JPH0423167B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to an air-fuel ratio control device for combustion equipment using gas, oil, or the like.

Conventional technology When burning gas or oil as fuel, stable combustion can be maintained by supplying the optimal amount of air depending on the fuel to prevent backfire, misfire, or incomplete combustion. This ratio of the amount of fuel and air is called the air-fuel ratio, and conventional methods have been devised to detect the combustion state and control the amount of fuel or air so as to always maintain an optimal air-fuel ratio.

A good example of an air-fuel ratio control system in an oil-burning machine is the one described in, for example, Japanese Patent Application Laid-open No. 119635/1983. This method detects the flame ion current of the flame with a flame rod inserted into the fire, and uses the fact that this flame ion current changes depending on the air-fuel ratio to set the flame current I _f at a certain combustion amount to the I _f at the optimal air-fuel ratio. This configuration controls the oscillation frequency of the fuel supply pump to maintain the same value. FIG. 7 shows this control characteristic. In FIG. 7, the horizontal axis I _f represents the flame current of the flame rod, and the vertical axis f represents the oscillation frequency of the fuel pump. Now, when the amount of air corresponding to the low combustion amount of the burner is being supplied, the pump frequency f is controlled so that the flame current I _f becomes the flame current value I _fL of the optimum air-fuel ratio. If the air-fuel ratio deviates and the flame current I _f becomes I _f ′, the pump frequency becomes f ′, the combustion amount is increased, and the flame current is controlled to return to I _fL . When the combustion amount is switched to high, it is controlled according to line B.

Problems to be Solved by the Invention However, the conventional air-fuel ratio control method as described above has two major problems. One is that the flame current I _f varies greatly depending on various conditions. For example, if the distance between the flame rod and the burner, the shape of the rod, the voltage applied to the rod, etc. change, the value of I _f will change.
Even if the same I _fL can be set, it does not necessarily mean that it is the optimal air-fuel ratio. The second problem is that when the control method shown in the conventional example is applied to an indoor open type combustion machine such as a fan heater, the flame current I _f changes even when the indoor oxygen concentration decreases (hereinafter referred to as oxygen deficiency). It's about doing.

Normally, in the absence of air-fuel ratio control, this characteristic is used, and when the flame _current If reaches a certain value, it is determined that there is an oxygen deficiency and indoor ventilation is encouraged or combustion is stopped. However, when controlling the air-fuel ratio, the pump frequency is adjusted so that the flame current is always maintained at I _fL even if oxygen deficiency occurs. Therefore, even if the indoor oxygen concentration drops to 16 to 15%, the burner continues to burn to a certain extent, and oxygen deficiency cannot be detected.

One way to detect this is to determine that there is an oxygen deficiency when the amount of change in the pump frequency f exceeds a certain value, but since the pump frequency f also changes depending on the amount of combustion, it is difficult to distinguish from this. This also required a complex control algorithm.

Means for Solving the Problems In order to solve the above problems, the present invention provides a fuel control device that controls the amount of fuel supplied to the burner and a combustion control device that controls the blower that supplies combustion air based on signals from the flame rod. The combustion control circuit includes an air-fuel ratio setting section that sets the air-fuel ratio at the beginning of operation of the combustor, and calculates and controls the combustion amount according to changes in load such as room temperature while maintaining the set air-fuel ratio. It consists of a combustion amount control section and a combustion detection section that detects flame rod radio waves, and the flame rod output is maximum when the air amount is supplied from the reference air output section that outputs a reference air amount to the air-fuel ratio setting section. The configuration includes a fuel adjustment section that adjusts the combustion amount, a peak detection section that detects that the flame rod output is at its maximum, and a storage section that stores the fuel adjustment value at this time. , the required fuel supply amount is calculated based on the value stored in this storage section.

Operation With the above configuration, the air-fuel ratio is adjusted at the start of operation of the device, and once the air-fuel ratio adjustment is completed, the air-fuel ratio thereafter is calculated and calculated from the value stored at the time of adjustment. In other words, during normal combustion, feedback control of the air-fuel ratio by flame current is not performed. Furthermore, when adjusting the air-fuel ratio, the air-fuel ratio is adjusted so as to reach the peak value of the flame current, rather than detecting the absolute value of the flame current _If .

Embodiments Embodiments of the present invention will be described below with reference to FIGS. 1 to 6. In the embodiment, an indoor open combustion hot air heater (fan heater) using an oil vaporization burner will be described as an example.

FIG. 1 shows a system block diagram of the present invention.
1 is a burner, in which fuel supplied from a fuel tank 2 by a fuel pump 3 and air blown by a blower 4 are vaporized and mixed by a vaporizer mixer 5;
burns with A flame rod 6 transmits the flame current I _f flowing through the flame of the burner 1 to the combustion detector 8 of the combustion control circuit 7. The blower 4 is controlled by an air amount control section 11 that calculates the amount of combustion air to be blown according to the temperature difference between a room temperature sensor 9 provided outside and a temperature setting value 10. On the other hand, the fuel pump 3 is controlled by a signal from the combustion amount control section 12. Note that when the combustion machine starts operating, the switches Sa and Sb are connected to the contacts in the direction opposite to that shown in the figure, and the blower 4 is controlled to supply a predetermined reference air amount from the reference air output section 13, and the fuel The pump 3 is adjusted by the fuel adjustment section 15 in accordance with the signal from the peak detection section 14 so that the flame _current If reaches its maximum value when the reference air amount is reached. When the adjustment is completed, the adjusted value, that is, the fuel pump output (frequency) when the flame current _If is at its peak, is stored in the storage unit 16.
Air-fuel ratio setting section 17 including reference air output section 13, peak detector 14, fuel adjustment section 15, and storage section 16
It is called. After this, the switches Sa and Sb return to the contact points shown in the figure, and thereafter calculate the oscillation frequency of the pump 3 according to the blower output from the air amount control section 11 using the value in the storage section 16 as a function, and calculate the oscillation frequency from the combustion amount control section 12. Provides pump drive output.

Next, we will explain the specific operation. Figure 2 is a graph showing the relationship between air-fuel ratio and flame current, and the horizontal axis shows the primary air ratio.
P _A (Here, the air-fuel ratio will be explained using the primary air ratio P _A.
P _A = Actual burner primary air amount/Theoretical primary air amount)
The vertical axis shows the flame current I _f . Lines A and B in the diagram differ depending on the amount of combustion; when the amount of combustion is large, line B is, and when it is small, line A is
It becomes a line. The flame current I _f is a curve with a peak at the point where P _A is 1.0, where P _A >1.0 (excess air side), P _A <1.0
(On the air-deficient side), it also draws a downward mountain-shaped curve.
Here, it is assumed that the burner is designed to achieve optimum combustion at a point P _A1 where P _A is slightly lower than 1. (This differs depending on the burner) Also, when P _A ≦ P _A2 , the burner undergoes incomplete combustion, so when the flame current I _f becomes less than I _fa or I _fb , the control circuit determines that there is an abnormality.

Since P _A is proportional to the amount of air supplied when the combustion amount is fixed at a certain combustion amount, the oscillation frequency f of the fuel pump 3 and the rotation speed n of the blower motor of the blower 4 with respect to the combustion amount Θ _F of the burner are as shown in Fig. 3a, As shown in b, there is a proportional relationship. Now, in Figure 2, when P _A = P _A1 , the motor rotation speed is nA, nB, and the pump frequency is fA,
becomes fB. nP is the motor rotation speed when P _A =1.0 at the combustion amount Θ _FB and is output from the reference air output section 13 . In the figure, the CDE line shows variations in the fuel pump, and even if the pump frequency fB is the same, the combustion amount is Θ _FB ′
~ Θ _FB ″. Therefore, the motor rotation speed nB
Even if P A is constant, P _A deviates from P _A1 . In order to solve this problem, it is necessary to adjust the pump frequency fB to fB' to fB'' according to the pump variation. In the present invention, this work is performed by the air-fuel ratio setting section 17.

FIG. 4 shows a flowchart when the air-fuel ratio setting section 17 is configured with a microcomputer, and FIG. 5 shows its characteristics. Here, an example will be explained in which the air-fuel ratio is set using the combustion amount _ΘFB . Now, when the pump frequency is fB, if the combustion amount is the standard value Θ _FB , the flame current I _f will peak at the air volume at the motor rotation speed nP. (Line C in Figure 5) To detect this, the peak detection unit 14 varies the motor rotation speed to n1 and n2, measures the flame currents I _f1 and I _f2 , and calculates the difference △f.
is determined to be a peak point when it is less than a certain value K. If the amount of combustion varies and is shown by line D in Figure 3, the amount of combustion at pump frequency fB is Θ _FB ′
becomes. Therefore, the peak point of the flame current occurs at nP′, which is larger than nP (air volume is large). The peak detection unit 14 determines the difference ΔT between the flame currents I _f1 ′ and I _f2 ′ of n1 and n2, and adjusts the pump frequency fB according to the direction of this slope.
increase or decrease. (Decrease here) Repeat this,
Move closer to line C as shown by the arrow in Figure 5.

As described above, the combustion amount Θ _FB pump frequency fB
When fB is determined, this frequency fB is stored in the storage unit 16.

On the other hand, the air amount control unit 11 determines the motor rotation speed n of the blower 4 according to the temperature difference ΔT between the temperature sensor 9 and the temperature setting value 10. (In this case, n indicates the value when the temporary air ratio P _A =P _A1 in Fig. 2.) Fig. 6 shows this characteristic. In FIG. 6, the horizontal axis shows the temperature difference ΔT (RS is the set temperature 10, Rt is the temperature sensor value 9) and the pump frequency f, and the vertical axis n shows the rotation speed of the motor. n _nax is the motor rotation speed at maximum combustion, and n _nio is the motor rotation speed at minimum combustion.

Once the rotational speed n of the motor is determined, the pump frequency f is calculated from this value. At this time, the pump frequency f varies from E to D in the figure. Here, if the pump frequency f at maximum combustion is determined by the air-fuel ratio setting section 17 to be fB, the combustion amount control section 12 operates to calculate the frequency f on the F line. (Calculation example f=(a・n+b)・fB where a and b are constants) With the above configuration, variations in the pump can be corrected, and combustion can always be performed at the desired combustion amount and air-fuel ratio.

In this embodiment, the air-fuel ratio setting unit 17 sets the pump frequency f at the time of maximum combustion Θ _FB , but the pump frequency f is not limited to this, and the same effect can be obtained no matter what combustion amount is set. Further, the same effect can be obtained even with a combustion machine other than a fan heater or a gas fuel.

In order to further improve safety, the variable range of the pump frequency f (maximum and minimum values of fB) is limited in the fuel adjustment unit 15, and when there is no peak point unless the frequency f is increased above this value, It may be configured to stop combustion when it is determined that the normal amount of air is not being sent due to dust clogging or the like, or that the normal combustion amount is not being produced. Also, the peak detection unit 14
By setting upper and lower limit values for the flame currents I _f1 and I _f2 at this time, it is possible to stop combustion if it is determined that there is poor insulation of the flame rod or that incomplete combustion has already occurred. It can be easily achieved.

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

(1) Since the combustion amount and air-fuel ratio are automatically set to the optimum point, there is no need for manual adjustment, and stable combustion can be maintained at all times.

(2) The air-fuel ratio setting section only operates for a certain period of time when the combustion machine starts to be used, and after that, it only determines the motor rotation speed and fuel supply amount by calculating based on the set values. . Therefore, even if oxygen deficiency occurs during combustion, the air-fuel ratio is not corrected, so oxygen deficiency can be detected by detecting changes in flame current, which is safe.

(3) The air-fuel ratio setting section does not control based on the absolute value of the flame current, but rather detects the peak point of the flame current. Therefore, even if there are differences in the distance between the rod electrodes, the shape of the rod, or the applied voltage, the peak point of the flame current will not be affected at all, and an accurate air-fuel ratio can be set.

[Brief explanation of drawings]

Fig. 1 is a control block diagram of a combustion control device according to an embodiment of the present invention, Fig. 2 is a characteristic diagram of flame current due to air-fuel ratio and flame rod, and Fig. 3 a and b are combustion amount, pump frequency, and blower motor rotation. Fig. 4 is a flow chart explaining the operation of the air-fuel ratio control section, Fig. 5 is its characteristic diagram, Fig. 6 is a characteristic diagram of the combustion amount control section, and Fig. 7 is a conventional FIG. 3 is a characteristic diagram of an air-fuel ratio control method. 1...Burner, 3...Fuel pump (fuel control device), 4...Blower, 6...Frame rod, 7
... Combustion control circuit, 8 ... Combustion detection section, 12 ...
Combustion control section, 13... Reference air output section, 14...
Peak detection section, 15...Fuel adjustment section, 16...Storage section, 17...Air-fuel ratio setting section.

Claims (1)

[Claims] 1. A burner that burns the fuel of the combustor, a fuel control device that controls the amount of fuel supplied to the burner,
It has a blower that supplies combustion air, a flame rod that is inserted into the combustion flame and detects the combustion state of the burner using flame ion current, and a combustion control circuit that drives and controls the fuel control device and the blower, and the combustion control circuit includes: , an air-fuel ratio setting section that sets combustion conditions at the start of operation of the combustor, a combustion amount control section that calculates and controls the combustion amount of the burner while maintaining the air-fuel ratio set by the air-fuel ratio setting section, and detects a flame rod output. The air-fuel ratio setting section includes a combustion detection section, and the air-fuel ratio setting section includes a reference air output section that outputs a predetermined amount of air from the blower, and a fuel adjustment section that adjusts the fuel supply amount so that the flame rod output is maximized at this time. , a peak detection section, and a storage section that stores the adjustment value of the fuel adjustment section and outputs it to the combustion amount control section when necessary.