JP3551779B2 - Internal combustion engine having lean NOx catalyst - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention is used as a three-way catalyst in an internal combustion engine having a lean NOx catalyst, more specifically, a catalytic converter which is an exhaust gas purifying means provided in an exhaust system of the internal combustion engine. The present invention relates to an internal combustion engine having a lean NOx catalyst that purifies nitrogen oxides in exhaust gas using a reducing agent when in a state.
[0002]
[Prior art]
A catalyst used in internal combustion engines where the atmosphere in the exhaust system such as gasoline lean burn engines and diesel engines is excessive in oxygen and low in hydrocarbons and carbon monoxide, and uses nitrogen oxides as hydrocarbons and carbon monoxide as reducing agents. A so-called lean NOx catalyst for purifying the catalyst is disclosed, for example, in Japanese Patent Application Laid-Open No. HEI 6-117225.
[0003]
This publication describes a technique in which a lean NOx catalyst purifies nitrogen oxides by using a hydrocarbon as a reducing agent. Hydrocarbons partially oxidize to form active species, which react with nitrogen oxides to reduce nitrogen oxides and produce nitrogen, hydrogen, oxygen, and carbon dioxide that are harmless to the human body I do. Hydrocarbons are the main components of gasoline and light oil that serve as fuel for internal combustion engines. Therefore, supplying the hydrocarbon as the reducing agent is nothing but extra supply of gasoline, light oil and other combustion fuel for internal combustion engines separately from the intended use.
[0004]
According to the technology described in the above publication, the supply of hydrocarbons to the lean NOx catalyst is performed separately from the supply by injection during a suction-compression stroke by a fuel injection device usually performed in an internal combustion engine. This is achieved by performing extra injection during the expansion stroke and the exhaust stroke. Of these injections, the former normal injection is called main injection, and the latter extra injection is called sub injection.
[0005]
[Problems to be solved by the invention]
However, in the technique described in this publication, the same fuel injection device is used for performing the main injection and the sub-injection, so the number of injections of the fuel injection device is larger than that in the case of only the main injection. For this reason, the burden on the fuel injection device increases, which may cause a failure of the fuel injection device.
[0006]
SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and enables an internal combustion engine having a lean NOx catalyst to supply a reducing agent such as hydrocarbons to the lean NOx catalyst without using a sub-injection. Thus, it is a technical problem to solve the above-mentioned adverse effects.
[0007]
[Means for Solving the Problems]
In order to solve the above problems, the internal combustion engine having the lean NOx catalyst of the present invention employs the following means.
(1) In an internal combustion engine having, in an exhaust system, a lean NOx catalyst for purifying nitrogen oxides in an oxygen-excess exhaust gas using a reducing agent, the concentration of carbon dioxide in intake air flowing through an intake system of the internal combustion engine is determined. It is characterized by comprising a concentration increasing means for increasing.
[0008]
Here, the “concentration increasing means” may be any means that can increase the concentration of carbon dioxide in the relative comparison between carbon dioxide and the other components among the components in the intake air containing carbon dioxide. Therefore, even if the concentration increasing means is means for adding carbon dioxide to the intake system, it is a means capable of increasing the concentration of carbon dioxide in comparison with other components by reducing other components in the intake gas. Or any.
[0009]
However, as the concentration increasing means, means for increasing the concentration of carbon dioxide in the intake system by using carbon dioxide contained in the outgas which is a gas immediately after exiting from the exhaust port of the internal combustion engine body, for example, exhaust gas recirculation It does not include so-called EGR, which is a device. In other words, the concentration increasing means is intended for a means capable of adding carbon dioxide having a concentration higher than the concentration of carbon dioxide contained in exhaust gas circulated to the intake system by the EGR to the intake system. Since the EGR reuses the combustion gas of the internal combustion engine, the concentration of carbon dioxide contained in the exhaust gas recirculated gas recirculated to the intake system by the EGR is variable depending on the combustion state of the internal combustion engine. Therefore, means for increasing the concentration of carbon dioxide in the intake system by using carbon dioxide contained in the outgas, such as EGR, is excluded because it is difficult to control the concentration of carbon dioxide.
[0010]
When the concentration of carbon dioxide increases in the intake system by the concentration increasing means, the reaction from hydrocarbons to carbon monoxide and from carbon monoxide to carbon dioxide becomes difficult. In extreme terms, if carbon dioxide is in a saturated state, the oxidation reaction between hydrocarbons that produce carbon dioxide and carbon monoxide will not proceed easily, so that hydrocarbons and carbon monoxide will be free in the exhaust gas of the internal combustion engine. In large amounts.
[0011]
That is, in the internal combustion engine having the lean NOx catalyst of the present invention, the proportion of the hydrocarbon and carbon monoxide alone in the exhaust gas of the internal combustion engine increases. Therefore, the lean NOx catalyst can very effectively purify nitrogen oxides by using these hydrocarbons and carbon monoxide as reducing agents.
[0012]
Since hydrocarbons and carbon monoxide are used as a reducing agent for nitrogen oxides, the supply of hydrocarbons, that is, the supply of fuel for combustion of the internal combustion engine is performed by sub-injection by a fuel injection device as in the related art. No need. That is, in the present invention, there is no technical concept of auxiliary injection. For this reason, if the amount of generation of hydrocarbons and carbon monoxide can be controlled well, the harm caused by the sub-injection, that is, the load on the fuel injection device can be reduced, and the fuel injection device can be hardly broken down.
(2) In the above item (1), the concentration increasing means is preferably an addition device for adding carbon dioxide to the intake system.
(3) In the above item (2), the addition device is a combustion device provided separately from the main body of the internal combustion engine, and the combustion gas emitted from the combustion device is introduced into an intake system of the internal combustion engine. Is desirable.
[0013]
Here, as the "combustion device", specifically, a combustion-type heater device using fuel for combustion of the internal combustion engine as a fuel is preferable. The combustion type heater device includes a combustion chamber main body, an air supply path for supplying combustion air to the combustion chamber main body from an intake pipe of the internal combustion engine, and a combustion chamber main body supplied from the air supply path to the combustion chamber main body. And a combustion gas discharge passage for discharging the burned combustion gas to the intake pipe.
[0014]
Further, the meaning of the "combustion device is provided separately from the main body of the internal combustion engine" means that the combustion device performs its own combustion without being affected by combustion in the cylinder of the internal combustion engine main body at all. This means that exhaust gas is set to be discharged to the intake pipe through the combustion gas discharge path.
(4) In the above item (3), it is preferable that the combustion device performs combustion at a pressure lower than a pressure at the time of combustion in a cylinder of the internal combustion engine.
[0015]
The “low pressure” here is, for example, the atmospheric pressure. This is because fuel is more likely to vaporize at lower atmospheric pressure than in a high-pressure cylinder of an internal combustion engine, and can be burned near the stoichiometric air-fuel ratio to increase the carbon dioxide emission concentration. In other words, it burns cleanly according to the theory, so the proportion of carbon dioxide in the combustion gas is high.
(5) In the above item (4), the combustion device operates when it is necessary to purify nitrogen oxides by the lean NOx catalyst.
[0016]
Here, "when it is necessary to purify nitrogen oxides by the lean NOx catalyst" means when specific conditions for purifying nitrogen oxides are met. The specific condition is, for example, when the catalyst is activated. That is, in the continuous selective reduction, the catalyst is not activated immediately after the engine is started because the catalyst is not activated immediately after the engine is started, but after a while, the catalyst is activated and functions. Therefore, when the purification of nitrogen oxides by the lean NOx catalyst is required, in the case of selective reduction, it is when the catalyst is activated and functions. In the case of intermittent storage reduction, the catalyst absorbs too much nitrogen oxide, that is, when the nitrogen oxide is in a saturated state.
(6) In the above item (3), the combustion device may be operated when the internal combustion engine is in a predetermined operation state, burn fuel, and warm engine-related elements with heat of combustion gas generated at the time of the combustion. .
[0017]
Here, "when the internal combustion engine is in a predetermined operating state" means that the internal combustion engine is operating during cold or extreme cold or after the internal combustion engine is started, and, for example, due to low fuel consumption. That is, when the amount of heat generated by the internal combustion engine itself is small and when the amount of heat received by the cooling water is small. The term “cold” refers to a time when the outside air temperature is approximately −10 ° C. to about 15 ° C., and the term “extremely cold” refers to a time when the outside air temperature is lower than approximately −10 ° C.
[0018]
The “engine-related element” refers to the engine cooling water or the internal combustion engine itself into which the combustion gas of the combustion type heater is introduced into the intake air.
(7) In the above item (1), the lean NOx catalyst may be a storage reduction type NOx catalyst.
[0019]
Here, the “storage reduction type” means that nitrogen oxides are sucked into a catalyst and temporarily held there, and then the hydrocarbons and / or carbon monoxide are supplied to the catalyst in an appropriate amount to purify the nitrogen oxides at once. This is an intermittent processing method.
(8) In the above item (1), the lean NOx catalyst may be a selective reduction type NOx catalyst.
[0020]
Here, the “selective reduction method” refers to a continuous treatment method for simultaneously and continuously purifying nitrogen oxides, hydrocarbons and carbon monoxide.
(9) When purifying nitrogen oxides with the lean NOx catalyst in the above item (6), it is preferable to make the air-fuel ratio of the combustion device rich.
[0021]
If the air-fuel ratio is rich, the amount of fuel in the air-fuel mixture in the combustion device is large, and the proportion of hydrocarbons and carbon monoxide as reducing agents increases accordingly, so that the lean NOx catalyst can easily purify nitrogen oxides. .
(10) In the above item (6), when it is necessary to purify the nitrogen oxides by the lean NOx catalyst during the operation of the combustion device, the fuel injection timing by the fuel injection device may be retarded. The fuel injection timing is originally set so that the fuel efficiency is optimized. However, if the fuel injection timing is retarded, the combustion is delayed accordingly. If the combustion is slow, the fuel that should be burned remains unburned, and the rate of generation of unburned gas increases. Therefore, the rate of hydrocarbons and carbon monoxide increases, and the lean NOx catalyst easily purifies nitrogen oxides.
(11) In the above item (10) It is preferable that the lean NOx catalyst is a storage reduction type NOx catalyst.
[0022]
Further, according to the internal combustion engine having the lean NOx catalyst of the present invention, the following operation and effect can be further obtained.
(1) By mixing the combustion gas emitted from the combustion device that operates when the internal combustion engine is in a predetermined operation state into the intake pipe of the internal combustion engine, fresh air flowing up to that point in the intake pipe becomes the combustion heat of the combustion gas. And the combustion gas is mixed with the intake air. Therefore, the warm-up can be promoted and the performance of the vehicle interior heater can be improved by utilizing the combustion heat of the combustion device. If a combustion heater is used as the combustion device, this is a warming-up promoting device usually provided in an internal combustion engine, and therefore, the combustion heater can be used in combination as a means for increasing the concentration of carbon dioxide.
[0023]
{Circle around (2)} Then, the combustion type heater emits a combustion gas having substantially no smoke, that is, a carbon dioxide-rich combustion gas containing no carbon. Therefore, if the combustion gas emitted from such a combustion type heater is sucked into the internal combustion engine, there is no concern about the wear and corrosion of the internal combustion engine as compared with the conventionally known EGR device, and the durability is improved. And it is possible to reduce nitrogen oxides from a low water temperature.
[0024]
(3) In addition, carbon dioxide itself has an effect of suppressing smoke. This is for the following reason. That is, thermal dissociation of carbon dioxide (that is, at ambient temperature of 1400 ° C., CO 2 ₂ → 2CO + O ₂ ) Re-burns soot and carbon dioxide oxidizes the produced carbon (ie, CO 2 ₂ + C → 2CO), the effect of suppressing smoke can be expected even when the internal combustion engine is under a high load.
[0025]
{Circle around (4)} Low-fuel-consumption engines such as diesel engines and gasoline-lean-burn engines use less combustion fuel, so that heat loss to cooling water is originally small. Therefore, the warm-up property of the internal combustion engine tends to be deteriorated even at room temperature, but the warm-up property can be greatly improved by operating the combustion type heater when necessary. As a result, emission during warm-up can be significantly improved. Moreover, in the combustion type heater, the combustion gas is introduced into the intake system via the combustion gas discharge path, and eventually reaches the cylinder of the internal combustion engine. Increase the amount of heat received. Therefore, the heater performance is improved.
[0026]
{Circle over (5)} Unburned components in the combustion gas at the time of starting the combustion type heater, etc., are burned again in the internal combustion engine, and when the unburned components reach the exhaust system of the internal combustion engine, the lean NOx catalyst provided in the exhaust system causes Can be purified.
[0027]
{Circle around (6)} Further, since the air supply passage and the combustion gas discharge passage of the combustion type heater are not directly open to the atmosphere, a noise reduction effect can be expected.
[0028]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings.
<Overall description of device>
The engine 1 as an internal combustion engine is a water-cooled type, and has an engine body 3 having a water jacket (not shown) through which cooling water circulates, and an intake device for feeding air necessary for combustion into a plurality of cylinders (not shown) of the engine body 3. 5, an exhaust device 7 for discharging exhaust gas after the air-fuel mixture has burned in the cylinder to the atmosphere, and a vehicle interior heater 9 for warming the interior of the vehicle in which the engine 1 is mounted. As the engine 1, a diesel engine or a direct injection gasoline lean burn engine is applied.
[0029]
The intake device 5 has an air cleaner 13 that takes in fresh air into a cylinder as a start end of the intake device 5. Then, between the air cleaner 13 and an intake port (not shown) of the engine body 3 at the end of the intake device 5, the compressor 15a of the turbocharger 15, which is an intake system structure, and the combustion of the engine body 3 in a cylinder (not shown). The combustion type heater 17, the intercooler 19, and the intake manifold 21 which burn under the atmospheric pressure which is lower than the pressure.
[0030]
These intake system structures belong to an intake pipe 23 having a plurality of connecting pipes.
The intake pipe 23 is divided into a downstream connection pipe 27 in which the outside air entering the intake device 5 is forcibly pushed by the compressor 15a to be in a pressurized state, and an upstream connection pipe 25 in which the outside air does not enter. Can be roughly classified.
[0031]
In FIG. 1, an upstream connecting pipe 25 includes a main pipe 29 having a rod shape extending straight from the air cleaner 13 toward the compressor 15 a, and a branch pipe 31 for a heater as a branch pipe connected to the main pipe 29 in a bypass shape. Consists of
[0032]
An outside air temperature sensor 32 is attached to a location near the downstream side of the air cleaner 13 in the main pipe 29. The outside air A entering the main flow pipe 29 from the air cleaner 13 is fresh air for the engine 1 and the combustion heater 17, and the temperature thereof is detected by the outside air temperature sensor 32.
[0033]
The heater branch pipe 31 includes the combustion type heater 17 in the middle thereof, connects the upstream portion of the combustion type heater 17 in the air flow direction with the main flow pipe 29, and supplies fresh air from the main flow pipe 29 to the combustion type heater 17. That is, a combustion (exhaust) gas which connects the air supply passage 33 for supplying air, a downstream portion of the combustion type heater 17 in the air flow direction with the main flow pipe 29, and outputs combustion (exhaust) gas from the combustion type heater 17 to the main flow pipe 29. And a gas discharge path 35. The air relating to the heater branch pipe 31 means not only the fresh air a1 but also the combustion gas a2 emitted from the combustion type heater 17. The combustion gas of the combustion type heater 17 is a gas which has almost no smoke, in other words, does not contain carbon. Therefore, it does not hinder use as intake air of the internal combustion engine.
[0034]
A combustion gas temperature sensor 36 and a CO 2 for detecting the concentration of carbon dioxide contained in the combustion gas are provided in a portion of the combustion gas discharge passage 35 near the combustion heater 17. ₂ A sensor 37 is mounted. The temperature of the combustion gas of the combustion type heater 17 before entering the main pipe 29 from the combustion type heater 17 by the combustion gas temperature sensor 36, ₂ The sensor 37 detects the concentration of carbon dioxide in the combustion gas.
[0035]
Further, of the connection points C1 and C2 of the air supply path 33 and the combustion gas discharge path 35 with the main pipe 29, the connection point C1 is located on the upstream side of the main pipe 29 from the connection point C2. Therefore, the outside air A from the air cleaner 13 is first divided into air a1 that branches off to the branch pipe 31 for the heater at the connection point C1 and air a1 ′ that branches the main flow pipe 29 to the connection point C2 without branching. In this case, the air a2 branched off at the connection point C1 and subjected to combustion by the combustion type heater 17 to become the combustion gas and the fresh air a1 ′ not branched off at the C1 merge into the combustion gas mixed air a3.
[0036]
The air a1 branched at the connection point C1 returns to the main pipe 29 as air a2 from the connection point C2 via the air supply path 33, the combustion heater 17 and the combustion gas discharge path 35. The air a2 returning to the main flow pipe 29 is a combustion gas having heat by being burned by the combustion type heater 17 burning under atmospheric pressure, and thus contains a large amount of carbon dioxide. When this gas is returned to the main pipe 29 and merges with the unbranched air a1 'at the connection point C2 to become the combustion gas mixed air a3, the combustion gas mixed air a3 contains a large amount of carbon dioxide. With this, intake air enters the engine body 3. The state of combustion of the combustion heater 17 is controlled, and the concentration of carbon dioxide can be freely adjusted by this control method.
[0037]
In FIG. 1, the downstream connecting pipe 27 is a pipe connecting the compressor 15a and the intake manifold 21, and the one shown in FIG. 1 has an L shape. Further, an intercooler 19 is arranged at a position near the intake manifold 21.
[0038]
On the other hand, the exhaust device 7 has an exhaust port (not shown) of the engine body 3 as a start end of the exhaust device 7 and an exhaust manifold 38, a turbine 15b of the turbocharger 15 and a catalyst between the exhaust port 7 and a muffler 41 at the end of the exhaust device 7. The converter 39 is provided on the exhaust pipe 42. The air flowing through the exhaust device 7 is indicated by reference numeral a4 as the exhaust gas of the engine 1.
[0039]
The catalytic converter 39 uses a lean NOx catalyst as a three-way catalyst in the inside thereof, and uses a reducing agent to reduce nitrogen oxides in the exhaust gas when the exhaust system is particularly in an oxygen-excess atmosphere state, that is, in a lean state. To purify. As the lean NOx catalyst, there are a selective reduction type and an occlusion reduction type, and either type may be used.
[0040]
Next, the structure of the combustion heater 17 is schematically shown in FIG.
The combustion heater 17 is connected to the water jacket of the engine body 3, and the combustion heater 17 has a cooling water passage 17a through which cooling water flows from the water jacket. The cooling water flowing in the cooling water passage 17a (indicated by a broken line arrow in FIG. 2) passes around a combustion chamber 17d which is a combustion part formed inside the combustion type heater 17, and passes therethrough. It is warmed by receiving heat from the combustion chamber 17d. This will be described in detail sequentially.
[0041]
The combustion chamber 17d includes a combustion tube 17b that emits a flame, and a cylindrical partition 17c that covers the combustion tube 17b to prevent the flame from leaking to the outside. The combustion chamber 17d is defined in the partition 17c by covering the combustion cylinder 17b with the partition 17c. The partition wall 17c is also covered by an outer wall 43a of the combustion heater 17, and a space is provided between the two. By providing this space, the cooling water passage 17a is formed between the inner surface of the outer wall 43a and the outer surface of the partition wall 17c.
[0042]
The combustion chamber 17d has an air supply port 17d1 and an exhaust discharge port 17d2 that are directly connected to the air supply path 33 and the combustion gas discharge path 35, respectively. The air a1 sent from the air supply path 33 enters the combustion chamber 17d from the air supply port 17d1 and travels therethrough to reach the exhaust discharge port 17d2. As described above, the air flows into the main pipe 29 as air a2. Therefore, the combustion chamber 17d is in the form of an air passage through which the air a1 changed by combustion passes through the air a2 in the combustion type heater 17.
[0043]
Then, after the combustion type heater 17 is burned, the air a2 returned to the main pipe 29 via the combustion gas discharge path 35 has heat because it is so-called exhaust gas discharged from the combustion type heater 17. Until the heated air a2 is discharged from the combustion heater 17, the heat of the air a2 is transmitted to the cooling water flowing through the cooling water passage 17a through the partition wall 17c, as described above. Warm the cooling water. Therefore, the combustion chamber 17d is also a heat exchange passage.
[0044]
The combustion cylinder 17b includes a fuel supply pipe 17e connected to a fuel pump (not shown), and receives the pump pressure of the fuel pump therefrom to supply combustion fuel to the combustion cylinder 17b. The supplied combustion fuel is vaporized in the combustion heater 17 to become vaporized fuel, and the vaporized fuel is ignited by an ignition source (not shown).
[0045]
Since the air supply passage 33 and the combustion gas discharge passage 35 are used only for the combustion type heater 17, they can be said to be members belonging to the combustion type heater 17.
Next, circulation of cooling water to the cooling water passage 17a will be described.
[0046]
The cooling water passage 17a has a cooling water inlet 17a1 connected to the water jacket of the engine body 3, and a cooling water outlet 17a2 connected to the vehicle interior heater 9.
[0047]
A water pipe W1 is interposed between the cooling water inlet 17a1 and the engine body 3, and a water pipe W2 is connected between the cooling water outlet 17a2 and the vehicle interior heater 9. The combustion heater 17 is connected to the water jacket of the engine body 3 and the vehicle heater 9 via the water pipes W1 and W2. Further, the vehicle interior heater 9 and the engine body 3 are also connected via a water pipe W3.
[0048]
Therefore, the cooling water in the water jacket of the engine body 3 flows in the following order: (1) from the cooling water inlet 17a1 to the combustion heater 17 via the water pipe W1, where it is heated. (2) This warmed cooling water reaches the vehicle interior heater 9 from the cooling water discharge port 17a2 of the combustion type heater 17 via the water pipe W2. (3) Then, the cooling water is subjected to heat exchange by the vehicle interior heater 9 to lower the temperature, and then returns to the water jacket via the water pipe W3.
[0049]
In this manner, the cooling water circulates between the engine body 3, the combustion type heater 17, and the vehicle interior heater 9 via the water pipe W1, the water pipe W2, and the water pipe W3.
In addition, a central processing controller (CPU) 47 for controlling the combustion heater 17 which is separate from the blower fan 45 and the engine electronic control unit (ECU) 46 is provided inside the combustion chamber main body 43. ing.
[0050]
The ECU 46 includes an outside air temperature sensor 32, a combustion gas temperature sensor 36, ₂ The sensor 37 and the rotation speed sensor 59 are electrically connected to the blower fan 45 and the fuel pump. When the CPU 47 determines that it is necessary to purify the nitrogen oxides by the lean NOx catalyst 39 in accordance with the parameters of the sensors 32, 36, 37, and 59, the combustion state of the combustion heater 17 is appropriately controlled, The momentum, size, temperature and the like of the flame of the combustion type heater 17 are maintained in an optimum state. By controlling the combustion state of the combustion heater 17 by the CPU 47, the temperature of the exhaust gas (combustion gas) of the combustion heater 17 and the amount of carbon dioxide contained in the combustion gas are adjusted.
[0051]
In the main pipe 29, between the connection points C1 and C2 of the air supply path 33 and the combustion gas discharge path 35 with the main pipe 29, in other words, in the main pipe 29, the combustion gas discharge path 35 An air flow meter 70 is provided upstream of the connection point C2 with the main flow pipe 29. The air flow meter 70 used in this embodiment is a hot wire type or film type air flow meter having a small pressure difference between the inlet side and the outlet side.
[0052]
What has been described above is the internal combustion engine I having the lean NOx catalyst according to the embodiment of the present invention.
<Effects of Embodiment>
Next, the operation and effect of the internal combustion engine I having such a lean NOx catalyst will be described.
[0053]
According to the internal combustion engine I having the lean NOx catalyst 39, the concentration of carbon dioxide in the intake system increases because the combustion gas a2 of the combustion heater 17 reaches the intake pipe 23 through the combustion gas discharge passage 35. Then, in the combustion in the cylinder of the engine body 3, the reaction from hydrocarbon to carbon monoxide and from carbon monoxide to carbon dioxide hardly occur.
[0054]
In other words, if it is considered in extreme terms that carbon dioxide is saturated in the cylinder, the chemical reaction between the hydrocarbon constituting carbon dioxide and carbon monoxide does not easily proceed, so that the hydrocarbon as the NOx reducing agent and the carbon monoxide Are in a free state and in an appropriate amount. Therefore, purification of nitrogen oxides can be made extremely effective.
[0055]
FIGS. 3, 4 and 5 compare the difference between the internal combustion engine I having the lean NOx catalyst and the conventional technology by the difference in the amount of generated nitrogen oxides, hydrocarbons and carbon monoxide. .
[0056]
FIGS. 3, 4 and 5 show the proportions of nitrogen oxides, hydrocarbons and carbon monoxide in the outgassing, respectively. The solid line in each figure is from the prior art, and the dashed line is from the internal combustion engine I having a lean NOx catalyst. The vertical axis of each figure indicates the amount of each harmful substance generated, and the horizontal axis indicates the timing of fuel injection timing by crank angle. The numerical value shown on the horizontal axis is the crank angle, and the numerical value 0 means the top dead center. Therefore, the more the vehicle moves to the right side of the drawing from 0, the so-called advance angle, and the further to the left side, the so-called retard angle.
[0057]
From these FIGS. 3A and 3B, it can be seen that the purification of nitrogen oxides is extremely effective because the inclination angle of the graph is extremely small. 4 and 5 that hydrocarbons and carbon monoxide are generated in larger amounts at all crank angles than before.
[0058]
Further, according to the internal combustion engine I having the lean NOx catalyst, the ratio of the presence of hydrocarbon and carbon monoxide alone increases. Since hydrocarbons and carbon monoxide are used as reducing agents, there is no need to supply hydrocarbons by sub-injection as in the prior art.
[0059]
For this reason, if the amount of generation of hydrocarbons and carbon monoxide can be controlled well, the harm caused by the sub-injection, that is, the load on the fuel injection device can be reduced, and the fuel injection device is less likely to fail. Further, purification of nitrogen oxides can be suitably controlled.
[0060]
How to control the amount of generation of hydrocarbons and carbon monoxide will be described later in the application section.
Further, in the internal combustion engine I having a lean NOx catalyst, by mixing the combustion gas coming out of the combustion type heater 17 into the intake pipe 23, the fresh air flowing up to that point in the intake system contains the combustion heat of the combustion gas. The combustion gas-mixed intake air a3 is obtained. Therefore, by using the combustion heat of the combustion type heater 17, it is possible to promote warm-up and improve the performance of the vehicle interior heater. Since the combustion type heater is usually provided in an internal combustion engine, the combustion type heater 17 can be used in combination as a means for increasing the concentration of carbon dioxide.
[0061]
Further, the combustion type heater 17 emits combustion gas which is essentially free of smoke, in other words, does not contain carbon and has a high concentration of carbon dioxide. Compared with the EGR device which can be said to be a known NOx reduction device, there is no need to worry about the wear and corrosion of the internal combustion engine, and the durability can be improved, and the reduction of nitrogen oxides from a low water temperature becomes possible.
[0062]
In addition, thermal dissociation of carbon dioxide (ie, at ambient temperatures of 1400 ° C., CO 2 ₂ → 2CO + O ₂ ) Re-burns soot and carbon dioxide oxidizes the produced carbon (ie, CO 2 ₂ (+ C → 2CO), the carbon dioxide itself also has a smoke suppression effect, so that even when the internal combustion engine is under a high load, the smoke suppression effect can be expected.
[0063]
In addition, low fuel consumption engines such as diesel engines and gasoline lean-burn engines have a small amount of combustion fuel, and therefore have low heat loss to the cooling water. Therefore, in these engines, the warm-up property tends to be deteriorated even at room temperature, but the warm-up property can be greatly improved by operating the combustion type heater 17 when necessary. As a result, emission during warm-up can be significantly improved. In addition, since the exhaust heat of the combustion heater 17 is recovered by the engine main body 3, the amount of heat received by the internal combustion engine-side cooling water Qw increases, so that the heater performance is improved.
[0064]
Since the combustion gas discharge passage 35 of the combustion heater 17 communicates with the intake pipe 23, unburned components in the combustion gas at the time of starting the combustion heater 17 burn again in the cylinder of the engine body 3. When this reaches the exhaust system of the internal combustion engine, it can be purified by a lean NOx catalyst 39 provided in the exhaust system.
[0065]
Further, since the air supply passage 33 and the combustion gas discharge passage 35 of the combustion heater 17 are not directly open to the atmosphere, a noise reduction effect can be expected.
<Application>
The following (1) and (2) will be described as methods for suitably controlling the purification of nitrogen oxides by controlling the amount of generation of hydrocarbons and carbon monoxide.
(1) When purifying nitrogen oxides by adjusting the air-fuel ratio of the combustion heater 17
When it is necessary to purify nitrogen oxides with the lean NOx catalyst, the air-fuel ratio of the combustion heater 17 is made rich.
[0066]
If the air-fuel ratio is rich, the amount of fuel in the air-fuel mixture of the combustion type heater 17 is large, and the proportion of hydrocarbons and carbon monoxide as reducing agents increases accordingly, so that the lean NOx catalyst 39 purifies nitrogen oxides. Easier to do. Therefore, the auxiliary injection can be made unnecessary.
(2) When purifying nitrogen oxides by changing the fuel injection timing
When it is necessary to purify the nitrogen oxides by the lean NOx catalyst 39 when the combustion heater 17 is operating, the fuel injection timing of the fuel injection device is later than when the reduction process has not been performed yet (when the reduction process has not been performed). Good corner. The fuel injection timing is usually set so that fuel efficiency is optimized. However, if the fuel injection timing is retarded, the combustion is delayed accordingly. If the combustion is slow, the fuel that should be burned remains unburned, and the proportion of unburned gas increases, so that the proportion of hydrocarbons and carbon monoxide increases, and the lean NOx catalyst easily purifies nitrogen oxides. Therefore, the auxiliary injection can be made unnecessary.
[0067]
Also, when the combustion of the heater 17 does not require the purification of the nitrogen oxides by the lean NOx catalyst 39, the fuel injection timing of the fuel injection device is set to be shorter than when the reduction processing is being performed (when the reduction processing is being performed). Advance. If the fuel injection timing is advanced, the time required for the combustion gas to be discharged from the combustion chamber becomes longer, so that the occurrence of afterburn can be expected, and the temperature of the exhaust system rises due to the occurrence of afterburn. Therefore, the activation of the lean NOx catalyst 39 proceeds, and the storage of nitrogen oxides in the catalyst 39 is promoted. When the intake of nitrogen oxides by the lean NOx catalyst 39 becomes excessive and the lean NOx catalyst 39 becomes saturated with nitrogen oxides, the fuel injection timing is delayed as described above to remove the nitrogen oxides from the lean NOx catalyst 39. Purify from.
[0068]
The operation control routine of the combustion type heater 17 in the case of purifying nitrogen oxides by changing the injection timing in this manner will be described with reference to the flowchart of FIG. In this case, the lean NOx catalyst 17 is of the storage reduction type.
[0069]
This routine is a part of a normal flowchart (not shown) for driving the engine 1 and includes steps 101 to 106 described below. The operations in the following procedure are all performed by the CPU of the ECU 46. The symbol S is used as a symbol indicating a step. For example, in the case of step 101, it is abbreviated as S101.
[0070]
When the process proceeds to this routine after the start of the engine 1, in S101, it is determined whether the combustion type heater 17 is operating, in other words, whether the combustion type heater operation is being performed. If an affirmative determination is made in S101, the process proceeds to S102, and if a negative determination is made, the process proceeds to S104.
[0071]
In S102, it is determined whether or not the conditions necessary for the reduction treatment of the NOx storage reduction catalyst are satisfied, that is, whether the NOx storage reduction catalyst is excessively absorbing nitrogen oxides and the nitrogen oxides are saturated. .
[0072]
If an affirmative determination is made in S102, the process proceeds to S103, and if a negative determination is made, the process proceeds to S106. In S103, the fuel injection timing is delayed, that is, the fuel injection timing is delayed, compared to when the reduction processing is not performed, and then this routine is ended.
[0073]
Return to S101.
If a negative determination is made in S101 and the process proceeds to S104, it is determined in S104 whether or not the conditions necessary for the reduction process of the NOx storage reduction catalyst are satisfied with the combustion type heater 17 not operating, that is, the storage reduction is performed in the same manner as in S102. It is determined whether the type NOx catalyst is excessively absorbing nitrogen oxides and is in a saturated state. If a positive determination is made in S104, the process proceeds to S105, and if a negative determination is made, this routine ends.
[0074]
In S105, the combustion type heater 17 is operated.
The story returns to S102.
If a negative determination is made in S102 and the process proceeds to S106, the fuel injection timing is advanced in S106 as compared with the time when the reduction process is performed, and then this routine ends.
[0075]
【The invention's effect】
As described above, according to the present invention, an internal combustion engine having a lean NOx catalyst in an exhaust system for purifying nitrogen oxides in an oxygen-excess exhaust gas using a reducing agent flows through the intake system of the internal combustion engine. It is equipped with a concentration increasing means for increasing the concentration of carbon dioxide in the intake air, so when the concentration of carbon dioxide increases in the intake system, hydrocarbons to carbon monoxide and from carbon monoxide to carbon dioxide Reaction becomes difficult. In extreme terms, if carbon dioxide is in a saturated state, the chemical reaction between hydrocarbons constituting carbon dioxide and carbon monoxide does not proceed, so that a large amount of hydrocarbons and carbon monoxide are in a free state. Therefore, in the internal combustion engine having the lean NOx catalyst of the present invention, the ratio of the presence of hydrocarbon and carbon monoxide alone increases. Therefore, purification of nitrogen oxides can be performed very effectively. Since hydrocarbons and carbon monoxide are used as reducing agents, there is no need to supply hydrocarbons by aggressive fuel supply by sub-injection used in the conventional technology. Therefore, the amount of generation of hydrocarbons and carbon monoxide can be controlled well, for example, by enriching the air-fuel ratio of a combustion heater when it is necessary to purify nitrogen oxides with a lean NOx catalyst, or by leaning the combustion heater. By delaying the fuel injection timing by the fuel injection device when it is necessary to purify nitrogen oxides by the NOx catalyst, the adverse effects caused by the sub-injection, that is, the load on the fuel injection device is reduced. it can.
[Brief description of the drawings]
FIG. 1 is a schematic configuration diagram of an embodiment of an internal combustion engine having a lean NOx catalyst according to the present invention.
FIG. 2 is a schematic sectional view of a combustion type heater.
FIG. 3 is a diagram showing the amount of generated nitrogen oxides in comparison with a conventional technique;
FIG. 4 is a diagram showing the amount of generated hydrocarbons in comparison with the conventional technology.
FIG. 5 is a diagram showing the amount of generated carbon monoxide in comparison with a conventional technique;
FIG. 6 is a flowchart showing an operation control routine of a combustion type heater when purifying nitrogen oxides by retarding the injection timing.
[Explanation of symbols]
1. Engine (internal combustion engine)
3. Engine body (body of internal combustion engine)
5. Intake device
7 Exhaust device
9 ... Heater for vehicle compartment
13 ... Air cleaner
15 ... Turbocharger
15a ... Compressor
15b: Turbocharger turbine
17. Combustion heater (concentration increasing means, addition device, combustion device)
17a: Cooling water passage of combustion type heater
17a1 Cooling water inlet
17a2 ... Cooling water outlet
17b ... combustion cylinder
17c ... cylindrical partition
17d ... combustion chamber
17d1… Air supply port
17d2 ... Exhaust exhaust port
17e ... fuel supply pipe
19. Intercooler
21 ... intake manifold
23 ... intake pipe
25 ... upstream connecting pipe
27… Downstream connecting pipe
29… Main tube
31 ... Branch for heater
32 ... Outside air temperature sensor
33 ... Air supply path
35 ... Combustion gas discharge path
36 ... Combustion gas temperature sensor
37 ... CO ₂ Sensor
38… Exhaust manifold
39: lean NOx catalyst
41 ... Muffler
42 ... exhaust pipe
43 ... Outer wall
45… Blower fan
46 ... ECU
47 ... CPU
49 ... Bypass passage
55… Outside air temperature sensor
59 ... rotation speed sensor
60: Mixed intake air temperature detection sensor
70 ... Air flow meter
80 ... intake pressure sensor
I: Internal combustion engine having a combustion type heater according to the embodiment
C1: Connection point between the air supply passage 33 and the main pipe 29
C2: connection point between the combustion gas discharge passage 35 and the main pipe 29
C3: connection portion between the bypass passage 49 and the combustion gas discharge passage 35
W1 ... Water pipeline
W2: Water pipeline
W3: Water pipeline
A: Outside air entering the main pipe 29 from the air cleaner 13
a1 ... Air branched from outside air A at connection point C1 and flowing through air supply path 33
a1 '... Air flowing through main flow pipe 29 to connection point C2
a2: Air that has been used as combustion gas by combustion of the combustion type heater 17
a3 ... Air mixed with combustion gas
a4 ... air flowing through the exhaust device 7

Claims (9)

In an internal combustion engine having an exhaust system having a lean NOx catalyst for purifying nitrogen oxides in an oxygen-excess exhaust gas using a reducing agent,
Wherein a separately provided is a combustion device and the main body of the internal combustion engine, the combustion gas emitted from the combustion device by adding carbon dioxide to the intake system by introducing into the intake system of the internal combustion engine flowing through the intake system An internal combustion engine having a lean NOx catalyst, comprising a combustion type heater for increasing the concentration of carbon dioxide in intake air. The internal combustion engine having a lean NOx catalyst according to claim 1, wherein the combustion type heater performs combustion at a pressure lower than a pressure at the time of combustion in a cylinder of the internal combustion engine. The internal combustion engine having a lean NOx catalyst according to claim 2, wherein the combustion type heater operates when purification of nitrogen oxides by the lean NOx catalyst is required. The combustion heater operates when the internal combustion engine is in a predetermined operating state, burns fuel, and heats engine-related elements with heat of combustion gas generated during the combustion. 3. An internal combustion engine having the lean NOx catalyst according to any one of 3. The internal combustion engine having a lean NOx catalyst according to claim 1, wherein the lean NOx catalyst is a storage reduction type NOx catalyst. The internal combustion engine according to claim 1, wherein the lean NOx catalyst is a selective reduction type NOx catalyst. The internal combustion engine having a lean NOx catalyst according to claim 4, wherein when the lean NOx catalyst needs to purify nitrogen oxides, the air-fuel ratio of the combustion heater is made rich. 5. The lean NOx catalyst according to claim 4, wherein when the combustion type heater needs to be operated to purify nitrogen oxides with the lean NOx catalyst, the fuel injection timing of the fuel injection device is retarded. Internal combustion engine. 9. The internal combustion engine having a lean NOx catalyst according to claim 8, wherein the lean NOx catalyst is a storage reduction type NOx catalyst.

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