JP6957752B2 - Internal combustion engine and nitrogen enrichment device - Google Patents

Description

The present invention uses nitrogen-enriched air as combustion air and performs combustion so that the mixing ratio of oxygen and fuel becomes the theoretical mixing ratio, and nitrogen-enriched engine suitable for this type of internal combustion engine. Regarding the device.

According to Patent Document 1, as an internal combustion engine for a vehicle, a part of oxygen in the air is removed to generate nitrogen-enriched air, and this nitrogen-enriched air is supplied to the combustion chamber of the internal combustion engine to provide a theoretical air-fuel ratio. An internal combustion engine is disclosed in which combustion is performed with a larger air-fuel ratio. In Patent Document 1, a nitrogen-enriched air generating unit in which a large number of polyimide resin hollow fibers are bundled is used, and heated and pressurized air is introduced into the center hole of the hollow fiber to oxygenate the wall of the hollow fiber. The structure is such that nitrogen-enriched air is obtained by the passage of molecules.

In the above-mentioned Patent Document 1, there is no particular disclosure about the composition of the space on the side where oxygen is discharged, and it is considered that the atmosphere, that is, the air having a normal oxygen concentration exists on the outside of the hollow fiber through which oxygen permeates. Therefore, essentially no oxygen partial pressure difference can be obtained between the inside and outside of the hollow fiber wall. Therefore, in order to remove oxygen and enrich the nitrogen, it is inevitably necessary to pressurize the air to a high pressure and introduce it into the hollow fiber. However, even if the air is pressurized in this way, the desired nitrogen richness is required. It may not be possible to achieve the conversion level.

Japanese Unexamined Patent Publication No. 2004-190570

In the present invention, the exhaust gas of an internal combustion engine is introduced as a sweep gas that assists the removal of oxygen into a nitrogen-enriched device for obtaining nitrogen-enriched air to be used for combustion.

Since the exhaust gas discharged from the internal combustion engine is a gas having a low oxygen concentration, the efficiency of oxygen removal from the air is improved by introducing this exhaust gas as a sweep gas into the nitrogen enrichment device.

According to the present invention, the efficiency of oxygen removal is improved by using the exhaust gas discharged by the internal combustion engine itself as the sweep gas introduced into the nitrogen enrichment device. Therefore, it becomes easy to obtain a high nitrogen enrichment level.

The explanatory view which shows typically the structure of the intake / exhaust system of the internal combustion engine which concerns on this invention. Explanatory drawing which shows an example of a sheet-like gas separation membrane. Explanatory drawing which shows an example of a hollow membrane as a gas separation membrane. The perspective view which shows an example of a gas separation membrane element in a partially cut-out form.

Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings.

FIG. 1 is a configuration explanatory view schematically showing a configuration of an intake / exhaust system of an internal combustion engine for a vehicle according to an embodiment to which the present invention is applied. The internal combustion engine 1 is an internal combustion engine that mainly burns in the vicinity of a theoretical mixing ratio (here, the mixing ratio means a mixing ratio of oxygen and fuel). For example, a spark of a 4-stroke cycle using gasoline as fuel. It consists of an ignition type internal combustion engine. Each cylinder of the internal combustion engine 1 is provided with a fuel injection valve 2 for supplying fuel into the cylinder and a spark plug 3 for igniting the air-fuel mixture formed in the cylinder. .. An intake port 6 opened and closed by an intake valve 5 and an exhaust port 8 opened and closed by an exhaust valve 7 are connected to the combustion chamber 4 of each cylinder. The fuel injection valve 2 may be arranged so as to inject fuel toward the intake port 6 upstream of the intake valve 5, which may be a so-called intake port injection type configuration. The fuel injection amount (in other words, the injection period) and the injection timing by the fuel injection valve 2 and the ignition timing by the spark plug 3 are controlled by the engine controller 10, respectively.

The internal combustion engine 1 includes, for example, a turbocharger 11 as a supercharger for supercharging the intake air. The turbocharger 11 includes a turbine 12 and a compressor 13.

A nitrogen enrichment device 16 is arranged in the middle of the intake passage 15 leading to the intake port 6 of the internal combustion engine 1 to generate nitrogen-enriched air by partially removing oxygen from the air taken in from the outside. An electronically controlled throttle valve 17 whose opening degree is controlled by a control signal from the engine controller 10 is arranged between the outlet of the nitrogen enrichment device 16 and the intake port 6 in the intake passage 15. The compressor 13 of the turbocharger 11 is located on the upstream side of the nitrogen enrichment device 16 in the intake passage 15, and further, the flow rate of air taken in from the outside (for example, mass flow rate) is measured on the upstream side of the compressor 13. An air flow meter 18 is provided. An air cleaner (not shown) is arranged on the upstream side of the air flow meter 18. Further, between the compressor 13 and the nitrogen enrichment device 16, for example, a water-cooled or air-cooled intercooler 19 for cooling the air flow compressed by the compressor 13 and having a high temperature is provided.

A catalyst converter 22 using a three-way catalyst for purifying exhaust gas is arranged in the middle of the passage 21 of the exhaust passage 21 connected to the exhaust port 8. The catalytic converter 22 is located on the downstream side of the turbine 12. An air-fuel ratio sensor 23 for detecting the so-called exhaust air-fuel ratio is arranged on the upstream side of the catalyst converter 22, that is, between the turbine 12 and the catalyst converter 22. The air-fuel ratio sensor 23 may be a so-called linear air-fuel ratio sensor that can obtain an output according to the exhaust air-fuel ratio, or an output indicating whether it is leaner or richer than the theoretical air-fuel ratio equivalent can be obtained. It may be a so-called O2 sensor. A silencer (not shown) is provided on the downstream side of the catalytic converter 22, and the tip of the exhaust passage 21 is open to the atmosphere via the silencer.

Further, on the downstream side of the catalytic converter 22, the exhaust branch passage 25 branches from the exhaust passage 21. The tip of the exhaust branch passage 25 is connected to the nitrogen enrichment device 16, and guides the exhaust gas to the nitrogen enrichment device 16 as a sweep gas that assists the removal of oxygen in the nitrogen enrichment device 16. In the middle of the exhaust branch passage 25, for example, a water-cooled or air-cooled exhaust gas cooler 26 for cooling the exhaust flow before being introduced into the nitrogen enrichment device 16 is provided. The tip side of the exhaust branch passage 25 further extending from the nitrogen enrichment device 16 may be open to the atmosphere as it is, or the exhaust passage 21 and the exhaust passage 21 are located upstream or downstream of the silencer (not shown) and downstream of the catalytic converter 22. It may be configured to merge.

In addition to the above-mentioned air flow meter 18 and air-fuel ratio sensor 23, the engine controller 10 includes a crank angle sensor (not shown) that indicates the engine rotation speed, and an accelerator (not shown) that detects the amount of depression of the accelerator pedal by the driver. Various sensors such as an opening sensor are connected.

The nitrogen enrichment device 16 includes an intake chamber 31 in which air taken in from the outside through an air cleaner (not shown) is introduced through an intake passage 15, and an exhaust chamber 32 in which exhaust gas is introduced through an exhaust branch passage 25. A gas separation film 33 that separates the intake chamber 31 and the exhaust chamber 32 from each other and allows oxygen to selectively permeate is provided. Therefore, a part of oxygen in the air flowing through the intake chamber 31 moves to the exhaust chamber 32 side through the gas separation membrane 33. Assuming that the intake passage 15 on the inlet side of the intake chamber 31 is referred to as the intake inlet passage 15A and the intake passage 15 on the outlet side of the intake chamber 31 is referred to as the intake outlet passage 15B, the intake inlet passage 15A has the same composition as the air. Air having (about 79% nitrogen, about 21% oxygen) flows, and a part of oxygen is removed from the intake outlet passage 15B, and nitrogen-enriched air containing a relatively large amount of nitrogen flows out. Further, assuming that the exhaust branch passage 25 on the inlet side of the exhaust chamber 32 is referred to as the exhaust inlet passage 25A and the exhaust branch passage 25 on the outlet side of the exhaust chamber 32 is referred to as the exhaust outlet passage 25B, the exhaust inlet passage 25A is essentially. Exhaust gas containing almost no oxygen flows out, and exhaust gas accompanied by oxygen that has passed through the gas separation film 33 flows out from the exhaust outlet passage 25B.

The gas separation membrane 33 is made of, for example, a known polymer membrane, and may be a sheet-like membrane as shown in FIG. 2 or a hollow membrane as shown in FIG.

That is, in the example of FIG. 2, the gas separation membrane 33 is configured as a sheet-like membrane 33 that separates the intake chamber 31 and the exhaust chamber 32. The sheet-like membrane 33 may be a self-supporting membrane that can be handled by itself, or is a composite membrane in which a separation function layer that selectively permeates oxygen and a support layer that supports the separation functional layer are laminated. May be good. Air flows on one side of the intake chamber 31 that sandwiches the sheet-like membrane 33 as shown by an arrow A, and exhaust gas that becomes a sweep gas flows on the other side of the exhaust chamber 32 as shown by an arrow G. Then, oxygen in the air flow A permeates through the sheet-like membrane 33 as shown by the arrow O2, and is discharged into the exhaust gas flow G which becomes the sweep gas. In the figure, the air flow A and the exhaust gas flow G flow in the same direction, but the air flow A and the exhaust gas flow G may flow in opposite directions.

In the example of FIG. 3, the gas separation membrane 33 is configured as a hollow membrane 33. That is, it is formed in a tubular shape having a relatively large diameter or a so-called hollow thread shape having a relatively small diameter. The hollow membrane 33 may be a self-supporting membrane that can be handled by itself, or is a composite membrane in which a separation function layer that selectively permeates oxygen and a support layer that supports the separation functional layer are laminated. May be good. In the example of the composite membrane, for example, a separation function layer is provided on the outer peripheral surface of the hollow support layer. In one example, air flows on the outside of the hollow membrane 33 as shown by an arrow A, and exhaust gas as a sweep gas flows on the inside of the hollow membrane 33 as shown by an arrow G. In the figure, the air flow A and the exhaust gas flow G flow in the same direction, but the air flow A and the exhaust gas flow G may flow in opposite directions.

In one preferred embodiment, in the nitrogen enrichment apparatus 16, as the gas separation membrane 33, a spiral type or pleated type gas separation membrane element in which the sheet-like membrane 33 is integrated and integrated is used. The gas separation membrane element is provided with a flow path that guides the flow of exhaust gas on the side of the exhaust chamber 32.

FIG. 4 shows a configuration example of the spiral type gas separation membrane element 41. The gas separation membrane element 41 spirally winds a plurality of sheet-shaped leaves 42 together with an air-side flow path member 43 around a gas collecting pipe 46 in which a plurality of gas passage holes (not shown) are opened. The nitrogen enrichment device 16 is configured by accommodating the gas separation membrane element 41 in a cylindrical casing (not shown).

Each leaf 42 is formed by superimposing a sheet-like film 33a and a sheet-like film 33b and adhering them to each other with an adhesive at a peripheral edge portion 42a, as shown by developing and cutting a part thereof. A gas-side flow path member 45 having a gap that allows the gas to flow between the facing surfaces of the sheet-like film 33a and the sheet-like film 33b is sandwiched between the sheet-like film 33a and the sheet-like film 33b. Examples of the structure of the gas-side flow path member 45 having a communication gap include a net, a mesh, and knitting. Further, in addition to the peripheral edge portion 42a, the sheet-like film 33a and the sheet-like film 33b are also adhered to each other in the partition portion 42b. The peripheral portion 42a and the partition portion 42b may have the sheet-like film 33a and the sheet-like film 33b adhered to each other via the gas-side flow path member 45. As a result, a flow path 47 through which the exhaust gas flows in a U-turn is formed inside the leaf 42 (that is, between the sheet-like film 33 and the sheet-like film 33b) as shown by an arrow G. The partition portion 42b is not limited to the shape shown in FIG. 4, and it is preferable that the partition portion 42b is provided so as to suppress the retention of the exhaust gas flow inside the leaf 42 and to spread the exhaust gas over the entire surface of the sheet-like film. One end of the exhaust gas flow path 47 in the leaf 42 communicates with the inlet portion 46a of the gas collecting pipe 46, and the other end communicates with the outlet portion. That is, the exhaust gas introduced from the inlet portion 46a of the gas collecting pipe 46 as shown by an arrow G1 flows through the U-turn-shaped flow path 47 inside each leaf 42, and exits at the other end of the gas collecting pipe 46. It is discharged from the portion as shown by the arrow G2.

Further, the air-side flow path member 43 interposed between the leaves 42 preferably has a structure having a communication gap so as to secure a flow path for air between two adjacent leaves 42, for example, a net. Examples include mesh and knitting. Air is guided to flow along the axial direction from one end to the other end of the cylindrical casing. That is, air flows along the surface of the sheet-like film 33 of each leaf 42 as shown by an arrow A. When the air flows in this way, a part of oxygen passes to the exhaust gas side through the sheet-like membrane 33. Therefore, the air flowing as shown by the arrow A becomes nitrogen-enriched air and flows out from the gas separation membrane element 41.

A configuration similar to the spiral type gas separation membrane element 41 described above is described in International Publication WO 2016/024523. A configuration example of a pleated gas separation membrane element is described in Japanese Patent Application Laid-Open No. 2007-222841. In the present invention, these known gas separation membrane elements can be used.

In the internal combustion engine 1 configured as described above, nitrogen-enriched air is generated by partially removing oxygen from the air in the nitrogen-enriching device 16, and the nitrogen-enriched air is used as the combustion chamber 4 of the internal combustion engine 1. It is supplied to and used for combustion. The injection amount of fuel supplied from the fuel injection valve 2 and the flow rate of the nitrogen-enriched air introduced into the combustion chamber 4 via the throttle valve 17 are determined by the known feedback control using the air-fuel ratio sensor 23 to determine the exhaust air-fuel ratio. Is controlled to be equivalent to the stoichiometric air-fuel ratio, in other words, the mixing ratio of oxygen and fuel in the combustion chamber 4 is controlled to be the stoichiometric mixing ratio. For example, the torque generated by the internal combustion engine 1 is detected or estimated in some way, the opening degree of the throttle valve 17 is controlled so that the torque according to the driver's request can be obtained, and then the fuel is adjusted to the theoretical mixing ratio. It is possible to control the injection amount by feedback. As a result, HC, CO, and NOx in the exhaust gas are simultaneously purified by the three-way catalyst of the catalyst converter 22.

It is also possible to estimate the oxygen concentration in the combustion chamber 4 by detecting the in-cylinder pressure with an in-cylinder pressure sensor (not shown), and the amount of oxygen in the combustion chamber 4 is calculated together with the amount of air detected by the air flow meter 18. You may ask for it.

By using nitrogen-enriched air having an oxygen concentration lower than that of the atmosphere as the combustion air, the amount of air required for the theoretical mixing ratio is increased. That is, the apparent air-fuel ratio becomes large. As a result, the combustion temperature is lowered and the combustion efficiency is improved as in the case of a general lean burn engine. Moreover, since the pumping loss is also reduced, the fuel consumption rate is improved along with the improvement of the combustion efficiency. On the other hand, unlike a general lean burn engine, there is no oxygen that is excessive with respect to the amount of fuel, so the generation of NOx is essentially reduced due to the low combustion temperature, and the reduction treatment under the catalyst is performed. It will be possible. Therefore, it is possible to simultaneously purify HC, CO, and NOx in the exhaust gas with a general three-way catalyst.

Here, in the configuration in which the exhaust gas of the internal combustion engine 1 is introduced as the sweep gas into the nitrogen enrichment device 16 as in the above embodiment, since the oxygen concentration in the exhaust gas is low, the gas separation membrane 33 is used. The efficiency of oxygen removal is increased. That is, the amount of oxygen permeated by the gas separation membrane 33 depends on the difference in oxygen partial pressure between one side and the other side of the gas separation membrane 33. Exhaust gas whose oxygen is consumed by combustion has a very low oxygen concentration in nature, and by using this as a sweep gas, it is possible to effectively support the removal of oxygen through the gas separation membrane 33. can. Therefore, it is possible to obtain a high nitrogen enrichment level with a relatively small nitrogen enrichment device 16. In other words, oxygen can be efficiently removed even if the difference in absolute pressure between the intake chamber 31 side and the exhaust chamber 32 side is small. The nitrogen enrichment level can be adjusted by the flow rate of the sweep gas. As a method of adjusting the flow rate of the sweep gas, for example, the distribution ratio of the exhaust gas distributed to the exhaust branch passage 25 of FIG. 1 can be used, and as a means of adjusting the distribution ratio, the exhaust gas downstream of the exhaust branch passage 25 A flow rate adjusting valve (not shown) provided in the passage 21 can be mentioned. This flow rate adjusting valve may be controlled by the engine controller 10.

For example, assuming that the theoretical air-fuel ratio is 14.7, in order to raise the apparent air-fuel ratio to around 30, the oxygen concentration, which is about 21% in the atmosphere, is halved, and the oxygen concentration is as high as 10% and nitrogen is about 90%. It is necessary to produce nitrogen-enriched air at the nitrogen-enriched level. If the destination of oxygen is the atmosphere as in the past, there is essentially no difference in oxygen partial pressure, so even if the absolute pressure is increased by a supercharger, the efficiency of oxygen removal is low. Therefore, such nitrogen It is generally difficult to obtain nitrogen-enriched air with high enrichment levels. Alternatively, a very large nitrogen enrichment device that is difficult to mount in a vehicle is required.

On the other hand, according to the above embodiment, a high level of nitrogen-enriched air can be easily generated by a relatively small nitrogen-enriching device 16 that can be mounted on a vehicle. In particular, in the above embodiment, the exhaust gas after passing through the three-way catalyst is introduced into the nitrogen enrichment device 16 as a sweep gas. Since the oxygen remaining in the exhaust gas is also consumed by passing through the three-way catalyst in this way, the exhaust gas introduced into the nitrogen enrichment device 16 contains almost no oxygen. Therefore, as compared with the case where the exhaust gas before passing through the three-way catalyst is introduced, the efficiency of oxygen removal can be further increased, and the subsidizing action of oxygen removal by the exhaust gas becomes more stable.

Further, in the above embodiment, since the air introduced into the intake chamber 31 is pressurized by the turbocharger 11, the absolute pressure can be higher than that of the exhaust gas in the exhaust chamber 32. By pressurizing the air in this way, oxygen removal becomes more efficient.

In one embodiment, as in the example described above, it is possible to generate nitrogen-enriched air with a high nitrogen-enriched level of about 10% oxygen and 90% nitrogen, whereby combustion at a theoretical mixing ratio is possible. It can be realized as having an apparent air-fuel ratio of about 30.

Further, since the exhaust gas serving as the sweep gas that assists oxygen removal is a gas that is simply generated by the operation or combustion of the internal combustion engine 1, no additional device for generating the sweep gas is required. Moreover, there is no additional energy consumption associated with the generation of sweep gas. Therefore, the improvement in fuel consumption performance obtained by increasing the apparent air-fuel ratio is not offset by the generation of sweep gas.

Although one embodiment of the present invention has been described in detail above, the present invention is not limited to the above embodiment, and various modifications can be made.

For example, the nitrogen enrichment device is not limited to the one using the polymer membrane of the above embodiment, and any type of nitrogen enrichment device may be used as long as the removed oxygen moves to the sweep gas. ..

Claims (7)

A spark-ignition internal combustion engine that operates with a mixture ratio of oxygen and fuel near the theoretical mixture ratio.
A nitrogen-enriching device that removes some oxygen from the outside air to obtain nitrogen-enriched air for combustion.
The three-way catalyst provided in the exhaust passage and
A means for feedback-controlling the mixing ratio to the vicinity of the theoretical mixing ratio by using an air-fuel ratio sensor so that HC, CO, and NOx in the exhaust gas of the internal combustion engine are simultaneously purified in the three-way catalyst.
With
During the feedback control , the nitrogen enricher introduces exhaust gas that has passed through the three-way catalyst as a sweep gas that assists in the removal of oxygen.
An internal combustion engine in which nitrogen-enriched air obtained by partially removing oxygen by this sweep gas is supplied to the combustion chamber of the internal combustion engine. The sweep gas is a gas that contains almost no oxygen as the exhaust gas passes through the three-way catalyst.
The internal combustion engine according to claim 1, wherein nitrogen-enriched air is obtained by moving a part of oxygen in the external air introduced into the nitrogen-enriching device to the sweep gas. The above nitrogen enrichment device
The intake chamber where outside air is introduced and
The exhaust chamber where the above exhaust gas is introduced and
A gas separation membrane through which oxygen selectively passes, and
With
The internal combustion engine according to claim 1 or 2, wherein the gas separation membrane is arranged so as to separate the intake chamber and the exhaust chamber. Further equipped with a supercharger that pressurizes the air taken in from the outside,
The internal combustion engine according to any one of claims 1 to 3, wherein air pressurized by the supercharger is introduced into the nitrogen enrichment device. It is a nitrogen enrichment device provided in a spark-ignition internal combustion engine that operates near the theoretical mixture ratio by feedback control using an air-fuel ratio sensor for the mixture ratio of oxygen and fuel.
This nitrogen enricher is
The intake chamber where outside air is introduced and nitrogen-enriched air is discharged,
A gas separation membrane that partially removes oxygen from the air,
As a sweep gas that assists in the removal of oxygen, an exhaust chamber into which the exhaust gas of the internal combustion engine purified by the three-way catalyst under the above feedback control is introduced, and
With
The nitrogen-enriched air discharged from the intake chamber is configured to be supplied to the combustion chamber of the internal combustion engine, and is also configured.
A nitrogen enrichment device in which the gas separation membrane is arranged so as to separate the intake chamber and the exhaust chamber. The nitrogen enrichment apparatus according to claim 5 , wherein the gas separation membrane is a sheet-like membrane or a hollow membrane. The gas separation membrane is a spiral type or pleated type gas separation membrane element in which the sheet-like membrane is integrated and integrated.
The nitrogen enrichment device according to claim 6 , wherein the gas separation membrane element includes a flow path for guiding a gas flow on the side of the exhaust chamber.

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