JPH06101495A - Turbo-compound type multicylinder gas engine - Google Patents

Abstract

PURPOSE:To provide a turbo-compound type multicylinder gas engine which improves thermal efficiency. CONSTITUTION:At least four or more cylinders are arranged such that two cylinders wherein an ignition order is non-consecutive form a group and a turbocharger 35 is arranged to each group, and an exhaust gas manifold is coupled to first and fourth cylinder and an exhaust manifold is coupled to second and third cylinders. A water injection nozzle 38 through which water is injected against the exhaust manifold is provided. Water injected through the water injection nozzle 38 is vaporized by an exhaust gas system, a flow rate of gas is increased, and a turbocharger 35 is driven.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multi-cylinder gas engine having an exhaust manifold for discharging exhaust gas from a combustion chamber and a turbocharger arranged downstream of the exhaust manifold.

[0002]

2. Description of the Related Art Conventionally, an engine using natural gas as a main fuel has been developed as a cogeneration engine by a government, a government research agency or a private company. In this cogeneration engine, power is taken out as electric energy by a generator, and heat of exhaust gas energy is heated by a heat exchanger to make hot water, which is used for hot water supply. Then, this cogeneration engine is expected to be used as an urban electricity supply system.

An engine using natural gas as fuel is disclosed in, for example, Japanese Patent Laid-Open No. 1-232119, Japanese Utility Model No. 3
There is one disclosed in Japanese Patent Publication No. 41068.

The engine for hydrogen / liquefied natural gas disclosed in Japanese Unexamined Patent Publication No. 1-2232119 supplies either hydrogen or liquefied natural gas as a fuel in a low load operation state of the engine, and A control means for supplying liquefied natural gas as a fuel in a high load operation state is provided.

Further, the gas-fired diesel engine disclosed in Japanese Utility Model Publication No. 3-41068 has a dual fuel in which a liquid fuel injection valve for injecting liquid fuel and a gas fuel injection valve for injecting gas fuel are provided in a cylinder cover. It is an injection type, and a gas fuel injection valve and a liquefied fuel gas tank in which gas fuel is stored are connected by two gas passages, a high pressure gas passage and a low pressure gas passage, and gas fuel is provided in each of the gas passages. A high-pressure compressor and a low-pressure compressor that pressurize the gas to different pressures and supply it to the gas fuel injection valve are respectively provided. And a low-pressure gas injection port for injecting the low-pressure gas.

[0006]

However, in a gas engine that uses natural gas as fuel, since the fuel is a gas body, the fuel gas is sucked from the intake port in the same manner as gasoline, and is compressed and ignited. The compression ratio cannot be increased, and the theoretical thermal efficiency (η = heat conversion of work / heat quantity of fuel) is not necessarily high. A gas engine that is normally used has a compression ratio of about 9 to 13 and a theoretical thermal efficiency of only 48%. When the gas engine is powered by electric energy, the net thermal efficiency is 34 to 3
The efficiency is 5%, and in some cases, less than 30%. Therefore, as cooling water loss and exhaust gas energy, 65 to 70% of the fuel is released, and this heat energy makes hot water by a heat exchanger, and even if it is used for hot water supply, the hot water becomes too large, It is the current situation that the equipment cannot be fully used. Therefore, the electric energy obtained from the gas engine is expensive.

Therefore, in the present situation, it is desired to improve the thermal efficiency when the electric energy is taken out from the gas engine. Therefore, it has been considered to improve the thermal efficiency by incorporating a heat shield type gas engine into the gas engine. The gas engine uses natural gas as fuel, and the fuel is gas. Therefore, when the gas is sucked in the suction stroke and then compressed, the compression becomes high and the temperature rises, and the phenomenon of self-ignition, that is, knocking occurs. However, the gas fuel of natural gas will self-ignite unless the compression ratio is 12 or less. Also, regarding the thermal efficiency of the engine, it has been theoretically and experimentally confirmed that the thermal efficiency decreases as the compression ratio decreases.

Further, in the heat shield engine, since the wall surface temperature of the combustion chamber rises, the problem of self-ignitability that the fuel supplied to the combustion chamber self-ignites before the ignition timing increases. That is, in the heat shield engine, the temperature of the combustion chamber wall surface rises to about 600 ° C. or higher. Therefore, when using natural gas, gasoline, or the like as the fuel, if the compression ratio is increased, When the intake air and the fuel gas from the fuel passage are mixed and highly compressed, self-ignition occurs, and combustion is started far before the top dead center TDC, causing knocking and failing to function as an engine. become.

Further, in the turbo compound type gas engine equipped with the turbocharger, there is a problem how to increase the thermal efficiency. The turbo compound gas engine is a combination of a reciprocating engine and a gas turbine. Since the two systems have different properties, the optimum combination is necessary for improving the performance. In a turbo compound with a low engine speed, a small air flow rate leads to a decrease in performance, and many conventional systems do not improve efficiency.

Further, in order to effectively recover the thermal energy of the exhaust gas discharged from the gas engine, water is injected into the exhaust gas passage and the injected water is evaporated to increase the gas mass of the exhaust gas. It is possible to make it.
Since the fuel is a gas in a gas engine, it is easy to mix the gas fuel and air, and the generation of exhaust soot contained in the exhaust gas after combustion is smaller than that of a liquid fuel.

Therefore, an object of the present invention is to increase the gas mass of exhaust gas discharged from multiple cylinders to effectively recover exhaust gas energy and improve thermal efficiency. Each group of cylinders is equipped with a turbocharger for each group, water is injected into the exhaust passage to evaporate water to generate steam, the gas mass is increased, and the turbo energy is increased by the steam energy and exhaust gas energy. (EN) A turbo compound multi-cylinder gas engine that drives a charger and an energy recovery device to improve recovery energy and improve thermal efficiency.

[0012]

In order to achieve the above object, the present invention is configured as follows. That is,
The present invention relates to a turbo having a combustion chamber for burning gas fuel, an exhaust manifold connected to an exhaust port for discharging exhaust gas from the combustion chamber, an exhaust pipe connected to the exhaust manifold, and a turbocharger connected to the exhaust pipe. In a compound-type multi-cylinder gas engine, each cylinder of at least four cylinders is made into a group of two cylinders whose ignition order is not continuous, and the exhaust manifold is constituted by each exhaust manifold connected to the exhaust port of each group, A turbo compound type multi-cylinder gas engine characterized in that a water injection nozzle is arranged in each exhaust pipe connected to each exhaust manifold, and the turbocharger is composed of each turbocharger connected to each exhaust pipe. Regarding

Further, in this turbo compound type multi-cylinder gas engine, a collective exhaust pipe is formed by collecting the exhaust pipes on the outlet side of each turbine of each turbocharger, an energy recovery device connected to the collective exhaust pipe, and It has a current collector that collects the electric power generated by the energy recovery device.

In the turbo compound multi-cylinder gas engine, one of the water injection nozzles injects water into the exhaust pipe at the end of the exhaust stroke of the first cylinder and at the end of the exhaust stroke of the fourth cylinder, The other water injection nozzle injects water into the exhaust pipe at the end of the exhaust stroke of the second cylinder and at the end of the exhaust stroke of the third cylinder.

[0015]

The turbo compound type multi-cylinder gas engine according to the present invention is constructed as described above and operates as follows. That is, in this turbo compound multi-cylinder gas engine, two cylinders are grouped, a turbocharger is connected to an exhaust pipe of each cylinder of each group, and a water injection nozzle is arranged in each of the exhaust pipes. The inside of the exhaust pipe is heated by the passage of the water, and when water is jetted from the water jet nozzle to the heated exhaust pipe, the jet water immediately evaporates. The mass of gas increases as water evaporates and steam is generated, and the evaporated steam energy drives each turbocharger in the wake to perform work. That is,
The mass of 18 gr of water, if evaporated to steam, is 22.
Increased to a gas mass of 4 liters. Therefore, the thermal energy given to the exhaust pipe is converted into vapor energy and effectively recovered, and the thermal efficiency can be improved.

In particular, since each cylinder is made up of two cylinders whose ignition order is not continuous, there is a rest state after the exhaust gas flows through the exhaust pipe, so that the exhaust gas flow is stopped. By controlling to inject water at the same timing, even if water is injected from the water injection nozzle and the pressure in the exhaust pipe increases, the exhaust valve closes the combustion chamber, and there is no backflow of steam. The turbine work can be increased without adding exhaust pressure to the engine work. In addition, the turbocharger is always driven by being given rotational energy from either exhaust gas or steam during the entire stroke, and the intake boost pressure can be raised by the compressor of the turbocharger during the intake stroke of the engine. The work amount can be increased, and the thermal efficiency can be improved.

[0017]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of a turbo compound type multi-cylinder gas engine according to the present invention will be described below with reference to the drawings. 1 is a schematic view showing an embodiment of a system of a turbo compound multi-cylinder gas engine according to the present invention, FIG.
Is an explanatory view showing an example of a water injection nozzle, and FIG. 3 is an explanatory view showing details of the system of FIG.

FIG. 1 shows an embodiment in which the turbo compound type multi-cylinder gas engine is applied to a 4-cylinder gas engine. This multi-cylinder gas engine includes a combustion chamber formed by a wall of a heat shield structure for burning gas fuel, an exhaust port 31 for discharging exhaust gas from the combustion chamber, an exhaust manifold 33A connected to the exhaust port 31, 33B,
Exhaust pipe 34 connected to the exhaust manifolds 33A and 33B
And a turbocharger 35 connected to the exhaust pipe 34. The collective exhaust pipe 44 connected to the outlet side exhaust pipe 43 of the turbine 40 of each turbocharger 35 is connected to the turbine 46 of the energy recovery device 45. In the energy recovery device 45, the generator 47 is operated by driving the turbine 46, and the electric power generated by the generator 47 is stored in the current collector 49 and used as an electric output. Also,
A generator 48 is provided on a crankshaft 50 of the multi-cylinder gas engine, and the rotational force is stored in a collector 49 as electric energy by the generator 48 and used as an electric output.

In this multi-cylinder gas engine, in particular, each cylinder is grouped into two, and exhaust manifolds 33A and 33B are provided at the exhaust ports 31 of each group,
The exhaust manifolds 33A and 33B are provided with a water injection nozzle 38, and further have a water injection pump 39 that operates to inject water from the water injection nozzle 38.

When the multi-cylinder gas engine is constructed as a 4-cylinder gas engine, the exhaust manifold is connected to the first cylinder #.
The exhaust manifold 33A is connected to the exhaust ports 31 of the first and fourth cylinders # 4 and the exhaust manifold 33B is connected to the exhaust ports 31 of the second cylinder # 2 and the third cylinder # 3. Water injection nozzle 3
8 and 38 are provided respectively. This four-cylinder gas engine is driven by repeating four cycles of an intake stroke, a compression stroke, an expansion stroke, and an exhaust stroke, and the ignition order is determined by considering the rotational balance of the crankshaft 50 in the first cylinder # 1 → the third cylinder. Cylinder # 3 → fourth cylinder # 4 → second cylinder # 2 is set.

Further, in this multi-cylinder gas engine,
Turbochargers 35, 35 are connected to the exhaust pipes 34, 34. The turbocharger 35 includes a turbine 40 driven by gas energy and a compressor 41 connected to the turbine 40 through a shaft. Compressed air from the compressor 41 can be supplied as intake air from the intake port 25 to each cylinder through the intake passage 42. In addition, the turbocharger 35
Although not shown in the figure, a generator / motor may be provided. By providing the turbocharger 35 with a generator / motor, the generator / motor can be driven by the operation of the turbine 40, and the rotational energy of the shaft can be recovered not only as the compressor but also as electric energy. Further, in this turbo compound type multi-cylinder gas engine, an energy recovery device 45 for recovering exhaust gas energy is provided downstream of the turbocharger 35.

In this multi-cylinder gas engine, each water injection nozzle 38, 38 has an exhaust manifold 33 for each cylinder.
It is controlled to inject water to A and 33B. By injecting water from the water injection nozzles 38, 38 at the end of the compression stroke of each cylinder, the exhaust pipe 34 has 4
Exhaust gas or steam flows over all one cycle,
The exhaust gas energy or steam energy always drives the turbocharger 35 in four cycles.

Referring to FIG. 5, exhaust manifold 33 connected to exhaust ports 31 of first cylinder # 1 and fourth cylinder # 4.
The operation on the A side will be described. In this turbo compound type multi-cylinder gas engine, during the exhaust stroke of the first cylinder # 1, the exhaust gas from the first cylinder # 1 flows from the exhaust manifold 33A to the exhaust pipe 34 through the collecting pipe 36 and the exhaust gas. Heats the inside of the exhaust manifold 33A, the collecting pipe 36 and the exhaust pipe 34 to drive the turbocharger 35.
Next, the first cylinder # 1 completes the compression stroke and shifts to the suction stroke. At this time, water is jetted from the water jet nozzle 38. The injected water is vaporized by the thermal energy stored in the exhaust system heated by the exhaust gas to generate steam. The generated vapor increases the gas mass and the exhaust pipe 3
It is sent to the turbocharger 35 from 4 and drives the turbocharger 35.

Next, the first cylinder # 1 shifts to the compression stroke after completion of the intake stroke, but the fourth cylinder # 4 is in the exhaust stroke during the compression stroke of the first cylinder # 1. Therefore, the exhaust gas from the fourth cylinder # 4 flows through the exhaust manifold 33A. The exhaust gas passing through the exhaust manifold 33A flows through the collecting pipe 36 to the exhaust pipe 34, and the exhaust gas drives the turbocharger 35. Next, the fourth cylinder # 4 completes the compression stroke and shifts to the suction stroke. At this time, water is jetted from the water jet nozzle 38. The injected water is vaporized by the thermal energy stored in the exhaust system heated by the exhaust gas to generate steam.
The generated vapor increases in gas mass and is sent from the exhaust pipe 34 to the turbocharger 35, where the turbocharger 3
Drive 5 Therefore, in this multi-cylinder gas engine,
The turbocharger 35 will always be driven with either exhaust gas or steam during the four strokes.

The operation on the side of the exhaust manifold 33B connected to the exhaust ports 31 of the second cylinder # 2 and the third cylinder # 3 is the same as the operation on the side of the exhaust manifold 33A. Omit it.

Next, with reference to FIG. 4, an embodiment of a heat shield type gas engine applicable to this multi-cylinder gas engine will be described. FIG. 4 is a sectional view showing one cylinder of a multi-cylinder gas engine. This gas engine includes a cylinder block 14, a cylinder head 7 fixed to the cylinder block 14, an intake port 25 formed in the cylinder head 7,
An intake valve 20 arranged in the intake port 25, an exhaust port 31 (FIG. 3) formed in the cylinder head 7, an exhaust valve 32 (FIG. 3) arranged in the exhaust port 31, a hole 19 formed in the cylinder head 7. The sub-chamber 2 formed by the wall body 3 of the heat shield structure arranged in the
Cylinder liner 22 fitted to 1 and the cylinder liner 2
Piston 1 reciprocating in cylinder 18 formed in 2
5, the main chamber 1 of the heat shield structure formed on the cylinder 18 side, and the communication hole 30 formed in the wall body 3 that connects the main chamber 1 and the sub chamber 2 with each other.

In this heat shield type gas engine, the main chamber 1
Is formed by a headliner 10 which is a wall body fitted in a hole 9 formed in the cylinder head 7. The headliner 10 includes a liner upper portion 28 that constitutes a part of the cylinder 18.
And the head lower surface portion 11. A wall body 3 forming the sub chamber 2 is integrally formed on the upper surface of the head lower surface portion 11. The wall 3 has a hole 19 in the cylinder head 7.
It is composed of an upper wall body 12 and a lower wall body 13 fitted to each other. On the lower surface 11 of the head, valve seats 26 of the intake and exhaust valves 20, 32 and a valve seat 24 of the communication hole valve 4 are formed.

In this heat shield type gas engine, a fuel tank 27 containing natural gas as a fuel, a pressure accumulating chamber 6 for accumulating the natural gas from the fuel tank 27,
In order to supply the natural gas of the pressure accumulating chamber 6 from the fuel inlet 23 to the sub chamber 2, a fuel passage 8 that connects the sub chamber 2 and the pressure accumulating chamber 6
A communication hole valve 4 arranged in a communication hole 30 that connects the main chamber 1 and the sub chamber 2 and a fuel valve 5 arranged in the fuel inlet 23 and opened in the intake stroke to supply natural gas to the sub chamber 2 are provided. is doing.

Further, in the region of the communication hole 30, the temperature of the communication gas becomes high due to the combustion gas, so that the communication hole valve 4 arranged in the communication hole 30 is made of ceramics such as silicon nitride and silicon carbide having high temperature strength and excellent heat resistance. Has been done. The fuel valve 5 has an electromagnetic valve driving device that is opened and closed by electromagnetic force, and the valve opening period is determined according to the engine load. When the fuel valve 5 opens the fuel inlet 23, gas fuel, which is natural gas, is supplied from the pressure accumulating chamber 6 to the sub chamber 2 in a required amount.

The piston 15 is a piston head 16 made of ceramics such as silicon nitride having excellent heat resistance.
And a piston skirt 17 fixed to the piston head 16 by a metal ring with a coupling ring 29.

A headliner 10 which is a wall forming the main chamber 1, and an upper wall 12 which constitutes a wall 3 forming the sub chamber 2
The lower wall body 13, the cylinder liner 22, and the piston head 16 are made of ceramics such as silicon nitride and silicon carbide having excellent heat resistance. Therefore, it has sufficient heat resistance and high temperature strength even if the gas temperature in the latter stage of combustion rises,
Emissions of unburned hydrocarbons, etc. are reduced, and a highly efficient engine can be constructed.

The heat shield type gas engine is constructed as described above and is operated as follows. This heat shield type gas engine is operated by sequentially repeating four strokes of an intake stroke, a compression stroke, an expansion stroke and an exhaust stroke. First, in the intake stroke, the intake valve 20 opens the intake port 25. Then, the intake air is supplied to the main chamber 1, and the communication valve 30 is closed by the communication hole valve 4 and the fuel valve 5
And the natural gas fuel is supplied from the pressure accumulating chamber 6 to the sub chamber 2 through the fuel passage 8. At this time, sub-chamber 2
Since the exhaust gas remaining after combustion remains in the
When the gas fuel from is introduced, the gas fuel receives heat and is activated in the sub chamber 2.

Next, in this heat shield type gas engine,
In the compression stroke, the communication hole 30 is closed by the communication hole valve 4, and the intake air is highly compressed in the main chamber 1 to increase the compression ratio. Next, in the final stage of the compression stroke, the communication hole valve 4 sets the communication hole 30
Through the communication hole 30 and high compression and high temperature (for example,
650 ° C.) a phased compressed air flowed from the main chamber 1 to the subchamber 2, the inhalation air is ignited combustion to promote mixing with gas fuel activated, NO _X in the fuel-rich rapidly developing combustion
, The flame of the sub-chamber 2 is ejected to the main chamber 1 and moves to the expansion stroke, promoting the mixing with the fresh air existing in the main chamber 1 to promote the secondary combustion in a short time. Complete. In this expansion stroke, the communication hole 30 is maintained in an open state, a flame is ejected from the sub chamber 2 to the main chamber 1 to perform work, and the communication hole 30 is closed by operating the communication hole valve 4 near the end of the exhaust stroke. To do.

As described above, this heat shield type gas engine is provided with the communication hole 30 and the fuel inlet 23 in the sub-chamber 2, and stores the natural gas from the fuel tank 27 storing the natural gas in the pressure accumulating chamber 6. The natural gas in the pressure accumulating chamber 6 is supplied from the fuel inlet 23 into the sub chamber 2 with the communication hole valve 4 closing the communication hole 30, and the intake air sucked from the intake port 25 to the main chamber 1 is connected to the communication hole valve. 4, the communication hole 30 is closed, and the intake air is not supplied to the sub chamber 2, the piston 15
The intake air is compressed in the rising compression stroke of
Even if the gas fuel is highly compressed inside, the gas fuel supplied into the sub chamber 2 is blocked from the main chamber 1 by the communication hole valve 4, so that it does not self-ignite and knocking does not occur.

Further, since the communication hole valve 4 opens the communication hole 30, the intake air having a high compression ratio flows from the main chamber 1 into the sub chamber 2, and the fuel gas and the intake air are mixed and ignited. High-speed combustion is performed in a fuel-rich state where the equivalence ratio is large, and the generation of NO _X is suppressed. Furthermore, the gas fuel from the pressure accumulating chamber 6 is introduced into the sub chamber 2 containing the exhaust gas after combustion, and the gas fuel receives heat in the sub chamber 2 and is activated.

[0036]

The turbo compound type multi-cylinder gas engine according to the present invention is constructed as described above and has the following effects. That is, in this turbo compound type multi-cylinder gas engine, the water injection nozzle provided in the collecting pipe of the exhaust manifold is provided, so that the water injected from the water injection nozzle becomes steam to increase the gas mass. Then, the steam energy drives the turbocharger to effectively recover the heat energy, and the thermal efficiency of the engine can be improved. Moreover, each cylinder of at least 4 cylinders or more is grouped into two cylinders whose firing order is not continuous, each exhaust manifold is connected to the exhaust port of each group, one turbocharger is provided in the group, and water is injected into each exhaust manifold. Since each nozzle is installed, even if the injected water becomes steam, the combustion chamber is closed by the exhaust valve, which does not increase the exhaust pressure with respect to the engine work, but increases the turbine work of the turbocharger. Can be made.

Further, the multi-cylinder gas engine is configured as a 4-cylinder gas engine, and the exhaust manifold connecting the exhaust manifold to the exhaust ports of the first cylinder and the fourth cylinder and the exhaust of the second cylinder and the third cylinder. The exhaust manifold is composed of an exhaust manifold connected to the port, and each of the exhaust manifolds is provided with a water injection nozzle. Therefore, the injection water is heated by the thermal energy remaining in the exhaust system, and evaporates to generate steam. The steam energy drives the turbocharger.

Also, in this multi-cylinder gas engine, gas fuel is supplied to the sub chamber with the communication hole blocked by the communication hole valve,
Supply intake air to the main room. Further, since there is no air in the sub chamber, the gas mass of the gas fuel can be supplied to the sub chamber with a large gas mass. Further, even if the intake air has a high compression pressure in the main chamber, the sub chamber is closed by the communication hole valve to be disconnected from the main chamber, and the activated gas fuel in the sub chamber self-ignites. Without knocking.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an embodiment of a system of a turbo compound type multi-cylinder gas engine according to the present invention.

FIG. 2 is an explanatory diagram showing an example of a water jet nozzle.

FIG. 3 is an explanatory diagram showing details of the system of FIG. 1.

FIG. 4 is a cross-sectional view showing an embodiment of a heat shield type gas engine incorporated in this turbo compound type multi-cylinder gas engine.

FIG. 5 is an explanatory diagram showing the relationship between the exhaust timing of exhaust gas from the first cylinder and the fourth cylinder and the water injection timing from the water injection nozzle in this turbo compound multi-cylinder gas engine.

[Explanation of symbols]

 1 Main Chamber (Combustion Chamber) 7 Cylinder Head 31 Exhaust Ports 33A, 33B Exhaust Manifold 34 Exhaust Pipe 35 Turbocharger 38 Water Injection Nozzle 39 Water Injection Pump 43 Exit Side Exhaust Pipe 44 Collecting Exhaust Pipe 45 Energy Recovery Device 49 Current Collector

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location F02B 61/00 E 7541-3G

Claims (3)

[Claims] 1. A combustion chamber for burning gas fuel, an exhaust manifold connected to an exhaust port for discharging exhaust gas from the combustion chamber, an exhaust pipe connected to the exhaust manifold, and a turbocharger connected to the exhaust pipe. In a turbo compound multi-cylinder gas engine, each cylinder of at least four cylinders is made into a group of two cylinders whose ignition sequence is not continuous, and the exhaust manifold is composed of exhaust manifolds connected to the exhaust ports of each group,
A turbo compound type multi-cylinder gas characterized in that a water injection nozzle is arranged in each exhaust pipe connected to each exhaust manifold, and the turbocharger is composed of each turbocharger connected to each exhaust pipe. engine. 2. A collective exhaust pipe that collects the exhaust side exhaust pipes of each turbine of each turbocharger, an energy recovery device connected to the collective exhaust pipe, and a power collection device that collects electric power generated by the energy recovery device. The turbo compound multi-cylinder gas engine according to claim 1, further comprising an electric appliance. 3. One of the water injection nozzles injects water into the exhaust pipe at the end of the exhaust stroke of the first cylinder and at the end of the exhaust stroke of the fourth cylinder, and the other water injection nozzle of the other water injection nozzle is the second cylinder. 2. The turbo compound type multi-cylinder gas engine according to claim 1, wherein water is injected into the exhaust pipe at the end of the exhaust stroke of the third cylinder and at the end of the exhaust stroke of the third cylinder.