JP2011002308A - Apparatus and method for detecting ignition and flameout - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an ignition and flameout detection apparatus and an ignition and flameout detection method capable of improving detection accuracy of ignition and flameout of hydrocarbon fuel.SOLUTION: The ignition and flameout detection apparatus comprises both of an oxygen sensor for detecting the concentration of oxygen in a combustion chamber or in the downstream of the combustion chamber for combusting hydrocarbon fuel and a determination means for determining at least either ignition or flameout of the hydrocarbon fuel on the basis of the difference or a relative ratio between a first output value of the oxygen sensor at a first applied voltage to the oxygen sensor and a second output value of the oxygen sensor at a second applied voltage.

Description

  The present invention relates to a misfire detection apparatus and a misfire detection method.

  A fuel cell is a device that generally obtains electric energy using hydrogen and oxygen as fuel. Since this fuel cell is excellent in terms of the environment and can realize high energy efficiency, it has been widely developed as a future energy supply system.

  In a fuel cell system including a reformer and a fuel cell, the amount of oxidant supplied is reduced in the exhaust pipe by controlling the opening of the air introduction valve based on the detection result of the air-fuel ratio sensor. Such a control technique is disclosed (for example, see Patent Document 1).

JP 2006-331990 A

  However, if the ignition state at the time of startup is determined using an oxygen sensor, unburned hydrocarbons undergo a decomposition reaction on the sensor. In this case, the oxygen concentration may not be detected accurately. As a result, there is a risk of misjudgment.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an ignition / misfire detection device and an ignition / fire detection method that can improve the accuracy of detection of misfire of a hydrocarbon fuel.

  An ignition detection device according to the present invention includes an oxygen sensor for detecting an oxygen concentration in a combustion chamber for burning hydrocarbon fuel or downstream of the combustion chamber, and a first oxygen sensor at a first applied voltage to the oxygen sensor. Determining means for determining at least one of ignition and misfiring of the hydrocarbon fuel based on a difference or relative ratio between the one output value and the second output value of the oxygen sensor at the second applied voltage. It is a feature. In the ignition / misfire detection device according to the present invention, since the difference or relative ratio of the output values of the plurality of applied voltages is used, it is possible to detect the ignition / misfire of the hydrocarbon fuel using the dissociation of hydrocarbons, The influence of changes over time can be avoided. Thereby, the ignition misfire detection accuracy of the hydrocarbon fuel can be improved.

  The determination means may determine that the hydrocarbon fuel has ignited when the absolute value of the difference between the first output value and the second output value is equal to or less than a predetermined value. The determination means may determine that the hydrocarbon fuel has ignited when the relative ratio of the high output value to the low output value of the first output value and the second output value is equal to or less than a predetermined value.

  The first applied voltage and the second applied voltage may be values in a voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is a predetermined value or less. The first applied voltage is a value in the first voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is not more than a predetermined value when the applied voltage is increased from zero. The second applied voltage is the applied voltage. The slope of the output of the oxygen sensor with respect to may be a value in the second or third voltage range that becomes a predetermined value or less when the applied voltage is increased from zero.

The first applied voltage is a value in a voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value below the redox potential of H ₂ O / H _{2 and} the redox potential of CO ₂ / CO. Also good. The second applied voltage may be a value in a voltage range of at least one of a redox potential of H ₂ O / H _{2 and} a redox potential of CO ₂ / CO.

  The determination means may determine that the hydrocarbon fuel is not ignited when the oxygen sensor output is equal to or less than a predetermined value.

  Another ignition misfire detection device according to the present invention includes an oxygen sensor for detecting an oxygen concentration in a combustion chamber for burning hydrocarbon fuel or downstream of the combustion chamber, and carbonization when the output of the oxygen sensor is a predetermined value or less. Determination means for determining that the hydrogen fuel has not been ignited. In another ignition misfire detection apparatus according to the present invention, the dissociation of hydrocarbons in the oxygen sensor can be used. Thereby, the ignition misfire detection accuracy of the hydrocarbon fuel can be improved.

  The ignition / misfire detection method according to the present invention includes a first output value of an oxygen sensor at a first applied voltage to an oxygen sensor that detects an oxygen concentration in a combustion chamber or downstream of the combustion chamber for burning hydrocarbon fuel. A determination step of determining at least one of ignition and misfiring of the hydrocarbon fuel based on a difference or relative ratio with a second output value of the oxygen sensor at the second applied voltage. is there. In the ignition / misfire detection method according to the present invention, since the difference or relative ratio of the output values of a plurality of applied voltages is used, it is possible to detect the ignition / misfire of the hydrocarbon fuel using the dissociation of hydrocarbons, The influence of changes over time can be avoided. Thereby, the ignition misfire detection accuracy of the hydrocarbon fuel can be improved.

  The determination step may be a step of determining that the hydrocarbon fuel has ignited when the absolute value of the difference between the first output value and the second output value is equal to or less than a predetermined value. The determination step may be a step of determining that the hydrocarbon fuel has ignited when the relative ratio of the high output value to the low output value of the first output value and the second output value is equal to or less than a predetermined value.

  The first applied voltage and the second applied voltage may be values in a voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is a predetermined value or less. The first applied voltage is a value in the first voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is not more than a predetermined value when the applied voltage is increased from zero. The second applied voltage is the applied voltage. The slope of the output of the oxygen sensor with respect to may be a value in the second or third voltage range that becomes a predetermined value or less when the applied voltage is increased from zero.

The first applied voltage is a value in a voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value below the redox potential of H ₂ O / H _{2 and} the redox potential of CO ₂ / CO. Also good. The second applied voltage may be a value in a voltage range of at least one of a redox potential of H ₂ O / H _{2 and} a redox potential of CO ₂ / CO.

  In the determination step, it may be determined that the hydrocarbon fuel is not ignited when the oxygen sensor output is equal to or less than a predetermined value.

  According to another ignition / ignition detection method according to the present invention, when the output of the oxygen sensor for detecting the oxygen concentration in the combustion chamber for burning the hydrocarbon fuel or downstream of the combustion chamber is equal to or lower than a predetermined value, the hydrocarbon fuel is not used. And a determination step for determining that the ignition is performed. In another ignition misfire detection method according to the present invention, hydrocarbon dissociation in an oxygen sensor can be used. Thereby, the ignition misfire detection accuracy of the hydrocarbon fuel can be improved.

  ADVANTAGE OF THE INVENTION According to this invention, the misfire detection apparatus and the misfire detection method which can improve the misfire detection accuracy of a hydrocarbon fuel can be provided.

1 is a schematic diagram illustrating an overall configuration of a misfire detection apparatus 100 according to a first embodiment. It is a figure for demonstrating the oxygen concentration detected by the oxygen sensor 10 when the hydrocarbon fuel is ignited and when it is not ignited. It is a figure for demonstrating the reaction formula which arises in the substance which exists in the vicinity of an oxygen sensor in the case of ignition of hydrocarbon fuel, and non-ignition, and an oxygen sensor. It is a diagram for explaining the redox potential of the redox potential and _CO 2 / CO of _{H 2} O / H _2. It is a diagram for explaining the redox potential of the redox potential and _CO 2 / CO of _{H 2} O / _H 2 at the time of ignition. It is a diagram for explaining the oxidation-reduction potential of the non-ignition redox _{H 2} O / _H 2 at potential and _CO 2 / CO. It is a figure for demonstrating a misfire determination. It is a figure which shows an example of the flowchart of ignition / misfire determination. It is a figure which shows the other example of the flowchart of ignition / misfire determination. It is a figure which shows the other example of the flowchart of ignition / misfire determination. It is a figure which shows the other example of the flowchart of ignition / misfire determination. It is a figure which shows the other example of the flowchart of ignition / misfire determination. FIG. 3 is a schematic diagram illustrating an overall configuration of a fuel cell system according to a second embodiment.

  Hereinafter, the best mode for carrying out the present invention will be described.

  FIG. 1 is a schematic diagram illustrating an overall configuration of a misfire detection apparatus 100 according to the first embodiment. A schematic cross section of an oxygen sensor 10 to be described later is shown. As shown in FIG. 1, the misfire detection apparatus 100 includes an oxygen sensor 10, an ammeter 20, a sensor power supply 30, a heater power supply 40, and a control unit 50. The misfire detection apparatus 100 is an apparatus that detects the misfire of a hydrocarbon fuel. Therefore, the oxygen sensor 10 is disposed in the combustion chamber of the hydrocarbon fuel or the exhaust pipe thereof.

  The oxygen sensor 10 is a limiting current type oxygen sensor, and an anode 12 is provided on one surface of the electrolyte 11, a cathode 13 is provided on the other surface of the electrolyte 11, and a porous substrate (not shown) in which pores are formed is a cathode. 13 is arranged so as to cover 13. A heater 15 is disposed on the electrolyte 11.

  The electrolyte 11 is made of an oxygen ion conductive electrolyte, for example, yttria-added stabilized zirconia. The anode 12 and the cathode 13 are made of a material having catalytic activity, for example, platinum. The anode 12 and the cathode 13 form an external circuit through wiring. In this external circuit, an ammeter 20 and a sensor power supply 30 are provided. A porous substrate (not shown) is made of, for example, porous alumina. The heater 15 is made of, for example, a platinum thin film. A heater power supply 40 is connected to the heater 15.

  The control unit 50 includes a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), and the like. The control unit 50 controls the sensor power supply 30 and the heater power supply 40 based on the detection result of the ammeter 20 and the like. Further, the control unit 50 determines whether or not the hydrocarbon fuel is ignited or misfired based on the detection result of the ammeter 20 or the like.

Next, an outline of oxygen concentration detection by the oxygen sensor 10 will be described. The control unit 50 controls the heater power supply 40 to supply power to the heater 15. Thereby, the electrolyte 11 is heated. After the temperature of the electrolyte 11 reaches a predetermined value, the control unit 50 controls the sensor power supply 30 so that the voltage applied to the anode 12 is relatively positive with respect to the voltage applied to the cathode 13. When voltage is applied to the anode 12 and the cathode 13, oxygen becomes oxygen ions in the cathode 13 and conducts through the electrolyte 11 according to the following formula (1). In the anode 12, oxygen ions become oxygen molecules according to the following formula (2).
O ₂ + 4e ⁻ → 2O ²⁻ (1)
2O ²⁻ → O ₂ + 4e ⁻ (2)

  Since the amount of oxygen transported to the cathode 13 is governed by the pores of the porous substrate (not shown), the current (limit current) generated by the reaction of the formulas (1) and (2) is the fineness of the porous substrate (not shown). It is determined by the oxygen gas diffusion amount in the hole. This oxygen gas diffusion amount is determined by the oxygen concentration outside the porous substrate (not shown).

  The control unit 50 acquires the output current of the oxygen sensor 10 according to the detection value of the ammeter 20. The output current of the oxygen sensor 10 is proportional to the oxygen concentration in the atmosphere. Based on this proportional relationship, the controller 50 detects the oxygen concentration of the atmosphere to which the oxygen sensor 10 is exposed.

However, when the hydrocarbon is not ignited, the oxygen sensor 10 may not be able to accurately detect the oxygen concentration. Further, the oxygen concentration detected by the oxygen sensor 10 changes according to the relationship between the redox potential of water vapor (H ₂ O) and carbon dioxide (CO ₂ ) and the voltage applied to the oxygen sensor 10. Hereinafter, the detected oxygen concentration of the oxygen sensor 10 when the hydrocarbon is ignited and when it is not ignited will be described with reference to FIGS. 2 and 3. In the following description, the voltage applied to the oxygen sensor 10 refers to this predetermined value when a voltage is applied by the external power source 30 so as to keep the potential difference between the cathode 13 and the anode 12 at a predetermined value. is there.

  FIG. 2 is a diagram for explaining the detected oxygen concentration of the oxygen sensor 10 when the hydrocarbon fuel is ignited and when it is not ignited. FIG. 3 is a diagram for explaining the substances existing in the vicinity of the oxygen sensor 10 and the reaction formula generated in the oxygen sensor 10 when the hydrocarbon fuel is ignited and not ignited.

In FIG. 2, the horizontal axis indicates the voltage applied to the oxygen sensor 10, and the vertical axis indicates the detected oxygen concentration of the oxygen sensor 10. As described above, the detected oxygen concentration of the oxygen sensor 10 is proportional to the output current of the oxygen sensor 10. As shown in FIG. 3 (a), 2.5 NL / min of methane (CH ₄ ) is supplied to the combustion chamber as a hydrocarbon fuel, and 40 NL / min of air (mainly O ₂ + N ₂ ) is supplied as an oxidant. Think about the case.

  If the hydrocarbon fuel is ignited and completely burned, the oxygen concentration in the atmosphere is about 10.8% in the case of the ratio shown in FIG. In practice, since true complete combustion is difficult to expect, the oxygen concentration detected by the oxygen sensor 10 may deviate from 10.8%. However, since this difference in oxygen concentration is negligible, it is not considered in this specification.

  As the applied voltage to the oxygen sensor 10 is increased from zero, the detected oxygen concentration of the oxygen sensor 10 increases, and the detected oxygen concentration of the oxygen sensor 10 is substantially constant (the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage). Appears in a voltage range where the value is less than or equal to a predetermined value. Hereinafter, this voltage range is referred to as a first range. This voltage range appears in the limiting current region of the oxygen sensor 10. In this first range, the oxygen sensor 10 can accurately detect the oxygen concentration in the atmosphere. As an example, the first range is around 0.4 V at 700 ° C.

Increasing the voltage applied to the oxygen sensor 10 in the above oxidation-reduction potential of H _{2 O} / H _2, at the cathode 13, the reduction reaction of the of H _{2 O} H ₂ produced by the combustion of a hydrocarbon fuel occurs. Since oxygen ions generated by this reduction reaction are conducted through the electrolyte 11, the oxygen concentration detected by the oxygen sensor 10 is increased.

When the voltage applied to the oxygen sensor 10 is further increased, the transport amount of H ₂ O to the cathode 13 is governed by the pores of the porous substrate (not shown). As a result, a voltage range appears in which the detected oxygen concentration of the oxygen sensor 10 is substantially constant (the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage is equal to or less than a predetermined value). Hereinafter, this voltage range is referred to as a second range. This second range appears when the voltage applied to the oxygen sensor 10 is equal to or higher than the redox potential of H ₂ O / H ₂ and lower than the redox potential of CO ₂ / CO. As an example, the second range is around 0.8 V at 700 ° C. If all the H ₂ O in the vicinity of the cathode 13 is reduced, the oxygen concentration detected by the oxygen sensor 10 is about 12.2%.

When the voltage applied to the oxygen sensor 10 is increased to the CO ₂ / CO oxidation-reduction potential, a reduction reaction of CO ₂ generated by combustion of hydrocarbon fuel to CO occurs at the cathode 13. Since oxygen ions generated by this reduction reaction are conducted through the electrolyte 11, the oxygen concentration detected by the oxygen sensor 10 is increased.

When the voltage applied to the oxygen sensor 10 is further increased, the transport amount of CO ₂ to the cathode 13 is governed by the pores of the porous substrate (not shown). As a result, a voltage range appears in which the detected oxygen concentration of the oxygen sensor 10 is substantially constant (the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage is equal to or less than a predetermined value). Hereinafter, this voltage range is referred to as a third range. The third range is manifested when the voltage applied to the oxygen sensor 10 is less than the redox potential of the redox potential more and CO 2 _{/ C} in CO 2 _/ CO. As an example, the third range is around 1.1 V at 700 ° C. If all the CO ₂ near the cathode 13 is reduced to CO, the oxygen concentration detected by the oxygen sensor 10 is about 15.4%.

When the voltage applied to the oxygen sensor 10 is increased to the redox potential of CO ₂ / C, a reduction reaction of CO ₂ generated by combustion of hydrocarbon fuel to C occurs at the cathode 13. Since oxygen ions generated by this reduction reaction are conducted through the electrolyte 11, the oxygen concentration detected by the oxygen sensor 10 is increased.

When the applied voltage to the oxygen sensor 10 is further increased, a voltage range appears in which the detected oxygen concentration of the oxygen sensor 10 is substantially constant (the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage is not more than a predetermined value). Hereinafter, this voltage range is referred to as a fourth range. The fourth range appears when the voltage applied to the oxygen sensor 10 is equal to or higher than the CO ₂ / C oxidation-reduction potential. In this fourth range, C (carbon) gradually precipitates and functions as an electrode in the same manner as platinum constituting the cathode 13. In this case, since the apparent electrode area gradually increases, the oxygen concentration detected by the oxygen sensor 10 in the fourth range gradually increases without becoming flat. As an example, the fourth range is around 1.1 V at 700 ° C. If all the CO _{2 in the} vicinity of the cathode 13 is reduced to C, the oxygen concentration detected by the oxygen sensor 10 is about 18.6%.

  As illustrated in FIGS. 3B to 3E, when the voltage applied to the oxygen sensor 10 changes, components generated by the combustion of the hydrocarbon fuel affect the oxygen concentration detected by the oxygen sensor 10. Therefore, the oxygen concentration detected by the oxygen sensor 10 varies according to the voltage applied to the oxygen sensor 10.

Next, a case where the hydrocarbon fuel is not ignited will be described. If the hydrocarbon fuel is not ignited, oxygen in the air is not consumed, so the oxygen concentration in the atmosphere should be about 18.8%. Therefore, the oxygen concentration detected by the oxygen sensor 10 should be higher than that at the time of ignition. However, the cathode 13 functions as a catalyst, and the hydrocarbon fuel is dissociated into C and H ₂ . Since oxygen ions generated at the cathode 13 are combined with C and H ₂ , the amount of oxygen ions conducted through the electrolyte 11 is reduced. As a result, a difference is generated between the oxygen concentration detected by the oxygen sensor 10 and the actual oxygen concentration in the atmosphere.

If the voltage applied to the oxygen sensor 10 is less than the redox potential of H ₂ O / H ₂ , the C and H ₂ are combined with oxygen ions at the cathode 13 as shown in FIG. Is done. Accordingly, oxygen ions that should be conducted through the electrolyte 11 are consumed, so that the oxygen concentration detected by the oxygen sensor 10 is lower than that at the time of ignition. From the above, when the hydrocarbon fuel is not ignited, the oxygen concentration detected by the oxygen sensor 10 is lower than when the hydrocarbon fuel is ignited. For example, when C and H ₂ near the cathode 13 all react with oxygen ions, the oxygen concentration detected by the oxygen sensor 10 is about 5.2%. Note that the first range appears even in the case of non-ignition. However, there may be a difference in voltage width and voltage value in the first range between ignition and non-ignition.

When the voltage applied to the oxygen sensor 10 is equal to or higher than the redox potential of H ₂ O / H ₂ and lower than the redox potential of CO ₂ / CO, the reduction reaction of H ₂ O at the cathode 13 as shown in FIG. Occurs. In this case, more oxygen ions are conducted through the electrolyte 11. Thereby, the oxygen concentration which the oxygen sensor 10 detects becomes high. For example, if all the H ₂ O in the vicinity of the cathode 13 is reduced, the oxygen concentration detected by the oxygen sensor 10 is about 11.7%. Note that the second range appears even in the case of non-ignition. However, there may be a difference in the voltage width and voltage value in the second range between ignition and non-ignition.

When the voltage applied to the oxygen sensor 10 becomes equal to or higher than the CO ₂ / CO redox potential, a CO ₂ reduction reaction occurs at the cathode 13 as shown in FIG. In this case, more oxygen ions are conducted through the electrolyte 11. Thereby, the oxygen concentration which the oxygen sensor 10 detects becomes high. For example, if all the CO ₂ near the cathode 13 is reduced, the oxygen concentration detected by the oxygen sensor 10 is about 18.8%. Note that the third range appears even in the case of non-ignition. However, there may be a difference in voltage range and voltage value in the third range between ignition and non-ignition.

When the voltage applied to the oxygen sensor 10 becomes equal to or higher than the redox potential of CO ₂ / C, a reduction reaction of CO ₂ to C occurs at the cathode 13 as shown in FIG. Thereby, the oxygen concentration which the oxygen sensor 10 detects becomes high. Note that the fourth range appears even in the case of non-ignition. However, there may be a difference in the voltage width and voltage value in the fourth range between ignition and non-ignition.

From the above, in the first range where the hydrocarbon fuel has not been ignited, the amount of oxygen ions conducted through the electrolyte 11 decreases with the oxidation of C and H ₂ caused by the dissociation of the hydrocarbon. The detected oxygen concentration of 10 is lower than that at the time of ignition. On the other hand, in the third range and the fourth range where the hydrocarbon fuel is not ignited, C and H ₂ generated by the dissociation of hydrocarbons are not oxidized, so that the oxygen concentration detected by the oxygen sensor 10 is higher than that during ignition. . By utilizing this phenomenon, it is possible to determine whether the hydrocarbon fuel has been ignited or not ignited using the oxygen sensor 10.

Hereinafter, the redox potential of H ₂ O / H ₂ , the redox potential of CO ₂ / CO, and the redox potential of CO ₂ / C will be described with reference to FIGS. 4 to 6, the horizontal axis represents temperature (° C.), the left vertical axis represents the redox potential, the right vertical axis represents −logPO ₂ , log (PCO ₂ / PCO), And log (PH ₂ O / PH ₂ ). PO ₂ represents oxygen partial pressure, PCO represents carbon monoxide partial pressure, PCO ₂ represents carbon dioxide partial pressure, PH ₂ O represents water vapor partial pressure, and PH ₂ represents hydrogen partial pressure. 4 to 6 are excerpts from the Electrochemical Handbook (Maruzen) edited by the Electrochemical Society, P83.

In FIG. 4, the redox potential line of H ₂ O / H ₂ when PH ₂ O: PH ₂ is 1: 1, and the redox potential of CO ₂ / CO when PCO ₂ : PCO is 1: 1. A potential line and a redox potential line of CO ₂ / C when PCO ₂ is 1 atm are shown. Redox potential linear _{H 2} O / H _2, the partial pressure ratio of _{H 2} O / H 2 indicates the boundary representing the one larger or smaller than. Further, the oxidation-reduction potential linear _CO 2 / CO _is the partial pressure ratio of CO 2 / CO indicates a boundary representing the one larger or smaller than.

H ₂ oxidation-reduction potential straight O / _{H 2} is _PH 2 O: PH ₂ changes according to, _CO 2 / CO oxidation reduction potential straight _PCO 2 of: changes according to the PCO, the oxidation of _CO 2 / C The reduction potential line changes according to PCO ₂ / a (C). Here, a (C) is the activity (= 1) of solid carbon. H ₂ O / H ₂ oxidation-reduction potential line, CO ₂ / CO oxidation-reduction potential line, and CO ₂ / C oxidation-reduction potential line when the hydrocarbon fuel is ignited and when not ignited, respectively. Change.

FIG. 5 is a diagram showing a redox potential line of H ₂ O / H _2, a redox potential line of CO ₂ / CO, and a redox potential of CO ₂ / C when the hydrocarbon fuel is ignited. When hydrocarbon fuel burns, there is almost no H ₂ and CO in the atmosphere. Therefore, PH ₂ O / PH ₂ and PCO ₂ / PCO increase. In FIG. 5, the H ₂ O / H ₂ redox potential line when PH ₂ O: PH ₂ is 4%: 4 ppm to 10%: 0.1 ppm, and PCO ₂ : PCO is 4%: 4000 ppm. The redox potential line for CO ₂ / CO when ˜4%: 4 ppm is shown. _{Further, PCO 2: a (C)} = 1atm (100%): 1~PCO 2: a (C) = 0.04atm (4%): redox potential of _CO 2 / C in the case of 1 is shown ing.

In the case of FIG. 5, at 700 ° C., the redox potential of H ₂ O / H ₂ is about 0.45 V to 0.7 V, and the redox potential of CO ₂ / CO is about 0.6 V to 1 V. . Although illustration is omitted, the oxidation-reduction potential of oxygen at 700 ° C. is about 0 V to 0.1 V when log (PO ₂ ) = 0 to −1. If PO ₂ is about 0.1%, the oxidation-reduction potential of oxygen is about 0.3 V at 700 ° C. Furthermore, at 700 ° C., the redox potential of _CO 2 / C if the CO ₂ partial pressure is 1 atm (100%) is about 1.0 V, CO ₂ partial pressure is 0.04 atm (4%) In this case, the redox potential of CO ₂ / C is about 1.1V.

FIG. 6 is a diagram showing a redox potential line of H ₂ O / H _2, a redox potential line of CO ₂ / CO, and a redox potential of CO ₂ / C when the hydrocarbon fuel is not ignited. . When the hydrocarbon fuel is not ignited, a large amount of H ₂ and CO are present in the atmosphere due to dissociation of the hydrocarbon. Therefore, PH ₂ O / PH ₂ and PCO ₂ / PCO are smaller than in the case of FIG. In FIG. 6, the H ₂ O / H ₂ redox potential line when PH ₂ O: PH ₂ is 3%: 30% to 3%: 300 ppm, and PCO ₂ : PCO is 0.1%: The redox potential line of CO ₂ / CO in the case of 10% to 0.1%: 100 ppm is shown. _{Further, PCO 2: a (C)} = 1atm (100%): 1~PCO 2: a (C) = 0.0004atm (400ppm): redox potential of _CO 2 / C in the case of 1 is shown Yes.

In the case of FIG. 6, at 700 ° C., the redox potential of H ₂ O / H ₂ is about 0.8V to 1.2V, and the redox potential of CO ₂ / CO is about 0.9V to 1.3V. It is. Although illustration is omitted, the oxidation-reduction potential of oxygen at 700 ° C. is about 0 V to 0.1 V when log (PO ₂ ) = 0 to −1. Furthermore, at 700 ° C., when the CO ₂ partial pressure is 1 atm (100%), the CO ₂ / C redox potential is about 1.0 V, and the CO ₂ partial pressure is 0.0004 atm (400 ppm). The redox potential of CO ₂ / C is about 1.2V.

As described with reference to FIGS. 4 to 6, the redox potential of H ₂ O / H ₂ , the redox potential of CO ₂ / CO, and the redox potential of CO ₂ / C have different values. The second range, the third range, and the fourth range shown in FIG. 2 are formed due to this difference in redox potential.

  Here, the amount of components in the combustion off-gas when the hydrocarbon fuel is ignited and not ignited can be predicted using the amount of hydrocarbon fuel supplied to the combustion chamber, the amount of air supplied, and the like as parameters. Based on this prediction, the oxidation-reduction potential can be estimated by the procedure described with reference to FIGS.

As described above, the curve in FIG. 2 is drawn using the oxygen redox potential, the H ₂ O / H ₂ redox potential, the CO ₂ / CO redox potential, and the CO ₂ / C redox potential as parameters. It is a curve. Therefore, you may determine the 1st range-4th range demonstrated in FIG. 2 based on the oxidation-reduction potential estimated in FIGS. Further, when increasing the applied voltage to the oxygen sensor 10, the first voltage range in which the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage is almost zero (predetermined value or less) is the first range, the second voltage The range may be determined as the second range, the third voltage range as the third range, and the fourth voltage range as the fourth range.

  Next, the misfire determination by the misfire detection apparatus 100 will be described. The curve of the oxygen concentration detected by the oxygen sensor 10 at the time of ignition in FIG. 2 can be obtained by burning hydrocarbon fuel in advance. By using this curve as a reference curve, it can be determined whether the hydrocarbon fuel is ignited or not ignited.

First, in the first range in which the hydrocarbon fuel is not ignited, the amount of oxygen ions conducted through the electrolyte 11 decreases with the oxidation of C and H ₂ caused by the dissociation of hydrocarbons. The oxygen concentration is lower than that during ignition. Therefore, it is possible to determine that the hydrocarbon fuel is not ignited when the oxygen concentration detected by the oxygen sensor 10 is equal to or less than a determination value (a value less than the detection oxygen concentration in the first range at the time of ignition). For example, by setting the determination value shown in FIG. 7 in advance, when the oxygen concentration detected by the oxygen sensor 10 is equal to or lower than the determination value, it can be determined that the hydrocarbon fuel is not ignited. This determination value can be set, for example, when the voltage applied to the oxygen sensor 10 is within the first range.

  An example of a flowchart in this case is shown in FIG. First, the control unit 50 controls the sensor power supply 30 to increase the voltage applied to the oxygen sensor 10 to the first range (step S1). Next, the control unit 50 determines whether or not the oxygen concentration detected by the oxygen sensor 10 is equal to or less than a determination value (step S2). When it is determined in step S2 that the detected oxygen concentration is equal to or lower than the determination value, the control unit 50 determines that the hydrocarbon fuel is not ignited (step S3). Thereafter, the control unit 50 ends the execution of the flowchart. When it is not determined in step S2 that the detected oxygen concentration is equal to or lower than the determination value, the control unit 50 determines that the hydrocarbon fuel has ignited (step S4). Thereafter, the control unit 50 ends the execution of the flowchart.

According to the flowchart of FIG. 8, it is possible to determine whether the hydrocarbon fuel has been ignited or not ignited according to the detected oxygen concentration of the oxygen sensor 10. In step S1, the first voltage range in which the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage is not more than a predetermined value by increasing the voltage applied to the oxygen sensor 10 from zero may be set as the first range. The voltage range in which the slope of the oxygen concentration detected by the oxygen sensor 10 with respect to the applied voltage is equal to or less than a predetermined value in the voltage range below the redox potential of H ₂ O / H ₂ and the CO ₂ / CO redox potential is defined as the first range. Also good.

  It is also possible to determine whether the hydrocarbon fuel has been ignited or not ignited based on the difference between the detected oxygen concentration in the first range and the detected oxygen concentration in the third range. In FIG. 7, the difference between the detected oxygen concentration C3 in the third range and the detected oxygen concentration C1 in the first range at the time of hydrocarbon fuel ignition is defined as a difference D1. The difference between the detected oxygen concentration C3 'in the third range and the detected oxygen concentration C1' in the first range when the hydrocarbon fuel is not ignited is defined as a difference D2. In this case, a relationship of difference D1 <difference D2 is obtained. Therefore, ignition and non-ignition of the hydrocarbon fuel can be determined based on the difference between the oxygen concentrations detected by the oxygen sensor 10 in the first range and the third range.

  An example of a flowchart in this case is shown in FIG. First, the control unit 50 increases the voltage applied to the oxygen sensor 10 to the third range (step S11). Next, the control unit 50 determines whether or not the difference X between the detected oxygen concentration in the third range detected by the oxygen sensor 10 and the detected oxygen concentration in the first range is greater than the determination value (step S12). . In addition, as the determination value in this case, a value greater than or equal to the difference D1 measured in advance can be used.

  When it is determined in step S12 that the difference X is larger than the determination value, the control unit 50 determines that the hydrocarbon fuel has not been ignited (step S13). Thereafter, the control unit 50 ends the execution of the flowchart. When it is not determined in step S12 that the difference X is larger than the determination value, the control unit 50 determines that the hydrocarbon fuel has ignited (step S14). Thereafter, the control unit 50 ends the execution of the flowchart.

  According to the flowchart of FIG. 9, it is possible to determine whether the hydrocarbon fuel has been ignited or not ignited based on the difference between the output values of the oxygen sensor 10 with respect to a plurality of types of applied voltages. In this case, there is an advantage that the influence of the change over time can be avoided as compared with the method using the absolute value of the output value of the oxygen sensor 10.

Note that the ignition and non-ignition of the hydrocarbon fuel can also be determined based on the difference between the detected oxygen concentration in the first range and the detected oxygen concentration in the second range using the same flowchart as in FIG. In step S11, the third voltage range may be set such that the voltage applied to the oxygen sensor 10 is increased from zero, and the third voltage range in which the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage falls below a predetermined value. A voltage range in which the slope of the oxygen concentration detected by the oxygen sensor 10 with respect to the applied voltage is equal to or less than a predetermined value in a voltage range equal to or higher than the redox potential of H ₂ O / H _{2 and} the redox potential of CO ₂ / CO is defined as a third range. Also good.

  Moreover, ignition and non-ignition of the hydrocarbon fuel can be determined based on a relative ratio between the detected oxygen concentration in the first range and the detected oxygen concentration in the third range. In FIG. 7, the relative ratio of the detected oxygen concentration C3 in the third range to the detected oxygen concentration C1 in the first range at the time of hydrocarbon fuel ignition is a relative ratio R1 (= C3 / C1). The relative ratio of the detected oxygen concentration C3 'in the third range to the detected oxygen concentration C1' in the first range when the hydrocarbon fuel is not ignited is a relative ratio R2 (= C3 '/ C1'). In this case, the relationship of relative ratio R1 <relative ratio R2 is obtained. Therefore, the ignition and non-ignition of the hydrocarbon fuel can be determined based on the relative ratio of the oxygen concentration detected by the oxygen sensor 10 in the first range and the third range.

  An example of a flowchart in this case is shown in FIG. First, the control unit 50 increases the voltage applied to the oxygen sensor 10 to the third range (step S21). Next, the control unit 50 determines whether or not the relative ratio Y of the detected oxygen concentration in the third range detected by the oxygen sensor 10 to the detected oxygen concentration in the first range is larger than the determination value (step S22). . In addition, as the determination value in this case, a value that is measured in advance with a relative ratio R1 or more can be used.

  When it is determined in step S22 that the relative ratio Y is greater than the determination value, the control unit 50 determines that the hydrocarbon fuel has not been ignited (step S23). Thereafter, the control unit 50 ends the execution of the flowchart. When it is not determined in step S22 that the relative ratio Y is greater than the determination value, the control unit 50 determines that the hydrocarbon fuel has ignited (step S24). Thereafter, the control unit 50 ends the execution of the flowchart.

  According to the flowchart of FIG. 10, ignition and non-ignition of hydrocarbon fuel can be determined based on the relative ratio of the output value of the oxygen sensor 10 to a plurality of types of applied voltages. In this case, there is an advantage that the influence of the change over time can be avoided as compared with the method using the absolute value of the output value of the oxygen sensor 10. Note that the ignition and non-ignition of the hydrocarbon fuel can also be determined based on the relative ratio between the detected oxygen concentration in the first range and the detected oxygen concentration in the second range, using the same flowchart as in FIG.

  Further, ignition and non-ignition of the hydrocarbon fuel can be determined based on the difference between the detected oxygen concentration in the first range and the detected oxygen concentration in the fourth range. In FIG. 7, the difference between the detected oxygen concentration C4 in the fourth range and the detected oxygen concentration C1 in the first range at the time of hydrocarbon fuel ignition is defined as a difference d1. The difference between the detected oxygen concentration C4 'in the fourth range and the detected oxygen concentration C1' in the first range when the hydrocarbon fuel is not ignited is defined as a difference d2. In this case, a relationship of difference d1 <difference d2 is obtained. Therefore, it is possible to determine whether the hydrocarbon fuel has been ignited or not ignited based on the difference between the oxygen concentrations detected by the oxygen sensor 10 in the first range and the fourth range.

  An example of a flowchart in this case is shown in FIG. First, the control unit 50 increases the voltage applied to the oxygen sensor 10 to the fourth range (step S31). Next, the control unit 50 determines whether or not the difference X between the detected oxygen concentration in the fourth range detected by the oxygen sensor 10 and the detected oxygen concentration in the first range is larger than the determination value (step S42). . In addition, as the determination value in this case, a value greater than or equal to the difference d1 measured in advance can be used.

  When it is determined in step S32 that the difference X is larger than the determination value, the control unit 50 determines that the hydrocarbon fuel has not been ignited (step S33). Thereafter, the control unit 50 ends the execution of the flowchart. When it is not determined in step S32 that the difference X is greater than the determination value, the control unit 50 determines that the hydrocarbon fuel has ignited (step S34). Thereafter, the control unit 50 ends the execution of the flowchart.

  According to the flowchart of FIG. 11, ignition and non-ignition of the hydrocarbon fuel can be determined based on the difference between the output values of the oxygen sensor 10 with respect to a plurality of types of applied voltages. In this case, there is an advantage that the influence of the change over time can be avoided as compared with the method using the absolute value of the output value of the oxygen sensor 10.

Note that the ignition and non-ignition of the hydrocarbon fuel can also be determined based on the difference between the detected oxygen concentration in the first range and the detected oxygen concentration in the second range using the same flowchart as in FIG. In step S31, the fourth voltage range in which the slope of the detected oxygen concentration of the oxygen sensor 10 with respect to the applied voltage is less than a predetermined value by increasing the voltage applied to the oxygen sensor 10 from zero may be set as the fourth range. , The slope of the oxygen concentration detected by the oxygen sensor 10 with respect to the applied voltage in a voltage range equal to or higher than the redox potential of H ₂ O / H _2, the redox potential of CO ₂ / CO, and the redox potential of CO ₂ / C. The following voltage range may be the fourth range.

  Moreover, ignition and non-ignition of the hydrocarbon fuel can also be determined based on the relative ratio between the detected oxygen concentration in the first range and the detected oxygen concentration in the fourth range. In FIG. 7, the relative ratio of the detected oxygen concentration C4 in the fourth range to the detected oxygen concentration C1 in the first range at the time of hydrocarbon fuel ignition is a relative ratio r1 (= C4 / C1). The relative ratio of the detected oxygen concentration C4 'in the fourth range to the detected oxygen concentration C1' in the first range when the hydrocarbon fuel is not ignited is a relative ratio r2 (= C4 '/ C1'). In this case, the relationship of relative ratio r1 <relative ratio r2 is obtained. Therefore, the ignition and non-ignition of the hydrocarbon fuel can be determined based on the relative ratio of the oxygen concentration detected by the oxygen sensor 10 in the first range and the fourth range.

  An example of a flowchart in this case is shown in FIG. First, the control unit 50 increases the voltage applied to the oxygen sensor 10 to the fourth range (step S41). Next, the control unit 50 determines whether or not the relative ratio Y of the detected oxygen concentration in the fourth range detected by the oxygen sensor 10 to the detected oxygen concentration in the first range is larger than the determination value (step S42). . In this case, as the determination value, a value measured in advance with a relative ratio r1 or more can be used.

  When it is determined in step S42 that the relative ratio Y is greater than the determination value, the control unit 50 determines that the hydrocarbon fuel has not been ignited (step S43). Thereafter, the control unit 50 ends the execution of the flowchart. When it is not determined in step S42 that the relative ratio Y is greater than the determination value, the control unit 50 determines that the hydrocarbon fuel has ignited (step S44). Thereafter, the control unit 50 ends the execution of the flowchart.

  According to the flowchart of FIG. 12, ignition and non-ignition of hydrocarbon fuel can be determined based on the relative ratio of the output value of the oxygen sensor 10 to a plurality of types of applied voltages. In this case, there is an advantage that the influence of the change over time can be avoided as compared with the method using the absolute value of the output value of the oxygen sensor 10. Note that the ignition and non-ignition of the hydrocarbon fuel can also be determined based on the relative ratio between the detected oxygen concentration in the first range and the detected oxygen concentration in the second range, using the same flowchart as in FIG.

As described above, in the present embodiment, ignition and non-ignition of the hydrocarbon fuel can be determined according to the oxygen concentration detected by the oxygen sensor 10. This determination is made possible for the first time by paying attention to the phenomenon in which the hydrocarbon fuel is dissociated by the catalytic function of the oxygen sensor 10. Furthermore, due to the relationship between the voltage applied to the oxygen sensor 10 and the redox potential of H ₂ O / H ₂ , the redox potential of CO ₂ / CO, and the redox potential of CO ₂ / C, By paying attention to the phenomenon that the detected oxygen concentration increases in a plurality of stages, ignition and non-ignition of the hydrocarbon fuel can be determined more accurately.

As described in FIGS. 4 to _6, the redox potential of _{H 2} O / H 2 is _PH 2 O: dominated by PH _2, the redox potential of _CO 2 / CO is _PCO 2: dominated by PCO The Therefore, depending on the ratio of PH ₂ O: PH ₂ and PCO ₂ : PCO, the redox potential of H ₂ O / H ₂ may be higher than the redox potential of CO ₂ / CO. In this case, the second range appears in a voltage range that is greater than or equal to the CO ₂ / CO redox potential and less than the H ₂ O / H ₂ redox potential, and the third range is the H ₂ O / H ₂ redox potential. It appears in the above voltage range.

  In this embodiment, methane is used as the hydrocarbon fuel, but the present invention is not limited to this. Even when a hydrocarbon fuel other than methane, for example, city gas, propane gas, kerosene, gasoline, light oil, or the like is used, ignition and non-ignition of the hydrocarbon fuel can be determined according to the above procedure.

  Next, an example in which the ignition / fire detection apparatus is applied to a fuel cell system will be described. FIG. 13 is a schematic diagram illustrating an overall configuration of a fuel cell system 200 according to the second embodiment. As shown in FIG. 13, the fuel cell system 200 includes a control unit 110, a fuel pump 121, a reforming water supply unit 130, air pumps 140a and 140b, a reformer 150, a fuel cell 160, and an oxygen sensor 170. In the present embodiment, for example, a solid oxide fuel cell (SOFC) can be used as the fuel cell 160. The oxygen sensor 170 has the same structure as the oxygen sensor 10 according to the first embodiment.

  The reformed fuel supply unit 120 includes a fuel pump 121 and a fuel flow meter 122. The reforming water supply unit 130 includes a heat exchanger 131, a condensed water tank 132, and a reforming water pump 133. The reformer 150 includes a reforming unit 151, a combustion chamber 152, and ignition means 153. The fuel cell 160 includes a cathode 161 and an anode 162, and an oxygen ion conductive electrolyte between the cathode 161 and the anode 162.

  The control unit 110 includes a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), and the like. The control unit 110 controls each part of the fuel cell system 200 based on detection results given from the fuel flow meter 122 and the oxygen sensor 170.

  The fuel pump 121 is a pump that supplies reformed fuel stored in the reformed fuel tank or city gas, kerosene, and the like supplied from the gas pipe to the reforming unit 151 in accordance with an instruction from the control unit 110. The heat exchanger 131 performs heat exchange between the tap water and the exhaust gas from the combustion chamber 152. The condensed water tank 132 is a tank that stores condensed water of exhaust gas from the combustion chamber 152. The reforming water pump 133 is a pump that supplies condensed water stored in the condensed water tank 132 to the reforming unit 151 as reforming water in accordance with an instruction from the control unit 110.

  In the reforming unit 151, a reformed gas containing hydrogen is generated from the reformed fuel from the fuel pump 121 and the air from the air pump 140a by a partial oxidation reaction. After the reformer 150 is warmed up, reformed gas is generated from the reformed fuel from the fuel pump 121 and the steam from the reformed water pump 133 by a steam reforming reaction.

  The air pump 140 b supplies a necessary amount of air to the cathode 161 in accordance with an instruction from the control unit 110. At the cathode 161, oxygen in the air is converted into oxygen ions. Oxygen that has not been converted into oxygen ions at the cathode 161 is supplied to the combustion chamber 152 as cathode offgas.

The reformed gas generated in the reforming unit 151 is supplied to the anode 162. In the anode 162, water is generated and electric power is generated from the oxygen ions converted in the cathode 161 and the hydrogen supplied to the anode 162. The generated electric power is used for a load such as a motor (not shown). The generated water becomes water vapor by the heat generated in the fuel cell 160. Water vapor generated at the anode 162, hydrogen that did not react with oxygen ions, reformed gas containing hydrogen that did not react with the reforming unit 151, hydrocarbons that did not react with the reforming unit 151, CO, CO ₂ and water vapor are supplied to the combustion chamber 152 as anode off gas.

  In the combustion chamber 152, anode off-gas and cathode off-gas are supplied. The ignition means 153 ignites the combustible component contained in the anode off gas according to the instruction from the control unit 110. In this case, the cathode off gas is used as the oxygen source. The combustion heat by the combustion reaction in the combustion chamber 152 is used for the steam reforming reaction in the reforming section 151. Exhaust gas generated by the combustion reaction is discharged to the outside. The oxygen sensor 170 detects the oxygen concentration in the combustion chamber 152 or on the downstream side of the combustion chamber 152.

  Also in the present embodiment, the control unit 110 can determine whether the hydrocarbon fuel is ignited or not ignited in the combustion chamber 152 based on the oxygen concentration detected by the oxygen sensor 170.

  Here, in the fuel cell 160, water is generated at the anode. Therefore, moisture is contained in the anode off gas. Since the anode off-gas is supplied as fuel to the combustion chamber 152, the exhaust gas from the combustion chamber 152 also contains water vapor. In this case, if an attempt is made to determine ignition and non-ignition using a temperature sensor, there is a possibility that an error occurs in the detection value of the temperature sensor. For example, the higher the amount of water vapor in the vicinity of the temperature sensor, the slower the combustion specific temperature rise. Therefore, the responsiveness of ignition detection is reduced.

  However, the influence of the water vapor concentration can be avoided by determining the ignition and misfire of the fuel based on the oxygen concentration detected by the oxygen sensor 170 as in this embodiment. Therefore, the effect of the present invention is particularly great for a combustion apparatus into which water vapor flows. In the present embodiment, a fuel cell including an oxygen ion conductive electrolyte is used as an example, but a fuel cell including a proton conductive electrolyte may be used.

DESCRIPTION OF SYMBOLS 10 Oxygen sensor 11 Electrolyte 12 Anode 13 Cathode 14 Cover 20 Ammeter 30 Sensor power supply 50 Control part 100 Light misfire detection apparatus

Claims (18)

An oxygen sensor for detecting an oxygen concentration in a combustion chamber for burning hydrocarbon fuel or downstream of the combustion chamber;
Based on the difference or relative ratio between the first output value of the oxygen sensor at a first applied voltage to the oxygen sensor and the second output value of the oxygen sensor at a second applied voltage. And a determination unit that determines at least one of ignition and misfire.   The said determination means determines that the said hydrocarbon fuel has ignited when the absolute value of the difference of the said 1st output value and the said 2nd output value is below a predetermined value. Misfire detection device.   The determination means determines that the hydrocarbon fuel has ignited when a relative ratio of a high output value to a low output value of the first output value and the second output value is equal to or less than a predetermined value. The misfire detection apparatus according to claim 1.   The first applied voltage and the second applied voltage are values in a voltage range in which an inclination of the output of the oxygen sensor with respect to the applied voltage is a predetermined value or less. The misfire detection apparatus described in 1. The first applied voltage is a value in a first voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value when the applied voltage is increased from zero.
The second applied voltage is a value in a second or third voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value when the applied voltage is increased from zero. The misfire detection apparatus according to any one of claims 1 to 4. The first applied voltage is a value in a voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value below the redox potential of H ₂ O / H _{2 and} the redox potential of CO ₂ / CO. The ignition / misfire detection apparatus according to any one of claims 1 to 5, wherein: The second applied voltage, any one of the preceding claims, characterized in that the value of at least one or more of the voltage range of the redox potential of H 2 oxidation-reduction potential of the _{O /} H ₂ and CO 2 _/ CO The misfire detection apparatus according to item 1.   The ignition / misfire detection apparatus according to claim 2 or 3, wherein the determination unit determines that the hydrocarbon fuel is not ignited when the output of the oxygen sensor is equal to or less than a predetermined value. An oxygen sensor for detecting an oxygen concentration in a combustion chamber for burning hydrocarbon fuel or downstream of the combustion chamber;
And a determination unit that determines that the hydrocarbon fuel is not ignited when an output of the oxygen sensor is equal to or less than a predetermined value.   A first output value of the oxygen sensor and a second applied voltage at a first applied voltage to an oxygen sensor for detecting an oxygen concentration in a combustion chamber for burning hydrocarbon fuel or downstream of the combustion chamber. A determination step of determining at least one of ignition and misfiring of the hydrocarbon fuel based on a difference or a relative ratio with a second output value of the oxygen sensor.   The determination step is a step of determining that the hydrocarbon fuel has ignited when an absolute value of a difference between the first output value and the second output value is equal to or less than a predetermined value. Item 15. The misfire detection method according to Item 10.   The determination step is a step of determining that the hydrocarbon fuel has ignited when a relative ratio of a high output value to a low output value of the first output value and the second output value is equal to or less than a predetermined value. The misfire detection method according to claim 10.   The said 1st applied voltage and the said 2nd applied voltage are the values of the voltage range from which the inclination of the output of the said oxygen sensor with respect to an applied voltage becomes below a predetermined value, The any one of Claims 10-12 characterized by the above-mentioned. The misfire detection method described in 1. The first applied voltage is a value in a first voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value when the applied voltage is increased from zero.
The second applied voltage is a value in a second or third voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value when the applied voltage is increased from zero. The misfire detection method according to any one of claims 10 to 13. The first applied voltage is a value in a voltage range in which the slope of the output of the oxygen sensor with respect to the applied voltage is less than or equal to a predetermined value below the redox potential of H ₂ O / H _{2 and} the redox potential of CO ₂ / CO. The method of detecting misfire according to any one of claims 10 to 14, wherein the method is provided. The second applied voltage is a value in a voltage range of at least one of an oxidation-reduction potential of H ₂ O / H _{2 and} an oxidation-reduction potential of CO ₂ / CO. The misfire detection method according to item 1.   The ignition / misfire detection method according to claim 11 or 12, wherein, in the determination step, when the oxygen sensor output is equal to or less than a predetermined value, it is determined that the hydrocarbon fuel is not ignited.   A determination step of determining that the hydrocarbon fuel is not ignited when an output of an oxygen sensor for detecting an oxygen concentration in a combustion chamber for burning hydrocarbon fuel or downstream of the combustion chamber is a predetermined value or less; A misfire detection method comprising:

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