JPH0749850B2 - Combustion control device - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to air-fuel ratio control and safety control in combustion equipment that uses gas, oil, or the like.

2. Description of the Related Art In recent years, when burning gas or petroleum as fuel, the mixture ratio of fuel and air, that is, the air-fuel ratio is optimally controlled to prevent the occurrence of incomplete combustion, and also to prevent the leakage of unburned gas due to misfire, etc. There is an increasing demand for a safety control function.

In order to perform these controls, it is best to detect the combustion state of the burner and control the amount of air or the amount of combustion to keep this state of combustion constant, and various means have been developed since the past. There is. However, in order to realize this control, it is no exaggeration to say that the performance of the control system is determined by the sensor that detects the combustion state of the burner. Currently, there are merits and demerits in each sensor for detecting a combustion state on the market, and when considering a household combustion device, the sensor is required to be inexpensive, durable and highly reliable.

Japanese Unexamined Patent Publication No. 51-31933 describes, as the above-mentioned combustion state detection sensor, means for controlling an air-fuel ratio by inserting an electrode rod into a flame and using a frame rod for detecting a flame ion current. . This block diagram is shown in FIG. In this example, kerosene is used as fuel, which is vaporized in a vaporization chamber 1 and mixed with air from a blower 3 in a mixing chamber 2 to form a flame 5 in a combustion chamber 4 for combustion. The control circuit 6 drives and controls the fuel pump 7 that supplies fuel oil and the blower 3. At the same time, the flame rod If is inserted into the flame 5 and insulated from the combustion chamber 4 and the insulator 8 by the flame rod 9. The flame current If flowing between the flame 5 and the combustion chamber 4 is detected by the control circuit 6, and the fuel is sent according to this flame current If. It is configured to control the drive amount of the pump 7. Generally, the flame current If has a correlation with the air-fuel ratio, and shows an upwardly convex curve having a peak near the air-fuel ratio m = 1. (See FIG. 5) Therefore, the air-fuel ratio can be controlled by controlling the fuel supply amount or the air amount so that the flame current If becomes a constant value. Here, the air-fuel ratio m = 1 means a state in which the theoretical air amount necessary for complete combustion of the fuel is supplied, where m> 1 is excess air and m <1 is excess fuel.

Problems to be Solved by the Invention Conventional combustors often burn near the air-fuel ratio m = 1 or at a place slightly lower than 1. However, in recent years, cleanliness of combustors has been required, and low N containing low nitrogen oxides (NOx).
It is moving to Ox combustion. It is known that lean combustion with an air-fuel ratio m of 1.4 to 1.6 is effective for this low NOx combustion. However, if such a combustion occurs,
The flame 5 does not become clear as shown in Fig. 8, but it comes into close contact with the surface of the burner and a thin combustion of several mm occurs. Therefore, the flame current If that can be detected by the frame rod 9 is several micro A or nano A.
It becomes a very small value and it is difficult to detect accurately due to the influence of noise. Further, as shown in FIG. 5, when the air-fuel ratio m is in the vicinity of 1.4 to 1.6, there is little change in the flame current If, and particularly when the combustion amount is low, it is extremely difficult to control the air-fuel ratio at this value remarkably. U

There is also a means for controlling the air-fuel ratio by the temperature of the combustion flame, but in this case the change in temperature is slow, and there is the problem that it takes time to determine if the burner has misfired, for example.

Means for Solving the Problems In order to solve the above problems, the present invention provides a flame rod inserted into the combustion flame of a burner and a temperature sensor for detecting the temperature of the burner or its vicinity, and the controller is a flame rod. An abnormal combustion detection unit that drives an abnormal reset unit that detects an abnormal combustion of the burner with a signal, and an air supply amount of the air supply unit or a fuel supply of the fuel control unit so that the temperature of the temperature sensor is maintained at a predetermined value. An air-fuel ratio control unit that controls the amount is provided.

Action With the above configuration, abnormality detection such as ignition and misfire of the burner and extreme deviation of the air-fuel ratio can be instantaneously detected by operating the signal from the frame rod. Further, the air-fuel ratio is controlled by a temperature signal with a stable signal and a large change amount, so that accurate air-fuel ratio control is possible.

Example Hereinafter, an example of the combustion control device of the present invention will be described with reference to the drawings. In the embodiment, an oil fan heater using kerosene as fuel will be described as an example.

In FIG. 1, the fuel oil is supplied to the carburetor 12 preheated by the heater 11 by the fuel pump 10, mixed with the air supplied by the burner motor 13, and burned on the surface of the burner 14. Here, the burner 14 has a shape having a large number of flame holes on the surface, and the air-fuel mixture is ejected from the flame holes and burns on the surface. The combustion exhaust gas is mixed with the air from the blower fan motor 15 and discharged into the room through a blowout port (not shown) to heat the room. controller
16 controls combustion of these burners. The room temperature signal from the room temperature sensor 17 is compared with the room temperature set value 18, the combustion coefficient K corresponding to the required combustion amount is calculated by the calculation unit 19, and the combustion amount setting unit 20 determines the combustion amount according to this value K. , Sends a signal to the pump drive unit 21 that drives the fuel pump 10. The fuel pump 10 uses a pulse pump here, so the pump drive
21 outputs the pulse frequency corresponding to the combustion amount. Further, the coefficient K determined by the calculation unit 19 is the fan motor rotation speed setting unit 22.
The rotation speed of the convection fan motor 15 is set by, and a signal is output to the fan motor drive unit 23. This prevents the user from feeling a feeling of cold air or a feeling of hot air as an air volume suitable for the amount of combustion. At the same time, the setting unit 25 determines the temperature of the temperature sensor 24 (here, a thermocouple is used) provided inside the burner 14 from the coefficient K. The air-fuel ratio control unit 26 sets the rotation speed by the burner motor rotation speed setting unit 27 so that the temperature of the thermocouple 24 is maintained at the temperature determined by the burner temperature setting unit 25,
The burner motor drive unit 28 drives the burner motor 13. Further, according to the combustion coefficient K, the flame current threshold value setting unit 30 of the abnormal combustion detection unit 29 determines the flame current threshold value, and the burner is set.
The flame current If of the flame is detected by the flame current detection unit 32 by the flame rod 31 facing the combustion flame 14 and the abnormality is determined by the threshold value and the abnormality determination unit 33 described above, and when abnormal combustion is determined, an abnormal reset is performed. An abnormal signal is output to the section 34, and the pump driving section 21 stops driving the pump 10 to stop combustion.

FIG. 2 shows how the burner temperature T _B detected by the thermocouple 24 changes with respect to the air-fuel ratio m. In the figure, the HML line shows the case where the combustion amount is different. From figure T
_It can be seen that _B has a certain correlation with the air-fuel ratio m. It is FIG. 3 that the characteristic of FIG. 2 is rewritten by the horizontal axis combustion amount Q _F.
Here, for example, if the temperature T _B is controlled to a constant value T _S1 , the combustion amount Q
_F is the air-fuel ratio is m1, when Q _F is M is m2, Q _F is a broken line a which is an intermediate of m2 and m3 when the H is obtained when the L. This is the first
In the figure, the burner motor rotation speed setting unit 27 may be controlled so that the temperature of the thermocouple 24 becomes T _S1 .

In Fig. 3, when the combustion amount Q _F is H, the burner temperature T _B is T _S2 , Q
_{When F} is L, the air-fuel ratio can be controlled to be substantially constant m3 even if the value of the combustion amount Q _F changes by controlling to the broken line b which becomes T _S3 .

This is because the set value T _S is changed by the burner temperature setting unit 25 according to the combustion coefficient K determined by the calculation unit 19 in FIG. 1, and the burner motor rotational speed is kept so that this set value is always maintained when the coefficient K is constant. Will be in control.

With the above, control of the air-fuel ratio m can be realized, but the thermocouple
The temperature change of 24 is very slow, and when a misfire or a sudden change of the air-fuel ratio occurs, the generation of carbon monoxide 10 due to the incomplete combustion will occur while waiting for the change of the burner temperature T _B It is very dangerous because it leads to. Therefore, as shown in FIG. 1, detection of abnormal combustion is performed by flame current If of flame rod 31
Detected by the change of. Fig. 4 compares the response time of the flame current If and the burner temperature T _B when the burner ignites and misfires. Flame current If with respect to the change in temperature T _B paper housing unit 26 from figure it can be seen that fast very responsive.

FIG. 5 shows the change characteristics of the flame current If with respect to the air-fuel ratio m.
It can be seen that it is more unstable than the change in burner temperature T _{B in} FIG. Also, the absolute value of the flame current If is very small, and in many cases it is actually unstable due to flame fluctuations and noise.
Therefore, it is very dangerous to perform the air-fuel ratio control with this signal, which causes a hunting phenomenon or the like. So flame current
If is used only to judge whether it is above or below a certain threshold, abnormal combustion detection is performed by taking advantage of the quick response.

In Fig. 5, when the combustion amount Q _F is H, the flame current If is the threshold value I _fa ＞ I
When f> I _fb, it is regarded as normal, and when it is out of this range, some kind of abnormality occurs and the abnormality is reset. In this case, a timer element may be provided to reset the abnormality when it continues for a certain period of time. The flame current thresholds I _fa and I _fb are changed according to the combustion amount Q _F as shown in the figure. This is determined by the flame current threshold value setting unit 30 according to the combustion coefficient K in FIG.

FIG. 6 shows a flow chart of the main parts when the above control is realized by a microcomputer or the like, and shows the numbers corresponding to FIG. Here, the burner temperature setting unit 25 sets the set temperature T _S as well as the upper and lower limit values T _sa and T _sb , and the abnormality determination unit 33a makes an abnormality determination even when the burner temperature T _B exceeds these values.
Further, the correction amount OB of the burner motor speed of the air-fuel ratio control unit 26
Even when M becomes a value equal to or greater than the limit correction amount BMf, it is judged as abnormal,
It constitutes a safety device with high redundancy.

FIG. 7 shows another embodiment in which the same functions as those in FIG. 1 are designated by the same reference numerals. Here, the air-fuel ratio control unit 26 is configured to control the combustion amount Q _F in accordance with the burner temperature T _b , and FIG. 1 shows a fuel amount reference type air-fuel ratio control for controlling the air amount while keeping the fuel constant. FIG. 7 shows an example of the air amount reference type air-fuel ratio control for controlling the combustion amount by keeping the air amount, that is, the burner motor rotation speed constant, and any means has the same effect.

In this embodiment, the oil fan heater has been described as an example, but the invention can be applied to a water heater and other combustion equipment. Further, even gas fuel can be easily realized by using a gas proportional control valve or the like instead of the fuel pump.

Effects of the Invention As described above, the combustion control device of the present invention has the following effects.

(1) The air-fuel ratio control acts to maintain a constant air-fuel ratio by the signal of the burner temperature T _b , which has a stable change, so that the control system is stable, and reliable and highly accurate control is possible. Becomes

(2) If abnormal combustion is detected, flame current by flame rod If
Since it is detected and determined by, the response is fast and the combustion can be stopped instantly.

(3) Since two types of sensors, burner temperature and frame rod, are used and each has an independent function, it is possible to judge this by the other sensor even if one of the sensors becomes abnormal. It is also fail-safe even when the sensor fails.

(4) Similarly, even if one sensor detects an abnormality for some reason, it can be detected by the other sensor, and a highly redundant control system can be realized.

[Brief description of drawings]

FIG. 1 is a block diagram of a combustion control system showing an embodiment of the present invention, FIG. 2 is a burner temperature characteristic diagram, FIG. 3 is an air-fuel ratio control characteristic diagram, and FIG. 4 is a burner temperature and flame current response. 5 is a characteristic diagram of flame current, FIG. 6 is a flow chart for realizing FIG. 1, FIG. 7 is a block diagram showing another embodiment, and FIG. 8 is a conventional example. FIG. 10 ... Fuel pump (fuel control means), 13 ... Burner motor (air supply means), 14 ... Burner, 16 ... Controller,
24 …… Thermocouple (burner temperature sensor), 26 …… Air-fuel ratio controller, 29 …… Abnormal combustion detector, 31 …… Frame rod, 34 …… Abnormal reset section.

Front page continued (72) Inventor Shozo Kogawa 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd. (72) Yasushi Hirata 1006 Kadoma, Kadoma City, Osaka Matsushita Electric Industrial Co., Ltd.

Claims (1)

[Claims] 1. A burner for burning fuel, a fuel control means for controlling the amount of fuel supplied to the burner, an air supply means for supplying combustion air, and a flame ion current which is inserted into a combustion flame of the burner. It comprises a flame rod for detection, a temperature sensor for detecting the temperature of the burner or its vicinity, and a controller for driving and controlling the fuel control means and the air supply means, and the controller uses the signal of the flame rod for abnormal combustion of the burner. And an abnormal combustion detection unit that outputs a signal to an abnormal reset unit that stops the drive of the fuel control unit to extinguish the burner, and the signal of the temperature sensor to maintain a predetermined set temperature. A combustion control device having an air-fuel ratio control unit for controlling the air supply amount of the air supply unit or the fuel supply amount of the fuel control unit.