Internal combustion engine

There is provided an internal combustion engine that uses a blended fuel consisting of hydrocarbon and alcohol, and can efficiently operate relative to a wide range of required load. The internal combustion engine includes: intake ports 4a and 4b and two injectors 5a and 5b. The injectors include a first injector 5a that injects a hydrocarbon fuel and a second injector 5b that injects an alcohol fuel. An optimum combustion mode is selected according to an operation state, and the ratio of the alcohol is properly adjusted according to the combustion mode. The intake ports includes a first intake port 4a that guides the hydrocarbon fuel to an inner peripheral portion of a combustion chamber, and a second intake port 4c that guides the alcohol fuel to an outer peripheral portion of the combustion chamber to control octane number distribution in a cylinder. The internal combustion engine further includes separating means 8 for adding water to a blended fuel consisting of alcohol and hydrocarbon to separate into the alcohol fuel consisting of the alcohol and the water and the hydrocarbon fuel.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to an internal combustion engine that uses a blended fuel consisting of hydrocarbon and alcohol.

2. Description of the Related Art

In recent years, compression ignition internal combustion engines such as homogeneous charge compression ignition internal combustion engines have been studied in order to increase gas mileage of an internal combustion engine and reduce emissions. The compression ignition internal combustion engine introduces oxygen-containing gas and fuel capable of compression self-ignition into a cylinder for compression and self-ignition.

However, the compression ignition internal combustion engine has a problem that control of ignition timing is difficult unlike an internal combustion engine of a spark ignition type, and an operable area with stability is narrow. More specifically, this problem is that using a fuel with high ignitability may easily cause knocking when a required load of the engine is increased, and using a fuel with low ignitability may easily cause misfire when the required load of the engine is reduced.

In order to solve the problem, a technique has been known of mixing a fuel with high ignitability and a fuel with low ignitability and supplying the mixed fuels to the engine (for example, see Japanese Patent Laid-Open No. 2001-355471). According to this technique, a mixing ratio between the fuels is adjusted according to a required load of a compression ignition internal combustion engine, thereby allowing a stable operation relative to a wide range of required load. In this technique, however, the fuel with high ignitability and the fuel with low ignitability need to be separately prepared and housed.

On the other hand, a technique has been also known of using a single fuel, and oxidizing part of the fuel when a required load of a compression ignition internal combustion engine is increased, thereby generating ignitability inhibiting substance (for example, see Japanese Patent Laid-Open No. 2000-213444). More specifically, this technique is to oxidize part of a hydrocarbon fuel such as gas oil to generate ignitability inhibiting substance such as formaldehyde. However, partial oxidation of hydrocarbon such as the gas oil to generate formaldehyde requires a long-time reaction at high temperature.

As a fuel of an internal combustion engine, a blended fuel consisting of hydrocarbon and alcohol has been studied. When ethanol is used as the alcohol, the blended fuel can obtain a so-called carbon neutral effect by ethanol, thereby contributing to a reduction in an emission amount of carbon dioxide. The carbon neutral effect means that plants that are raw materials of ethanol absorb carbon dioxide through photosynthesis in its growing process, and thus burning ethanol to generate carbon dioxide is not considered to emit additional carbon dioxide as a whole.

However, when the blended fuel is supplied to a cylinder as a single fuel like gasoline and ignited by spark ignition, a sufficiently high efficiency cannot be obtained.

SUMMARY OF THE INVENTION

The present invention has an object to provide an internal combustion engine that solves the above described problems, uses a blended fuel consisting of hydrocarbon and alcohol, and can efficiently operate relative to a wide range of required load.

In order to achieve the object, the present invention provides an internal combustion engine comprising: intake ports that guide combustion exhaust gas to a combustion chamber; and two injectors that inject fuels to the intake ports, wherein the injectors comprise a first injector that injects a hydrocarbon fuel and a second injector that injects an alcohol fuel.

In the internal combustion engine according to the present invention, the first injector injects the hydrocarbon fuel, and the second injector injects the alcohol fuel, and thus jet quantities of the hydrocarbon fuel and the alcohol fuel can be independently controlled according to a required load of the internal combustion engine. Thus, according to the internal combustion engine of the present invention, jet ratios of the hydrocarbon fuel and the alcohol fuel can be easily adjusted, thereby allowing control to an optimum combustion mode and an efficient operation relative to a wide range of required load.

Specifically, the jet ratios of the hydrocarbon fuel and the alcohol fuel are adjusted so that the ratio of the hydrocarbon fuel injected from the first injector is higher than the ratio of the alcohol fuel injected from the second injector at low load, and the ratio of the alcohol fuel injected from the second injector is higher than the ratio of the hydrocarbon fuel injected from the first injector at high load.

In the internal combustion engine according to the present invention, the combustion chamber may comprise an ignition plug so as to be switchable between self compression ignition and forced ignition with the ignition plug. In this case, the internal combustion engine is controlled to an optimum combustion mode according to a required load. Specifically, when the compression ignition is possible, the ratio of the alcohol fuel is properly maintained, and ignition timing is properly controlled. When the forced ignition with the ignition plug is performed, the ratio of the alcohol fuel is controlled so as to prevent knocking even when ignition timing is set to provide maximum efficiency.

In the internal combustion engine according to the present invention, the intake ports comprise a first intake port that guides the hydrocarbon fuel injected from the first injector to an inner peripheral portion of the combustion chamber, and a second intake port that guides the alcohol fuel injected from the second injector to an outer peripheral portion of the combustion chamber. As the first intake port, for example, a general straight type intake port may be used. As the second intake port, for example, a swirl port may be used.

The first and second intake ports can form octane number distribution in the combustion chamber by the fuels guided to the combustion chamber so that an area with a low octane number is formed in the inner peripheral portion of the combustion chamber and an area with a high octane number is formed in the outer peripheral portion of the combustion chamber, thereby preventing knocking at high load. The first and second intake ports are used together with the adjustment of the jet ratios of the alcohol fuel and the hydrocarbon fuel, thereby further reliably preventing knocking at high load.

Further, the internal combustion engine according to the present invention may separately comprises the alcohol fuel and the hydrocarbon fuel, and preferably comprises separating means for adding water to a blended fuel consisting of alcohol and hydrocarbon to separate into the alcohol fuel consisting of the alcohol and the water and the hydrocarbon fuel consisting of the hydrocarbon.

When the water is added to the blended fuel by the separating means, the alcohol is soluble in the water to form an alcohol/water mixture, while the hydrocarbon is insoluble in the water and separated from the mixture. The mixture containing water has a larger specific gravity than the hydrocarbon, and thus the mixture and the hydrocarbon are separated into two upper and lower layers by gravity. Thus, two kinds of fuels of the alcohol fuel consisting of the mixture and the hydrocarbon fuel consisting of the hydrocarbon can be easily obtained from the single blended fuel by the separating means.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Now, an embodiment of the present invention will be described in more detail with reference to the accompanying drawings.FIG. 1is a system configuration diagram showing an exemplary configuration of an internal combustion engine according to the present invention,FIG. 2shows a variation of in take ports inFIG. 1, andFIG. 3is an illustrative sectional view of a cylinder comprising the intake ports inFIG. 2.

As shown inFIG. 1, the internal combustion engine according to the embodiment comprises a cylinder head2comprising two intake valves1aand1b, and an intake pipe3connected to the intake valves1aand1b. The cylinder head2forms atop of an unshown cylinder, and the cylinder is provided with an ignition plug.

A tip of the intake pipe3is divided into two parts to form an intake port4aconnected to the intake valve1aand an intake port4bconnected to the intake valve1b. The intake ports4aand4bboth are of a straight type, and an injector5athat injects a hydrocarbon fuel to the intake port4a, and an injector5bthat injects an alcohol fuel to the intake port4bare provided in the intake pipe3. The cylinder head2comprises exhaust gas valves6aand6btogether with the intake valves1aand1b, and the exhaust gas valves6aand6bare connected to an unshown exhaust pipe.

The internal combustion engine comprises a fuel tank7that stores a blended fuel consisting of alcohol and hydrocarbon, and a separating device8that adds water to the blended fuel supplied from the fuel tank7to separate the blended fuel into an alcohol fuel consisting of an alcohol/water mixture and a hydrocarbon fuel consisting of hydrocarbon. The separating device8is connected to the injector5avia a conduit9athat supplies the hydrocarbon fuel, and connected to the injector5bvia a conduit9bthat supplies the alcohol fuel.

Further, the internal combustion engine comprises a control device10that controls jet quantities and jet ratios of the hydrocarbon fuel injected from the injector5aand the alcohol fuel injected from the injector5b. The control device10is connected to operation state amount sensors11a,11b, . . . ,11nthat detect various amounts relating to an operation state of the internal combustion engine.

Next, an operation of the internal combustion engine will be described.

The internal combustion engine according to the embodiment uses a blended fuel consisting of liquid hydrocarbon and alcohol such as ethanol, and the blended fuel is stored in the fuel tank7. The blended fuel is supplied from the fuel tank7to the separating device8, and mixed with water added by the separating device8.

The alcohol that constitutes the blended fuel is soluble in water, while the liquid hydrocarbon is insoluble in water. Thus, when the water is mixed with the blended fuel as described above, the alcohol and the water are mixed to form a mixture, while the liquid hydrocarbon is separated. The water/alcohol mixture containing water has a larger specific gravity than the liquid hydrocarbon, and thus the water/alcohol mixture and the liquid hydrocarbon are separated into two upper and lower layers by gravity. Then, a liquid hydrocarbon layer is formed in an upper layer, and a water/alcohol mixture layer is formed in a lower layer.

Then, the conduit9ais connected to a part where the liquid hydrocarbon layer is formed in the separating device8, and the conduit9bis connected to a part where the water/alcohol mixture layer is formed, thereby allowing the liquid hydrocarbon and the water/alcohol mixture to be easily independently drawn. The liquid hydrocarbon separated by the separating device8is supplied as the hydrocarbon fuel to the injector5avia the conduit9a, and the water/alcohol mixture is supplied as the alcohol fuel to the injector5bvia the conduit9b.

In the internal combustion engine according to the embodiment, the operation state amount sensors11a,11b,11ndetect operation state amounts such as the temperature, pressure, torque, or RPM of the engine, and outputs detection signals to the control device10. The control device10grasps an operation state of the engine from the detection signals of the operation state amount sensors11a,11b, . . . ,11nto set an optimum combustion mode. Then, the control device10sets the jet quantities and the jet ratios of the hydrocarbon fuel injected from the injector5aand the alcohol fuel injected from the injector5baccording to the set combustion mode. The jet ratios of the fuels are generally adjusted so that the ratio of the hydrocarbon fuel injected from the injector5ais higher than the ratio of the alcohol fuel injected from the injector5bat low load, and the ratio of the alcohol fuel injected from the injector5bis higher than the ratio of the hydrocarbon fuel injected from the injector5aat high load. For compression ignition, however, the ratio of the alcohol fuel is adjusted so as to obtain optimum ignition timing. For forced ignition with the ignition plug, the ratio of the alcohol fuel is adjusted so as to prevent knocking even when ignition timing is optimum.

Then, the control device10detects knocking. When detecting no knocking, the control device10maintains the setting of the jet quantities and the jet ratios and the setting of the ignition mode. When detecting the knocking, the control device10adjusts the jet quantities and the jet ratios of the fuels so that the ratio of the alcohol fuel injected from the injector5bis increased. The control device10delays the ignition timing of the ignition plug when the ratio of the alcohol fuel injected from the injector5bcannot be increased any more.

In the internal combustion engine according to the embodiment, the jet quantities and the jet ratios of the hydrocarbon fuel injected from the injector5aand the alcohol fuel injected from the injector5bare independently set. Then, the hydrocarbon fuel injected from the injector5aand the alcohol fuel injected from the injector5bare linearly supplied from the straight type intake ports4aand4binto the cylinder, and mixed in the cylinder. Thus, according to the internal combustion engine of the embodiment, an average octane number and an average air/fuel ratio of the fuels injected into the cylinder can be continuously adjusted to prevent knocking at high load.

In the internal combustion engine inFIG. 1, the intake ports4aand4bboth are of the straight type, but as shown inFIG. 2, a swirl type intake port4cmay be used instead of the straight type intake port4b. In the configuration inFIG. 2, the hydrocarbon fuel injected from the injector5ais linearly supplied to the inner peripheral portion of the cylinder by the straight type intake port4a, while the alcohol fuel injected from the injector5bis introduced into the cylinder while being circulated in a curved manner by the swirl type intake port4c, and supplied intensively to the outer peripheral portion of the cylinder by centrifugal force.

Thus, as shown inFIG. 3, a low concentration area15with a low alcohol concentration is formed around an ignition plug13provided in the center of the cylinder12and in the inner peripheral portion of the cylinder12, and a high concentration area14with a high alcohol concentration is formed in the outer peripheral portion along an inner wall of the cylinder12. Thus, in the fuels injected into the cylinder12, octane number distribution can be formed having a lower octane number in the inner peripheral portion of the cylinder12and a higher octane number in the outer peripheral portion, thereby effectively preventing knocking at high load. The octane number distribution can be continuously adjusted by changing the jet ratios of the hydrocarbon fuel injected from the injector5aand the alcohol fuel injected from the injector5b.

In the configuration inFIG. 2, air/fuel ratio distribution may be adjusted by changing the jet quantities of the hydrocarbon fuel injected from the injector5aand the alcohol fuel injected from the injector5b.

In the configuration inFIG. 2, an average octane number and an average air/fuel ratio may be adjusted as in the configuration inFIG. 1. The adjustment of the octane number distribution and the air/fuel ratio distribution is performed together with the adjustment of the average octane number and the average air/fuel ratio, thereby further effectively preventing knocking at high load.

In the internal combustion engine according to the embodiment, the blended fuel consisting of liquid hydrocarbon and alcohol is separated by the separating device8to obtain the hydrocarbon fuel and the alcohol fuel, but the hydrocarbon fuel and the alcohol fuel may be previously housed in different tanks.