JPH0331969B2 - - Google Patents

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, this method requires the sensor element to be placed in the harsh atmosphere of combustion.
Sensor elements often fail and have 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, a flow path for fuel air, or combustion gas, and these spaces individually and as a whole create a vibration system such as acoustic vibration or Helmholtz vibration. It has countless natural vibration modes, and under normal flame combustion, even if the heat generation rate fluctuates, combustion will occur regardless of these natural vibrations. It is being said.
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 not only converts into sound energy and generates noise, but also sometimes causes mechanical or thermal damage to the combustion equipment. In recent years, a lot of research has been done on the mechanism behind this combustion. This is something that is being researched.

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 vibration is a vibration caused by the acoustic natural vibration of the combustion chamber, and occurs when one mode of this acoustic natural vibration resonates with fluctuations in the heat generation rate due to combustion. It is a natural vibration that has a high frequency, and is characterized by its 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 consider these research results,
The inventor conducted basic experiments and investigated the air-fuel ratio and the occurrence of oscillatory combustion, and found that this oscillatory combustion clearly occurs in air-rich or fuel-rich conditions where the air-fuel ratio deviates greatly from the ideal combustion state of 1. This is something that has been acknowledged to occur.
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 constructs 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 guided to photoelectric conversion means 4 via lens 3 and converted into an electrical signal. This photoelectric conversion means 4 is composed of a pair of photoelectric sensors 21 and 22 and a differential amplifier 23, as shown in FIG. After this photoelectric signal is amplified by an amplifier 5, frequency analysis is performed by a spectrum analyzer 6, and the results are outputted as data to a recorder 7. The air-fuel ratio can be changed by changing the amount of air supplied near the burner. In addition,
In this experiment, municipal gas was used for combustion, and its pressure was controlled to a constant value by a gas pressure control valve 8. FIGS. 2a to 2f show an example of the data results of this experiment dataed out 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, the second
Figure b is A/F = 0.83, Figure 2 c is A/F = 0.94,
Figure 2 d shows A/F = 1.07, Figure 2 e shows A/F =
1.26, Fig. 2 f is the data of A/F = 1.42.

From this data result, in Figure 2a, approximately 30Hz,
The natural vibrations of approximately 60Hz and 90Hz are approximately 30Hz in Fig. 2 f.
It can be seen that natural vibrations of Hz occur. That is, it is clear that when the air-fuel ratio deviates from the value of 1, which 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 an acoustic resonance vibration. An important experimental result is that oscillatory combustion occurs due to changes in the air-fuel ratio.

Furthermore, Figure 3 shows the power spectrum of the bandpass filter at 30Hz, which is the frequency domain of the first-order natural vibration seen in Figures 2a and f, and α, which is the ratio of the power spectrum of the entire frequency domain. , illustrates the relationship with the air-fuel ratio A/F. 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. The reason why α becomes large again near A/F=1.4 is considered to be due to the excited first-order 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 determining the value of α. The flame optical signal converted into an electric signal by the photoelectric sensor 11 is amplified by the amplifier 12, and then the DC component light of the flame is removed by the high-pass filter 13, and then input to the natural vibration band-pass filter 14. The pass frequency band of this bandpass filter 14 is matched to the frequency band of natural vibration in which 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 bandpass filter 14 is rectified by a rectifier circuit 15, converted to direct current by an integrator circuit 16, and then converted to a direct current by a divider circuit 15.
Enter 0. 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 high-pass filter 13 is also input to the filter 17. This filter 17 is not necessarily necessary; for example, as in the example shown in FIG. 3, the power spectrum of the entire frequency range that does not pass through this filter 17 is input to the rectifier circuit 18 at the next stage. In short, air fuel ratio A/
The filter characteristics of the filter 17 are selected so that there is a unique relationship between F and the power spectrum ratio α. Note that when a high-pass filter is used as the filter 17, it cuts out low frequency components, so there is an advantage that the time constant of the integrating circuit 19 can be made small and high-speed response can be realized. The output of the filter 17 is similarly rectified by a rectifier circuit 18 and converted to direct current by an integrating circuit 19.
It is input to the division circuit 20. In the example of the data in FIG. 3, this input value is the power spectrum that is the denominator of α. The division circuit 20 is the integration circuit 16
The output value of the integrating circuit 19 is divided and the result of the calculation is output. 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. In addition, the division circuit 20
Instead, a subtraction circuit can also be used.

Generally, the natural vibration of oscillatory combustion differs depending on the combustion device. It will become more practical if the natural vibration hand-pass filter is made to have a variable frequency or one that can be selected from a plurality of filters in order to match the frequency of the natural vibration. As described above, according to the present invention, the electric signal corresponding to the change in the amount of flame output from the photoelectric conversion means is inputted to the first and second power spectrum detection means, and each output of the power spectrum detection means is inputted to the first and second power spectrum detection means. Since the structure is configured to calculate the ratio or difference between the two, there is no need to analyze the flame light, there is no need for a diffraction grating, etc., and a highly reliable air-fuel ratio detection device can be obtained with a simple and inexpensive structure. .

Furthermore, if the photoelectric sensor that converts the optical signal of the flame into an electrical signal becomes dirty, the output of the photoelectric sensor will be multiplied by k times (k<1) due to this dirt;
Since the ratio or difference between the outputs of the power spectrum detection means is calculated, k cancels each other out during this calculation, and dirt on the photoelectric sensor does not affect the calculation result.

Further, since it has a differential configuration in which the output signals of the pair of photoelectric sensors are input to the differential amplifier 23, the effects of ambient light also cancel each other out.

As a result, there is an effect that the air-fuel ratio can be detected with high accuracy.

[Brief explanation of drawings]

Figure 1 is a block 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 block diagram showing the configuration of an air-fuel ratio detection device according to one embodiment of the present invention, and FIG. FIG. 3 is a block diagram showing a part of the system. 11...Photoelectric sensor, 12...Amplifier, 13...
...High pass filter, 14...Band pass filter, 15...Rectifier circuit, 16...Integrator circuit, 17
... Filter, 18 ... Rectifier circuit, 19 ... Integrating circuit, 20 ... Divide circuit, 21, 22 ... Photoelectric sensor, 23 ... Differential amplifier.

Claims (1)

[Claims] 1. A photoelectric conversion means that has a pair of photoelectric sensors and a differential amplifier that inputs the output of the photoelectric sensor and outputs an electric signal corresponding to a change in the amount of light of a flame, and a frequency bandwidth of the output signal of the photoelectric conversion means. and 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 photoelectric sensor. An air-fuel ratio detecting device comprising: second power spectrum detecting means for detecting the power spectrum; and calculating means for detecting the air-fuel ratio by calculating the ratio or difference between the respective outputs of the first and second power spectrum detecting means.