Two-stroke engine and four-stroke engine

A two-stroke engine (1) includes a cylinder (2) having a scavenging port (23) and an exhaust port (24), a piston (3) provided in the cylinder (2), a first ejection part (61) for ejecting liquid ammonia into a combustion chamber (20), and a supercharger (5) for pressurizing a suction gas to generate a scavenging gas. In the two-stroke engine (1), the first ejection part (61) ejects liquid ammonia into the combustion chamber (20) within a period of time from when supply of the scavenging gas through the scavenging port (23) into the combustion chamber (20) is started until when the piston (3) next reaches top dead center. It is thus possible to reduce the temperature of gas within the combustion chamber (20) by the heat of vaporization of the liquid ammonia, reduce the pressure in the combustion chamber (20) during compression, and reduce the amount of compression work.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a 35 U.S.C. §§371 national phase conversion of PCT/JP2011/078050, filed Dec. 5, 2011, which claims priority to Japanese Patent Application No. P2010-274547, filed Dec. 9, 2010, the contents of which are incorporated herein by reference. The PCT International Application was published in the Japanese language.

TECHNICAL FIELD

The present invention relates to an engine including a supercharger.

BACKGROUND ART

Engines that burn ammonia gas have conventionally been proposed. For example, Japanese Patent Application Laid-Open No. 5-332152 discloses a technique for decomposing ammonia gas into hydrogen and nitrogen by the heat of exhaust gas from a combustion chamber and using the above hydrogen gas to efficiently burn ammonia gas that is separately supplied into the combustion chamber. Japanese Patent Application Laid-Open No. 2010-159705 discloses a technique used in an ammonia-burning internal combustion engine in which the latent heat of vaporization of liquid ammonia ejected into an intake port of a cylinder is used to reduce the temperature of intake air supplied into the combustion chamber.

Incidentally, there is a constant demand for improving energy efficiency in various types of engines. With engines including a cylinder and a piston, a reduction in the amount of work in a compression stroke contributes greatly to improving energy efficiency. However, with engines provided with a supercharger, high-pressure air compressed by the supercharger is supplied to the cylinder and causes an increase in the amount of compression work.

SUMMARY OF INVENTION

The present invention is intended for a two-stroke engine, and it is an object of the present invention to reduce the amount of compression work in the engine.

The two-stroke engine according to the present invention includes a cylinder, a piston provided in the cylinder, a supercharger for pressurizing a suction gas to generate a scavenging gas, a scavenging port formed in the cylinder and for supplying the scavenging gas from the supercharger into a combustion chamber that is a space enclosed by the cylinder and an upper surface of the piston, an exhaust port formed in the cylinder and for exhausting gas within the combustion chamber out of the combustion chamber, and an ejection part for ejecting liquid ammonia into the combustion chamber within a period of time from when supply of the scavenging gas through the scavenging port into the combustion chamber is started until when the piston next reaches top dead center.

According to the present invention, it is possible to reduce the temperature of the gas within the combustion chamber by the heat of vaporization of the liquid ammonia, reduce the pressure in the combustion chamber during compression, and reduce the amount of compression work.

In a preferred embodiment of the present invention, the scavenging port and the ejection part are provided in a lower portion of the cylinder. The scavenging gas is thus directly cooled at the time of inflow. This makes it possible to further reduce the amount of compression work.

In another preferred embodiment of the present invention, the two-stroke engine further includes a reduction catalyst for, along with ammonia gas, reducing nitrogen oxide. The reduction catalyst is provided on a path of the exhaust gas exhausted from the combustion chamber, and the ejection part ejects the liquid ammonia into the combustion chamber within a period of time during which the gas within the combustion chamber is being exhausted through the exhaust port.

In an aspect of the present invention, a part of burnt gas remains as residual gas in the combustion chamber when the exhaust port is closed, and the ejection part ejects the liquid ammonia into the combustion chamber after the exhaust port is closed. It is thus possible to reduce the amount of compression work while reducing nitrogen oxide in the exhaust gas.

In another aspect of the present invention, the two-stroke engine further includes another ejection part for, when the piston is positioned in a vicinity of the top dead center, ejecting fluid including ammonia into the combustion chamber to cause combustion of gas in the combustion chamber. In this case, more preferably, the ejection part serves as the other ejection part. The structure of the two-stroke engine can thus be simplified.

The structure of the two-stroke engine can also be simplified by supplying the scavenging gas from the supercharger to the scavenging port without cooling the scavenging gas by a cooling medium.

The present invention is also intended for a four-stroke engine. The four-stroke engine includes a cylinder, a piston provided in the cylinder, a supercharger for pressurizing a suction gas to generate an intake gas, an intake port formed in the cylinder and for supplying the intake gas from the supercharger into a combustion chamber in an intake stroke, the combustion chamber being a space enclosed by the cylinder and an upper surface of the piston, an ejection part for ejecting liquid ammonia into the combustion chamber within a period of time from when supply of the intake gas through the intake port into the combustion chamber is started until when the piston reaches top dead center in a compression stroke, and an exhaust port formed in the cylinder and for exhausting gas in the combustion chamber out of the combustion chamber in an exhaust stroke performed after an expansion stroke in which the gas within the combustion chamber burns. It is thus possible to reduce the temperature of the gas in the combustion chamber by the heat of vaporization of the liquid ammonia, reduce the pressure in the combustion chamber during compression, and reduce the amount of compression work.

DESCRIPTION OF EMBODIMENTS

FIG. 1illustrates a configuration of a two-stroke engine1according to a first embodiment of the present invention. The two-stroke engine1inFIG. 1is a marine internal combustion engine and uses ammonia gas as primary fuel. The two-stroke engine1includes a cylinder2and a piston3provided in the cylinder2. The piston3is movable in the vertical direction inFIG. 1. Note that the vertical direction inFIG. 1is not necessarily the direction of gravity.

The cylinder2has a cylindrical cylinder liner21and a cylinder cover22attached to the top of the cylinder liner21. A large number of through holes are circumferentially arranged in the vicinity of a lower end portion of the cylinder liner21, and a cluster of these through holes constitute a scavenging port23for supplying a scavenging gas described later into the cylinder2. A scavenging chamber231is provided around the scavenging port23, and the scavenging port23communicates with a scavenging pipe41through the scavenging chamber231.

The cylinder cover22has an exhaust port24for exhausting gas within the cylinder2out of the cylinder2. The exhaust port24is provided with an exhaust valve25that opens and closes the exhaust port24. The gas exhausted through the exhaust port24out of the cylinder2(hereinafter, referred to as “exhaust gas”) is guided through an exhaust path241to an exhaust pipe42. The actual two-stroke engine1includes a plurality of cylinders2, and the cylinders2are connected to a single scavenging pipe41and a single exhaust pipe42.

The two-stroke engine1further includes a supercharger5that is a turbocharger and an air cooler43that cools air supplied from the supercharger5by a cooling medium such as sea water. The exhaust gas in the exhaust pipe42is sent to a turbine51of the supercharger5. The exhaust gas that is used to rotate the turbine51is exhausted out of the two-stroke engine1via a reduction catalyst7for reducing nitrogen oxide (NOX). A compressor52of the supercharger5uses rotary power generated by the turbine51to pressurize a suction gas (air) taken in from outside of the two-stroke engine1. The compressed air (hereinafter, referred to as “scavenging gas”) is cooled by the air cooler43and then supplied into the scavenging pipe41. In this way, the supercharger5generates a scavenging gas by pressurizing the suction gas using the exhaust gas.

The piston3includes a thick disk-shaped piston crown31inserted in the cylinder liner21, and a piston rod32having one end connected to the bottom surface of the piston crown31. The other end of the piston rod32is connected to a crank mechanism not shown. In the two-stroke engine1inFIG. 1, the space enclosed by the cylinder liner21, the cylinder cover22, the exhaust valve25, and the upper surface of the piston crown31forms a combustion chamber20for burning ammonia gas and air.

The two-stroke engine1further includes a first ejection part61and a second ejection part62both for ejecting liquid ammonia into the combustion chamber20. The first ejection part61is disposed in a lower portion of the cylinder liner21(specifically, the lower half of a range in which the upper surface of the piston crown31passes through in one stroke of the piston3from top dead center to bottom dead center), and more specifically, in the vicinity of the scavenging port23. The second ejection part62is disposed in the cylinder cover22. The first ejection part61and the second ejection part62are connected to a liquid ammonia tank63. Note that the first ejection part61is housed in a recessed portion formed in the inner surface of the cylinder liner21and thus does not interfere with the movement of the piston crown31.

Next is a description of operations of the two-stroke engine1.FIG. 2is a timing chart illustrating opening and closing operations of the scavenging port23, the exhaust port24, and the first ejection part61. In the two-stroke engine1illustrated inFIG. 1, the position of the piston3indicated by dashed double-dotted lines is the top dead center, and the position of the piston3indicated by solid lines is the bottom dead center. InFIG. 2, the time at which the piston3is positioned at the top dead center is denoted by “TDC,” and the time at which the piston3is positioned at the bottom dead center is denoted by “BDC” (the same applies toFIGS. 4 and 5, which are described later). The horizontal axis inFIG. 2can also be taken as indicating the crank angle in the aforementioned crank mechanism.

In the two-stroke engine1, when the piston3is positioned in the vicinity of the top dead center, the exhaust valve25moves upward as indicated by the dashed double-dotted lines inFIG. 1so that the exhaust port24is closed and gas (scavenging gas and ammonia gas as described later) within the combustion chamber20are compressed. The second ejection part62ejects liquid ammonia into the combustion chamber20, and accordingly vaporized ammonia ignites spontaneously, causing combustion (expansion) of the gas in the combustion chamber20. This causes the piston3to be pushed down toward the bottom dead center. Note that the gas within the combustion chamber20does not necessarily have to ignite spontaneously, and the ignition of the gas in the combustion chamber20may be caused by a spark plug or the like.

After the combustion of gas in the combustion chamber20, the exhaust valve25moves downward to open the exhaust port24before the piston3reaches the bottom dead center (see the middle section inFIG. 2). This starts exhaust of burnt gas in the combustion chamber20. The gas exhausted from the combustion chamber20(e.g., “exhaust gas”) is, as described previously, sent through the exhaust path241and the exhaust pipe42to the turbine51of the supercharger5and is exhausted out of the two-stroke engine1after passing through the reduction catalyst7. In the two-stroke engine1, a cam mechanism connected to a crank shaft of the crank mechanism causes the exhaust valve25to move up and down (i.e., causes the exhaust port24to be opened or closed).

When the piston3has moved to the vicinity of the bottom dead center and the upper surface of the piston crown31is positioned below the scavenging port23, the combustion chamber20communicates with the scavenging chamber231. In other words, the scavenging port23is opened to start the supply of the scavenging gas within the scavenging chamber231into the combustion chamber20as shown in the upper section inFIG. 2. Then, the first ejection part61starts ejecting liquid ammonia (i.e., the first ejection part61is opened) as shown in the lower section inFIG. 2. The liquid ammonia emitted into the combustion chamber20is immediately vaporized and accordingly gaseous ammonia (ammonia gas) is mixed into the scavenging gas.

At this time, the scavenging gas within the combustion chamber20is cooled by the heat of vaporization (latent heat of vaporization) of the liquid ammonia. Part of the scavenging gas within the combustion chamber20and part of ammonia gas obtained by vaporization of the liquid ammonia immediately reach the exhaust port24and are exhausted from the combustion chamber20. In other words, part of the scavenging gas and part of the ammonia gas pass through the combustion chamber20. The exhaust gas including the ammonia gas thus reaches the reduction catalyst7through the exhaust pipe42and the turbine51, and nitrogen oxide in the exhaust gas is reduced with the ammonia gas and the reduction catalyst7.

The piston3that has passed through the bottom dead center changes to move upward, and the first ejection part61continues to eject liquid ammonia until immediately after the change to the upward movement of the piston3. Since the upper surface of the piston crown31has reached above the scavenging port23after the first ejection part61stopped ejecting liquid ammonia (i.e., after the first ejection part61was closed), the scavenging port23is closed and the supply of the scavenging gas into the combustion chamber20is stopped. Then, the exhaust port24is closed with the exhaust valve25and the combustion chamber20is sealed. The piston3further moves upward so that the scavenging gas and the ammonia gas within the combustion chamber20are compressed, and when the piston3reaches in the vicinity of the top dead center, the second ejection part62ejects liquid ammonia into the combustion chamber20, causing combustion in the combustion chamber20. The two-stroke engine1repeats the above-described operations.

As described above, in the two-stroke engine1inFIG. 1, the first ejection part61ejects liquid ammonia into the combustion chamber20within a period of time from when the supply of the scavenging gas through the scavenging port23into the combustion chamber20is started until when the piston3next reaches the top dead center (i.e., until when the compression stroke is completed, but not including the time at which the compression stroke is completed). It is thus possible in the two-stroke engine1to reduce the temperature of the gas (mainly the scavenging gas) within the combustion chamber20by the heat of vaporization of the liquid ammonia, reduce the pressure in combustion chamber20during compression, and reduce the amount of compression work. Consequently, the two-stroke engine1can achieve improved energy efficiency.

In the two-stroke engine1, the scavenging port23and the first ejection part61are disposed in a lower portion of the cylinder2, and the ejection of liquid ammonia into the combustion chamber20is started immediately after the start of supply of the scavenging gas into the combustion chamber20. This enables the scavenging gas to be directly cooled at the time of inflow, making it possible to reduce the pressure in the combustion chamber20from the beginning of the compression stroke and to further reduce the amount of compression work.

In the two-stroke engine1, the reduction catalyst7that, along with the ammonia gas, reduces nitrogen oxide is further provided on the path of the exhaust gas exhausted from the combustion chamber20, and the first ejection part61ejects liquid ammonia into the combustion chamber20while the gas within the combustion chamber20is being exhausted through the exhaust port24. The ammonia gas used to cool the scavenging gas can thus be guided in an unburnt state to the reduction catalyst7, and nitrogen oxide in the exhaust gas can be appropriately reduced with the reduction catalyst7and the ammonia gas. Note that the path of the exhaust gas in the two-stroke engine1ranges from the exhaust path241to the site at which the exhaust gas is discharged into the atmosphere, and the reduction catalyst7may be disposed at any site on the path of the exhaust gas.

FIG. 3illustrates another exemplary configuration of the two-stroke engine. A two-stroke engine1ainFIG. 3is the same as the two-stroke engine1inFIG. 1, with the exception that the reduction catalyst7is omitted. Thus, the same reference numerals are given to parts of the configuration that are the same as inFIG. 1.FIG. 4is a timing chart illustrating opening and closing operations of a scavenging port23, an exhaust port24, and a first ejection part61of the two-stroke engine1a.

In the present example of operations, the timing of the opening and closing operations of the scavenging port23and the exhaust port24is the same as that in the example of operations inFIG. 2, but the timing of the opening and closing operations of the first ejection part61differs from that inFIG. 2. Specifically, after the piston3has moved upward from the bottom dead center and the scavenging port23and the exhaust port24are closed in order (see the upper and middle sections inFIG. 4), the first ejection part61is opened as shown in the lower section inFIG. 4to eject liquid ammonia into the combustion chamber20for a fixed period of time. In this case, the scavenging gas within the combustion chamber20is cooled in a state in which the combustion chamber20is sealed. Then, when the piston3has reached in the vicinity of the top dead center, the second ejection part62ejects liquid ammonia into the combustion chamber20, causing combustion in the combustion chamber20. At this time, in two-stroke engine1a, substantially the entire amount of ammonia gas within the combustion chamber20burns.

As described above, in the two-stroke engine1a, the first ejection part61ejects liquid ammonia into the combustion chamber20only within the period of time after the exhaust port24is closed until when the piston3next reaches the top dead center, and the scavenging gas within the combustion chamber20is cooled. This prevents the two-stroke engine1awithout the reduction catalyst7from encountering a situation in which the vaporized gas of liquid ammonia ejected from the first ejection part61is exhausted from the combustion chamber20before burning in the combustion chamber20(i.e., prevents the ammonia gas from passing through the combustion chamber20). As a result, it is possible to prevent the ammonia gas from being exhausted out of the two-stroke engine1aand to reduce the amount of compression work in the two-stroke engine1aby cooling the scavenging gas within the combustion chamber20.

Note that with a two-stroke engine with a reduction catalyst, the passing of the ammonia gas through the combustion chamber20may be prevented by the first ejection part61ejecting liquid ammonia only after the exhaust port24is closed. In this case, a supply part for supplying ammonia or another reducing agent to the reduction catalyst is separately provided.

Next, another example of operations of the two-stroke engine1ainFIG. 3will be described.FIG. 5is a timing chart illustrating opening and closing operations of the scavenging port23, the exhaust port24, and the first ejection part61according to the other example of operations.

In the present example of operations, the timing of the opening and closing operations of the scavenging port23and the first ejection part61is the same as that in the example of operations inFIG. 4, but the timing of the opening and closing operations of the exhaust port24differs from that inFIG. 4. Specifically, as shown in the upper and middle sections inFIG. 5, after the piston3has passed through the bottom dead center, the exhaust port24is closed before the scavenging port23. At this time, in the two-stroke engine1a, part of high-temperature burnt gas remains as residual gas in the combustion chamber20. After the scavenging port23is closed, the first ejection part61ejects liquid ammonia into the combustion chamber20for a fixed period of time as shown in the lower section inFIG. 5, and the gas including the scavenging gas and the residual gas within the combustion chamber20is cooled by the heat of vaporization of the liquid ammonia. Then, when the piston3reaches in the vicinity of the top dead center, the second ejection part62ejects liquid ammonia into the combustion chamber20, causing combustion in the combustion chamber20.

As described above, in the two-stroke engine1a, part of the burnt gas remains as residual gas in the combustion chamber20when the exhaust port24is closed, and liquid ammonia is ejected into the combustion chamber20containing the scavenging gas and the residual gas by the first ejection part61after the exhaust port24is closed. It is thus possible to reduce the temperature of the gas in the combustion chamber20and to reduce the pressure in the combustion chamber20during compression while reducing the heat load on the cylinder2. It is also possible to reduce the amount of oxygen in the gas contained in the combustion chamber20during combustion. Consequently, nitrogen oxide in the exhaust gas can be reduced while reducing the amount of compression work.

The two-stroke engine1aaccording to the present example of operations prevents the passing of ammonia gas through the combustion chamber because the first ejection part61ejects liquid ammonia only after the exhaust port24is closed. Alternatively, in the case where a reduction catalyst7is provided as in the two-stroke engine1inFIG. 1, the first ejection part61may also eject liquid ammonia before the exhaust port24is closed.

FIG. 6illustrates yet another exemplary configuration of the two-stroke engine. InFIG. 6, only part of the configuration of a two-stroke engine1bis illustrated. The two-stroke engine1binFIG. 6is the same as the two-stroke engine1inFIG. 1, with the exception that the first ejection part61is omitted. Thus, the same reference numerals are given to parts of the configuration that are the same as inFIG. 1.

In the two-stroke engine1binFIG. 6, the ejection of liquid ammonia into the combustion chamber20by the first ejection part61inFIG. 1is realized by a second ejection part62. Specifically, after the supply of the scavenging gas through the scavenging port23into the combustion chamber20is started, the second ejection part62provided in the cylinder cover22ejects liquid ammonia into the combustion chamber20before the piston3next reaches the top dead center.

Here, if an ejection part for ejecting liquid ammonia for cooling the scavenging gas is disposed in the cylinder liner21(i.e., the side portion of the cylinder2), the ejection part cannot eject liquid ammonia into the combustion chamber20when the upper surface of the piston crown31is positioned above that ejection part. This considerably limits the length of time during which liquid ammonia for cooling the scavenging gas can be ejected.

In contrast, in the two-stroke engine1binFIG. 6, an ejection part for ejecting liquid ammonia for cooling the scavenging gas (i.e., the second ejection part62) is disposed in the cylinder cover22and always faces the combustion chamber20. This increases the degree of freedom in the timing of ejection of liquid ammonia for cooling the scavenging gas. In addition, in the two-stroke engine1binFIG. 6, one ejection part serves as both the ejection part for ejecting liquid ammonia into the combustion chamber20and causing combustion in the combustion chamber20and the ejection part for ejecting liquid ammonia for cooling the scavenging gas. In other words, the ejection part for cooling the scavenging gas serves also as the other ejection part. Thus, the configuration of the two-stroke engine can be simplified.

The two-stroke engines1,1a, and1binFIGS. 1, 3, and 6can cool the scavenging gas within the combustion chamber20by the ejection of liquid ammonia for cooling the scavenging gas. Thus, the air cooler43can be made compact. Depending on the design of a two-stroke engine, it is possible to omit an air cooler between the supercharger5and the scavenging pipe41as in a two-stroke engine1cillustrated inFIG. 7. In the two-stroke engine1cinFIG. 7, the scavenging gas is supplied from the supercharger5to a scavenging port23through a scavenging pipe41and a scavenging chamber231without being cooled by a cooling medium (i.e., a heating medium for reducing the temperature of the scavenging gas). Thus, in the two-stroke engine1cwhere an air cooler is omitted, the engine configuration can be simplified (the same applies to a four-stroke engine1dinFIG. 8, which will be described later).

FIG. 8illustrates a configuration of a four-stroke engine1daccording to a second embodiment of the present invention. The four-stroke engine1dinFIG. 8includes a cylinder2d, a piston3dprovided in the cylinder2d, an intake port23dand an exhaust port24dthat are formed in the cylinder2d, an ejection part61dconnected to a liquid ammonia tank63d, and a supercharger5dfor pressurizing a suction gas to generate an intake gas.

In the four-stroke engine1d, the intake gas from the supercharger5dis supplied into a combustion chamber20d, which is a space enclosed by the cylinder2dand the upper surface of the piston3d, by opening a valve provided in the intake port23din an intake stroke in which the piston3dmoves from the top dead center to the bottom dead center. Then, a compression stroke is performed with the intake port23dclosed in which the intake gas in the combustion chamber20dis compressed by the piston3dmoving from the bottom dead center to the top dead center. In actuality, the ejection part61dejects liquid ammonia into the combustion chamber20dwithin a period of time from when the supply of the intake gas through the intake port23dinto the combustion chamber20dis started in the immediately previous intake stroke until when the piston3dreaches the top dead center in the compression stroke. Through this, the intake gas in the combustion chamber20dis cooled by the heat of vaporization of the liquid ammonia.

When the piston3dis positioned in the vicinity of the top dead center, the ejection part61dagain ejects liquid ammonia into the combustion chamber20dand causes combustion of gas including ammonia and the intake gas in the combustion chamber20d. After an expansion stroke in which the piston3dmoves from the top dead center to the bottom dead center due to the combustion of gas in the combustion chamber20d, an exhaust stroke is performed in which the piston3dmoves from the bottom dead center to the top dead center. In the exhaust stroke, the valve provided in the exhaust port24dis opened to exhaust the gas within the combustion chamber20dout of the combustion chamber20d. The exhaust gas exhausted out of the cylinder2dis guided via the supercharger5dto a reduction catalyst7d, and nitrogen oxide in the exhaust gas is reduced with the reduction catalyst7dand ammonia gas that is separately supplied to the reduction catalyst7d.

As described above, in the four-stroke engine1dinFIG. 8, the ejection part61dejects liquid ammonia into the combustion chamber20dwithin a period of time from when the supply of the intake gas through the intake port23dinto the combustion chamber20dis started until when the piston3dreaches the top dead center in the compression stroke (i.e., until when the compression stroke is completed). It is thus possible in the four-stroke engine1dto reduce the temperature of the gas (mainly the intake gas) in the combustion chamber20dby the heat of vaporization of the liquid ammonia, reduce the pressure in the combustion chamber20din a compression stroke, and reduce the amount of compression work. Consequently, the four-stroke engine1dcan achieve improved energy efficiency.

In the four-stroke engine1dinFIG. 8, another ejection part for ejecting liquid ammonia for cooling the intake gas may be provided separately from the ejection part61d. In this case, the other ejection part may be provided in a side portion of the cylinder2das in the two-stroke engines1,1a, and1cinFIGS. 1, 3, and 7.

Alternatively, in the four-stroke engine1d, the period of time during which the exhaust port24dis open and the period of time during which the intake port23dis open may overlap each other. In this case, the ejection part61dmay eject liquid ammonia into the combustion chamber20dwithin a period of time during which both of the exhaust port24dand the intake port23dare open. This allows the ammonia gas that is used to cool the intake gas to be guided in an unburnt state to the reduction catalyst7dand allows nitrogen oxide in the exhaust gas to be reduced with the ammonia gas and the reduction catalyst7d.

Meanwhile, in the four-stroke engine1d, the passing of ammonia gas through the combustion chamber20dis prevented if the ejection part61dejects liquid ammonia into the combustion chamber20donly when the exhaust port24dis closed. In this case, part of burnt gas may remain as residual gas in the combustion chamber20dwhen the exhaust port24dis closed. This reduces nitrogen oxide in the exhaust gas.

While the above has been a description of embodiments of the present invention, the present invention is not limited to the above-described embodiments and can be modified in various ways.

In the two-stroke engines, for example, the liquid ammonia ejected from the second ejection part62may be mixed with petroleum fuel or the like. Alternatively, ammonia gas, mixed gas-liquid ammonia, or a mixture of such ammonia and petroleum fuel or the like may be ejected from the second ejection part62(the same applies to the four-stroke engine). In such two-stroke engines, the combustion of gas in the combustion chamber20is caused by the second ejection part62ejecting a fluid containing ammonia (which may be a fluid containing only ammonia) when the piston is positioned in the vicinity of the top dead center.

As another alternative, the combustion of gas in the combustion chamber20may be caused by the second ejection part62ejecting highly flammable fuel (e.g., hydrogen gas or light oil) in order to assure the combustion of ammonia gas that is filled in the combustion chamber20by the ejection of liquid ammonia from the first ejection part61. As yet another alternative, the above fuel may be emitted from another ejection part different from the second ejection part62. In this case, when the piston is positioned in the vicinity of the top dead center, the second ejection part62ejects liquid ammonia and the other ejection part ejects the above fuel. As described previously, the combustion of gas in the combustion chamber20may be caused by a spark plug or the like.

In the above-described embodiments, liquid ammonia for cooling the scavenging gas (or the intake gas) is continuously ejected through an ejection part for a fixed period of time. Alternatively, the ejection part may perform a plurality of ejection operations within the same period of time so that the combustion chamber is filled with ammonia gas while the scavenging gas in the combustion chamber is being cooled. Liquid ammonia for cooling may be ejected in a gas-liquid state mixed with air or the like.

The two-stroke engines may be configured such that an exhaust port is provided in the cylinder liner21(a side portion of the cylinder2) similarly to the scavenging port23inFIG. 1and is opened and closed by the movement of the piston3. The scavenging port may be opened and closed using a value, similarly to the exhaust port24inFIG. 1.

The superchargers5and5dmay be configured to pressurize a suction gas using power obtained from a crank shaft other than using the exhaust gas from the combustion chamber.

The two-stroke engines and the four-stroke engine according to the above-described embodiments may be used in various applications aside from marine applications, such as in automobiles or prime motors for electric power generation.

The configurations of the above-described embodiments and variations may be appropriately combined as long as there are no mutual inconsistencies.

REFERENCE SIGNS LIST