CN116205157A

CN116205157A - Fuel injection method for influencing combustion characteristics of formaldehyde/PODEn dual-fuel compression ignition mode

Info

Publication number: CN116205157A
Application number: CN202310089166.4A
Authority: CN
Inventors: 张鼎成; 张光德; 陈书郅
Original assignee: Wuhan University of Science and Engineering WUSE
Current assignee: Wuhan University of Science and Engineering WUSE
Priority date: 2023-02-09
Filing date: 2023-02-09
Publication date: 2023-06-02

Abstract

The invention discloses a fuel injection method for influencing combustion characteristics of a formaldehyde/PODEn dual-fuel compression ignition mode, which comprises the following steps: s1, simulating a simulation foundation, S2, calculating a model: s2.1, model establishment, S2.2, model verification, S3, simulation calculation result analysis. In the invention, the influence of the direct injection time in a cylinder on the combustion characteristics such as cylinder pressure, heat release rate, average indication pressure, flame retarding period and the like and the emission characteristics of particulate matters are researched one by modifying the direct injection time in the cylinder, and the optimal injection time corresponding to each strategy is analyzed and compared on the premise of ensuring the economical efficiency, the dynamic property and the lower pollutant emission of the engine.

Description

Fuel injection method for influencing combustion characteristics of formaldehyde/PODEn dual-fuel compression ignition mode

Technical Field

The invention relates to the technical field of diesel engines, in particular to an oil injection method for influencing combustion characteristics of a formaldehyde/PODEn dual-fuel compression ignition mode.

Background

The diesel engine has higher compression ratio, can obtain higher fuel utilization rate and combustion efficiency, effectively reduces unburned hydrocarbon (Total Hydro Carbons, THC) and carbon monoxide (CO) in a cylinder, but simultaneously has serious emission pollution of Nitrogen Oxides (NOX), particularly Particulate Matter (PM);

methanol is favored by students because of the high oxygen content, low carbon content and latent heat of vaporization characteristics, and can effectively improve the combustion and emission characteristics of a diesel engine, but because of the low cetane number and high ignition point, polymethoxy dimethyl ether (PODEn) is required to be introduced as a pilot fuel for supporting combustion, and advanced combustion technologies including Homogeneous Charge Compression Ignition (HCCI), reactive Control Compression Ignition (RCCI), premixed compression ignition (PCCI) and the like are combined, so that the requirements of clean low emission are met, and the working condition range of efficient combustion of fuel is widened.

At present, scholars at home and abroad develop and research on the application of methanol/PODEn dual fuel on a diesel engine;

the combustion results of different methanol ratios are compared in the improved explosion-proof machine, and the research shows that: with the increase of the proportion, compared with the single fuel combustion starting point, the combustion speed is accelerated, the pressure rise rate and the heat release rate peak value are greatly improved, and then NOx emission is reduced under the small load working condition and CO and THC are raised in emission tests of different loads; however, when the load is large, NOx is increased and then reduced, and CO and THC are gradually reduced.

The combustion characteristics of different loads are researched under the maximum rotation speed and torque by adopting a high-pressure common rail engine, and the results show that methanol can reduce the in-cylinder pressure, prolong the flame retardant period and delay the heat release starting point, and the increase of the mass of methanol under medium and low loads can lead the peak value of the heat release rate to be increased firstly and then be reduced, and the peak value of the heat release rate to be gradually increased under high load.

The influence of the EGR rate on the combustion of the mixed fuel is studied, and the influence is more obvious when the peak value of the cylinder pressure heat release rate is reduced and the load is large, wherein the combustion stagnation period and the combustion duration are prolonged along with the increase of the EGR rate.

The RCCI combustion characteristics of the mixed fuel are researched on a three-cylinder supercharged diesel engine, and the RCCI combustion characteristics of the mixed fuel are found to be prolonged along with the improvement of the methanol mixing ratio, the flame-retarding period of dual fuel is prolonged, the explosion pressure in the cylinder is reduced, and when the mass ratio of methanol to air is higher than 80%, the effective heat efficiency is up to 31%, which is higher than that of a methanol/diesel combined combustion mode.

The inventor deeply researches the influence mechanism of a single injection and two injection oil injection strategy on the combustion emission characteristics of a methanol/PODEn premixed compression ignition mode under the working condition of low load and low rotation speed on the basis of the former work, and in a controllable range, the influence on the combustion characteristics such as cylinder pressure, heat release rate, average indication pressure, flame retardation period and the like and the emission characteristics of particulate matters are researched one by modifying the direct injection oil injection time, so that the optimal oil injection time corresponding to each strategy is analyzed and compared on the premise of ensuring the economical efficiency, the dynamic property and the lower pollutant emission of the engine.

Disclosure of Invention

The invention provides a fuel injection method for influencing combustion characteristics of a formaldehyde/PODEn dual-fuel compression ignition mode, which solves the technical problem that a fuel injection strategy of single injection and double injection influences the combustion emission characteristics of the methanol/PODEn pre-mixed compression ignition mode, and in a controllable range, the influence of the fuel injection strategy on the combustion characteristics such as cylinder pressure, heat release rate, average indication pressure, flame retardant period and the like and the emission characteristics of particulate matters are researched one by modifying the fuel injection time of direct injection in a cylinder, so that the technical problem of optimal fuel injection time corresponding to each strategy is analyzed and compared on the premise of ensuring the economical efficiency, the dynamic property and the lower pollutant emission of an engine.

In order to solve the technical problems, the invention provides a fuel injection method for influencing combustion characteristics of a formaldehyde/PODEn dual-fuel compression ignition mode, which comprises the following steps:

s1, simulating a simulation foundation: and (3) establishing an operation model through commercial fluid simulation software CONVERGE and performing simulation tests.

S2, calculating a model:

s2.1, establishing a model, and selecting a physicochemical model and a combustion model in a test.

S2.2, model verification, in order to ensure the accuracy and the rigor of a simulation calculation model, the simulation model verification is carried out on an original test engine model, and the established simulation model can accurately represent the combustion emission characteristics of the mixed fuel.

S3, analyzing simulation calculation results; and modeling through CONVERGE simulation software in the early stage, and then carrying out model verification to finally obtain a scientific and reliable simulation model.

S3.1, under the injection strategy of single injection, the influence of different injection moments on the combustion characteristics such as the cylinder pressure, the heat release rate, the average indication pressure, the flame retardant period and the like and the emission characteristics of particulate matters of the methanol/PODEn dual-fuel premixed compression ignition;

s3.2, influence of two-time injection pre-injection time on combustion and emission, and influence of different injection time on combustion characteristics such as methanol/PODEn dual-fuel pre-mixing compression ignition cylinder pressure, heat release rate, average indicated pressure, flame-retarding period and the like and particulate matter emission characteristics under an injection strategy of two-time injection.

Preferably, in step S1), the fuel injection mode of the simulation test is that methanol is injected through an air inlet channel and fully mixed with air into a cylinder, the PODEn fuel adopts direct injection in the cylinder, when the compression stroke is at the end, namely when the piston goes up to the vicinity of the upper dead point, the PODEn reaches the ignition limit, and is immediately compression-ignited, the surrounding methanol-air mixture is ignited while combustion is performed, so that a mixed combustion state is formed.

Preferably, in step S3), the scientific and reliable simulation model researches the influence of different injection moments on single injection and different pre-injection moments (SOI 1) on two injections for the engine model, searches the law of the injection strategy on the combustion emission characteristics of methanol/PODEn, and lays a test foundation for subsequent improvement of injection parameters, thereby optimizing the injection strategy, improving the combustion economy and reducing the emission of pollutants.

Compared with the related art, the fuel injection method for influencing the combustion characteristics of the formaldehyde/PODEn dual-fuel compression ignition mode has the following beneficial effects:

1) The premixed compression ignition combustion mode of the methanol/PODEn mixed fuel is to improve the activity and concentration layering of the mixed fuel by directly injecting PODEn diesel oil (high cetane number fuel) in a cylinder to jointly influence the combustion process, and changing an oil injection strategy is an important way for effectively controlling the combustion process.

2) In a single injection strategy, the peak value of cylinder pressure and heat release rate can be effectively improved when the injection time is comprehensively evaluated at-22 CA, the air inlet equivalent ratio is reduced, full combustion is facilitated, and the combustion efficiency is improved.

3) In the two-injection strategy, as the SOI1 advances, the main pre-injection time interval becomes longer, the pre-injection fuel oil is fully diffused and the reaction time becomes longer, so that the heat release rate curve gradually has the characteristic of two-stage heat release, when the SOI1 is-39 degrees CA, the flame-retarding period and the combustion duration are obviously increased, and the temperature of the cylinder and the cylinder wall is obviously reduced by the longer oil injection interval, so that the peak value of the cylinder pressure and the heat release rate is reduced, and the reaction process tends to be mild.

4) In the two-time injection strategy, along with the delay of pre-injection, the compression ignition time is shortened, the flame-retarding period is shortened, the whole combustion center of gravity is moved backwards, more unburned and incompletely combusted hydrocarbon fuel exists in a cylinder due to the aggravation of the narrow gap effect, but the two-time injection has remarkable inhibiting effects on the root, NOx and CO, and the emission performance is greatly improved, wherein the effect is most obvious when SOI1 is-27 degrees CA.

Drawings

FIG. 1 is a flow chart of a method of injection of fuel affecting combustion characteristics of a formaldehyde/PODEn dual fuel compression ignition mode;

FIG. 2 is a schematic diagram of the results of a simulation model versus bench test fit;

FIG. 3 is a schematic diagram of cylinder pressure test results of the methanol/PODEn dual-fuel premixed compression ignition at different injection moments;

FIG. 4 is a schematic diagram of the experimental results of heat release rate of methanol/PODEn dual-fuel premixed compression ignition at different injection moments;

FIG. 5 is a schematic diagram of experimental results of the influence rule of the oil injection time on the average indicated pressure and the indicated thermal efficiency;

FIG. 6 is a graph showing experimental results of trends of influences of different injection moments on a flame retardant period and a combustion duration;

FIG. 7 is a schematic diagram of experimental results of the influence of the injection time on the emissions of Soot and NOx;

FIG. 8 is a schematic diagram of experimental results of the influence of the injection timing on HC and CO emissions;

FIG. 9 is a graph showing experimental results of the effect of different SOI1 on methanol/PODEn premixed combustion cylinder pressure;

FIG. 10 is a graph showing experimental results of the effect of different SOI1 on the heat release rate of methanol/PODEn premixed combustion;

fig. 11 is a schematic diagram of experimental results of the influence rule of SOI1 on the average indicated pressure and the indicated thermal efficiency;

FIG. 12 is a graph showing experimental results of the effect of SOI1 on combustion phasing retard and combustion duration;

FIG. 13 is a schematic diagram of experimental results of the influence of the pre-injection time on the emissions of Soot and NOx;

FIG. 14 is a graph showing experimental results of the influence of pre-injection timing on HC and CO emissions;

FIG. 15 is a data diagram of main technical parameters of a single cylinder diesel engine research model;

FIG. 16 is a data graph of physicochemical property parameters of two fuels;

fig. 17 is a data diagram of model boundary conditions.

Detailed Description

Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals refer to the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary only for explaining the present invention and are not to be construed as limiting the present invention.

In the description of the present invention, it should be understood that if there are terms such as "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "clockwise", "counterclockwise", etc., the indicated azimuth or positional relationship is based on the azimuth or positional relationship shown in the drawings, it is merely for convenience of description and simplification of the description, and does not indicate or imply that the indicated apparatus or element must have a specific azimuth, be constructed and operated in a specific azimuth, and thus should not be construed as limiting the present invention. Furthermore, the terms "first," "second," and the like, are used for descriptive purposes only and are not to be construed as indicating or implying a relative importance or implicitly indicating the number of technical features indicated. Thus, a feature defining "a first" or "a second" may explicitly or implicitly include one or more of the described features. In the description of the present invention, the meaning of "a plurality" is two or more, unless explicitly defined otherwise.

In the description of the present invention, it should be noted that the terms "mounted," "connected," and "coupled" are to be construed broadly, as well as, for example, fixedly coupled, detachably coupled, or integrally coupled, unless otherwise specifically indicated and defined. Either mechanically or electrically. Can be directly connected or indirectly connected through an intermediate medium, and can be communicated with the inside of two elements or the interaction relationship of the two elements. The specific meaning of the above terms in the present invention can be understood by those of ordinary skill in the art according to the specific circumstances.

An oil injection method for influencing combustion characteristics of a formaldehyde/PODEn dual fuel compression ignition mode, comprising the following steps:

s1, simulating a simulation foundation: in order to search the influence rule of the single injection and the two injection strategies of the mixed fuel on the combustion process of the methanol/PODEn in the PCCI mode, an operation model is built through commercial fluid simulation software CONVERGE by using a method of coupling chemical reaction dynamics and a CFD model, and a simulation test is carried out.

S2, calculating a model:

s2.1, establishing a model, namely, testing a selected physicochemical model and a combustion model, selecting an RNG k-epsilon model as a calculated turbulence model in the aspect of a combustion calculation model, selecting a Multi-component model as a calculated evaporation model, wherein the model presumes liquid drops as high-quality diffusivity and high-evaporation rate, the internal components of the liquid drops are uniformly distributed, and a KH-RT model is used as a crushing model, wherein the KH model can accurately predict the primary crushing position of spraying, and RT predicts secondary crushing of the liquid drops; the Walljet1 model is mainly used for simulating and calculating interaction force between jet flow and rebound splashing of liquid drops and wall film expansion and liquid drops in motion caused by inertia after the oil drops strike a wall surface, the traditional SAGE model is used for describing the built-in state of oil-gas mixed combustion, the simulation calculation is mainly used for researching the combustion process of methanol/PODEn dual fuel with the crank angle of-130-114 degrees CA, the model is of a symmetrical structure, the calculation efficiency is improved for simplifying calculation amount, the structural modeling of an air inlet pipeline and an air outlet pipeline is omitted, the number of oil injection holes of an engine is 5, a 1/5 sector area of an air cylinder is selected as a calculation model, and the self-contained grid automatic generation technology of CONVERGE software and various grid control technologies provide great convenience for simulation expansion, the basic grid size of the model is 3.0mm, and an accurate simulation calculation result is obtained through self-adaptive encryption after grid division.

S2.2, model verification, in order to ensure the accuracy and the rigor of a simulation calculation model, the simulation model verification is carried out on an original test engine model, the working condition verified in the simulation model verification is a dual-fuel combustion mode with the small load and the methanol energy ratio of 35.2%, and the oil injection parameters comprise: the single-cylinder circulation fuel injection quantity of PODEn is 21.59mg, the fuel injection time is-22 CA, the fuel injection duration is 20 CA, the fuel injection pressure is 20MPa, and the boundary temperature is shown in FIG. 17 by referring to the original test bench;

as shown in figure 2, the result of the fitting comparison between the simulation model and the bench experiment shows that under the working condition of small load, the high-oxygen-content fuel burns to generate a large amount of oxygen to promote the combustion process, so that the reaction is rapid, the cylinder pressure and the heat release rate in a short period are instantly increased, the heat release rate is centralized, the cylinder pressure curves are basically consistent, the peak exceeding part of the heat release rate curves is within the allowable range of 5%, and the established simulation model can be considered to accurately represent the combustion emission characteristics of the mixed fuel

S3.1, the influence of single injection time on combustion and emission is shown in the graph of FIG. 3 and FIG. 4, under the injection strategy of single injection, the cylinder pressure and heat release rate curves of different injection time on methanol/PODEn dual-fuel premixed compression ignition are shown in the graph of FIG. 3 and FIG. 4, with the advance of the injection time, the ignition time and combustion phase are slightly advanced, the cylinder pressure peak value and heat release rate peak value are advanced and obviously increased, the cylinder pressure peak value of-26 DEG CA is changed from 5.49MPa to 5.73MPa compared with the cylinder pressure peak value of-18 DEG CA, the heat release rate peak value is changed from 138.045J/-226.124J/° CA, the mixing of PODEn and methanol air mixture is advanced along with the injection time, the diffusion time is sufficient, the flame retardant period is prolonged, the formed premixed gas is increased, and due to the fact that the PODEn motion viscosity is high, most of dual fuels are in a uniform mixing state, the premixed combustion proportion is increased, and the high-temperature high-pressure environment in the cylinder promotes the diffusion combustion process, so that the cylinder temperature cylinder pressure is greatly increased, and the combustion efficiency is further improved;

as can be seen with reference to fig. 5; the IMEP is greatly influenced by the oil injection moment, the IMEP is approximately in a trend of rising and then lowering, the change of the IMEP has a close influence on the indicated thermal efficiency, the change trend is basically consistent with the change trend, analysis shows that the cylinder pressure peak value and the heat release rate peak value are both reduced along with the reduction of the oil injection advance angle, the combustion duration is prolonged, the IMEP caused by the reduction of the cylinder temperature is reduced, on the other hand, compared with the earlier injection moment, the later injection moment has longer cooling time of the cylinder wall temperature, the reduction of the cylinder temperature, the non-concentrated combustion and slow heat release speed, the incomplete combustion is caused, the IMEP and the indicated thermal efficiency are reduced, the IMEP and the indicated thermal efficiency with the oil injection moment of-22 DEG CA can be obviously seen to be respectively 2.281bar and 45%, and the cylinder pressure after the upper dead center is far greater than the cylinder pressure for postponing the oil injection, so that the effective work and the indicated work of the engine are increased;

as can be seen with reference to fig. 6; the fuel injection timing is delayed to shorten the flame retarding period, the combustion duration in the cylinder is gradually prolonged, the ignition time is slightly delayed along with the fuel injection according to the heat release rate curve, the combustion time is delayed, so that the negative work of the cylinder is reduced, the combustion rate is accelerated, the time of compression ignition is shortened, the flame retarding period is shortened, the reaction is severe in the early stage, the combustion center is advanced, the premixed combustion proportion is greatly improved, the heat release rate is increased, the mixing and diffusion time of the PODEn diesel fuel and the methanol air mixture which are directly injected is shortened, the distribution in the cylinder is uneven, the piston needs longer reaction combustion in the power stroke stage, and the combustion process is prolonged to lengthen the combustion duration;

as can be seen with reference to fig. 7 and 8; simulation mainly discusses soot and NO _X The change rule of the emission amount of conventional harmful substances such as HC, CO and the like is shown in fig. 7, wherein the quantity of NO is increased after the reduction of the fuel injection time _X The trend of gradual rising is presented, when the oil injection time gradually advances from-22 DEG CA to-18 DEG CA, the emissions of the boot and the NOx are increased, and as the former, the oil injection is carried out at-22 DEG CA, the thermal efficiency and the in-cylinder combustion condition are indicated to be better, the oil injection time is continuously delayed, the diffusion time of the injected fuel is greatly shortened because the piston is closer to the top dead center, the diffusion combustion proportion is reduced, and the local high temperature and the oxygen-enriched state are caused to contribute to NO due to the high oxygen-containing characteristic of the fuel _X In addition, the generation amount of Soot is increased because the combustion center of gravity is delayed, the temperature in the cylinder is greatly reduced, more Soot cannot be oxidized due to incomplete combustion of the late fuel, as can be seen from fig. 8, HC generation is gradually increased and CO is gradually reduced with the delay of the injection time, the average effective pressure is reduced due to the reduction of the injection advance angle, the cylinder pressure cylinder temperature is obviously reduced, the mixed gas is compressed, the local equivalence ratio is increased, the air-fuel ratio is lean, the narrow gap effect is enhanced, and the HC emission is obviously increased; the reduction of CO is due to the fact that in-cylinder fuel provides an oxygen-enriched environment, and the longer flame retardant period ensures that CO and oxygen are fully mixed, so that oxidation reaction is greatly promoted;

s3.2, influence of two-time injection pre-injection time on combustion and emission; considering that the cylinder temperature and cylinder pressure which suddenly rises during combustion under a small load working condition is required to be reduced, the utilization rate of PODEn fuel is improved, the section changes a two-time injection strategy to study the influence of pre-injection time (SOI 1) on the methanol/PODEn dual-fuel combustion characteristic, in the two-time injection strategy, multiple experiments prove that the pre-injection and main injection quantity of PODEn are reasonably distributed according to the proportion of 2:8 of the total quantity of single injection, so that the pre-main injection quantity is 4.318mg and 17.272mg respectively, the pre-main injection duration is 4 degrees and 16 degrees respectively, the main injection time is consistent with an original model and is-22 degrees CA, and meanwhile, the pre-injection time is respectively provided with four groups of variables of-39 degrees CA, -35 degrees CA, -31 degrees CA and 27 degrees CA under the advance of ensuring that the pre-injection time does not conflict;

referring to fig. 9, as SOI1 advances, the ignition time and the cylinder pressure peak value slightly advance, but the cylinder pressure peak value slightly decreases, so that the pressure rise rate obviously decreases, as fig. 10 shows that the heat release rate peak value advances and gradually decreases, the combustion duration slightly increases, but compared with single oil injection shortening is obvious, -39 ° CA decreases from 200.954J/° CA to 161.255J/° CA compared with-27 ° CA, 19.8% is reduced, as SOI1 delays, the pre-main injection time interval decreases, the combustion reaction time of the mixture gas in pre-injection is shorter, the heat release amount is less, the ignition promotion effect on main injection is weakened, and the pre-injection premixed gas and the mixture gas formed by main injection are ignited and burned together, so that the heat release rate peak value is higher; with the increase of the pre-main spraying interval, the heat release amount of the pre-spraying is large, the ignition promoting effect on the main spraying is large, the ignition time is advanced, the premixed gas formed by the main spraying is reduced, the heat release rate curve is reduced as a whole, and the combustion duration is increased;

referring to fig. 11, as the delay of SOI1, both IMEP and indicated thermal efficiency show a trend of decreasing first and then increasing, the inflection point appears when the pre-injection time is-31 ° CA, at this time, IMEP and indicated thermal efficiency decrease to 2.241bar and 44.04%, respectively, and as the delay of SOI1, the peak value of cylinder pressure and heat release rate increases slightly, the ignition time is delayed, the combustion reaction process is intense, the combustion duration is shortened, and further IMEP decreases, and indicated thermal efficiency also decreases, but SOI1 is subject to a main pre-injection interval time at-27 ° CA, which is almost equal to the in-cylinder combustion condition during single injection, the pre-injection and main injection of mixed gas burn almost simultaneously, and IMEP and indicated thermal efficiency slightly rise.

Referring to fig. 12, it is clear that the combustion duration is reduced due to the delay of SOI1, and the combustion duration is approximately reduced, and as is clear from the cylinder pressure and heat release rate curves, no matter the advance or delay of the pre-injection time, the change of the ignition time of methanol/PODEn and the heat release rate curve before CA10 has little influence, so that the change of the combustion duration is closely related to SOI1, and as SOI1 is delayed, the main pre-injection interval is shortened, the in-cylinder fuel equivalent ratio is increased due to the accumulation of the mixture of two injections, the in-cylinder combustion temperature is increased after co-combustion, the heat release rate peak value is overall increased, the combustion effect is better, and the combustion duration is shortened under severe combustion conditions;

referring to fig. 13, it can be seen that with the delay of SOI1, soot emission tends to be substantially reduced, NO _X Emission increases and then decreases, in the test, the root and NO _X The peak value of the emission amount respectively appears at-35 DEG CA and-31 DEG CA of SOI1, because the delay of the pre-injection time promotes the heat release quantity in the cylinder to be more concentrated, the temperature in the cylinder rises rapidly in a short time, in addition, under the combustion supporting effect of the high oxygen content fuel, the oxidation reaction is greatly promoted, and the soot reduces NO _X Increased, but subsequent reduction of NOx due to too short a two injection time interval, resulting in an increased burn rate and a shortened high temperature reaction time, thereby inhibiting NOx formation;

as can be seen from fig. 14, with the delay of the pre-injection timing, the HC emissions increase and the CO emissions decrease continuously, because with the delay of SOI1, the combustion phase gradually lags, the fuel mixture injected at the pre-injection timing cannot be fully combusted, the mixture injected at the main injection timing is compression-ignited together, and the latent heat of vaporization characteristic of methanol absorbs part of heat, so that the combustion temperature decreases significantly, the HC oxidation process is suppressed greatly, the CO is more concentrated due to the sufficient oxygen alone and easier oxidation of HC, the combustion center of gravity is delayed, the accumulation of premixed gas promotes and accelerates the oxidation of CO together with the oxygen-rich atmosphere in the cylinder, and the emissions are reduced.

The main technical parameters of the single-cylinder diesel research model are shown in figure 15;

the physicochemical properties of the two fuels are shown in fig. 16.

In order to search the influence mechanism of different fuel injection strategies on the combustion characteristics and harmful emissions of high-oxygen-content fuel in an engine in a premixed compression ignition combustion mode, numerical simulation and simulation operation are carried out on the structure and operation parameters of a certain engine based on CFD simulation software CONVERGE, the combustion and emission characteristics of the methanol/PODEn mixed fuel under different fuel injection strategies are researched, and the influence of different fuel injection moments on the dynamic performance and economy of the methanol/PODEn mixed fuel under each fuel injection strategy is analyzed. The results show that: in single oil injection, the oil injection time is advanced to greatly raise the peak value of cylinder pressure and heat release rate, so that the fuel utilization rate is increased, and the pollutants are obviously reduced, wherein-26 DEG CA is respectively raised by 4.5 percent and 63.8 percent compared with-18 DEG CA, and finally the emissions of boot and NO are obtained _X HC is reduced by 2.7%, 38.3% and 25.9%, but the fuel injection timing is properly delayed, the combustion duration is increased, and the combustion speed is effectively controlled; adopts a strategy of two oil injections, and along with the advance of the pre-injection time (SOI 1), the pre-injection time and the main injection time are adoptedThe interval is prolonged, the cylinder pressure is not greatly changed, the heat release rate curve gradually has the trend of two peaks, the peaks are slightly reduced and advanced, and the harmful emissions NO of-39 DEG CA are compared with-27 DEG CA _X The HC and HC are effectively controlled, and respectively reduced by 6.6% and 47.5%.

Although embodiments of the present invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made therein without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.

Claims

1. A fuel injection method for influencing combustion characteristics of a formaldehyde/PODEn dual fuel compression ignition mode, comprising the steps of:

S2, calculating a model:

s2.1, establishing a model, and testing a selected physicochemical model and a combustion model.

S3, analyzing simulation calculation results; modeling by the converge simulation software in the early stage, and then carrying out model verification to finally obtain a scientific and reliable simulation model.

2. The fuel injection method for influencing the combustion characteristics of a formaldehyde/PODEn dual-fuel compression ignition mode according to claim 1, wherein in the step S1), the fuel injection mode of the simulation test is to inject methanol through a gas inlet channel and fully mix the methanol with air into a cylinder, PODEn fuel adopts in-cylinder direct injection, when the piston moves up to the vicinity of a top dead center in the end of a compression stroke, PODEn reaches a fire limit and is then compression-ignited, the PODEn combusts while igniting surrounding methanol-air mixture to form a mixed combustion state, compared with methanol/diesel, the methanol/PODEn combined fuel has higher oxygen content, which can effectively improve the in-cylinder oxygen deficiency condition and greatly reduce THC and CO emission with small load when the engine is under a large load, the high oxygen content also contributes to combustion supporting and improves the combustion efficiency, the PODEn cetane number is 1.5 times that of diesel, the ignition performance of combustion is improved, the combustion is more uniform, and due to lower kinematic viscosity and smaller fuel particle size, the atomization effect is promoted, the fuel is fully mixed, and soot emission is further reduced.

3. The fuel injection method for influencing the combustion characteristics of the formaldehyde/PODEn dual-fuel compression ignition mode according to claim 1, wherein in step S3), a scientific and reliable simulation model is used for researching the influence of different injection moments on single injection and different pre-injection moments (SOI 1) on two injections aiming at the engine model, searching the rule of a fuel injection strategy on the combustion emission characteristics of methanol/PODEn, and laying a test foundation for improving fuel injection parameters subsequently, optimizing fuel injection strategies, improving combustion economy and reducing pollutant emission.