JP4081154B2 - Exhaust gas recirculation gas engine - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas recirculation (EGR) gas engine of a type in which high load operation is normally performed for a long time, such as for cogeneration driving.
[0002]
[Prior art]
Conventionally, as a NO _x reduction measure in the exhaust, and motor gasoline engines, in a diesel engine or the like cogeneration, which employs an exhaust recirculation system to recirculate the air supply system and exhaust by low temperature treatment (EGR) Is known. However, EGR has not been conventionally used in a cogeneration gas engine.
[0003]
[Problems to be solved by the invention]
Gas engine as applicable to cogeneration drive or the like, even more than the effect of reducing the exhaust NO _x, since the high-load operation is made long in the normal, as knocking measures, is effective to employ the EGR is there. Since the temperature rise in the combustion chamber is suppressed by EGR, the knocking limit (upper limit value of the net average effective pressure) at which the end gas near the inner wall surface of the cylinder liner is ignited rises, and the output is increased correspondingly. In the case of a diesel engine, knocking cannot occur because it is not a spark ignition type. In addition, automobile gasoline engines are rarely operated at such a high load that the knocking limit is reached.
[0004]
However, when adopting EGR in a gas engine, a point to be noted is that the exhaust pressure introduced into the air supply system by EGR must be stable. Assuming that the knocking limit increases due to EGR, when a high load is applied such that the net average effective pressure in the cylinder exceeds the knocking limit when EGR is not performed, the exhaust pressure suddenly decreases and When exhaust gas is not introduced into the air system, the engine is knocked down to the knocking limit value when EGR is not performed.
[0005]
In addition, when the load is applied from the idling state where the load is zero, the boost pressure, that is, the supply air pressure does not increase suddenly, and as the load increases, the throttle downstream pressure at the supply port increases at a stroke. Reach atmospheric pressure. Then, there is no pressure difference between the upstream and downstream of the throttle, and no further load is applied. To apply more load, you must wait for the boost pressure to rise.
[0006]
The load value at this time is the upper limit value when the load is applied. However, when EGR is performed, the throttle downstream pressure is already higher when idling than when EGR is not performed, and the boost pressure is reached earlier when the load is applied. Therefore, the upper limit value of the load obtained when the load is applied is reduced as compared with the case where EGR is not performed. In order to apply for cogeneration operation, there may be a situation in which the state is shifted from a zero load state to a high load state at a stretch.
[0007]
[Means for Solving the Problems]
The present invention uses the following means in order to solve the above problems.
[0008]
In claim 1, the supercharger (3) is connected to an exhaust manifold extending from the cylinder head (1a) of the gas engine (1), and the turbine section (3a) of the supercharger (3) is connected. The exhaust that has passed passes through the exhaust cooler (4) and is discharged from the exhaust discharge pipe (5), and an EGR pipe (6) branched from the exhaust discharge pipe (5) is connected to the EGR pipe. (6) On the upper side, an EGR regulator (8) and an EGR control valve (9) are interposed from the upstream side, and an EGR mixer (11) is provided at the junction of the EGR pipe (6) and the supply pipe (12). In the gas engine equipped with the exhaust gas recirculation system, the EGR control valve (9) is closed and the exhaust gas recirculation system is closed when the load factor is at least "the set load factor when the load is applied". The “set load factor at the time of loading” is the EGR In the closed state of the control valve (9), when the EGR ratio, which is the ratio of the EGR exhaust to the original air-fuel mixture, is operated at 0% without exhaust gas recirculation, after the engine is started, the throttle (14) This is the load factor when the pressure of the supply air pressure sensor (S1) provided in the supply manifold downstream of the engine reaches atmospheric pressure. If the load factor exceeds this value, the knocking limit will be exceeded and knocking will easily occur. It is set to a certain limit load factor (W ₁ ).
[0009]
According to a second aspect of the present invention, in the exhaust gas recirculation gas engine according to the first aspect, an EGR regulator (8) disposed in the EGR pipe (6) is detachably provided.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described with reference to the accompanying drawings. Figure 1 is schematic diagram of intake and exhaust system and a control system of the EGR type gas engine of the present invention, FIG. 2 is a correlation diagram of the NO _x amount and the knocking limit for EGR rate, Fig. 3 is a throttle downstream pressure P ₁ · P for the load factor ₂ and a graph of the boost pressure P ₃ and the electromagnetic valve opening / closing timing T. FIG. 4 is a schematic diagram of the supply / exhaust system of the EGR type gas engine and its control system when the EGR regulator 8 is omitted.
[0011]
First, a basic air supply / exhaust system structure of a gas engine according to the present invention will be described with reference to FIG. An exhaust pipe (exhaust manifold) extending from the cylinder head 1 a of the gas engine 1 is connected to the three-way catalyst 2, and the exhaust gas from which NO _x , HC and CO have been removed through the three-way catalyst 2 is excessive. It passes through the turbine section 3 a of the feeder 3, is introduced into the exhaust cooler (heat exchanger) 4, and is discharged through the exhaust discharge pipe 5. Since the exhaust gas passes through the three-way catalyst 2 on the upper side of the exhaust cooler 4, NO _x is also removed at the time of reaching the exhaust cooler 4, and also by condensation due to cooling of the exhaust cooler 4, Nitric acid is not generated, and corrosion of the exhaust system piping such as the exhaust discharge pipe 5 is eliminated.
[0012]
The EGR pipe 6 is branched from the exhaust discharge pipe 5 on the lower side of the exhaust cooler 4 and connected to the air supply pipe 12. In the EGR pipe 6, an EGR exhaust cooler (heat exchanger) 7, an EGR regulator 8, and an EGR control valve 9 are provided from the upstream side. An EGR mixer 11 is provided. In the air supply system, an air-fuel mixer 10 is disposed upstream of the EGR mixer 11. In the air-fuel mixer 10, the air A and the fuel gas G are mixed at a constant ratio (a constant excess air ratio) to generate an original air-fuel mixture. The EGR mixer 11 adds the exhaust gas E from the EGR pipe 6 to the original air-fuel mixture, which becomes an EGR air-fuel mixture that is sent from the blower portion 3b of the supercharger 3 and supplied to the air supply cooler (intercooler) 13 After that, the supply amount is adjusted by the throttle 14 and reaches the air supply port of the cylinder head 1a. The output adjustment, that is, the boost pressure (supply pressure) adjustment is based on the opening adjustment of the throttle 14, and the throttle 14 is automatically controlled by the electronic governor 15.
[0013]
A control system in the air supply / exhaust system of FIG. 1 will be described. As input means to the controller C, a supply air pressure sensor S1 is provided in the intake manifold downstream of the throttle 14, a rotation speed sensor S2 is provided in the crankshaft of the engine 1, a first exhaust sensor S3 is provided upstream of the three-way catalyst 2 in the exhaust pipe, and A second exhaust sensor S4 is provided in the exhaust discharge pipe 5. The first exhaust sensor S3 and the second exhaust sensor S4 are sensors for detecting the oxygen concentration in the exhaust gas. The effectiveness of the three-way catalyst 2 is measured by comparing the detection values of both sensors S3 and S4, and the catalyst replacement timing is determined. Use for confirmation. The fuel gas supply pipe 10a to the air / fuel mixer 10 includes a fuel gas G supply amount detection sensor S5 and an air / fuel ratio control valve for adjusting the fuel gas G supply amount to the air / fuel mixer 10. The electronic governor 15, the air-fuel ratio control valve 16, and the EGR control valve 9, which is an open / close valve for the EGR pipe 6, are controlled based on these inputs.
[0014]
Here, the output improvement effect by the provision of EGR (exhaust gas recirculation system) will be described with reference to FIG. When the air-fuel ratio (excess air ratio) is constant, the temperature in the combustion chamber increases as the net average effective pressure increases. The spontaneous ignition of the end gas near the cylinder liner in the combustion chamber, which causes knocking, is likely to occur when the temperature in the combustion chamber (particularly near the inner wall of the cylinder liner) reaches a certain level. The net average effective pressure at which this temperature is reached is the knock limit, that is, the upper limit value of the net average effective pressure. By the way, the exhaust E introduced from the EGR pipe 6 into the air supply pipe 12 does not contain oxygen O ₂ that contributes to combustion (mostly nitrogen N ₂ and carbon dioxide CO ₂ ). It becomes a cooling element. When the EGR mixture is supplied with the same net average effective pressure, the temperature in the combustion chamber during combustion is lower than when only the original mixture is supplied. Therefore, when the EGR mixture is supplied, the upper limit value of the net average effective pressure, that is, the knocking limit can be increased as compared with the case of supplying the original mixture, and the output can be improved correspondingly. Of course, if the temperature rise in the combustion chamber is suppressed, generation of NO _x due to combustion can be suppressed, and NO _x in the exhaust gas can be reduced. 2, there is shown the correlation of knock limit X and the exhaust amount of NO _x Y for EGR ratio (mixing ratio of EGR exhaust of the original mixture), as increasing the EGR rate, the knocking limit X rises, Further, it is understood that the exhaust amount of NO _x Y is reduced.
[0015]
However, the supply pressure of the exhaust E from the EGR pipe 6 to the EGR mixer 11 must also be stable for the effect of such EGR. The EGR mixer 11 which is a venturi mixer does not function effectively unless the upstream side is positive pressure. If the exhaust E supply from the EGR pipe 6 suddenly stagnate when the EGR operation is applied and the load is higher than the knocking limit without EGR, the knocking limit will be restored to the original level. The average effective pressure exceeds the knocking limit, which is the upper limit value, and knocking occurs. In FIG. 1, the EGR regulator 8 is provided in the EGR pipe 6 as described above in order to stably supply the exhaust E adjusted in pressure by the EGR regulator 8 from the EGR pipe 6 to the EGR mixer 11. is there.
[0016]
Next, referring to FIG. 3, a system for controlling the EGR operation timing based on the engine load will be described. In the graph of FIG. 3, the load factor W (%) is taken on the horizontal axis, the pressure P is taken on the vertical axis, and exhaust gas is sufficiently supplied to the turbine section 3a of the supercharger 3, so that the supercharger 3 operates effectively. It is assumed that the boost pressure P3 (supply pressure) has risen to the atmospheric pressure (P ₀ ) that is the operating lower limit pressure (idling state). The throttle downstream pressure (supply pressure) is a pressure value detected by the supply air pressure sensor S1 of the supply port, and is an EGR rate of 0%, that is, a pressure value P ₁ when only the original mixture is supplied. And the pressure value P ₂ when the EGR mixture is supplied at a constant EGR rate (for example, 30%).
[0017]
The load factor W is the ratio of the actual load to the rated upper limit value of the load, and is obtained by comparing the actual rotational speed detected by the rotational speed sensor S2 with the set rotational speed based on the opening adjustment of the throttle 14. It is done. When the load is applied from the idling state, the throttle downstream pressure rapidly increases, but the boost pressure P3 does not increase suddenly and remains at substantially the atmospheric pressure P ₀ because the rise of the supercharger 3 is delayed.
[0018]
When EGR is not performed (EGR rate 0%), the initial load (when load factor is ₀ ) is low because the throttle downstream pressure P ₁ (<P ₀ ) is low, and the limit load factor is W ₁ (for example, 50%). Load can be applied. However, when EGR is performed (for example, an EGR rate of 30%), the throttle downstream pressure reaches the atmospheric pressure P ₀ as soon as the load is applied, as much as the initial throttle downstream pressure P ₂ (<P ₀ ) increases. The limit load factor W ₂ (for example, 20%) becomes small (W ₂ <W ₁ ), and a sufficient load cannot be applied (the load factor that can be charged only (W ₁ −W ₂ ) is reduced. In order to increase the limit load factor at the time to W ₁ , EGR is not performed at the time of low load (when the load is applied), that is, the set load factor at the time of load application up to the load factor W _{1 as} shown in FIG. The opening time T of the EGR control valve 9 is set so that the load factor is W ₁ or more, and when the load factor is smaller than that, the EGR control valve 9 is closed and the supply pipe from the EGR pipe 6 is increased. No introduction of exhaust E to 12 Therefore, based on the opening and closing control of the EGR control valve 9, the throttle downstream pressure to the load factor, transitions as a thick line in FIG.
[0019]
In FIG. 3, the set load factor when the load is applied is set to the limit load factor W ₁ when the EGR rate is 0%. Of course, the set load factor when the load is applied is the limit load factor W _1. When a smaller value is acceptable (for example, the set load factor at the time of loading is 40%), the EGR control valve 9 may be opened at least when the load factor reaches this set load factor. When the set load factor is reached when the load is applied, the EGR can be immediately activated. However, in the case of very low load, increase the effect of knocking limit by EGR is not related, the average effective pressure of the cylinder based on the throttle downstream pressure P ₁ at the time of setting the load factor reaches is sufficiently lower than the knocking limit value If it exists, the EGR control valve 9 may be kept closed until the limit load factor W ₁ .
[0020]
When the opening / closing control of the EGR control valve 9 shown in FIG. 3 is introduced, the EGR regulator 8 in the EGR pipe 6 shown in FIG. 1 can be deleted (shown in FIG. 4). This is because the EGR is performed when the load factor is set to a limit load factor W ₁ or more for setting the valve opening timing T of the EGR control valve 9, and at this stage, the throttle downstream pressure P ₂ is sufficiently high. (The pressure higher than the atmospheric pressure P ₀ ), the pressure on the exhaust side is also high, and the pressure of the exhaust E in the EGR pipe 6 is also the same as that of the raw air-fuel mixture from the air-fuel mixer 10. Always higher than pressure. Therefore, in the EGR mixer 11 that is a venturi mixer, the air supply system side has a negative pressure compared to the EGR pipe 6 side, and the exhaust E from the EGR pipe 6 is always introduced. Therefore, when the EGR regulator 8 is detachable and the cost is reduced, the EGR regulator 8 may be deleted.
[0021]
In this configuration, since the exhaust gas after passing through the three-way catalyst is introduced into the exhaust gas recirculation system, exhaust gas without NO _x can be circulated to the air supply system, and furthermore, when an exhaust gas recirculation system is provided. In the exhaust cooler, there is a possibility that NO _x condenses, nitrifies, and corrodes the exhaust system piping. However, by passing the exhaust through the three-way catalyst on the upstream side of the cooler, Such corrosion in the exhaust system piping can be avoided.
[0022]
In addition, the exhaust gas in the exhaust gas recirculation system is introduced into a venturi mixer disposed at the junction with the air supply system in a state in which the exhaust gas is adjusted to a pressure higher than that of the air supply system by a regulator. The introduction of exhaust gas from the circulation system to the supply system is stable. Therefore, because the exhaust pressure from the exhaust recirculation system is not stable, suddenly no exhaust gas is introduced into the air supply system, so that the knocking limit will be lowered when exhaust recirculation is not performed, and sudden knocking will occur. Without worrying about, it is possible to control the supply air pressure and to apply a load assuming the knocking limit increased by exhaust gas recirculation.
[0023]
【The invention's effect】
Since the present invention is configured as described above, the following effects can be obtained.
That is, as described in claim 1, a turbocharger (3) is connected to an exhaust manifold extending from a cylinder head (1a) of a gas engine (1), and a turbine section of the supercharger (3) ( The exhaust gas that has passed through 3a) passes through the exhaust gas cooler (4) and is discharged from the exhaust gas discharge pipe (5), and an EGR pipe (6) branched from the exhaust gas discharge pipe (5) is installed. An EGR regulator (8) and an EGR control valve (9) are provided on the EGR pipe (6) from the upstream side, and an EGR mixing section is formed at the junction of the EGR pipe (6) and the supply pipe (12). In a gas engine equipped with an exhaust gas recirculation system provided with a vessel (11), when the load factor is at least equal to or less than the “set load factor when the load is applied”, the EGR control valve (9) is closed to The recirculation system is configured to be shut off, and the “set load factor at the time of loading” is When the GR control valve (9) is closed and the exhaust gas recirculation is not performed and the EGR ratio, which is the ratio of the EGR exhaust to the original air-fuel mixture, is operated at 0%, the throttle (14 ) Is the load factor when the pressure of the supply air pressure sensor (S1) provided in the supply manifold downstream of the pressure reaches atmospheric pressure , and if the load factor is higher than that, it exceeds the knocking limit and the limit at which knocking is likely to occur. The limit load factor (W ₁ ) is set so that the knocking limit (upper limit value of the net average effective pressure) is increased by providing an exhaust gas recirculation system in the gas engine due to the suppression effect of the temperature rise in the combustion chamber. Accordingly, the output can be increased especially under a high load.
[0024]
Furthermore, when the load is applied (when the load is low), the load factor can be obtained up to at least the set load factor when the load is applied by shutting off the exhaust gas recirculation system. And at the time of a high load at least equal to or higher than the set load rate, exhaust gas recirculation can increase the knocking limit and increase the output.
[0025]
When the control according to claim 1 is adopted as described in claim 2, the exhaust gas is recirculated when the exhaust pressure is higher than the mixed pressure (before the exhaust gas is introduced) in the supply system. Even if the exhaust gas is not used, the internal pressure of the exhaust gas recirculation system is higher than that of the air supply system via the venturi mixer, so the exhaust gas from the exhaust gas recirculation system to the air supply system via the venturi mixer Introduction is stable.
Therefore, when the EGR regulator 8 is detachable and the cost is reduced, the EGR regulator 8 may be deleted.
[Brief description of the drawings]
FIG. 1 is a schematic diagram of a supply / exhaust system of an EGR type gas engine of the present invention and a control system thereof.
FIG. 2 is a correlation diagram of NO _x amount and knocking limit with respect to EGR rate.
FIG. 3 is a graph showing throttle downstream pressures P ₁ and P ₂ and boost pressure P ₃ with respect to a load factor, and a solenoid valve opening / closing timing T;
FIG. 4 is a schematic diagram of an air supply / exhaust system of an EGR type gas engine and its control system when the EGR regulator 8 is omitted.
[Explanation of symbols]
1 Engine (gas engine)
DESCRIPTION OF SYMBOLS 1a Cylinder head 1b Crankshaft 2 Three-way catalyst 3 Supercharger 3a Turbine part 3b Blower part 4 Exhaust cooler (heat exchanger)
5 Exhaust discharge pipe 6 EGR pipe 7 EGR cooler (heat exchanger)
8 EGR regulator 9 EGR control valve (solenoid valve)
10 Air-fuel mixer 11 EGR mixer (Venturi mixer)
12 Air supply pipe 13 Air supply cooler (intercooler)
14 Throttle 15 Electronic governor 16 Air-fuel ratio control valve

Claims (2)

A turbocharger (3) is connected to an exhaust manifold extending from the cylinder head (1a) of the gas engine (1), and the exhaust gas passing through the turbine section (3a) of the supercharger (3) is cooled by exhaust gas. The EGR pipe (6) branched from the exhaust discharge pipe (5) is connected to the EGR pipe (6). An EGR regulator (8) and an EGR control valve (9) are interposed from the upstream side, and an EGR mixer (11) is provided at the junction of the EGR pipe (6) and the supply pipe (12). In a gas engine equipped with a recirculation system, the EGR control valve (9) is closed to shut off the exhaust gas recirculation system when the load factor is at least equal to or less than the “set load factor at load application”. The “set load factor at the time of loading” is the closed state of the EGR control valve (9). When the EGR ratio, which is the ratio of the EGR exhaust to the original air-fuel mixture, is operated at 0% without exhaust gas recirculation, it is provided in the air supply manifold downstream of the throttle (14) after the engine is started. The load factor when the pressure of the supply air pressure sensor (S1) reaches the atmospheric pressure, and if the load factor is higher than that, it exceeds the knocking limit and becomes the limit load factor (W ₁ ) that is the limit at which knocking is likely to occur. Exhaust gas recirculation type gas engine characterized by setting.   The exhaust gas recirculation type gas engine according to claim 1, wherein an EGR regulator (8) disposed in the EGR pipe (6) is detachably provided.

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