JP7750271B2 - power plant - Google Patents

Description

The present invention relates to a power plant equipped with an internal combustion engine that uses hydrogen as its primary fuel.

Spark-ignition internal combustion engines that use hydrogen as fuel are known. Patent Document 1 below describes an internal combustion engine that operates in a lean state, where the fuel equivalence ratio is greater than the stoichiometric composition and there is an excess of air when using hydrogen as fuel, to suppress abnormal combustion. Non-Patent Document 1 below describes that supplying ammonia to a hydrogen-fueled engine can slow combustion. Patent Document 2 below describes a technology that uses hydrogen and carbon monoxide reformed from fuel to produce ammonia from nitrogen oxides in the exhaust gas from the combustor, and recirculates the produced ammonia together with the exhaust gas into the intake air.

JP 2016-156304 A Patent No. 7153327

Gu Xin and five others, "Effect of ammonia addition on combustion and emission characteristics of hydrogen-fueled engine under lean-burn condition," International Journal of Hydrogen Energy 47 (2022) pp. 9762-9774, [online], February 8, 2022, Elsevier Ltd, [Retrieved August 24, 2023], Internet <URL: https://www.sciencedirect.com/science/article/abs/pii/S0360319922000544>

Internal combustion engines that use hydrogen as fuel are prone to abnormal combustion, such as pre-ignition, in which fuel spontaneously ignites before being ignited by the spark plug. Setting the fuel equivalence ratio to lean reduces the ignition and combustibility of the mixture, thereby suppressing abnormal combustion. However, in a lean condition, i.e., in a state with excess air, it is difficult to efficiently purify the nitrogen oxides generated by combustion.

The present invention aims to at least one of suppressing abnormal combustion in an internal combustion engine that uses hydrogen as its main fuel, and efficiently purifying nitrogen oxides in the exhaust gas from the internal combustion engine, in a power plant equipped with such an internal combustion engine.

The power plant of the present invention comprises an internal combustion engine that generates power by burning an air-fuel mixture containing hydrogen, and a reformer that receives a portion of the exhaust gas from the internal combustion engine and hydrogen and reacts the nitrogen oxides in the exhaust gas with the hydrogen to produce ammonia. The internal combustion engine has an ammonia injector that directly injects the ammonia produced by the reformer into the cylinders.

By supplying ammonia, which is flame-retardant, into the cylinder, abnormal hydrogen combustion can be suppressed.

The above-mentioned power plant may be provided with a separator that separates at least one of water and nitrogen from the ammonia-containing gas produced by the reformer, and the ammonia-containing gas from which at least one of water and nitrogen has been separated by the separator is sent to the ammonia injector. This allows for the supply of ammonia-containing gas with a high concentration of ammonia, and by reducing the amount of gas, the work required to compress the gas can be reduced.

The above-mentioned power plant may be equipped with a post-reforming condenser that cools the ammonia-containing gas produced by the reformer to condense the water, and the ammonia dissolved in the water condensed by the post-reforming condenser is sent to the ammonia injector as ammonia water. Because a liquid is pressurized, the work required for pressurization can be reduced compared to when a gas is compressed. In addition, because liquid water is supplied to the cylinder, the heat of vaporization of the water can be expected to cool the inside of the cylinder.

The above-mentioned power plant may be equipped with a pre-reformer condenser that cools a portion of the exhaust gas from the internal combustion engine to condense and separate water, and the exhaust gas after condensing and separating the water is sent to the reformer. By removing water from the exhaust gas, the efficiency of the reformer can be increased. Furthermore, a separator may be equipped that separates nitrogen from the ammonia-containing gas produced from the exhaust gas after water separation by the reformer, and the ammonia-containing gas from which the water and nitrogen have been separated is sent to the ammonia injector. Ammonia-containing gas with a high concentration of ammonia can be supplied, and the reduced amount of gas reduces the work required to compress the gas.

In the above power plant, the ammonia injector may inject ammonia toward high-temperature areas within the cylinder. This can suppress the occurrence of abnormal combustion originating from high-temperature areas.

In the above power plant, the ammonia injector may inject ammonia toward the spark plug. This can suppress the occurrence of abnormal combustion originating from the spark plug.

The above-mentioned power plant may be equipped with an oxidation-reduction catalyst device that purifies the exhaust gas from the internal combustion engine. By suppressing abnormal combustion, the composition of the gas in the cylinder can be made stoichiometric, and when the exhaust gas has a stoichiometric composition, an oxidation-reduction catalyst device can be used that simultaneously purifies unburned fuel and nitrogen oxides.

In the above-mentioned power plant, the hydrogen introduced into the reformer may be hydrogen used for fuel. This eliminates the need to prepare a separate substance for reducing nitrogen oxides to ammonia.

By supplying ammonia, which is flame-retardant, to the cylinder, abnormal hydrogen combustion can be suppressed. By suppressing abnormal combustion, the composition of substances in the cylinder can be made stoichiometric, and in this case, unburned fuel and nitrogen oxides can be simultaneously purified using an oxidation-reduction catalyst.

1 is a diagram schematically illustrating an example of a power plant according to the present invention. FIG. 10 is a diagram schematically illustrating another example of a power plant according to the present invention. FIG. 10 is a diagram schematically illustrating still another example of a power plant according to the present invention. FIG. 10 is a diagram schematically illustrating still another example of a power plant according to the present invention. FIG. 10 is a diagram schematically illustrating still another example of a power plant according to the present invention.

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is a diagram schematically illustrating the configuration of a power plant 10. The power plant 10 includes an internal combustion engine 12, a spark-ignition engine that uses hydrogen as its primary fuel. The internal combustion engine 12 has an engine body 16 that defines roughly cylindrical cylinders 14. Pistons (not shown) that reciprocate along the central axes of the cylinders 14 are disposed within the cylinders 14, and the movement of the pistons is transmitted to the crankshaft, which is the output shaft of the internal combustion engine, via connecting rods. This internal combustion engine 12 is a so-called in-line four-cylinder engine, having four cylinders 14 arranged in series. The number and arrangement of cylinders are not limited to this, and the number of cylinders may be 2, 3, 6, or 8, for example, or the engine may have a V-shaped cylinder arrangement. Each cylinder 14 is provided with a spark plug 18 for igniting the fuel-air mixture.

The internal combustion engine 12 includes an intake pipe 20 and an intake manifold 22 that form an intake flow path through which air is supplied to the cylinders 14, i.e., the intake air. The intake pipe 20 is provided with a throttle valve 24 for adjusting the intake flow path. An intake air flow sensor 25 for detecting the intake air flow rate is provided downstream of the throttle valve 24 in the intake pipe 20. The intake manifold 22 has an intake flow path connected to the intake pipe 20 and four intake flow paths branching from this intake flow path. Each of the four branched flow paths is connected to four intake ports formed in the engine body 16 and connected to the four cylinders 14, respectively. Each of the four branched flow paths of the intake manifold 22 is provided with a hydrogen injector 26 that injects hydrogen, the main fuel, into the flow path. The hydrogen injected from the hydrogen injector 26 is supplied from a hydrogen tank 28.

The internal combustion engine 12 includes an exhaust manifold 30 and an exhaust pipe 32 that form an exhaust flow path for air discharged from the cylinders 14, i.e., the exhaust gas. The exhaust manifold 30 has four exhaust flow paths that connect to four exhaust ports formed in the engine body 16, respectively, and an exhaust flow path that merges these four exhaust flow paths into one and connects to the exhaust pipe 32. The four exhaust ports are connected to the four cylinders 14, respectively, and guide exhaust gas from inside the cylinders 14 to the exhaust manifold 30.

The power plant 10 includes a redox catalyst device 34 that oxidizes unburned hydrogen in the exhaust gas of the internal combustion engine 12 and reduces nitrogen oxides produced by combustion in the cylinders 14. The redox catalyst device 34 is located in the exhaust pipe 32. The catalyst in the redox catalyst device 34 may be, for example, a three-way catalyst used in gasoline-fueled internal combustion engines. An air excess ratio sensor 36 is located in the exhaust pipe 32 upstream of the redox catalyst device 34. The air excess ratio sensor 36 detects the oxygen concentration in the exhaust gas, and the air excess ratio relative to the fuel is calculated based on this oxygen concentration. Based on the air excess ratio, the amount of fuel supplied to the cylinders 14 is controlled so that the composition of substances in the cylinders 14 is stoichiometric. The amount of air supplied to the cylinders 14 can be detected by the intake air volume sensor 25, and fuel corresponding to the detected air volume is supplied to the cylinders 14. The fuel consists of hydrogen injected from the hydrogen injector 26 and ammonia injected from the ammonia injector 38, described below. The amount of fuel supplied is controlled by controlling the hydrogen injector 26 and the ammonia injector 38. By maintaining a stoichiometric composition of materials in the cylinder 14, the oxidation-reduction catalyst device 34 can simultaneously purify hydrogen and nitrogen oxides in the exhaust. When purifying nitrogen oxides under lean conditions, a selective reduction catalyst or nitrogen oxide storage reduction catalyst is used, but by maintaining a stoichiometric composition of materials in the cylinder and using an oxidation-reduction catalyst, the efficiency of purifying nitrogen oxides can be improved.

The power plant 10 includes an ammonia supply system that reacts nitrogen oxides in the exhaust gas of the internal combustion engine 12 with hydrogen to reform them into ammonia and supplies the reformed ammonia into the cylinders 14. The ammonia supply system includes a reformer 42 to which exhaust gas is supplied via a branch pipe 40 branching off from the exhaust pipe 32. The branch pipe 40 is provided with a flow control valve 43 that adjusts the flow rate of exhaust gas flowing from the exhaust pipe 32 to the branch pipe 40. Hydrogen is supplied to the reformer 42 from a hydrogen supply valve 44. This hydrogen can be hydrogen that is diverted from the main fuel. In the reformer 42, the nitrogen oxides in the exhaust gas react with the supplied hydrogen in the presence of a catalyst to produce ammonia. The reaction formula is shown below.
2NO+5H ₂ → 2NH ₃ +2H ₂ O

The generated gas containing ammonia (hereinafter referred to as ammonia-containing gas) is compressed by a compressor 46 and sent to an ammonia injector 38 provided in each cylinder 14. The ammonia-containing gas is directly injected from the ammonia injector 38 into the cylinder 14. The power plant 10 supplies the ammonia-containing gas delivered from the reformer 42 to the cylinder 14 with its original composition, that is, directly. The ammonia-containing gas may be injected toward a high-temperature portion within the cylinder 14. The high-temperature portion can be determined empirically, experimentally, or by numerical calculation using an in-cylinder combustion model. The high-temperature portion is, for example, a spark plug.

Ammonia is less flammable than hydrogen, and supplying ammonia to the cylinder 14 can suppress abnormal hydrogen combustion. In particular, by injecting ammonia toward high-temperature areas within the cylinder 14, which are the starting points for abnormal combustion, abnormal combustion can be suppressed efficiently with a small amount of ammonia.

Figure 2 is a schematic diagram showing the configuration of a power plant 50 according to a second embodiment of the present invention. Components identical to those of the power plant 10 described above are designated by the same reference numerals, and their description will be omitted. The power plant 50 includes a separator 52 that separates at least one of water (water vapor) and nitrogen from the ammonia-containing gas produced in the reformer 42. Water separation is achieved using a separation membrane that allows permeation of either ammonia or water but not the other. Nitrogen separation is also achieved using a separation membrane that allows permeation of either ammonia or nitrogen but not the other. Separation membranes that separate ammonia and water can be made of, for example, polyethylene or polypropylene. Separation membranes that separate ammonia and nitrogen can be made of, for example, polyimide or silicon. The separated water and nitrogen are released into the atmosphere. The ammonia-containing gas from which water and nitrogen have been removed is compressed by a compressor 46 and sent to the ammonia injector 38. The power plant 50 supplies the ammonia-containing gas delivered from the reformer 42 to the cylinder 14 via the separator 52.

By eliminating at least one of water and nitrogen, the amount of gas compressed by the compressor 46 is reduced, reducing the work required to compress the ammonia-containing gas. Furthermore, gas with a high ammonia concentration can be supplied to the cylinder 14.

Figure 3 is a schematic diagram showing the configuration of a power plant 60 according to a third embodiment of the present invention. Components identical to those of the power plant 10 described above are designated by the same reference numerals and will not be described further. The power plant 60 includes a post-reforming condenser 62 that cools the ammonia-containing gas produced in the reformer 42 and condenses the water (water vapor) in the gas. Ammonia is water-soluble and dissolves in the condensed water to form ammonia water. Nitrogen, being virtually insoluble in water, remains in a gaseous state, is separated from the ammonia water, and is released into the atmosphere. The ammonia water is pressurized by a pump 64 and sent to an ammonia injector 66. The ammonia injector 66 has a structure suitable for injecting a liquid. Within the cylinder 14, the ammonia water evaporates to form water vapor and ammonia gas. The power plant 60 converts the ammonia-containing gas delivered from the reformer 42 into ammonia water via the post-reforming condenser 62, which then supplies the ammonia water to the cylinder 14.

Because the water is pressurized as a liquid rather than a gas, the work required to pressurize it is reduced. Furthermore, because the water is supplied to the cylinder 14 as a liquid, the heat of vaporization cools the inside of the cylinder 14, particularly the combustion chamber, as it evaporates. Cooling the inside of the cylinder 14 and lowering the temperature reduces the ignition and combustibility of the hydrogen, making it possible to suppress abnormal combustion.

Figure 4 is a schematic diagram showing the configuration of a power unit 70 according to a fourth embodiment of the present invention. Components identical to those of the power unit 10 described above are assigned the same reference numerals, and their description will be omitted. The power unit 70 includes a pre-reformer condenser 72 that cools the exhaust gas before it is sent to the reformer 42 and condenses the water (water vapor) in the exhaust gas. The water condensed in the pre-reformer condenser 72 is separated and released. The exhaust gas from which the water has been separated is sent to the reformer 42. The power unit 70 may include a heater 74 that heats the exhaust gas in the reformer 42 or before it is sent to the reformer 42. By using the heater 74 to increase the temperature of the exhaust gas cooled in the pre-reformer condenser 72, the efficiency of the catalyst in the reformer 42 can be improved. The power unit 70 supplies the ammonia-containing gas sent from the reformer 42 to the cylinders 14 with its original composition, i.e., directly. By separating water from the exhaust gas before it is sent to the reformer 42, the concentration of nitrogen oxides increases, improving the reforming efficiency in the reformer 42.

Figure 5 is a schematic diagram showing the configuration of a power plant 80 according to a fourth embodiment of the present invention. Components that are the same as those of the power plant 10 described above are assigned the same reference numerals, and their description will be omitted. The power plant 80 includes a pre-reformer condenser 82 that cools the exhaust gas before it is sent to the reformer 42 and condenses the water (water vapor) in the exhaust gas. The water condensed in the pre-reformer condenser 82 is separated and released. The exhaust gas from which the water has been separated is sent to the reformer 42. The power plant 80 may include a heater 84 that heats the exhaust gas in the reformer 42 or before it is sent to the reformer 42. By using the heater 84 to increase the temperature of the exhaust gas cooled in the pre-reformer condenser 82, the efficiency of the catalyst in the reformer 42 can be improved.

The power unit 80 is equipped with a separator 86 that separates nitrogen from the ammonia-containing gas produced in the reformer 42. Nitrogen separation is performed using a separation membrane that allows the passage of one of ammonia and nitrogen but not the other. The separated nitrogen is released into the atmosphere. The ammonia-containing gas, from which water has been removed in the pre-reforming condenser 82 and from which nitrogen has been removed in the separator 86, is compressed by the compressor 46 and sent to the ammonia injector 38. The power unit 80 supplies the ammonia-containing gas sent from the reformer 42 to the cylinder 14 via the separator 86.

By eliminating water and nitrogen, the work of the compressor 46 to compress the ammonia-containing gas can be reduced. Furthermore, gas with a high ammonia concentration can be supplied to the cylinder 14.

The above-described power units 10, 50, 60, 70, and 80 may be power units mounted on a vehicle and used to drive the vehicle. Furthermore, the oxidation-reduction catalyst device 34 may be replaced with an exhaust purification device that purifies nitrogen oxides.

<Additional Notes>
[1]
an internal combustion engine that obtains power by burning a mixture containing hydrogen;
a reformer into which a portion of the exhaust gas from the internal combustion engine and hydrogen are introduced and which reacts the nitrogen oxides in the exhaust gas with the hydrogen to produce ammonia;
Equipped with
the internal combustion engine has an ammonia injector that directly injects the ammonia generated by the reformer into a cylinder,
Power plant.
[2]
The power plant according to the above item [1],
a separator that separates at least one of water and nitrogen from the ammonia-containing gas produced by the reformer, and the ammonia-containing gas from which at least one of water and nitrogen has been separated is sent to the ammonia injector.
Power plant.
[3]
The power plant according to the above item [1],
a post-reforming condenser that cools the ammonia-containing gas produced by the reformer and condenses the water, and the ammonia dissolved in the condensed water is sent to the ammonia injector as ammonia water;
Power plant.
[4]
The power plant according to the above item [1],
a pre-reformer condenser that cools a portion of the exhaust gas from the internal combustion engine to condense and separate water, and the exhaust gas after condensing and separating the water is sent to the reformer;
Power plant.
[5]
The power plant according to the above item [4],
a separator that separates nitrogen from the gas containing ammonia produced by the reformer, and the gas containing ammonia from which water and nitrogen have been separated is sent to the ammonia injector.
Power plant.
[6]
The power plant according to any one of the above items [1] to [5], wherein the ammonia injector injects ammonia toward a high-temperature portion inside the cylinder.
[7]
The power plant according to any one of the above items [1] to [5], wherein the ammonia injector injects ammonia toward an ignition plug.
[8]
The power plant according to any one of the above items [1] to [7], further comprising an oxidation-reduction catalyst device that purifies exhaust gas from the internal combustion engine.
[9]
The power plant according to any one of the above items [1] to [8], wherein the hydrogen introduced into the reformer is hydrogen that is used as fuel.
[10]
The power plant according to any one of the above items [1] to [9], wherein the power plant is mounted on a vehicle and drives the vehicle.
[11]
The power plant according to the above item [1],
a pre-reformer condenser that cools a portion of the exhaust gas from the internal combustion engine to condense and separate water, and the exhaust gas after condensing and separating the water is sent to the reformer;
a separator that separates nitrogen from the ammonia-containing gas produced by the reformer;
The gas containing ammonia from which water and nitrogen have been separated is sent to the ammonia injector.
Power plant.

10, 50, 60, 70, 80 Power unit, 12 Internal combustion engine, 14 Cylinder, 18 Spark plug, 26 Hydrogen injector, 34 Redox catalyst device, 38 Ammonia injector, 42 Reformer, 44 Hydrogen supply valve, 46 Compressor, 52, 86 Separator, 62 Post-reforming condenser, 64 Pump, 66 Ammonia injector, 72, 82 Pre-reforming condenser, 74, 84 Heater.

Claims (9)

an internal combustion engine that obtains power by burning a mixture containing hydrogen;
a reformer into which a portion of the exhaust gas from the internal combustion engine and hydrogen are introduced and which reacts the nitrogen oxides in the exhaust gas with the hydrogen to produce ammonia;
Equipped with
the internal combustion engine has an ammonia injector that directly injects the ammonia generated by the reformer into a cylinder,
Power plant. 2. The power plant of claim 1,
a separator that separates at least one of water and nitrogen from the ammonia-containing gas produced by the reformer, and the ammonia-containing gas from which at least one of water and nitrogen has been separated is sent to the ammonia injector.
Power plant. 2. The power plant of claim 1,
a post-reforming condenser that cools the ammonia-containing gas produced by the reformer and condenses the water, and the ammonia dissolved in the condensed water is sent to the ammonia injector as ammonia water;
Power plant. 2. The power plant of claim 1,
a pre-reformer condenser that cools a portion of the exhaust gas from the internal combustion engine to condense and separate water, and the exhaust gas after condensing and separating the water is sent to the reformer;
Power plant. 5. The power plant according to claim 4,
a separator that separates nitrogen from the gas containing ammonia produced by the reformer, and the gas containing ammonia from which water and nitrogen have been separated is sent to the ammonia injector.
Power plant. The power plant described in any one of claims 1 to 5, wherein the ammonia injector injects ammonia toward a high-temperature portion within the cylinder. The power plant according to any one of claims 1 to 5, wherein the ammonia injector injects ammonia toward an ignition plug. The power plant according to any one of claims 1 to 5, comprising an oxidation-reduction catalyst device that purifies exhaust gas from the internal combustion engine. 6. The power plant according to claim 1, wherein the hydrogen introduced into the reformer is hydrogen used as fuel.