JPS605768B2 - internal combustion engine - Google Patents

Description

[Detailed description of the invention]

The present invention relates to an internal combustion engine, and particularly to an internal combustion engine that can reduce harmful components in exhaust gas as much as possible. Harmful components emitted from internal combustion engines, namely nitrogen oxides (N
○x) Various devices have been researched and developed to reduce carbon monoxide (CO) and hydrocarbons (HC); The goal is to prevent this from happening. Regarding the HC and CO, these can be oxidized relatively easily by providing a reburning device such as an oxidation catalyst or a thermal reactor in the engine exhaust system and further maintaining the exhaust temperature at a high temperature. However, with regard to N○x, post-treatment in the exhaust system is difficult, and although reduction catalysts are being researched, these catalysts have problems in terms of performance, durability, and maintaining the exhaust gas in a reducing atmosphere. be. Therefore, it is extremely important how to suppress the generation of N○x in the engine combustion chamber. Exhaust recirculation (E
GR), which recirculates part of the exhaust gas to the intake system to suppress the maximum combustion temperature of fuel in the combustion chamber to some extent, thereby suppressing the generation of N*x. This EG
R mixes inert exhaust gas that is not involved in fuel combustion into the intake air-fuel mixture to suppress the maximum combustion temperature and suppress the generation of N○x. Carbon dioxide (C02) and water vapor (B20) contained in the residual gas remaining in the room and nitrogen in the intake air (
It is possible to reduce N*x by increasing the ratio of gas that does not participate in combustion (hereinafter referred to as inert gas including EGR) to the fuel, such as N2). However, if the amount of these inert gases is increased, the production of NOx can be reduced approximately proportionally, but on the other hand, the combustion time of the mixture becomes longer and the stability of the combustion of the mixture becomes unstable. As a result, the output performance and fuel efficiency deteriorate.For this reason, the proportion of the inert gas cannot be increased much, and as a result, there is a natural limit to the reduction of N○x. There is a problem that HC and CO generated in the combustion chamber increase because the stability of combustion of gas is impaired.Therefore, even if a large amount of inert gas is mixed into the intake mixture, the stability of the engine will be affected. In order to ensure output performance, it is best to shorten the combustion time of the intake air-fuel mixture as much as possible, that is, to perform early combustion to stabilize combustion and effectively utilize combustion pressure.Reducing this combustion time This can be achieved by minimizing the distance of fire propagation from the ignition point of the spark plug in the engine combustion chamber.Furthermore, the combustion time can also be shortened by reducing the air-fuel ratio of the intake air-fuel mixture. On the other hand, regarding HC and CO generated in the combustion chamber, the exhaust system can be improved by maintaining the exhaust temperature at a relatively high temperature and slightly increasing the concentration of HC and CO in the exhaust before it flows into the reburning device. The oxidation treatment can be effectively carried out using a reburning device.In embodying this technical idea, the present invention uses an air-fuel mixture with an average concentration near the stoichiometric air-fuel ratio or a more moderate concentration in the engine's normal operating range. By appropriately setting the installation position of the spark plug installed in the combustion chamber, it is possible to shorten the combustion time, thereby increasing the amount of inert gas mixed into the intake air-fuel mixture, and increasing the amount of NOx. Aiming for a moderate reduction,
Furthermore, when inert gas is mixed in, the exhaust gas recirculation device has a loop-type characteristic that maximizes the exhaust gas recirculation rate in a specific driving range, thereby reducing N, especially when driving in urban areas.
○ Remarkably reduces x, at the same time maintains appropriate concentrations of HC and CO in the exhaust, and maintains the exhaust temperature at a relatively high temperature to effectively oxidize HC and CO in the exhaust system. The purpose is to provide institutions with the following objectives. Embodiments of the present invention will be described below with reference to the drawings. 0 In Fig. 1, 2 is an intake manifold, 3 is an engine body, and 4 is a reactor attached to the exhaust system, and a heat-resistant oxidation catalyst material 4a is placed outside the reactor near the exhaust outlet. The reactor here includes a thermal reactor and an exhaust manifold reactor. 5 indicates an exhaust pipe, and the IJ factor 4 oxidizes unburned harmful components in the exhaust gas, namely carbon monoxide (CO) and hydrocarbons (HC), using secondary air from the secondary air supply device 6. A part of the exhaust gas is appropriately controlled according to engine operating conditions and recirculated into the intake manifold 2 by an exhaust recirculation device 8 consisting of an exhaust recirculation passage 9 and an exhaust recirculation control valve 10, as described later. The device 1 is set so that it can supply an air-fuel mixture close to the stoichiometric air-fuel ratio or a very rich mixture as an average of the air-fuel ratio of i3.5 to 15 in the engine's normal operating range. N○x at
In addition to suppressing the amount of fuel produced, high engine output can be obtained by improving ignitability and shortening combustion time. ``As shown in Figures 3 to 6, the position of the ignition plug 12 in the combustion chamber 1 is determined by the position of the ignition plug 12, which is located in the combustion chamber 1.'' In order to significantly reduce N○x, the recirculated exhaust gas that does not participate in combustion is Even if the proportion of inert gas contained in the fuel is increased, the optimum position is set to ensure stable combustion with short combustion time and little cycle fluctuation.In other words, the optimum position is set within the fire propagation distance. In order to shorten the ignition point of spark plug 2 (
The volume inside the combustion chamber surrounded by a spherical surface drawn from the center point of the spark gap 5 with a radius R expressed by the following formula is the volume of the combustion chamber surrounded by the cylinder head and the top surface of the piston at the top dead center of the piston 16. This is a position in a range where the value is 35% or more. However, 8: Ignition advance angle, N: Engine speed (1200 to 24
0 enemies. p. m) Vc: Combustion speed Here, 8' is the smallest advance angle determined by ensuring exhaust temperature and stable engine operation, and of course is the angle before top dead center expressed in crank angle. The radius R is the combustion volume (the volume of combustion inside the combustion chamber) that spreads in a spherical shape around the ignition point in the combustion chamber 11 during the period from ignition of the intake air-fuel mixture before the piston top dead center to the piston top dead center. radius of the volume in which the intake air-fuel mixture was burned. Therefore, since this radius R can be expressed as the product of the combustion speed Vc of the air-fuel mixture and the time t from ignition to the piston top dead center, this time t can be expressed as the engine speed N and the ignition advance. Represented by the angle 8, the radius R is therefore

It can be obtained using the formula [1}. Here, R is the engine rotation speed N in the normal operating range of the engine, that is, approximately 1200 to 240 RPM. p. In the range of m, the ignition advance angle 8 is set to increase as the engine speed increases, so it remains almost constant regardless of the engine speed. Generally, the combustion speed Vc is approximately 15 m/s, and the engine speed N = 2.
00 enemies. p. For example, if the ignition advance angle is set to 8 = 30o to obtain the best combustion characteristics when driving in the city at m, the radius R at this time is calculated using the above formula {1}.
:Kyo. Chicks OX15: 3.75×I. -2 (skin) Ni37.5 Willow. On the other hand, in a normal internal combustion engine, when the piston descends from top dead center by 15% of the total stroke length, that is, when the crank angle is approximately 40 degrees after top dead center, 80% of the total intake air-fuel mixture is It has been confirmed through experiments by the inventors that stable engine characteristics can be obtained if combustion is performed at % or more. Therefore, as can be seen from the characteristic diagram of the combustion ratio (weight) and combustion volume ratio of the intake air-fuel mixture (these have been confirmed through experiments) as shown in Figure 2, approximately It is sufficient if 20% is burned, and the combustion volume ratio at this time is approximately 35%.Here, the combustion ratio is the weight ratio of the burned mixture to the total intake mixture, and the combustion volume ratio and is the volume ratio of the combusted air-fuel mixture to the volume of the total intake air-fuel mixture, that is, the volume of the combustion chamber surrounded by the cylinder head and the top surface of the piston.Therefore, as mentioned above, the volume inside the combustion chamber surrounded by the radius R is the volume of the combustion chamber surrounded by the cylinder head and the upper surface of the piston. Stable engine characteristics can be obtained by installing the ignition plug at a position that accounts for 35% or more of the combustion chamber volume at top dead center.
In the case of wedge-type or bathtub-type combustion chambers, if the spark plug 12 is to be placed in a position that satisfies the above conditions, it is necessary to (where the distance is greatest) is the neighborhood. here"
By forming a recess 16a in the upper surface of the piston 16 as shown in the figure within the range included in the radius R, the combustion volume can be further expanded. In other words, the combustion volume can be expanded by gathering as much of the combustion chamber volume as possible near the ignition area. As mentioned above, the combustion time is significantly shortened by using a rich mixture and optimizing the installation position of the spark plug. The ratio of carbon (C02), water vapor (Japanese 20), and nitrogen (N2) in the intake air to the fuel can be greatly increased, thereby ensuring the safety of the engine and suppressing the maximum combustion temperature. can significantly reduce NOx. Therefore, for the fuel burned in the combustion chamber 11,
N2, C02, particles ○, surplus 02 that are not involved in fuel combustion
When the weight ratio P of gas such as
= 13.5 to 22.5. Here, regarding the range of the weight ratio P, its lower limit is 13
．． 5, if the amount of gas not involved in combustion is reduced below that, the effect of reducing N○x will be weakened, and the upper limit of 22
．． 5. If the amount of gas is increased further, the stability of combustion will be impaired even if a rich mixture is used as mentioned above and the ignition plug is set at the optimal position, and the NOx
It was set in consideration of the fact that the reduction effect of P is significantly reduced, and fuel efficiency and output performance are extremely deteriorated.If it is within this range of weight ratio P, based on the above-mentioned setting of the ignition dry position,
During the expansion stroke of the engine, the combustion ratio (weight) of the intake air-fuel mixture when the piston 16 drops approximately 400 degrees in crank angle from top dead center is 80% or more of the total, which means that the combustion time is short or the combustion energy is low. As a result of numerous experiments, it has become clear that this can be effectively extracted as engine output. Next, in order to specifically obtain the weight ratio P, The amount of residual gas in the cylinder is increased by making the overlap with the exhaust valve 22 relatively large.In other words, as shown in FIG. About 2
20 to 500, the weight ratio of residual gas to the intake air amount becomes approximately 15 to 25%.Here, we will briefly explain the theoretical formula for determining the weight ratio P. Weight ratio with air is 1
:14.7 (in the case of gasoline), and the composition ratio (volume ratio) of 02 and N2 in the air can be considered to be 21:79, so the respective molecular weights (N2; 28, 02:32)
Based on this, the weight ratio of fuel to N2 at this stoichiometric air-fuel ratio is determined to be 1:11.3. Therefore, the inert gas weight ratio of the mixture at the stoichiometric air-fuel ratio (excluding exhaust gas) is P=11.3. Next, to explain the case where exhaust gas is mixed into the intake air-fuel mixture, the specific weight of air and exhaust gas can be considered to be almost the same. If the stoichiometric ratio of the amount of combusted fuel (in the case of a thin case) is x%, y%, and z% (by weight) to the stoichiometric intake air amount, then the weight ratio of the fuel to the inert gas is 1: (11-3
114-7XX and Tsunetomizo). Here, the amount of intake air in the stoichiometric ratio of the amount of burned fuel will be explained for each air-fuel ratio. i When the air-fuel ratio of the intake air-fuel mixture is the stoichiometric air-fuel ratio, the amount of burned fuel is the total amount of fuel taken into the engine, and the intake air amount at the stoichiometric ratio of this total fuel amount is the total amount of fuel. This is the amount of intake air. Therefore, in this case, the amount of intake air in the stoichiometric ratio of the amount of burned fuel corresponds to the total amount of intake air. i
i When the air-fuel ratio of the intake air-fuel mixture is leaner than the stoichiometric air-fuel ratio, the amount of burned fuel is the total amount of fuel taken into the engine, and the amount of intake air in the stoichiometric ratio of this total amount of fuel is the total amount of intake air. It is the remainder after subtracting the amount of surplus air from Therefore, in this case, the amount of intake air in the stoichiometric ratio of the amount of burned fuel is the remainder after subtracting the amount of excess air from the total amount of intake air. To give a specific example, when the air-fuel ratio is 16, the amount of intake air in the stoichiometric ratio of the amount of burned fuel (assumed to be 1 kg) is 14.7k9, and the amount of surplus air is 1.3k9. still,
Surplus air is an inert gas that does not participate in combustion, and the stoichiometric ratio of the amount of burned fuel is inhaled. 〇: 8.8%. (vi) When the air-fuel ratio of the intake air-fuel mixture is richer than the stoichiometric air-fuel ratio, the amount of burned fuel is the stoichiometric ratio of the total amount of intake air taken into the engine, so the stoichiometric amount of the amount of burned fuel is The theoretical intake air amount is the total intake air amount. To give a specific example, the stoichiometric intake air amount of the air-fuel ratio force Mi 13 anastomotic/combusted survey (band = 0.8 chest) is 13k9. In this case, surplus fuel (unburnt fuel) of 0.12k9 is generated, but it is so small that it can be ignored.
Therefore, with respect to the amount of intake air in the stoichiometric ratio of the amount of burned fuel, the amount of recirculated exhaust gas is x%, the amount of residual gas is y%, and the amount of surplus air is z.
As a percentage, the weight ratio P for each air-fuel ratio is ``If the air-fuel ratio is the stoichiometric air-fuel ratio or below the stoichiometric air-fuel ratio, z: 0, so P: 1143-14. If it is thinner, enter the excess air ratio (in the stoichiometric air-fuel ratio, ^ = 1) and z = (input - 1)XI
This is because OO. Therefore, ``For example, if a mixture with a stoichiometric air-fuel ratio (A/F = 14.7) is supplied and the weight ratio to the amount of intake air is 15% residual gas and 30% recirculated exhaust gas, the The weight ratio P of non-participating gas is 4
Since 5% exhaust gas + nitrogen = 6.6 + 11.3 = 17.9, it becomes 1:17.9. Here, as illustrated in Fig. 8, for example, the weight ratio of the inert gas P 17.2
If the intake and exhaust valve overlap is set to 400 in crank angle, the residual gas ratio will be approximately 21%, while the exhaust recirculation rate (exhaust recirculation amount relative to the total intake air amount) may be approximately 19%. become. In other words, when trying to increase the exhaust gas recirculation rate to ensure the setting conditions for the weight ratio of the inert gas, the exhaust gas recirculation control valve 1
Carbon and other deposits tend to adhere to the cylinders, which tends to make exhaust recirculation control inaccurate. Accordingly, if the exhaust gas recirculation rate is reduced accordingly, fluctuations in the inert gas weight ratio can be minimized to the extent possible. From this, in order to obtain a predetermined weight ratio P, the overlap between the intake and exhaust valves is made relatively large at the same time as exhaust gas recirculation, or in addition to this, an exhaust pressure regulating valve (not shown) is provided in the exhaust passage. Control residual gas. In this way, even if there is a relatively large amount of inert gas components that do not participate in combustion in the combustion chamber 11, combustion can be achieved by using a rich mixture and by igniting the spark plug 12 installed at an appropriate position. This is carried out in an extremely short period of time, and it is possible to achieve a significant reduction in N○x while ensuring stable combustion with little cycle fluctuation. Further, as the exhaust gas recirculation device, a loop type exhaust gas recirculation rate pattern characteristic is used, as shown in FIG. 9, for example. That is, according to this exhaust gas recirculation system, the engine rotation speed is 1,400 to 200, which is above the flat road running load curve R/L and is in the normal engine operating range. p. -150 when the suction negative pressure is set in the urban driving area where the driving speed is 100 m, and at a position where acceleration is frequent, that is, in the area where acceleration is most frequently performed in the regular driving area.
Since the reflux rate has a characteristic that the maximum value of the reflux rate is centered in the region of ~120Q Hg and the reflux rate gradually decreases from the center, it is possible to This suppresses fluctuations in the gas weight ratio, maintains engine stability with fast combustion, and achieves a significant reduction in NOx. Furthermore, in order to achieve this rapid combustion, it is effective to make the ignition plug 12 protrude from the mounting wall surface as much as possible within a range that can withstand the heat load. In other words, since fire spreads around the ignition point in a spherical shape, combustion occurs fastest if the ignition point of the spark plug is located at the center of the combustion chamber space. However, in reality, this is impossible to achieve due to the durability of the ignition plug, but as a result of repeated experiments based on this idea, the distance from the mounting wall surface of the ignition spear 12 to the ignition point is 2 to 7 willows. By making it stand out in the range, it became possible to improve combustion efficiency without compromising durability. In this case, the spark gap between spark plugs 1-2 is 1.1 to 2.0, and the ignition energy is 10 to 2.
It was confirmed that it is even more effective when the amount is about (millijoules). Furthermore, by setting the surfaces facing the center electrode 13 of the center electrode 13 of the spark plug 12 and the side electrodes 14 to about 1/4 of the current size (currently used center electrode plugs are 2 to 2.50), the electrode It was also confirmed that the electric field could be increased to further improve ignitability without causing melting and damage. Next, in order to further promote the shortening of the combustion time described above, a squish castle S is formed. The squish castle S is formed by the difference in area between the lower surface of the combustion chamber and the cylinder bore, but if we consider the squish area A and the cylinder bore area, A/Ao = 0.1 to 0.45, squish thickness St = 1.05 to 2 .5 Willow. When the squish region S is provided, severe turbulence is generated in the air-fuel mixture during the compression stroke due to the rise of the piston 16, and the squish is promoted, resulting in more uniform fuel distribution and ``disturbance in flame propagation during fueling, resulting in combustion. The time becomes even shorter. If the squish area is smaller than this, effective squish cannot be expected, and if it exceeds this range, HC will increase due to flame cooling, so the above value is set as the optimal range. In addition, by creating a swirl in the intake air-fuel mixture in addition to this squish effect, the combustion becomes more stable by promoting the mixing of fuel and air.In this way, the N○x In order to further reduce HC and CO, which are other harmful exhaust components, an exhaust temperature drop prevention device has been installed. As shown in FIG. 6, a heat-resistant boat liner 20 is attached to the exhaust port 19 to maintain the high temperature of the exhaust, and as shown in FIG. By reducing the passage surface area by creating a so-called siamed port structure in which the cylinders are assembled, exhaust heat is prevented from escaping to the cylinder head 18, and the exhaust temperature can be maintained at a high temperature.In other words, this internal combustion Since the engine uses a relatively large amount of inert gas, combustion is suppressed to a certain extent, which makes it difficult to suppress the generation of HC and CO, but by attaching a boat liner to the exhaust boat in this way, In addition, if a Siamese port is used to ensure a high exhaust temperature, performance and fuel efficiency will be impaired compared to ensuring a high exhaust temperature by delaying the ignition timing considerably from the optimum ignition timing (MB.T). Reactor 4
The oxidation efficiency of HC and CO can be increased. As described above, this reactor 4 is equipped with a heat-resistant oxidation catalyst material 4a at its outlet, so even if the exhaust temperature before the engine warms up is low, the oxidation catalyst material 4a
If C, CO can be oxidized and the exhaust temperature rises to ensure the reaction temperature of the reactor 4, the oxidation reaction of both the reactor 4 and the catalyst material 4a will reduce C○, HC.
The oxidation treatment can be carried out efficiently. still,
In this embodiment, the oxidation catalyst was placed in the reactor, but the oxidation catalyst may be provided in a separate container slightly downstream of the reactor. According to experiments conducted by the present inventors, by providing the exhaust boat 19 with the port liner 20 and making it a Siamese port, the valve diameter dE of the exhaust valve 22 can be changed to the bore diameter of the cylinder head 17. On the other hand, fertilizer = (0.40~0.
50) By setting it to D, the exhaust temperature can be maintained at a high temperature even more effectively, and by setting the valve seal 1 of the intake valve 21 to dl = (0.45 to 0.55)D. It was confirmed that fuel efficiency could be further improved by reducing bombing loss. The reason why the secondary air supply system 6 is required for the oxidation of HC and CO in the reactor 4 is because the air-fuel ratio of the intake air-fuel mixture is so rich that the oxidation reaction in the reactor 4 is not sufficiently carried out. This is because the secondary air supply device 6 is equipped with an air pump 7 as shown in the figure, and also has an intermittent negative pressure generated based on the exhaust pulsation, which causes the secondary air to be pumped through the check valve during the exhaust. Next, means for sucking air can be used.
As described above, according to the present invention, a relatively large amount of inert gas such as recirculated exhaust gas and residual gas is allowed to exist in the combustion chamber under certain specific conditions, and the air-fuel mixture of the intake air-fuel mixture is By appropriately setting the mounting position of the engine, it is possible to shorten the combustion time and significantly reduce N○x without interfering with engine operating performance, especially in the engine's normal operating range. Furthermore, when inert gas is mixed in, the exhaust By making the characteristics of the recirculation device a loop-type characteristic that has its maximum value in a specific driving range, we are able to thoroughly reduce NOx, especially when driving in urban areas, and at the same time maintain the high temperature of the exhaust gas without deteriorating fuel efficiency.
, it has the practical advantage of being able to effectively remove CO.

[Brief explanation of drawings]

Figure 1 is a schematic plan view of the internal combustion engine of the present invention, Figure 2 is an explanatory diagram showing the relationship between combustion volume and combustion rate in a normal internal combustion engine; The figure is the same plan view. ``Figures 5 and 6 are cross-sectional explanatory diagrams of different examples of combustion chamber shapes, Figure 7 is an explanatory diagram showing the overlap of intake and exhaust valves, and Figure 8 is a diagram showing the overlap between residual gas and recirculated exhaust gas. Explanatory diagram showing proportions, No. 9
The figure is an explanatory diagram showing the recirculation rate characteristics of the exhaust gas recirculation device. 1... Carburizer, 2... Intake manifold, 3... Engine body, 4... Reactor, 4a... Oxidation catalyst material, 6... Next air supply device, 8... ... Exhaust recirculation device, 1 1 ... Combustion chamber, 12 ... Spark plug,
16...Piston, 17...To the cylinder 18...Cylinder head, 21...Intake valve, 22...E-air valve. Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9

Claims (1)

[Claims] 1 In a simple-shaped combustion chamber such as a hemispherical, wedge-shaped, or bathtub-shaped combustion chamber, the volume inside the combustion chamber surrounded by a spherical surface drawn with a radius of 37.5 mm from the ignition point of a single spark plug is the piston. The combustion chamber is installed at a position near the maximum thickness of the combustion chamber and close to the center of the combustion chamber so that the volume is 35% or more of the combustion chamber volume at top dead center, and a squeezing area is provided at an appropriate area ratio to the cylinder bore area. In addition, the overlap of the intake and exhaust valves is approximately 22cm in crank angle.
50 degrees, and an exhaust gas recirculation device that recirculates part of the exhaust gas into the intake air. p. suction negative pressure is -150 m
It has a loop type characteristic in which the exhaust gas recirculation rate is maximum in the region of ~-200 mmHg, and the weight ratio of gases such as nitrogen, carbon dioxide, and water vapor that are not involved in the combustion of fuel to the fuel combusted in the combustion chamber is 13.5 ~ 22.5, while setting the air-fuel ratio of the intake air-fuel mixture generated by the fuel supply device of the engine intake system to near the stoichiometric air-fuel ratio or a slightly rich mixture, and creating a swirl in the intake air-fuel mixture. The exhaust system is equipped with an exhaust temperature drop prevention device that suppresses a drop in exhaust temperature, a reactor connected to the exhaust port and containing an oxidation catalyst material, and a secondary air supply device installed upstream of the reactor. An internal combustion engine characterized by