JPH0642742A - Method for sensing misfire of burner - Google Patents

Abstract

PURPOSE:To enable a misfire of a burner to be detected rapidly and accurately by a method wherein a variation rate of decreasing in burner temperature and its temperature after a fuel valve is opened. CONSTITUTION:It is defected by a temperature sensing block 2 if a burner temperature is less than a predetermined value. AND gate 4 is not opened unless a time elapses more than a specified period of time by an on-delay timer 3B so as to make a misfire sensing signal null. In addition, an output of an on-delay timer 3A and another output of AND gate 4 are given to an OR gate 5. Accordingly, when the variation rate of decreasing of burner temperature is continued for more than a predetermined time in its state more than a specified value, or after a specified time (t1) elapses after a fuel valve is opened and the burner temperature is decreased to a value less than its predetermined value, it is judged that this is a misfire state. With such an arrangement, it is possible to prevent any erroneous operation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to the case where the burner misfire cannot be directly monitored by visual observation or the like, and the burner temperature is measured by a temperature detector and the change amount thereof is monitored to check the state of misfire. The present invention relates to a detection method for indirectly detecting.

[0002]

2. Description of the Related Art The main flame monitoring techniques adopted to identify the combustion state of a burner are those that monitor the temperature in the vicinity of the flame, those that use a flame rod, and the flame or burner of the burner. There is one that optically monitors the existing combustion chamber.

As an example of temperature-based misfire monitoring, a metal body is provided so as to surround the burner crater, and when the temperature of the metal body falls below a predetermined value, it is judged as misfire (hereinafter referred to as "the "1. Prior art").
It is disclosed in Japanese Patent No. 17713.

The one using a frame rod utilizes the fact that a large number of ions are generated at the place where the flame is generated. Therefore, an electrode is inserted into the flame and a voltage is applied between the electrode and the burner. The presence or absence of flame is determined by the presence or absence of current flowing between the electrode and burner.

As an application of this flame rod, an anode and a cathode are installed in the flame, and the range of the current value for maintaining the stable combustion state of the burner against the change of the combustion amount or the air ratio is set in advance. When the current value between the electrodes is within the above range, "flame is present." When the current value exceeds the above range, or when the current value is below the above range and is not zero, "device abnormality" Japanese Patent Laid-Open No. 1-318808 discloses a burner flame monitoring technique (hereinafter, referred to as "second conventional technique") that determines that "no flame" occurs when the current value becomes zero.

As an example of optical monitoring, radiant light from a flame is introduced into an optical fiber through a lens, transmitted to a monitoring device by the optical fiber, and photoelectrically converted, and a direct current component of the photoelectric conversion output is blocked. Japanese Patent Laid-Open No. 61-205725 discloses a method of amplifying an AC component, detecting and rectifying it, and comparing the detected and rectified output with a reference value to detect the presence or absence of a flame (hereinafter referred to as "third prior art"). Is disclosed in.

[0007]

In the above-mentioned first prior art, there is a problem that it takes a long time to detect a misfire because it is necessary to wait until the temperature reaches a predetermined value. Further, if the predetermined value is set to a high level in order to shorten the time until the detection of misfire, the possibility of misjudging a misfire increases even though the flame has not disappeared.

In the second prior art, since it is determined that no flame is present (including misfire) when the detected current value is zero, it is extremely important to correct the zero point drift of the ammeter (zero point adjustment). Is exposed to a flame, the oxidative deterioration of the electrode material is likely to proceed, and along with this, the zero point drift is likely to occur, and it is necessary to frequently adjust the zero point. Even if the judgment level without flame is set to a non-zero finite value, the above situation does not change.

In the third prior art in which the radiant light from the flame is condensed by the lens, the lens (if an optical window for protecting the lens is provided separately, that optical window)
If soot adheres to the part facing the flame, the amount of light that can be coupled to the optical fiber changes, and it is difficult to make an accurate misfire determination unless the reference value for the misfire determination is set properly each time.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to make it possible to detect burner misfire quickly and accurately.

[0011]

In order to solve such a problem, according to the present invention, the burner temperature is measured by a temperature detector, and the burner temperature and its change amount are monitored to detect the misfire state of the burner. When the rate of decrease in the burner temperature exceeds a predetermined value for a predetermined time or more, or when the temperature falls below a predetermined value after a predetermined time has elapsed from the time when the fuel valve was opened, the burner The feature is that it is detected as a misfire.

Further, according to the present invention, when the burner temperature temporarily rises, the burner misfire detection based on the burner temperature drop change rate monitoring is temporarily blocked for a certain period of time. By doing so, it is possible to prevent malfunction, and further, when the fuel flow rate decreases, for a certain period of time, while temporarily preventing the misfire detection of the burner based on the decrease rate of change of the burner temperature, It is possible to prevent malfunction by changing the monitoring time of the rate of change of decrease in the burner temperature according to the fuel flow rate and performing monitoring.

[0013]

By monitoring the temperature of the burner and its rate of temperature change, misfire of the burner can be detected quickly and accurately. Further, when the temperature temporarily rises or when the fuel flow rate as the burner load decreases, the misfire detection is disabled for a certain period of time respectively, so that malfunctions due to flame fluctuations or burner load fluctuations can be prevented. To do so.

[0014]

1 is a block diagram showing an embodiment of the present invention, 1 is a temperature change rate detecting block, 2 is a temperature detecting block, 3A and 3B are on-delay timers, 4 is an AND gate, and 5 is an OR gate. . In the temperature change characteristic of the burner tip as shown in FIG. 2, when the temperature decrease starts due to misfire, not only the temperature decrease change rate dT / dt becomes equal to or lower than a certain value (L _T ) but also that state remains for a certain time. (T
2) Since it is considered that the above operation will continue, this is detected by the temperature change rate detection block 1 and the on-delay timer 3A. Further, the temperature detection block 2 detects whether or not the burner temperature has become equal to or lower than a predetermined value ( _TL ). At this time, it becomes the predetermined value _TL from the time point (t = 0) when a fuel valve (not shown) is opened. It takes a certain period of time t1 as shown in FIG. 2 to reach it, so during this period, the misfire detection signal is blocked (blocked) so as not to be output.

That is, when the temperature detection block 2 detects whether or not the burner temperature has become equal to or lower than the predetermined value T _L , the on-delay timer 3B sets a constant time t.
If one or more has not elapsed, the AND gate 4 is prevented from opening and the misfire detection signal is invalidated. Also,
Since the output of the on-delay timer 3A and the output of the AND gate 4 are given to the OR gate 5, the state in which the rate of change of the burner temperature decrease is equal to or higher than a predetermined value continues for a predetermined time or a state in which the fuel valve is opened. When the burner temperature falls below a predetermined value after a lapse of a certain time t1 from, it is determined that the misfire state. Although the temperature change rate detection block, the temperature detection block, and the like are shown here as hardware, they are actually handled by software processing.

FIG. 3 is a block diagram showing a modification of the present invention. This is to change the dotted line portion of FIG. 1 as shown, and in addition to the temperature change rate detection block 1, the temperature change rate detection block 1A, the off delay timer 6, the negative gate (inverter) 7 and the AND gate 4A. It is configured by adding. That is, in the temperature change characteristic of the burner tip as shown in FIG. 4, the burner temperature may temporarily rise due to fluctuations of the flame and then drop after a certain time. Therefore, during this period, the misfire detection signal is blocked so as not to be output. It is a thing. Therefore, here, when the temperature change rate detection block 1A detects that the temperature rise change rate is equal to or higher than H _T , the off-delay timer 6 outputs an output for a fixed time, and the output is blocked by the negative gate 7. Therefore, the malfunction is prevented.

FIG. 5 is a block diagram showing still another modification of the present invention. This is also to change the dotted line portion of FIG. 1 as shown, and in addition to the temperature change rate detection block 1, an off-delay timer 6A, a negative gate 7A, a fuel change rate detection block 8 and a function generator 9 including a ROM. Etc. are added and configured. This is because in the temperature change characteristics of the burner tip as shown in FIG. 6, the temperature starts to drop when the fuel (fuel flow rate) decreases, but the decrease in temperature is constant due to the delay time factor of the plant even if the decrease in fuel stops. Time t
No. 4 focuses on continuing. Therefore, when the fuel change rate detection block 8 detects that the fuel change rate has become less than or equal to L _F and is turned off, an output is output for t4 hours via the off-delay timer 6A, and the output is output by the negative gate 7A. The output from the temperature change rate detection block 1 is invalidated by reversing and preventing the AND gate 4B from opening.

The temperature change at the tip of the burner differs depending on whether the amount of fuel used is large or small, and the temperature decrease rate after misfire is ΔT1 / Δt, ΔT2 / Δ as shown in FIG.
Since t becomes (ΔT1 / Δt> ΔT2 / Δt),
Unless the monitoring time Δt of the temperature decrease rate is made variable depending on the size of the fuel, reliable misfire detection cannot be performed. Therefore, as shown in FIG. 5, the function generator 9 is provided, and the differential time dt (Δt) of the temperature is obtained from the flow rate signal F of the fuel,
This is applied to the temperature change rate detection block 1. Therefore, the temperature change rate detection block 1 monitors the temperature decrease rate with a large dt when the flow rate signal F is large and with a small dt when the flow rate signal F is small.

[0019]

According to the present invention, the misfire is detected by monitoring the burner temperature and the rate of change thereof, so that there is an advantage that a quick and accurate detection can be performed. Also, because the burner temperature may temporarily rise due to temporary factors such as flame fluctuations and then drop after a certain period of time, the misfire detection signal may not be output during this period, or the fuel may be reduced. In this case, the detection operation to detect misfire from the burner temperature change rate is blocked and the temperature change rate monitoring time is changed according to the fuel flow rate until a predetermined time elapses after the fuel change rate falls below a certain value. By monitoring the rate of change of the burner temperature, it is possible to prevent malfunction.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of the present invention.

FIG. 2 is an explanatory diagram for explaining the operation of FIG.

FIG. 3 is a block diagram showing a modified example of the present invention.

FIG. 4 is an explanatory diagram for explaining the operation of FIG.

FIG. 5 is a block diagram showing another modification of the present invention.

FIG. 6 is an explanatory diagram for explaining the operation of FIG. 5 when the fuel is reduced.

FIG. 7 is an explanatory diagram for explaining the operation of FIG. 5 when the fuel flow rate is different.

[Explanation of symbols]

1, 1A ... Temperature change rate detection block, 2 ... Temperature detection block, 3A, 3B ... On-delay timer, 4, 4A, 4
B ... AND gate, 5 ... OR gate, B ... Off delay timer, 7, 7A ... Negative gate, 8 ... Flow rate change rate detection block, 9 ... Function generator.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Hideki Yoshioka Inventor Hideki Yoshioka 1-1, Tanabe Nitta, Kawasaki-ku, Kawasaki-shi, Kanagawa Fuji Electric Co., Ltd.

Claims (3)

[Claims] 1. A burner temperature is measured by a temperature detector,
In order to detect the misfire state of the burner by monitoring the burner temperature and its change amount, when the state in which the rate of change in the decrease of the burner temperature becomes a predetermined value or more continues for a predetermined time or more, or the fuel valve is opened. A burner misfire detection method, wherein when the temperature falls below a predetermined value after a lapse of a predetermined time from the time point, it is detected as a burner misfire. 2. A malfunction is prevented by temporarily preventing misfire detection of the burner based on the rate of change in the decrease rate of the burner temperature for a certain period of time after the burner temperature temporarily rises. The misfire detection method for a burner according to claim 1, wherein: 3. When the fuel flow rate decreases, a burner misfire detection based on monitoring the rate of change of the burner temperature decrease is temporarily blocked for a certain period of time, and the burner temperature decrease changes in accordance with the fuel flow rate. The misfire detection method for a burner according to claim 1, wherein malfunction is prevented by changing and monitoring the rate monitoring time.