JP2007278244A - Internal combustion engine using reformed gas - Google Patents

Abstract

A reformed gas-utilizing internal combustion engine that can generate and add reformed gas only when fuel consumption can be reliably improved.
Reforming conditions are acquired (step S100), and reforming efficiency under the conditions is predicted (step S102). Further, a fuel efficiency improvement rate is calculated when the reformed gas is added to the hydrocarbon-based fuel under the current operating conditions (step S104). Then, based on the reforming efficiency and the fuel efficiency improvement rate, the reforming process is performed by the fuel reformer under the current operating conditions, and the obtained reformed gas is added to the hydrocarbon-based fuel for operation. A total fuel consumption improvement rate is calculated (step S106). The overall fuel efficiency improvement rate is compared with a reference value (step S108). When the overall fuel efficiency improvement rate exceeds the reference value, generation and addition of reformed gas are executed (step S110). Generation and addition are stopped (step S112).
[Selection] Figure 4

Description

  The present invention includes a fuel reformer that reforms a fuel to generate a reformed gas containing hydrogen gas, and can be used by adding the reformed gas obtained by the reforming process to a hydrocarbon-based fuel. The present invention relates to an internal combustion engine using reformed gas.

  Conventionally, as disclosed in, for example, Patent Document 1, an internal combustion engine that uses hydrogen gas as a fuel together with a hydrocarbon-based liquid fuel such as gasoline is known. Since hydrogen gas is more combustible than liquid fuel, adding hydrogen gas to liquid fuel can extend the combustion limit to the lean side, enabling super lean burn operation with excellent fuel efficiency. Become. In addition, knocking can be suppressed by adding hydrogen gas to the liquid fuel at high loads, and high-efficiency operation in a high-load region becomes possible by expanding the knock limit.

In the technique described in Patent Document 1, a hydrogen tank is used as a supply source of hydrogen gas. However, in this method of storing hydrogen gas in a gaseous state, it is difficult to mount hydrogen gas sufficiently because the mounting efficiency on a vehicle is not good, and the situation where hydrogen gas can be used is limited. Therefore, as disclosed in Patent Document 2 and Patent Document 3, a technology has been proposed in which a reformer that reforms a liquid hydrogen compound is provided and hydrogen gas is generated on the vehicle by reforming the hydrogen compound. . In the technique described in Patent Document 2, a hydrocarbon fuel, specifically decalin, is used as the hydrogen compound to be reformed. In the technique described in Patent Document 3, a hydrocarbon fuel, specifically methylcyclohexane, is used as a hydrogen compound to be reformed. According to these methods, the hydrogen gas is more easily mounted on a vehicle than when it is stored in a gaseous state, the usable amount of hydrogen gas per replenishment is remarkably increased, and hydrogen is more widely used. It becomes possible to use gas.
JP 2004-116398 A JP 2004-10051 A Japanese Patent Laying-Open No. 2005-147124

  However, when a hydrogen compound is reformed to obtain hydrogen gas (specifically, a reformed gas containing a large amount of hydrogen gas), there is a considerable heat loss during the reforming process. In order to comprehensively determine the fuel consumption, heat loss during the reforming process should be taken into consideration in the fuel consumption. In this case, the fuel consumption is not always improved by the addition of hydrogen gas. For example, when reforming is performed using a catalyst, the reforming efficiency of the hydrogen compound varies greatly depending on the catalyst temperature. If the reforming efficiency is too low, the heat loss is relatively large with respect to the amount of hydrogen gas produced by the reforming, so that the overall fuel consumption is worsened by performing the reforming process. there is a possibility.

  The present invention has been made to solve the above-described problems, and the internal combustion engine using reformed gas that can generate and add the reformed gas only when the fuel consumption can be reliably improved. The purpose is to provide an institution.

In order to achieve the above object, a first invention includes a fuel reformer that reforms a hydrogen compound to generate a reformed gas containing hydrogen gas, and performs the reforming process by the fuel reformer. First, the first operation mode in which the optimum operation is performed using only the hydrocarbon fuel, the reforming process by the fuel reformer is performed, and the obtained reformed gas is added to the hydrocarbon fuel for the optimum operation. In the internal combustion engine using reformed gas that can select the second operation mode in which
Reforming condition acquisition means for acquiring reforming conditions in the fuel reformer;
First index value calculation means for calculating a first index value that is an index of predicted reforming efficiency when the reforming process is performed by the fuel reformer under the obtained reforming conditions;
This is an indicator of the fuel efficiency improvement rate when the optimal operation is performed using only the hydrocarbon fuel when the reformed gas is added to the hydrocarbon fuel under the current operating conditions and the optimal operation is performed. 2nd index value calculation means for calculating 2 index values;
Based on the first index value and the second index value, it becomes an index of the overall fuel consumption improvement rate when the first operation mode is selected when the second operation mode is selected under the current operation condition. Third index value calculating means for calculating a third index value;
The third index value is compared with a predetermined reference value, and when the third index value exceeds the reference value, the second operation mode is selected, and when the third index value is equal to or less than the reference value, the first index value is selected. An operation mode selection means for selecting an operation mode;
It is characterized by having.

According to a second invention, in the first invention,
The optimum operation in the first operation mode is stoichiometric operation or lean burn operation, and the optimum operation in the second operation mode is a super lean burn operation realized by addition of reformed gas, and the current operation condition is satisfied. Accordingly, the addition ratio of the reformed gas is set.

According to a third invention, in the first invention,
The internal combustion engine is an internal combustion engine for a hybrid vehicle that is mounted on a hybrid vehicle and drives the vehicle in cooperation with a motor;
The optimum operation in the first operation mode is a high load region operation near the knock limit, and the optimum operation in the second operation mode is a high load region operation near the knock limit that is expanded by addition of reformed gas. The reforming gas addition ratio is set according to the current operating conditions.

  According to the first invention, the reforming process by the fuel reformer is performed only when the total fuel efficiency improvement rate considering the reforming efficiency exceeds the reference value, and the reforming obtained by the reforming process is performed. The internal combustion engine is operated by adding gas to the hydrocarbon-based fuel. When the overall fuel efficiency improvement rate considering the reforming efficiency is below the reference value, the reforming process by the reformer is not performed, and the internal combustion engine is operated using only the hydrocarbon-based fuel as fuel. As a result, it is possible to prevent wasteful reforming processing and use of wasteful reformed gas that do not contribute to improvement of fuel consumption, and to improve fuel efficiency reliably as a whole.

  According to the second invention, when the super lean burn operation is performed by adding the reformed gas, it is possible to reliably obtain the effect of improving the fuel consumption by the super lean burn operation.

  According to the third invention, when the knock limit is expanded by the addition of the reformed gas, it is possible to reliably obtain the effect of improving the fuel consumption by the high load range operation near the expanded knock limit.

  First, an outline of a reformed gas utilizing internal combustion engine as an embodiment of the present invention will be described.

  In general, if hydrogen-rich reformed gas obtained by reforming hydrogen compounds is added to hydrocarbon-based fuels, fuel efficiency can be improved by realizing ultra-lean burn operation and expanding the knock limit during high-load operation It is said. However, the fuel consumption here means the fuel consumption focused only on the amount of heat of the fuel directly subjected to combustion, and does not mean the total fuel consumption focused on the amount of heat consumed by the entire internal combustion engine. In the following, the fuel efficiency focused only on the amount of heat of the fuel used for direct combustion is referred to as simple fuel efficiency, and the overall fuel efficiency focused on the amount of heat consumed in the entire internal combustion engine is referred to as total fuel efficiency.

  When generating the reformed gas containing hydrogen gas from the hydrogen compound, there is a considerable heat loss. When the ratio of heat loss to the calorific value of the reformed gas is large, that is, when the reforming efficiency is low, if the reformed gas is generated from a hydrogen compound and added, the simple fuel efficiency is improved, but the overall fuel efficiency is reversed. May be reduced. Therefore, the reformed gas-utilizing internal combustion engine of the present embodiment first determines whether or not improvement of the total fuel consumption can be expected in consideration of the reforming efficiency. The reformed gas is generated only when the improvement of the overall fuel consumption can be expected.

  In the following, the operation mode in which the optimum operation is performed using only the hydrocarbon fuel is defined as the first operation mode, the reformed gas is generated from the hydrogen compound on the vehicle, and the obtained reformed gas is converted into the hydrocarbon system. The operation mode in which the optimum operation is performed by adding to the fuel is defined as the second operation mode. The term “optimal operation” as used herein means an operation that can achieve the best or equivalent fuel consumption within a range in which exhaust emission and drivability can be satisfactorily maintained under the current operating conditions. For example, in the case of an internal combustion engine that uses gasoline as a hydrocarbon-based fuel, when the internal combustion engine is operated in a low-medium load range, the optimum operation in the first operation mode can be stoichiometric operation. The optimum operation in the second operation mode in the load region can be a super lean burn operation with an excess air ratio of 2 or more.

In the present embodiment, the total fuel consumption improvement rate is calculated as an index for determining which of the first operation mode and the second operation mode is selected. The total fuel consumption improvement rate means the improvement rate of the total fuel consumption with respect to the case of driving in the first driving mode when driving in the second driving mode under the current driving conditions. The overall fuel efficiency improvement rate is expressed by the following equation (1).
Total fuel efficiency improvement rate = G0 / ((G1-C × G2) + G2)) (1)

  In the above equation (1), G0 is the amount of fuel supplied to the combustion chamber in the first operation mode, and G1 is the amount of fuel supplied to the combustion chamber in the second operation mode (fuel amount converted to hydrocarbon fuel). ). G2 is the amount of hydrogen compound used for reforming (the amount of fuel converted to hydrocarbon fuel), and C is the reforming efficiency. Therefore, C × G2 means the amount of reformed gas obtained by reforming (the amount of fuel converted to hydrocarbon-based fuel), and subtracting C × G2 from G1 (G1−C × G2) is the second It means the amount of hydrocarbon fuel supplied to the combustion chamber in the operation mode. That is, the sum of the amount of hydrocarbon fuel (G1-C × G2) supplied to the combustion chamber and the amount of hydrogen compound G2 used for reforming is consumed in the entire internal combustion engine in the second operation mode. Fuel amount.

On the other hand, the improvement rate of the simple fuel consumption realized by adding the reformed gas to the hydrocarbon fuel is expressed by the following equation (2). That is, the ratio of the fuel amount G0 supplied to the combustion chamber in the first operation mode to the fuel amount G1 supplied to the combustion chamber in the second operation mode becomes the simple fuel consumption improvement rate.
Simple fuel efficiency improvement rate = G0 / G1 (2)

  As can be seen by comparing the above equations (1) and (2), if the reforming efficiency C is 1 (that is, 100%), the overall fuel efficiency improvement rate is equal to the simple fuel efficiency improvement rate. However, since the reforming efficiency C is actually less than 1, the overall fuel efficiency improvement rate is lower than the simple fuel efficiency improvement rate. As is clear from equation (1), the lower the reforming efficiency C, the lower the overall fuel efficiency improvement rate.

  The calculation formula for calculating the reforming efficiency C is different depending on the reforming method. For example, when a hydrocarbon-based fuel is used as the hydrogen compound, examples of the reforming method include a method using a reforming catalyst and a method using low-temperature plasma. Specific examples of the method using the reforming catalyst include a reforming method using a partial oxidation reaction, a reforming method using a steam reforming reaction, or a reforming method using a combination thereof. Further, a reformed gas containing hydrogen can be obtained by dehydrogenating an organic hydride (for example, methylcyclohexane) with a reforming catalyst. In the method using low temperature plasma, specifically, the hydrocarbon fuel is decomposed into a gas component containing hydrogen by performing direct current pulse discharge (LEP discharge) on the hydrocarbon fuel.

In the case of a reforming method using a partial oxidation reaction, the reforming efficiency C can be calculated by the following equation (3). The total reformed gas generation amount means the total calorific value of the combustible gas contained in the reformed gas. For example, when the reformed gas contains hydrogen, carbon monoxide, carbon dioxide, water vapor, methane and nitrogen as its components, the total calorific value of the combustible gases hydrogen, carbon monoxide and methane is the total calorific value of the reformed gas. Is calculated as The calorific value of the raw material is the calorific value of the hydrocarbon fuel used for generating the reformed gas. Note that since the partial oxidation reaction is an exothermic reaction, it is not necessary to supply heat necessary for the reaction to proceed.
Reforming efficiency C = reformed gas heating value / raw material heating value (3)

In the case of a reforming method using a steam reforming reaction, the reforming efficiency C can be calculated by the following equation (4). Since the steam reforming reaction is an endothermic reaction, it is necessary to supply heat from the outside in order to advance the reaction. In addition, when utilizing the waste heat of an internal combustion engine as a heat source, the amount of supplied heat can be reduced and the reforming efficiency can be increased accordingly.
Reforming efficiency C = reformed gas heat generation amount / (raw material heat generation amount + supplied heat amount) (4)

In the case of a reforming method using a dehydrogenation reaction of an organic hydride, the reforming efficiency C can be calculated by the following equation (5). Since the dehydrogenation reaction is an endothermic reaction, it is necessary to supply heat from the outside in order to advance the reaction. When the waste heat of the internal combustion engine is used as a heat source, the amount of supplied heat can be reduced correspondingly to increase the reforming efficiency.
Reforming efficiency C = reformed gas heat generation amount / (raw material heat generation amount + supply heat amount) (5)

In the case of the reforming method using low temperature plasma, the reforming efficiency C can be calculated by the following equation (6). The amount of heat supplied in equation (6) means the amount of heat necessary to drive the power generator and generate electrical energy for discharge. An alternator or a regenerative power generator can be used as the power generator.
Reforming efficiency C = reformed gas heat generation amount / (raw material heat generation amount + supply heat amount) (6)

In the present embodiment, using the simple fuel consumption improvement rate calculated by the above equation (2) and the reforming efficiency calculated by any one of the above equations (3) to (6), for example, The total fuel efficiency improvement rate is calculated by the equation (7). In the formula (7), A is a simple fuel consumption improvement rate and C is a reforming efficiency. B is a hydrogen equivalent gas addition ratio, and D is a hydrogen equivalent gas ratio in the reformed gas.
Overall fuel efficiency improvement rate = A / (1-B / D + B / (D × C)) (7)

  The hydrogen equivalent gas addition ratio B is defined as the ratio of the total calorific value of the hydrogen equivalent gas to the total calorific value of the fuel (hydrocarbon fuel and reformed gas) supplied to the combustion chamber in the second operation mode. The hydrogen equivalent gas ratio D in the reformed gas is defined as the ratio of the total calorific value of the hydrogen equivalent gas to the total calorific value of the reformed gas. The hydrogen equivalent gas means hydrogen gas and a gas (for example, acetylene) corresponding to hydrogen gas in terms of combustibility among gas components contained in the reformed gas.

  In the above equation (7), the hydrogen equivalent gas addition ratio B is a value determined by the operating conditions of the internal combustion engine, and the hydrogen equivalent gas ratio D in the reformed gas is a value determined by the reforming method and reforming conditions. These values can be obtained in advance by experiments or the like. The simple fuel consumption improvement rate A is also a value determined by driving conditions, and this value can also be obtained in advance by experiments or the like. Further, the reforming efficiency C is a value determined by the reforming conditions, and this value can also be obtained in advance by experiments or the like. In the present embodiment, a map in which the values of A, B, C, and D are associated with each related condition is prepared, and each value corresponding to the condition is read from the map during operation of the internal combustion engine ( 7) Calculate the formula.

  When the total fuel efficiency improvement rate calculated by the equation (7) is 1 or less, there is no merit of generating and using the reformed gas at least from the viewpoint of fuel efficiency. On the other hand, when the overall fuel efficiency improvement rate is greater than 1, there is an advantage of generating and using the reformed gas at least from the viewpoint of fuel efficiency. Therefore, when the total fuel efficiency improvement rate is 1 or less, the reformed gas is not generated, and the internal combustion engine is operated using only the hydrocarbon-based fuel as fuel. If the overall fuel efficiency improvement rate is greater than 1, reformed gas is generated, and the generated reformed gas is added to the hydrocarbon-based fuel to operate the internal combustion engine. As a result, it is possible to prevent wasteful reforming processing and use of wasteful reformed gas that do not contribute to improvement of fuel consumption, and to improve fuel efficiency reliably as a whole.

  It is not determined based on whether or not the overall fuel efficiency improvement rate is greater than 1, but a reference value is determined in consideration of other merits or demerits other than fuel efficiency, and whether or not the overall fuel efficiency improvement rate is greater than the reference value. It may be determined whether or not the reformed gas is generated.

  Hereinafter, more specific embodiments of the present invention will be described with reference to the drawings.

Embodiment 1 FIG.
First, Embodiment 1 of the present invention will be described with reference to FIGS.

  FIG. 1 is a diagram showing a system configuration of a reformed gas-utilizing internal combustion engine as Embodiment 1 of the present invention. The reformed gas utilizing internal combustion engine of the present embodiment includes an engine body 2 configured as a spark ignition type four-stroke engine. Although not shown, the engine body 2 has a plurality of cylinders. A combustion chamber 12 is provided for each cylinder, and a spark plug 14 is attached to the top of each combustion chamber 12. The combustion chamber 12 is connected with an intake passage 4 through which new gas is introduced and an exhaust passage 6 through which combustion gas is discharged. An intake valve 8 for controlling the communication state is provided at a connection portion between the combustion chamber 12 and the intake passage 4, and an exhaust valve 10 for controlling the communication state is provided at a connection portion between the combustion chamber 12 and the exhaust passage 6. It has been. A throttle 18 for adjusting the amount of intake air is disposed in the intake passage 4.

  An injector 16 for supplying fuel to the combustion chamber 12 is attached downstream of the throttle 18 and upstream of the intake valve 8. The injector 16 is provided for each cylinder. The fuel injected from the injector 16 is a hydrocarbon fuel such as gasoline, and this fuel is stored in the fuel tank 20. The fuel is sucked up from the fuel tank 20 by the fuel pump 22 and supplied to the injector 16 of each cylinder.

  The reformed gas utilizing internal combustion engine of the present embodiment is configured such that a reformed gas obtained by reforming a hydrocarbon fuel can be used as a fuel in addition to the hydrocarbon fuel injected from the injector 16. . Further, the reformed gas utilizing internal combustion engine of the present embodiment includes a fuel reformer 30 in order to generate reformed gas on the vehicle without receiving external supply.

  The fuel reformer 30 generates a reformed gas containing hydrogen gas using a hydrocarbon-based fuel stored in the fuel tank 20 as a raw material. The fuel reformer 30 according to the present embodiment employs a reforming method using a partial oxidation reaction by a reforming catalyst. However, any of the above-described methods can be adopted as the reforming method according to the present invention, and the reforming method is not limited to the partial oxidation reaction by the reforming catalyst. When a different reforming method is employed, a fuel reformer having a configuration corresponding to the method may be provided.

  The fuel reformer 30 includes a reformer 32 in which a reforming catalyst is disposed. In the reformer 32, a mixture of hydrocarbon fuel and air is supplied onto the reforming catalyst, whereby a partial oxidation reaction of the hydrocarbon fuel occurs and a reformed gas containing hydrogen gas is generated. It is like that.

  The reforming efficiency of the hydrocarbon fuel depends on the temperature of the reforming catalyst. When the catalyst temperature does not reach the activation temperature, or when the catalyst temperature is below the appropriate temperature range where the activation temperature is reached but the reforming efficiency is maximized, sufficient reforming efficiency cannot be obtained. For this reason, the reformer 32 is provided with a temperature sensor 72 for monitoring the catalyst temperature.

  Connected to the reformer 32 is a premixer 36 for supplying hydrocarbon fuel and air to the reformer 32 in a premixed state. A reformed fuel injector 38 for supplying a hydrocarbon-based fuel for reforming into the premixer 36 is attached to the premixer 36. The reformed fuel injector 38 is connected to the same fuel tank 20 to which the injector 16 provided in each cylinder is connected. The fuel sucked up from the fuel tank 20 by the fuel pump 22 is distributed to the injector 16 of each cylinder and the reformed fuel injector 38 of the fuel reformer 30.

  The premixer 36 is connected to an air passage 44 for supplying air into the premixer 36. An air intake 50 is formed in the intake passage 4 upstream of the throttle 18, and the other end of the air passage 44 is connected to the air intake 50. A blower 40 is disposed in the air passage 44, and reforming air taken from the air intake 50 by the blower 40 is supplied to the premixer 36 through the air passage 44. The blower 40 is provided with a flow rate control valve for adjusting the flow rate of air supplied to the premixer 36. The hydrocarbon-based fuel and air thus supplied to the premixer 36 are uniformly mixed in the premixer 34 to form a mixture, and this mixture is supplied to the reformer 32.

  A heat exchanger 34 is provided adjacent to the reformer 32. The air passage 44 passes through the heat exchanger 34. The partial oxidation reaction occurring in the reformer 32 is an exothermic reaction, and the temperature of the reforming catalyst rises as the reaction proceeds. The reforming efficiency of the reformed gas decreases even if the catalyst temperature is too high. Further, if the catalyst temperature is too high, the reforming catalyst may be deteriorated. In the fuel reformer 30, the temperature rise of the reforming catalyst is suppressed by cooling the reformer 32 by heat exchange with the air flowing through the heat exchanger.

  The reformed gas generated by the partial oxidation reaction in the reformer 32 is supplied into the intake passage 4 through the reformed gas passage 46 connecting the reformer 32 and the intake passage 4. A reformed gas supply port 52 is formed in the intake passage 4 upstream of the throttle 18 and downstream of the air intake 50, and the reformed gas passage 46 is connected to the reformed gas supply port 52. The reformed gas passage 46 intersects with the air passage 44, and the heat exchanger 42 is disposed at the intersection. The reformed gas is cooled by heat exchange in the heat exchanger 42.

  The reformed gas-utilizing internal combustion engine of this embodiment includes an ECU (Electronic Control Unit) 70 as a control device that controls the operation of the entire system. Based on signals from a plurality of sensors in the system including the temperature sensor 72, the ECU 70 comprehensively includes various devices related to the operation of the system, such as the injector 16, the spark plug 14, the throttle 18, the fuel reformer 30, and the like. I have control. Regarding the fuel reformer 30, the ECU 70 controls the reformed fuel injector 38 and the blower 40.

  Below, control of the fuel reformer 30 implemented by ECU70 is demonstrated. In the present embodiment, the reformed gas is used to expand the lean limit in the low and medium load range. The reformed gas obtained by the partial oxidation reaction of hydrocarbon fuel contains a large amount of hydrogen gas excellent in combustibility. For this reason, by adding the reformed gas to the air-fuel mixture supplied into the combustion chamber 12, the combustion limit can be expanded to the lean side, and the super lean burn operation can be realized. The flowchart of FIG. 4 shows a control routine executed by the ECU 70 when the engine main body 2 is in the low / medium load range.

  In the first step S100 of the routine shown in FIG. 4, the reforming conditions for executing the reforming process in the fuel reformer 30 are acquired. Here, conditions that have a particularly large influence among conditions affecting reforming efficiency, such as the temperature of the reforming catalyst, the amount of water vapor contained in the intake air, and the amount of fuel supplied from the reforming fuel injector 38, are acquired as reforming conditions. Is done. The amount of steam is mentioned as the reforming condition because steam reforming reaction can also occur in parallel when steam is contained in the air. Further, the reason why the fuel supply amount is mentioned as the reforming condition is that the generation ratio of each component contained in the reformed gas also changes according to the fuel amount. When a method other than the reforming catalyst is selected as the reforming method, conditions different from the above are selected as the reforming conditions. For example, when reforming is performed using low temperature plasma, the power generation efficiency of the power generation apparatus may be selected as one of the reforming conditions.

  In the next step S102, the reforming efficiency is calculated based on the acquired reforming conditions. Specifically, the value of the reforming efficiency corresponding to the reforming condition is read from a map created in advance. FIG. 2 is a graph showing the relationship between the reforming catalyst temperature and the reforming efficiency when a plurality of reforming conditions other than the reforming catalyst temperature are fixed. A map obtained by determining the relationship between the reforming catalyst temperature and the reforming efficiency by changing the reforming conditions other than the reforming catalyst temperature is recorded on the map.

  In the next step S104, the fuel efficiency improvement rate is calculated when the super lean burn operation is performed by adding hydrogen gas (reformed gas) under the current operating conditions. The fuel efficiency improvement rate here is a simple fuel efficiency improvement rate that does not consider the reforming efficiency. The hydrogen gas addition rate is determined by the current operating conditions, and a simple fuel consumption improvement rate corresponding to the hydrogen gas addition rate is required. The relationship between the operating conditions, the hydrogen gas addition rate, and the relationship between the hydrogen gas addition rate and the simple fuel efficiency improvement rate is stored in the map, and necessary information is read out from the map.

  In the next step S106, an overall fuel efficiency improvement rate considering the reforming efficiency is calculated. Specifically, the total fuel consumption improvement rate is calculated by the above equation (7). The value of the reforming efficiency obtained in step S102 is substituted for C in the equation (7), and the value of the simple fuel consumption improvement rate obtained in step S104 is substituted for A in the equation (7). The value of the hydrogen-equivalent gas addition ratio corresponding to the current operating condition is read from the map and assigned to B in the equation (7). In addition, the value of the hydrogen-equivalent gas ratio in the reformed gas corresponding to the reforming condition is read from the map and assigned to D in the equation (7).

  FIG. 3 is a graph showing the relationship between the overall fuel efficiency improvement rate and the reforming efficiency when the values of A, B, and C are fixed in equation (7). Here, the hydrogen equivalent gas addition ratio B is 0.2, and the hydrogen equivalent gas ratio D in the reformed gas is 0.43. When the hydrogen equivalent gas addition ratio B is set to 0.2, the super lean burn operation with an excess air ratio of 2 can be realized, and the simple fuel consumption can be improved by 18%. That is, in this case, the simple fuel consumption improvement rate A is 1.18. In the example shown in FIGS. 2 and 3, when the reforming catalyst temperature is 650 ° C., the reforming efficiency is about 0.7, and the overall fuel efficiency improvement rate is smaller than 1. On the other hand, when the reforming catalyst temperature is 750 ° C., the reforming efficiency is about 0.8, and the overall fuel efficiency improvement rate is greater than 1.

  In step S108, it is determined whether or not the overall fuel efficiency improvement rate calculated in step S106 is greater than one. If the overall fuel efficiency improvement rate is greater than 1, it can be determined that there is a merit of performing the reforming process by the fuel reformer 30 and adding the obtained hydrogen gas to the hydrocarbon-based fuel at least from the viewpoint of fuel efficiency. On the other hand, when the overall fuel efficiency improvement rate is 1 or less, at least from the viewpoint of fuel efficiency, it can be determined that there is no merit of adding hydrogen gas to the hydrocarbon-based fuel until the reforming process is executed.

  Thus, if the result of determination in step S108 is that the overall fuel efficiency improvement rate is greater than 1, the process of step S110 is executed. In step S110, the reforming of the hydrocarbon-based fuel is performed by the operation of the fuel reformer 30. Then, hydrogen gas (reformed gas) obtained by reforming the hydrocarbon fuel is supplied to the combustion chamber 12 together with the hydrocarbon fuel injected from the injector 16. In the engine body 2, a super lean burn operation is performed by adding hydrogen gas. In the present embodiment, the super lean burn operation by the addition of hydrogen gas is the optimum operation in the second operation mode described above.

  On the other hand, if the result of determination in step S108 is that the overall fuel efficiency improvement rate is 1 or less, the process of step S112 is executed. In step S112, the operation of the blower 40 and the reformed fuel injector 38 is stopped, and the reforming of the hydrocarbon fuel and the supply of hydrogen gas to the combustion chamber 12 are both stopped. In the engine body 2, the super lean burn operation is not performed, and the stoichiometric operation using only the hydrocarbon-based fuel injected from the injector 16 is performed. In the present embodiment, the stoichiometric operation using the hydrocarbon-based fuel is the optimum operation in the first operation mode described above.

  By executing the routines described above, it is possible to prevent unnecessary reforming treatment and wasteful use of hydrogen gas that do not contribute to improving fuel efficiency, and to reliably obtain the effect of improving fuel efficiency by super lean burn operation. Will be able to.

  In the present embodiment, the ECU 70 executes the process of step S100 of the routine shown in FIG. Further, the “first index value calculating means” of the first invention is realized by executing the process of step S102, and the “second index” of the first invention is realized by executing the process of step S104. Value calculating means "is realized. Then, by executing the process of step S106, the “third index value calculating means” of the first invention is realized, and by executing the processes of steps S108, S110 and S112, "Operation mode selection means" is realized.

Embodiment 2. FIG.
Next, a second embodiment of the present invention will be described with reference to FIGS.

  The reformed gas utilizing internal combustion engine of the present embodiment is configured as an internal combustion engine for a hybrid vehicle that is mounted on a hybrid vehicle and drives the vehicle in cooperation with a motor. However, the system configuration of the reformed gas utilizing internal combustion engine itself is the same as that of the first embodiment, and the system configuration shown in FIG. 1 is adopted. There is no limitation on the combination of the engine body 2 and the motor, that is, the configuration of the hybrid system.

  In the hybrid vehicle, the engine speed and torque of the engine body 2 can be arbitrarily controlled, and the engine body 2 can positively use a high load range. FIG. 5 is a diagram showing the relationship between the operating range of the engine body 2 and the fuel consumption. As can be seen from the relationship between the iso-output line and the iso-fuel consumption line shown in the figure, the fuel economy improves as the driving range is lower, even if the output is the same. This is because the friction loss decreases as the rotational speed decreases. Therefore, high fuel efficiency can be realized by driving in the driving range as close to the knock limit as possible.

  In the present embodiment, the reformed gas generated by the fuel reformer 30 is used for expanding the knock limit. A reformed gas obtained by reforming a hydrocarbon-based fuel contains a large amount of hydrogen gas excellent in combustibility. For this reason, knocking at high load can be suppressed by adding the reformed gas to the air-fuel mixture supplied into the combustion chamber 12, and the knock limit can be expanded as shown in FIG. According to this, it becomes possible to operate in the operation region on the higher load side as compared with the case where hydrogen gas is not added, and higher fuel efficiency can be realized. However, the fuel consumption mentioned here is simply a simple fuel consumption, and just because the simple fuel consumption is improved does not necessarily improve the overall fuel consumption. This is because the overall fuel efficiency is affected by the reforming efficiency as described above.

  Therefore, in the present embodiment, the fuel reformer 30 is controlled according to the flowchart of FIG. The flowchart of FIG. 6 shows a control routine executed by the EU 70 in the present embodiment.

  In the first step S200 of the routine shown in FIG. 6, the reforming conditions when the fuel reforming apparatus 30 executes the reforming process, specifically, the temperature of the reforming catalyst, the amount of water vapor contained in the intake air, Among the conditions affecting the reforming efficiency, such as the amount of fuel supplied from the reformed fuel injector 38, a condition that has a particularly large effect is acquired. In the next step S202, the reforming efficiency value corresponding to the reforming condition is read from a previously created map.

  In the next step S204, the addition rate of hydrogen gas (reformed gas) is determined according to the current operating conditions, and the operating range, that is, the knock limit that is expanded by the addition of hydrogen gas is determined according to the addition rate of hydrogen gas. The driving range in the vicinity is determined. And the fuel consumption improvement rate at the time of driving | running in the determined driving | operation area | region is calculated | required. The fuel efficiency improvement rate here is a simple fuel efficiency improvement rate that does not consider the reforming efficiency. The operating conditions and the hydrogen gas addition ratio, the hydrogen gas addition ratio and the operating range, and the relationship between the operating range and the simple fuel consumption improvement rate are stored in the map, and necessary information is read from the map.

  In the next step S206, an overall fuel efficiency improvement rate is calculated in consideration of the reforming efficiency. Specifically, the total fuel consumption improvement rate is calculated by the above equation (7). The value of the reforming efficiency obtained in step S202 is substituted for C in the equation (7), and the value of the simple fuel consumption improvement rate obtained in step S204 is substituted for A in the equation (7). The value of the hydrogen-equivalent gas addition ratio corresponding to the current operating condition is read from the map and assigned to B in the equation (7). In addition, the value of the hydrogen-equivalent gas ratio in the reformed gas corresponding to the reforming condition is read from the map and assigned to D in the equation (7).

  In step S208, it is determined whether or not the overall fuel consumption improvement rate calculated in step S206 is greater than one. If the overall fuel efficiency improvement rate is greater than 1, it can be determined that there is a merit of performing the reforming process by the fuel reformer 30 and adding the obtained hydrogen gas to the hydrocarbon-based fuel at least from the viewpoint of fuel efficiency. On the other hand, when the overall fuel efficiency improvement rate is 1 or less, at least from the viewpoint of fuel efficiency, it can be determined that there is no merit of adding hydrogen gas to the hydrocarbon-based fuel until the reforming process is executed.

  Thus, if the result of determination in step S208 is that the overall fuel efficiency improvement rate is greater than 1, the process of step S210 is executed. In step S210, the reforming of the hydrocarbon-based fuel is performed by the operation of the fuel reformer 30. Then, hydrogen gas (reformed gas) obtained by reforming the hydrocarbon fuel is supplied to the combustion chamber 12 together with the hydrocarbon fuel injected from the injector 16. In the engine body 2, a high load region operation is performed near the knock limit that is expanded by the addition of hydrogen gas. In the present embodiment, the high load region operation near the knock limit expanded by the addition of hydrogen gas is the optimum operation in the second operation mode described above.

  On the other hand, if the result of determination in step S208 is that the overall fuel efficiency improvement rate is 1 or less, the process of step S212 is executed. In step S212, the operation of the blower 40 and the reformed fuel injector 38 is stopped, and the reforming of the hydrocarbon fuel and the supply of hydrogen gas to the combustion chamber 12 are both stopped. In the engine body 2, only a hydrocarbon fuel injected from the injector 16 is used to perform a high load range operation near the knock limit. In the present embodiment, the high load region operation in the vicinity of the knock limit using only the hydrocarbon-based fuel is the optimum operation in the first operation mode described above.

  By executing the routine described above, it is possible to prevent wasteful reforming treatment and wasteful use of hydrogen gas that do not contribute to improving fuel efficiency, and high loads near the knock limit expanded by the addition of hydrogen gas. It is possible to reliably obtain the effect of improving the fuel consumption by the area driving.

  In the present embodiment, the ECU 70 executes the process of step S200 of the routine shown in FIG. Further, the “first index value calculating means” of the first invention is realized by executing the process of step S202, and the “second index” of the first invention is realized by executing the process of step S204. Value calculating means "is realized. Then, by executing the process of step S206, the “third index value calculating means” of the first invention is realized, and by executing the processes of steps S208, S210, and S212, the process of the first invention is realized. "Operation mode selection means" is realized.

Others.
Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and modifications can be made without departing from the spirit of the present invention. For example, the following modifications may be made.

  In the system configuration of FIG. 1, the reformed gas is supplied to the intake passage 4, but the reformed gas may be compressed by a high-pressure pump and supplied directly into the combustion chamber 12. The same applies to the injector 16, and fuel may be directly injected into the combustion chamber 12. Further, the reformed gas may be mixed with hydrocarbon fuel and injected from the injector 16.

  In the fuel reformer 30 according to the above embodiment, the reformed gas is obtained by partially oxidizing the hydrocarbon fuel, but the reformed gas is obtained by steam reforming the hydrocarbon fuel. It may be. Alternatively, hydrocarbon-based fuel, air, and steam may be supplied to the reforming catalyst, and both the partial oxidation reaction and the steam reforming reaction may be caused to obtain the reformed gas. Further, the hydrocarbon-based fuel injected from the injector 16 is not used for reforming, but a hydrogen compound dedicated to reforming is stored separately from the hydrocarbon-based fuel, and this is reformed to produce hydrogen gas. You may make it obtain.

  Moreover, you may provide the fuel reformer which dehydrogenates organic hydride and obtains hydrogen gas. In this case, the organic hydride for reforming and the hydrocarbon fuel obtained together with the hydrogen gas by reforming can be used as the main fuel injected from the injector 16.

  Furthermore, a fuel reformer that obtains hydrogen gas by a method other than the reforming catalyst may be provided. For example, an apparatus that generates hydrogen gas by decomposing a hydrogen compound by generating low-temperature plasma or an apparatus that generates hydrogen gas by electrolysis of water may be used.

It is a figure which shows the system configuration | structure of the internal combustion engine using reformed gas as Embodiment 1 of this invention. It is a graph which shows an example of the relationship between reforming catalyst temperature and reforming efficiency. It is a graph which shows an example of the relationship between a comprehensive fuel consumption improvement rate and reforming efficiency. It is a flowchart shown about the routine of control performed in Embodiment 1 of this invention. It is a figure which shows the relationship between the engine operating range and fuel consumption which are determined from an engine speed and a torque. It is a flowchart shown about the routine of control performed in Embodiment 2 of this invention.

Explanation of symbols

2 Engine body 4 Intake passage 6 Exhaust passage 12 Combustion chamber 14 Spark plug 16 Injector 18 Throttle 20 Fuel tank 22 Fuel pump 30 Fuel reformer 32 Reformer 34 Heat exchanger 36 Premixer 38 Reformed fuel injector 40 Blower 42 Heat exchanger 44 Air passage 46 Reformed gas passage 50 Air intake 52 Reformed gas supply port 70 ECU
72 Temperature sensor

Claims (3)

It has a fuel reformer that reforms a hydrogen compound to produce a reformed gas containing hydrogen gas, and does not perform the reforming process by the fuel reformer, and uses only a hydrocarbon-based fuel for optimum operation. A reformed gas capable of selecting a first operation mode to be performed and a second operation mode in which the reforming process is performed by the fuel reformer and the obtained reformed gas is added to the hydrocarbon-based fuel to perform the optimum operation. In use internal combustion engine,
Reforming condition acquisition means for acquiring reforming conditions in the fuel reformer;
First index value calculation means for calculating a first index value that is an index of predicted reforming efficiency when the reforming process is performed by the fuel reformer under the obtained reforming conditions;
This is an indicator of the fuel efficiency improvement rate when the optimal operation is performed using only the hydrocarbon fuel when the reformed gas is added to the hydrocarbon fuel under the current operating conditions and the optimal operation is performed. 2nd index value calculation means for calculating 2 index values;
Based on the first index value and the second index value, it becomes an index of the overall fuel consumption improvement rate when the first operation mode is selected when the second operation mode is selected under the current operation condition. Third index value calculating means for calculating a third index value;
The third index value is compared with a predetermined reference value, and when the third index value exceeds the reference value, the second operation mode is selected, and when the third index value is equal to or less than the reference value, the first index value is selected. An operation mode selection means for selecting an operation mode;
A reformed gas utilization internal combustion engine comprising:   The optimum operation in the first operation mode is stoichiometric operation or lean burn operation, and the optimum operation in the second operation mode is a super lean burn operation realized by addition of reformed gas, and the current operation condition is satisfied. 2. The reformed gas utilizing internal combustion engine according to claim 1, wherein the reformed gas addition ratio is set accordingly. The internal combustion engine is an internal combustion engine for a hybrid vehicle that is mounted on a hybrid vehicle and drives the vehicle in cooperation with a motor;
The optimum operation in the first operation mode is a high load region operation near the knock limit, and the optimum operation in the second operation mode is a high load region operation near the knock limit that is expanded by addition of reformed gas. 2. The internal combustion engine using reformed gas according to claim 1, wherein the ratio of addition of the reformed gas is set according to current operating conditions.

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