Ammonia Engine System

Abstract

To quickly create a great amount of combustion gas by using a combustor.SOLUTION: A combustor 40 has: a circular tubular box body 41 which is open at a first end, and closed at a second end 41b, and through which there flow an ammonia gas mixed with air, and a combustion gas generated by combustion of the ammonia gas; an introduction part for introducing the ammonia gas and the air into the box body 41 so that a tubular flow F1 is generated; an ignition plug 44 arranged at the second end 41b side in the box body 41, and having a positive electrode 45 and a negative electrode 46; and an ignition unit for generating a spark P1 between the positive electrode 45 and the negative electrode 46. A negative pressure region A1 is formed in one portion in the box body 41. The positive electrode 45 and the negative electrode 46 are arranged respectively at positions which make a distance L1 between the positive electrode 45 and the negative electrode 46 shorter than a distance L2 between the positive electrode 45 and an internal peripheral face 41d of the box body 41 so that a flame P2 generated between the positive electrode 45 and the negative electrode 46 by the spark P1 is formed only within the negative pressure region A1.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention ,a Regarding the ammonia engine system. [Background technology]

[0002] The combustor described in Patent Document 1 has a cylindrical housing, an introduction section, and an ignition plug. A first end of the housing is open and a second end of the housing is closed. Fuel mixed with oxidizing gas and combustion gas generated by burning the fuel flow inside the housing. The introduction section introduces the fuel and oxidizing gas into the housing so that a tubular flow is generated. The ignition plug is disposed at the second end inside the housing. The combustion gas is ignited by the spark plug, generating a flame inside the housing. The combustion gas is discharged from the first end of the housing. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2004-93114 Summary of the Invention [Problem to be solved by the invention]

[0004] In order to quickly discharge a large amount of combustion gas from the combustor, it has been desired to generate a large amount of combustion gas in the combustor soon after the flame is generated. [Means for solving the problem]

[0005] A combustor that solves the above problem comprises a cylindrical housing having an open first end and a closed second end, through which a fuel mixed with an oxidizing gas and a combustion gas generated by the combustion of the fuel flow; at least one inlet portion that introduces the fuel and the oxidizing gas into the housing so as to generate a tubular flow; an ignition plug disposed inside the housing on the second end side and having a positive electrode and a negative electrode; and an ignition unit that generates a spark between the positive electrode and the negative electrode, wherein a negative pressure region is generated in a part of the housing, and the positive electrode and the negative electrode are respectively disposed at positions where the distance between the positive electrode and the negative electrode is shorter than the distance between the positive electrode and the inner surface of the housing, so that a flame generated between the positive electrode and the negative electrode by the spark is formed only in the negative pressure region.

[0006] An ammonia engine system that solves the above-mentioned problems is an ammonia engine system that includes the above-mentioned combustor, a reforming catalyst that is warmed up by the combustion gas, and an ammonia engine to which hydrogen discharged from the reforming catalyst is supplied, and is characterized in that the distance between the positive electrode and the negative electrode is a distance that allows the ammonia engine to be started within a start-up time required for a vehicle in which the ammonia engine system is mounted.

[0007] According to each of the above configurations, the flame generated between the positive electrode and the negative electrode flows toward the center of the negative pressure in the negative pressure region. The flow of fuel mixed with oxidizing gas generated in the negative pressure region causes the flame to grow from the second end toward the first end of the casing. The positive electrode and the negative electrode are respectively arranged so that the flame generated between the positive electrode and the negative electrode by a spark is formed only in the negative pressure region. Therefore, the flame generated between the positive electrode and the negative electrode is less affected by the flow of fuel mixed with oxidizing gas toward the second end, which flows near the inner surface of the casing. Therefore, compared to when a flame is generated between the positive electrode and the inner surface of the casing, the flame grows more quickly from the second end toward the first end of the casing. Therefore, a large amount of combustion gas can be generated in the combustor quickly. [Effects of the Invention]

[0008] According to the present invention, a large amount of combustion gas can be generated in the combustor at an early stage. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram of an ammonia engine system according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram showing a combustor, an ignition plug, and an ignition unit. [Figure 3] FIG. 3 is a cross-sectional view taken along line 3-3 in FIG. 2. [Figure 4] FIG. 4 is a cross-sectional view taken along line 4-4 in FIG. [Figure 5] FIG. 2 is an enlarged cross-sectional view of a portion of the combustor. [Figure 6] 10 is a graph showing the relationship between the radial position of the housing and the pressure inside the housing. [Figure 7] 1 is a graph showing the time required to start the ammonia engines of Examples and Comparative Examples. DETAILED DESCRIPTION OF THE INVENTION

[0010] An embodiment of a combustor and an ammonia engine system will be described below with reference to FIGS. <Outline of ammonia engine system> As shown in Fig. 1, the ammonia engine system 10 has an ammonia engine 11. The ammonia engine system 10 of this embodiment is mounted on an engine vehicle 50. The ammonia engine 11 uses ammonia (NH3) gas as fuel. A combustion chamber 11a is formed inside the ammonia engine 11.

[0011] The ammonia engine system 10 has an intake passage 12, an air cleaner 19, a main injector 14, and a main throttle valve 15. Air is introduced into the combustion chamber 11a from the intake passage 12. The air cleaner 19 removes foreign matter such as dust and dirt contained in the air. The air cleaner 19 is provided at the end of the intake passage 12. The air from which foreign matter has been removed by the air cleaner 19 flows into the intake passage 12.

[0012] The main injector 14 is, for example, an electromagnetic injection valve. Ammonia gas is supplied to the main injector 14 from an ammonia gas supply unit (not shown). The main injector 14 supplies ammonia gas to the intake passage 12 by injecting the ammonia gas into the intake passage 12. The ammonia gas supplied from the main injector 14 to the intake passage 12 is introduced into the combustion chamber 11a together with the air flowing through the intake passage 12.

[0013] The main throttle valve 15 is provided in the intake passage 12 upstream of the point where ammonia gas is supplied from the main injector 14. The main throttle valve 15 is, for example, an electromagnetic flow control valve that can adjust the opening of the intake passage 12.

[0014] The ammonia engine system 10 has an exhaust flow path 13 and an exhaust catalyst unit 16. Exhaust gas generated in the combustion chamber 11a is introduced into the exhaust flow path 13 from the combustion chamber 11a. The exhaust catalyst unit 16 is provided in the exhaust flow path 13. The exhaust catalyst unit 16 has a three-way catalyst 17 and an SCR catalyst 18. The three-way catalyst 17 oxidizes ammonia gas remaining in the exhaust gas flowing through the exhaust flow path 13, thereby removing ammonia gas from the exhaust gas. The three-way catalyst 17 is activated by the heat of the exhaust gas. The SCR catalyst 18 is provided downstream of the three-way catalyst 17 in the exhaust flow path 13. The SCR catalyst 18 is a selective catalytic reduction catalyst. The SCR catalyst 18 reduces nitrogen oxides (NOx) contained in the exhaust gas flowing through the exhaust flow path 13 to nitrogen (N2) using ammonia. Furthermore, the SCR catalyst 18 captures and removes ammonia that has passed through the three-way catalyst 17.

[0015] The ammonia engine system 10 has a reformer 23. The reformer 23 has a box-shaped storage section 23a with a space formed inside. A reforming catalyst 23b is provided inside the storage section 23a. In other words, the ammonia engine system 10 has the reforming catalyst 23b. For example, a carrier having a honeycomb structure (not shown) may be provided inside the storage section 23a. The reforming catalyst 23b may be provided inside the storage section 23a by applying the reforming catalyst 23b to this carrier. The reforming catalyst 23b has the function of decomposing ammonia into hydrogen and the function of burning the ammonia. The reforming catalyst 23b is, for example, an ATR (Autothermal Reformer) type ammonia reforming catalyst. The reformer 23 generates a reformed gas containing hydrogen by reforming ammonia gas with the reforming catalyst 23b.

[0016] The ammonia engine system 10 includes a reformed gas passage 31, a cooler 32, and a stop valve 33. One end of the reformed gas passage 31 is connected to the reformer 23. The other end of the reformed gas passage 31 is connected to the intake passage 12 downstream of the main throttle valve 15. The reformed gas generated by the reformer 23 is introduced into the reformed gas passage 31, and the reformed gas is introduced from the reformed gas passage 31 into the intake passage 12.

[0017] The cooler 32 cools the reformed gas flowing through the reformed gas passage 31. The cooler 32 cools the reformed gas, for example, by exchanging heat between the reformed gas and cooling water flowing inside the cooler 32. The reformed gas cooled by the cooler 32 is introduced into the intake passage 12 through the reformed gas passage 31. This makes it possible to prevent damage to intake system components such as the main throttle valve 15 due to the heat of the reformed gas. Since the volume expansion of the reformed gas is suppressed as the reformed gas is cooled, the gas can more easily flow from the intake passage 12 into the combustion chamber 11a.

[0018] The stop valve 33 is provided in the reformed gas passage 31 downstream of the cooler 32. The stop valve 33 is, for example, an on-off valve that opens and closes the reformed gas passage 31. The ammonia engine system 10 has a first air flow path 24a, a first injector 25, and a first throttle valve 26. One end of the first air flow path 24a is connected to the intake air flow path 12 on the upstream side of the main throttle valve 15. The other end of the first air flow path 24a is connected to the reformer 23. A portion of the air introduced into the intake air flow path 12 via the air cleaner 19 is introduced into the first air flow path 24a. Air is introduced from the first air flow path 24a to the reformer 23.

[0019] The first injector 25 is, for example, an electromagnetic injection valve. Ammonia gas is supplied to the first injector 25 from an ammonia gas supply unit (not shown). The first injector 25 supplies ammonia gas to the first air flow path 24a by injecting the ammonia gas into the first air flow path 24a. The ammonia gas supplied from the first injector 25 to the first air flow path 24a is introduced into the reformer 23 together with the air flowing through the first air flow path 24a.

[0020] The first throttle valve 26 is provided in the first air flow path 24a upstream of the point where ammonia gas is supplied from the first injector 25. The first throttle valve 26 is, for example, an electromagnetic flow control valve that can adjust the opening of the first air flow path 24a.

[0021] The ammonia engine system 10 has a second air flow path 24b, a chamber 27, a second injector 28, a second throttle valve 29, and a combustor 40. One end of the second air flow path 24b is connected to the first air flow path 24a on the upstream side of the first throttle valve 26. The other end of the second air flow path 24b is connected to the chamber 27. A portion of the air flowing through the first air flow path 24a is introduced into the second air flow path 24b. The chamber 27 is box-shaped with a space formed inside. Air is introduced from the second air flow path 24b into the space inside the chamber 27.

[0022] The second injector 28 is, for example, an electromagnetic injection valve. Ammonia gas is supplied to the second injector 28 from an ammonia gas supply unit (not shown). The second injector 28 supplies ammonia gas to the internal space of the chamber 27 by injecting the ammonia gas into the internal space of the chamber 27. Air introduced into the chamber 27 from the second air flow path 24b and ammonia gas supplied to the chamber 27 from the second injector 28 are mixed inside the chamber 27. As a result, ammonia gas mixed with air is generated inside the chamber 27. In this embodiment, the ammonia gas corresponds to the fuel, and the air corresponds to the oxidizing gas. The ammonia gas mixed with air is introduced from the chamber 27 to the combustor 40.

[0023] The second throttle valve 29 is provided in the second air flow path 24b and is, for example, an electromagnetic flow control valve that can adjust the opening of the second air flow path 24b.

[0024] The combustor 40 generates combustion gas by burning ammonia gas as fuel. The combustion gas generated by the combustor 40 is introduced into the reformer 23. The ammonia engine system 10 includes a temperature sensor 35, an ignition switch 36, and a control unit 37. The temperature sensor 35 detects the temperature of the reformer 23. When the driver of the vehicle 50 operates the ignition switch 36, the ignition switch 36 outputs an operation signal to the control unit 37. The control unit 37 is composed of a CPU, RAM, ROM, an input / output interface, etc.

[0025] The control unit 37 performs various controls based on, for example, the detection value of the temperature sensor 35 and the operation signal of the ignition switch 36. The control unit 37 controls the main injector 14, the main throttle valve 15, the first injector 25, the first throttle valve 26, the second injector 28, the second throttle valve 29, the stop valve 33, etc.

[0026] <Control by control unit> The control unit 37 executes start control to start the ammonia engine 11. The control unit 37 executes start control on the condition that it determines, based on an operation signal from the ignition switch 36, that the ignition switch 36 has been turned on.

[0027] In the start control, the control unit 37 injects ammonia gas from the first injector 25 and the second injector 28. The control unit 37 opens the first throttle valve 26, the second throttle valve 29, and the stop valve 33. Subsequently, in the start control, the control unit 37 starts the ammonia engine 11 by controlling a starter motor (not shown) to crank the ammonia engine 11. Furthermore, in the start control, the control unit 37 injects ammonia gas from the main injector 14 and opens the main throttle valve 15.

[0028] During startup control, the control unit 37 determines whether the temperature of the reformer 23 is equal to or higher than a specified temperature based on the detection value of the temperature sensor 35. The specified temperature is a temperature at which ammonia gas can be combusted, for example, approximately 200°C. When the control unit 37 determines that the temperature of the reformer 23 is equal to or higher than the specified temperature, the control unit 37 stops the injection of ammonia gas from the second injector 28 and closes the second throttle valve 29. This stops the introduction of air and ammonia gas supplied from the chamber 27 to the combustor 40. As the combustion of ammonia gas in the combustor 40 stops, the introduction of combustion gas from the combustor 40 to the reformer 23 is stopped. In this way, startup control by the control unit 37 is terminated.

[0029] During the period from the end of the start control until the ammonia engine 11 is stopped, the control unit 37 may adjust the opening of the main throttle valve 15 or change the injection timing of the main injector 14. The control unit 37 may adjust the opening of the first throttle valve 26 to appropriately adjust the amount of air introduced from the first air passage 24a to the reformer 23. The control unit 37 may also change the injection timing of the first injector 25 as appropriate.

[0030] The control unit 37 executes stop control to stop the ammonia engine 11. The control unit 37 executes stop control on the condition that it determines, based on an operation signal from the ignition switch 36, that the ignition switch 36 has been turned off.

[0031] In the stop control, the control unit 37 stops the injection of ammonia gas from the main injector 14 and the first injector 25. In the stop control, the control unit 37 closes the main throttle valve 15, the first throttle valve 26, and the stop valve 33. This stops the ammonia engine 11.

[0032] <Combustion reaction in the reformer> Air and ammonia gas are introduced into the reformer 23 from the first air flow path 24a, and combustion gas is introduced into the reformer 23 from the combustor 40. The reforming catalyst 23b is warmed up by the combustion gas. As a result, an ammonia combustion reaction occurs in the reformer 23, in which ammonia gas chemically reacts with oxygen in the air, as shown in Equation 1 below.

[0033] NH3+3 / 4O2→3 / 2H2O+1 / 2N2+Q…(Formula 1) The reformer 23 generates a mixed gas containing moisture (H2O) and nitrogen (N2) through the combustion reaction of ammonia. The reformer 23 is heated by the combustion heat generated by the combustion reaction of ammonia.

[0034] <Reforming reaction in the reformer> When the temperature of the reformer 23 reaches a temperature at which reforming is possible, reforming of the ammonia gas by the reforming catalyst 23b begins. The above-mentioned temperature at which reforming is possible is, for example, about 300°C to 400°C. Specifically, in reforming the ammonia gas, a reforming reaction occurs in the reformer 23 in which ammonia is decomposed into hydrogen (H2) and nitrogen by combustion heat, as shown in the following formula 2.

[0035] NH3→3 / 2H2+1 / 2N2-Q…(Formula 2) Through the reforming reaction, the reformer 23 generates a reformed gas containing hydrogen and nitrogen. The reformed gas is discharged from the reforming catalyst 23b. That is, the hydrogen contained in the reformed gas is discharged from the reforming catalyst 23b. The reformed gas is introduced from the reformer 23 into the reformed gas flow path 31, and then introduced into the intake flow path 12 via the reformed gas flow path 31.

[0036] <Supply of reformed gas to the combustion chamber> The reformed gas introduced from the reformed gas passage 31 into the intake passage 12 is supplied from the intake passage 12 to the combustion chamber 11a of the ammonia engine 11. That is, hydrogen discharged from the reforming catalyst 23b is supplied to the ammonia engine 11. The reformed gas is supplied to the combustion chamber 11a together with ammonia gas supplied from the main injector 14 to the intake passage 12 and the air in the intake passage 12. Because the ammonia gas and the hydrogen in the reformed gas are mixed in the combustion chamber 11a, the ammonia gas is more likely to burn in the combustion chamber 11a. In the combustion chamber 11a, the ammonia gas burns together with the hydrogen in the reformed gas. After the start-up control by the control unit 37 is initiated, the ammonia engine 11 starts up by burning the ammonia gas together with the hydrogen in the combustion chamber 11a.

[0037] <Combustor details> As shown in FIG. 2, the combustor 40 has a cylindrical housing 41. A first end 41a of the housing 41 is open. A blocking wall 42 is provided at a second end 41b of the housing 41. The blocking wall 42 is, for example, disk-shaped. The blocking wall 42 blocks the second end 41b of the housing 41. This blocks the second end 41b of the housing 41. The housing 41 and the blocking wall 42 are made of a conductive metal material. An example of a conductive metal material is stainless steel.

[0038] As shown in FIG. 3 , the combustor 40 has four inlet portions 43. Each inlet portion 43 is, for example, tubular, and has a flow path 43a formed therein. One end of each inlet portion 43 is connected to the chamber 27, and the other end of each inlet portion 43 is connected to the housing 41. In a cross section perpendicular to the axis L of the housing 41, each of the four inlet portions 43 is connected to the housing 41 such that the flow path 43a extends in a tangential direction to an inner circumferential surface 41d of the housing 41. The inlet portions 43 may be formed integrally with the housing 41. Alternatively, the inlet portions 43 may be formed separately from the housing 41 and fixed to the housing 41.

[0039] The flow path 43a of the introduction part 43 communicates with the interior of the housing 41 via introduction holes 41c formed in the housing 41. Four introduction holes 41c are formed in the housing 41. The introduction holes 41c are formed, for example, in a middle portion of the housing 41 in the direction in which the axis L of the housing 41 extends. The four introduction holes 41c are spaced apart from one another at equal intervals in the circumferential direction of the housing 41.

[0040] Ammonia gas mixed with air is introduced from the inside of chamber 27 into flow path 43a of introduction part 43. The ammonia gas mixed with air flows through flow path 43a and is then introduced from flow path 43a into the inside of housing 41. In this way, introduction part 43 introduces ammonia gas as fuel and air as an oxidizing gas into housing 41. Since introduction part 43 is connected to housing 41 so that flow path 43a extends in the tangential direction of inner circumferential surface 41d of housing 41, the ammonia gas and air introduced from introduction part 43 into housing 41 flow in the circumferential direction of housing 41 along inner circumferential surface 41d of housing 41.

[0041] As shown in FIG. 2, the combustor 40 has an ignition plug 44. The ignition plug 44 is disposed on the second end 41b side within the housing 41. The ignition plug 44 includes a positive electrode 45 and a negative electrode 46. The positive electrode 45 and the negative electrode 46 are spaced apart from each other in the radial direction of the housing 41. The positive electrode 45 is attached to the housing 41 via an insulating member 47, for example, so as to penetrate the blocking wall 42. The insulating member 47 is made of an insulating material having pressure resistance and heat resistance, such as ceramic.

[0042] The positive electrode 45 and the negative electrode 46 are, for example, cylindrical and extend in the direction of the axis L of the casing 41. A tip 45a of the positive electrode 45 in the direction of the axis L of the casing 41 is located inside the casing 41. More specifically, in the direction of the axis L of the casing 41, a part of the positive electrode 45 including the tip 45a is located inside the casing 41, and the other part of the positive electrode 45 is located outside the casing 41. In the direction of the axis L of the casing 41, the tip 45a of the positive electrode 45 is located between the introduction hole 41c of the casing 41 and the blocking wall 42.

[0043] The positive electrode 45 is provided inside the housing 41, for example, on the axis L of the housing 41. The negative electrode 46 is provided inside the housing 41, for example, at a position shifted from the axis L of the housing 41 in the radial direction of the housing 41 and away from the inner circumferential surface 41d of the housing 41.

[0044] The combustor 40 has an ignition unit 51. The ignition unit 51 has an igniter 52 and a power supply 53. The power supply 53 turns the igniter 52 on and off. The on and off operations of the igniter 52 by the power supply 53 may be controlled by the control unit 37. In the starting control, the igniter 52 may be turned on by the power supply 53. The igniter 52 is connected to the positive electrode 45 via an electric wire 54. The igniter 52 supplies a pulse voltage to the positive electrode 45 via the electric wire 54.

[0045] <Flow of ammonia gas and air in the combustor> 4, the ammonia gas and air introduced into the housing 41 from the introduction part 43 flow in the circumferential direction of the housing 41 along the inner peripheral surface 41d of the housing 41, thereby generating a tubular flow F1 of the ammonia gas mixed with air inside the housing 41. In other words, the introduction part 43 introduces the ammonia gas and air into the housing 41 so as to generate the tubular flow F1. The ammonia gas mixed with air flows inside the housing 41.

[0046] The ammonia gas and air flow inside the casing 41 to form a tubular flow F1, and flow from the opening of the inlet hole 41c on the inner circumferential surface 41d toward each of the first end 41a and the second end 41b of the casing 41. The flow of ammonia gas and air from the opening of the inlet hole 41c on the inner circumferential surface 41d toward the second end 41b of the casing 41 is schematically shown as gas flow F2 by dashed arrows in Figure 4. Gas flow F2 is generated near the inner circumferential surface 41d of the casing 41.

[0047] The ammonia gas and air flowing toward the second end 41b of the housing 41 with gas flow F2 are turned back by the blocking wall 42 and flow toward the first end 41a of the housing 41. The flow of ammonia gas and air from the second end 41b toward the first end 41a of the housing 41 in this manner is shown as gas flow F3 by dashed arrows in Fig. 4. Gas flow F3 is generated in the central portion of the housing 41 in the radial direction of the housing 41.

[0048] <Negative pressure area> As shown in FIG. 5, a negative pressure region A1 is generated in a portion of the casing 41 of the combustor 40. The negative pressure region A1 is generated by a tubular flow F1 that flows along the inner circumferential surface 41d of the casing 41. Specifically, the negative pressure region A1 is a region located at the center of the casing 41 in the radial direction of the casing 41. For example, the axis L of the casing 41 is the center of negative pressure in the negative pressure region A1. Of the space inside the casing 41, a region between the negative pressure region A1 and the inner circumferential surface 41d of the casing 41 in the radial direction of the casing 41 is a positive pressure region A2.

[0049] FIG. 6 is a graph showing the relationship between the radial position of the housing 41 and the pressure inside the housing 41. The horizontal axis of FIG. 6 represents the radial position of the housing 41 in a cross section of the housing 41 taken along the axis L. A position on the horizontal axis where the value is 0 (zero) indicates a position on the axis L of the housing 41. A range on the horizontal axis greater than 0 (zero) indicates a position on one side of the axis L in the radial direction of the housing 41, and a range less than 0 (zero) indicates a position on the other side of the axis L in the radial direction of the housing 41. Within a range on the horizontal axis greater than 0 (zero), a larger value on the horizontal axis indicates a position closer to the inner circumferential surface 41d of the housing 41. Within a range on the horizontal axis less than 0 (zero), a smaller value on the horizontal axis indicates a position closer to the inner circumferential surface 41d of the housing 41. The vertical axis of FIG. 6 represents the pressure inside the housing 41. On the vertical axis, the range greater than 0 (zero) indicates that the pressure inside the housing 41 is positive pressure, and the range less than 0 (zero) indicates that the pressure inside the housing 41 is negative pressure. As shown in Figure 6, the central portion in the radial direction of the housing 41 is under negative pressure. Other portions of the housing 41 are under positive pressure. It is clear from the graph in Figure 6 that a negative pressure region A1 and a positive pressure region A2 are created inside the housing 41.

[0050] <Combustion of ammonia gas> 2 and 4, when a high voltage is applied from igniter 52 to positive electrode 45, a discharge occurs between positive electrode 45 and negative electrode 46, generating a spark P1 between positive electrode 45 and negative electrode 46. That is, ignition unit 51 generates spark P1 between positive electrode 45 and negative electrode 46. Spark P1 ignites ammonia gas inside housing 41. When the ammonia gas inside housing 41 is ignited, power supply 53 may turn off igniter 52.

[0051] As shown in FIG. 5, when a spark P1 ignites ammonia gas, the ammonia gas burns, generating a flame P2. The flame P2 is schematically shown in FIG. 5 by dot hatching. The flame P2 is generated between the positive electrode 45 and the negative electrode 46 by the spark P1. The spark P1 generates the flame P2 in the region where the distance between the positive electrode 45 and the negative electrode 46 is the shortest. Therefore, the flame P2 also generates in the region where the distance between the positive electrode 45 and the negative electrode 46 is the shortest. In this embodiment, the region where the distance between the positive electrode 45 and the negative electrode 46 is the region between the positive electrode 45 and the negative electrode 46 in the radial direction of the casing 41. When the ammonia gas burns, combustion gas is generated inside the casing 41. The combustion gas generated by the combustion of the ammonia gas as fuel flows inside the casing 41. The combustion gas is introduced into the reformer 23 from the first end 41a of the casing 41.

[0052] Immediately after generation, the flame P2 flows toward the axis L of the housing 41, which is the center of negative pressure in the negative pressure region A1, as indicated by the flame flow F4 indicated by the solid arrow in Figure 5. The gas flow F3 of ammonia gas and air generated in the negative pressure region A1 causes the flame P2 to grow from the second end 41b toward the first end 41a of the housing 41. The growth of the flame P2 promotes the generation of combustion gas by the combustion of ammonia gas within the housing 41. The closer the flame P2 is to the first end 41a of the housing 41, the closer it is to the inner circumferential surface 41d of the housing 41. Near the inner circumferential surface 41d of the housing 41, the flame P2 grows along the tubular flow F1 within the housing 41.

[0053] <Position of positive and negative electrodes> The positive electrode 45 and the negative electrode 46 are disposed at positions where a distance L1 between the positive electrode 45 and the negative electrode 46 is shorter than a distance L2 between the positive electrode 45 and the inner peripheral surface 41d of the housing 41. The distance L1 is the shortest distance between the positive electrode 45 and the negative electrode 46. The distance L2 is the shortest distance between the positive electrode 45 and the inner peripheral surface 41d of the housing 41. In this embodiment, the distances L1 and L2 are distances in the radial direction of the housing 41.

[0054] Discharge from the positive electrode 45 is directed to either the negative electrode 46 or the inner circumferential surface 41d of the casing 41, whichever is closest to the positive electrode 45. Because the distance L1 between the positive electrode 45 and the negative electrode 46 is shorter than the distance L2 between the positive electrode 45 and the inner circumferential surface 41d of the casing 41, discharge occurs between the positive electrode 45 and the negative electrode 46. This generates a spark P1 between the positive electrode 45 and the negative electrode 46.

[0055] The positive electrode 45 and the negative electrode 46 are arranged so that a flame P2 generated between the positive electrode 45 and the negative electrode 46 by a spark P1 is formed only in the negative pressure region A1. In detail, the region between the positive electrode 45 and the negative electrode 46, where the flame P2 is generated, is separated by a distance L1, and is located within the negative pressure region A1.

[0056] <Relationship between distance between positive and negative poles and starting time> The larger the distance L1 between the positive electrode 45 and the negative electrode 46, the larger the size of the flame P2 immediately after generation. Under conditions in which the positive electrode 45 and the negative electrode 46 are arranged so that the flame P2 is formed only in the negative pressure region A1, the larger the size of the flame P2 immediately after generation, the faster the flame P2 grows from the second end 41b to the first end 41a of the casing 41. Therefore, a large amount of combustion gas can be generated in the combustor 40 quickly.

[0057] As shown in FIG. 1, the reforming catalyst 23b is warmed up by introducing the combustion gas generated in the combustor 40 into the reformer 23. Producing a large amount of combustion gas in the combustor 40 quickly warms up the reforming catalyst 23b, allowing the reformer 23 to quickly produce reformed gas containing hydrogen. Furthermore, the reformed gas can be introduced quickly from the reformer 23 into the combustion chamber 11a of the ammonia engine 11 via the reformed gas flow path 31 and the intake flow path 12, allowing the ammonia engine 11 to be started quickly. As described above, under the condition that the positive electrode 45 and the negative electrode 46 are arranged so that the flame P2 is formed only in the negative pressure region A1, the longer the distance L1 between the positive electrode 45 and the negative electrode 46, the shorter the start-up time of the ammonia engine 11. The distance L1 between the positive electrode 45 and the negative electrode 46 in this embodiment is a distance that allows the ammonia engine 11 to be started within the start-up time required for the vehicle 50 equipped with the ammonia engine system 10. The distance L1 between the positive electrode 45 and the negative electrode 46 is greater than the distance at which a flame P2 can be generated when a spark P1 ignites ammonia gas, for example.

[0058] As shown in FIG. 7 , the time T required to start the ammonia engine 11 was measured for an example in which discharge was performed between the positive electrode 45 and the negative electrode 46, and for a comparative example in which discharge was performed between the positive electrode 45 and the inner circumferential surface 41d of the housing 41. Here, time T is the time from when the ignition switch 36 was turned on until the start of the ammonia engine 11 was completed. In this measurement, the distance L1 between the positive electrode 45 and the negative electrode 46 in the example was 5 mm, and the distance L2 between the positive electrode 45 and the inner circumferential surface 41d of the housing 41 in the comparative example was 15 mm. Time T was measured multiple times for both the example and the comparative example under conditions where the excess air ratio λ was approximately 1.1. The excess air ratio λ is the value obtained by dividing the mass of air actually supplied by the theoretically required minimum air mass. In FIG. 7 , the measured value for the example is indicated by point E1, and the measured value for the comparative example is indicated by point E2. As indicated by points E1 and E2, the time T for the example tended to be shorter than the time T for the comparative example. From the experimental results, it is clear that in the example in which discharge is performed between the positive electrode 45 and the negative electrode 46, the time T required to start the ammonia engine 11 tends to be shorter than in the comparative example in which discharge is performed between the positive electrode 45 and the inner circumferential surface 41d of the housing 41.

[0059] [Effect] Next, the operation of this embodiment will be described. FIG. 5 shows a comparative example in which a discharge occurs between the positive electrode 45 and the inner circumferential surface 41d of the housing 41. As indicated by the two-dot chain line in FIG. 5, the flame P3 in the comparative example occurs between the positive electrode 45 and the inner circumferential surface 41d of the housing 41. Therefore, immediately after generation, the flame P3 in the comparative example is formed in the negative pressure region A1 and the positive pressure region A2. The portion of the flame P3 formed in the positive pressure region A2 receives a gas flow F2, which is a flow of ammonia gas and air flowing toward the second end 41b near the inner circumferential surface 41d of the housing 41. As indicated by the flame flow F5 indicated by the two-dot chain line with an open arrow, the flame P3 in the comparative example flows toward the axis L of the housing 41, which is the center of negative pressure in the negative pressure region A1. The gas flow F3, which is a flow of ammonia gas and air generated in the negative pressure region A1, causes the flame P3 to grow from the second end 41b toward the first end 41a of the housing 41. However, since a portion of the flame P3 is affected by the gas flow F2 as described above, the flame P3 in the comparative example does not easily grow from the second end 41b of the housing 41 toward the first end 41a.

[0060] In this embodiment, a flame P2 is generated between the positive electrode 45 and the negative electrode 46. As indicated by flame flow F4, the flame P2 immediately after generation flows toward the axis L of the casing 41, which is the center of negative pressure in the negative pressure region A1. Due to gas flow F3, which is a flow of ammonia gas and air generated in the negative pressure region A1, the flame P2 grows from the second end 41b toward the first end 41a of the casing 41. The positive electrode 45 and the negative electrode 46 are arranged so that the flame P2 generated between the positive electrode 45 and the negative electrode 46 by the spark P1 is formed only in the negative pressure region A1. Therefore, the flame P2 generated between the positive electrode 45 and the negative electrode 46 is less affected by gas flow F2, which is a flow of ammonia gas and air toward the second end 41b flowing near the inner circumferential surface 41d of the casing 41. The flame P2 in this embodiment grows more easily from the second end 41b toward the first end 41a of the casing 41 than the flame P3 in the comparative example.

[0061] [effect] According to the above embodiment, the following effects can be obtained. (1) The positive electrode 45 and the negative electrode 46 are arranged so that a flame P2 generated between the positive electrode 45 and the negative electrode 46 by a spark P1 is formed only in the negative pressure region A1. Therefore, compared to the case where a flame P3 is generated between the positive electrode 45 and the inner circumferential surface 41d of the housing 41, the flame P2 grows more quickly from the second end 41b toward the first end 41a of the housing 41. Therefore, a large amount of combustion gas can be generated in the combustor 40 more quickly.

[0062] (2) The reforming catalyst 23b is warmed up by the combustion gas generated in the combustor 40. By generating a large amount of combustion gas in the combustor 40 early, the reforming catalyst 23b can be warmed up early, and hydrogen can be generated early in the reforming catalyst 23b. Furthermore, hydrogen can be discharged from the reforming catalyst 23b to the ammonia engine 11 early, and the ammonia engine 11 can be started early.

[0063] [Example of change] The above embodiment can be modified as follows: The above embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

[0064] The distance L1 between the positive electrode 45 and the negative electrode 46 may be equal to the distance at which a flame P2 can be generated when a spark P1 ignites the ammonia gas. The positive electrode 45 and the negative electrode 46 may be positioned apart from each other in a direction intersecting the diameter of the housing 41. In this case, a flame P2 may be generated between the positive electrode 45 and the negative electrode 46 in the direction intersecting the diameter of the housing 41. In this case, the positive electrode 45 and the negative electrode 46 are also disposed so that the flame P2 generated between the positive electrode 45 and the negative electrode 46 is formed only in the negative pressure region A1.

[0065] The position of the positive electrode 45 inside the housing 41 may be shifted from the axis L of the housing 41. In other words, as long as the positive electrode 45 and the negative electrode 46 are disposed so that the flame P2 generated between the positive electrode 45 and the negative electrode 46 is formed only in the negative pressure region A1, the positions of the positive electrode 45 and the negative electrode 46 inside the housing 41 can be changed as appropriate.

[0066] The introduction part 43 is not limited to one that introduces ammonia gas mixed with air into the housing 41. For example, among the plurality of introduction parts 43, some introduction parts 43 may introduce only ammonia gas into the housing 41, and other introduction parts 43 may introduce only air into the housing 41. In short, it is sufficient that the introduction part 43 introduces ammonia gas and air into the housing 41 so as to generate the tubular flow F1.

[0067] The number of introduction sections 43 included in the combustor 40 may be three or less, or may be five or more. In short, it is sufficient that the combustor 40 has at least one introduction section 43. Note that the expression "at least one" used in this specification means "one or more" of the desired options. As an example, the expression "at least one" used in this specification means "only one option" or "both of two options" if the number of options is two. As another example, the expression "at least one" used in this specification means "only one option" or "any combination of two or more options" if the number of options is three or more.

[0068] The main injector 14 may be configured to inject ammonia gas directly into the combustion chamber 11a. The combustor 40 and the ammonia engine system 10 may use a fuel other than ammonia gas. For example, the combustor 40 and the ammonia engine system 10 may use a hydrocarbon gas or the like as a fuel.

[0069] The combustor 40 and the ammonia engine system 10 may use oxygen as the oxidizing gas. The ammonia engine system 10 can also be applied to a hybrid vehicle 50. [Explanation of symbols]

[0070] A1...negative pressure region, F1...tubular flow, L1, L2...distance, P1...spark, P2...flame, 10...ammonia engine system, 11...ammonia engine, 23b...reforming catalyst, 40...combustor, 41...casing, 41a...first end, 41b...second end, 41d...inner surface, 43...introduction portion, 44...spark plug, 45...positive electrode, 46...negative electrode, 50...vehicle, 51...ignition unit.

Claims

[Claim 1] a cylindrical housing having an open first end and a closed second end, through which a fuel mixed with an oxidizing gas and a combustion gas generated by the combustion of the fuel flow; at least one inlet that introduces the fuel and the oxidizing gas into the housing so as to generate a tubular flow; a spark plug disposed on the second end side in the housing and including a positive electrode and a negative electrode; a combustor having an ignition unit that generates a spark between the positive electrode and the negative electrode, and a negative pressure region is generated in a part of the housing; a reforming catalyst that is warmed up by the combustion gas; an ammonia engine to which hydrogen discharged from the reforming catalyst is supplied, the positive electrode and the negative electrode are respectively disposed at positions where a distance between the positive electrode and the negative electrode is shorter than a distance between the positive electrode and an inner peripheral surface of the casing so that a flame generated between the positive electrode and the negative electrode by the spark is formed only in the negative pressure region; The distance between the positive electrode and the negative electrode is a distance that allows the ammonia engine to be started within a start time required for a vehicle on which the ammonia engine system is mounted.

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