JP2024051907A - Combustion equipment - Google Patents

Abstract

[Problem] When a burner in a combustion device misfires, abnormal ignition is suppressed and re-ignition of the burner is controlled. [Solution] A burner 12 is stored inside a housing 11 provided with an exhaust port 11a. A blower fan 17 supplies air to the burner 12. An igniter 18 ignites a mixture of gaseous fuel and air supplied to the burner 12. If misfire is detected based on the output of a flame rod 19 after the burner 12 has been ignited, re-ignition control of the burner 12 is executed. In the re-ignition control, when a misfire is detected, it is determined whether or not the inside of the housing 11 is in a state in which abnormal ignition is predicted to occur, and different conditions are selected based on the result of the determination to execute an ignition retry. [Selected Figure] Figure 1

Description

The present invention relates to a combustion device, and more specifically to reignition control in the event of a misfire.

In a heat source machine that circulates and heats a heat medium to be supplied to a heating terminal by burning fuel in a burner, when a burner misfire is detected, ignition retries to reignite the burner are repeatedly performed, as described in Patent Publication 3841737 (Patent Document 1).

Patent document 1 describes that a low-temperature ignition retry mode or a high-temperature ignition retry mode is selected depending on whether the heat medium is supplied to a high-temperature heating terminal or a low-temperature heating terminal.

Patent No. 3841737

When a water heater, which is an example of a combustion device, is installed and the surrounding exterior walls are painted, the water heater may be covered with a shield such as vinyl to prevent paint from adhering, temporarily making the combustion device housing airtight. If the burner is ignited under such conditions, ventilation may be insufficient, resulting in a lack of oxygen concentration, which may prevent the burner from continuing to burn and cause an accident.

In this case, if ignition retry control is repeatedly executed, there is a risk that the gas concentration inside the housing will increase due to unburned gas released during the ignition operation or misfire. As a result, if abnormal ignition occurs when the gas concentration is higher than a certain concentration, there is a concern that it may lead to combustion, causing the inside of the housing to reach an excessively high temperature.

The present invention was made to solve these problems, and the purpose of the present invention is to suppress abnormal ignition and control the re-ignition of the burner when the burner of a combustion device misfires.

In one aspect of the present invention, the fuel device includes a housing provided with an exhaust port, a burner housed in the housing, a gas supply valve, a blower fan, an ignition device, a flame rod for detecting the flame of the burner, and a control unit. The gas supply valve is provided to supply gaseous fuel to the burner. The blower fan is configured to supply air to the burner. The ignition device is configured to ignite the mixture of gaseous fuel and air supplied to the burner. The control unit executes reignition control of the burner when a misfire is detected based on the output of the flame rod after the burner is ignited. When a misfire is detected, the control unit controls the gas supply valve, the blower fan, and the ignition device to determine whether or not the inside of the housing is in a state in which abnormal ignition is predicted, and to select a first condition for reignition control and execute an ignition retry if it is determined that the state is in which abnormal ignition is predicted, and to select a second condition for reignition control and execute an ignition retry if it is determined that the state is not in which abnormal ignition is predicted.

According to the present invention, when a burner misfires in a combustion device, the conditions for re-ignition control are switched based on the result of determining whether the state inside the housing is such that abnormal ignition is predicted to occur, thereby making it possible to suppress abnormal ignition and control the re-ignition of the burner.

1 is a schematic diagram illustrating a configuration of a water heater 100, which is an example of equipment equipped with a combustion device according to the present embodiment. 1 is a block diagram illustrating a schematic configuration of a combustion device according to an embodiment of the present invention. 4 is a flowchart illustrating re-ignition control by the combustion device according to the present embodiment. 4 is a table for comparing abnormal ignition suppression conditions and normal conditions in the reignition control shown in FIG. 3 . 6 is a graph showing a simulation result of gas concentration inside a housing during re-ignition control in the combustion device according to the present embodiment. FIG. 2 is a block diagram illustrating a gas concentration estimation model.

The following describes in detail an embodiment of the present invention with reference to the drawings. Note that in the following, the same or corresponding parts in the drawings are given the same reference numerals, and in principle, their description will not be repeated.

Figure 1 is a schematic diagram illustrating the configuration of a water heater 100, which is an example of equipment mounted on a combustion device according to this embodiment.

As shown in FIG. 1, the water heater 100 has a combustion device 10, a heat exchanger 30, a water inlet pipe 40, a water outlet pipe 50, and a bypass pipe 60.

The combustion device 10 includes a burner 12, a capacity switching valve 16, an igniter 18, and a frame rod 19, all of which are housed in a housing 11. The combustion device 10 further includes a gas supply pipe 13, a main gas valve 14, a proportional valve 15, and a controller 20 (see FIG. 2). In the following description, it is assumed that there are multiple burners 12 arranged in the housing 11, but there may be only one burner 12. In addition, a blower fan 17 that supplies air to the burner 12 is attached to the lower side of the housing 11, and an exhaust port 11a is provided on the upper side. The heat exchanger 30 is housed in the housing 11 and is arranged above the burner 12.

Fuel gas, which is a representative example of "gaseous fuel", is supplied to the gas supply pipe 13 via a gas supply port 13a. A main gas valve 14, a proportional valve 15, and a capacity switching valve 16 are arranged on the path of the gas supply pipe 13. The main gas valve 14 is arranged upstream of the proportional valve 15 on the path of the gas supply pipe 13. The capacity switching valve 16 is arranged downstream of the proportional valve 15 on the path of the gas supply pipe 13. A plurality of burners 12 are connected to the gas supply pipe 13 downstream of the capacity switching valve 16. The main gas valve 14, the proportional valve 15, and the capacity switching valve 16 correspond to one embodiment of a "gas supply valve".

The main gas valve 14 is, for example, a solenoid valve. The supply and stop of fuel gas to the gas supply pipe 13 is switched by opening and closing the main gas valve 14. The proportional valve 15 is, for example, a proportional solenoid valve. The flow rate of fuel gas flowing through the gas supply pipe 13 is adjusted by adjusting the opening degree of the proportional valve 15. In other words, the amount of fuel gas supplied to the burner 12 can be adjusted by the proportional valve 15.

The capacity switching valve 16 is made up of multiple valves. In the example of FIG. 1, the capacity switching valve 16 is made up of valves 16a to 16c. Each of the valves 16a to 16c is, for example, a solenoid valve. The capacity switching valve 16 makes it possible to supply fuel gas to only some of the multiple burners 12.

More specifically, by opening valve 16a, it is possible to supply fuel gas to only some of the burners 12 (the three burners 12 located first to third from the right in FIG. 1). Also, by opening valve 16b, it is possible to supply fuel gas to only some of the burners 12 (the two burners 12 located fourth and fifth from the right in FIG. 1). Furthermore, by opening valves 16a and 16b, it is possible to supply fuel gas to only the five burners 12 located first to fifth from the right in FIG. 1. By opening all of valves 16a to 16c, it is possible to supply fuel gas to all of the burners 12.

The fuel gas supplied to the burner 12 from the gas supply pipe 13 is ejected from an outlet (not shown) provided on the burner 12. The blower fan 17 attached to the lower part of the housing 11 takes in air from outside the housing 11 and supplies it to the burner 12. The air supplied by the blower fan 17 is mixed with fuel gas (gaseous fuel) inside the burner 12 (hereinafter, the fuel gas mixed with air is also referred to as "mixed gas"). The amount of air supplied is increased by increasing the rotation speed of the blower fan 17. Note that when fuel gas is not supplied to the burner 12, the blower fan 17 can be operated to perform scavenging, which discharges unburned mixed gas and exhaust gas using air introduced into the housing 11 through the burner 12.

The igniter 18 is disposed near the burner 12. When a voltage is applied to the igniter 18, a spark is generated in the igniter 18. This spark ignites the mixed gas, causing a flame to be generated from the burner 12.

In the burner 12, a flame is generated and a mixture of gaseous fuel and air is burned to generate high-temperature combustion gas. The combustion gas rises inside the housing 11, exchanges heat in the heat exchanger 30, and is then discharged from the exhaust port 11a. The heat exchanger 30 has, for example, a primary heat exchanger 31 and a secondary heat exchanger 32.

The flame rod 19 is disposed near the burner 12. More specifically, the tip of the flame rod 19 is disposed in the flame generated from the burner 12. When the flame rod 19 comes into contact with the flame generated from the burner 12, a current flows through the flame rod 19. Therefore, the presence or absence of a flame in the burner 12 can be detected by the flame rod 19.

The frame rod 19 is formed, for example, from a conductive metal material. The metal material that constitutes the frame rod 19 contains an element that forms an insulating oxide when oxidized. This element is, for example, aluminum (Al) or silicon (Si).

As shown in FIG. 1, one end of the water inlet pipe 40 is connected to the water supply. The other end of the water inlet pipe 40 is connected to the inlet of the secondary heat exchanger 32. The outlet of the secondary heat exchanger 32 is connected to the inlet of the primary heat exchanger 31. One end of the hot water outlet pipe 50 is connected to the outlet of the primary heat exchanger 31. The other end of the hot water outlet pipe 50 is connected to, for example, a hot water tap 70. The bypass pipe 60 is connected to the water inlet pipe 40 at one end and to the hot water outlet pipe 50 at the other end.

The operation of the water heater 100 will be described below. Water is supplied from one end of the water inlet pipe 40. A portion of the water supplied to the water inlet pipe 40 is supplied to the bypass pipe 60. The remainder of the water supplied to the water inlet pipe 40 is supplied to the secondary heat exchanger 32. The water supplied to the secondary heat exchanger 32 is heated by heat exchange with the latent heat of the combustion gas generated in the combustion device 10 (burner 12).

The water that has passed through the secondary heat exchanger 32 is supplied to the primary heat exchanger 31. The water supplied to the primary heat exchanger 31 is further heated by heat exchange with the sensible heat of the combustion gas generated in the combustion device 10 (burner 12). The water that has passed through the primary heat exchanger 31 is supplied to the hot water outlet pipe 50.

The water that passes through the primary heat exchanger 31 and is supplied to the hot water outlet pipe 50 is mixed with water supplied to the hot water outlet pipe 50 from the bypass pipe 60, and the temperature is adjusted. This temperature-adjusted water is supplied, for example, from the hot water tap 70. In addition, a flow rate adjustment valve (not shown) may be further provided to control the flow rate ratio supplied from the water inlet pipe 40 to the bypass pipe 60.

Figure 2 is a block diagram of the combustion device 10. As shown in Figure 2, the controller 20 has a CPU (Central Processing Unit) 21, an input/output interface 22, a timer 23, and a memory unit 24. The timer 23 and the memory unit 24 are connected to the CPU 21. The controller 20 is configured, for example, by a microcomputer.

The controller 20 is connected to the main gas valve 14, the proportional valve 15, the capacity switching valve 16 (valves 16a to 16c), the blower fan 17, the igniter 18, and the frame rod 19 via the input/output interface 22. Although not shown, the controller 20 accepts user operations input to the remote control 110 via the input/output interface 22. For example, user operations include turning on and off the operation switch of the water heater 100, setting the target hot water outlet temperature, etc.

The CPU 21 can supply fuel gas to the burner 12 by generating control commands for the main gas valve 14, the proportional valve 15, and the capacity switching valve 16 via the input/output interface 22 so that the main gas valve 14, the proportional valve 15, and the capacity switching valve 16 are in an open state.

At this time, the number of burners (the number of combustion burners) to which fuel gas is supplied among the multiple burners 12 can be adjusted by controlling the capacity switching valve 16. For example, as described above, when only valve 16b is open, the number of combustion burners is two, when valves 16a and 16b are open, the number of combustion burners is five, and when all valves 16a to 16c are open, the number of combustion burners is ten.

The CPU 21 also generates a control command for the blower fan 17 via the input/output interface 22 to supply air into the housing 11. In particular, the amount of air supplied into the housing 11 through the burner 12 is controlled by the rotation speed command value for the blower fan 17.

Furthermore, the CPU 21 controls the igniter 18 to operate (spark) via the input/output interface 22 at an appropriate timing. This ignites the mixed gas in the burner 12 to which the fuel gas is supplied, and a flame is generated in the burner 12. Furthermore, the CPU 21 can detect the presence or absence of a flame in the burner 12 based on the output from the flame rod 19. This allows the CPU 21 to detect the ignition of the burner 12 after ignition, and the loss of flame after ignition.

Figure 3 shows a flowchart explaining the re-ignition control by the combustion device according to this embodiment. The control process shown in Figure 3 is started when the CPU 21 loads a program previously stored in the memory unit 24, for example, and an ignition process is requested of the combustion device 10 according to the operating state of the water heater 100. For example, when the hot water tap 70 is opened with the operation switch of the water heater 100 turned on and the flow rate of the water inlet pipe 40 rises above a predetermined minimum operating flow rate (MOQ), the control process of Figure 3 is started.

Referring to FIG. 3, the CPU 21 executes ignition processing in step (hereinafter also simply referred to as "S") 110. Specifically, the main gas valve 14 is opened, the proportional valve 15 is opened to a predetermined opening according to a predetermined ignition pattern, and a portion of the capacity switching valve 16 is opened so that combustion gas is supplied to X burners 12 (X: natural number), and then a voltage is applied to the igniter 18, thereby executing the ignition processing in S110. As a result, in S120, the X burners 12 are in a combustion state.

After the ignition process, the CPU 12 determines in S130 whether a misfire has occurred due to the output of the flame rod 19. If no misfire is detected (NO in S130), the combustion state (S120) continues. While the combustion state continues, in order to control the temperature of the hot water outlet from the outlet pipe 50 to the target hot water outlet temperature, the amount of heat generated by the entire burner 12, i.e., the flow rate of the fuel gas, is controlled by adjusting the opening of the proportional valve 15 and the number of combustion burners using the capacity switching valve 16.

During combustion (S120), if the flow rate of the water inlet pipe 40 falls below the MOQ in response to the closing of the hot water tap (not shown), or if the operation switch of the water heater 100 is turned off and a request is made to the combustion device 10 to extinguish the fire, the control process of FIG. 3 is terminated by an interrupt process.

If a misfire is detected after combustion (YES in S130), re-ignition control is executed from S140 onwards.

In S140, the CPU 121 determines whether the state inside the housing 11 at the time of misfire is such that abnormal ignition is expected to occur. As described above, abnormal ignition occurs when the burner 12 ignites in a state in which the airtightness of the housing 11 is increased and the gas concentration is higher than a certain concentration determined by the gas type, the specifications of the burner 12 (ignitable range, etc.), and the shape of the housing 11.

The inventors have found that the time elapsed from ignition to misfire can be used to determine whether or not an abnormal ignition is likely to occur, rather than the direct gas concentration. Specifically, they have found that when the water heater 100 is covered with a shield such as vinyl, making the housing 11 more airtight than expected at the time of design, the time elapsed from ignition to misfire detection is significantly shorter. Therefore, in S140, the above-mentioned determination can be made based on whether or not the time elapsed from when the burner flame is detected by the ignition process (S110) to when a misfire is detected is shorter than a predetermined determination time (e.g., about 10 seconds).

The above-mentioned elapsed time varies depending on the design (shape and airtightness) of the housing 11 and the specifications of the burner 12, so the judgment time in S140 can be determined, for example, based on the results of actual experiments for each model of water heater 100 (combustion device 10).

When the CPU 21 judges NO at S140, it executes re-ignition control under normal re-ignition conditions (hereinafter referred to as "normal conditions") through S150 to S162, whereas when the CPU 21 judges YES at S140, it executes re-ignition control under re-ignition conditions for suppressing abnormal ignition (hereinafter referred to as "abnormal ignition suppression conditions"). The abnormal ignition suppression conditions correspond to the "first condition" of the re-ignition control, and the normal conditions correspond to the "second condition" of the re-ignition control.

First, the normal condition will be described. In response to a NO judgment in S140, the CPU 21 closes the main gas valve 14 in S150 after Tn1 [s] has elapsed since the detection of a misfire (YES judgment in S130), and then in S152 operates the blower fan 17 at a predetermined scavenging rotation speed for a predetermined scavenging time Tn2 [s]. For example, the scavenging rotation speed is set to be higher than the rotation speed that is typically used when fuel is burned in the burner 12.

That is, Tn1 [s] in S150 corresponds to the duration of fuel gas supply after misfire detection under normal conditions, and Tn2 [s] in S152 corresponds to the scavenging time until the first ignition retry when misfire is detected under normal conditions.

Furthermore, after scavenging in S152 is completed, the CPU 21 executes an ignition retry in S154. In S154 under normal conditions, the main gas valve 14 is opened and a voltage is applied to the igniter 18 while the capacity switching valve 16 is controlled so that the number of combustion burners is Xn. With the main gas valve 14 open, the state in which the igniter 18 generates sparks due to the application of voltage continues for Tn3 [s]. In other words, Tn3 [s] corresponds to the fuel gas supply time associated with the operation of the igniter 18 during an ignition retry under normal conditions.

After the ignition retry (Tn3 [s]) in S154, the CPU 21 determines in S156 whether the output of the flame rod 19 indicates a non-ignition or ignition state. If the flame rod 19 continues to detect a flame for a certain period of time, S156 returns NO, assuming that ignition has occurred. In this case, the supply of fuel gas by the main gas valve 14 continues, and the process returns to S120 (combustion state) described above.

On the other hand, if no flame is detected by the flame rod 19, it is determined that no ignition has occurred and S156 returns YES. In this case, the CPU 21 closes the main gas valve 14 to cut off the supply of fuel gas, and proceeds to S158, where it operates the blower fan 17 at a scavenging rotation speed for a predetermined scavenging time Tn4 [s].

After scavenging is completed by S158, the CPU 21 determines in S170 whether the number of retries for re-ignition under normal conditions is equal to or greater than a predetermined upper limit number Nn. If the number of retries is less than Nn (NO in S160), the process returns to S154, and ignition retry is performed under normal conditions. In other words, the scavenging time Tn4 [s] in S158 corresponds to the scavenging time provided between ignition retries in the event of misfire in re-ignition control under normal conditions.

When the number of retries is equal to or greater than Nn (YES in S160), the CPU 21 notifies the user of an error in S162. For example, the error can be notified by outputting a message that the user can perceive visually or audibly using the remote control 110.

For example, the number of retries in the judgment of S160 can be calculated based on a count value that is cleared at the latest when the judgment of S140 is NO, and then incremented each time S154 is executed.

Next, the abnormal ignition conditions will be described. In response to a YES determination in S140, the CPU 21 closes the main gas valve 14 in S170 after Tf1 [s] has elapsed since the misfire was detected (YES determination in S130), and then operates the blower fan 17 at the same rotation speed as in S152 for a predetermined scavenging time Tf2 [s] in S172.

That is, Tf1 [s] in S170 corresponds to the duration of fuel gas supply after misfire detection under abnormal ignition suppression conditions, and Tn2 [s] in S172 corresponds to the scavenging time until the first ignition retry when misfire is detected under abnormal ignition suppression conditions.

Furthermore, after scavenging in S172 is completed, the CPU 21 executes an ignition retry in S174. In S174 under the abnormal ignition suppression condition, the main gas valve 14 is opened and a voltage is applied to the igniter 18 while the capacity switching valve 16 is controlled so that the number of combustion burners is Xf. With the main gas valve 14 open, the state in which the igniter 18 generates sparks due to the application of voltage continues for Tf3 [s]. In other words, Tf3 [s] corresponds to the fuel gas supply time associated with the operation of the igniter 18 during an ignition retry under the abnormal ignition suppression condition.

After the ignition retry (Tf3 [s]) in S174, the CPU 21 determines in S176 whether the output of the flame rod 19 indicates a non-ignition or ignition state. As in S156, if a flame is continuously detected by the flame rod 19 for a certain period of time, it is determined that ignition has occurred and a NO determination is made in S176. In this case, the supply of fuel gas by the main gas valve 14 continues, and the process returns to S120 (combustion state) described above.

On the other hand, if the CPU 21 determines that ignition has not occurred (YES in S176), the supply of fuel gas is cut off by closing the main gas valve 14, and the process proceeds to S178. In S178, the blower fan 17 is operated at the same scavenging rotation speed as in S158 for a predetermined scavenging time Tf4 [s].

After scavenging is completed by S178, the CPU 21 determines whether the number of retries for re-ignition under abnormal ignition suppression conditions is equal to or greater than a predetermined upper limit number Nf by S180, which is the same as S170. The upper limit number Nf may be the same value as the upper limit number Nn in S160, or may be a different value.

When the number of retries is less than Nf (NO in S180), the CPU 21 returns the process to S174, and ignition retry is performed again under the abnormal ignition suppression condition. That is, the scavenging time Tf4 [s] in S178 corresponds to the scavenging time provided between ignition retries in the event of misfire in the re-ignition control under the abnormal ignition suppression condition.

When the number of retries is equal to or greater than Nf (YES in S180), the CPU 21 notifies the user of an error in S182. The error notification in S182 may include a message to improve the condition that may cause abnormal ignition, for example, a message recommending removing any obstruction covering the water heater 100 before operating the water heater again.

Figure 4 shows a chart comparing the abnormal ignition suppression conditions and normal conditions for the reignition control shown in Figure 3.

As illustrated in FIG. 4, the abnormal ignition suppression conditions are set so that, compared to the normal conditions, at least one of the following is achieved: a reduction in the amount of fuel gas supplied to the burner 12 through ignition retries, and an extension of the scavenging time by the blower fan 17 (i.e., an increase in the amount of air supplied by the blower fan 17).

Referring to FIG. 4, the time from when misfire is detected by S140 until the main gas valve 14 is closed, i.e., the duration of fuel gas supply after misfire detection, Tf1 [s] (S170) under abnormal ignition suppression conditions is set shorter than Tn1 [s] (S150) under normal conditions (Tf1<Tn1).

On the other hand, the scavenging time until the first ignition retry when misfire is detected in S140 can be set to the same value under abnormal ignition suppression conditions and normal conditions (Tf2 = Tn2). It is also possible to set Tf2 ≥ Tn2, but if Tf2 = Tn2, the ignition retry (S174) starts early, allowing for early recovery from misfire and suppressing a drop in the hot water outlet temperature of the water heater 100.

Furthermore, the number of burners to which fuel gas is supplied during re-ignition, i.e., the number of combustion burners, Xf under the abnormal ignition suppression condition (S174) is set to be smaller than Xn under the normal condition (S154).

Furthermore, regarding the fuel gas supply time until the igniter 18 is activated during ignition retry, Tf3 [s] under abnormal ignition suppression conditions (S174) is set to be equal to or less than Tn3 [s] under normal conditions (S154). For example, under abnormal ignition conditions, Tf3 is set to a fixed value of T3a regardless of the number of retries, whereas under normal conditions, Tn3 can be periodically set to either T3b (T3b>T3a) or Tn3=T3a depending on the number of retries.

As an example, when the number of retries is 1, Tn3 is set to T3b, and the next two retries are set to Tn3 = T3a. A set pattern for three ignition retries is treated as one set, and this set pattern is repeated to set Tn3 according to the number of retries. In this way, since Tf3 < Tn3 in the first ignition retry and Tf3 ≦ Tn3 in subsequent ignition retries, it can be understood that the total value of the fuel gas supply time until ignition (i.e., the cumulative value of the fuel gas supply amount) through one or more (Nn, Nf or less) ignition retries (S152, S72) is smaller under abnormal ignition suppression conditions than under normal conditions.

Furthermore, for the scavenging time when ignition does not occur during ignition retry, Tf4 [s] under abnormal ignition suppression conditions (S178) is set to be equal to or greater than Tn4 [s] under normal conditions (S158). For example, under abnormal ignition conditions, Tf4 is set to a fixed value of T4a regardless of the number of retries, whereas under normal conditions, Tn4 can be periodically set to either T4b (T4b < T4a) or Tn4 = T4a depending on the number of retries.

As an example, when the number of retries is 1 or 2, Tn4 is set to T4b, and the next time Tn4 is set to T4a. A set pattern for three ignition retries is treated as one set, and the set pattern is repeated to set Tn4 according to the number of retries. In this way, Tf4>Tn4 in the first ignition retry, and Tf4≧Tn4 in subsequent ignition retries. Therefore, it can be understood that the total value of the scavenging time (S158, S178) during misfire (i.e., the cumulative value of the airflow by the blower fan 17) through one or more (Nn, Nf or less) ignition retries is larger under abnormal ignition suppression conditions than under normal conditions.

The settings of the above-mentioned parameter values Tf1 to Tf4, Tn1 to Tn4, Xf, and Xn are not limited to the above examples, and can be set in any manner so that, under abnormal ignition suppression conditions, the amount of fuel gas supplied from the burner 12 is reduced and/or the scavenging time by the blower fan 17 is lengthened (i.e., the amount of air supplied is increased) compared to normal conditions.

In contrast, under normal conditions, compared to the abnormal ignition suppression conditions, the amount of fuel gas supplied from the burner 12 is increased, making ignition easier, and the scavenging time is shortened, making it possible to re-ignite quickly. In other words, the ignition suppression conditions reduce the ease of ignition and the speed of re-ignition, so they are only applied in cases where abnormal ignition is predicted to occur.

Figure 5 is a graph showing an example of a simulation of the gas concentration inside the housing during reignition control in the combustion device according to this embodiment. The vertical axis of Figure 5 shows the gas concentration estimate from the simulation, and the horizontal axis is the time axis. Also shown on the vertical axis is the allowable upper limit gas concentration Xmx, which corresponds to the lower explosion limit concentration and is assumed as the threshold for the occurrence of abnormal ignition.

In FIG. 5, the curve showing the change in gas concentration in the housing 11 over time under re-ignition control under normal conditions as described in FIG. 4 is indicated by reference numeral 101, and a similar curve under re-ignition control under normal conditions is indicated by reference numeral 102. In the simulation of FIG. 5, the amount of gas discharged from the housing 11 is calculated assuming that the housing 11 is highly airtight.

Both symbols 101 and 102 show the change in gas concentration when misfire is detected at 20 seconds (YES in S130) and Nn = Nf = 9, resulting in no ignition even after nine re-ignition attempts (S154, S174).

Since all nine times of ignition were misfires, in each of the reference symbols 101 and 102, the estimated gas concentration value increases according to the amount of fuel gas supplied from the burner 12 of the number of combustion burners Xn and Xf each time T1n, T1f, or Tf3, Tn3 is provided. On the other hand, the estimated gas concentration value decreases according to the rotation speed of the blower fan 17 each time scavenging times Tn2, Tf2, or Tn4, Tf4 are provided.

As can be seen from FIG. 5, in the re-ignition control under normal conditions shown by reference numeral 101, when re-ignition is repeated, the estimated gas concentration value exceeds the allowable upper limit gas concentration Xmx, and if ignition is successful under these conditions, there is a risk of abnormal ignition occurring.

In contrast, in the re-ignition control under the abnormal ignition suppression condition shown by reference numeral 102, the amount of fuel gas supplied at the time of re-ignition and the extension of the scavenging time ensure that even if re-ignition is repeated, the gas concentration does not reach the allowable upper limit gas concentration Xmx, and even if ignition is successful under these conditions, abnormal ignition can be suppressed.

In this way, with the combustion device according to this embodiment, when a burner misfires, re-ignition control is performed by selecting normal conditions and abnormal ignition suppression conditions based on a determination of whether the state inside the housing is such that abnormal ignition is predicted to occur, thereby suppressing abnormal ignition and controlling the re-ignition of the burner.

In addition, in S140 of FIG. 3, whether or not the state inside the housing 11 at the time of misfire is in a state where abnormal ignition is expected to occur is not limited to the above-mentioned determination based on the elapsed time from ignition to misfire, and may be determined by other methods. For example, it is also possible to perform the determination in S140 by comparing the actual measured value of the gas concentration inside the housing 11 with the allowable upper limit gas concentration Xmx in FIG. 5.

Specifically, by disposing a gas concentration sensor (not shown) inside the housing 11, it is possible to execute the judgment in S140 using the gas concentration measurement value Xp by the sensor at the time of misfire (YES judgment in S130).

Alternatively, the determination in S140 can be performed by further using an estimated value from a gas concentration estimation model as the gas concentration inside the housing 11.

Figure 6 shows an example of input parameter values of the gas concentration estimation model. As shown in Figure 6, the gas concentration estimation model 25 receives the open/close information of the main gas valve 14, the proportional valve 15, and the capacity switching valve 16 as input parameters for calculating the gas supply amount Gsp(t) into the housing 11. For example, while the main gas valve 14 is closed, the gas supply amount Gsp(t) = 0, while while the main gas valve 14 is open, a lookup table or calculation formula can be created in advance for calculating the gas supply amount Gsp(t) > 0 according to the combination of the opening degree of the proportional valve 15 and the number of combustion burners X adjusted by the capacity switching valve 16.

The gas concentration estimation model 25 further receives combustion information based on the output of the flame rod 19 as an input parameter for calculating the amount of unburned gas Grm(t) relative to the amount of gas supply Gsp(t). During the period when combustion is turned on by the combustion information, the amount of unburned gas Grm(t) is calculated by multiplying the amount of gas supply Gsp(t) by a predetermined unburned rate α (%) (Grm(t) = α · Gsp(t)). On the other hand, during the period when combustion is turned off by the combustion information, the entire amount of gas supply Gsp(t) is assumed to remain in the housing 11 (i.e., α = 1.0), and the calculation is made as Grm(t) = Gsp(t).

On the other hand, the amount of gas exhausted from the housing 11, Gex(t), can be calculated based on the dimensional parameters (constants) of the housing 11, including the exhaust port 11a, and reflecting the rotation speed of the blower fan 17 and the combustion information (combustion on/off).

Then, by introducing a differential equation or the like that reflects the increase in concentration according to the unburned gas amount Grm(t) and the decrease in concentration according to the gas emission amount Gex(t), a gas concentration estimation model 25 can be constructed that sequentially calculates the estimated gas concentration value GXp(%) within the housing 11.

For example, it is also possible to determine YES in S140 when the increase (Xp-GXp) in the gas concentration measurement value Xp (%) by a gas concentration sensor (not shown) relative to the gas concentration estimation value GXp (%) calculated by the gas concentration estimation model 25 using the gas exhaust amount Gex (t) when the airtightness of the housing 11 is normal becomes greater than the determination value. When the gas concentration sensor and gas concentration estimation model 25 are used in this way, it becomes possible to perform the determination in S140 without excessively increasing the accuracy required for the measurement value of the gas concentration sensor itself, compared to when the gas concentration measurement value Xp (%) is directly compared to the allowable upper limit gas concentration Xmx.

Alternatively, the determination in S140 can be made by directly or indirectly detecting that the airtightness of the housing 11 has increased, such as by arranging a proximity sensor (not shown) to detect the presence of an obstruction to the exhaust port 11a.

In this embodiment, gas is used as an example of the gaseous fuel burned by the burner, but the re-ignition control described in this embodiment can also be applied to combustion devices that burn other gaseous fuels with a burner.

In addition, in this embodiment, a water heater is used as an example of a device equipped with a "combustion device," but the re-ignition control according to this embodiment can be applied to a gaseous fuel combustion device installed in any device other than a water heater.

The embodiments disclosed herein should be considered to be illustrative and not restrictive in all respects. The scope of the present invention is indicated by the claims, not by the above description, and is intended to include all modifications within the meaning and scope of the claims.

10 Combustion device, 11 Housing, 11a Exhaust port, 12 Burner, 13 Gas supply pipe, 13a Gas supply port, 14 Main gas valve, 15 Proportional valve, 16 Capacity switching valve, 16a, 16b, 16c Valve, 17 Blower fan, 18 Igniter, 19 Flame rod, 20 Controller, 22 Input/output interface, 23 Timer, 24 Memory unit, 25 Gas concentration estimation model, 30 Heat exchanger, 31 Primary heat exchanger, 32 Secondary heat exchanger, 40 Water inlet pipe, 50 Hot water outlet pipe, 60 Bypass pipe, 70 Hot water tap, 100 Hot water heater, 110 Remote control, Nf, Nn Upper limit number of times (ignition retry), Tf1, Tf3, Tn1, Tn3 Fuel gas supply time, Tf2, Tf4, Tn2, Tn4 Scavenging time, Xf, Xn Number of combustion burners.

Claims (9)

A housing having an exhaust port;
A burner housed within the housing; and
a gas supply valve for supplying gaseous fuel to the burner;
A blower fan for supplying air to the burner;
an ignition device for igniting the mixture of the gaseous fuel and the air supplied to the burner;
A flame rod for detecting the flame of the burner;
a control unit that executes a re-ignition control of the burner when a misfire is detected based on an output of the flame rod after the burner is ignited,
The control unit controls the gas supply valve, the blower fan, and the ignition device so that, when the misfire is detected, the control unit determines whether or not the state inside the housing is in a state where abnormal ignition is predicted to occur, and if it determines that the state is in a state where abnormal ignition is predicted to occur, the control unit selects a first condition of the re-ignition control and executes an ignition retry, and if it determines that the state is not in a state where abnormal ignition is predicted to occur, the control unit selects a second condition of the re-ignition control and executes the ignition retry. The ignition retry is repeated multiple times when ignition is not performed,
The combustion device according to claim 1 , wherein the first condition is set so that the amount of the gaseous fuel supplied from the gas supply valve to the burner through the ignition retry is less than when the second condition is selected. The combustion device according to claim 2, wherein the first condition is set so that the supply duration from when the misfire is detected until the supply of the gas fuel by the gas supply valve is stopped is shorter than when the second condition is selected. A plurality of the burners are provided,
the gas supply valve includes a capacity switching valve for switching the number of combustion burners to which the gas fuel is supplied among the plurality of burners,
3. The combustion apparatus according to claim 2, wherein the first condition is set so that the number of the combustion burners in each ignition retry is smaller than that when the second condition is selected. The combustion device according to claim 2, wherein the first condition is set so that the supply time of the gaseous fuel accompanying the operation of the ignition device in each ignition retry is equal to or shorter than when the second condition is selected. The ignition retry is repeated multiple times when ignition is not performed,
When the ignition retry is repeated a plurality of times, scavenging of the inside of the housing is performed by the blower fan supplying the air between the ignition retries,
2. The combustion device according to claim 1, wherein the first condition is set so that an amount of air blown from the blower fan between the ignition retries when the ignition retries are repeated a plurality of times is smaller than an amount of air blown from the blower fan between the ignition retries when the second condition is selected. The combustion device according to claim 6, wherein the amount of air blown from the blower fan during the scavenging performed between the detection of the misfire and the first ignition retry is equivalent between the first condition and the second condition. The ignition retry is repeated multiple times when ignition is not performed,
2. The combustion device according to claim 1, wherein the control unit notifies a user of an error when the number of repetitions of the ignition retry reaches a predetermined upper limit number when the first condition is selected and when the second condition is selected. The combustion device according to any one of claims 1 to 8, wherein, when the misfire is detected, the control unit determines that the state is predicted to result in the occurrence of the abnormal ignition if the elapsed time from the detection of ignition based on the output of the flame rod to the detection of the misfire is shorter than a predetermined judgment time, whereas, when the elapsed time is longer than the judgment time, the control unit determines that the state is not predicted to result in the occurrence of the abnormal ignition.

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