JPS60213725A - Air-fuel ratio detecting device - Google Patents

Abstract

PURPOSE:To enable easy detection of air fuel ratio, by detecting a value of a ratio between the power spectrum of a band-pass filter within the frequency range of primary natural vibration and the power spectrum of a full frequency range. CONSTITUTION:A titled device comprises a photoelectric sensor 11, which outputs an electric signal responding to a change in a light volume of flame, a first power spectrum detecting means 13 which detects a power spectrum of a part or all of the frequency band width of an output signal from the photoelectric sensor 11, and a second power spectrum detecting means 14 which detects the power spectrum, within the frequency band width of the output signal of the photoelectric sensor 11, of a component having a frequency within the frequency band of natural vibration of a combustion device. This causes a dividing circuit 20 to divide the output values of an integrating circuit 16 and an integrating circuit 19. A relation between the value and an air-fuel ratio A/F of flame enables detection of the air-fuel ratio A/F.

Description

[Detailed description of the invention] The present invention relates to an air-fuel ratio detection device used in a combustion device.

There is a demand for controlling the air-fuel ratio of combustion in order to improve the operating efficiency of boiler combustion and to comply with automobile exhaust gas regulations.

In response to this demand, conventional methods have focused on the change in oxygen amount from excess fuel to excess air in the combustion state, and detected this oxygen amount with an oxygen concentration meter such as a zirconia oxygen concentration meter to detect the air-fuel ratio. The commonly used method is to do so.

However, since this method requires the sensor element to be placed in a harsh atmosphere of combustion, the sensor element frequently fails and has a short lifespan. Furthermore, since a special material is used for the sensor element, it is expensive and cannot be said to be of general use. Furthermore, the responsiveness was not sufficient.

The present invention was made in view of the above circumstances, and it has been discovered that there is a certain relationship between the oscillatory combustion of flame and the air-fuel ratio, and it is an object of the present invention to make it possible to reliably detect the air-fuel ratio using this relationship. The present invention provides an air-fuel ratio detection device that has the following features.

Even if the flame is in a so-called normal combustion state, when viewed locally, the combustion of a flame is in a turbulent state with fluctuations in pressure, speed, etc., and the heat generation rate constantly fluctuates over time. It has the characteristic of being On the other hand, a combustion device necessarily forms a finite space such as a combustion chamber and a flow path for fuel, air, or combustion gas, and these spaces individually and as a whole generate a vibration system such as acoustic vibration or Helmholtz vibration. It has countless natural vibration modes. When the flame is in a state of normal combustion, even if there are fluctuations in the rate of heat generation, combustion occurs regardless of these natural vibrations. However, under certain specific conditions, some process in the combustion reaction connects with the natural vibration and resonates, resulting in automatic oscillations with extremely clear periodicity. This is oscillatory combustion, a phenomenon that has been known for a long time. Once this vibration combustion generates vibrations, it becomes sound energy and not only generates noise, but also causes mechanical or thermal damage to the combustion equipment. Many studies have been conducted on this topic.

Vibratory combustion is broadly classified into Helmholtz vibration and acoustic resonance vibration based on the mechanism of its occurrence. Helmholtz vibration is a natural vibration of gas that occurs when a closed container has holes that are small compared to the size of the container, and its characteristics are that the frequency is low and that the fuel supply system also vibrates. On the other hand, acoustic resonance vibrations are vibrations caused by acoustic natural vibrations of the combustion chamber, and any one mode of these acoustic natural vibrations resonates with fluctuations in heat generation rate due to combustion activity. It is a natural vibration that occurs, and its characteristic is that it has a high frequency.

Research on oscillatory combustion has shown that oscillatory combustion does not always occur, but occurs when the operating conditions of the device fall within a certain range. In order to examine these research results, the present inventor conducted basic experiments and investigated the air-fuel ratio and the occurrence of oscillatory combustion, and found that if the air-fuel ratio deviates significantly from the ideal combustion state, which is 1, the air-rich or fuel-rich It is recognized that this oscillatory combustion clearly occurs under these conditions.

The present invention uses the phenomenon of oscillatory combustion that occurs due to changes in the air-fuel ratio to disclose an air-fuel ratio detection device that is completely different from conventional ones. That is, the present invention constitutes an air-fuel ratio detection device by using the frequency component of self-excited vibration of a flame optical signal generated by oscillatory combustion that occurs in an air-rich or fuel-rich state.

Next, the present invention will be explained in detail based on the data results of basic experiments conducted by the present inventor. Figure 1 shows a block diagram of the basic experiment. Flame 2 burning in combustion chamber 1 is imaged on photoelectric sensor 4 via lens 3 and converted into an electrical signal. After this photoelectric signal is amplified by an amplifier 5, frequency analysis is performed by a spectrum analyzer 6, and the results are data-outed to a recorder 7. The air-fuel ratio can be adjusted by changing the amount of air supplied to the burner.
It can be changed. In this experiment, city gas was used as the fuel, and its pressure was controlled to a constant value by a gas pressure control valve 8. FIGS. 2(a) to 2(f) show an example of the data results of this experiment, data output by a recorder. The horizontal axis is the frequency of the flame optical signal, and the vertical axis corresponds to the log value of the amplitude of this optical signal. A/F
indicates the air-fuel ratio, and Fig. 2 (a) shows A/F = 0.68,
Figure 2 (b) shows A/F=0.83, Figure 2 (C) shows A/F=0.83, and Figure 2 (C) shows A/F=0.83.
F = 0.94, A/F = 1.07 in Fig. 2(d),
Fig. 2(e) shows A/F=1-26, Fig. 2(f) shows A/F=1-26, and Fig. 2(f) shows A/F=1-26.
The data is F=1.42.

From this data result, in Figure 2 (a), approximately 30 H2
.

The natural vibrations of about 60 H2 and about 90 H2 are shown in Fig. 2 (f).
It can be seen that a natural vibration of approximately 30 H2 is generated. That is, it is clear that when the air-fuel ratio deviates from the value of l that is the ideal combustion state, oscillatory combustion occurs and natural vibrations are excited. Since this natural vibration in this experiment has a low frequency, it is presumed to be based on Helmholtz vibration, but from the configuration of the present invention described later, the excited natural vibration is not limited to Helmholtz vibration, but is It may also be resonance vibration (in short, an important experimental result is that oscillatory combustion occurs due to changes in the air-fuel ratio).

Furthermore, Figure 3 shows the ratio of the power spectrum of the 30 H2 bandpass filter, which is the frequency domain of the first-order natural vibration seen in Figures 2 (a) and (f), and the power spectrum of the entire frequency domain. The relationship between α, which is the value of α, and the air-fuel ratio A/F is illustrated. The data are recorded as vertical bars indicating the variation in the experiment. As can be seen from this data, the proportion of frequency components in the natural vibration region increases as the A/F value decreases. α is A/
The excited 1 becomes larger again near p=1.4.
This is thought to be due to the following natural vibration.

As is clear from FIG. 3, if the value of α is detected, the air-fuel ratio can be uniquely detected. FIG. 4 shows an embodiment for calculating the value of α. The original signal of the flame converted into an electric signal by the photoelectric sensor 11 is amplified by the amplifier 12, then the direct current component light of the flame is removed by the bypass filter 13, and then input to the bandpass filter 14 for natural vibration. The pass frequency band of this bandpass filter 14 is adjusted to the frequency region of natural vibration where oscillatory combustion occurs. Here, the natural vibration is not limited to the first order, but may be of any type that is most likely to occur. The output of the pantone filter 14 is rectified by a rectifier circuit 15, converted to direct current by an integrator circuit 16, and then input to a divider circuit 20. In the example of the data in FIG. 3, this input value becomes the power spectrum that is the numerator of α.

On the other hand, the output of the no-pass filter 13 is
is also entered. This filter 17 is not necessarily necessary; for example, as in the example shown in FIG. 3, the power spectrum in the entire frequency range that does not pass through this filter 17 is input to the next stage rectifier circuit 1B. In short, the filter characteristics of the filter 17 are selected so that there is a unique relationship between the air-fuel ratio A/F and the power spectrum ratio α. Note that when a no-pass filter is used as the filter 17, low frequency components are cut, so there is an advantage that the time constant of the integrating circuit 190 can be made small and high-speed response can be achieved.The output of the filter 17 is Similarly, after being rectified by the rectifier circuit 18 and converted to direct current by the integrating circuit 19, it is input to the divider circuit 20.If we look at the data example in Figure 3, the power spectrum where this input value is the division factor of α The division circuit 20 divides the output values of the integration circuits 16 and 19, and outputs the result of the calculation.

In the example of the data in FIG. 3, since the output value of this division corresponds to α, the air-fuel ratio A/F of the flame can be detected from this value. Furthermore, instead of the division circuit 20, a subtraction circuit may be used.

Generally, the natural vibration of oscillatory combustion differs depending on the combustion device. From now on, in order to match the frequency of the natural vibration, the bandpass filter for natural vibration will be a frequency variable one.
Alternatively, it would be even more practical if it could be selected from a plurality of options. There is also a fourth photoelectric sensor.
The sensor is not limited to the one shown in the figure, but it is also possible to use a combination of two photoelectric sensors 21, 22 and a differential amplifier 23 as shown in FIG. By using this differential configuration, the air-fuel ratio can be detected without being affected by disturbance light.

As described above, according to the present invention, the air-fuel ratio can be detected in a non-contact manner, resulting in higher stability and longer life than when using a contact type sensor such as a zirconia oxygen concentration meter. Additionally, since the vibrations of the flame are detected optically, the response is fast.

[Brief explanation of drawings]

Figure 1 is a block configuration diagram of the basic experimental equipment for the present invention, and Figure 2 is a graph showing the relationship between the log value of the amplitude of the optical signal and A/F obtained in experiments using the equipment shown in Figure 1. , FIG. 3 is a graph showing the relationship between α and the air-fuel ratio, FIG. 4 is a pull diagram showing the configuration of an air-fuel ratio detection device according to one embodiment of the present invention, and FIG. 5 is a graph showing another embodiment of the present invention. FIG. 3 is a prolag diagram showing a portion of an example. 11... Photoelectric sensor, 12... Amplifier, 13...
Bypass filter, 14...Band pass filter, 1
5... Rectifier circuit, 16... Integrating circuit, 17... Filter, 18... Rectifying circuit, 19... Integrating circuit, 2
0...Division circuit, 21.22...Photoelectric sensor, 23
...Differential amplifier. OH2f200H2 2 times OH2f200H2 el

Claims (1)

[Claims] a photoelectric sensor that outputs an electrical signal corresponding to a change in the amount of light of a flame; a first power spectrum detection means that detects a power spectrum of part or all of the frequency band of the output signal of the photoelectric sensor; and the photoelectric sensor. a second power spectrum detection means for detecting a power spectrum of a component having a frequency within the frequency band of the natural vibration of the combustion device among the frequency band width of the output signal of the output signal; and the first and second power spectrum detection means. An air-fuel ratio detection device comprising calculation means for calculating a ratio or a difference between outputs of the means.