device for supplying fuel to internal combustion engine which is capable of improving combustion of an internal combustion engine without using a very high fuel injection pressure.
This object is achieved by a method for supplying fuel to an internal combustion engine wherein the liquid fuel used is a multi-component fuel having a mixture of components, comprising, a step of adjusting a temperature and a pressure of liquid fuel so that all the components of the liquid fuel reach a supercritical state and the liquid fuel becomes fuel in the supercritical state and a step of supplying the fuel in the supercritical state to a combustion chamber of the internal combustion engine wherein the pressure and the temperature in the combustion chamber are selected so that the state of the fuel supplied into the combustion chamber changes from the supercritical phase to a liquid phase in the combustion chamber.
In this aspect of the present invention, the liquid fuel is in a supercritical state, and this supercritical state fuel is supplied to the combustion chamber. In the supercritical state, both the temperature and the pressure of the liquid fuel are higher than the critical values. In this condition, the liquid fuel becomes a gaseous fluid which has a very high density and has physical properties very near to those of a liquid. However, since the pressure and the temperature in the combustion chamber are selected so that the fuel supplied to the combustion chamber changes from the supercritical phase to a liquid phase, when the liquid fuel in the supercritical state is injected from the fuel injection valve into the combustion chamber, it forms a fine mist of fuel and disperses into the combustion chamber. Further, since the fuel mist is generated by a change of phases, i.e., from the supercritical gas phase to the liquid phase, the size of the liquid fuel particles of the mist becomes extremely small.
As explained later, the critical pressure of liquid fuel is relatively low (for example, in case of diesel fuel, the critical pressure is generally much lower than 10 MPa). Therefore, by injecting fuel in the supercritical state, it is possible to improve the combustion of an engine by forming a very fine mist of fuel in the combustion chamber without raising the fuel injection pressure to a very high level.
According to another aspect of the present invention, there is provided a method for supplying fuel to an internal combustion engine for a vehicle comprising a step for reforming liquid fuel by adjusting the temperature and pressure of the fuel on the vehicle in such a manner that at least some of the components of the fuel are in a supercritical state and a step for supplying the fuel, after it is reformed, to a combustion chamber of an internal combustion engine.
In this aspect of the invention, liquid fuel is reformed on the vehicle by bringing the fuel into the supercritical state. Liquid fuel, such as diesel fuel, contains a relatively large amount of heavy components such as normal paraffin components and aromatic hydrocarbons having large molecular weights. These components, when burned in the combustion chamber, form particulate matter (carbon particles) in the exhaust gas. It is found that these heavy normal paraffin components are cracked at a relatively low temperature and produce light components such as normal paraffin having low molecular weight when the fuel is kept in the supercritical state. Therefore, in this aspect of the invention, liquid fuel containing a large amount of heavy components is reformed on the vehicle, and the reformed fuel which contains a large amount of light components is supplied to the combustion chamber of the engine. Therefore, the combustion of the engine is improved.
The reformed fuel may be supplied to the engine in the supercritical state. In this case, the combustion of the engine is further improved due to the improvement in the atomization of the fuel and the increase in the amount of the light components in the supplied fuel.
Further, in the above aspects of the invention, when diesel fuel is used, an oxygen-containing substance may be added to the fuel before it reaches the supercritical state. In this specification, the term “oxygen-containing substance” means a substance such as water or methanol which contains oxygen or a hydroxyl group. When the fuel containing the oxygen-containing substance is burned, production of aromatic hydrocarbons during the combustion is suppressed and, thereby, the combustion is improved. Further, when the fuel containing an oxygen-containing substance is reformed in the supercritical state, production of aromatic hydrocarbons is suppressed during the cracking of heavy normal paraffin. Therefore, the combustion of the engine is improved.
In another aspect of the present invention, there is provided a device for supplying fuel to an internal combustion engine wherein the liquid fuel used is a multi-component fuel having a mixture of components, comprising a fuel tank for storing the liquid fuel, a fuel injection valve for injecting fuel into a combustion chamber of an internal combustion engine wherein the pressure and the temperature in the combustion chamber are selected so that the fuel supplied to the combustion chamber becomes a liquid phase, a fuel supply path between the fuel tank and the fuel injection valve, supercritical state generating means disposed in the fuel supply path between the fuel tank and the fuel injection valve for adjusting a temperature and a pressure of the fuel so that at least some of the components of the liquid fuel reach a supercritical state before the fuel is injected into the combustion chamber.
According to this aspect of the invention, liquid fuel reaches a supercritical state due to the supercritical state generating means before it is injected into the combustion chamber. Ther
Hiei Makoto
Ishikiriyama Mamoru
Kamiya Sumio
Miyazaki Syozi
Takahashi Yasushi
Finnegan Henderson Farabow Garrett & Dunner L.L.P.
Huynh Hai
Toyota Jidosha & Kabushiki Kaisha
Wolfe Willis R.
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