JPS62245021A - Combustion control device - Google Patents

Abstract

PURPOSE:To make it possible to maintain stable combustion conditions by a method wherein at least either the amount of air supplied or the amount of fuel supplied is adjusted and controlled by the minimum value retrieval output signal of flame current which is detected with a flame rod. CONSTITUTION:A combustion rate control part 11 calculates the combustion rate in accordance with the difference between the temperature measured by a room temperature sensor 13 and the set temperature 14 in order to control a fuel pump 3. When the result of calculation at the combustion rate control part 11 is larger than the predetermined amount, an air flow rate control part 12 calculates the air flow rate in proportion to the combustion rate in order to control a fan 4. Or, when the result of calculation is smaller than the predetermined value, a flame rod 10 detects flame current If in order to control the fan 4 in such a manner that the flame current If turns to be minimum and the resultant fan output is stored in a storage part 19. When the combustion rate is larger than the predetermined rate, the air flow rate control part 12 calculates the rotational speed of the fan 4 in accordance with the oscillation frequency of the fuel pump 3 by means of the contents of memory of the storage part 19 in order to obtain the driving output of the fan 4.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention 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 preventing backfire, misfire, or incomplete combustion by supplying the fuel and air at an optimal ratio. 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.

As a method of air-fuel ratio control in oil-burning equipment, for example, the method described in Japanese Patent Application Laid-Open No. 61-24917 can be considered. This detects the flame ion current of the flame with a flame rod inserted into the flame, and uses the fact that this flame ion current changes depending on the air-fuel ratio to adjust the driving frequency of the fuel supply pump to optimize the air-fuel ratio. It is configured to do this.

FIG. 6 shows an example of the flame ion current value If. The horizontal axis is the primary air ratio l, and here the air-fuel ratio will be explained in terms of the primary air ratio.

Typical input range (3000-1000kcal/h)
Then, the flame ion current value If is approximately μ=0.8 to 0.
The distribution has a peak at 9. Therefore, by adjusting the pump driving frequency and determining the amount of kerosene supplied so that the flame ion current value 1i becomes the maximum value, the air-fuel ratio is controlled and a stable combustion state is maintained.

Problems to be Solved by the Invention In the conventional example described above, a burner with m structure was used so that the most stable combustion state could be maintained at μ = 0.8 to 0.9.
There is also a burner configured to maintain the most stable combustion state around μm 1.5. Full-fire combustion burners (hereinafter referred to as full-fire combustion burners) generally have a low flame temperature,
It has the feature that nitrogen oxides (NO3C), which are harmful components in exhaust gas, are extremely low, and it is known that the W tanker configuration is highly effective in reducing NOx.

However, the conventional air-fuel ratio control means as described above determines the kerosene supply amount so that the flame ion current value H becomes the maximum value. I ended up adjusting u=0.8 to 0.9, and μ=
The problem was that a stable combustion state around 1.5 could not be maintained.

The present invention aims to solve such conventional problems, and aims to maintain a stable combustion state by adjusting μ to around 1.5 in a full-primary combustion burner.

Means for Solving the Problems In order to solve the above problems, the combustion control device of the present invention includes:
A burner for burning fuel, a fuel supply means for supplying fuel to the burner, a blower for supplying combustion air, a flame rod inserted into a combustion flame, and a control circuit section for controlling combustion of the burner, The control circuit section includes an air-fuel ratio setting section that sets an air-fuel ratio when the combustion amount is below a predetermined amount, and calculates the combustion amount based on the air-fuel ratio set by the air-fuel ratio setting section when the combustion amount is above a predetermined amount. The air-fuel ratio setting section includes a flame current detection section that detects the ionic current of the flame by the flame rod, and a combustion control section that changes and controls the flame current detection section. a minimum value search unit for searching; an adjustment unit for adjusting at least one of the amount of air supplied by the blower or the amount of fuel supplied by the fuel supply means based on the output signal of the minimum value search unit; and storing the adjustment value of the adjustment unit. The combustion control section has a combustion amount control section that calculates a combustion amount based on the output signal of the storage section and controls the fuel supply means, and an air amount control section that calculates an air amount and controls the blower. The configuration includes a control section.

Effect: With the above-described configuration, the present invention adjusts the air-fuel ratio so that the output signal of the flame current detection section becomes the minimum value during low-calorie combustion, and always maintains a stable combustion state around p = 1.5. It is.

Embodiments Below, one embodiment of the present invention will be described based on the accompanying drawings. 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, which is a full-primary combustion burner in which a flame port is entirely formed with a wire mesh on the outside of a punched plate having a large number of small holes, and fuel is supplied from a fuel tank 2 by a fuel pump 3 and air is blown by a blower 4. Air is vaporized and mixed by a vaporization mixer 5 and combusted by a burner 1. The control circuit section 6 includes an air-fuel ratio setting section 7, a combustion control section 8, and a timer section 9, and performs safe combustion in the burner 1 in response to signals from the flame rod 10 and other sensors. The combustion control section 8 includes a combustion amount control section 11 and an air amount control section 12, and controls the combustion amount control section 11 and the fuel pump 3. If the calculation result of the combustion amount control section 11 is greater than or equal to a predetermined amount, the switch 15 is connected to the contact shown in the figure, and the air amount control section 12 calculates the amount of air according to the amount of combustion and controls the blower 4 using the amount of air.

If the combustion amount calculated by the combustion amount control section 11 is less than or equal to a predetermined amount, the switch 15 is connected to a contact point in the opposite direction as shown in the figure, and the air-fuel ratio setting section 7 sets the air-fuel ratio.

Flame current detection section 1 detects flame current If using flame rod 10.
6 detects the flame current, and the blower 4 is adjusted by the adjustment unit 18 according to the output signal of the minimum value search unit 17 so that the flame current 11 becomes the minimum value. When the adjustment is completed, this adjusted value, that is, the flame current I
The blower output (rotation speed) when f is the minimum value is stored in the storage unit 19. The flame current detection section 16, the minimum value search section 17, the adjustment section 18, and the storage section 19 constitute an air-fuel ratio setting section 7. When the combustion amount is greater than or equal to the predetermined amount, the switch 15 returns to the contact point shown in the figure, and the air amount control section 12 blows air according to the oscillation frequency output of the fuel pump 3 from the combustion amount control section 11.The detailed operation will be explained next. . FIG. 2 shows the characteristic of the flame current If in an all-fire combustion burner.

Lines A and B in the diagram are the difference depending on the amount of combustion, and when the amount of combustion is small, it is A.
line, and when it is large, it becomes line B. When the combustion amount is small, %=0
．． The ion concentration in the flame is highest near 9, and as l increases, the ion concentration decreases.

It has been confirmed that in a full-fire combustion burner, the flame adheres closely to the burner when the pitch is around 0.9, and as fi increases, the flame grows longer. As the flame grows, the part of the flame with the highest ion density approaches the flame rod. Therefore, in the region of μ70.9, as the flame ion current If becomes louder, there are two phenomena: a decrease due to a decrease in ion concentration, and an increase due to the area with high ion density approaching the flame rod, due to the effects of both. V))t
It has been confirmed that the characteristic is that of the A line, which takes the minimum extreme value around = 1.5 to 1.6. On the other hand, when the combustion amount is large, the ion concentration in the flame is the highest near p-0 and 9, and the influence of the increase due to the area with high ion density approaching the flame rod is small, and the lowest extreme value is reached. Do not take B
It has been confirmed that this is a characteristic of the line.

Since the noise is proportional to the amount of air supplied when the combustion amount is fixed at a certain combustion amount, the oscillation frequency of the fuel pump 3 (and the rotation speed n of the blower motor of the blower 4 are shown in Figures a and b) Now, in Figure 2, μ=j
When , the motor rotation speeds are nA and nB, and the pump frequencies are fA and fB. In the diagram, C, D, and B lines are fuel pump 3
Even if the pump frequency is the same, the combustion amount varies from QFA' to QPA'. Therefore, even if the motor rotation speed nA is constant, it deviates from μ=μm.

In order to solve this problem, it is necessary to adjust the motor rotation speed to nA/or n7 depending on the pump variation. In the present invention, this work is performed by the air-fuel ratio setting section 7.

FIG. 4 shows a flowchart in the case where the air-fuel ratio setting section 7 is configured by a microcomputer and will be described. now.

If the QPA is below the predetermined amount, the adjustment unit 18
The blower 4 is driven so that the motor rotates at a motor rotation speed nA corresponding to FA, and nA is stored as the optimum rotation speed nAo. The flame current detection section 16 detects the flame current 1 at that time.The minimum value search section 17 detects the flame current 11 as the minimum value If,
n, and outputs an instruction to the adjustment unit 18 to increase the motor rotation speed by Δn. Compare the flame current xl at that time with the minimum value Ifmtn, and if I( is small, that Ifmtn is
is stored as a new minimum value Ifmin, the motor rotation speed at that time is stored as a new optimum rotation speed nAo, and an instruction is output to the adjustment unit 18 to increase the motor rotation speed by Δn. Conversely, if If is larger than Lfmin, △
A signal is output to the adjustment unit 18 so that the value is decreased by n. From then on,
When 15<If,, 4U, rewrite Il to new Ifmin and the motor rotation speed to new nAo, shift the motor rotation speed by △n in the same direction, and If > Ifmin.
In this case, repeat the operation of shifting by △n in the opposite direction. △n
Adjustment is complete if two reversals occur in the direction of shifting by the amount n.
Once Ao is determined, this value is stored in the storage unit 19.

On the other hand, the combustion amount control section 11 calculates the combustion amount according to the temperature difference ΔT between the temperature sensor 13 and the temperature set value 14, and connects the switch 15 to the contact point shown in the figure if the calculation result is a predetermined amount or more. △
FIG. 5 shows the characteristics of the oscillation frequency of the fuel pump 3 depending on T and the combustion amount. The characteristics on the right side of Figure 5 are the temperature difference △T on the horizontal axis.
(Rs is the set temperature 14, RT is the value of the temperature sensor 13)
, the vertical axis indicates the pump frequency and indicates the operating characteristics of the combustion amount control section 11. The diagram on the left shows the operating characteristics of the static electricity amount control unit 12, with the horizontal axis representing the rotation speed n of the fan motor and the vertical axis representing the pump frequency f. Once the pump frequency amount is determined according to the temperature difference ΔT, the air amount control unit 12 calculates and determines the motor rotation speed n based on this value. The value of nAo stored in the storage unit 19 of the unit 7 is used as a coefficient for calculation. For example, with the calculation formula motor rotation speed n'=L-nAo(a-f +b), the optimal blower motor rotation speed n according to the frequency amount can be calculated.
is determined. Note that in the above formula, a and b are constants. From the above, in Figure 5, when there is no pump variation, the F line is on the F line, and when there is pump variation as shown in Figure 3, when it is on the high combustion amount side, the G
When it is on the low combustion amount side, it is controlled on the H line. or,
When the combustion amount exceeds a predetermined amount for a long period of time, a signal is periodically input from the timer section 9, and the air-fuel ratio is set by forcibly reducing the combustion amount to a predetermined amount or less.

With the above configuration, the amount of air is automatically adjusted according to variations in the pump, and combustion can be performed while always maintaining an optimal combustion state.

Furthermore, in order to improve safety, the variable range (maximum value and minimum value) of the motor rotation speed n is limited in the adjustment section 18, and if the rotation speed n is not brought above this value, if there is no minimum extreme value, it is garbage. It may be configured to stop combustion when it is determined that a normal amount of air is not being sent due to a jam or the like, or that a normal amount of combustion is not being produced. Furthermore, by setting upper and lower limit values for the value of the flame current 1i at this time, the minimum value search unit 17 can easily stop the combustion as a result of detecting poor insulation of the flame rod or incomplete combustion.

Although the present embodiment has been explained using a petroleum 7 unheater, similar effects can be obtained using combustion equipment other than a fan heater or gas fuel.

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

(1) Since the air-fuel ratio is automatically set to the optimum point, no manual adjustment is required and a stable combustion state can be maintained at all times.

2) Since l can be adjusted to around 1.5 to 1.6, it can be applied to combustion control in full-fire combustion burners with low NOx.

(3) Since the flame current is controlled not by the absolute value but by the minimum value, the distance of the rod electrode, the rod shape, etc.
Even if there is a difference in applied voltage, etc., it is corrected and accurate air-fuel ratio control is possible without being affected.

G4) Since the air-fuel ratio is set when the combustion amount is low, the adjusted value at that time is stored, and the stored value is used to control even when the combustion amount is high, a stable combustion state can be maintained over a wide range of combustion amounts.

[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 primary air ratio and flame current, and Fig. 3 is a diagram showing the relationship between combustion amount, pump frequency, and blower motor rotation speed. FIG. 4 is a flowchart showing the operation flow of the air-fuel ratio setting section, FIG. 5 is a characteristic diagram of the combustion control section, and FIG. 6 is a characteristic diagram of the conventional air-fuel ratio control method. 1...Burner, 3...Fuel supply means,
4...Blower, 6...Control circuit section, 7
...Air-fuel ratio setting section, 8...Combustion control section, 10...Frame rod, 11...
Combustion amount control section, 12... Air amount control section, 16.
... Flame current detection section, 17 ... Minimum value search section, 18 ... Adjustment section, 19 ... Storage section. Name of agent: Patent attorney Toshio Nakao and 1 other person1-
Par lo---Frame rod connection 2 Fig. 1 - Figure 3 Moda Wj car &amp; ) AT-F!s-
F? -rt'ri Figure 6 1 x; strong female,)

Claims (2)

[Claims] (1) a burner that burns fuel, a fuel supply means that supplies fuel to the burner, and a blower that supplies combustion air;
It has a flame rod inserted into a combustion flame, and a control circuit section that controls combustion of the burner, and the control circuit section includes an air-fuel ratio setting section that sets an air-fuel ratio when the combustion amount is below a predetermined amount, and an air-fuel ratio setting section that sets an air-fuel ratio when the combustion amount is below a predetermined amount. When the amount exceeds a predetermined amount, the air-fuel ratio setting section has a combustion control section that calculates and controls the combustion amount based on the air-fuel ratio set by the air-fuel ratio setting section, and the air-fuel ratio setting section controls the ionic current of the flame by the flame rod. A flame current detection unit that detects a flame current, a minimum value search unit that searches for a point where the output signal of the flame current detection unit has a minimum value, and an output signal of the minimum value search unit that determines the amount of air supplied to the blower or the fuel supply. The combustion control unit includes an adjustment section that adjusts at least one of the amount of fuel supplied to the means, and a storage section that stores the adjustment value of the adjustment section, and the combustion control section calculates the combustion amount and controls the fuel supply means. and an air amount control section that calculates the amount of air and controls the blower, and at least one of the combustion amount control section and the air amount control section calculates based on the output signal of the storage section. . (2) The combustion control device according to claim 1, wherein the control circuit section includes a timer section that periodically lowers the combustion amount to a predetermined amount or less for a certain period of time and outputs a drive signal to the air-fuel ratio setting section.