JPH06317199A - Air-fuel ratio controlling method/equipment for lean-burn engine - Google Patents

Abstract

PURPOSE:To reduce the concentration of oxides of nitrogen by detecting the number of revolutions of a lean-burn engine, calculating the rotational variation based on this detection value in order to judge whether or not the rotational variation lies within the tolerance, and controlling air-fuel ratio to a lean side when the rotational variation lies within the tolerance but to a rich side when it is out of the tolerance. CONSTITUTION:This gas engine 1 is supplied with a mixture of fuel gas and air via an air supplying passage 3, fuel supplying passage 4, a mixer 5, and a mixture supplying passage 6. A by-path passage 7 is branched off from the fuel supplying passage 4, and this by-path passage 7 and the mixture supplying passage 6 meet via a by-path valve 8. The opening of the by-path valve 8 is determined by a CPU 10, or a controlling means. The CPU 10 detects the number of revolutions of a gas engine in order to calculate the rotational variation. When the rotational variation lies within the tolerance, the air-fuel ratio is controlled to a lean side, while, when the variation is out of the tolerance, the ratio is controlled to a rich side. Thus, the concentration of oxides of nitrigen can be restricted to the limit.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to a method and apparatus for controlling the air-fuel ratio of a lean burn gas engine in combination with a generator or heat pump.

[0002]

2. Description of the Related Art In order to control the air-fuel ratio of a lean burn gas engine, open control in which the air-fuel ratio is set to a predetermined value in advance has been most often used. Further, although the absolute number is extremely small, control using a so-called “λ sensor” is also performed.

[0003]

However, when the open control is adopted, individual variations of mass-produced engines, environmental conditions, and the like (in the nitrogen oxide concentration of a lean burn gas engine, the influence of humidity is particularly noticeable). (To be large), so that the air-fuel ratio can be adjusted to the operating limit (when combined with the generator set, the allowable frequency fluctuation of the electric power)
I have no choice but to set it on the rich side. Therefore, it was not possible to sufficiently reduce the nitrogen oxide concentration.

On the other hand, when the λ sensor is used, there is a problem that the λ sensor itself is expensive and the cost is high. Further, since the combustion state of the engine changes due to variations in the air-fuel ratio control system using the λ sensor and environmental conditions, it is difficult to control near the operating limit.
Inevitably, the control target λ must be set small and set with a margin. As a result, the air-fuel ratio was set to the rich side, which was still insufficient for reducing the nitrogen oxide concentration.

On the other hand, when the lean-burn gas engine is combined with a generator, it is important that the quality of the electric power from the generator, that is, the power frequency is uniform and the fluctuation is small. When a so-called gas engine heat pump (GHP) is configured by combining a lean burn gas engine with a heat pump, the engine speed changes in response to a thermal load, but there is little fluctuation in the engine speed at each engine speed. Things are required.

The present invention has been proposed in view of the problems of the prior art, and it is possible to reduce the nitrogen oxide concentration as much as possible, and moreover, it occurs when combined with a generator or a gas engine, for example, It is an object of the present invention to provide a method and an apparatus for controlling the air-fuel ratio of a lean-burn gas engine so that various undesired fluctuations such as fluctuations in power frequency are within allowable values.

[0007]

As a result of various researches and developments, the inventor has shown, as shown in FIG. 1, fluctuations in frequency of electric power from a generator combined with a lean burn gas engine (shown in the upper half of FIG. 1). It has been noted that the characteristics (shown in FIG. 1) directly appear in the fluctuations in the rotational speed of the gas engine (the characteristics shown in the lower half of FIG. 1). At the same time, the inventor also noticed that, as shown in FIG. 2, the fluctuation in the rotational speed of the gas engine increases as the air-fuel ratio (λ) increases. Here, the operation limit of the lean burn gas engine combined with the generator is an air-fuel ratio that satisfies the allowable value of the frequency fluctuation of the electric power.

The above is the same when the lean burn gas engine and the heat pump are combined. That is, even when controlling a gas engine heat pump configured by combining a heat pump and a lean burn gas engine, the rotational speed of the gas engine is detected, and an allowable value of rotational speed fluctuation corresponding to the rotational speed is calculated. There is a need.

The air-fuel ratio control method for a lean-burn gas engine according to the present invention based on the above-mentioned findings includes a step of detecting the rotational speed of the lean-burn gas engine, and a rotational fluctuation value calculated from the detected rotational speed. A step of determining whether the rotational fluctuation value is within the allowable range, and if the rotational fluctuation value is within the allowable range, the air-fuel ratio is controlled to the lean side, and if it is outside the allowable range, the rich side is controlled. The process includes and.

Further, the air-fuel ratio control apparatus for the lean burn gas engine of the present invention detects the rotational speed of the lean burn gas engine and a rotational fluctuation value from the detected rotational speed to calculate the rotational fluctuation value. Judgment means for judging whether or not it is within the permissible range, and air-fuel ratio control means for controlling the air-fuel ratio to the lean side when the rotational fluctuation value is within the permissible range and to the rich side if it is outside the permissible range. , And are included.

Here, it is preferable that the above lean burn gas engine is combined with a generator or with a heat pump to form a gas engine heat pump.

[0012]

According to the air-fuel ratio control method and apparatus for a lean burn gas engine of the present invention having the above-described structure, the rotational speed of the lean burn gas engine combined with the generator is detected, and the detected rotation is detected. The rotational fluctuation value is calculated from the number to determine whether the rotational fluctuation value is within the allowable range, and when the rotational fluctuation value is within the allowable range, the air-fuel ratio is controlled to shift to the lean side. If it is outside the allowable range, control is performed so as to shift to the rich side. In other words, since the control shifts to the lean side or steps as long as the rotation fluctuation value is within the allowable range, it is not necessary to perform the control on the rich side more than necessary unlike the conventional control. Since the lean side is controlled as much as possible, the nitrogen oxide concentration is reduced as much as possible.

Here, as the control shifts or steps to the lean side, the fluctuation of the rotation speed increases, but according to the present invention, when the control goes too far to the lean side and the fluctuation value of the rotation speed exceeds a predetermined range. Is stepped to the rich side.
As shown in FIG. 2, if the control is stepped to the rich side, fluctuations in the rotational speed of the gas engine are reduced. As is apparent from FIG. 1, if the fluctuation of the rotational speed of the gas engine is within the predetermined range, the fluctuation value of the frequency of the electric power from the generator combined with the gas engine is also within the predetermined range. .

As described above, according to the present invention, when the frequency fluctuation of the supplied electric power is within a certain range,
The control stepped to the lean side is performed as much as possible. Therefore, it is possible to obtain so-called "good quality" electric power having a uniform frequency, and at the same time, it is possible to reduce the nitrogen oxide concentration as much as possible under the control stepped to the lean side.

Further, when a gas engine heat pump is constructed by combining a lean burn gas engine and a heat pump, the set rotational speed of the gas engine changes in response to a cooling or heating load (thermal load), and the change occurs. The permissible value of the rotational speed fluctuation is determined in response to the set rotational speed. The other actions are similar to those in the case where the generator and the gas engine are combined.

[0016]

Embodiments of the present invention will be described below with reference to FIGS.

FIG. 3 shows a lean burn gas engine 1 to which the present invention is applied and a generator 2 combined with it. A mixture of fuel gas and air is supplied to the gas engine 1 through an air supply passage 3, a fuel supply passage 4, a mixer 5, and a mixture supply passage 6. A bypass passage 7 branches off from the fuel supply passage 4, and the bypass passage 7
Merges with the mixture supply passage 6 via the bypass valve 8. In other words, the bypass passage 7 bypasses the mixer 5.

The bypass valve 8 is opened and closed by an actuator 9 composed of, for example, a stepping motor, and its opening is determined by a CPU 10 which is a control means. Then, a detection signal from the rotary pickup 11 that detects the rotation speed of the gas engine 1 and a detection signal of the load sensor 12 that detects the load of the generator 2 are input to the CPU 10.
The output of the rotary pickup 11 is also sent to the throttle valve control means 14 that controls the throttle valve 13 provided in the mixture supply passage 6.

The air-fuel ratio of the gas engine 1 depends on the bypass valve 8
It is performed by adjusting the opening degree of. In the embodiment shown in FIG. 3, the opening degree control of the bypass valve 8 is performed by the CPU 10 and the actuator 9 according to the flowchart shown in FIG. 4, but before explaining the control shown in the flowchart of FIG. The main routine of the air-fuel ratio control shown in FIG. 5 will be described.

In FIG. 5, when the operation of the gas engine 1 and the generator 2 is started (steps S1 and S2), the load of the generator 2 is detected by the load sensor 12, and the detection result is determined by the CPU 10 (step S3). ). Then, first, it is determined whether or not the steady operation is being performed (step S4).

During unsteady operation (step S4 is N
O) Load fluctuation, start / stop control is performed (step S
5) If it is a steady operation (YES in step S4), to what extent the fluctuation of the rotation speed of the gas engine 1 is allowed according to the load determined in step S3, that is, the rotation fluctuation allowable value is set to Determine (Step S
6). Then, the rotation variation value is calculated or determined from the detection result of the rotary pickup 11 (step S7), and the opening degree of the bypass valve 8 is controlled using the calculation (determination) result of the rotation variation value (step S8). Note that step S7 will be described later with reference to FIG. 6, and details of step S8 will be described later with reference to FIG.

After controlling the opening degree of the bypass valve 8, the system waits for a period necessary for changing the combustion state of the gas engine 1 and the operating state of the generator 2 (step S9). Then, the load of the generator 2 is determined again (step S3).

The above-described calculation or determination process of the rotation fluctuation value (step S7 in FIG. 5) will be described with reference to FIG. First, the output from the rotary pickup 11 is read a predetermined number of times (for example, n) (NO in steps S10 and S11). If the reading of a predetermined number of times is completed (YES in step S11), the n variation data is used to calculate or determine the rotation fluctuation value. Here, "calculation or determination" of the rotation fluctuation value
The phrase "is used" means that the method of obtaining the rotation fluctuation value from the output of the rotary pickup 11 is not limited to arithmetic processing (there are many types), but there are various methods. This is to clarify that there is no limitation.

When the rotation fluctuation value is calculated or determined, the numerical value is stored (step S13) and the process returns to the initial stage (step S14).

A step of controlling the opening degree of the bypass valve 8 using the rotation fluctuation value calculated or determined in this way (FIG. 5).
Step S8) will be described with reference to FIG.
When controlling the opening degree of the bypass valve, first, the rotation fluctuation allowable value obtained in step S6 of FIG. 5 is read (step S20). Next, the rotation fluctuation value obtained in the step described above with reference to FIG. 6 and step S7 in FIG. 5 is read (step S21). Then, it is determined whether or not the rotation fluctuation value is within the range of the rotation fluctuation allowable value (step S2).
2).

In the embodiment shown in FIG. 3, the actuator 9 for controlling the opening degree of the bypass valve 8 is composed of a stepping motor. Then, based on the determination result in step 22, when the opening degree of the bypass valve 8 is decreased to increase the air-fuel ratio, the lean side is stepped, and when the air-fuel ratio is decreased, the rich side is stepped. Has been done. That is, when the rotation fluctuation value is within the rotation fluctuation allowable value range (YES in step S22), the CPU 10 controls the stepping motor so that the control is made leaner and the nitrogen oxide concentration is further reduced. Send a signal to step to the lean side. Therefore, the step position is calculated (step S23), the step speed is calculated (step S24), and then the lean side is stepped (steps S25 and S26).

On the other hand, when the rotational fluctuation value exceeds the allowable rotational fluctuation value range (NO in step S22), the air-fuel ratio is set too high and the frequency fluctuation of the electric power from the generator 2 is somewhat increased. to decide. Then, necessary processing is performed to reduce the air-fuel ratio and make the control rich. That is, the step position is calculated (step S27), the step speed is calculated (step S28), and then the rich side is stepped (steps S29 and S3).
0).

After the necessary processing is performed based on the determination result of step S22, the control is returned to the initial stage (step S31).

Although the above embodiments describe the combination of the lean burn gas engine and the generator, the present invention is also applicable to the combination of the gas engine and the heat pump. FIG. 7 shows a gas engine heat pump 20 configured by combining the gas engine 1 and the heat pump 22, and the heat pump 22 includes a condenser 24 and an evaporator 26. For other configurations, see FIG.
Since the embodiment shown by 1 and the embodiment shown in FIG. 3 are substantially the same, duplicate description will be omitted.

The operation of the embodiment shown in FIG. 7 is also shown in FIG.
It is almost the same as the embodiment shown by. However, in the main routine of the air-fuel ratio control shown in FIG. 5, the rotation fluctuation allowable value is determined immediately after it is determined that the operation is steady (after determining that step S4 is YES). This is not done in the air-fuel ratio control main routine (FIG. 8) of the embodiment shown. In the control routine shown in FIG. 8, after it is determined that the operation is steady (step S4 is Y
Detection means (sensor: not shown) for detecting a cooling load or a heating load (thermal load) after determining that it is ES)
The number of revolutions of the gas engine 1 is determined based on the detection result of (1) (step S40 in FIG. 8), and the rotation fluctuation allowable value is determined based on the number of revolutions of the gas engine determined in step S40 (step S42). However, the process or algorithm for determining the rotation fluctuation allowable value in step S42 differs depending on each case, and thus detailed description thereof will be omitted.

With respect to other configurations and effects, the embodiment combined with the gas engine heat pump 20 is substantially the same as the embodiment combined with the generator 2. Therefore, duplicate description will be omitted.

It should be noted that the illustrated embodiment is merely an example and is not intended to limit the technical scope of the present invention.

[0033]

The effects of the present invention are listed below.

(1) Since information is obtained from the engine body by the rotary pickup, it is not affected by engine performance, sensors, or variations in them.

(2) Since the control is performed on the basis of the fluctuation of the rotational speed which is a parameter related to the rotational speed of the gas engine, it is not affected by changes in environmental conditions such as humidity.

(3) It is not necessary to perform control on the rich side more than necessary as in conventional control.

(4) Since control is performed on the lean side as much as possible, control can be performed near the operating limit, and the nitrogen oxide concentration can be suppressed to the limit.

(5) Since the control system can be simplified, reliability and durability can be improved and cost can be reduced.

(6) Since the control is performed on the basis of the fluctuation of the rotation speed, the quality of the electric power from the generator is directly evaluated.

(7) The fluctuation value of the frequency of the electric power from the generator combined with the lean burn gas engine can be kept within a certain range.

(8) So-called "good quality" with uniform frequency
Electric power can be obtained, and at the same time, the nitrogen oxide concentration can be reduced as much as possible under the control stepped to the lean side.

(9) Since the control is performed on the basis of the fluctuation of the rotational speed, the operability of the gas engine heat pump is directly evaluated.

(10) The fluctuation of the operation of the gas engine heat pump combined with the lean burn gas engine can be kept within a certain range.

(11) The nitrogen oxide concentration can be reduced as much as possible under the lean step control while the gas engine heat pump can be operated appropriately.

[Brief description of drawings]

FIG. 1 is a characteristic diagram showing a relationship between a frequency fluctuation characteristic of electric power from a generator and a rotation fluctuation of a lean burn gas engine.

FIG. 2 is a characteristic diagram showing the relationship between the rotation fluctuation of the lean burn gas engine and the air-fuel ratio.

FIG. 3 is a block diagram showing a combination of a lean burn gas engine and a generator according to an embodiment of the present invention.

FIG. 4 is a view showing a flowchart of a bypass valve opening control routine.

5 is a diagram showing a main flowchart of the embodiment shown in FIG.

FIG. 6 is a diagram showing a flowchart of a control routine for calculating or determining a rotation fluctuation value.

FIG. 7 is a block diagram showing a combination of a lean burn gas engine and a heat pump according to an embodiment of the present invention.

FIG. 8 is a diagram showing a main flowchart of the embodiment shown in FIG.

[Explanation of symbols]

 1 ... Lean combustion gas engine 2 ... Generator 3 ... Air supply passage 4 ... Fuel supply passage 5 ... Mixer 6 ... Mixture supply passage 7 ... Bypass passage 8 ... -Bypass valve 9 ... Actuator 10 ... CPU 11 ... Rotation pickup 12 ... Load sensor 13 ... Throttle valve 14 ... Throttle valve control means 20 ... Gas engine heat pump 22 ... Heat pump 24 ... Condenser 26 ... Evaporator

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location F02M 21/02 311 E

Claims (2)

[Claims] 1. A step of detecting the rotational speed of a lean burn gas engine, a step of calculating a rotational fluctuation value from the detected rotational speed to determine whether the rotational fluctuation value is within an allowable range, A method of controlling the air-fuel ratio of a lean-burn gas engine, comprising the step of controlling the air-fuel ratio to the lean side when the rotational fluctuation value is within the permissible range, and controlling it to the rich side if outside the permissible range. . 2. A detecting means for detecting the rotational speed of the lean burn gas engine, and a judging means for calculating a rotational fluctuation value from the detected rotational speed to judge whether or not the rotational fluctuation value is within an allowable range. And a lean-burn gas engine that controls the air-fuel ratio to the lean side when the rotational fluctuation value is within the allowable range and to the rich side when the rotational fluctuation value is outside the allowable range. Air-fuel ratio controller.