High-load optimization method and device for diesel micro-ignition high-pressure direct injection methanol engine

Abstract

The invention provides a high-load optimization method and device for a diesel micro-ignition high-pressure direct injection methanol engine. The method comprises the steps that methanol injection pressure is set, the methanol injection duration and the combustion duration are shortened, and the indication heat efficiency of the engine is optimized; a fuel injection strategy is set, diesel injection timing or methanol injection timing is adjusted, the combustion duration is shortened, and the engine indication heat efficiency is optimized; and an exhaust gas recirculation strategy is introduced, the exhaust gas recirculation proportion is set, NOx emission is reduced to reach the IMO Tier III standard level, and working condition parameters of the dual-fuel engine under the high-load optimal working condition are obtained. According to the high-load optimization method and device for the diesel micro-ignition high-pressure direct injection methanol engine, the methanol injection pressure is increased to 100 MPa, the post-injection strategy of diesel 8CAD ATDC injection is adopted, and 20% exhaust gas recirculation is introduced; and the indicated thermal efficiency of the engine under high load is successfully improved, and the emission of nitrogen oxides is reduced.

Description

Technical Field

[0001] The present invention relates to the field of engine optimization, and in particular to a high-load optimization method and device for a diesel micro-ignition high-pressure direct injection methanol engine. Background Art

[0002] The main problems of diesel micro-ignition high-pressure direct injection methanol engine under high load are low indicated thermal efficiency and nitrogen oxides (NO x ) high emission problem. Compared with other load conditions, the indicated thermal efficiency of the engine under high load is lower, and the longer combustion duration is the main reason limiting the improvement of the indicated thermal efficiency. Due to the low calorific value of methanol, even if the flow rate of the methanol injector is increased, the methanol injection duration is still very long, resulting in a longer combustion duration. The longer combustion duration under high load reduces the combustion isochoricity, limits the engine's work capacity, and leads to low indicated thermal efficiency. NO under high load x The reasons for high emissions are reflected in three aspects: first, the temperature in the cylinder is high under high load, and the diffusion combustion of a large proportion of methanol further increases the local combustion temperature; second, the combustion duration is long under high load, which increases the time of high temperature persistence; third, the intake pressure is high under high load, and the excess air coefficient in the cylinder is larger, which promotes NO x Large amounts of emissions are generated. Summary of the Invention

[0003] The purpose of the present invention is to provide a method and device for optimizing a high-load diesel micro-ignition high-pressure direct injection methanol engine. By optimizing the path of "increasing the methanol injection pressure to 100 MPa - adopting a diesel-8CADATDC injection post-injection strategy - introducing a 20% exhaust gas recirculation ratio", the method successfully improves the indicated thermal efficiency of the engine under high load and reduces NO x emission.

[0004] To achieve the above object, the present invention provides a high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine, comprising the following steps:

[0005] Stage 1: Setting the methanol injection pressure range;

[0006] Phase 2: Based on the first phase, set the injection strategy and adjust the diesel injection timing or methanol injection timing;

[0007] Stage 3: Based on the second stage, exhaust gas recirculation is introduced into the engine and the exhaust gas recirculation ratio is set.

[0008] Preferably, in the first stage, the methanol injection pressure range is 60MPa to 100MPa, and the diesel injection pressure range is 60MPa to 100MPa.

[0009] Preferably, in the second stage, the injection strategy is a diesel post-injection strategy, wherein:

[0010] The diesel injection timing is -8CAD ATDC, and the methanol injection timing is -10CAD ATDC.

[0011] Preferably, in the third stage, the exhaust gas recirculation ratio is 0% to 40%.

[0012] Preferably, a numerical simulation research method is used to optimize the high-load operating condition, wherein the methanol substitution rate is 97.2%, the intake pressure is 0.2 MPa, and the intake temperature is 30°C.

[0013] Preferably, the indicators achieved by the dual-fuel engine under high load optimal working conditions include indicated thermal efficiency of 45.96%, combustion efficiency of 99.47%, NO x The specific emission is 1.82g / kW·h, the Soot specific emission is 0.055g / kW·h, the CO specific emission is 0.63g / kW·h, and the THC specific emission is 0.021g / kW·h.

[0014] Preferably, the methanol injection pressure is 100 MPa.

[0015] Preferably, the diesel injection pressure is 80 MPa.

[0016] Preferably, the exhaust gas recirculation ratio is 20%.

[0017] A high-load optimization device for a diesel micro-ignition high-pressure direct injection methanol engine, comprising

[0018] The first optimization module is used to optimize the methanol injection pressure;

[0019] The second optimization module is used to adjust the injection strategy;

[0020] The third optimization module is used to adjust the exhaust gas circulation rate.

[0021] Therefore, the present invention adopts the above-mentioned high-load optimization method and device for a diesel micro-ignition high-pressure direct injection methanol engine, and the technical effects are as follows:

[0022] By increasing the methanol injection pressure and adopting a diesel post-injection strategy, the combustion duration can be shortened and the engine indicated thermal efficiency can be effectively improved.

[0023] The exhaust gas recirculation method is used to regulate the engine, reduce the temperature in the cylinder, slow down the heat release rate of methanol combustion, and at the same time extend the ignition delay period, increase the methanol mixing time, reduce the intake volume, reduce the oxygen content in the cylinder, and effectively reduce the engine NO x Emissions generated. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 In-cylinder pressure and heat release rate curves and basic parameter settings for high-load initial working conditions;

[0025] Figure 2 To improve the combustion and emission characteristics under high load and methanol injection pressure; Figure 2 (a) To indicate thermal efficiency and combustion duration; Figure 2 (b) is the combustion thermal efficiency and NO x emission;

[0026] Figure 3 Changes in combustion and emission characteristics under high load conditions by retarding diesel injection timing; Figure 3 (a) To indicate thermal efficiency and combustion duration; Figure 3 (b) is the combustion thermal efficiency and NO x emission;

[0027] Figure 4 The in-cylinder pressure, heat release rate and average in-cylinder temperature curves under high load and different exhaust gas recirculation rates; Figure 4 (a) is the cylinder pressure and heat release efficiency; Figure 4 (b) is the average temperature in the cylinder;

[0028] Figure 5 Combustion paths at different exhaust gas recirculation rates at high load CA50;

[0029] Figure 6 Changes in combustion and emission characteristics at high loads with increased exhaust gas recirculation rates; Figure 6 (a) To indicate thermal efficiency and combustion duration; Figure 6 (b) is the combustion thermal efficiency and NO x emission;

[0030] Figure 7 Combustion and emission characteristic change curves during high load optimization; Figure 7 (a) is the combustion characteristic curve; Figure 7 (b) is the emission characteristic curve. DETAILED DESCRIPTION

[0031] The technical solution of the present invention is further described below with reference to the accompanying drawings and embodiments.

[0032] Unless otherwise defined, technical or scientific terms used in the present invention shall have the same meaning as commonly understood by one of ordinary skill in the art to which the present invention belongs.

[0033] The main parameters of the diesel micro-ignition high-pressure direct injection methanol engine used in the following examples are shown in Table 1. The engine is equipped with a methanol high-pressure direct injection injector and a diesel direct injection injector, which can realize diesel micro-ignition high-pressure direct injection methanol combustion.

[0034] Table 1 Main parameters of the engine

[0035]

[0036]

[0037] Example 1

[0038] Ultra-high methanol injection pressure can effectively shorten the injection duration and combustion duration, and achieve optimization of high-load operating conditions. However, the current prototype is limited by the fuel supply capacity of the methanol high-pressure pump, and ultra-high pressure injection cannot be achieved under high load. Therefore, numerical simulation research methods are used to optimize high-load operating conditions. Figure 1 Table 2 shows the basic settings and performance indicators of the high-load initial working condition. Since the partial cycle simulation method is used, that is, the numerical simulation of the engine from the closing of the intake valve to the opening of the exhaust valve is performed, the calculated indicated thermal efficiency is the indicated thermal efficiency of the engine during the working stage (from the time when the intake valve closes to the time when the exhaust valve opens); the NO x The emission is 7.30g / kW·h, and the optimization goal is to reduce it to the IMO Tier III medium-speed engine standard level.

[0039] Table 2 Engine combustion and emission characteristics under high load initial operating conditions

[0040]

[0041] A high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine comprises the following steps:

[0042] Optimizing methanol injection pressure

[0043] Increasing the methanol injection pressure can shorten the methanol injection duration and combustion duration, thereby improving the engine indicated thermal efficiency. Figure 2 As the methanol injection pressure increases, the engine indicated thermal efficiency and combustion duration, combustion efficiency and NO x It can be seen that by increasing the methanol injection pressure, the combustion duration can be shortened to a great extent, and the indicated thermal efficiency can be effectively improved. At the same time, as the methanol injection pressure increases from 60MPa to 80MPa, the engine NO x Emissions are reduced and combustion efficiency is significantly improved. When the methanol injection pressure is further increased to 100MPa, NO x Emissions rebounded slightly, and combustion efficiency decreased slightly. However, compared with the initial working condition, NO x Emissions are lower and the combustion efficiency is significantly higher. Therefore, in general, increasing the methanol injection pressure to 100MPa is a better choice. At this time, the engine indicated thermal efficiency is increased by 1.11 percentage points, and NO xEmissions decreased from 7.30g / kW·h to 7.07g / kW·h.

[0044] Adjusting injection strategy

[0045] In the diesel post-injection strategy, diesel will be injected into the cylinder after methanol injection, and ignite the methanol after compression ignition, thereby further shortening the combustion duration and improving the engine's indicated thermal efficiency. Figure 3 As the diesel injection timing is delayed, the engine indicated thermal efficiency and combustion duration as well as combustion efficiency and NO x The changes in emissions, where the diesel injection timing -15CAD ATDC working condition is the diesel front injection strategy, and the diesel injection timing -8CAD ATDC and -6CAD ATDC working conditions are the diesel post-injection strategy. It can be seen that as the injection strategy switches from diesel front injection to diesel post-injection strategy, the combustion duration is greatly shortened, but it also causes NO x Compared with the diesel injection timing of -8CAD ATDC and -6CAD ATDC in the diesel post-injection, the indicated thermal efficiency under the diesel injection timing of -8CAD ATDC is significantly improved compared with the diesel pre-injection condition, and only NO x However, as the diesel injection timing is further delayed to -6CAD ATDC, although the combustion duration is further shortened, the indicated thermal efficiency and combustion efficiency are greatly reduced, and NO x Emissions increased significantly, and the indicated thermal efficiency was even lower than that of the diesel front injection condition. Therefore, in general, the diesel post-injection strategy with a diesel injection timing of -8CAD ATDC is the best choice, which can effectively improve the engine thermal efficiency. At this time, the engine indicated thermal efficiency increased by 1.01 percentage points, while NO x Emissions increased slightly by 0.28g / kW·h.

[0046] Introducing exhaust gas recirculation

[0047] Introducing exhaust gas recirculation into the engine can effectively reduce NO x emission. Figure 4 Figure 3 shows the effect of EGR (Exhaust Gas Recirculation) on the engine's in-cylinder pressure, heat release rate, and average in-cylinder temperature. It can be seen that the introduction of EGR reduces the average in-cylinder temperature, which decreases further with increasing EGR rate. This decrease in average in-cylinder temperature increases the ignition delay, delaying ignition timing. It also slows the methanol combustion heat release rate, delaying the combustion exotherm, and leading to a decrease in peak in-cylinder pressure.

[0048] Further analysis of the impact of EGR on the combustion path, Figure 5The “equivalence ratio-temperature” distribution cloud diagram in the cylinder at different EGR rates at CA50 is shown. As can be seen from the figure, as the EGR rate increases, the “equivalence ratio-temperature” distribution cloud diagram in the cylinder moves towards the low temperature area. This is mainly because after the introduction of EGR, the average specific heat capacity of the working fluid in the cylinder increases, which greatly reduces the temperature in the cylinder, making the combustion path and NO x The intersection area of ​​the generated area is reduced, effectively avoiding NO x The reduction of in-cylinder temperature prolongs the ignition delay period, increases the mixing time of methanol spray, and reduces the local equivalence ratio in the rich zone; but at the same time, EGR also reduces the oxygen concentration in the cylinder, making the local equivalence ratio in the lean zone richer.

[0049] Figure 6 As the EGR rate increases, the engine indicated thermal efficiency and combustion duration, combustion efficiency and NO x As can be seen from the figure, as the EGR rate increases, the engine NO x The emission is greatly reduced, but it also leads to a decrease in the indicated thermal efficiency and an increase in the combustion duration. When 20% EGR is introduced, the indicated thermal efficiency decreases slightly, the combustion efficiency increases slightly, and NO x Emissions are significantly reduced and reach the IMO Tier III standard level. When the EGR rate is further increased to 36%, although NO x Emissions, but will lead to a significant decline in indicated thermal efficiency and combustion efficiency. Therefore, in general, the introduction of 20% EGR is the best choice, which can effectively reduce NO x Emissions, at this time the engine NO x Emissions can meet the requirements of IMO Tier III emission standards, while the indicated thermal efficiency is slightly reduced by 0.08 percentage points.

[0050] Low indicated thermal efficiency and NOx emission in diesel micro-ignition high-pressure direct injection methanol engine at high load x To address high emissions, we optimized combustion and emissions performance under high-load initial operating conditions by adjusting fuel injection parameters and injection strategy and introducing exhaust gas recirculation. Table 3 shows the specific parameters for each step in the high-load optimization process.

[0051] Table 3 Engine operating parameters during high load optimization

[0052]

[0053]

[0054] *When optimizing methanol injection pressure, diesel and methanol injection timings were adjusted to ensure the same CA50.

[0055] Figure 7 The curves showing the changes in engine combustion and emission characteristics during high-load optimization are shown. From the combustion and emission curves in the figure, we can see that by increasing the methanol injection pressure to 100MPa – adopting the diesel-8CAD ATDC injection post-injection strategy – introducing a 20% exhaust gas recirculation ratio, the NO emissions under high load were successfully reduced. x Emissions were reduced to the standard of an IMOTier III medium-speed engine, a reduction of 75.1%. The engine's indicated thermal efficiency improved significantly, by 2.05 percentage points compared to the initial operating conditions, while combustion efficiency also slightly increased by 0.59 percentage points. Compared to the initial operating conditions, engine THC emissions were reduced by more than half, while CO emissions increased by 1.38 times, but still only reached 0.63 g / kW·h. The optimized basic parameters and performance indicators for high-load operation are shown in Table 4. In summary, through high-load engine combustion and emissions optimization, the diesel mild-ignition high-pressure direct injection methanol engine achieved efficient and clean combustion under high-load conditions.

[0056] Table 4 Basic parameters and performance indicators of high load conditions after optimization

[0057]

[0058]

[0059] (1) High load indicates low thermal efficiency and NO x The main reasons for high emissions are: the long duration of methanol injection at high load and the long duration of combustion reduce the combustion isovolumetric degree and limit the improvement of engine thermal efficiency. At the same time, the high temperature in the cylinder at high load is high, the high temperature duration is long, and the excess air coefficient in the cylinder is large, which leads to NO x the significant generation of emissions;

[0060] (2) Through the optimization path of “increasing the methanol injection pressure to 100 MPa – adopting a diesel-8CAD ATDC injection post-injection strategy – introducing a 20% exhaust gas recirculation ratio”, the engine indicated thermal efficiency under high load was successfully improved and NO emissions were reduced. x Compared with the initial working condition, the indicated thermal efficiency increased by 2.05 percentage points, the combustion efficiency increased slightly by 0.59 percentage points, and NO x Emissions were reduced to the IMO Tier III medium-speed engine standard, with THC emissions reduced by 53.1%. Although CO emissions increased by 1.38 times, they were still only 0.63g / kW·h. This ultimately achieved efficient and clean combustion under high-load conditions.

[0061] A high-load optimization device for a diesel micro-ignition high-pressure direct injection methanol engine, comprising

[0062] The first optimization module is used to optimize the methanol injection pressure;

[0063] The second optimization module is used to adjust the injection strategy;

[0064] The third optimization module is used to adjust the exhaust gas circulation rate.

[0065] Therefore, the present invention adopts the above-mentioned diesel micro-ignition high-pressure direct injection methanol engine high-load optimization method and device to optimize the engine combustion and emission performance, effectively improving the low indicated thermal efficiency and NO x The problem of high emissions.

[0066] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the same. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solutions of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine, characterized in that: The following steps are involved: Stage 1: Setting the methanol injection pressure range; Phase 2: Based on the first phase, set the injection strategy and adjust the diesel injection timing or methanol injection timing; Stage 3: Based on the second stage, exhaust gas recirculation is introduced into the engine and the exhaust gas recirculation ratio is set.

2. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: In the first stage, the methanol injection pressure range is 60MPa~100MPa, and the diesel injection pressure range is 60MPa~100MPa.

3. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: In the second stage, the injection strategy is the diesel post-injection strategy, in which The diesel injection timing is -8CAD ATDC, and the methanol injection timing is -10CAD ATDC.

4. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: In the third stage, the exhaust gas recirculation ratio is 0% to 40%.

5. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: Numerical simulation research methods were used to optimize the high-load operating conditions, where the methanol substitution rate was 97.2%, the intake pressure was 0.2 MPa, and the intake temperature was 30°C.

6. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: The indicators achieved by the dual-fuel engine under high load optimal working conditions include indicated thermal efficiency of 45.96%, combustion efficiency of 99.47%, NO x The specific emission is 1.82g / kW·h, the Soot specific emission is 0.055g / kW·h, the CO specific emission is 0.63g / kW·h, and the THC specific emission is 0.021g / kW·h.

7. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: The methanol injection pressure is 100 MPa.

8. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: Diesel injection pressure 80MPa.

9. The high-load optimization method for a diesel micro-ignition high-pressure direct injection methanol engine according to claim 1, characterized in that: The exhaust gas recirculation rate is 20%.

10. A high-load optimization device for a diesel micro-ignition high-pressure direct injection methanol engine, characterized in that: include The first optimization module is used to optimize the methanol injection pressure; The second optimization module is used to adjust the injection strategy; The third optimization module is used to adjust the exhaust gas circulation rate.

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