Method for improving methanol substitution rate of four-stroke medium-speed diesel-methanol dual-fuel engine

Abstract

The invention relates to the technical field of four-stroke medium-speed diesel-methanol dual-fuel engines. The invention discloses a method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine. The method comprises the following steps: connecting a deflation unit to a main engine air inlet cavity in advance; when the main engine operates in the methanol dual-fuel mode, the method comprises the following steps that an air inlet valve on the main engine is controlled to be opened in the exhaust stroke stage; an exhaust valve on the main engine is controlled to be closed in the intake stroke stage; methyl alcohol is controlled to be injected at the air inlet top dead center position in the air inlet stroke; wherein in the process from the beginning of methanol injection to the closing of the exhaust valve, the deflation unit is controlled to be started to deflate air entering the air inlet cavity of the main engine. Exhaust waste heat is improved in a deflation mode of the deflation unit, methanol steam is heated to be fully mixed with pressurized air as much as possible, the gas temperature of methanol entering the air cylinder is increased, the methanol combustion efficiency is improved, and then the methanol replacement rate is increased.

Description

Technical Field

[0001] The invention relates to the technical field of four-stroke medium-speed diesel-methanol dual-fuel engines, and in particular to a method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine. Background Art

[0002] The diesel-methanol dual-fuel engine is a new energy main engine that uses a mixture of diesel and methanol fuels; the main purpose of its design is to optimize the energy usage structure through a dual-fuel system, reduce diesel consumption, reduce harmful emissions, and use methanol as an alternative energy source to reduce dependence on a single energy source and achieve a more environmentally friendly and economical effect.

[0003] The working modes of the diesel-methanol dual-fuel engine include: diesel mode and methanol dual-fuel mode; when operating in methanol dual-fuel mode, the diesel is first compressed and ignited, and then the methanol participates in the combustion. The specific working mode is as follows: during the intake stroke, the pressurized air and methanol mixture enter the cylinder, and the piston moves downward to the bottom dead center; the piston continues to move upward, and the diesel is injected into the cylinder and is mixed with the air and methanol gas that entered the cylinder in the previous stroke and then compressed. The piston reaches the top dead center. This stage is the compression stroke; then it is the power stroke, the diesel and methanol are burned and work is done, and the piston moves downward to the bottom dead center; then the piston moves upward to exhaust, which is the exhaust stroke.

[0004] At present, the mainstream diesel-methanol dual-fuel engines mainly have two forms: intake manifold injection and direct injection. Regardless of the method of adding methanol, the mixed combustion of diesel and methanol is still in the exploratory stage. Methanol gas is mixed with air to participate in the combustion of diesel. Due to the physical and chemical characteristics of methanol itself and the large latent heat of methanol vaporization, it is difficult for methanol to be completely burned after entering the cylinder. Even only a small part of methanol participates in combustion and work, and the methanol substitution rate is low.

[0005] Therefore, solving the problem of methanol combustion in cylinder has become an important issue that each OEM needs to solve urgently. In this context, how to improve the methanol combustion efficiency has become a key technology to increase the methanol substitution rate; the above is a technical problem that technicians in this field need to solve urgently.

[0006] The information disclosed in this background technology section is only intended to enhance the understanding of the overall background of the invention and should not be regarded as an acknowledgment or any form of suggestion that the information constitutes the prior art already known to a person skilled in the art. Summary of the invention

[0007] In view of the above technical problems, an embodiment of the present invention provides a method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine to solve the problems raised in the above background technology.

[0008] The present invention provides the following technical solutions:

[0009] A method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine, wherein a venting unit is pre-connected to an air intake cavity of a main engine; when the main engine is running in a methanol dual-fuel mode, the method comprises the following steps:

[0010] The intake valve on the control host is opened during the exhaust stroke stage;

[0011] The exhaust valve on the control host is closed during the intake stroke stage;

[0012] Control the methanol to start injection at the intake top dead center position during the intake stroke;

[0013] In the process from the start of methanol injection to the closing of the exhaust valve, the air release unit is controlled to open to release the air entering the main engine air intake cavity.

[0014] Preferably, the air release unit includes a control valve; the control valve is connected to a cover plate of the air inlet cavity of the main engine, and an air port of the control valve is led to the atmosphere through a pipeline.

[0015] Preferably, the opening and closing degree of the air release port on the air release unit is controlled according to different load states of the host.

[0016] Preferably, in the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 25%, the opening and closing degree of the air release port on the air release unit is 20%.

[0017] Preferably, in the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 50%, the opening and closing degree of the air release port on the air release unit is 50%.

[0018] Preferably, in the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 75%, the opening and closing degree of the air release port on the air release unit is 70%.

[0019] Preferably, in the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 100%, the opening and closing degree of the air release port on the air release unit is 40%.

[0020] Preferably, when the host ends the methanol dual-fuel mode and is in the diesel mode, the air bleed unit is controlled to be closed.

[0021] A method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine provided by an embodiment of the present invention has the following beneficial effects: the present invention increases the exhaust waste heat by releasing air through a release unit, so as to heat the methanol vapor so that it is mixed with the pressurized air as fully as possible, thereby increasing the gas temperature after the methanol enters the cylinder, improving the methanol combustion efficiency and thus improving the methanol substitution rate. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the intake and exhaust valve switching during the intake and exhaust strokes of a diesel-methanol dual-fuel engine;

[0023] The solid circle in the inner circle of the figure is the intake and exhaust stroke cycle circle, the uppermost part of the circle is the piston upward apex / top dead center TDC, and the lowermost part of the circle is the piston downward stop apex / bottom dead center BDC;

[0024] Going outward in sequence, the dotted line is the stroke from the exhaust valve opening position to the exhaust valve closing position; the double-dotted line is the stroke from the intake valve opening position to the intake valve closing position; and the dotted line is the maximum position stroke from the methanol injection opening to the closing position. DETAILED DESCRIPTION

[0025] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative work are within the scope of protection of the present invention.

[0026] Design principle of the present invention:

[0027] Figure 1 As shown in the figure, it can be seen that there is an overlap between the opening and closing of the exhaust valve and the opening and closing of the intake valve. There is also an overlap (shaded part) between the start of methanol injection and the closing of the exhaust valve. Although the intake and exhaust overlap angle is large, methanol can only be injected from the top dead center, because at this time the piston starts to move downward, and the negative pressure in the cylinder can bring methanol gas into the cylinder.

[0028] During the methanol injection process, the exhaust valve is still in the open state and has not yet been closed, but methanol has begun to be injected and enters the cylinder along with the air, and the exhaust gas residual heat continues to heat the methanol vapor entering the cylinder; the above moments are the primary prerequisites of this scheme, and at this stage, the methanol vapor is preheated with the help of the exhaust gas residual heat;

[0029] Subsequently, the air intake of the main engine is reduced and the oxygen-rich state of the main engine is reduced by bleeding air through the bleeding unit to ensure that during the compression stroke, relatively less diesel will be ignited with the help of the heat of the compressed air. In this way, the remaining heat of the compressed air is used to continue to increase the exhaust temperature to compensate for the heat absorbed by the methanol, so that the methanol can be better gasified and burned and replace diesel combustion. The above operations are all carried out during the shaded time. If the shaded time is missed, the exhaust temperature will no longer affect the methanol gasification process.

[0030] In view of the problems mentioned in the above background technology, the embodiment of the present invention provides a method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine to solve the above technical problems. The specific technical solution is as follows:

[0031] Example 1

[0032] A method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine, wherein a venting unit is pre-connected to an air intake cavity of a main engine; when the main engine is running in a methanol dual-fuel mode, the method comprises the following steps:

[0033] The intake valve on the control host is opened during the exhaust stroke stage;

[0034] The exhaust valve on the control host is closed during the intake stroke stage;

[0035] Control the methanol to start injection at the intake top dead center position during the intake stroke;

[0036] In the process from the start of methanol injection to the closing of the exhaust valve, the air release unit is controlled to open to release the air entering the main engine air intake cavity.

[0037] The accuracy control of the intake valve and exhaust valve can be controlled by the electronic control system; for diesel-methanol dual-fuel engines with high speed, considering that the valves cannot open and close accurately in time when the engine is running at high speed, the opening and closing time of the valves in the whole stroke will be advanced or delayed due to the different mechanical technologies of various manufacturers;

[0038] Therefore, for high-speed engines, the exhaust valve can be controlled to close at the end of the exhaust stroke, and when the exhaust valve is completely closed, it will be delayed to the intake stroke; correspondingly, in order for the intake valve to open during the intake stroke, it is also necessary to pre-control the opening of the intake valve at the end of the exhaust stroke and before the start of the intake stroke.

[0039] At the same time, the methanol injection timing is controlled to be at the intake top dead center TDC 0°; injection at this position can ensure that as much methanol vapor as possible enters the cylinder, and the negative pressure generated in the cylinder due to the downward movement of the piston can prevent methanol gas from overflowing into the exhaust pipe; and this position is the maximum overlap angle from the methanol entering the cylinder to the closing of the exhaust valve. The design of the maximum overlap angle can increase gas fluidity and allow as much exhaust residual heat as possible to heat the methanol gas entering the cylinder.

[0040] In this embodiment, the air release unit includes a control valve; the control valve is connected to the cover plate of the main engine air intake cavity, and the air port of the control valve is led to the atmospheric environment through a pipeline; because the air intake volume of different models is different, different specifications of control valves can be selected according to the air intake volume of the main engine.

[0041] In this embodiment, the opening and closing degree of the air release port on the air release unit is controlled according to different load states of the host machine; the opening and closing degree of the air release port here can be understood as the valve opening degree.

[0042] In this embodiment, in the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, preferably:

[0043] When the main engine load is 25%, the opening and closing degree of the air vent on the air vent unit is 20%;

[0044] When the main engine load is 50%, the opening and closing degree of the air vent on the air vent unit is 50%;

[0045] When the main engine load is 75%, the opening and closing degree of the air vent on the air vent unit is 70%;

[0046] When the main engine load is 100%, the opening and closing degree of the air release port on the air release unit is 40%.

[0047] In this embodiment, when the host ends the methanol dual-fuel mode and enters the diesel mode, the air bleed unit is controlled to be closed; in the diesel mode, controlling the air bleed unit to be closed can ensure that the diesel injected into the cylinder has enough oxygen to support full combustion.

[0048] Embodiment 2:

[0049] The opening range of the air release unit is controlled according to the intake pressure and exhaust temperature of the host under different loads to detect the combustion efficiency of methanol. The intake pressure and exhaust temperature are displayed in real time through the sensor data collected by the host detection alarm system;

[0050] Figure 1As shown in the figure; methanol begins to be injected at the intake top dead center TDC0°. At this time, the exhaust valve has not yet closed, and the exhaust waste heat can still exist in the cylinder. At this time, the methanol gas can fully absorb the exhaust waste heat after entering the cylinder; the methanol vaporization latent heat value is 1109kJ / kg, and the diesel vaporization latent heat value is 240kJ / kg. Methanol needs to absorb more heat to facilitate gasification and combustion, but after methanol enters the cylinder, the main engine exhaust temperature will drop by about 40-70℃. It is difficult to maintain the heat absorbed by methanol by relying solely on normal exhaust waste temperature.

[0051] Therefore, by controlling the bleed unit to bleed air, the air intake volume of the main engine is reduced, and the oxygen-rich state of the main engine is reduced. During the compression stroke, relatively small amounts of diesel will be ignited with the help of the heat of the compressed air, reducing the diesel combustion efficiency. In this way, the remaining heat of the compressed air is used to increase the exhaust temperature and then the exhaust residual temperature, which is used to compensate for the heat absorbed by methanol, thereby allowing the methanol to be better gasified and burned.

[0052] Through real-time data collection and display of the host detection alarm, when the host is 25% loaded, the valve opening is controlled to be about 20%. The host detection alarm system can see that the intake pressure drops by about 0.3 bar and the exhaust temperature rises by 30°. When the exhaust temperature rises, the temperature inside the cylinder rises, and the combustion efficiency of methanol in the cylinder is improved, which can indirectly reflect the proportion of methanol replacing fuel, that is, the methanol substitution rate, which can increase by 5%.

[0053] If the valve opening is less than 20%, the intake pressure drops by 0.1-0.15bar, and the exhaust temperature rises by only 10℃, and the effect is not obvious; if the valve opening is greater than 20%, the intake pressure drops by more than 0.3bar, and other conditions caused by insufficient air intake of the main engine will occur. Therefore, when the main engine is 25% loaded, controlling the valve opening to about 20% is the best position.

[0054] As above, when the main engine is at 50% load, the valve opening is about 50%, the intake pressure drops about 0.3 bar, the exhaust temperature rises by 30°, and the methanol substitution rate increases by 7%. At this time, the valve opening is the best position; when the main engine is at 75% load, the valve opening is about 70%, the intake pressure drops about 0.4 bar, the exhaust temperature rises by 50°, and the methanol substitution rate increases by 10%. At this time, the valve opening is the best position; at 100% load, the valve opening is about 40%, the intake pressure drops about 0.25 bar, the exhaust temperature rises by 25°, and the methanol substitution rate increases by 5%. At this time, the valve opening is the best position. See Table 1 for specific experimental data.

[0055] Table 1

[0056]

[0057]

[0058] As shown in Table 1 above, by installing a gas release unit to release gas, methanol gasification temperature compensation can be effectively performed, which effectively improves the methanol substitution rate. Figure 1 The setting of the methanol injection timing and the main engine intake and exhaust timing makes this invention easy to install and implement, and can effectively improve the methanol substitution rate.

[0059] The device embodiments described above are merely illustrative, wherein the units described as separate components may or may not be physically separated, and the components shown as units may or may not be physical units, and may be located in one place or distributed over multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of this embodiment.

[0060] In the present invention, unless otherwise clearly stipulated and limited, the terms such as "installation", "setting", "connection", "fixation" and "screw-on" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integrated connection; it can be a mechanical connection or an electrical connection; it can be a direct connection or an indirect connection through an intermediate medium, and it can be the internal connection of the components or the interaction relationship between the components. Unless otherwise clearly defined, for ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to the specific circumstances.

[0061] It is understandable that those skilled in the art can make equivalent substitutions or changes based on the technical solution and concept of the present invention, and all these changes or substitutions should fall within the protection scope of the claims attached to the present invention.

Claims

1. A method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine, characterized in that: The exhaust unit is pre-connected to the air inlet cavity of the main engine; the main engine includes the following steps when operating in methanol dual fuel mode: The intake valve on the control host is opened during the exhaust stroke stage; The exhaust valve on the control host is closed during the intake stroke stage; Control the methanol to start injection at the intake top dead center position during the intake stroke; In the process from the start of methanol injection to the closing of the exhaust valve, the air release unit is controlled to open to release the air entering the main engine air intake cavity.

2. The method for improving the methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that: The air release unit comprises a control valve; the control valve is connected to the cover plate of the air inlet cavity of the main engine, and the air port of the control valve is led to the atmosphere through a pipeline.

3. The method for improving methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that: The opening and closing degree of the air release port on the air release unit is controlled according to different load states of the main engine.

4. The method for improving methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that: In the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 25%, the opening and closing degree of the air release port on the air release unit is 20%.

5. The method for improving methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that: In the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 50%, the opening and closing degree of the air release port on the air release unit is 50%.

6. The method for improving methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that: In the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 75%, the opening and closing degree of the air release port on the air release unit is 70%.

7. The method for improving methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that: In the step of controlling the opening and closing degree of the air release port on the air release unit according to different load states of the host, when the host load is 100%, the opening and closing degree of the air release port on the air release unit is 40%.

8. The method for improving methanol substitution rate of a four-stroke medium-speed diesel-methanol dual-fuel engine according to claim 1, characterized in that: When the host ends the methanol dual-fuel mode and enters the diesel mode, the air bleed unit is controlled to be closed.

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