JPH06100335B2 - Combustion control device - Google Patents

Description

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

2. Description of the Related Art When burning gas or oil as a fuel, by supplying the fuel and air in an optimal ratio, it is possible to prevent backfire, misfire, or incomplete combustion and maintain stable combustion. The ratio of this fuel to the air amount is called the air-fuel ratio, and conventionally there has been considered a means for detecting the combustion state and controlling the fuel or the air amount so as to always maintain the optimum air-fuel ratio.

As an air-fuel ratio control system for oil burning equipment, for example, the one described in Japanese Patent Laid-Open No. 61-24917 is often considered. This is to detect the flame ion current of the flame by the flame rod inserted into the flame and utilize the fact that this flame ion current changes depending on the air-fuel ratio to adjust the drive frequency of the fuel supply pump to optimize the air-fuel ratio. This is the configuration.
FIG. 6 shows an example of the flame ion current value I _f . The horizontal axis represents the primary air ratio μ, and the air-fuel ratio will be described herein by the primary air ratio μ. In a typical input range (3000 to 1000 kcal / h), the flame ion current value I _f has a distribution with a peak at approximately μ = 0.8 to 0.9. Therefore, the pump driving frequency is adjusted to determine the kerosene supply amount so that the flame ion current value _If becomes the maximum value, thereby performing the air-fuel ratio control and maintaining a stable combustion state.

Problems to be Solved by the Invention In the above conventional example, the burner configured to maintain the most stable combustion state at μ = 0.8 to 0.9 was used, but μ = 1.
There is also a burner configured to maintain the most stable combustion state around 5. (Hereinafter, referred to as all primary combustion burners)
It is known that all primary combustion burners generally have a low flame temperature and very few nitrogen compounds (NOx), which are harmful components in exhaust gas, and have a great effect on reducing NOx. There is.

However, since the conventional air-fuel ratio control means as described above determines the kerosene supply amount so that the flame ion current value _If becomes the maximum value, it is adjusted to μ = 0.8 to 0.9, and in the vicinity of μ = 1.5. There was a problem that a stable combustion state could not be maintained.

The present invention solves such a conventional problem, and an object of the present invention is to maintain a stable combustion state by adjusting around μ = 1.5 in all primary combustion burners.

Means for Solving the Problems In order to solve the above problems, the combustion control device of the present invention is
A cylinder having a large number of small holes, a burner formed by providing a wire mesh on the outside of the cylinder, a fuel supply means for supplying fuel to the burner, a blower for supplying combustion air, and a frame rod inserted in the combustion flame. And a control circuit section for performing combustion control of the burner, the control circuit section being a flame current detection section for detecting an ion current of a flame by the flame rod,
A minimum value search unit that searches where the output signal of the flame current detection unit has a minimum value, and controls the amount of fuel supplied by the fuel supply means within a range that is predetermined by the output signal of the minimum value search unit. The configuration has a combustion amount control unit.

Action The present invention has the above-described configuration to adjust the air-fuel ratio so that the output signal of the flame current detection unit becomes the minimum value and maintain a stable combustion state at around μ = 1.5.

Embodiments Embodiments of the present invention will be described below with reference to the accompanying drawings. In the embodiment, an indoor open combustion type 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. Reference numeral 1 denotes a burner, which is an all-primary combustion burner in which a flame port is formed by a wire mesh on the outside of a punching plate having a large number of small holes. It is vaporized and mixed by the vaporization mixer 5 and burned in the burner 1. Reference numeral 6 is a frame rod for transmitting the flame current _If flowing in the flame of the burner 1 to the flame current detection unit 8 of the control circuit unit 7. A minimum value search unit 9 outputs a signal for changing the combustion amount to the combustion amount control unit 10 so that the output signal of the flame current detection unit 8 is minimized. The combustion amount control unit 10 adjusts the pump 3 by the output signal of the minimum value search unit 9 to adjust the amount of fuel supplied.

Figure 2 shows the characteristics of the flame ion current I _f in all primary combustion burners. The ion concentration in the flame is highest around μ = 0.9, and the ion concentration decreases as μ increases. With all primary combustion burners, it was confirmed that the flame adheres to the burner around μ = 0.9 and the flame extends as μ increases. As the flame grows, the part of the flame with the highest ion density approaches the frame rod. Therefore, in the region of μ> 0.9, as the flame ion current I _f increases, there is a phenomenon of decrease due to a decrease in ion concentration, and a phenomenon of increase due to a portion with a high ion density approaching the frame rod. It has been confirmed that the characteristics shown in Fig. 2 have the smallest extremum around µ = 1.5 to 1.6. FIG. 3 shows a characteristic diagram of the relationship between the combustion amount Q _F and the flame current I _f at a constant air amount. The flame current I _f becomes a curve having a minimum minimum value with a combustion amount slightly smaller than the combustion amount Q _F0 corresponding to μ = 1.5. This is because there is an influence of a decrease in flame current due to a decrease in combustion amount. Q _F > Q _F0 is μ <1.5, Q _F <Q _F0 is μ>
At 1.5, draw a curve that is symmetrical to the curve shown in Fig. 2.

Next, an example of the operation of the minimum value search unit 9 will be described based on the flowchart of FIG. K is a variable indicating the increasing / decreasing direction of the combustion amount, and is +1 when increasing and -1 when decreasing.
, And the initial value is +1 for convenience. Burning amount control unit
10 is the fuel pump 3 so that it burns with a predetermined combustion amount Q _F.
To drive. The flame current detection unit 8 detects the flame current _If at that time. The minimum value search unit 9 stores the flame current I _f as I _{fmin and} changes the combustion amount by K × ΔQ _F. That is, the combustion amount is Δ
A signal is output to the combustion amount control unit 10 so as to increase by Q _F. Compared with flames current I _f and the minimum value I _fmin at that time, I _f is less if the I _f stores a new minimum value I _fmin combustion amount K
× Change by ΔQ _F. That is, a signal is output to the combustion amount control unit 10 so as to further increase the combustion amount by ΔQ _F. Conversely, I _f is I
If it is larger than _fmin , a value obtained by multiplying K by -1 is set as a new K, and the combustion amount is changed by K × ΔQ _F. That is, a signal is output to the combustion amount control unit 10 so as to reduce the combustion amount by ΔQ _F.
After that, when I _f <I _fmin is rewritten to new I _fmin the I _f K
Is used as it is, and when I _f > I _fmin , K is multiplied by −1 to obtain a new K, and the operation of changing the combustion amount by K × Q _F is repeated. That is, the combustion amount is 1 when I _f <I _fmin
When ΔQ _F and I _f > I _{fmin in} the same direction as the first time, the operation of shifting by ΔQ _{F in the} opposite direction from the previous time is repeated. If Q _F goes out of a predetermined range Q _{Fmin to} Q _Fmax during this process, it is determined to be abnormal and combustion is stopped. By the above operation, the combustion is controlled to be maintained where the flame current _If is minimum.

Next, another example of the operation of the minimum value search unit 9 will be described with reference to FIG. The control circuit unit 7 controls the amount of air supplied from the blower 4 to Q _A1 , Q
Output to switch to _A2 . Line A shows the combustion amount QF =
When the supply air amount Q _A0 corresponding to mu = 1.5 of Q _F ion current characteristics in combustion rate Q _F0 is _{Q A1 <Q A0 <Q A2} , and fire the ion current when the amount of supply air of Q _A1 The difference ΔI _f of flame ion current at Q _A2 is small. B line is Q _F ＞ Q _F0 , C line is Q _F 〈Q
_These are the characteristics of _F0 , and when the supply air amount is Q _A1 and Q
_Since the flame ion current difference ΔI _{f at A2} becomes large, the combustion amount control unit 10 adjusts the combustion amount Q _F by increasing or decreasing so that this ΔI _f becomes smaller than a certain value. Current I _f
It keeps the combustion at the point where is minimum.

In the above configuration, the fuel pump 3 is adjusted so that the flame ion current _If is minimized, and the supplied fuel amount is controlled, so that a stable combustion state can be maintained around μ = 1.5 to 1.6.

Although the oil fan heater has been described in this embodiment, the same effect can be obtained by using a combustion device or gas fuel other than the fan heater.

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

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

(2) Since it can be adjusted to around μ = 1.5 to 1.6, it can be applied to combustion control in all primary combustion burners with low NO _x .

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

(4) Since the fuel supply means is controlled according to the variation of the blower, the response is quick, and the air-fuel ratio can be adjusted immediately even if it shifts due to a sudden abnormality.

[Brief description 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, FIG. 3 is a characteristic diagram of combustion amount and flame current, and FIG. FIG. 5 is a flow chart explaining an example of the operation, FIG. 5 is a characteristic view showing another example of the operation, and FIG. 6 is a characteristic view of a conventional air-fuel ratio control system. 1 ... Burner, 3 ... Fuel supply means, 4 ... Blower, 6
...... Frame rod, 7 ...... Control circuit part, 8 ...... Flame current detection part, 9 ...... Minimum value search part, 10 ...... Combustion amount control part.

Claims (1)

[Claims] 1. A cylinder having a large number of small holes, a burner formed by providing a wire mesh on the outside of the cylinder, fuel supply means for supplying fuel to the burner, and a blower for supplying combustion air.
A flame rod inserted into the combustion flame, and a control circuit unit for controlling combustion of the burner, the control circuit unit detecting a flame ion current by the flame rod, and a flame current detecting unit. Of the output signal of the minimum value search unit, and a combustion amount control unit for controlling the fuel supply amount of the fuel supply means within a range predetermined by the output signal of the minimum value search unit. A combustion control device configured to have.