JPH0141885B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application The present invention relates to combustion safety technology for hot air heating devices.

Conventional configurations and their problems In recent years, gas and oil fan heaters have been increasingly used as home heating appliances due to their economic efficiency, quick heating, and ease of use. These fan heaters release combustion exhaust gas into the room, so clean combustion technology and incomplete combustion prevention technology are important technical issues. Against this background, the hot air heating device disclosed in Japanese Patent Application Laid-open No. 57-198946 shows extremely excellent characteristics in terms of cleanliness, and generates a large amount of nitrogen oxides (hereinafter referred to as NOx) during normal use. is 3 to 5 ppm (O ₂ =
(calculated as 0%), which is extremely low. However, in such a combustion device, if the equivalence ratio φ becomes 1 or more due to some reason (for example, oxygen deficiency or damper blockage), the above-mentioned cleanliness will not be achieved. This problem will be explained using FIG. 1. The premixture in the mixing tube 1 is set at an equivalence ratio of φ0.85 to 0.9,
After being ejected from the primary flame hole 2, a surface combustion flame exhibiting a uniform temperature distribution is formed on the same primary flame hole 2.
That is, it is an all-primary surface combustion burner. This significantly suppresses NOx generation. Further, the pressure equalizing plate 3 provided upstream of the combustion exhaust gas maintains a uniform temperature within the primary combustion chamber 4, and also contributes to the oxidation of intermediate products, which is effective in expanding the combustion range.
All of the above arguments hold true when the equivalence ratio φ is 1.0 or less, and if this assumption is violated, the process described below will follow and combustion will become unstable. That is, if the equivalence ratio φ exceeds 1.0, unburned gas whose oxidation reaction cannot be completed by the primary air alone will come into contact with the secondary air on the pressure equalizing plate 3 and form a flame. In this state, the flame formed in the primary combustion chamber 4 lacks stability and expands, so it touches the pressure equalizing plate and some of the oxidation reaction is frozen, resulting in CO, R-
A large amount of CHO etc. will be generated.

Thus, the conventional all-primary surface combustion burner
When the equivalence ratio φ is 1.0 or less, excellent clean combustion properties are achieved, but when the equivalence ratio φ exceeds 1.0, there is a problem that a very dangerous combustion state occurs.

On the other hand, incomplete combustion prevention technology for all-primary surface combustion burners, as shown in the above-mentioned Japanese Patent Application Laid-Open No. 57-198946, applies technology that uses oxygen concentration sensors and flame detection elements such as flame rods and thermocouples. Although there are technologies available, the latter technology for preventing incomplete combustion has not yet been established.
The former also had the disadvantage of slow responsiveness in ignition/misfire detection due to problems related to thermal response.

Purpose of the Invention The present invention solves such conventional problems, and whether the equivalence ratio φ is 1.0 or more or 1.0 or less,
It is an object of the present invention to provide a hot air heating device that performs stable clean combustion and has a reliable function of preventing incomplete combustion.

Structure of the Invention In order to achieve this object, the present invention comprises a primary flame hole composed of an electromagnetic valve for controlling fuel supply and a wire mesh, a punched plate, or a ceramic plate having small holes, and the primary flame hole is connected to the primary combustion chamber. and a surface combustion burner formed of a casing formed with a secondary combustion chamber and surrounded by a casing having a secondary flame hole; A comparison circuit section for comparing flame signals obtained from the guide plate, flame detection elements provided above the primary flame hole and above the secondary flame hole, respectively, and the flame signals obtained from both the flame detection elements, and an output signal of the comparison circuit section is inputted. and a drive circuit that drives the electromagnetic valve.

According to this configuration, when the equivalence ratio φ<1, the flame is an all-primary surface combustion flame that is formed only on the primary flame hole, and since the flame surface is protected by the primary combustion chamber, the flame is There is no inflow, resulting in a uniform, low-temperature flame, and NOx generation is suppressed. on the other hand,
The output signals of the flame detection elements on the primary and secondary flame holes are always the output signals on the primary flame hole because there is a flame zone only above the primary flame hole and the flame zone is downstream from the flame zone above the secondary flame hole. becomes larger. If the equivalence ratio becomes φ≧1 due to oxygen deficiency, damper blockage, etc., unburned matter or intermediate products that have not completed combustion on the primary flame hole will be rectified as a parallel flow by the air channel in the secondary flame hole. The secondary air forms a stable secondary flame, so low NOx combustion is maintained even under such conditions. In addition, since flames are formed on the primary flame hole and the secondary flame hole, the output signals of each flame detection element may be approximately equal, or the output signal of the flame detection element on the secondary flame hole may be large. Therefore, the relationship of the output signals under the condition of equivalence ratio φ<1 is reversed. By detecting this reversal phenomenon and controlling fuel supply, incomplete combustion prevention technology can be established.

DESCRIPTION OF EMBODIMENTS An embodiment of the present invention will be described below with reference to FIGS. 2 and 3. Note that the same parts as in FIG. 1 are given the same numbers. The primary flame hole 2 of the surface combustion burner 5 is curved toward the downstream side of the air-fuel mixture, and is in pressure contact with the mixing tube 1 located below. The primary combustion chamber 4 is constructed inside a casing 6 that is formed by standing up vertically from the end of the primary flame hole 2 toward the combustion exhaust gas downstream side and tilting it inward from an appropriate position. 7 is provided at the end of the inclined surface. One end of the guide plate 8 a that passes through the front side of the housing 6 and stands upwardly passes below the surface combustion burner 5 and is joined to the lower end of the air supply port 9 .
Similarly, the guide plate 8b has one end passing through the rear side of the casing 6 and rising upward, and the other end passing between the surface combustion burner 5 and the guide plate 8a and stopping directly below the surface combustion burner 5. The secondary combustion chamber 10 has the guide 8
a, 8b, and its position is secondary flame hole 7
It is above. The rectifying plate 11 is provided above the secondary combustion 10, and a flame rod A12 is installed above the primary flame hole and a flame rod B is installed above the secondary flame hole as a flame detection element.
13, and also includes a solenoid valve 14 for controlling fuel supply, a comparison circuit section 15, and a drive circuit 1.
There are 6.

According to the above configuration, in the case of an air-fuel mixture with an equivalence ratio φ<1, a surface combustion flame is formed on the primary flame hole 2 through the mixing tube 1, but the secondary air is prevented from flowing into the primary combustion chamber 4 by the casing. 6, the cooling of the flame surface by secondary air is suppressed, and at the same time, the temperature inside the primary combustion chamber 4 can be maintained at a uniform temperature field, resulting in low NOx combustion and excellent control of the combustion amount. It becomes something. Next, let's consider the ion current value characteristics due to flame rod. The relationship between the ion current value I _f and the equivalence ratio φ is shown in Figure 4, where the horizontal axis represents the equivalence ratio φ,
The ion current value I _f is plotted on the vertical axis. Note that curve a is the current value characteristic for frame rod A, and curve b is the current value characteristic for frame rod B. Under the condition of equivalence ratio φ<1, which is currently under consideration, the output signal from the comparator circuit section 15 always indicates that the ion current value of flame rod A (hereinafter referred to as _Ifa ) is higher than that of ion current of flame rod B. Indicates that it is larger than the current value (hereinafter referred to as I _fb ). In this case, the combustion is determined to be normal, and the solenoid valve 14 remains open.

Next, considering the case where the equivalence ratio φ≧1, as mentioned above, since there is no inflow of secondary air into the primary combustion chamber 4, there is a A flame is formed, and unburnt gas, intermediate products, etc. diffuse and mix with secondary air on the secondary flame hole 7,
Burns completely. This means that under the condition of equivalence ratio φ≧1, although the conventional all-primary surface combustion burner causes incomplete combustion, the surface combustion burner based on the present invention does not cause incomplete combustion and is stable. Two-stage low NOx combustion is performed. Examining the ion current value characteristics under the same equivalence ratio φ again using FIG. 4, when the equivalence ratio φ≧1,
I _fb becomes larger than I _fa , and the equivalence ratio φ<
It can be seen that the current value characteristics of both cases are reversed.

Here, the comparison circuit section 15 compares I _fa and I _fb ,
If the condition of I _fa ≦ I _fb is satisfied, it is assumed that a sequence is applied in which the drive circuit 16 closes the fuel supply solenoid valve 14 . Under this sequence, the principle of operation as a safety device under the following two combustion conditions will be shown. Note that even under conditions where both are combined, the operating situation is the same.

(1) When φ>1 (oxygen partial pressure does not change) and the initial equivalence ratio φ is set to 0.85, the relationship I _fa > I _fb exists as shown in Figure 4, and combustion is normal. I judge that. In fact, it's normal. However, due to damper blockage, decrease in fan rotation speed, etc., φ≧
When it becomes 1, I _fa ≦ I _fb for the reason mentioned above. As a result, it was determined that the combustion was abnormal,
Drive circuit 16 closes solenoid valve 14 . This ensures safety.

(2) O ₂ ≦18% (when oxygen partial pressure decreases) When the initial O ₂ concentration is 20.9%, there is a relationship of I _fa > I _fb .
However, if the engine continues to operate for a long time, the oxygen concentration in the room decreases, and the relationship between I _fa and I _fb reverses accordingly.

That is, under the condition of O ₂ ≦18%, I _fa ≦ I _fb .

As a result, the solenoid valve 14 closes and combustion stops. A concrete representation of this is shown in FIG. In Figure 5, the horizontal axis is O ₂ concentration, the vertical axis is I _f ,
The solid line a represents _Ifa , the solid line b represents _Ifb , and _the solid line c represents CO/ _CO2 . As can be seen from the figure, I _fa = I _fb becomes O ₂ = 18%, and in that case,
CO/CO ₂ is almost the same as when O ₂ = 21%, and even at extremely low O ₂ , CO/CO ₂ does not rise and can be burned stably.

Effect of the invention According to the present invention, the following effects can be obtained.

(1) Stable combustion with suppressed CO generation and low NOx can be achieved over an extremely wide range from primary combustion to diffuse combustion.

(2) A reliable incomplete combustion prevention device can be established. Specifically, it is possible to reliably cut off the fuel supply at O ₂ =18%, damper blockage (corresponding to equivalence ratio φ≧1), etc.

(3) Even if the incomplete combustion prevention device is activated (O ₂ = 18% or less, damper blockage, etc.), almost no CO is generated from the surface combustion burner.

(4) Combustion can be performed with less CO generation even under conditions of low O ₂ concentration.

[Brief explanation of drawings]

Figure 1 is a cross-sectional view of a conventional low NOx burner, Figure 2 is a cross-sectional view of a conventional low NOx burner.
The figure is a partially sectional front view of a hot air heating device that is an embodiment of the present invention, FIG. 3 is a cross-sectional view taken along line A-A in FIG. 2, and FIG. 4 explains the effects of the present invention. Fig. 5 is a diagram showing the equivalence ratio φ vs. ion current characteristic, and FIG. 5 is a diagram showing the O ₂ concentration vs. ion current characteristic and CO/CO ₂ characteristic. 2... Primary flame hole, 4... Primary combustion chamber, 5... Surface combustion burner, 6... Housing, 7... Secondary flame hole, 8
a, 8b...Guide plate, 10...Secondary combustion chamber, 1
2, 13...Flame detection element, 14...Solenoid valve, 1
5... Comparison circuit section, 16... Drive circuit.

Claims (1)

[Claims] 1 A primary flame hole is constituted by a solenoid valve that controls fuel supply and a wire mesh, a punched plate, or a ceramic plate having small holes, and a primary combustion chamber is formed, and the primary flame hole is surrounded by a casing having a secondary flame hole. a surface-combustion burner that passes through the side surface of the casing and extends upward to form a secondary combustion chamber and surrounds the casing; a guide plate that extends above the primary flame hole and above the secondary flame hole; and a comparison circuit section that compares flame signals obtained from the two flame detection elements, and a drive circuit that receives the output signal of the comparison circuit section and drives the solenoid valve. heating equipment.