JPH0741879Y2 - Combustion control device for gas engine - Google Patents

Description

[Detailed Description of the Invention] [Industrial field of application] The present invention relates to a combustion control device for a gas engine, which can particularly reduce the NOx generation amount, and at the time of engine start, sudden load increase, etc. The present invention relates to a combustion control device for a stationary gas engine capable of ensuring a sufficient output when a high output is required.

[Prior Art] An industrial stationary engine for driving an air conditioning compressor, a generator, a water pump, etc. has been conventionally known (see, for example, Japanese Utility Model Laid-Open No. 62-119417). Generally, in such a stationary engine, unlike an automobile engine, it is operated at a relatively stable load, and it is possible to receive fuel directly from a fixed fuel supply source such as a gas plug or a gas tank. Therefore, an inexpensive gas such as natural gas or propane gas can be used as a fuel (for example, for a gas engine using propane gas as a fuel, see JP-A-63-5152).

[Problems to be Solved by the Invention] In general, gas fuel (at normal temperature and pressure) has a smaller carbon content than liquid fuel such as gasoline, and therefore when this fuel is used, the engine output becomes relatively low. Therefore, generally, in a conventional stationary gas engine, in order to improve the output, the air-fuel ratio (weight ratio of air to fuel A / F, the same applies below) is set to a relatively rich side for operation. Is being carried out. However, when the air-fuel ratio is set to the rich side in this way, there is a problem that the NOx (nitrogen oxide) concentration in the exhaust gas becomes high.

In recent years, NOx regulations have come to be applied to stationary gas engines, and measures for reducing the NOx generation amount are required. Therefore, by setting the air-fuel ratio to the lean side, NOx
Although a countermeasure to reduce the amount of generation is conceivable, if this is done, there is a problem that the output of the engine decreases as described above, and the output becomes insufficient at the time of high output demand such as at the time of starting or when the load suddenly increases.

The present invention has been made in view of the above-mentioned conventional problems, and can reduce the amount of NOx generated and can secure a sufficient output when a high output is required at the time of starting, sudden load increase, etc. An object is to provide a combustion control device for a gas engine.

[Means for Solving the Problem] The inventors of the present application conducted a detailed study on the characteristics of the NOx generation amount of the gas engine with respect to the operating state, and when the air-fuel ratio was set to the rich side, NOx in the medium output range was set. We discovered the fact that the amount of NOx produced was high and that the amount of NOx produced was low in the high or low output range. In addition, as described above, when the air-fuel ratio is set to the lean side, the NOx generation amount is significantly reduced in the entire operating range.

Also, in stationary gas engines, unlike automobile engines, etc., the throttle valve can be freely opened and closed during operation, so by changing the engine output due to changes in the air-fuel ratio, the throttle valve can be opened and closed. Can be compensated.

In order to achieve the above object, the present invention is a combustion control device provided for a gas engine in which the intake air amount can be changed by opening and closing a throttle valve. There are two types of air-fuel ratio characteristics, rich set and lean set. Normally, the engine is operated with the rich set, while the operating condition of the engine is such that the rich set causes a large amount of NOx generation. When entering, a combustion control device for a gas engine is provided, which is configured to operate the engine with a lean set and operate a throttle valve in an opening direction to compensate for a reduction in output due to lean intake air. To do.

[Advantage and effect of the invention] According to the present invention, the NOx that has a relatively high output in the air-fuel ratio characteristic and the output that is lower than that in the rich set
Two kinds of lean set with low generation amount are set. And
Although the engine is operated with the rich set in the high output region, the NOx generation amount is relatively small in this region as described above. Therefore, when a high output is required at the time of starting the engine or when the load is suddenly increased, a sufficient output can be secured according to the output demand, and the NOx generation amount can be reduced.

On the other hand, since the engine is operated with the lean set in the operating range where the NOx generation amount is increased with the rich set, that is, in the medium output range, the NOx generation amount is reduced. At this time, since the intake air becomes lean, the engine output should originally decrease with this, but here the throttle valve is operated in the opening direction,
Along with this, the amount of intake air increases and the pumping loss is reduced, so the engine output is increased and the output reduction due to lean intake air is compensated. Therefore, even in this operating region (medium output region), the required output can be sufficiently secured while reducing the NOx generation amount.

Therefore, it is possible to secure a sufficient output while reducing the NOx generation amount in the entire operation region.

[Examples] Examples of the present invention will be specifically described below.

As shown in FIG. 1, an intake passage 2 is provided for supplying intake air to a stationary gas engine 1. The intake passage 2 has a mixer 3 for mixing fuel gas with intake air in order from the upstream side. And a throttle valve 5 which is opened and closed by the actuator 4. The engine 1
The combustion gas of is discharged through the exhaust passage 6.

Then, a fuel gas supply passage 7 is provided to supply the fuel gas to the mixer 3, and an upstream end 7a of the fuel gas supply passage 7 is connected to a fuel gas supply source 8 (for example, a gas tank, a gas plug), The downstream end 7b is open to the venturi portion 9 of the mixer 3. In the venturi portion 9, as the intake amount is larger, that is, when the intake flow is faster, the intake pressure decreases in accordance with the general law regarding the hydrodynamic pressure and the flow velocity. On the other hand, since a slight gauge pressure (for example, 50 mm water column) is applied to the fuel gas supply passage 7, the fuel gas is supplied to the venturi portion 9 (mixer 3) almost in proportion to the intake air flow, and The fuel ratio is kept almost constant.

Further, a fuel gas bypass passage 11 having a diameter smaller than that of the fuel gas supply passage 7 is provided by branching from a portion slightly upstream of the downstream end portion 7b of the fuel gas supply passage 7, and the downstream end of the fuel gas bypass passage 11 is provided. The part 11b is open to the venturi part 9. The fuel gas bypass passage 11 is provided with a solenoid valve 12 for opening and closing the fuel gas bypass passage 11. When the solenoid valve 12 is opened, the fuel gas is supplied from the fuel gas bypass passage 11 to the mixer 3 almost in proportion to the intake amount by the same mechanism as in the fuel gas supply passage 7. There is. The fuel gas bypass passage 11
Has a smaller diameter than the fuel gas supply passage 7, the fuel gas supplied from the fuel gas bypass passage 11 is less than the fuel gas supplied from the fuel gas supply passage 7.

In the above configuration, when the solenoid valve 12 is closed, the fuel gas is supplied only through the fuel gas supply passage 7, so the air-fuel ratio becomes relatively lean, but this state will be referred to as lean set hereinafter. Further, when the solenoid valve 12 is opened, the fuel gas is supplied through both the fuel gas supply passage 7 and the fuel gas bypass passage 11, so that the air-fuel ratio becomes relatively rich. In the following, this state is referred to as rich set. .

In order to perform rich / lean switching control of the air-fuel ratio characteristic according to the operating state of the engine 1 and open / close control of the throttle valve 5 (hereinafter, such control is simply referred to as combustion control), a microcomputer The control unit 13 is composed of an intake pressure P detected by an intake pressure sensor 14, an engine speed N detected by a rotation speed sensor 15, and a throttle detected by a throttle sensor 16. The actuator 4 and the solenoid valve 12 are controlled using the opening TVθ and the engine target speed Ne set by the operator as control information.

The control method of the combustion control of the engine 1 by the control unit 13 will be described below with reference to the flowchart shown in FIG.

When the control is started, the target revolution speed Ne, the engine revolution speed N, the intake pressure P, and the throttle opening TVθ are read in step S1.

Next, in step S2, it is compared whether or not the engine speed N is equal to the target speed Ne.

As a result of the above comparison, if N = Ne (YES), engine 1
Is rotating exactly according to the preset target number of revolutions, and therefore the output is appropriate, and it is not necessary to change the operating state in terms of output. Therefore, it is determined whether the operating state of the engine 1 is in the region where the NOx generation amount should be suppressed, and N
If it is in the operation region where the Ox generation amount should be suppressed, the control is advanced to the NOx generation amount adjustment routine of steps S3 to S5 in order to make the air-fuel ratio characteristic lean set.

In step S3, it is compared whether or not the solenoid valve 12 is closed. As a result of comparison, solenoid valve 12
If NO is opened (NO), the air-fuel ratio characteristic is a rich set, so to determine whether the operating state is in a region where the amount of NOx generated is relatively large (near the middle output region). , Step S4 is executed.

In step S4, it is compared whether or not the operating state of the engine 1 is within the area A in FIG. As shown in FIG. 3, the operating region of the engine 1 is represented by the engine speed N and the intake pressure P. Here, the straight lines l ₁ and l ₂ are
Each shows the upper limit and the lower limit of the operable range when the solenoid valve 12 is opened (rich set), and the region A shows an operating region where the output is high and the NOx generation amount is relatively small.
Region B shows an operating region where the amount of NOx generated is particularly large.

As a result of the above comparison, if the operating state of the engine 1 is in the region A (YES), it is considered that the NOx generation amount is relatively small, and therefore it is not necessary to switch to the lean set, so nothing is done. Then, the process returns to step S1.

As a result of the comparison in step S4, if the operating state of the engine 1 is not within the region A in FIG. 3 (NO), it is considered that the NOx generation amount is relatively large, and therefore the NOx generation amount is reduced. In step S5, the solenoid valve 12 is closed, the air-fuel ratio characteristic is switched to lean set, and then the process returns to step S1.

If the solenoid valve 12 is closed (YES) as a result of the comparison in step S3 described above, nothing is done because it is already a lean set, and then the process returns to step S1.

As described above, during rich set (solenoid valve 12
Open), the amount of NOx generated is particularly high in the medium output range,
Although the NOx generation amount decreases in the high output region or the low output region, an example of this measured data is shown in FIG.

In FIG. 4, the solid line shows the characteristics of the engine output at the rich set with respect to the engine speed N and the intake pressure P, and the broken line shows the engine speed N and the engine output of the NOx concentration index I of the exhaust gas. Shows the characteristics for. The NOx concentration index I is an index of the NOx generation amount, and is proportional to the NOx concentration in the exhaust gas. As is clear from FIG. 4, NOx in the medium output range (intake pressure −200 mmHg vicinity)
The concentration index I is extremely high at 100 to 110.

Further, as described above, at the time of lean set (the solenoid valve 12 is closed), the NOx generation amount becomes relatively small in the entire output region. In Fig. 5, an example of this actual measurement data is expressed according to Fig. 4. I will show you how. As is clear from FIG. 5, the NOx concentration index I is low in the entire operating region of the engine 1.

Fig. 6 shows the characteristics of engine output with respect to air-fuel ratio and NOx.
An example of the measured data of the characteristic of the concentration index I with respect to the air-fuel ratio is shown. As is apparent from FIG. 6, the engine output monotonously decreases as the air-fuel ratio increases, but the NOx concentration index I shows a peak at a certain air-fuel ratio. As shown by S, when the engine speed N is 1800 rpm and the throttle valve is fully opened (WOT), if the air-fuel ratio is changed from 16.3 to 21.4, the NOx concentration index I becomes 16 However, the engine output at this time is 7 P.S.
%)descend.

FIG. 7 shows the characteristics of the excess air ratio λ at which the NOx concentration peaks, with respect to the engine speed N and the engine output.
As is clear from FIG. 7, the excess air ratio λ at which the NOx concentration peaks is approximately 1.03, except when the engine speed is low and the load is light.
It is in the range of ~ 1.08.

By the way, as a result of the comparison in step S2 described above, N ≠ Ne
If (NO), since the engine output is excessive or insufficient, the output adjustment routine of steps S6 to S11 is executed to adjust the output.

In step S6, it is compared whether or not the engine speed N is higher than the target speed Ne.

As a result of the comparison, if N> Ne (YES), the engine output is excessive, so the throttle valve 5 is operated in the closing direction in step S7 in order to reduce the engine output. After this, the control returns to step S1 and continues, but as long as N> Ne, step S1 → step S2 → step S6 → step S7 is repeatedly executed, and the throttle valve 5 is closed until N = Ne. The operation is repeated.

As a result of the comparison in step S6, if N <Ne (NO), the engine output is insufficient, so steps S8 to
The output is increased with S11. First, in step S8, it is compared whether or not the throttle valve 5 is fully open. As a result of the comparison, if the throttle valve 5 is not fully opened (NO), the throttle valve 5 is operated in the opening direction in step S9. After this, the control returns to step S1 and continues,
Unless N <Ne and the throttle valve 5 is not fully opened, step S1 → step S2 → step S6 → step S8
→ Step S9 is repeatedly executed, and the opening operation of the throttle valve 5 is repeated until N = Ne.

As a result of the comparison in step S8, if the throttle valve 5 is fully opened (YES), the throttle valve 5 cannot be opened any further, so that the engine output cannot be increased by controlling the throttle valve 5. Therefore, in step S10, it is compared whether or not the solenoid valve 12 is closed. If the solenoid valve 12 is closed (lean set), the solenoid valve 12 is closed in step S11.
Is opened, the air-fuel ratio characteristic is switched to the rich set, the engine output is increased, and then the process returns to step S1.

As a result of the comparison in step S10, the solenoid valve 1
If 2 is opened (NO), the rich set has already been made, so step S11 is skipped, and thereafter, the process returns to step S1.

By such control, it is possible to secure a sufficient output at the time of high output demand such as engine start and sudden load increase, while reducing the amount of NOx generated.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of a gas engine equipped with a combustion control device according to the present invention. FIG. 2 is a flowchart showing a control method of combustion control by the control unit. Figure 3 shows engine operating limits, high power range, and NOx.
FIG. 6 is a diagram showing a region where a large amount is generated, with respect to engine speed and intake pressure. FIG. 4 is a diagram showing the engine output with respect to the engine speed and the intake pressure and the NOx concentration index with respect to the engine speed and the engine output when the air-fuel ratio characteristic is set to a rich set. Fig. 5 shows the case where the air-fuel ratio is lean set,
It is a figure similar to FIG. Fig. 6 shows characteristics of engine output with respect to air-fuel ratio and NOx
It is a figure which shows the characteristic with respect to an air-fuel ratio of a concentration index. FIG. 7 is a diagram showing the characteristics of the excess air ratio at which the NOx concentration reaches a peak, with respect to the engine speed and the engine output. 1 ... Engine, 2 ... Intake passage, 3 ... Mixer, 4 ... Actuator, 5 ... Throttle valve, 6 ... Exhaust passage, 7 ...
Fuel gas supply passage, 8 ... Fuel gas supply source, 9 ... Venturi part, 11 ... Fuel gas bypass passage, 12 ... Solenoid valve, 13 ... Control unit.

Claims (1)

[Scope of utility model registration request] 1. A combustion control device provided for a gas engine in which an intake air amount can be changed by opening and closing a throttle valve, wherein air-fuel ratio characteristics of the engine are set to two types, a rich set and a lean set. , Normally, while operating the engine with the rich set, when the operating state of the engine enters the operating range where the NOx generation amount increases with the rich set, while operating the engine with the lean set, A combustion control device for a gas engine, wherein a throttle valve is operated in an opening direction to compensate for a reduction in output due to lean intake air.