CN112384689A - Diesel and methanol combined combustion engine and control method thereof - Google Patents

Diesel and methanol combined combustion engine and control method thereof Download PDF

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CN112384689A
CN112384689A CN201980034534.7A CN201980034534A CN112384689A CN 112384689 A CN112384689 A CN 112384689A CN 201980034534 A CN201980034534 A CN 201980034534A CN 112384689 A CN112384689 A CN 112384689A
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methanol
diesel
engine
alcohol
injection
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CN112384689B (en
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姚春德
姚安仁
王斌
吴涛阳
胡江涛
陈超
高健
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Tianjin University
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Tianjin University
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/08—Other arrangements or adaptations of exhaust conduits
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/30—Controlling fuel injection
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
    • F02M21/00—Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form
    • F02M21/02—Apparatus for supplying engines with non-liquid fuels, e.g. gaseous fuels stored in liquid form for gaseous fuels
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/30—Use of alternative fuels, e.g. biofuels

Abstract

A diesel and methanol combined combustion engine comprises a diesel engine, a methanol injection system, a methanol electric control unit, a methanol supply system and a post-processor combination; the methanol injection system is positioned on an engine air inlet channel; the methanol electric control unit and the methanol supply system are connected with the methanol injection system; the post-processor combination comprises a methanol special selective catalytic reduction system, a diesel particulate filter and a diesel oxidation catalyst, wherein the methanol special selective catalytic reduction system and the diesel particulate filter are controlled by a methanol electric control unit, and the post-processor combination is arranged on an engine exhaust pipe. By adopting the diesel and methanol combined combustion technology, the high-efficiency combustion of the diesel engine can be realized, and the heat efficiency of the engine can be remarkably improved particularly under medium and large load working conditions; the diesel and methanol combined combustion technology can reduce NO without the assistance of ureaxAnd root emissions. Also relates to a control method of the diesel and methanol combined combustion engine.

Description

Diesel and methanol combined combustion engine and control method thereof
Technical Field
The invention belongs to the field of engines, and particularly relates to a diesel and methanol combined combustion engine and a control method thereof.
Background
Methanol automobiles are divided into ignition type methanol passenger vehicles and commercial vehicles and compression ignition type methanol commercial vehicles, wherein the ignition type methanol passenger vehicles and the commercial vehicles adopt a technical route similar to that of a traditional gasoline engine, but the cold start of the engine is difficult due to high latent heat of vaporization of methanol, so that the engine needs to be started by adopting gasoline, after the engine is fully warmed, methanol fuel is completely used, homogeneous mixed gas is formed in an air inlet channel, and then premixed mixed gas is ignited by a spark plug. The technical route adopted by the ignition type methanol commercial vehicle is similar to that of a methanol passenger vehicle. The technical route of the compression ignition type methanol commercial vehicle is mainly a diesel and methanol combined combustion technology. This is because the auto-ignition temperature of methanol is high, and compression ignition cannot be realized at most operating conditions of the compression ignition engine, so diesel oil is needed to ignite the methanol premixed gas. The diesel and methanol combined combustion engine adopts a pure diesel working mode under the working conditions of starting and idling, and adopts a diesel and methanol combined combustion mode, which is called DMCC mode for short, after the temperature and other conditions of cooling water meet the requirements.
Most of the heavy-duty diesel engines satisfying the emission regulations of the fifth and above state of the art at present adopt a combination of a Diesel Oxidation Catalyst (DOC), a urea selective catalytic reduction system (urea SCR) and a Diesel Particulate Filter (DPF) postprocessor. The use of such an aftertreatment assembly requires continuous urea injection into the exhaust pipe, which increases the cost of use for the user. At the same time, in order to regenerate the DPF, it is necessary to inject diesel oil into the exhaust pipe to oxidize the carbon particles collected inside the DPF, which causes a phenomenon of burning inside the DPF and also increases fuel costs for users.
The diesel and methanol combined combustion technology has the characteristic of high emission of carbon monoxide and unburned hydrocarbon, and the emission of nitrogen dioxide accounts for a high proportion of nitrogen oxide emission, and the nitrogen dioxide is a key group for passive regeneration of the DPF.
For the above reasons, there is a need to develop a solution to the problem of smoke emission (PM) overrun of heavy vehicles, and to significantly reduce the fuel cost of the vehicle owner.
Disclosure of Invention
The invention aims to overcome the defects in the prior art and provides a diesel and methanol combined combustion engine and a control method thereof.
The purpose of the invention is realized by the following technical scheme:
a diesel and methanol combined combustion engine comprises a diesel engine, wherein diesel of the diesel engine adopts an in-cylinder direct injection mode, and further comprises a methanol injection system, a methanol electronic control unit, a methanol supply system and a post-processor combination; the methanol injection system is positioned on an engine air inlet channel; the methanol electronic control unit and the methanol supply system are connected with the methanol injection system; the post-processor combination comprises a methanol special selective catalytic reduction system, a diesel particulate filter and a diesel oxidation catalyst, wherein the methanol special selective catalytic reduction system and the diesel particulate filter are controlled by a methanol electric control unit, the post-processor combination is installed on an engine exhaust pipe, and the methanol special selective catalytic reduction system, the diesel particulate filter and the diesel oxidation catalyst are sequentially arranged in the sequence of being connected with the engine exhaust pipe.
Further, still include throttle position sensor, water temperature sensor, tachometric sensor and methyl alcohol level sensor, throttle position sensor installs throttle pull rod pivot department at the high-pressure oil pump, water temperature sensor installs on the condenser tube way, tachometric sensor installs on flywheel dish shell, methyl alcohol level sensor installs in methyl alcohol supply system's methyl alcohol incasement.
Further, the methanol electronic control unit is connected with an ECU of the diesel engine, and the rotating speed, the accelerator pedal, the cooling water temperature and the air inlet temperature pressure signal are obtained from the message.
Further, the methanol injection system consists of a methanol nozzle and a methanol sprayer.
Further, a methanol injector is also disposed in the exhaust pipe of the diesel engine.
Further, the reducing agent of the methanol-dedicated selective catalytic reduction system is methanol; nitrogen dioxide and nitric oxide are reduced by using incomplete combustion products in the cylinder.
Further, the methanol supply system comprises a methanol tank, a methanol pump coarse filter, a methanol liquid level meter, an electric methanol pump, a methanol filter, an alcohol pressure regulating valve, a methanol distribution pipe, an alcohol inlet pipe and an alcohol return pipe; methanol pump coarse strainer and methyl alcohol level gauge install in the methyl alcohol case, and methyl alcohol flows through methyl alcohol pump coarse strainer, electronic methyl alcohol pump, methyl alcohol filter, mellow wine pressure regulating valve in proper order, again through advancing mellow wine pipe to methyl alcohol distributing pipe and methyl alcohol nozzle, passes through between mellow wine pressure regulating valve and the methyl alcohol case back mellow wine union coupling.
The other technical scheme provided by the invention is as follows:
a control method of a diesel and methanol combined combustion engine is based on the diesel and methanol combined combustion engine and comprises the following processes:
step 1, starting an engine in a pure diesel combustion mode;
step 2, the engine burns in a pure diesel mode;
and step 3, judging whether the following conditions are met or not, namely:
the first condition is as follows: whether the methanol supply system has the conditions, namely whether the methanol pressure reaches a set value or not and whether the methanol liquid level is higher than a lower limit value or not;
and a second condition: whether the temperature of the cooling water of the engine is larger than or equal to a set threshold value, namely whether the temperature of the cooling water of the engine reaches 60 ℃;
and (3) carrying out a third condition: whether the engine does not reach a full load interval, namely whether an accelerator pedal is not at a 100% working point;
and a fourth condition: whether the part below the inclined line of the no-load accelerator is separated or not, namely whether the engine and the gearbox are not separated or not;
if all the conditions are met, turning to the step 4, otherwise, returning to the step 2;
and 4, injecting alcohol, and performing combined combustion of diesel oil and methanol.
Further, the methanol injection system determines the alcohol injection amount as follows:
step 4-1, firstly, determining a target alcohol injection amount basic value by obtaining the operating condition of the engine and combining a methanol injection pulse spectrum (MAP) on the basis of confirming the engine operating condition information;
step 4-2, correcting the basic value of the target alcohol injection amount through the influence of the temperature of the cooling water on the working condition of the diesel and methanol combined combustion engine;
step 4-3, comparing the maximum alcohol injection amount with the maximum alcohol injection amount of the engine at the current rotating speed, and taking the smaller value as the final alcohol injection amount;
and 4-4, inquiring the alcohol spraying amount and a methanol MAP, determining the driving pulse width of the electromagnetic valve, outputting the driving pulse width to a methanol nozzle, and controlling the alcohol spraying amount by the nozzle electromagnetic valve.
Further, the methanol injection pulse spectrum (MAP) in the step 4-1 is determined by adopting an interpolation method, which comprises the following specific steps:
one dimension of the methanol MAP is the engine speed n, and the other dimension is the accelerator pedal opening degree alpha; the MAP graph grid points have 5 points, wherein the points 1-4 are two-dimensional data points determined in a bench calibration test, the point 5 represents a working condition point, each point is a methanol control injection quantity m corresponding to specific engine speed n and accelerator opening degree alpha, namely the engine speed at the point 1 is n1Throttle opening is alpha1The methanol injection amount is m1At point 2, the engine speed is n2Throttle opening is alpha2The methanol injection amount is m2At point 3, the engine speed is n3Throttle opening is alpha3The methanol injection amount is m3Engine speed at point 4Is n4Throttle opening is alpha4The methanol injection amount is m4At point 5, the engine speed is n5Throttle opening is alpha5The methanol injection amount is m5For the purpose of understanding the interpolation process and the formula description, the intermediate points 5' and 5 "are introduced, corresponding to the methanol injection quantities m5' and m5″；
Firstly, judging the MAP graph network region where the engine operation condition point 5 is positioned, namely determining the current engine speed n5And accelerator opening degree alpha5Four adjacent calibration MAP points;
then, according to the accelerator opening degree alpha1And alpha2Interpolating the direction to obtain m5' the specific calculation formula is as follows:
Figure BDA0002792414490000031
go to m5After interpolation, the throttle opening alpha is adjusted3And alpha4Interpolating in the direction to find m5", the calculation formula is as follows:
Figure BDA0002792414490000032
find m5' and m5"thereafter, the methanol control amount m at the engine operation point 5 is not obtained yet5Value, also required at engine speed n1And n4Interpolation is carried out in the direction, and m is finally obtained5The calculation formula is as follows:
Figure BDA0002792414490000033
obtaining an engine operation working condition point 5 (n) after three times of interpolation5，α5) Corresponding methanol injection control amount m5。
Furthermore, a passive regeneration strategy is adopted for the diesel particle filter in the post-processor combination, carbon particles in the diesel particle filter are oxidized by nitrogen dioxide with higher concentration in tail gas, when the front-back pressure difference of the diesel particle filter is larger, methanol is injected through a methanol injector arranged on an exhaust pipe, carbon particles trapped in the diesel particle filter are combusted and oxidized, and finally the carbon particles are connected with a diesel oxidation catalyst and used for oxidizing unburned carbon hydrogen and carbon monoxide.
Compared with the prior art, the technical scheme of the invention has the following beneficial effects:
firstly, under the combined combustion mode of diesel oil and methanol, the work-doing fuel in the cylinder not only comprises directly-injected diesel oil, but also comprises methanol fuel, and because the methanol fuel can do work, the output power of the engine can be increased. The driver can passively reduce the depth of the accelerator pedal, so that the diesel injection amount is reduced, the engine power can meet the vehicle running requirement, and the purpose of reducing the diesel consumption is achieved.
And compared with the traditional diesel engine, the diesel and methanol combined combustion engine has cleaner emission and can reduce NOx and root emission at the same time.
And the diesel and methanol combined combustion engine is provided with a post-processor combination comprising a methanol SCR, a DPF and a DOC, and the methanol SCR reducing agent is an incomplete combustion product (including methanol) formed by methanol at high temperature, so that the urea SCR is omitted, and the use cost of urea can be saved.
And fourthly, the diesel and methanol combined combustion engine can operate in a DMCC mode and can also work in a pure diesel mode, the working mode can be switched, and the application scene is flexible.
Drawings
FIG. 1 is a graph comparing heat release rates for pure diesel mode and DMCC mode; in the figure, the abscissa represents the crank angle in degrees and the ordinate represents the cylinder pressure in mpa.
FIG. 2 is a graph showing the distribution and comparison of the equivalence ratio of the main heat release cylinder temperature in the pure diesel mode and the DMCC mode, wherein the abscissa represents the cylinder temperature and the ordinate represents the local equivalence ratio.
FIG. 3 is a flow chart of control of a diesel and methanol combined combustion engine.
FIG. 4 is a diagram showing a local connection relationship of the system in the embodiment.
FIG. 5 is a schematic of a methanol injection quantity control strategy.
FIG. 6 is a schematic diagram of a methanol MAP network architecture.
FIG. 7 shows a methanol MAP correction control routine in the embodiment.
FIG. 8 is a schematic diagram of a methanol supply system.
FIG. 9 is a diagram of a post-processing system connection.
Detailed Description
The invention is described in further detail below with reference to the figures and specific examples. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
The diesel and methanol combined combustion technology can realize high-efficiency combustion of a diesel engine, and particularly can obviously improve the heat efficiency of the engine under medium and large load working conditions, which is determined by the physical and chemical properties of methanol. Methanol has higher latent heat of vaporization, and when the methanol is sprayed into the air inlet channel to form a homogeneous mixed gas, the vaporization of the methanol can absorb a large amount of heat, so that the temperature in a cylinder can be greatly reduced, and the stagnation period of the diesel oil can be prolonged. The longer combustion lag period of the diesel oil can lead the diesel oil to have enough time to carry out full atomization, and the diesel oil and the methanol-air mixed gas form high-activity combustible mixed gas. When the boundary conditions in the cylinder reach the ignition conditions of the portion of the combustible mixture, the portion of the combustible mixture will be ignited simultaneously in a homogeneous compression ignition manner. The combustion mode can greatly improve the proportion of constant pressure combustion, and meanwhile, the combustion duration of the combustion mode is shorter. The temperature in the cylinder is obviously reduced in the later stage of the power stroke, so that the heat dissipation loss is effectively reduced, and the heat efficiency of the engine is improved. FIG. 1 is a comparison of cylinder pressure and heat release rate for pure diesel mode versus DMCC mode, where it can be seen that DMCC mode has significantly lower in-cylinder pressure during the compression stroke than pure diesel mode, which greatly reduces the negative compression work. When the piston reaches a top dead center, the pure diesel mode starts to generate combustion exothermic reaction, so that the pressure in the cylinder is continuously increased, but the volume change rate in the cylinder is smaller according to the motion law of the piston, and the higher pressure is not converted into effective output work. In the DMCC mode, since combustion occurs 10 degrees after the upper point, the in-cylinder pressure significantly decreases when the piston starts moving downward, but after combustion starts, the in-cylinder pressure rapidly increases, and the highest in-cylinder pressure is close to that in the pure diesel mode, but at this time, the rate of change of the in-cylinder volume is high, and high pressure can be converted into effective work output. The pressure in the cylinder after the DMCC mode starts to burn is obviously higher than that in the pure diesel mode, but after the piston moves to 40 degrees after the top dead center, the pressure in the cylinder in the DMCC mode is lower than that in the pure diesel mode, because the combustion duration of the DMCC mode is short, the post-combustion phenomenon is less, the heat dissipation loss is increased due to the fact that the higher post-combustion proportion is increased, and meanwhile the energy taken away by exhaust gas is increased. Therefore, the efficient combustion mechanism of the diesel and methanol combined combustion technology is as follows: the high latent heat of vaporization of the methanol and the inhibiting effect on low-temperature ignition of the diesel extend the combustion lag period of the diesel, so that the diesel is fully mixed with the mixed gas of the methanol and the air, and homogeneous compression ignition combustion is realized, which is a mechanism of high-efficiency combustion of the combined combustion technology of the diesel and the methanol. The reduction of the pressure of the compression stroke, the reduction of the heat dissipation loss in the later period of the power stroke, the reduction of the exhaust loss and the recovery of the methanol evaporation atomization waste heat are the keys of high thermal efficiency of the diesel and methanol combined combustion technology.
The combined combustion technology of the diesel and the methanol can simultaneously reduce NOx and root emission. Fig. 2 is a comparison of the distribution of the temperature equivalence ratio in the main heat release cylinder in the pure diesel mode and the DMCC mode, and it can be seen from the figure that the DMCC mode completely avoids the root generation region, and has NO intersection with the region with higher NO generation rate, which is also the key for reducing NOx emission. The main reasons for the DMCC mode to reduce the soot emissions are as follows: the local equivalence ratio can be effectively reduced by adopting a methanol premixing mode; the high oxygen content ratio of the methanol ensures that the methanol does not generate soot in the combustion process; the extension of the diesel oil stagnation period leads to the reduction of the local equivalence ratio of the diesel oil. The DMCC mode reduces NOx emissions for the following reasons: the high latent heat of vaporization of the methanol reduces the temperature in the cylinder and realizes low-temperature combustion; the methanol is premixed in a high proportion, so that a heat release area is more uniform, and a local high-temperature area is reduced; the high methanol combustion speed shortens the duration of high combustion temperature, thereby reducing NOx emission.
Example 1:
aiming at a mechanical pump engine, the application occasion is mainly a non-road engine, including a ship engine, a diesel generator set, engineering machinery and the like, and also includes road vehicles with the emission standards of China and below.
The diesel oil and methanol combined combustion engine comprises: but the diesel engine of pure diesel fuel of using, diesel engine's diesel oil adopts the direct mode of spouting in the jar, still includes: the system comprises a methanol injection system, a methanol electronic control unit, a methanol supply system, a post-processor combination, an accelerator position sensor, a water temperature sensor, a rotating speed sensor, a methanol liquid level sensor and a methanol injector, wherein the methanol injection system is positioned on an air inlet channel of a diesel engine; the methanol injection system comprises: a methanol nozzle and a methanol sprayer;
as shown in fig. 8, the methanol supply system mainly includes a methanol tank, a methanol pump strainer, a methanol level meter, an electric methanol pump, a methanol filter, an alcohol pressure regulating valve, a methanol distribution pipe, and an alcohol inlet pipe and an alcohol return pipe.
The methanol supply system comprises a methanol tank 1, a methanol pump coarse filter 2, a methanol liquid level meter 3, an electric methanol pump 4, a methanol filter 5, an alcohol pressure regulating valve 6, a methanol distribution pipe 7, an alcohol inlet pipe 9 and an alcohol return pipe 10; the methanol pump coarse filter 2 and the methanol liquid level meter 3 are arranged in the methanol tank 1, methanol sequentially flows through the methanol pump coarse filter 2, the electric methanol pump 4, the methanol filter 5 and the alcohol pressure regulating valve 6, then flows to the methanol distribution pipe 7 and the methanol nozzle 8 through the alcohol inlet pipe 9, and the alcohol pressure regulating valve 6 is connected with the methanol tank 1 through the alcohol return pipe 10.
Due to the corrosive effect of methanol on parts of materials, stainless steel materials should be selected as materials for alcohol-containing parts. In order to avoid electrochemical corrosion, the methanol supply system should be designed to realize electro-liquid separation, and the alcohol-related part should be made of stainless steel. In the system, the alcohol inlet pipe and the alcohol return pipe are both rubber pipes, but the rubber is alcohol-resistant rubber, so that common rubber cannot be used, and high-fluorine rubber, nitrile rubber, silicon rubber, polytetrafluoroethylene or chloroprene rubber is adopted. The methanol level gauge should also be made of stainless steel.
Fig. 9 is a diagram of an ultra-low emission post-treatment system of a diesel and methanol combined combustion technology, from which it can be seen that an original engine is first connected with a methanol-dedicated selective catalytic reduction system (methanol SCR), the reducing agent of which is an incomplete combustion product (including methanol) formed by methanol at a high temperature. Then, the DPF is connected to a Diesel Particulate Filter (DPF) which is mostly operated by a passive regeneration strategy to oxidize carbon particles trapped in the DPF by nitrogen dioxide in exhaust gas, and if a large differential pressure across the DPF is detected, it is necessary to inject methanol into an exhaust pipe to burn and oxidize the trapped carbon particles in the DPF. And finally to a Diesel Oxidation Catalyst (DOC) for oxidation of unburned hydrocarbons and carbon monoxide.
The accelerator position sensor is the key for acquiring the intention of a driver, and meanwhile, the output power of the engine can be acquired through the accelerator position sensor. The rotation speed sensor is used for monitoring the working rotation speed of the engine. The water temperature sensor is used for monitoring the temperature of cooling water of the engine. The methanol liquid level sensor is used for monitoring the methanol liquid level of the methanol tank. The rotation speed and the accelerator pedal signal are used for interpolation calculation of methanol MAP, the cooling water temperature signal and the intake air temperature pressure signal are used for correction of methanol MAP, see figure 7, and the methanol electronic control unit controls on-off of a methanol pump and power-on time of a methanol nozzle.
The cooling water temperature versus methanol MAP modified equation is as follows:
MI＝MI1×(1+fTw)
wherein: MI is the target jet width, MI1 is the basic jet width, fTwThe correction coefficient is the cooling water temperature.
The formula of the correction coefficient of the cooling water temperature is as follows:
fTw＝0.3×(Tw-Tw0)/(Twh-Tw0)-0.3
wherein: t iswIs the current cooling water temperature value, TwhTo set the high value of the cooling water temperature, Tw0The set cooling water temperature threshold value of whether alcohol is sprayed or not is adopted.
The mode switching diagram of the diesel and methanol combined combustion technology is shown in figure 3. The working principle of the diesel and methanol combined combustion technology is that the engine is started in a pure diesel mode, and when the engine reaches the set cooling water temperature, the engine starts to enter a DMCC mode, and the diesel ignites the methanol premixed gas. As can be seen from fig. 3, when the pure diesel mode is switched to the DMCC mode, several conditions are determined, including methanol level, cooling water temperature, rotation speed, and accelerator pedal. The temperature of the cooling water is set to be 60 ℃, and when the temperature of the cooling water reaches or exceeds 60 ℃, the engine can be switched to a diesel and methanol combined fuel working mode. In order to realize efficient and safe combustion in a DMCC mode, methanol does not participate in work in a part below an unloaded throttle oblique line and a full throttle interval, wherein the part below the unloaded throttle oblique line is a small-load working interval of an engine, the methanol participates in combustion in the interval to reduce the combustion efficiency, and the methanol is injected to cause fuel waste due to no power output in the interval. The maximum cylinder pressure and the maximum pressure rise rate can be exceeded by adding methanol in the full load interval, and the engine can be damaged, so that the methanol does not participate in combustion in the full throttle interval.
As shown in fig. 3, the method of controlling the engine described above includes the following processes:
step 1: the diesel engine is started in a pure diesel combustion mode;
step 2: burning in a pure diesel mode;
and step 3: judging whether the following conditions are met or not, namely:
the first condition is as follows: whether the methanol supply system has the conditions, namely whether the methanol pressure reaches a set value (the normal working pressure of the methanol injection system is 0.4MPa) or not, and whether the methanol liquid level is higher than a lower limit value or not;
and a second condition: whether the cooling water temperature is greater than or equal to a set threshold value, namely whether the engine cooling water temperature reaches 60 ℃;
and (3) carrying out a third condition: whether the engine does not reach a full load interval, namely whether an accelerator pedal is not at a 100% working point;
and a fourth condition: whether the part below the idling throttle inclined line is separated, namely whether the engine and the gearbox are not separated.
If all the conditions are met, turning to the step 5, otherwise, returning to the step 2;
and 4, step 4: and (5) alcohol injection, and implementing combined combustion of diesel oil and methanol.
Under the combined combustion mode of diesel oil and methanol:
when all the methanol and the air meet the set conditions, the methanol is continuously sprayed into the air inlet channel, and then forms homogeneous mixed gas in the air inlet channel along with the air, and then enters the cylinder. The in-cylinder work-doing fuel will include not only direct-injected diesel, but also methanol fuel, since methanol fuel will do work, the engine output will increase. This can make the driver reduce accelerator pedal deeply by the passivity to reduce diesel injection volume, make the engine send power can satisfy vehicle driving needs finally.
For the combined combustion technology of diesel and methanol, the injection amount of methanol is the core of control. The alcohol injection amount of the methanol injection system is the alcohol injection amount of each cylinder in each cycle when the diesel engine works in a diesel and methanol combined combustion mode. For a diesel and methanol combined combustion engine, the alcohol injection amount is the most basic and important parameter, and the effective control of the alcohol injection amount each time needs to be realized under different working conditions, namely the required alcohol injection amount of a diesel and methanol combined combustion vehicle under different working conditions and operation requirements, and how to realize a target value. The amount of alcohol sprayed depends mainly on two factors: one is the alcohol spraying pressure; the second is the opening time of the methanol nozzle. In fact, the system controls the alcohol injection pressure to be a fixed value by means of a pressure regulating valve, and the alcohol injection quantity per time is basically in direct proportion to the injection duration. And inquiring basic alcohol injection amount through a methanol MAP graph, and determining the nozzle driving pulse width by a nozzle electromagnetic valve.
As shown in fig. 5, the determination method of the alcohol injection amount of the methanol injection system is as follows:
step 4-1: firstly, determining a target alcohol injection amount basic value by obtaining the operating condition of an engine and combining a methanol MAP (MAP) on the basis of confirming the engine operating condition information;
step 4-2: the correction of the basic value determines the correction alcohol amount through the influence of the temperature of the cooling water on the working condition of the diesel and methanol combined combustion engine;
step 4-3: finally, comparing the maximum alcohol injection amount with the maximum alcohol injection amount of the engine at the current rotating speed, and taking the smaller value as the final alcohol injection amount;
step 4-4: then inquiring the alcohol spraying amount and a methanol MAP graph, determining the driving pulse width of the electromagnetic valve, outputting the driving pulse width to a methanol nozzle, and finishing the alcohol spraying amount control by the nozzle electromagnetic valve.
In the step 4-1, the interpolation method of the methanol MAP is as follows:
one dimension of the methanol MAP is the engine speed n, the other dimension is the accelerator pedal opening degree alpha, and the most important concept in the method is a grid; as shown in FIG. 6, there are 5 points in the MAP grid, wherein points 1-4 are two-dimensional data points determined in the bench calibration test, point 5 represents operating point, each point is a methanol control injection amount m corresponding to specific engine speed n and throttle opening alpha, that is, the engine speed at point 1 is n1Throttle opening is alpha1The methanol injection amount is m1At point 2, the engine speed is n2Throttle opening is alpha2The methanol injection amount is m2At point 3, the engine speed is n3Throttle opening is alpha3The methanol injection amount is m3At point 4, the engine speed is n4Throttle opening is alpha4The methanol injection amount is m4At point 5, the engine speed is n5Throttle opening is alpha5The methanol injection amount is m5For the purpose of understanding the interpolation process and the formula description, the intermediate points 5' and 5 "are introduced, corresponding to the methanol injection quantities m5' and m5″。；
Firstly, judging a MAP graph network area where an engine operation condition point 5 is located, namely determining four calibration MAP points close to the current engine speed n5 and the accelerator opening degree alpha 5;
then, according to the accelerator opening degree alpha1And alpha2Interpolating the direction to obtain m5' the specific calculation formula is as follows:
Figure BDA0002792414490000081
go to m5After interpolation, the throttle opening alpha is adjusted3And alpha4Interpolating in the direction to find m5", the calculation formula is as follows:
Figure BDA0002792414490000091
find m5' and m5"thereafter, the methanol control amount m at the engine operation point 5 is not obtained yet5Value, also required at engine speed n1And n4Interpolation is carried out in the direction, and m is finally obtained5The calculation formula is as follows:
Figure BDA0002792414490000092
obtaining an engine operation working condition point 5 (n) after three times of interpolation5，α5) Corresponding methanol injection control amount m5。
The DPF in the postprocessor combination adopts a passive regeneration strategy, carbon particles in the DPF are oxidized by means of high-concentration nitrogen dioxide in tail gas, when the front-back pressure difference of the DPF is large, methanol is injected through a methanol injector arranged on an exhaust pipe, carbon particles trapped by combustion and oxidation are carried out in the DPF, and the DPF is finally connected with a DOC (catalyst control system) and used for oxidizing unburned carbon and carbon monoxide.
Example 2:
aiming at the diesel engine with the emission standard of the fourth country and above, an electronic control high-pressure common rail Electronic Control Unit (ECU) is adopted, and the ECU supports the communication of a Controllable local Area network (CAN). For the engine, an accelerator position sensor, a water temperature sensor and a rotating speed sensor are not required to be installed when the diesel and methanol combined combustion technology is additionally installed, and a specific schematic diagram is shown in FIG. 4. As CAN be seen from the figure, the methanol electronic control unit obtains signals of the rotating speed, the accelerator pedal, the cooling water temperature and the intake air temperature and pressure from a diesel ECU CAN message. The rotation speed and the accelerator pedal signal are used for interpolation calculation of the methanol MAP, and the cooling water temperature signal and the intake air temperature pressure signal are used for correction of the methanol MAP. The methanol electric control unit controls the on-off of the methanol pump and the power-on time of the methanol nozzle.
The rest is the same as in example 1.
The present invention is not limited to the above-described embodiments. The foregoing description of the specific embodiments is intended to describe and illustrate the technical solutions of the present invention, and the above specific embodiments are merely illustrative and not restrictive. Those skilled in the art can make many changes and modifications to the invention without departing from the spirit and scope of the invention as defined in the appended claims.

Claims (11)

1. A diesel and methanol combined combustion engine comprises a diesel engine, wherein diesel of the diesel engine adopts an in-cylinder direct injection mode, and is characterized by further comprising a methanol injection system, a methanol electric control unit, a methanol supply system and a post-processor combination; the methanol injection system is positioned on an engine air inlet channel; the methanol electronic control unit and the methanol supply system are connected with the methanol injection system; the post-processor combination comprises a methanol special selective catalytic reduction system, a diesel particulate filter and a diesel oxidation catalyst, wherein the methanol special selective catalytic reduction system and the diesel particulate filter are controlled by a methanol electric control unit, the post-processor combination is installed on an engine exhaust pipe, and the methanol special selective catalytic reduction system, the diesel particulate filter and the diesel oxidation catalyst are sequentially arranged in the sequence of being connected with the engine exhaust pipe.
2. The diesel and methanol combined combustion engine of claim 1, further comprising an accelerator position sensor, a water temperature sensor, a rotation speed sensor and a methanol liquid level sensor, wherein the accelerator position sensor is installed at a rotating shaft of an accelerator pull rod of the high-pressure oil pump, the water temperature sensor is installed on a cooling water pipeline, the rotation speed sensor is installed on a flywheel disc shell, and the methanol liquid level sensor is installed in a methanol tank of the methanol supply system.
3. The combined diesel and methanol combustion engine of claim 1, wherein the methanol electronic control unit is connected with the diesel engine ECU, and acquires signals of the rotating speed, the accelerator pedal, the cooling water temperature and the intake air temperature and pressure from the messages.
4. The diesel methanol combined combustion engine of claim 1, wherein the methanol injection system is comprised of a methanol injection nozzle and a methanol injector.
5. A diesel and methanol combined combustion engine as set forth in any one of claims 1-4, characterized in that a methanol injector is further disposed in the exhaust pipe of the diesel engine.
6. A diesel and methanol combined combustion engine as in any one of claims 1-4, wherein the reductant of the methanol specific selective catalytic reduction system is methanol; nitrogen dioxide and nitric oxide are reduced by using incomplete combustion products in the cylinder.
7. A diesel and methanol combined combustion engine as set forth in any one of claims 1-4, wherein the methanol supply system comprises a methanol tank, a methanol pump strainer, a methanol level gauge, an electric methanol pump, a methanol filter, an alcohol pressure regulating valve, a methanol distribution pipe, and an alcohol inlet pipe and an alcohol return pipe; methanol pump coarse strainer and methyl alcohol level gauge install in the methyl alcohol case, and methyl alcohol flows through methyl alcohol pump coarse strainer, electronic methyl alcohol pump, methyl alcohol filter, mellow wine pressure regulating valve in proper order, again through advancing mellow wine pipe to methyl alcohol distributing pipe and methyl alcohol nozzle, passes through between mellow wine pressure regulating valve and the methyl alcohol case back mellow wine union coupling.
8. A control method of a diesel and methanol combined combustion engine based on claim 1 is characterized by comprising the following processes:
step 1, starting an engine in a pure diesel combustion mode;
step 2, the engine burns in a pure diesel mode;
and step 3, judging whether the following conditions are met or not, namely:
the first condition is as follows: whether the methanol supply system has the conditions, namely whether the methanol pressure reaches a set value or not and whether the methanol liquid level is higher than a lower limit value or not;
and a second condition: whether the temperature of the engine cooling water is greater than or equal to a set threshold value, namely whether the temperature of the engine cooling water reaches 60 ℃;
and (3) carrying out a third condition: whether the engine does not reach a full load interval, namely whether an accelerator pedal is not at a 100% working point;
and a fourth condition: whether the part below the inclined line of the no-load accelerator is separated or not, namely whether the engine and the gearbox are not separated or not;
if all the conditions are met, turning to the step 4, otherwise, returning to the step 2;
and 4, injecting alcohol, and performing combined combustion of diesel oil and methanol.
9. The control method of a diesel and methanol combined combustion engine as set forth in claim 8, wherein the methanol injection system determines the amount of injected alcohol as follows:
step 4-1, firstly, determining a target alcohol injection amount basic value by obtaining the operating condition of the engine and combining a methanol injection pulse spectrum (MAP) on the basis of confirming the engine operating condition information;
step 4-2, correcting the basic value of the target alcohol injection amount through the influence of the temperature of the cooling water on the working condition of the diesel and methanol combined combustion engine;
step 4-3, comparing the maximum alcohol injection amount with the maximum alcohol injection amount of the engine at the current rotating speed, and taking the smaller value as the final alcohol injection amount;
and 4-4, inquiring the alcohol spraying amount and a methanol MAP, determining the driving pulse width of the electromagnetic valve, outputting the driving pulse width to a methanol nozzle, and controlling the alcohol spraying amount by the nozzle electromagnetic valve.
10. The control method of a diesel and methanol combined combustion engine as set forth in claim 9, wherein the methanol injection pulse spectrum (MAP) in step 4-1 is determined by interpolation, specifically as follows:
one dimension of the methanol MAP is the engine speed n, and the other dimension is the accelerator pedal opening degree alpha; the MAP graph grid points have 5 points, wherein the points 1-4 are two-dimensional data points determined in a bench calibration test, the point 5 represents a working condition point, each point is a methanol control injection quantity m corresponding to specific engine speed n and accelerator opening degree alpha, namely the engine speed at the point 1 is n1Throttle opening is alpha1The methanol injection amount is m1At point 2, the engine speed is n2Throttle opening is alpha2The methanol injection amount is m2At point 3, the engine speed is n3Throttle opening is alpha3The methanol injection amount is m3At point 4, the engine speed is n4Throttle opening is alpha4The methanol injection amount is m4At point 5, the engine speed is n5Throttle opening is alpha5The methanol injection amount is m5For the convenience of understanding the interpolation process and the formula description, the intermediate points 5' and 5 ″ are introduced, corresponding to the methanol injection amounts m5' and m5″；
Firstly, judging the MAP graph network region where the engine operation condition point 5 is positioned, namely determining the current engine speed n5And accelerator opening degree alpha5Four adjacent calibration MAP points;
then, according to the accelerator opening degree alpha1And alpha2Interpolating the direction to obtain m5' the specific calculation formula is as follows:
Figure FDA0002792414480000031
go to m5After interpolation, the throttle opening alpha is adjusted3And alpha4Interpolating in the direction to find m5", the calculation formula is as follows:
Figure FDA0002792414480000032
find m5' and m5"thereafter, the methanol control amount m at the engine operation point 5 is not obtained yet5Value, also required at engine speed n1And n4Interpolation is carried out in the direction, and m is finally obtained5The calculation formula is as follows:
Figure FDA0002792414480000033
obtaining an engine operation working condition point 5 (n) after three times of interpolation5，α5) Corresponding methanol injection control amount m5。
11. The control method of the diesel and methanol combined combustion engine as set forth in claim 8, wherein the diesel particulate filter in the post-processor combination adopts a passive regeneration strategy to oxidize carbon particles in the diesel particulate filter by means of higher concentration of nitrogen dioxide in the exhaust gas, when the pressure difference between the front and the rear of the diesel particulate filter is larger, methanol is injected through a methanol injector arranged on the exhaust pipe, the trapped carbon particles are combusted and oxidized inside the diesel particulate filter, and finally the methanol injector is connected with the diesel oxidation catalyst for oxidizing unburned carbon and carbon monoxide.
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