JPH09126061A - Exhaust gas reflux device for diesel engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce a discharge amount of NOx by performing EGR at all load areas by a method wherein first and second exhaust gas reflux passages are provided and a cooling device to cool exhaust gas reflux of which is executed through the second exhaust gas reflux passage is arranged, in a device to jointly use liquefied petroleum gas and light oil. SOLUTION: In a diesel engine to jointly use LPG and light oil, one end of a branch pipe 6 is connected to the middle of an exhaust gas pipe 2, and the ends on one side of exhaust gas reflux passages 8 and 9 are connected to the other end of the branch pipe 6 through a two-way switch valve 7. The ends on the other side of the exhaust gas reflux passages 8 and 9 are respectively connected to an intake pipe 3. Further, an EGR valve 10 is located in a spot situated upper stream from the two-way switch valve 7. In a case of an engine load factor being 60% or more, the two-way switch valve 7 is switched so that cold EGR is executed, a part of exhaust gas is introduced to the intake pipe 3 through the exhaust gas reflux passage 9 togetherwith intake air, and after the exhaust gas is cooled in the middle thereof by an intercooler 5, it is sucked in a combustion chamber 1.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to LPG as a fuel.
The present invention relates to an exhaust gas recirculation device for a diesel engine that uses both (liquefied propane gas) and light oil.

[0002]

2. Description of the Related Art It is effective to use an EGR (exhaust gas recirculation) device in order to reduce NOx emissions from an engine. This EGR device mixes a part of the exhaust gas discharged from the engine into the intake air, and the intake air mixed with the exhaust gas suppresses the temperature rise during combustion in the combustion chamber. It is possible to reduce the NOx generated when the temperature becomes high.

As an embodiment of EGR, Japanese Patent Laid-Open No. 6-28
As disclosed in Japanese Patent No. 8306, there are a hot EGR that mixes exhaust gas into the intake air as it is and a cold EGR that mixes exhaust gas into the intake air after being cooled by an intercooler or the like. And has disadvantages.

On the other hand, one of the types of diesel engines is a combination of LPG and light oil as fuel.
This type of diesel engine uses only light oil as a fuel until the engine load reaches a predetermined value (for example, a load factor of 20%), and when the engine load rises more than that, LPG is mixed in the intake air. , LPG mixed air is compressed in the combustion chamber, and light oil is injected into the compressed air mixed with LPG to burn the light oil and LPG. Since LPG has a low carbon content, it produces less black smoke than a diesel engine of the type that uses only light oil as fuel.

[0005]

When hot EGR is used, the temperature of intake air becomes high. Therefore, if this hot EGR is adopted in a diesel engine that uses both LPG and light oil as fuel, the LPG will suddenly increase at high load. It becomes easy to burn and knock. Therefore, in such a diesel engine, EGR cannot be performed at the time of a high load in which the NOx emission amount is the largest.

On the other hand, according to cold EGR, the temperature of intake air becomes low. Therefore, if this cold EGR is adopted in a diesel engine that uses LPG and light oil as fuel, knocking at high load can be prevented, Even under a high load, the EGR can reduce the emission amount of NOx.

However, the amounts of HC and CO discharged at the beginning of LPG injection at low and medium loads are smaller in hot EGR than in cold EGR.

Therefore, the present invention reduces NOx emissions by performing EGR in all load regions in a diesel engine that uses both LPG and light oil as fuel, and prevents knocking at high loads, and , HC and C at the beginning of LPG injection at low / medium load
The amount of O 2 emitted can be reduced.

[0009]

According to the first aspect of the present invention,
In a diesel engine that uses both liquefied propane gas and light oil as fuel, a first exhaust gas recirculation passage that recirculates a portion of exhaust gas from an exhaust pipe to an intake pipe, and a portion of exhaust gas from the exhaust pipe to the intake pipe A second exhaust gas recirculation path for recirculation, a cooling device for cooling the exhaust gas recirculated through the second exhaust gas recirculation path, and an exhaust gas recirculation path for switching between the first exhaust gas recirculation path and the second exhaust gas recirculation path. Since a switching device is included, a part of the exhaust gas is returned to the intake pipe through the first exhaust gas recirculation path by switching the switching device to perform hot EGR, and a part of the exhaust gas is included in the second exhaust gas by switching the switching device. Cold EGR is performed by recirculating to the intake pipe through the recirculation passage.

According to a second aspect of the present invention, in a diesel engine equipped with a turbocharger, which uses liquefied propane gas and light oil together as fuel, a first exhaust gas recirculation for recirculating a part of exhaust gas from an exhaust pipe to an intake pipe. A passage and a second exhaust gas recirculation passage for returning a part of the exhaust gas from the exhaust pipe to the blower side of the turbocharger in the intake pipe;
The switching device has a cooling device for cooling the exhaust gas recirculated through the second exhaust gas recirculation passage and a switching device for switching the exhaust gas recirculation passage between the first exhaust gas recirculation passage and the second exhaust gas recirculation passage. Hot EGR is performed by causing a part of the exhaust gas to recirculate to the intake pipe through the first exhaust gas recirculation passage by switching the above-mentioned, and a part of the exhaust gas is recirculated to the intake pipe through the second exhaust gas recirculation passage by switching the switching device. To perform cold EGR. The exhaust gas recirculated through the second exhaust gas recirculation passage is uniformly mixed into the intake air by the blower.

According to a third aspect of the present invention, in the first or second aspect of the invention, the engine load is less than a predetermined value.
Control means for switching the switching device to recirculate the exhaust gas through the first exhaust gas recirculation passage in the engine operating region, and to recirculate the exhaust gas through the second exhaust gas recirculating passage in the second engine operating region where the load of the engine is a predetermined value or more. Since it is provided, in the first engine operating region where the engine load is small, hot EGR is performed to reduce the emission amount of HC and CO and the NOx emission amount, and in the second engine operating region where the engine load is large. Cold E
By performing GR, knocking is prevented and the amount of NOx emission is reduced.

According to a fourth aspect of the present invention, in the second or third aspect of the present invention, the intercooler is used as the cooling device. Therefore, in the diesel engine equipped with the turbocharger, the intercooler is an existing equipment, and the turbocharger is used. Cold EGR with diesel engine
There is no need to newly provide a cooling device to perform the above.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a schematic diagram showing the overall structure of a diesel engine that uses LPG and light oil as fuel. This diesel engine includes an exhaust pipe 2 that discharges exhaust gas generated by combustion in the combustion chamber 1, an intake pipe 3 that sucks air into the combustion chamber 1, and a turbocharger 4.
It has an intercooler 5 which is a cooling device. The turbocharger 4 has a turbine 4 a arranged at the tip of the exhaust pipe 2 and a blower 4 b arranged in the middle of the intake pipe 3, and the intercooler 5 is arranged in the middle of the intake pipe 3. It is provided in.

One end of a branch pipe 6 is connected in the middle of the exhaust pipe 2 to branch and guide a part of the exhaust gas flowing in the exhaust pipe 2. One end of the first exhaust gas recirculation passage 8 and one end of the second exhaust gas recirculation passage 9 are connected to the other end of the branch pipe 6 via a two-way switching valve 7 that is a switching device. The first
The other end of the exhaust gas recirculation passage 8 is connected to the intake pipe 3 at a position downstream of the intercooler 5, and the other end of the second exhaust gas recirculation passage 9 is connected to the intake pipe 3 upstream of the blower 4b. Are connected in the position. Further, an EGR valve 10 for switching the branch pipe 6 between open and closed is provided upstream of the two-way switching valve 7 in the branch pipe 6.

The intake pipe 3 is provided with a gas injector 11 for controlling the fuel supply amount of LPG, which can be opened and closed. In addition, the gas injector 11 and the LPG
A paper riser 13 for vaporizing LPG is provided between the fuel tank 12 and the fuel tank 12.

Next, in this diesel engine, there is a control means for switching and controlling the two-way switching valve 7, the EGR valve 10, and the gas injector 11 in accordance with the engine load, the engine speed and the like. A controller 14 is provided. As a concrete switching control by the controller 14, the gas injector 11 is put in the “closed” state so that only the light oil is used as the fuel until the engine load reaches a predetermined value (for example, a load factor of 20%). When the load rises above a predetermined value, the gas injector 11 is kept in the "open" state for a certain period according to the load condition of the engine so that the LPG is mixed into the intake air flowing through the intake pipe 3. Further, the exhaust gas is recirculated through the first exhaust gas recirculation passage 8 in the first operating region where the engine load is less than a predetermined value (load factor 60%), and the second engine operating region is in the second engine operating region where the engine load is equal to or more than the predetermined value. The two-way switching valve 7 is switched so that the exhaust gas is recirculated through the exhaust gas recirculation passage 9.

With this structure, when the diesel engine is operated in the EGR state, it is determined whether the engine load factor is less than 60%, as described in the flowchart of FIG. To be done.
If the engine load factor is less than 60%, hot E
The two-way switching valve 7 is switched under the control of the controller 14 so that GR is executed. For this reason, a part of the exhaust gas flowing through the exhaust pipe 2 flows through the branch pipe 6 and the first exhaust gas recirculation passage 8 into the intake pipe 3, and together with the intake air flowing through the intake pipe 3, the combustion chamber 1 Hot EGR is performed by being sucked in.

On the other hand, when the engine load factor is 60% or more, the two-way switching valve 7 is switched by the control of the controller 14 so that cold EGR is executed. Then, a part of the exhaust gas flowing in the exhaust pipe 2 flows in the branch pipe 6 and the second exhaust gas recirculation passage 9, flows into the intake pipe 3 on the upstream side of the blower 4b, and flows into the intake pipe 3. The generated exhaust gas is uniformly mixed with the intake air by the blower 4b. The exhaust gas flows in the intake pipe 3 together with the intake air, is cooled by the intercooler 5 in the middle thereof, and the cooled exhaust gas is sucked into the combustion chamber 1 together with the intake air, whereby cold EGR is performed. Therefore,
Since the exhaust gas for performing cold EGR is cooled by using the intercooler 5 which is the existing equipment in the diesel engine having the turbocharger 4, it is not necessary to provide a new cooling device for cold EGR. It is possible to prevent an increase in points and an increase in manufacturing cost.

Next, in this diesel engine, only light oil is used as fuel until the engine load factor is 20%, and the gas injector 11 is in the "closed" state. On the other hand, when the engine load factor is 20% or more, the gas injector 11 "opens" depending on the operating state of the engine.
State and the LPG stored in the fuel tank 12
Is supplied into the intake air flowing through the intake pipe 3, and LPG and light oil are used together as fuel.

When LPG and light oil are used together as fuel, the second engine load factor of 60% or more is used.
Cold EGR is performed in the operating region. By performing this cold EGR, the temperature of the intake air sucked into the combustion chamber 1 can be suppressed to a low temperature, so that the LPG compressed together with the intake air can be prevented from burning at once in the combustion chamber 1, and the LPG can be prevented. It is possible to prevent knocking that occurs when the fuel is burned at once in the combustion chamber 1. Therefore,
By performing cold EGR at high load,
It is possible to reduce the emission amount of NOx while preventing knocking. Further, since this LPG has a smaller carbon content than light oil, it emits a small amount of black smoke even when operated under a high load condition, and produces a large amount of black smoke even if EGR is performed.
It does not occur that the engine is led into the combustion chamber 1 because a large amount of black smoke is introduced into the combustion chamber 1 due to the EGR.

On the other hand, the first engine load factor of less than 60%
Hot EGR is performed in the operating region. Then, by performing this hot EGR, the temperature of the intake air taken into the combustion chamber 1 becomes high, so that the LP in the intake air is increased.
When the LPG containing a low concentration of G was initially introduced, cold E
Compared to GR, LPG burns better, and HC and C
Emission of O is reduced. Therefore, by performing hot EGR at low and medium loads, it is possible to reduce the emissions of HC and CO at the beginning of LPG injection at the time of this low and medium loads, as well as the emissions of NOx.

[0022]

According to the invention of claim 1, in a diesel engine that uses liquefied propane gas and light oil together as fuel, a switching device switches between hot EGR and cold EGR, and cold EGR is performed at high load. It is possible to prevent knocking and reduce the amount of NOx emission by performing the above, and by performing hot EGR at low and medium loads, HC and CO when the LPG at the beginning of LPG injection is in a lean state.
It is possible to reduce the emission amount of NOx and the emission amount of NOx.

According to the second aspect of the invention, in the diesel engine equipped with a turbocharger, which uses liquefied propane gas and light oil together as fuel, the switching device switches between hot EGR and cold EGR.
By performing cold EGR at high load, knocking can be prevented and NOx emission amount can be reduced, and by performing hot EGR at low / medium load, when the LPG at the beginning of LPG injection is in a lean state. It is possible to reduce the emissions of HC and CO as well as the emissions of NOx. Further, in the case of cold EGR, the exhaust gas recirculated to the intake pipe is recirculated on the upstream side of the blower of the turbocharger. The gas can be uniformly mixed into the intake air by the blower, and good cold EGR can be performed.

According to the invention of claim 3, the hot EG
Switching between R and cold EGR can be automatically performed according to the operating state of the engine, and the EGR in an optimum state can always be executed.

According to the invention described in claim 4, the intercooler is used as the cooling device, the intercooler is the existing equipment in the diesel engine equipped with the turbocharger, and the cold EGR is used in the diesel engine equipped with the turbocharger. It is not necessary to newly provide a cooling device to perform the above, and it is possible to prevent an increase in the number of parts and an increase in manufacturing cost.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing an overall structure of a diesel engine according to an embodiment of the present invention.

FIG. 2 is a graph showing an operating region of an engine in which switching between hot EGR and cold EGR is performed.

FIG. 3 is a flowchart illustrating switching control between hot EGR and cold EGR.

[Explanation of symbols]

 2 exhaust pipe 3 intake pipe 4 turbocharger 4b blower 5 cooling device 7 switching device 8 first exhaust gas recirculation path 9 second exhaust gas recirculation path 14 control means

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[Procedure amendment]

[Submission date] December 22, 1995

[Procedure amendment 1]

[Document name to be amended] Statement

[Correction target item name] Claims

[Correction method] Change

[Correction contents]

[Claims]

[Procedure amendment 2]

[Document name to be amended] Statement

[Correction target item name] 0001

[Correction method] Change

[Correction contents]

[0001]

TECHNICAL FIELD The present invention relates to LPG as a fuel.
The present invention relates to an exhaust gas recirculation device for a diesel engine that uses both (liquefied petroleum gas) and light oil.

[Procedure 3]

[Document name to be amended] Statement

[Correction target item name] 0009

[Correction method] Change

[Correction contents]

[0009]

According to the first aspect of the present invention,
In a diesel engine that uses both liquefied petroleum gas and light oil as fuel, a first exhaust gas recirculation path that recirculates a portion of exhaust gas from an exhaust pipe to an intake pipe, and a portion of exhaust gas from the exhaust pipe to the intake pipe A second exhaust gas recirculation path for recirculation,
The switching device has a cooling device for cooling the exhaust gas recirculated through the second exhaust gas recirculation passage and a switching device for switching the exhaust gas recirculation passage between the first exhaust gas recirculation passage and the second exhaust gas recirculation passage. Hot EGR is performed by causing a part of the exhaust gas to recirculate to the intake pipe through the first exhaust gas recirculation passage by switching the above-mentioned, and a part of the exhaust gas is recirculated to the intake pipe through the second exhaust gas recirculation passage by switching the switching device. To perform cold EGR.

[Procedure amendment 4]

[Document name to be amended] Statement

[Correction target item name] 0010

[Correction method] Change

[Correction contents]

The invention according to claim 2 is a liquefied fossil fuel
In a diesel engine equipped with a turbocharger that uses oil gas and light oil in combination, a first exhaust gas recirculation path that recirculates a portion of exhaust gas from an exhaust pipe to an intake pipe, and a portion of exhaust gas from the exhaust pipe A second exhaust gas recirculation path that recirculates to the blower side of the turbocharger in the intake pipe, a cooling device that cools the exhaust gas that recirculates through this second exhaust gas recirculation path, and an exhaust gas recirculation path that is the first exhaust gas recirculation path. And the switching device for switching to the second exhaust gas recirculation passage, hot EGR is performed by switching part of the exhaust gas to the intake pipe through the first exhaust gas recirculation passage by switching the switching device, and switching of the switching device. Thus, cold EGR is performed by returning a part of the exhaust gas to the intake pipe through the second exhaust gas recirculation passage. The exhaust gas recirculated through the second exhaust gas recirculation passage is uniformly mixed into the intake air by the blower.

[Procedure Amendment 5]

[Document name to be amended] Statement

[Correction target item name] 0022

[Correction method] Change

[Correction contents]

[0022]

According to the invention described in claim 1, in a diesel engine which uses both liquefied petroleum gas and light oil as fuel, hot EGR and cold EG are provided by a switching device.
Switching to R, cold E under heavy load
By performing GR, knocking can be prevented and NOx emissions can be reduced, and by performing hot EGR at low and medium loads, HC and CO emissions when the LPG at the beginning of LPG injection is lean. The amount of NOx can be reduced as well as the amount of NOx.

[Procedure correction 6]

[Document name to be amended] Statement

[Correction target item name] 0023

[Correction method] Change

[Correction contents]

According to the second aspect of the present invention, in a diesel engine equipped with a liquefied petroleum gas and light oil as fuel and equipped with a turbocharger, a switching device switches between hot EGR and cold EGR, and a high load is applied. By performing cold EGR at times, knocking can be prevented and NOx emission amount can be reduced, and by performing hot EGR at low and medium loads, HC when the LPG at the time of LPG injection is low and Reduces CO emissions and NO
The exhaust gas amount of x can be reduced, and the exhaust gas that recirculates to the intake pipe during cold EGR is recirculated upstream of the blower of the turbocharger. Therefore, this exhaust gas is evenly distributed in the intake air by the blower. It can be mixed and good cold EGR can be performed.

Claims (4)

[Claims] 1. A diesel engine that uses both liquefied propane gas and light oil as fuel, and a first exhaust gas recirculation path for returning a part of exhaust gas from an exhaust pipe to an intake pipe, and a part of the exhaust gas for the exhaust pipe. A second exhaust gas recirculation path for recirculating the exhaust gas to the intake pipe, a cooling device for cooling the exhaust gas recirculated through the second exhaust gas recirculation path, and an exhaust gas recirculation path for the first exhaust gas recirculation path and the second exhaust gas recirculation path. An exhaust gas recirculation device for a diesel engine, comprising: a switching device for switching to a recirculation path. 2. A diesel engine equipped with a turbocharger, which uses liquefied propane gas and light oil together as fuel, and a first exhaust gas recirculation path for recirculating a part of exhaust gas from an exhaust pipe to an intake pipe; A second exhaust gas recirculation passage that recirculates a part of the exhaust gas from the exhaust pipe to the blower side of the turbocharger in the intake pipe, a cooling device that cools the exhaust gas recirculated through the second exhaust gas recirculation passage, and an exhaust gas recirculation. An exhaust gas recirculation device for a diesel engine, comprising: a switching device that switches a path between the first exhaust gas recirculation path and the second exhaust gas recirculation path. 3. Exhaust gas is recirculated through a first exhaust gas recirculation passage in a first engine operating region where the engine load is less than a predetermined value, and exhausted through a second exhaust gas recirculation passage in a second engine operating region where the engine load is a predetermined value or more. The exhaust gas recirculation device for a diesel engine according to claim 1 or 2, further comprising control means for switching the switching device so as to recirculate the gas. 4. The exhaust gas recirculation device for a diesel engine according to claim 2, wherein an intercooler is used as the cooling device.