JP2003239795A - Premixed compression self-ignition engine and method of controlling the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a premixed compression self-ignition engine which reduces generation of knocking and generation of NOX, while achieving an extremely high thermal efficiency by increasing the compression ratio, and also to provide a method of controlling the same. <P>SOLUTION: In the premixed compression self-ignition engine, the premixed air in which a fuel and air are mixed is compressed in a combustion chamber 3 and self-ignited and burned. The excess air ratio is 2.5-3.0, and the temperature of the supply air is 80°C or lower, or preferably about 40°C. The combustion in the combustion chamber is performed slowly, and the period of heat generation is slowed to 20-40°CA. The slow combustion prevents knocking, and as the combustion temperature is lowered, generation of NOX is significantly reduced. As the combustion is slowly performed, the density of oxygen in the premixed gas guided into the combustion chamber 3 is 17% or lower by circulating burned exhaust gas in the premixed gas, and a combustion inhibitor is added to the premixed gas. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for controlling a premixed compression self-ignition engine in which a premixed air mixture in which fuel and air are premixed is compressed in a combustion chamber to perform self ignition combustion.

[0002]

2. Description of the Related Art Premixed compression ignition combustion type engines have been attracting attention from the viewpoint of reduction of harmful emissions and energy saving. This premixed compression self-ignition combustion type engine takes advantage of the features of both conventional gasoline engines and diesel engines, has good fuel efficiency, and can significantly reduce exhaust gas pollution. Better than the engine. That is, the engine of the premixed compression self-ignition combustion system emits less nitrogen oxides (NO _x ) and soot and can achieve a high efficiency comparable to that of a diesel engine.

In this premixed compression self-ignition combustion type engine, fuel and air are mixed to form a premixed gas, which is then supplied to a combustion chamber and compressed by a piston for self-ignition. According to this combustion engine,
Small amount of fuel ignition in lean premixed gas prepared by mixing a large amount of air, but may be burned, it is possible to reduce the generation of the NO _X is suppressed low therefore the combustion temperature.

Further, soot is not generated because the fuel and air are completely mixed and homogeneous combustion can be performed without causing oxygen deficiency.
In addition, this combustion type engine has the characteristic of high thermal efficiency because it burns at a high compression ratio similar to that of a diesel engine.

The engine of the premixed compression self-ignition combustion system is
Although it has excellent performance as described above, the combustion is performed uniformly by the homogeneous premixed gas, so the combustion speed is very fast and knocking easily occurs, so a high compression ratio is required to avoid knocking. However, there is a problem that it is difficult to improve the thermal efficiency. Furthermore, in the engine operation under high load, the maximum ultimate pressure becomes excessive due to the rapid pressure rise of homogeneous combustion, and there is a problem that the engine operation under high load is difficult from the viewpoint of the pressure resistance of the engine and occurrence of knocking.

[0006]

In view of the above-mentioned problems of the conventional premixed compression self-ignition engine, the present invention increases the compression ratio and realizes high thermal efficiency, while at the same time knocking An object of the present invention is to provide a premixed compression ignition engine that suppresses the generation of NO _X and reduces the generation of NO _X , and a control method thereof.

[0007]

In order to solve the above-mentioned problems, the present invention provides a premixed compression self-ignition engine in which a premixed gas mixture of fuel and air is compressed in a combustion chamber to perform self-ignition combustion. That is, the combustion period in the combustion chamber is 20 to 4 including the top dead center (TDC) of the piston.
Provided is a premixed compression ignition engine that slows down to a crank angle (CA) of 0 ° and a control method thereof.

As described above, in the premixed compression self-ignition engine and the control method thereof according to the present invention, the combustion in the combustion chamber is slowly performed to lower the combustion temperature. Can avoid knock by slowing the combustion, and, with a decrease in the combustion temperature, the occurrence of the NO _X can be reduced significantly. Conventionally, the heat generation time in autoignition of a premixed compression autoignition engine is -5 to 5 ° from TDC.
Since it is about CA, that is, about 10 CA in the heat generation period, combustion is remarkably slowed in the premixed compression ignition engine and the control method thereof according to the present invention.

In the present invention, the excess air ratio is 2.5 to 3.0.
By lowering it to a certain level, the supply pressure supplied to the combustion chamber can be reduced, which can increase the compression ratio up to the maximum ultimate pressure that is limited by the engine pressure resistance value and greatly improve the thermal efficiency. it can.

Further, in the present invention, the combustion temperature is slowed down as described above to avoid the occurrence of knocking, and the supply air temperature is set to 80 ° C. or lower, preferably about 40 ° C. As a result, the supply pressure can be reduced, the compression ratio can be increased until the maximum ultimate pressure reaches the engine pressure resistance value, and the thermal efficiency can be dramatically improved. As a result, it becomes possible to operate the engine at a high load, that is, at a high average effective pressure, which was impossible in the conventional lean premixed compression self-ignition engine.

In order to perform the slow combustion according to the present invention, the flue gas is circulated and mixed with the premixed gas to significantly reduce the oxygen concentration of the premixed gas introduced into the combustion chamber to 17% or less. Is preferred. Further, in order to perform the slow combustion according to the present invention, water (H ₂ O), methanol, i
It may be carried out by adding about 20% of an additive for suppressing combustion such as octane and silicone oil to the premixed air by mixing it, or by introducing the combustion inhibitor into the combustion chamber separately from the premixed air. .

When the combustion inhibitor is premixed in the premixed air,
The premixture introduced into the combustion chamber tends to be delayed in ignition due to the mixing of the combustion inhibitor, and the combustion is slowed down.
On the other hand, if the combustion inhibitor is introduced into the combustion chamber separately from the premixed gas, the ignition timing of the premixed gas itself does not change much, but the combustion becomes slow and the heat generation period, that is, the combustion period becomes long. The combustion can be slowed down with good responsiveness to load fluctuations and rotation speed fluctuations.

When the combustion suppressant is introduced into the combustion chamber separately from the premixed gas, as is clear from the above, it is possible to introduce the combustion suppressor into the combustion chamber with good timing for combustion in the combustion chamber. It is particularly necessary, and for that purpose, it is effective to detect the piston position in the combustion chamber and to control the introduction timing of the combustion inhibitor based on the detected piston position.

Further, in the above-described control method for the premixed compression self-ignition engine of the present invention, when the premixed gas supplied to the combustion chamber is pressurized by the turbocharger, the supply air can be easily brought to a predetermined compression ratio. Can be increased to

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below based on the embodiments shown in FIGS.

(First Embodiment) First, referring to FIG.
An embodiment will be described. In FIG. 1, reference numeral 1 represents a cylinder of a premixed compression ignition engine, in which a piston 2 is fitted, and a combustion chamber 3 is formed above the piston 2. An intake hole 4 and an exhaust hole 5 are provided above the cylinder 1. 6 is a premixed gas supply line, and 7 is an exhaust line.

Reference numeral 8 is a supercharger which pressurizes the premixed gas introduced to the intake hole 4. An exhaust turbine 9 drives the supercharger 8 to rotate. Reference numeral 10 denotes a cooler, which cools the premixed gas leaving the supercharger 8. An exhaust gas circulation line 11 is an exhaust turbine 9
It is provided to guide a part of the exhaust gas that has exited to the premixed gas supply line 6. The exhaust gas circulation line 11 has a cooler 1
2 and a flow control valve 13 are provided.

Reference numeral 14 is a fuel supply line, and 15 is a combustion inhibitor supply line. The fuel supply line 14 is provided with a flow rate control valve 16, and the combustion inhibitor supply line 15 is provided with a flow rate control valve 17. Although not shown in the drawing, the fuel supply line 14 and the combustion inhibitor supply line 15 may be provided between the supercharger 8 and the intake hole 4. Further, the fuel can be directly injected into the combustion chamber 3.

A flow meter 18 detects the flow rate of air flowing to the premixed gas supply line 6. Reference numeral 19 denotes a control device, which is a pressure signal in the cylinder from a pressure gauge 20 provided in the cylinder 1,
An intake air temperature from a thermometer 21 provided near the inlet of the intake hole 4 of the premixed air supply line 6 and an air flow rate from a flow meter 18 provided in the premixed air supply line 6 are input.

On the other hand, from the control device 19, the flow rate control valve 13 provided in the exhaust gas circulation line 11, the flow rate control valve 16 provided in the fuel supply line 14, and the flow rate control provided in the combustion inhibitor supply line 15 are controlled. A flow control signal for valve 17 is provided. The controller 19 also includes a cooler 1 provided in the premixed gas supply line 6 after the supercharger 8.
A control signal for controlling the flow rate of the refrigerant is given to 0.

In the premixed compression self-ignition engine of FIG. 1 equipped with the control system described above, the premixed gas supply line 6 is controlled by the flow rate control valve 16 to a flow rate based on the air flow rate detected by the flow meter 18. The supplied amount of fuel and the amount of combustion inhibitor controlled by the flow rate control valve 17 are respectively supplied. In addition, a control device 19 is provided in the premixed gas supply line 6.
The amount of exhaust gas controlled by the flow rate control valve 13 is mixed with the signal from.

Thus, the oxygen concentration is set to 17% or less, and H
A precharged mixture containing about 20% of a combustion inhibitor such as ₂ O, methanol, i-octane and silicone oil is a supercharger.
After being pressurized by, it is cooled to 80 ° C. or lower, preferably about 40 ° C. by the cooler 10 and introduced into the combustion chamber 3 of the cylinder 1 through the intake hole 4.

By the above operation, in the combustion chamber 3, the combustion of the premixture is slowed down due to the decrease of the oxygen concentration and the decrease of the combustion temperature due to the addition of the combustion inhibitor, and the combustion period (heat generation period) in the combustion chamber 3 To a crank angle of 20-40 °. Thereby avoiding the occurrence of knocking by slowing the combustion, it is possible to significantly reduce the NO _X generated by the reduction of the combustion temperature. Further, since the fuel and air burn in a lean premixed state, soot is less likely to occur. Furthermore, the supply air pressure decreases due to the decrease in the supply air temperature, and the maximum ultimate pressure in the combustion chamber is reduced.

These results are shown qualitatively in FIG. FIG. 4A shows the operating state of the conventional premixed compression self-ignition engine, in which the maximum pressure in the combustion chamber exceeds the engine allowable pressure and there is a high peak in the combustion temperature. On the other hand, (b) shows the case according to the present invention, in which the maximum pressure exceeding the engine allowable pressure disappears, and the combustion temperature is gently reduced.

Next, as described above, the heat generation period is set to 20.
FIG. 5 shows the result of examining the excess air ratio λ in the case of ˜40 ° CA, and FIG. 6 shows the result of examining the supply air temperature Ts. FIG. 5 shows the supply pressure, the compression ratio, and the thermal efficiency when the heat generation period is changed from 15 to 40 in the crank angle under the condition that the engine allowable pressure value is 200ata and the supply temperature is 80 ° C. (353K). The change of is shown in (a), (b), and (c) for four types of excess air ratio λ = 2.0, 2.5, 3.0, and 4.0, respectively. As can be seen from these figures, the thermal efficiency is 48 at the compression ratio 18 at the excess air ratios of 2.5 to 3.0 as compared with the excess air ratios of 3.0 to 4.0 and 2.0 to 2.5. ．
1 to 48.5%, compression ratio 19 and thermal efficiency 48.5 to 48.
At 7% and a compression ratio of 20, a very high thermal efficiency of 48.7 to 48.8% can be achieved. Further, in this way, under the lean premixed compression self-ignition condition, it is clear that the effect opposite to the conventional idea for improving the thermal efficiency, that is, the thermal efficiency can be improved as the combustion is slowed and the heat generation period is extended. became.

FIG. 6 shows that the engine allowable pressure value is 200ata.
Under the condition that the excess air ratio is 3.0, the change of the air supply pressure, the compression ratio, and the thermal efficiency when the heat generation period is changed to 15 to 40 ° at the crank angle are described as follows: the air supply temperature is 60 ° C (333K), 7
The three patterns of 0 ° C. (343K) and 80 ° C. (353K) are shown in (a), (b), and (c), respectively. As shown in these figures, the lower the supply air temperature is, the lower the temperature is shown to be 60 ° C in the figure, but the required engine output is obtained by preferably lowering the temperature to about 40 ° C. Therefore, the supply pressure decreases, and the compression ratio can be increased until the maximum ultimate pressure reaches the engine withstand pressure value, and the thermal efficiency can be improved.

Under a condition that the engine allowable pressure value is 200 ata, the excess air ratio is 3.0, and the supply air temperature is 333 K, the compression ratio is 18
It was revealed that extremely high thermal efficiencies such as a thermal efficiency of 49.0%, a thermal efficiency of 49.3% at a compression ratio of 19 and a thermal efficiency of 49.5% at a compression ratio of 20 can be achieved. Also, under such a lean premixed ignition condition,
Similar to the above, it has been clarified that the effect is opposite to the conventional idea for improving the thermal efficiency, that is, the thermal efficiency can be improved by slowing the combustion and extending the heat generation period.

(Second Embodiment) Next, a second embodiment will be described with reference to FIG.
An embodiment will be described. In FIG. 2, the combustion suppressant supply line 15 is directly connected to the combustion chamber 3 of the cylinder 1 without being connected to the premixed gas supply line 6. The other configurations are the same as those shown in FIG. 1, and the corresponding equivalent portions are denoted by the same reference numerals as those in FIG. 1, and duplicated description thereof will be omitted.

As described above, when the combustion suppressant is directly introduced into the combustion chamber 3, the combustion suppressor does not change the ignition timing of the premixed gas supplied from the premixed gas supply line 6 to the combustion period. Can be changed. Therefore, it becomes easier to realize the combustion period of 20 to 40 ° CA in the present invention. The other actions and effects are similar to those of the first embodiment, and the description thereof will be omitted.

(Third Embodiment) Next, referring to FIG.
An embodiment will be described. In FIG. 3, reference numeral 22 is an encoder that detects the rotation of the crankshaft 23. The signal of the encoder 22 is given to the control device 19. Also in the case of the third embodiment, the combustion inhibitor is directly supplied into the combustion chamber 3 as in the case of the second embodiment.

In this third embodiment, the rotation of the crankshaft 23 is detected by the encoder 22, and the injection timing of the combustion suppressing agent can be set to an arbitrary advance angle or retard angle with respect to the top dead center. An angle signal is sent to 19 so that the heat generation period can be appropriately controlled and instructed. Figure 3
2 is substantially the same as that shown in FIG. 2, and the same reference numerals as those in FIG. 2 are attached to them, and the duplicated description thereof will be omitted.

Although the present invention has been specifically described based on the illustrated embodiments, the present invention is not limited to these embodiments, and various modifications are possible within the scope of the present invention shown in the claims. Needless to say, changes and modifications may be added. For example, in the illustrated embodiment, the exhaust gas is recirculated and the combustion inhibitor is injected, but the point is that the heat generation period in the combustion chamber is 20 to 40 °.
If the CA can be slowed down, either one of the measures may be taken. Further, in the illustrated embodiment, in addition to the above, cooling of the premixed gas and adoption of the supercharger are performed, but these may be appropriately selected and adopted as long as the conditions shown in the claims are satisfied.

[0033]

As described above, according to the present invention, in a premixed compression self-ignition engine in which a premixed gas mixture of fuel and air is compressed in a combustion chamber to perform self-ignition combustion, a heat generation period, that is, a combustion chamber. There is provided a premixed compression ignition engine and a control method therefor, in which the combustion period at TDC is slowed down to a crank angle (CA) of 20 to 40 °.

Further, in the premixed compression self-ignition engine and the control method thereof according to the present invention, the excess air ratio is 2.5 to 3.
Since the pressure is reduced to about 0, the supply air pressure supplied to the combustion chamber can be reduced, and the compression ratio can be increased until the maximum ultimate pressure determined by the pressure resistance value of the engine is reached, thereby dramatically improving thermal efficiency. You can

Further, in the present invention, the combustion air is slowed down as described above to avoid the occurrence of knocking, and the supply air temperature is set to 80 ° C. or lower, preferably about 40 ° C., so that the supply air pressure is lowered. And the compression ratio can be increased, so that the thermal efficiency can be greatly improved.

In the method for controlling the premixed compression self-ignition engine according to the present invention, the combustion in the combustion chamber can be performed slowly to avoid knocking, and the combustion temperature is lowered by slowing the combustion. So
The generation of NO _x can be significantly reduced.

The slowing of combustion according to the present invention can be easily carried out by circulating and mixing the combustion exhaust gas into the premixed gas to significantly reduce the oxygen concentration of the premixed gas introduced into the combustion chamber to 17% or less. it can. In addition, the slowing of combustion according to the present invention is carried out by adding about 20% of additives such as water (H ₂ O), methanol, i-octane, and silicone oil, which suppress combustion, to the premixed gas and mixing them. Alternatively, the combustion inhibitor can be effectively introduced by introducing it into the combustion chamber separately from the premixed gas.

In the present invention, the combustion inhibitor is introduced into the combustion chamber separately from the premixed gas, the piston position in the combustion chamber is detected, and the combustion inhibitor is introduced based on the detected position. In this case, the introduction of the combustion suppressing agent can be controlled to be optimum.

Further, in the above-described method for controlling the premixed compression self-ignition engine of the present invention, in which the premixed gas supplied to the combustion chamber is pressurized by the turbocharger, the supply air is supplied up to a predetermined pressure. , Can be easily increased.

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing a premixed air supply system in a premixed compression ignition engine for explaining a first embodiment of the present invention.

FIG. 2 is an explanatory diagram showing a premixed gas supply system in a premixed compression ignition engine for explaining a second embodiment of the present invention.

FIG. 3 is an explanatory diagram showing a premixed air supply system in a premixed compression ignition engine for explaining a third embodiment of the present invention.

FIG. 4 is an explanatory view showing the effect of the control method according to the present invention, which is observed in the pressure and temperature in the combustion chamber, in comparison with the conventional method,
(A) shows the case according to the conventional method, and (b) shows the case according to the present invention.

FIG. 5 shows a case in which the heat generation period is 15 to 40 ° CA,
In the graph which shows the result of having examined the influence of the excess air ratio (a)
Is the supply pressure, (b) is the compression ratio, and (c) is the change in thermal efficiency.

FIG. 6 is a graph showing the results of examining the influence of the supply air temperature when the heat generation period is set to 15 to 40 ° CA, (a) is the supply pressure, (b) is the compression ratio, and (c) is the thermal efficiency. Shows the change.

[Explanation of symbols]

1 cylinder 2 pistons 3 Combustion chamber 4 intake holes 5 exhaust holes 6 Premixed air supply line 7 exhaust line 8 supercharger 9 exhaust turbine 10 Cooler 11 Exhaust gas circulation line 12 Cooler 13 Flow control valve 14 Fuel supply line 15 Combustion suppressant supply line 16 Flow control valve 17 Flow control valve 18 Flowmeter 19 Control device 20 pressure gauge 21 Thermometer 22 encoder 23 crankshaft

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 41/02 351 F02D 41/02 351 380 380D 41/04 355 41/04 355 45/00 362 45/00 362A F02M 25/00 F02M 25/00 A 25/022 25/02 AK (72) Inventor Kenji Shinya 1-8 Kochiura, Kanazawa-ku, Yokohama-shi 1 Mitsubishi Heavy Industries, Ltd. Basic Technology Research Laboratory (72) Inventor Muta Kenji 1-8-1, Sachiura, Kanazawa-ku, Yokohama-shi Mitsubishi Heavy Industries, Ltd., Fundamental Technology Research Laboratory (72) Inventor Toshiaki Monaka 1-8-1, Sachiura, Kanazawa-ku, Yokohama-shi, Mitsubishi Heavy Industries Ltd. (72) Inventor Noburou Goto 1-8-8, Koura, Kanazawa-ku, Yokohama City Mitsubishi Heavy Industries, Ltd. Basic Technology Research Laboratory (72) Inventor Hiroyuki Endo 5-717-1, Fukahori-cho, Saki-shi Mitsubishi Heavy Industries, Ltd. Nagasaki Research Institute (72) Inventor Kengo Tanaka 5-717-1, Fukahori-cho, Nagasaki-shi Nagasaki Research Institute F-term (reference) 3G084 AA00 BA00 BA08 BA09 BA11 BA20 BA26 DA02 DA10 DA12 DA38 EA11 EC01 FA02 FA07 FA21 FA33 FA38 3G092 AA00 AA17 AA18 AB16 AB17 BA04 BB02 DB03 DC10 DE15S EA08 FA16 FA17 FA18 HA01Z HA04Z HA05Z HA08Z HA05Z HA08Z HA05Z HA08Z 3G092 AA00 MA11 ND04 NE01 NE06 PA01Z PA07Z PA10Z PC01Z PE01Z PE04Z PE08Z

Claims (6)

[Claims] 1. A premixed compression self-ignition engine in which a premixed mixture of fuel and air is compressed in a combustion chamber to perform self-ignition combustion, with an excess air ratio of 2.5 to 3.0 and 80 ° C.
Hereinafter, a premixed gas oxygen concentration control system and / or a combustion inhibitor addition system for supplying a premixed gas, preferably cooled to about 40 ° C., to a combustion chamber and slowing the combustion of the premixed gas A premixed compression self-ignition engine having: 2. The oxygen concentration of the premixed gas introduced into the combustion chamber is adjusted to 17 by circulating combustion exhaust gas to the premixed gas.
% Or less, The control method for the premixed compression ignition engine according to claim 1, wherein 3. The method for controlling a premixed compression ignition engine according to claim 1, wherein a combustion inhibitor is added to the premixed air in a line in which the premixed air is supplied to the combustion chamber. . 4. The method for controlling a premixed compression ignition engine according to claim 1, wherein a combustion inhibitor is introduced into the combustion chamber separately from the premixed gas. 5. The method for controlling a premixed compression ignition engine according to claim 4, wherein the introduction of the combustion inhibitor into the combustion chamber is timed at the position of the piston. 6. The method of controlling a premixed compression self-ignition engine according to claim 2, wherein a turbocharger for pressurizing the premixed gas supplied to the combustion chamber is used.