JPS6242212B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a safe combustion method and device, and in particular, it uses a gas sensor made of a metal oxide semiconductor whose resistance value changes depending on the gas, a solid electrolyte whose electromotive force changes depending on the oxygen partial pressure, etc. to measure the equivalent of combustion gas. The present invention relates to a method and apparatus for detecting ratios. Note that in this specification, combustion gas refers to both a mixed gas of fuel and air and exhaust gas after combustion thereof. 2. Description of the Related Art In order to prevent incomplete combustion in combustion devices such as stoves and water heaters, a technique is known in which combustion is controlled by detecting the equivalence ratio of combustion gas using a gas sensor. For example, Japanese Patent Application Laid-Open No. 56-30520 discloses a technique for detecting the composition of combustion exhaust gas using a gas sensor made of a metal oxide semiconductor. In this technology, the gas sensor is installed downstream of the combustion surface to prevent the influence of unburned gas. Furthermore, JP-A No. 56-91128 describes detecting the composition of exhaust gas from a stove or the like using a gas sensor made of a solid electrolyte, and also describes the use of a cover to surround the gas sensor and burner to prevent ambient air from entering. There is. However, with either technique, (a) the gas sensor can only be placed downstream of the combustion surface; There are problems such as (b) insufficient sensitivity to changes in the equivalence ratio of combustion gas, and (c) the sensitivity of the gas sensor decreases at low temperatures. The inventor's findings regarding the causes of such problems will be explained based on the drawings. FIG. 1 shows the arrangement of a metal oxide semiconductor gas sensor 02 in a burner 01 of the safety premix type. FIG. 2 shows a case in which a cover 03 is combined with this to prevent ambient air from entering. Note that the upper end of the cover 03 is opened to serve as an exhaust gas discharge port. Both devices use a combustion process using a burner to remove unreacted components. Therefore, gas sensor 0
2 cannot be placed upstream of the burner. Even in the wake of the combustion surface, trace amounts of unreacted components are actually contained in the exhaust gas. However, no measures have been taken to remove such unreacted components. The presence of unreacted components reduces the detection accuracy of the gas sensor. This problem becomes especially serious at low temperatures. The present invention aims to (a) eliminate restrictions on the mounting position of the gas sensor due to the combustion surface, (b) improve the detection accuracy of the gas sensor, especially at low temperatures, and (c)
The aim is to provide a new technology that prevents the mixing of ambient air. The safe combustion method of the present invention is characterized in that it utilizes a combustion gas recirculation process. (a) the recirculation zone can also be formed upstream of the normal combustion surface, (b) the recirculation process achieves sufficient chemical equilibrium of the combustion gases, and (c) the surrounding area of the recirculation zone The gas flow can be used as an air curtain to the surrounding air. The device according to the second invention of the present application causes recirculation of combustion gas by means of a bluff body opposed to the flame opening of the burner, and a gas sensor is disposed in the recirculation area. In the device of the third invention of the present application, the flame port of the burner is provided facing near the peripheral edge of the bluff body, and the gas sensor is arranged in the recirculation area generated between the burner and the bluff body. The device of the fourth invention of the present application is provided with a bluff body disposed non-perpendicularly to the direction of fuel discharge from the flame port of the burner,
A gas sensor is provided in the recirculation area formed between the bluff body and the burner. Here, as a gas sensor, SnO ₂ , TiO ₂ ,
There are methods that utilize changes in the resistance value of metal oxide semiconductors such as CoO and MgFe ₂ O ₄ , and methods that use changes in the electromotive force of solid electrolytes such as ZrO ₂ . Furthermore, the term bluff body used in this specification refers to a nonlinear object, that is, an object that generates a circulating vortex around it. As the burner, it can be applied to a liquid fuel burner such as a gas burner or a spray combustion type burner. Burners are not limited to safe premixed types.
It can also be applied to systems that utilize secondary air. This is because it is sufficient that the fuel and air be mixed before coming into contact with the gas sensor. In the case of burners using secondary air, the air is mixed with the fuel gas, for example upstream or around the recirculation zone. The control means includes a solenoid valve, a buzzer, a lamp, etc. Embodiments of the present invention will be described below with reference to the drawings. Note that in these Examples, a safety premixed gas burner was used. In Fig. 3, 2 is a plate-shaped burner made of ceramic, and its surface has many flame holes 6, 8, 1.
0, 12, etc. are provided. A bluff body 4 is provided facing the burner 2 on the upstream side of a normal combustion surface (the position where combustion is almost completed when there is no bluff body is called a "normal combustion surface"). The bluff body 4 is made of disc-shaped ceramic,
The front surface (hereinafter, the lower burner side will be referred to as "front" and the opposite side to the burner will be referred to as "rear") is formed into an arcuate cross-section.
The bluff body 4 is attached to the burner 2 by a support (not shown). SnO ₂ sintered gas sensor 1
4 is housed in a recess provided on the rear surface of the bluff body 4. A pair of Pt electrodes (not shown) are connected to gas sensor 1.
4 and connect the gas sensor to the detection circuit shown in FIG. Combustion gas is ejected from the burner 2 and ignited.
Combustion gas from flame ports 8, 10, etc. is bluff body 4
and flows along the bluff body 4. At the rear of the bluff body 4 there is a recirculation area for the combustion gases, in which the gases circulate for a long time. Arrows indicate gas flow. The gas in the recirculation region is in almost perfect chemical equilibrium, with almost no unreacted components present. This is because the flame spreads to this area and combustion progresses, while the gas continues to swirl for a long time. Since the gas remains in this region for a long time, equilibrium is almost perfect even when the temperature is low and the combustion rate is low. A recirculation region can also be created upstream of the normal combustion surface. Therefore, the normal combustion surface is not a constraint on the mounting position of the gas sensor. The recirculation area is surrounded by a surrounding gas flow. Ambient air flows with this gas flow and does not affect the gas sensor. FIG. 4 shows an example using another burner 16, in which a ceramic heat-resistant chip 20 is attached to the tip of a metal pipe 18. The bluff body 4 is attached to the heat-resistant chip 20, and the gas sensor 14 is attached to the bluff body 4 using lead wires 22 and 24 which also serve as electrodes. In principle, the technique of the present invention does not require a cover surrounding the gas sensor. However, this does not preclude the use of a cover. For example, as shown in FIG. 5, a box-shaped ceramic cover 26 (not shown) with an open upper portion may be used to completely isolate the gas sensor 14 from the surrounding air. The technique of the present invention can be applied to various burners. FIG. 6 shows an example of application to a burner 28 in which a nozzle 30 is surrounded by a refractory material 32 and a conical combustion chamber 34 is provided. A bluff body 36 made of ceramic is inserted into the tip of the nozzle 30, and a gas sensor 14 is attached to the back of the bluff body 36.
The combustion gas flows as shown by the arrow in the figure, and a circulating vortex is generated behind the bluff body 36. A circulating vortex may be formed on the upstream side of the bluff body. This example is shown in the seventh example.
As shown in the figure. The arrangement of the flame ports 38, 40, 42, 44, etc. is changed so that combustion gas flows along the periphery of the bluff body 4 and does not blow into the center of the bluff body 4. In this way, a vortex is generated between the bluff body 4 and the burner 2, and the gas composition in this vortex is detected by the gas sensor.
Detected by 4. It is not necessary for the bluff body to be arranged perpendicular to the direction of fuel discharge from the burner. For example, as shown in FIG. 8, the tip of a burner 52 having a large number of flame ports 46, 48, 50, etc. is surrounded by a bluff body 54 made of cylindrical ceramic with a narrowed opening, and a circulating vortex is formed at the bottom of the bluff body 54. You may let them. Alternatively, as shown in FIG. 9, the bluff body 56 may be mounted obliquely to the burner 2 to generate a circulating vortex between the burner 2 and the bluff body 56. Although the SnO ₂ sintered body 14 was used as the gas sensor in each of the above embodiments, various other materials may be used. For example, as shown in FIG. 10, a ZrO ₂ solid electrolyte gas sensor 60 may be used. By the way, if the temperature dependence of the gas sensor, the resistance-temperature characteristics of metal oxide semiconductors, or the temperature dependence of the electromotive force of solid electrolytes becomes a problem, the temperature of the gas sensor can be detected by various resistance temperature detectors, and the circuit All you have to do is compensate. As the temperature measuring resistor, one using the temperature coefficient of resistance of platinum, a high temperature thermistor such as Al ₂ O ₃ , etc. are preferable. An example of a detection circuit used in the present invention is shown in FIG. A power source 62 and a load resistor 64 are connected in series to the gas sensor 14, the voltage applied to the load resistor 64 is detected by a comparator 66, and a control means 70 such as a solenoid valve or a buzzer is operated via a relay 68. Note that when using the solid electrolyte gas sensor 60, the electromotive force of the gas sensor 60 may be used instead of the voltage applied to the load resistor 64. The results of trial tests regarding the effects of the present invention are shown in the table. The test was conducted for each device shown in Figures 1 to 10.
This was done by examining the output of the gas sensor with respect to changes in the combustion gas equivalence ratio (hereinafter referred to as λ). The heating temperature of the gas sensor corresponds to normal usage conditions
900℃ and 600 corresponding to reduced combustion load
There were two types: ℃. In the comparative example, the detection sensitivity decreases when the gas sensor is brought closer to the burner. If a cover is not used, secondary air intrusion becomes a problem. Such a problem does not arise with the technique of the present invention. In the comparative example, the detection sensitivity is inferior to that of the present invention, and the decrease in sensitivity is particularly significant at low temperatures.

【table】

[Table] As explained above, in the present invention, the gas sensor can be placed closer to the burner than the normal combustion surface, and the detection sensitivity to changes in the equivalence ratio can be improved, eliminating restrictions on the mounting position of the gas sensor. It also has the characteristics of being able to improve detection sensitivity at low temperatures and preventing deterioration in detection accuracy due to the effects of ambient air.

[Brief explanation of the drawing]

FIGS. 1 and 2 are horizontal sectional views showing a conventional safe combustion device. FIGS. 3 to 10 are horizontal cross-sectional views of essential parts of safe combustion devices according to embodiments of the present invention.
FIG. 11 is a diagram showing an example of a detection circuit used in the present invention. 2, 16, 28, 52... burner, 4, 36,
56, 54... Bluff body, 14... Gas sensor made of metal oxide semiconductor, 60... Gas sensor made of solid electrolyte.

Claims (1)

[Claims] 1. In a method of controlling combustion by detecting the equivalence ratio of combustion gas from a burner with a gas sensor, a recirculation region of the combustion gas is formed to achieve chemical equilibrium of the combustion gas, and this recirculation process A safe combustion method characterized by bringing the gas that has passed through the process into contact with a gas sensor as a test gas. 2. A safety combustion device comprising a burner and a gas sensor for detecting the equivalence ratio of combustion gas from the burner, and a control means operated by the output of the gas sensor, which is provided with a bluff body facing the flame opening of the burner. Further, a safe combustion device characterized in that the gas sensor is provided at a position downstream of the bluff body where a recirculation region of combustion gas is formed during combustion. 3. A safety combustion device comprising a gas sensor for detecting the equivalence ratio of a burner and combustion gas from the burner, and a control means operated by the output of this gas sensor, in which a bluff body is provided facing the burner, and a bluff body is provided facing the burner. flame ports are provided at opposite positions near the periphery of the bluff body so that a recirculation area is formed between the burner and the bluff body during combustion, and the flame openings are located at positions where the recirculation area is formed. A safe combustion device comprising the gas sensor. 4 A safety combustion device comprising a burner and a gas sensor for detecting the equivalence ratio of combustion gas from the burner, and a control means operated by the output of this gas sensor, which Safe combustion characterized in that a bluff body is provided at right angles so that a recirculation area is formed between the bluff body and the burner during combustion, and the gas sensor is provided at a position where this recirculation area is formed. Device.