JP2002267159A - Air-fuel ratio control method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an air-fuel ratio control method and device capable of effectively obtaining a combustion state for getting the maximum heat generation rate of a supplied fuel quantity by controlling the air-fuel ratio while the mass flow rate of each of air quantity and fuel quantity is always monitored and grasped. SOLUTION: In the air-fuel ratio control method and device, at least one of the mass flow rate of air quantity and the mass flow rate of fuel quantity is measured to control combustion on the basis of the mass flow rate and increase or decrease at least one of the air quantity and the fuel quantity during the combustion. At least one of the air quantity and the fuel quantity is increased or decreased to burn air or fuel on the basis of the change of the combustion state due to the above-described increase or decrease so that the air fuel ratio becomes a theoretical air-fuel ratio.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an air-fuel ratio control method and an air-fuel ratio control apparatus for use in a combustor such as a gas-fired boiler or a combustion furnace for controlling combustion so as to obtain maximum combustion efficiency. Things.

[0002]

2. Description of the Related Art (1) Conventionally, when combustion air from a fan motor and gas (fuel gas such as city gas, propane gas, etc.) are mixed and burned by a burner, the combustion state is optimized. 2. Description of the Related Art There is known an apparatus that performs control for adjusting the amount of air and the amount of fuel to feed the burner (hereinafter, referred to as air-fuel ratio control). The amount of air is adjusted by air flow control (air amount adjustment system) by damper, inverter control, etc., and the amount of fuel is adjusted by a motor valve or an opening adjustment type valve called a proportional valve (fuel amount adjustment system). I have. For example, (a) the coordination between the air amount adjustment system and the fuel amount adjustment system is adjusted by a mechanical link mechanism, (b) an equalization proportional method in which the air pressure is reflected on the fuel pressure, and (c) the air amount adjustment. There is known a method of independently controlling the flow rate independently of the system and the fuel amount adjusting system.

[0003] (2) The detection of the flow rate in the above-described combustion control includes, for example, (a) converting the air amount or the fuel amount itself or the ratio of the air amount and the fuel amount (air-fuel ratio) to a differential pressure by a flow meter or a pressure gauge. There is known a method of performing air-fuel ratio control based on (b) a flow value obtained by calculating a flow value from an opening position of the damper or the control valve.

(3) The result of the air-fuel ratio control is
(A) As a method of judging from the composition of exhaust gas after combustion, an excess or deficiency of oxygen, that is, a deviation from a stoichiometric air ratio (a ratio of a theoretical air amount to a fuel amount) is determined by an oxygen sensor, a carbon monoxide sensor, or the like. Air-fuel ratio control that adjusts the amount of air or fuel by detecting whether optimal combustion has been performed by detecting with a carbon dioxide sensor or the like, or (b) the temperature of hot air, the temperature of hot water, and the generation of hot air output from the combustion device It is also known to make a determination based on whether or not a combustion product such as a steam amount has reached a maximum value. In the example using an oxygen sensor, the air amount control system or the fuel amount control system controls the amount of oxygen contained in exhaust gas to be minimized when air and fuel are sent to the burner, that is, the fuel amount is controlled. There is also known an air-fuel ratio control for controlling the amount of air so that there is no unburned portion and preventing the amount of air from becoming excessive, and for minimizing the generation of carbon monoxide and soot due to lack of oxygen. That is, if the amount of air (the amount of oxygen) is less than the theoretical amount of air, incomplete combustion occurs and the amount of generated heat decreases. On the other hand, if the amount of air exceeds the theoretical amount of air, the surplus air takes away heat and the effective calorific value decreases. This is because burning with the theoretical amount of air maximizes the amount of heat obtained by heat exchange. For example, in the case of a hot water boiler, the generated hot water temperature and the amount of hot water are maximized by burning with the theoretical amount of air. In the case of a steam boiler and the like, the amount of generated evaporation is similarly maximized.

[0005]

As described above, the conventional air-fuel ratio control device is constituted, but since the measurement of the air amount and the fuel amount does not measure the mass flow rate itself, the boiling fuel is used. According to the law, there is a change in the density of air and fuel due to a change in temperature, so that the air-fuel ratio at which the maximum calorific value can be obtained cannot be uniquely obtained. That is, since the air-fuel ratio control is performed on the premise of the density of air and fuel at the reference temperature, it is not always possible to perform the combustion control that can obtain the maximum calorific value depending on the temperature and the pressure under various operating conditions. could not. In addition, it is necessary to correct the volume flow rate in accordance with the ambient temperature.Although mass flow meters are conventionally known, they are expensive and have a large heat capacity, so that the air-fuel ratio is low. It could not be used for control.

For example, even in the case of city gas (natural gas), the calorific value is supplied so as to be within a certain standard range. For example, in the case of 13 A of natural gas, the unit volume at a standard temperature and a standard pressure is provided. The calorific value per unit is 42000KJ / m3
４46000 KJ / m3. However, the composition of the fuel may change due to a change in the content ratio of methane or the like in order to achieve the above-mentioned heat generation value. Even within the above calorific value range,
Since the mass per unit of fuel changes, an accurate air-fuel ratio cannot be maintained. Further, with a flow rate sensor having a slow response, when the flow rate changes every moment due to a change in fuel pressure, the mass flow rate cannot be measured accurately enough to be used for air-fuel ratio control. On the other hand, the masses of air and fuel vary with temperature and pressure in accordance with Boyle-Charles law. For this reason, in a control method in which the constant value opening of the pressure detecting means, the air amount adjusting means and the fuel amount adjusting means is regarded as a constant value flow rate, when the temperature or pressure of air or fuel changes, accurate air In some cases, the amount or fuel amount could not be determined, and an air-fuel ratio deviation sometimes occurred. Therefore, in particular, in a combustion apparatus in which the combustion amount is continuously varied, it was not possible to obtain the maximum calorific value in each combustion position from a small combustion amount to a large combustion amount.

For example, at the maximum combustion amount position (100%), even if the air-fuel ratio is optimally maintained, the 75% position, the 65% position,
The air-fuel ratio could not be maintained optimally at each of the 45% position and the like. In particular, in adjusting the fuel amount, even if the opening of the fuel amount adjusting valve is adjusted so that the fuel amount becomes 80%, there is provided a means for confirming whether the fuel amount sent to the burner has become 80%. Did not. The amount of fuel is
Whether the fuel control valve has adjusted the fuel amount from the direction of the maximum fuel position (for example, in the counterclockwise direction) (X direction in FIG. 7A) or adjusted from the direction of the minimum fuel amount position (for example, the clockwise direction). 7 (b) (Y direction), the opening of the fuel control valve changes within the range of play.

This is because a gap between the shaft MS of the motor and the shaft VS of the fuel control valve causes play of the opening (see FIG. 7C). Furthermore, since this play increases with the aging, periodic maintenance is required. Specifically, even if the fuel amount is adjusted to the 80% fuel amount position, the fuel amount may be 82% or 78%. Therefore, when it is considered that the energy obtained by the combustion such as the combustion temperature and the steam amount is maximized at the fuel amount of 80%, the actual fuel amount may be, for example, 82%, and there is still room for improvement in the air-fuel ratio. May remain.
Furthermore, it is difficult to maintain an optimum air-fuel ratio due to the influence of temperature and atmospheric pressure. The above problems are caused by the fact that the mass flow rate of the fuel is not accurately grasped.

More specifically, the problem can be solved by measuring the atmospheric pressure and air temperature, correcting and calculating the density of the fuel, and calculating the mass flow rate. However, the combustion control device itself includes a pressure sensor, a temperature sensor, and a correction sensor. It is necessary to provide calculation means, and the configuration becomes complicated. That is, even if an attempt is made to obtain the maximum heat generation amount with respect to the input amount of the fuel amount, an accurate input value of the fuel amount cannot be measured for the above-described reason. Therefore, conventionally, input (effective)
Combustion control to make the maximum heat generation state from the heat generation amount could not be performed. The present invention has been made in order to solve the above-described problems, and by performing air-fuel ratio control while constantly monitoring and grasping the mass flow of the air amount and the fuel amount, the maximum heat generation amount of the supplied fuel amount can be reduced. It is an object of the present invention to provide an air-fuel ratio control method and an air-fuel ratio control device capable of achieving an obtained combustion state.

[0010]

In order to solve the above-mentioned problems, the air-fuel ratio control method and apparatus according to the first and fifth aspects of the present invention provide a method for controlling the mass flow of the air amount and the mass flow of the fuel amount. Measuring at least one of the mass flow rates,
Combustion is controlled based on the mass flow rate, and at least one of the air amount and the fuel amount is increased or decreased during the combustion control.Based on the change in the combustion state due to the increase or decrease, the air is adjusted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. At least one of the fuel amount and the fuel amount is adjusted for combustion. Since the mass flow rate of the air amount or the fuel amount is measured, the mass of the air or the fuel can be reliably detected. Also, by measuring the mass flow rate,
An optimum air-fuel ratio is obtained at any combustion amount position from the minimum fuel amount position to the maximum fuel position.

Further, at least one of the air amount and the fuel amount is increased or decreased during the combustion control, and based on a change in the combustion state due to the increase or decrease, at least the air amount or the fuel amount is adjusted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Combustion with the optimum air-fuel ratio can be always performed by controlling the combustion by adjusting either one. Further, it is possible to correct the fluctuation of the control amount due to the time change of the air amount and the combustion amount adjusting means, and to always obtain the optimum air-fuel ratio state. In the air-fuel ratio control method and apparatus according to the second and sixth aspects of the present invention, the mass flow rate is measured using a micro flow sensor. By using a micro flow sensor, it is possible to measure an accurate mass flow rate. Further, the air-fuel ratio control method according to claim 3 of the present invention determines a change in the combustion state based on the amount of heat generated during combustion and evaluates whether the air-fuel ratio is in the stoichiometric air-fuel ratio state. I have.

A change in the combustion state can be easily determined based on the amount of heat generated during combustion, and the evaluation of the air-fuel ratio can be reliably performed. In the air-fuel ratio control method according to a fourth aspect of the present invention, the maximum heat value during combustion is determined based on the combustion temperature or the heating state of the object to be heated. The maximum calorific value during combustion can be easily determined by using various objects to be heated, such as the combustion temperature itself, the temperature of hot water, the amount of generated steam, and the temperature of steam.

[0013]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 shows the configuration of an embodiment of the present invention. In the figure, reference numeral 1 denotes a blower, which has a fan motor 1a at one end and a duct 1b connected to the fan motor 1a. Note that the fan motor 1a includes a fan (not shown) that rotates at a constant rotation speed, and the outside air is sucked in by the fan and the air is sent into the duct 1b. The operation / stop of the fan motor 1a is controlled by the supply air amount control unit 11.

A damper 2 for adjusting the flow rate of the combustion air flowing into the duct 1b is provided at the outlet of the fan motor 1a. The damper 2 is configured to rotate about a drive shaft 2b by a drive unit 2a. The opening degree of the damper 2 is adjusted so that the amount is slightly larger than the theoretical air amount in the burner 8 (for example, 1.05 to 1.1 times the theoretical air amount; different depending on the burner).
The reason for setting the ratio to 1.05 to 1.1 times is that there is an empirical rule that combustion at this ratio is the best. (In the claims, "theoretical air ratio" is described, but in actuality, an air amount obtained by multiplying the theoretical air amount by this factor is supplied because fuel and air cannot be completely agitated in the combustion chamber as expected.)

A burner 8 is provided downstream of the duct 1b. A predetermined amount of gas (city gas, propane gas, etc.) is supplied to the burner 8 from outside the duct via a gas pipe 7 and a fuel amount control valve 4. In the burner 8, the combustion air and gas are mixed and burned. Burner 8
A heat exchanger 6 is provided downstream of. The heat exchanger 6
Are cooling water pipes 6b made of copper and fins 6 connecting them.
c. The cooling water pipe 6b is configured such that water supplied from one end passes through the cooling water pipe and is discharged from the other end. A heat transfer section temperature sensor 6a is disposed near the heat exchanger 6, and detects a change in the combustion state based on the temperature of the heat transfer section.

An exhaust port (chimney) 9 is provided in a part of the burner 8, and the combustion gas passing through the duct 1 is exhausted through the exhaust port 9. Duct 1
b, a flow sensor (detection means) 3 is provided,
The gas pipe 7 has a fuel amount control valve 4 upstream of the burner 8.
Sensor (detection means) that measures the fuel flow downstream of
5 are provided. The flow rate sensor 3 detects a flow rate of the combustion air in the duct 1 and a flow rate signal F corresponding to the flow rate.
S is supplied to the air-fuel ratio control device 10. As the flow sensor 3, for example, a thermal flow sensor 20 shown in FIG. 2 is used.

FIG. 2 is a front view showing the structure of the thermal type flow sensor 20. The thermal type flow sensor 20 includes a duct 1b
Two tubes 21 and 22 arranged side by side in a direction perpendicular to the direction of air flow in the inside, and a tube 26 connecting an end of the tube protruding outside the duct 1b and a through hole 25 of the sensor body 24, 27 and a flow sensor 28 provided in the through hole 25 of the sensor main body 24.

Next, the configuration of the flow sensor unit 28 is shown in FIG. FIG. 3 is a perspective view showing a flow sensor unit of the thermal flow sensor. As shown in FIG.
Is 20 μm thick on a 1.7 mm square semiconductor chip 28a.
m, and a micro-flow sensor (registered trademark) 28 having a heating resistance pattern 28c and temperature-sensitive resistance patterns 28d and 28e is mounted on the diaphragm 28b.

In this micro flow sensor, a predetermined current is supplied to the heating resistor pattern 28c to generate heat, and the resistance values of the temperature-sensitive resistor patterns 28d and 28e are set to a certain value. The combustion air flowing through the duct 1b is
It flows in from the hole 21a of one cylindrical body 21 shown in FIG. 2, and flows out of the hole 22a of the cylindrical body 22 through the tube 26, the through hole 25, and the tube 27. At this time, the heat distribution on the semiconductor chip changes according to the flow rate of the air flowing through the micro flow sensor 28. As a result, the resistance values of the temperature-sensitive resistance patterns 28d and 28e change. This change in the resistance value is detected by the air-fuel ratio controller 10. Since the above-described flow sensor unit 28 is configured to be very small,
Very good sensitivity, excellent response (several msec), and always accurate flow measurement. In order to collect dust contained in the air for combustion, fine irregularities such as mats are provided on the surfaces inside the cylinders 21 and 22 of the micro flow sensor described above. (See Patent No. 2880398)

On the other hand, the mass flow meter 5 for measuring the amount of fuel is
As shown in FIG. 1, it is arranged in the gas pipe 7. Since the amount of dust in the gas pipe is smaller than that of the duct 1b for supplying air, unlike the mass flow meter 3 provided in the duct 1b, the gas pipe does not need to have a dust trap structure as shown in FIG. good. Since the mass flow meter 5 has a function of measuring the mass flow rate similarly to the flow rate sensor 3, the mass flow rate of the gas supplied to the burner 8 is measured using only the flow rate sensor unit (micro flow sensor 28) shown in FIG. Measure. The air-fuel ratio control unit (control means) 10 controls the air amount control damper 2 based on the generated heat amount instruction from the combustion device control unit 12 for the air amount.
With respect to the opening degree and the fuel amount, the opening degree of the fuel amount control valve 4 is calculated. This specific procedure is performed based on the flowchart shown in FIG.

Hereinafter, this flowchart will be described. First, the required heat value Q (KJ / h) is calculated by the combustion device controller 12 (step S10). Next, a fuel amount corresponding to the required calorific value is obtained (step S1).
1). Here, for example, in the combustion device shown in FIG. 1, when the required heat generation amount is Q (KJ / h) and the fuel is natural gas, the heat generation amount per unit volume is E (KJ / m3). For example, a fuel amount of Q / E (m3) is supplied.

Next, a fuel control valve opening corresponding to the fuel amount obtained in step S11 is obtained (step S12). The fuel control valve opening is controlled based on the measurement value of the mass flow meter 5 so that the fuel supply amount per unit time becomes Q / E (m3). Although a detailed description of the relationship between the flow rate and the opening degree is omitted, the relationship between the opening degree of the fuel control valve and the flow rate is stored in advance in the air-fuel ratio control device 10 as a table or a functional expression as shown in FIG. Thus, the required fuel control valve opening can be easily obtained.

The optimum amount of air for the fuel amount of Q / E (m3) can be determined by a method for obtaining a theoretical amount of air (for example, Japanese Society of Burner Research Vol. 74, pp. 17, 1993). Theoretical air amount = 11.424 (n + 1 /
3) / (n + ／) (m3 / kg) Here, n is obtained from the carbon number of the paraffin-based fuel CnH2n + 2. As with the fuel amount, an air amount control damper position for obtaining the air amount is obtained from 1.05 to 1.1 times the calculated theoretical air amount, and the damper position is adjusted (step S1).
3). The adjustment of the damper position is performed based on the measured value of the mass flow meter 3. As described above, a good air-fuel ratio state, that is, the amount of air and fuel to be supplied to the burner, which will generate the maximum heat value, can be obtained.

Further, after the position of the air amount control damper and the position of the fuel amount control valve have reached the control target values, it is determined whether or not the air-fuel ratio needs to be checked (step S1).
4). When it is necessary to check the air-fuel ratio, the actual air amount and the fuel amount are measured again by the air mass flow meter 3 and the fuel flow meter 5, and the measured flow value at the opening position of the fuel amount control valve is used. , The air amount is recalculated, and the air amount is adjusted so as to maintain the air-fuel ratio in a good state. This is because the fuel control valve opening may be different from the indicated flow rate as described above.
Here, the deviation of the air-fuel ratio is corrected.

Next, a method for maintaining the above-described air-fuel ratio control in an optimal state (a method for evaluating the air-fuel ratio control) will be described with reference to the combustion apparatus shown in FIG. 1 and a flowchart shown in FIG. Here, an example in which the evaluation of the air-fuel ratio control is performed while the combustion state is detected by the heat transfer section temperature sensor 6a will be described.

In performing the evaluation, the air amount and the fuel amount whose air-fuel ratio has been improved by the above-described control routine are burned by the burner 8, and become the flame F to heat the water pipe 6b of the heat exchanger 6. are doing. Therefore, in the above-described combustion control routine, the air-fuel ratio control is performed, and a favorable (almost optimal)
The air-fuel ratio control result evaluation routine is started with the air-fuel ratio attained (steps S20, S21).

First, while measuring the temperature measured by the heat transfer section temperature sensor 6a, the amount of air is reduced by a very small amount, for example, 1% (step S22). As a result, the air-fuel ratio control is evaluated based on whether the temperature measured by the heat transfer section temperature sensor 6a fluctuates up and down (step S24).
That is, (1) when the temperature rises, the air-fuel ratio is improved more than the original air amount position, and (2) when the temperature decreases, the air-fuel ratio deteriorates more than the original air amount position. It will be done. Therefore, in the case of (1), the air amount is further reduced (for example, 1%), and the air-fuel ratio is evaluated again (step S24).

In the case of (2), the position of the original air amount is closer to the optimum air-fuel ratio, so the air amount is increased by, for example, 1% (step S25). And
It is determined whether or not the temperature measured by the heat transfer section temperature sensor 6a increases (step S26). If the temperature increases, the air amount is further increased (for example, 1%), and the air-fuel ratio is evaluated again (step S26). S27). If the temperature of the heat transfer section of the sensor 6a does not rise in step S26, step S2
In steps S2 to S27, the position of the air amount where the temperature measured by the heat transfer section temperature sensor 6a is the highest is determined as the position where the optimum air-fuel ratio is obtained, and the flow rate sensor is set so that this air amount can be continuously supplied. The opening degree of the air amount control damper 2 is controlled on the basis of the output (step S28).

Subsequently, returning to the control routine shown in FIG. 4, it is determined whether or not the combustion control should be continued (step S1).
5) If it is to be continued, the combustion control is continued while the air-fuel ratio is evaluated at regular intervals. If it should not be continued, the combustion control is stopped and the combustion is terminated (step S16). Although the evaluation of the air-fuel ratio control result described above is performed for a predetermined time (for example, every three minutes), it may be performed at all times. Further, the evaluation may be performed at all times when the combustion amount is changed, and the time may be determined when the combustion amount is constant. Further, in this example, the evaluation was performed using the heat transfer unit temperature, but based on the heating state of the object to be heated such as the combustion temperature itself, which is the output of the combustion device, the hot water temperature, the generated steam amount or the steam temperature, Similar evaluation of the air-fuel ratio control result may be performed. In the evaluation of the air-fuel ratio control, the fuel amount may be increased or decreased instead of increasing or decreasing the air amount, or both the air amount and the fuel amount may be increased or decreased.

Further, steps S10 to S1
In the combustion control routine described in 6, the supply air amount may be fixed, and only the fuel amount may be measured by the mass flow sensor 5 to perform combustion control. Conversely, the supply fuel amount may be fixed,
Combustion control may be performed by measuring only the supplied air amount with the mass flow sensor 3. In the above-described embodiment, the combustor using gas (natural gas, propane gas) has been described.
Without being limited to this, another fuel such as kerosene or light oil may be used.

As described above, the air-fuel ratio control apparatus of the present invention detects the combustion air amount or the fuel amount flow rate by the air flow amount or the fuel amount mass flow rate detecting means. Can detect the mass of
An optimum air-fuel ratio can be obtained at any of the combustion amount positions from the minimum fuel amount position to the maximum fuel position. Therefore, it is possible to obtain the maximum calorific value at the input fuel amount accurately grasped by calculation, and to determine whether the generated heat amount is the maximum as a result of the actual combustion. Since the evaluation of the combustion based on the true optimum air-fuel ratio can be performed based on the generated hot water temperature or the generated steam amount or the increase / decrease of the steam temperature, it is possible to always perform the combustion for obtaining the maximum heat generation state. That is, it is possible to correct the fluctuation of the control amount due to the time change of the air amount or the combustion amount adjusting means, and to always obtain the optimum air-fuel ratio state.

Further, when an initial flow rate cannot be obtained due to some control abnormality in the air or fuel supply means, for example, clogging of the air filter or clogging of the fuel pipe, when the air filter is clogged, At the time of clogging, it is possible not to supply a fuel amount more than the maximum air supply amount. Further, according to the present invention, as shown in FIG. 6, the fact that the mass flow rate of the fuel and the mass flow rate of the air are in a proportional relationship is used, so that there is no need for an arithmetic means for calculating the mass flow rate. That is, since the air amount or the fuel amount is measured by the mass flow rate by measuring the air amount or the fuel amount by the mass flow meter, it is not necessary to measure the air temperature or the air pressure when performing the air-fuel ratio control. Also, the output value of the mass flow meter itself is
Since the mass input to the burner itself, when calculating the heat input, simply multiplying the measured flow rate value by the heat value per unit volume of fuel, the input heat value can be obtained, so the calculation means becomes simple, Not only is there no need for a fuel temperature sensor or pressure sensor, but also there is no need for temperature and pressure correction calculation means.

Further, since the fuel temperature sensor and the pressure sensor have no time delay required for measurement, the instantaneous air amount and fuel amount can be measured. In addition, in the evaluation of the air-fuel ratio control result, as shown by way of example, depending on the output of the combustion device, the hot water temperature, the generated steam amount or the steam temperature, the heat transfer section temperature, etc.
Easy to evaluate. Maintenance is also facilitated because a time-consuming, expensive, short-lived sensor such as the measurement of oxygen concentration or carbon monoxide concentration is not used. In the air-fuel ratio control, even in an internal combustion engine, an external combustion engine, a carbon monoxide generator and a catalytic combustion device of a fuel cell, the combustion state evaluation index may be applied to, for example, the amount of carbon monoxide generated.

[0034]

According to the air-fuel ratio control method and apparatus according to the first and fifth aspects of the present invention, since the mass flow rate of the air amount and the fuel amount is measured, the mass of the air and the fuel can be reliably determined. Can be detected. Also, by measuring the mass flow rate,
An optimum air-fuel ratio is obtained at any combustion amount position from the minimum fuel amount position to the maximum fuel position. Further, during the combustion control, at least one of the air amount and the fuel amount is increased or decreased, and based on a change in the combustion state due to the increase or decrease, at least one of the air amount and the fuel amount is adjusted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. Therefore, combustion at the optimum air-fuel ratio can always be performed. Further, it is possible to correct the fluctuation of the control amount due to the time change of the air amount and the combustion amount adjusting means, and to always obtain the optimum air-fuel ratio state.

Further, the air-fuel ratio control method and apparatus according to the second and sixth aspects of the present invention enable accurate measurement of the mass flow rate by using a micro flow sensor. Further, according to the air-fuel ratio control method described in claim 3 of the present invention, a change in the combustion state can be easily determined based on the amount of heat generated during combustion, and the air-fuel ratio can be reliably evaluated. . Further, according to the air-fuel ratio control method described in claim 4 of the present invention, the maximum calorific value during combustion can be easily determined based on the combustion temperature or the heating state of the object to be heated.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an embodiment.

FIG. 2 is a structural diagram of the air mass flow sensor of FIG. 1;

FIG. 3 is a structural diagram of a mass flow rate sensor unit for an air amount or a fuel amount.

FIG. 4 is a flowchart of control at the start of air-fuel ratio control.

FIG. 5 is a flowchart of a method for evaluating an air-fuel ratio control result.

FIG. 6 is a graph of a mass flow rate of a fuel and a mass flow rate of an air quantity in a state where a maximum amount of heat is generated.

FIG. 7 “Play” of an example of the air amount or fuel amount adjusting means.
FIG. 3 is a partial cross-sectional view showing a configuration that can perform the following.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Blower 2 Air amount control damper 3 Air amount mass flow meter 4 Fuel amount control valve 5 Fuel amount mass flow meter 6 Heat exchanger 6a Heat transfer part temperature sensor 7 Fuel (gas) piping 8 Burner 9 Heat exhaust port 10 Air-fuel ratio control Device 11 Air flow control unit 12 Combustion device control unit 28 Micro flow sensor

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification code FI Theme coat ゛ (Reference) F02D 45/00366 F02D 45/00 366B F23N 1/02 F23N 1/02 D

Claims (6)

[Claims] 1. A combustion control method for controlling an air-fuel ratio, comprising measuring a mass flow rate of at least one of a mass flow rate of an air quantity and a mass flow rate of a fuel quantity, and performing combustion based on the measured mass flow rate. During the combustion control, at least one of the air amount and the fuel amount is increased or decreased, and at least the air amount and the fuel amount are adjusted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio based on a change in the combustion state due to the increase or decrease. An air-fuel ratio control method, characterized in that either one of them is adjusted for combustion. 2. The air-fuel ratio control method according to claim 1, wherein the mass flow rate is measured using a micro flow sensor. 3. The method according to claim 1, wherein a change in the combustion state is determined based on a calorific value during combustion, and whether or not the air-fuel ratio is in a stoichiometric air-fuel ratio state is evaluated. The air-fuel ratio control method described in the above. 4. The air-fuel ratio control method according to claim 3, wherein the maximum calorific value during combustion is determined based on a combustion temperature or a heating state of an object to be heated. 5. A combustion control device for controlling an air-fuel ratio, wherein said mass flow rate measuring means measures at least one of a mass flow rate of an air quantity and a mass flow rate of a fuel quantity, and said mass flow rate measuring means. During the combustion control based on the measured mass flow rate, at least one of the air amount and the fuel amount is increased or decreased, and based on the change in the combustion state due to the increase or decrease, the air amount is adjusted so that the air-fuel ratio becomes the stoichiometric air-fuel ratio. And an air-fuel ratio control means for adjusting and burning at least one of the fuel amounts. 6. The air-fuel ratio control device according to claim 5, wherein said mass flow rate measuring means is a micro flow sensor.