JPH033798Y2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an air-fuel ratio control device for always keeping the mixture ratio of fuel and air supplied to a combustor appropriate to achieve optimal combustion.

Originally, there are many types of combustion machines, such as boilers, automobile engines, and dryers, but all of these machines mix air and fuel in the appropriate ratio to increase thermal efficiency, and produce non-polluting exhaust. It is released into the atmosphere as a gas. In order to obtain an appropriate mixture ratio of air amount and fuel, an air-fuel ratio control device S as shown in FIG. 3 has conventionally been used.

This conventional example describes a case where a boiler M is used as the combustor D. A temperature sensor T is provided in the combustion chamber N in the boiler M, and a zirconia oxygen concentration meter (oxygen sensor) is installed in the exhaust pipe E. abbreviated)
_O2 is installed. The control unit C performs calculations based on the signals from the temperature sensor T and water temperature sensor W.
The opening of solenoid valve V ₁ for air A and solenoid valve V ₂ for fuel F is adjusted so that predetermined amounts of air A and fuel F flow. Mixed combustion occurs in burner B, and exhaust gas is released into the atmosphere through exhaust pipe E.

On the other hand, the oxygen sensor O ₂ installed in the exhaust pipe E generates an electromotive force e as shown in Fig. 5 depending on the concentration of oxygen in the exhaust gas, and based on the generated signal, for example, a proportional-integral control device (PI control The amount of air is mainly corrected using a combustion chamber (referred to as a combustion chamber), and the exhaust gas after combustion by burner B is controlled so that it is always within the optimum combustion range shown in Fig. 4. Figure 4 shows the relationship between excess air ratio and thermal efficiency. As the excess ratio range increases, heat loss of exhaust gas increases and thermal efficiency decreases, and at the same time, NO, NO ₂ , SO ₂ etc. of harmful gases are released into the atmosphere. Further, when the excess ratio is small, that is, as the fuel content increases, heat loss due to incomplete combustion increases rapidly, and thermal efficiency also decreases accordingly. In other words, the optimum combustion range is when the air/fuel mixture ratio has an excess air ratio of slightly greater than 1, in which heat loss is small and thermal efficiency is at its best.

However, in the above conventional example, the oxygen sensor
The electromotive force e of O ₂ does not necessarily change at an excess air ratio of 1 depending on the composition of the gas burned in burner B. For example, in the case of i-butane 0.1% fuel in Figure 5, it is shown in the diagram at each temperature. As shown, it changes depending on the temperature of the exhaust gas. Therefore, the electromotive force e of the oxygen sensor O ₂ is 0.4V.
When performing the above PI control with ``threshold value'',
At temperatures below 800°C, the excess air ratio approaches 0.5 and fluctuates, making it impossible to operate in the optimum combustion range shown in Figure 4, resulting in poor thermal efficiency and unstable exhaust gas components. For this purpose, the special public
As disclosed in Publication No. 12002, it is also possible to arrange the oxygen sensor in the exhaust pipe at a distance downstream of the catalyst body which is suspended in the exhaust pipe by a plurality of stays with strong spring properties. , the exhaust gas from which the unbalanced components have been removed by passing through the catalyst and the exhaust gas containing the unbalanced components flowing from around the catalyst mix in front of the oxygen sensor and hit the oxygen sensor, so this also occurs. The power will change. Furthermore, since the oxygen sensor is disposed in the main exhaust passage, it is affected by the speed of exhaust gas depending on combustion conditions, causing a problem in that the set electromotive force changes.

This is due to unbalanced components of the exhaust gas and changes in the flow of the exhaust gas.The present invention aims to eliminate these drawbacks by providing a bypass passage that joins the main exhaust gas passage of the combustor. The feature is that an oxidation catalyst is installed in the bypass passage and an oxygen sensor is installed downstream of the oxidation catalyst.The oxygen sensor detects the oxygen concentration of the exhaust gas that has passed through the oxidation catalyst, and detects excess air that is almost unaffected by the exhaust temperature. rate is 1
It is designed to generate electromotive force in the vicinity.

Examples will be described below with reference to the drawings.

FIG. 1 is a schematic diagram of the main parts for explanation of an air-fuel ratio control device 10 according to the present invention, and common devices with FIG. 3 are omitted. The air and fuel mixed by the burner 4 in the combustor 3 are combusted, and the exhaust gas 5 is caused to pass through a main exhaust gas passage 6 and a bypass passage 7 that merges with the passage 6, and is oxidized into the bypass passage 7. A catalyst 1 is disposed, and an oxygen sensor 2 is further disposed downstream thereof. oxygen sensor 2
detects the oxygen concentration of the passing gas 5' after passing through the oxidation catalyst 1 and generates the electromotive force
Although there are slight differences in gas composition and concentration compared to Figure),
Stable electromotive force can be obtained with excess air ratio around 1 up to relatively low temperatures. Figure 2 shows i-butane
5th in the characteristic diagram measured with this device for 0.1% fuel.
The reason why this product is better than the conventional product shown in the figure is that the oxidation catalyst reduces unbalanced components in the exhaust gas.

As described above, the present invention has a main exhaust gas passage and a bypass passage arranged side by side in the combustion chamber, an oxidation catalyst that is in close contact with the inner wall of the bypass passage pipe, and an oxygen sensor installed in the bypass passage downstream of the oxidation catalyst. By regulating the flow rate of exhaust gas flowing through the passage, changes in the flow of exhaust gas are minimized, and the catalyst saturates the unbalanced hydrocarbons contained in the exhaust gas, keeping the electromotive force of the oxygen sensor constant. It can be done.

[Brief explanation of drawings]

Fig. 1 is a schematic diagram of the main parts of the present invention, Fig. 2 is its measurement diagram, and Fig. 3 is a schematic diagram of the conventional explanatory diagram.
FIG. 4 shows a diagram of excess air ratio and thermal efficiency, and FIG. 5 shows a measurement diagram using a conventional device. 1...Oxidation catalyst, 2, O ₂ ...Oxygen sensor, 3,
D...Combustor, 6...Main exhaust gas passage, 7...Bypass passage, 10, S...Air-fuel ratio control device, A...
...Air, F...Fuel.

Claims (1)

[Scope of utility model registration request] In an air-fuel ratio control device that burns fuel and air in the combustion chamber of a combustor and adjusts combustion conditions by detecting the oxygen concentration in the exhaust gas, a main exhaust gas passage and a bypass passage are installed in parallel in the combustion chamber, and the The other end of the bypass passage is connected to the main exhaust gas passage, an oxidation catalyst is disposed in close contact with the inner wall of the bypass passage pipe, and an oxygen sensor is further disposed downstream of the oxidation catalyst and within the bypass passage. Air-fuel ratio control device.