JP7610838B2 - Ammonia co-firing method, ammonia co-firing engine and ship equipped with the same - Google Patents

Description

The present invention relates to an ammonia co-fuel combustion method, an ammonia co-fuel combustion engine, and a ship equipped with the same.

In order to reduce greenhouse gas (GHG) emissions, improvements to ship shapes and navigation methods have been adopted. For marine engines, GHG reduction technologies using alternative fuels are being considered. Examples of alternative fuels include the use of carbon-free fuels such as hydrogen and ammonia (NH ₃ ). Ammonia does not emit carbon dioxide (CO ₂ ) when burned, and can be easily liquefied under atmospheric pressure, making it easy to store and transport. Focusing on these properties of ammonia, research and development is being conducted on its use as fuel.

A technology has been disclosed that increases the combustion rate of ammonia by controlling the formation of an ammonia premixture in a combustion chamber in which the ammonia concentration is higher on the inner wall surface side than in the center (Patent Document 1). In addition, a technology has been disclosed that effectively uses urea water to improve the combustion efficiency of an internal combustion engine when using urea water to purify nitrogen oxides contained in the exhaust gas of the internal combustion engine (Patent Document 2).

In addition, a configuration has been disclosed in which ammonia and highly combustible substances other than ammonia can be supplied to the combustion chamber in an ammonia-burning internal combustion engine (Patent Documents 3 and 4). A configuration has been disclosed in which operating parameters are controlled so that the mixture supplied to the combustion chamber becomes more combustible when the amount of ammonia supplied to the combustion chamber increases or when the ratio of ammonia supplied to the total amount of ammonia and highly combustible substances supplied to the combustion chamber increases. This suppresses the decrease in combustibility of the auxiliary fuel (highly combustible substance) caused by ammonia. In addition, when the ratio of ammonia in the total fuel supplied to the internal combustion engine is high, the injection timing of the non-ammonia fuel is advanced compared to when it is low. This allows the mixture in the combustion chamber to be burned appropriately.

In addition, a technology has been disclosed for an internal combustion engine for burning ammonia, which is equipped with an exhaust purification device that has excellent nitrogen oxide purification performance by including an ammonia feeder that supplies ammonia to the combustion chamber and a nitrogen oxide selective reduction catalyst that is arranged in the engine exhaust passage (Patent Document 5).

JP 2020-148198 A JP 2009-97419 A International Publication No. 2011/136151 International Publication No. 2011/132604 JP 2014-211155 A

As described above, technology related to internal combustion engines that use ammonia as fuel has been developed, but if the amount of ammonia supplied increases, the ammonia and nitrous oxide (N ₂ O), which have a high global warming potential, contained in the exhaust gas may cause air pollution. Therefore, it is necessary to reduce the ammonia and nitrous oxide contained in the exhaust gas in ammonia co-firing engines.

The objective of this invention is to provide an ammonia co-fuel engine with improved exhaust gas properties.

An ammonia co-firing method in an engine that co-firing ammonia and liquid fuel according to claim 1 is an ammonia co-firing method in an engine that co-firing ammonia and liquid fuel, which is characterized in that, when supplying the ammonia, air, and the liquid fuel to a combustion chamber of the engine and igniting them by compression ignition to co-firing them, a supply timing of the liquid fuel to the combustion chamber is made later than a supply start timing of the ammonia and the air, and the supply timing of the liquid fuel is advanced as a ratio of the supply amount of the ammonia to the total supply amount of the liquid fuel and the ammonia becomes larger , and an advance angle as the supply timing of the liquid fuel is set in a range of more than -40° and not more than -55° with respect to a top dead center (TDC) of the engine, in which the combustion phase of the engine can be retarded .

Here, it is preferable that the liquid fuel is supplied by multi-stage injection.

It is also preferable that the liquid fuel is diesel.

It is also preferable to premix the ammonia and the air before supplying them to the combustion chamber.

It is also preferable that the ratio of the amount of ammonia supplied to the total amount of the liquid fuel and the ammonia supplied is in the range of 1% to 95%.

It is also preferable to purify nitrogen oxides (NOx) in the exhaust gas discharged from the combustion chamber using the ammonia in a selective catalytic reduction system.

It is also preferable to use the ammonia that slips during the co-combustion of the ammonia and the liquid fuel in the combustion chamber to reduce the nitrogen oxides (NOx).

A compression ignition type ammonia co-fuel engine that co-fuels ammonia according to claim 8 includes a combustion chamber, an ammonia supply means that supplies the ammonia to the combustion chamber, an air supply means that supplies air to the combustion chamber, a liquid fuel supply means that supplies liquid fuel to the combustion chamber, a fuel ratio setting means that sets a ratio of the supply amount of the ammonia to a total supply amount of the liquid fuel and the ammonia, and a supply timing control means that controls the supply timing of the liquid fuel by the liquid fuel supply means according to the ratio setting of the fuel ratio setting means, and is characterized in that the supply timing of the liquid fuel to the combustion chamber is delayed from the supply start timing of the ammonia and the air, and the supply timing of the liquid fuel is advanced by the supply timing control means as the ratio of the supply amount of the ammonia set by the fuel ratio setting means becomes larger, and the advance angle as the supply timing of the liquid fuel is set in a range of more than -40° and not more than -55° with respect to the top dead center (TDC) of the engine, in which the combustion phase of the engine can be delayed .

Here, it is preferable that the supply timing control means controls the supply of the liquid fuel by the liquid fuel supply means to inject the liquid fuel in multiple stages.

It is also preferable that the liquid fuel is diesel.

It is also preferable to inject the ammonia into the air supply path of the air supply means, and to mix the ammonia with the air before supplying it to the combustion chamber.

It is also preferable that the ratio of the amount of ammonia supplied to the total amount of the liquid fuel and the ammonia supplied is in the range of 1% to 95%.

It is also preferable to provide a selective catalytic reduction system in the exhaust path of the exhaust gas, which uses the ammonia to purify NOx in the exhaust gas discharged from the combustion chamber.

It is also preferable to have an ammonia supply control means for controlling the supply of the ammonia used in the selective catalytic reduction system.

It is also preferable that the ship be equipped with an ammonia co-fuel engine, characterized by being equipped with the above-mentioned ammonia co-fuel engine.

The ammonia co-firing method in an engine that co-firings ammonia and liquid fuel according to claim 1 is an ammonia co-firing method in an engine that co-firings ammonia and liquid fuel, in which the ammonia, air, and liquid fuel are supplied to a combustion chamber of the engine and ignited by compression ignition to co-firing the ammonia, the timing of supplying the liquid fuel to the combustion chamber is delayed from the timing of starting supply of the ammonia and the air, and the timing of supplying the liquid fuel is advanced as the ratio of the amount of supply of the ammonia to the total amount of supply of the liquid fuel and the ammonia increases, and the advance angle as the timing of supplying the liquid fuel is set in a range of more than -40° and less than -55° with respect to the top dead center (TDC) of the engine, which allows the combustion phase of the engine to be delayed , thereby reducing ammonia slip and nitrogen oxides (NOx) such as nitrous oxide, and improving the properties of the exhaust gas. In addition, the properties of the exhaust gas can be improved while maintaining stable combustion in the ammonia co-firing method in an engine that co-firing ammonia and liquid fuel.

Here, the liquid fuel is supplied by multi-stage injection, which can improve the properties of the exhaust gas more than with a single injection.

In addition, by using diesel as the liquid fuel, the properties of the exhaust gas can be improved in the ammonia co-firing method using general diesel as fuel. In addition, by pre-mixing the ammonia and the air and supplying them to the combustion chamber, the properties of the exhaust gas can be improved.

In addition, by setting the ratio of the amount of ammonia supplied to the total amount of the liquid fuel and the ammonia supplied in the range of 1% to 95%, it is possible to increase the ammonia co-firing rate while further improving the properties of the exhaust gas.

In addition, by purifying the nitrogen oxides (NOx) in the exhaust gas discharged from the combustion chamber with a selective catalytic reduction system using the ammonia, it is possible to reduce the nitrogen oxides (NOx) in the exhaust gas by utilizing the ammonia used for combustion in an ammonia co-combustion method in an engine that co-combustes ammonia and liquid fuel. Furthermore, by sharing the ammonia supply source and supply system, the system can be simplified.

In addition, by using the ammonia that slips during the co-combustion of the ammonia and the liquid fuel in the combustion chamber to reduce the nitrogen oxides (NOx), it is possible to reduce the nitrogen oxides (NOx) in the exhaust gas by using the ammonia contained in the exhaust gas supplied from the same supply source.

A compression ignition type ammonia co-fuel engine that co-fuels ammonia, which corresponds to claim 8 , includes a combustion chamber, an ammonia supply means for supplying the ammonia to the combustion chamber, an air supply means for supplying air to the combustion chamber, a liquid fuel supply means for supplying liquid fuel to the combustion chamber, a fuel ratio setting means for setting a ratio of the supply amount of the ammonia to the total supply amount of the liquid fuel and the ammonia, and a supply timing control means for controlling the supply timing of the liquid fuel by the liquid fuel supply means according to the ratio setting of the fuel ratio setting means, and the supply timing of the liquid fuel to the combustion chamber is delayed from the supply start timing of the ammonia and the air, and the supply timing control means advances the supply timing of the liquid fuel as the ratio of the supply amount of the ammonia set by the fuel ratio setting means becomes larger, and the advance angle as the supply timing of the liquid fuel is set in a range of more than -40° and not more than -55° with respect to the top dead center (TDC) of the engine, which makes it possible to retard the combustion phase of the engine, thereby reducing ammonia slip and nitrogen oxides (NOx) such as nitrous oxide, and improving the properties of the exhaust gas. In addition, it is possible to maintain stable combustion in an engine that combusts ammonia and liquid fuel in an ammonia co-combustion method while improving the properties of exhaust gas.

Here, the supply timing control means controls the supply of the liquid fuel by the liquid fuel supply means to inject the liquid fuel in multiple stages, thereby improving the properties of the exhaust gas compared to a single injection.

In addition, by using diesel as the liquid fuel, the properties of the exhaust gas can be improved in an ammonia co-fuel engine using general diesel as fuel. In addition, by injecting the ammonia into the air intake path of the air intake means and mixing the ammonia and the air in advance before supplying them to the combustion chamber, the properties of the exhaust gas can be improved.

In addition, by setting the ratio of the amount of ammonia supplied to the total amount of the liquid fuel and the ammonia supplied in the range of 1% to 95%, it is possible to increase the ammonia co-firing rate while further improving the properties of the exhaust gas.

In addition, by providing a selective catalytic reduction system in the exhaust path of the exhaust gas that uses the ammonia to purify NOx in the exhaust gas discharged from the combustion chamber, it is possible to reduce nitrogen oxides (NOx) in the exhaust gas by utilizing the ammonia used for combustion in an ammonia-mixed combustion engine that mixes ammonia and liquid fuel. Furthermore, the system can be simplified by sharing the ammonia supply source and supply system.

In addition, by providing an ammonia supply control means for controlling the supply of the ammonia used in the selective catalytic reduction system, the ammonia contained in the exhaust gas can be used to reduce nitrogen oxides (NOx) in the exhaust gas.

In addition, by making a ship equipped with an ammonia-mixed combustion engine, which is characterized by being equipped with the above-mentioned ammonia-mixed combustion engine, it is possible to realize a ship with improved exhaust gas properties.

FIG. 1 is a configuration diagram of an ammonia-mixed combustion engine according to an embodiment of the present invention. FIG. 2 is a diagram showing conditions in an ammonia co-firing test in an embodiment of the present invention. FIG. 1 is a diagram showing the results of a test for reducing emissions of unburned ammonia, etc. FIG. 1 is a diagram showing a combustion history in a test for reducing emissions of unburned ammonia, etc. FIG. 1 is a diagram showing a combustion history in a test for reducing emissions of unburned ammonia, etc. FIG. 4 is a graph showing the relationship between the timing of liquid fuel injection and the crank angle at which the normalized cumulative heat release reaches a predetermined value. FIG. 13 is a diagram showing the results of a test to confirm the effect of the pilot injection amount of diesel. FIG. 1 is a diagram showing a combustion history in a test to confirm the effect of a pilot injection amount of diesel. FIG. 13 is a diagram showing the results of a test to confirm the effect of an ammonia supply amount. FIG. 1 is a diagram showing a combustion history in a test to confirm the effect of an ammonia supply amount. FIG. 1 is a diagram showing a combustion history in a test to confirm the effect of an ammonia supply amount. FIG. 11 is a diagram showing the results of an effect confirmation test of multi-stage injection of liquid fuel. FIG. 11 is a diagram showing the results of an effect confirmation test of multi-stage injection of liquid fuel. FIG. 11 is a diagram showing the results of an effect confirmation test of multi-stage injection of liquid fuel.

As shown in FIG. 1, the ammonia-mixed combustion engine 100 according to the embodiment of the present invention includes a piston 10, a cylinder 12, a combustion chamber 14, an intake path 16, an intake valve 18, an exhaust path 20, an exhaust valve 22, ammonia supply means for combustion 24, a pressure regulator 26, a liquid fuel supply means 28, a high-pressure pump 30, a selective catalytic reduction (SCR) system 32, ammonia supply means for reduction 34, and a control device 36. The ammonia-mixed combustion engine 100 is preferably mounted on a ship and functions as a main engine for driving a propeller, or as an auxiliary engine.

In each cylinder of the ammonia co-fuel engine 100, the piston 10 and cylinder 12 form a combustion chamber 14. That is, the cylinder 12 is formed by combining a cylinder block and a cylinder head, and the piston 10 is arranged so that it can reciprocate within the bore of the cylinder block, and the cylinder head is connected to face the piston 10 and surround the bore. The space surrounded by the piston 10 and the cylinder 12 forms the combustion chamber 14.

Each cylinder of the ammonia co-fuel engine 100 is provided with an intake path 16 and an exhaust path 20. An intake valve 18 is provided in the intake path 16. An exhaust valve 22 is provided in the exhaust path 20. A crank angle sensor (not shown) that detects the rotational angle position of the crankshaft according to the movement of the piston 10 is provided in each cylinder, and the intake valve 18 and the exhaust valve 22 are controlled to open and close according to the rotational angle position detected by the control device 36. That is, the intake valve 18 is opened and closed according to the rotational angle position of the crankshaft, and the timing of intake into the cylinder is controlled. In addition, the exhaust valve 22 is opened and closed according to the rotational angle position of the crankshaft, and the exhaust from the cylinder is controlled.

Further, the intake passage 16 is provided with a combustion ammonia supply means 24. A cylinder 102 of ammonia (NH ₃ ) is connected to the combustion ammonia supply means 24 via a pressure regulator 26. Liquefied ammonia is stored in the cylinder 102. The combustion ammonia supply means 24 includes a flowmeter and an injection valve, and receives ammonia whose pressure is controlled by the pressure regulator 26, and injects the ammonia into the intake passage 16 so as to achieve a set flow rate and a mixture ratio with air. The pressure regulator 26 controls the pressure of the ammonia and the ammonia supply flow rate supplied from the combustion ammonia supply means 24, and this is performed by a fuel ratio setting means 36a of the control device 36, which will be described later. The combustion ammonia supply means 24 can also be configured to supply ammonia directly to the cylinder 12 in addition to the intake passage 16.

In this way, by injecting ammonia into the intake passage 16, the supplied ammonia can be mixed with air as an oxidizer and supplied to the combustion chamber 14. Ammonia can be supplied not only as a liquid but also as a gas. Also, other oxidizers such as oxygen-enriched air or pure oxygen may be used instead of air. Also, other auxiliary fuels such as hydrogen (H ₂ ), natural gas, LPG, etc. may be added. The supply of the mixture of ammonia and air to the combustion chamber 14 is performed together with the intake stroke in the ammonia co-fuel engine 100, and is started, for example, before the pilot injection of liquid fuel described below.

Each cylinder of the ammonia-mixed combustion engine 100 is provided with a liquid fuel supply means 28 and a high-pressure pump 30. The liquid fuel supply means 28 is equipped with an electronic fuel injection valve, and receives liquid fuel pressurized by the high-pressure pump 30 and injects the liquid fuel into the combustion chamber 14. The liquid fuel can be, for example, diesel, heavy oil, propane, etc. When the liquid fuel is diesel, it is preferable to pressurize the liquid fuel by the high-pressure pump 30 to about 100 MPa. The amount of liquid fuel supplied from the liquid fuel supply means 28 is controlled by a fuel ratio setting means 36a of the control device 36 described later. The timing of the injection of the liquid fuel by the liquid fuel supply means 28 is controlled by a supply timing control means 36b of the control device 36 described later. For example, pilot injection of liquid fuel is performed at a timing before the top dead center (TDC) during the compression stroke of the ammonia-mixed combustion engine 100.

The ammonia co-fuel engine 100 is provided with an SCR system 32. The SCR system 32 performs post-treatment to reduce nitrogen oxides (NOx) in the exhaust gas. The SCR system 32 utilizes the action of a catalyst to reduce nitrogen oxides to nitrogen (N ₂ ) and water (H ₂ O) using ammonia contained in the exhaust gas, thereby suppressing the emission of nitrogen oxides contained in the exhaust gas.

The ammonia co-fuel engine 100 also includes a reduction ammonia supply means 34. The reduction ammonia supply means 34 includes a supply valve and supplies ammonia into the exhaust path 20 to promote the reduction reaction of the nitrogen oxide in the SCR system 32. The supply of ammonia by the reduction ammonia supply means 34 is controlled by an ammonia supply control means 36c of the control device 36.

In the ammonia co-fuel engine 100 of this embodiment, the system can be simplified by sharing at least a portion of the supply source and supply system for the ammonia used as fuel and the ammonia used in the reduction reaction in the SCR system 32.

The amount of ammonia used as fuel supplied to the ammonia-mixed combustion engine 100 can be increased and supplied to the selective catalytic reduction system 32 as unburned slipped ammonia for use in reducing nitrogen oxides. In this case, delicate ratio control is required, so it is preferable to provide an ammonia detection means in the exhaust path 20 and precisely control the amount of ammonia supplied by the supply timing control means 36b of the control device 36.

The control device 36 controls the ammonia-mixed combustion engine 100. The control device 36 includes, for example, a programmable computer and a signal generating circuit for generating signals sent to each part of the ammonia-mixed combustion engine 100. The control device 36 functions as a fuel ratio setting means 36a, a supply timing control means 36b, and an ammonia supply control means 36c.

The fuel ratio setting means 36a is a means for controlling the ratio of the amount of ammonia supplied to the total amount of ammonia and liquid fuel supplied in the ammonia-mixed combustion engine 100. That is, the fuel ratio setting means 36a adjusts the ratio of the amount of ammonia supplied to the total amount of ammonia and liquid fuel supplied, thereby controlling the ratio of the amount of ammonia supplied to the total amount of ammonia and liquid fuel to a desired value. The ratio of the amount of ammonia supplied to the total amount of ammonia and liquid fuel supplied may be set to a constant value in advance, or may be set according to the operating state of the ammonia-mixed combustion engine 100. For example, the ratio of the amount of ammonia supplied to the total amount of ammonia and liquid fuel supplied may be set according to the output value of a sensor that detects the amount of ammonia supplied or the amount of liquid fuel supplied. The ratio of the amount of ammonia supplied may also be controlled according to the load on the ammonia-mixed combustion engine 100. For example, when the load suddenly increases, the ratio of diesel, which has a large heat value and a fast combustion speed, may be increased.

The supply timing control means 36b is a means for controlling the timing and duration of ammonia supply by the combustion ammonia supply means 24, and the timing and duration of liquid fuel supply by the liquid fuel supply means 28. The supply timing control means 36b adjusts the timing and duration of ammonia supply and the timing and duration of liquid fuel supply according to the ratio of the amount of ammonia supply to the total amount of ammonia and liquid fuel supply set by the fuel ratio setting means 36a.

The ammonia supply control means 36c is a means for controlling the supply of ammonia to the SCR system 32. The ammonia supply control means 36c controls the reducing ammonia supply means 34 according to the amount of nitrogen oxides (NOx) contained in the exhaust gas of the ammonia co-fuel engine 100, and adjusts the amount of ammonia supplied to the SCR system 32.

[Ammonia and diesel mixed combustion test]
Hereinafter, a description will be given of a test of mixed combustion of ammonia and diesel using the ammonia mixed combustion engine 100. Fig. 2 shows main specifications of the ammonia mixed combustion engine 100 used in the test.

The ammonia was taken out in a liquefied state in a cylinder 102, kept at about 40°C, and decompressed to 0.3 MPa by a pressure regulator 26, and then supplied to an injection valve (gas injector: 110764 QUANTUM) of the combustion ammonia supply means 24 installed near the inlet of the combustion chamber 14 of the intake path 16. A buffer cylinder was provided in front of the injection valve to suppress ammonia pressure pulsation. The supply pipe was maintained at a temperature of 264 K or higher to prevent ammonia condensation. The amount of ammonia supplied was adjusted by adjusting the opening time of the injection valve. In the test, diesel was used as the liquid fuel. The diesel was pressurized to 100 MPa by a high-pressure pump 30 and supplied into the fuel accumulator, and was injected into the combustion chamber 14 at the desired crank angle by an electronically controlled injection valve of the liquid fuel supply means 28.

During the test, the torque was automatically controlled so that the rotation speed was kept at the set value by an electric load device connected to the ammonia-mixed combustion engine 100. The pressure inside the cylinder of the ammonia-mixed combustion engine 100 was obtained for 50 cycles at every 0.5° crank angle using a piezoelectric pressure gauge (GH14P AVL) and a charge amplifier (FI PIEZO AVL), and the average was used as the measurement data. Regarding the exhaust gas components, total hydrocarbons (THC) were measured using an FID analyzer (600HFID CAI). Gases other than THC, such as nitric oxide (CO), carbon dioxide (CO ₂ ), nitric oxide (NO), nitrogen dioxide (NO ₂ ), ammonia (NH ₃ ), and water (H ₂ O), were measured using an FTIR exhaust gas analyzer (FAST2200 Iwata Denko). The gas analyzer simultaneously sampled and measured multiple high-temperature components. The sampling line and sampling filter were heated to 191°C, and ammonia in exhaust gas containing water was accurately detected. The calibration curve used to quantify ammonia concentration in the FTIR exhaust gas analyzer can measure up to 3000 ppm, but for reference, ammonia concentrations far exceeding 3000 ppm were also measured. The level of smoke pollution in the exhaust gas was measured using a smoke meter (GSM-3, Tsukasa Sokuken).

<Tests to reduce emissions of unburned ammonia, etc.>
Tests were conducted on the emissions of carbon dioxide (CO ₂ ), nitric oxide (CO), hydrocarbons (HC), nitrogen oxides (NOx), nitrous oxide (N ₂ O), and unburned ammonia (NH ₃ ) when an ammonia co-firing engine 100 was operated using a mixture of ammonia and diesel as fuel.

In the test, diesel, which is a liquid fuel, was injected from the liquid fuel supply means 28. The diesel was injected as a pilot injection after the supply of ammonia to the combustion chamber 14 started during the intake stroke and before the top dead center (TDC) was reached during the compression stroke. In other words, the timing at which the supply of the ammonia-air mixture started was set to precede the timing at which the pilot injection of diesel started.

The pilot injection amount of diesel, the ammonia supply flow rate, and the engine speed were kept constant at 24 mg, 45 L/min, and 1500 rpm, respectively. The ratio of the ammonia supply amount to the total supply amount of diesel and ammonia was maintained at approximately 45%. The timing of the pilot injection of diesel was varied from -10° to -65° before top dead center (BTDC) of the engine at intervals of 5° in crank angle (negative angles mean before top dead center). During the test, combustion in the ammonia co-fuel engine 100 was stable, and the fluctuation of the mean effective pressure was less than 1.5%. Note that the pilot injection of diesel was limited to -65° before top dead center (BTDC) because the load and speed became unstable when the pilot injection was set to -70°.

Figure 3 shows the net thermal efficiency, the ratio of the ammonia supply amount, and the amount of exhaust of various gases with respect to the change in the timing of the pilot injection of diesel. The net thermal efficiency is the ratio of the braking output to the total lower heating value of ammonia and diesel. In Figure 3, the concentration of nitrogen oxides (NOx) indicates the sum of NO and _NO2 . Also, the unburned ammonia ( _NH3 ) ratio indicates the ratio of the amount of ammonia ( _NH3 ) released to the amount of ammonia ( _NH3 ) supplied.

When the timing of the pilot injection of diesel fuel advances beyond -25° relative to the top dead center (TDC), the amount of emissions of nitric oxide (CO), nitrous oxide (N ₂ O), and unburned ammonia (NH ₃ ) tends to decrease. Therefore, in order to reduce the amount of emissions of nitric oxide (CO), nitrous oxide (N ₂ O), and unburned ammonia (NH ₃ ), it is preferable to advance the timing of the pilot injection of diesel fuel beyond -25° relative to the top dead center (TDC). On the other hand, in order to stably operate the ammonia co-fuel engine 100, it is preferable to delay the timing of the pilot injection of diesel fuel beyond -70° relative to the top dead center (TDC). In other words, it is preferable to set the timing of the pilot injection of diesel fuel in the range of -25° to -70° relative to the top dead center (TDC).

In particular, when the timing of the pilot injection of diesel was in the range of -30° to -65°, the emissions of nitric oxide (CO), nitrous oxide (N ₂ O), and unburned ammonia (NH ₃ ) were dramatically reduced. Furthermore, when the timing of the pilot injection of diesel was in the range of -40° to -55°, the emissions of nitric oxide (CO), nitrous oxide (N ₂ O), and unburned ammonia (NH ₃ ) were more significantly reduced.

On the other hand, nitrogen oxides (NOx) peaked when the timing of the pilot injection of diesel was in the range of -30° to -45°. Furthermore, as the timing of the pilot injection of diesel was advanced from -30°, the emissions of nitric oxide (CO) and hydrocarbons (HC) tended to increase. When the timing of the pilot injection of diesel exceeded -50°, the emissions of nitrogen oxides (NOx) and nitric oxide (CO) gradually decreased, while the emissions of hydrocarbons (HC) increased. These changes are presumably due to a combination of the low combustion temperature in the ammonia co-fuel engine 100 and the collision of the injected diesel with the wall of the combustion chamber.

Figures 4 and 5 show the history of the pressure in the cylinder 12 of the ammonia co-fuel engine 100, the heat release rate and normalized cumulative heat release, and the injection signal indicating the timing of the pilot injection of diesel when the timing of the pilot injection of diesel is changed from -10° to -60°. As shown in Figures 4 and 5, the combustion phase is advanced up to the timing of the pilot injection of diesel of -40°, and in contrast, the combustion phase is delayed when the timing of the pilot injection of diesel exceeds -40°.

Figure 6 shows the crank angle when the normalized cumulative heat release reaches 10%, 50% and 90% at the timing of pilot injection of diesel. In Figure 6, the crank angles when the normalized cumulative heat release reaches 10%, 50% and 90% are shown as CA10, CA50 and CA90, respectively. From Figure 6, the combustion stage changed when the timing of pilot injection of diesel is -40° in all cases where the normalized cumulative heat release is 10%, 50% and 90%. That is, when the timing of pilot injection of diesel is -10° to -40°, the crank angle when the normalized cumulative heat release reaches 10%, 50% and 90% tends to be advanced as the timing is advanced. On the other hand, when the timing of pilot injection of diesel is -40° to -65°, the crank angle when the normalized cumulative heat release reaches 10%, 50% and 90% tends to be delayed as the timing is advanced. As the timing of the pilot injection of diesel fuel was advanced from -10° to -30°, the difference in crank angles at which the normalized cumulative heat release was 10% and 90% was reduced. Then, as the timing of the pilot injection of diesel fuel was advanced beyond -30°, the difference in crank angles at which the normalized cumulative heat release was 10% and 90% increased. In other words, the effect of the pilot injection timing of diesel fuel on the combustion phase changed from advanced to retarded.

By pilot-injecting diesel fuel earlier than top dead center (TDC), more time is available for the diesel fuel to mix with the ammonia (NH ₃ ) and air mixture, thus making the mixture more homogeneous in the combustion chamber 14. This presumably shifts the combustion mode from conventional diesel combustion (CDC) to partial homogeneous charge compression ignition (PPCI) combustion.

When the combustion mode shifts from diesel combustion (CDC) to partial homogeneous charge compression ignition (PPCI), the mixture of non-reactive ammonia (NH ₃ ) and air and the injected diesel fuel are mixed more during the longer ignition delay time. Before the diesel fuel is ignited, OH species are generated and react with ammonia (NH ₃ ), accelerating the decomposition of ammonia (NH ₃ ). If the combustion chamber 14 is still in a high temperature state after the ammonia (NH ₃ ) is decomposed, nitrous oxide (N ₂ O) is thermally decomposed. In other words, it is presumed that the emission of unburned ammonia (NH ₃ ) and nitrous oxide (N ₂ O) can be reduced by mixing diesel fuel into the mixture of non-reactive ammonia (NH ₃ ) and air to accelerate the decomposition of ammonia (NH ₃ ).

When the combustion mode is shifted to partial homogeneous charge compression ignition (PPCI), the amount of unburned ammonia (NH ₃ ) and nitrous oxide (N ₂ O) emissions decreases, but as shown in Figure 3, when the timing of the pilot injection of diesel is advanced, the net thermal efficiency decreases. When the timing of the pilot injection of diesel is advanced, the crank angle (CA50) at which the normalized cumulative heat release is 50% is moved before the top dead center (TDC). This is presumably the main reason for the decrease in net thermal efficiency.

<Test to confirm the effect of pilot fuel injection amount>
A test was conducted to confirm the effect of the pilot injection amount of diesel on partial homogenous charge compression ignition (PPCI) combustion when an ammonia-mixed combustion engine 100 using a mixture of ammonia and diesel as fuel was operated. In the test, the engine speed, the timing of the pilot injection of diesel and the ammonia supply flow rate were maintained at 1500 rpm, -50° and 46 L/min, respectively, while the pilot injection amount of diesel was changed. During the test, the combustion in the ammonia-mixed combustion engine 100 was stable, and the fluctuation of the mean effective pressure was less than 1.2%.

Figure 7 shows the net thermal efficiency, the ratio of the ammonia supply amount, and the amount of emissions of various gases when the pilot injection amount of diesel is changed from 17.8 mg to 22.8 mg. This pilot injection amount of diesel corresponds to 45% to 51% when converted into the ratio of the ammonia supply amount to the total supply amount of diesel and ammonia. Also, Figure 8 shows the pressure in the cylinder 12 of the ammonia co-fuel engine 100, the heat release rate and normalized cumulative heat release, and the history of the injection signal indicating the timing of the pilot injection of diesel when the pilot injection amount of diesel is changed.

As shown in FIG. 7, the net thermal efficiency decreased as the amount of injected diesel increased. As the injection amount of diesel increased, the amount of carbon dioxide (CO ₂ ) emissions increased, and the amount of nitrogen oxide (CO) and hydrocarbon (HC) emissions also increased slightly. As shown in FIG. 7 and FIG. 8, there was a correlation between the amount of nitrogen oxide (NOx) emissions and the tendency of the peak pressure in the cylinder 12. Also, as shown in FIG. 7, as the pilot injection amount of diesel increased, the amount of nitrogen oxide (CO) and hydrocarbon (HC) emissions tended to increase. Also, as the pilot injection amount of diesel increased, the amount of unburned ammonia (NH ₃ ) and nitrous oxide (N ₂ O) emissions tended to decrease. However, when the pilot injection amount of diesel exceeded 19.7 mg, the decreasing tendency of the amount of unburned ammonia (NH ₃ ) and nitrous oxide (N ₂ O) emissions became smaller. These results indicate that diesel is effective as a liquid fuel in partial homogeneous charge compression ignition (PPCI) combustion of ammonia (NH ₃ ).

<Test to confirm the effect of ammonia supply amount>
A test was conducted to confirm the effect of the ammonia supply flow rate when the ammonia-mixed combustion engine 100 using a mixture of ammonia and diesel as fuel was operated. In the case where pilot injection of diesel was performed at two timings, −45° and −60° before top dead center (BTDC), the engine speed was kept constant at 1500 rpm, and the pilot injection amount of diesel was kept constant at 21 mg, while the ammonia supply amount was changed. The ammonia supply amount was changed in the range of 38% to 58% in terms of the ratio of the ammonia supply amount to the total supply amount of diesel and ammonia. During the test, the combustion in the ammonia-mixed combustion engine 100 was stable, and the fluctuation of the mean effective pressure was less than 1.4%. The fluctuation of the mean effective pressure tended to decrease to about 1% as the ammonia supply flow rate increased.

Figure 9 shows the net thermal efficiency, the ratio of the ammonia supply amount, and the amount of exhaust of various gases with respect to the ammonia supply flow rate. Figures 10 and 11 show the pressure in the cylinder 12 of the ammonia co-fuel engine 100, the heat release rate and normalized cumulative heat release, and the history of the injection signal indicating the timing of the pilot injection of diesel when the ammonia supply flow rate is changed when pilot injection of diesel is performed at two timings, -45° and -60° before top dead center (BTDC), respectively.

As described above, in the ammonia-mixed combustion engine 100, the amount of unburned ammonia (NH ₃ ) and nitrous oxide (N ₂ O) emissions can be reduced by mixing ammonia with liquid fuel such as diesel and burning it. That is, the amount of unburned ammonia (NH 3 ) and nitrous oxide (N ₂ O) emissions can be reduced in a range of 1% to 95% in terms of the ratio of the amount of ammonia supplied to the total amount of diesel and ammonia supplied. In particular, the reduction in the amount of unburned ammonia (NH _{3 )} and nitrous oxide (N ₂ O) emissions is remarkable in a range of 30% to 70% in terms of the ratio of the amount of ammonia supplied to the total amount of diesel and ammonia supplied, and is more remarkable in a range of 45% to 60%.

However, as shown in Figure 9, when the ratio of the ammonia feed flow rate increased, the net thermal efficiency, nitrogen oxides (NOx) and unburned ammonia (NH ₃ ) increased regardless of the timing of the pilot injection of diesel. The increase in the amount of nitrogen oxides (NOx) emissions may be due to the oxidation of nitrogen atoms in ammonia (NH ₃ ) and nitrogen atoms in the intake air, but it was difficult to identify the source of the nitrogen oxides (NOx). Also, as shown in Figures 10 and 11, the combustion phase was retarded and approached top dead center (TDC) as the ratio of the ammonia feed flow rate increased. Also, as the ratio of the ammonia feed flow rate increased, the net thermal efficiency and the peak pressure in the cylinder 12 became higher.

When the timing of the pilot injection of diesel was set to -45°, the amount of nitric oxide (CO) emissions increased with an increase in the ratio of the ammonia supply flow rate. When the timing of the pilot injection of diesel was set to -60°, the amount of nitric oxide (CO) emissions remained approximately constant with an increase in the ratio of the ammonia supply flow rate. In the range where the ratio of the ammonia supply flow rate was less than about 46%, the amount of nitric oxide (CO) emissions was smaller when the timing of the pilot injection of diesel was set to -45° than when it was set to -60°. On the other hand, in the range where the ratio of the ammonia supply flow rate was about 46% or more, the amount of nitric oxide (CO) emissions was smaller when the timing of the pilot injection of diesel was set to -60° than when it was set to -45°. From this, from the viewpoint of reducing the amount of nitric oxide (CO) emissions, it is preferable to advance the timing of the supply of diesel as the ratio of the amount of ammonia supply to the total amount of diesel and ammonia supply increases.

There was relatively little change in hydrocarbon (HC) emissions when the timing of the pilot injection of diesel was changed. This is presumably related to incomplete combustion, which produces nitric oxide (CO) and hydrocarbon (HC) emissions.

As shown in Figures 10 and 11, the maximum pressure in the cylinder 12 was higher when the pilot injection timing of diesel was set at -45° than when it was set at -60°. Also, the temperature of the combustion chamber 14 increased with increasing ammonia feed flow rate. As shown in Figure 9, the increase in nitric oxide (CO) emissions with the ammonia feed flow rate when the pilot injection timing of diesel was set at -45° may be caused by thermal dissociation of carbon dioxide (CO ₂ ) at high temperatures. In contrast, the change in nitric oxide (CO) emissions with the change in ammonia feed flow rate when the pilot injection timing of diesel was set at -60° was relatively small.

When diesel was pilot-injected at -60°, an increase in nitrous oxide (N ₂ O) was observed in the range where the ratio of the ammonia supply flow rate was small. This is presumably due to the fact that the pressure in the cylinder 12 was relatively low, resulting in a low combustion temperature, as shown in Figure 11.

As shown in Figures 10 and 11, the ignition timing of combustion tended to be delayed with an increase in the ratio of the ammonia supply flow rate, whether the timing of the pilot injection of diesel was set to -45° or -60°. When the timing of the pilot injection of diesel was set to -60° and the ammonia supply flow rate was 65 L/min, the net thermal efficiency reached 32%. This was close to the net thermal efficiency of 34% when the engine was operated using only diesel without supplying ammonia.

<Test to confirm the effect of multiple liquid fuel injection>
A test was conducted to confirm the influence of multi-stage pilot injection of diesel fuel when an ammonia-fueled engine 100 using a mixture of ammonia and diesel fuel was operated. In the test, the total injection amount, ammonia supply flow rate, and engine speed in the pilot injection of diesel fuel were kept constant at 24 mg, about 48 L/min, and 1500 rpm, respectively. The ratio of the ammonia supply amount to the total supply amount of diesel fuel and ammonia was maintained at about 45%. In the case of single injection, the timing of the pilot injection of diesel fuel was changed from -10° to -65° at intervals of 5° in crank angle before the top dead center (BTDC) of the engine. In the case of two-stage injection, the timing of the pilot injection of diesel fuel was changed from -45° to -65° at intervals of 5° in crank angle before the top dead center (BTDC) of the engine, and the sub-injection was changed from -35° to 55° for each. That is, the sub-injection was performed at -5° before the main injection in crank angle. In the following description, two-stage injection will be described using the timing of main injection.

Figures 12 to 14 show the net thermal efficiency, the ratio of ammonia supply, and the amount of emissions of various gases relative to the timing of pilot injection of diesel. In Figures 12 to 14, circles indicate the case where pilot injection of diesel was performed as a single injection, and triangles indicate the case where pilot injection of diesel was performed as a two-stage injection.

When the timing of the pilot injection of diesel was changed from -10° to -65°, the amount of nitric oxide (CO) emissions from single injection showed an increasing trend, peaked at -45°, and then showed a decreasing trend. In contrast, the amount of nitric oxide (CO) emissions from two-stage injection showed an increasing trend, but the amount of nitric oxide (CO) emissions was lower than that of single injection at all timings.

In addition, when the timing of the pilot injection of diesel was changed from -10° to -65°, the emissions of unburned ammonia (NH ₃ ) and nitrous oxide (N ₂ O) showed a decreasing trend, and the emissions dropped sharply especially when the injection timing was advanced from -30°. However, there was no significant difference in the emissions of unburned ammonia (NH ₃ ) and nitrous oxide (N ₂ O) between single injection and two-stage injection at any timing.

When the timing of the pilot injection of diesel was changed from -10° to -65°, nitrogen oxides (NOx) tended to increase, peaked at -45°, and then tended to decrease. When the timing of the pilot injection of diesel was changed from -10° to -65°, hydrocarbon (THC) emissions tended to increase. However, nitrogen oxides (NOx) and hydrocarbon (THC) emissions were the same or reduced in two-stage injection compared to single injection.

As described above, by using multiple injections in pilot injection of diesel, the amount of emissions of various gases can be kept at the same level or reduced compared to single injection.

The present invention can be widely applied not only to devices that require power, such as generators as main engines and auxiliary engines for ships, but also to ammonia co-fuel engines throughout the land and marine industries.

10 piston, 12 cylinder, 14 combustion chamber, 16 intake path, 18 intake valve, 20 exhaust path, 22 exhaust valve, 24 combustion ammonia supply means, 26 pressure regulator, 28 liquid fuel supply means, 30 high pressure pump, 32 SCR system, 34 reduction ammonia supply means, 36 control device, 36a fuel ratio setting means, 36b supply timing control means, 36c ammonia supply control means, 100 ammonia co-fuel engine, 102 cylinder.

Claims (15)

An ammonia co-firing method in an engine that co-firing ammonia and liquid fuel, comprising:
A method for co-firing ammonia in an engine, comprising: supplying the ammonia, air, and liquid fuel to a combustion chamber of the engine and igniting the ammonia, air, and liquid fuel by compression ignition to co-firing the ammonia, the method comprising: delaying a supply timing of the liquid fuel to the combustion chamber relative to a supply start timing of the ammonia and the air; and advancing the supply timing of the liquid fuel as a ratio of a supply amount of the ammonia to a total supply amount of the liquid fuel and the ammonia becomes larger; and setting an advance angle as the supply timing of the liquid fuel in a range of more than -40° and not more than -55° with respect to a top dead center (TDC) of the engine, which makes it possible to retard a combustion phase of the engine . The method for co-firing ammonia in an engine according to claim 1, characterized in that the liquid fuel is supplied by multi-stage injection. The method for co-firing ammonia in an engine according to claim 1 or 2, characterized in that the liquid fuel is diesel. The method for co-firing ammonia in an engine according to any one of claims 1 to 3, characterized in that the ammonia and the air are pre-mixed and supplied to the combustion chamber. The method for co-firing ammonia in an engine according to any one of claims 1 to 4 ,
A method for co-firing ammonia in an engine, wherein a ratio of a supply amount of the ammonia to a total supply amount of the liquid fuel and the ammonia is in a range of 1% to 95%. The method for co-firing ammonia in an engine according to any one of claims 1 to 5 ,
A method for co-firing ammonia in an engine, comprising purifying nitrogen oxides (NOx) in exhaust gas discharged from the combustion chamber using the ammonia in a selective catalytic reduction system. The method for co-firing ammonia in an engine according to claim 6 ,
A method for co-firing ammonia in an engine, comprising: reducing the nitrogen oxides (NOx) by utilizing ammonia that has slipped during co-firing of the ammonia and the liquid fuel in the combustion chamber. There is a compression ignition type ammonia co-combustion engine that co-combusts ammonia.
A combustion chamber;
an ammonia supply means for supplying the ammonia to the combustion chamber;
an air supply means for supplying air to the combustion chamber;
A liquid fuel supply means for supplying liquid fuel to the combustion chamber;
a fuel ratio setting means for setting a ratio of a supply amount of the ammonia to a total supply amount of the liquid fuel and the ammonia;
a supply timing control means for controlling a supply timing of the liquid fuel by the liquid fuel supply means in accordance with the ratio set by the fuel ratio setting means,
An ammonia-mixed combustion engine, characterized in that a supply timing of the liquid fuel to the combustion chamber is made later than a supply start timing of the ammonia and the air, and the supply timing of the liquid fuel is advanced by the supply timing control means as the ratio of the supply amount of the ammonia set by the fuel ratio setting means becomes larger, and an advance angle as the supply timing of the liquid fuel is set in a range of more than -40° and not more than -55° with respect to a top dead center (TDC) of the engine, which makes it possible to retard a combustion phase of the engine. The ammonia co-fuel engine according to claim 8 ,
The ammonia-mixed combustion engine, wherein the supply timing control means controls the supply of the liquid fuel by the liquid fuel supply means to be injected in multiple stages. 10. The ammonia-mixed combustion engine according to claim 8 or claim 9 , wherein the liquid fuel is diesel. The ammonia co-fuel engine according to any one of claims 8 to 10 ,
An ammonia-mixed combustion engine, comprising: injecting the ammonia into an intake passage of the intake means; and mixing the ammonia and the air in advance and supplying the resulting mixture to the combustion chamber. The ammonia co-fuel engine according to any one of claims 8 to 11 ,
1. An ammonia co-fuel engine, wherein a ratio of a supply amount of the ammonia to a total supply amount of the liquid fuel and the ammonia is in a range of 1% or more and 95% or less. The ammonia co-fuel engine according to any one of claims 8 to 12 ,
An ammonia co-fuel engine, comprising a selective catalytic reduction system in an exhaust path for the exhaust gas, the selective catalytic reduction system using the ammonia to purify nitrogen oxides (NOx) in the exhaust gas discharged from the combustion chamber. 14. The ammonia co-fuel engine according to claim 13 , further comprising an ammonia supply control means for controlling the supply of the ammonia used in the selective catalytic reduction system. A ship equipped with an ammonia-mixed combustion engine, comprising the ammonia-mixed combustion engine according to any one of claims 8 to 14 .

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