Dynamic Regulation and Performance Optimization Method of Low-Pressure EGR Rate for Low-Speed Diesel Engines

Abstract

A method for dynamically adjusting the low-pressure EGR rate and optimizing the performance of a low-speed diesel engine, comprising: calibrating the opening degree V1 of the exhaust gas bypass control valve, the opening degree V2 of the air bypass control valve, the nitrogen oxide concentration C1 of the exhaust gas in the exhaust system, and the oxygen concentration C2 of the scavenging box mixed gas under various load conditions during the diesel engine bench test; obtaining the calibrated opening degree V of the exhaust gas bypass control valve under this operating condition during the operation of the diesel engine 1ref , the calibrated opening degree V of the air bypass control valve 2ref , the calibrated concentration C of nitrogen oxides in the exhaust gas of the exhaust system 1ref and the calibrated oxygen concentration C of the scavenging box mixed gas 2ref , according to the differences between the measured values of C1 and C2 and C 1ref and C 2ref , fine-tune the opening degree V of the air bypass control valve 2act , so as to realize the dynamic adjustment of the low-pressure EGR rate and the performance optimization. The present invention can dynamically fine-tune the EGR rate of the diesel engine during ship operation, ensure that the performance of the diesel engine is always in a better state, realize the dynamic adjustment of the low-pressure EGR rate of the main engine and the performance optimization, and avoid the situation of excessive diesel engine emissions or deterioration of the performance condition.

Description

Technical Field

[0001] The present invention relates to a low-speed two-stroke diesel engine adopting a low-pressure EGR (exhaust gas recirculation) system, and particularly relates to a method for dynamically adjusting the low-pressure EGR rate and optimizing the performance of a low-speed diesel engine, belonging to the technical field of diesel engines. Background Art

[0002] With the increasing emphasis on environmental protection by people, the corresponding emission regulations for controlling nitrogen oxide emissions, carbon emissions, and sulfur compound emissions of diesel engines are becoming increasingly strict. Since dual-fuel diesel engines can effectively reduce carbon emissions and significantly reduce sulfur compound emissions in the gas mode, and at the same time, in the Otto cycle mode, the nitrogen oxide emissions of diesel engines can also be significantly reduced, which can directly meet the IMO Tier III emission regulations. Therefore, dual-fuel diesel engines are increasingly widely used in ship power.

[0003] The low-pressure EGR (exhaust gas recirculation) technology is to introduce a part of the gas from the exhaust gas after the supercharger of the diesel engine, and after purification, it is mixed with the fresh air inhaled by the diesel engine to the scavenging manifold, so that the O 2 content in the scavenging air of the diesel engine is reduced, and the CO 2 content is correspondingly increased. In this way, the peak temperature of diesel engine combustion will be greatly reduced, thereby improving the combustion stability of the gas under the Otto cycle, reducing the methane slip, and reducing the nitrogen oxide emissions in the fuel mode to meet the IMO Tier III emission regulations. Therefore, the application of low-pressure exhaust gas recirculation (EGR) technology in ship diesel engines is becoming more and more extensive, especially widely used in low-pressure dual-fuel diesel engines.

[0004] The low-pressure EGR technology usually includes introducing the exhaust gas of part of the exhaust system into the scavenging box system, and its main purpose is to increase the CO 2 content in the scavenging box; and introducing part of the fresh air into the exhaust gas exhaust system, and its main purpose is to reduce the O 2 content in the scavenging box.

[0005] In the workshop bench test of a low-pressure EGR diesel engine, the exhaust gas recirculation rate (EGR rate) under each load will be calibrated by comprehensively considering the emission characteristics and performance optimization of the diesel engine. However, during the actual operation of the ship, due to the changes in load conditions, environmental factors, etc., it is also a relatively difficult problem to accurately achieve the pre-defined EGR rate. Not to mention, at the same time, by comprehensively considering the emission status of the diesel engine and dynamically fine-tuning the EGR rate, the performance of the diesel engine can always be in a better state.

[0006] How to dynamically fine-tune the EGR rate during operation while ensuring that the EGR rate of the diesel engine is basically consistent with the pre-calibrated value, taking into account both the performance and emissions of the diesel engine, and ensuring that the performance of the diesel engine is always in a better state, which is a problem that we need to solve. Summary of the Invention

[0007] The present invention provides a method for dynamically adjusting the low-pressure EGR rate and optimizing the performance of a low-speed diesel engine, which solves the problem that during ship operation, due to changes in load conditions, environmental factors, etc., there is a certain deviation between the actual EGR rate of the diesel engine and the expected requirements, resulting in excessive emissions or deterioration of the performance of the diesel engine.

[0008] The technical solution of the present invention is as follows:

[0009] A method for dynamically adjusting the low-pressure EGR rate and optimizing the performance of a low-speed diesel engine, characterized in that the method for dynamically adjusting the low-pressure EGR rate and optimizing the performance includes:

[0010] During the diesel engine bench test, considering the performance and emissions of the diesel engine, calibrate the opening V of the exhaust gas bypass control valve for introducing exhaust gas from the exhaust system to the scavenging system under each load condition 1 , the opening V of the air bypass control valve for introducing air into the exhaust manifold 2 , the nitrogen oxide concentration C of the exhaust gas in the exhaust system 1 and the oxygen concentration C of the mixed gas in the scavenging box 2 ;

[0011] During the operation of the diesel engine, according to the main engine speed and torque conditions, obtain the calibrated opening V of the exhaust gas bypass control valve 1ref , the calibrated opening V of the air bypass control valve 2ref , the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref and the calibrated oxygen concentration C of the mixed gas in the scavenging box 2ref under this operating condition, and adjust the opening of the regulating control valve accordingly according to the corresponding calibrated opening V of the exhaust gas bypass control valve 1ref and the calibrated opening V of the air bypass control valve 2ref ;

[0012] According to the differences between the measured values of the nitrogen oxide concentration C of the exhaust gas in the exhaust system 1 and the oxygen concentration C of the mixed gas in the scavenging box 2 and the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref and the calibrated oxygen concentration C of the mixed gas in the scavenging box 2ref , adjust the real-time opening V of the air bypass control valve 2act ​​​​​Fine-tuning is carried out to achieve dynamic regulation of the low-pressure EGR rate and performance optimization, so that the performance of the diesel engine is in an optimal state on the basis of meeting the emission requirements of the diesel engine.

[0013] Furthermore, the dynamic regulation of the low-pressure EGR rate is based on the following strategy:

[0014] 1) When the oxygen concentration C of the scavenging box mixed gas 2 < the calibrated oxygen concentration C of the scavenging box mixed gas 2ref At this time, the real-time opening V of the air bypass control valve 2act is appropriately reduced until the oxygen concentration C of the scavenging box mixed gas 2 ≥ the calibrated oxygen concentration C of the scavenging box mixed gas 2ref until;

[0015] 2) When the oxygen concentration C of the scavenging box mixed gas 2 ≥ the calibrated oxygen concentration C of the scavenging box mixed gas 2ref , and the nitrogen oxide concentration C of the exhaust gas in the exhaust system 1 < the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref At this time:

[0016] If (C 2 - C 2ref ) / C 2ref ≤ 0.03, then the real-time opening V of the air bypass control valve 2act is appropriately reduced until the nitrogen oxide concentration C of the exhaust gas in the exhaust system is satisfied 1 ≥ the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref Or (C 2 - C 2ref ) / C 2ref > 0.03 until one of the conditions is met;

[0017] If (C 2 - C 2ref ) / C 2ref > 0.03, an alarm signal for the nitrogen oxide concentration sensor of the exhaust gas is issued, requiring timely calibration or replacement of the nitrogen oxide concentration sensor of the exhaust gas. At the same time, during this period, the dynamic regulation of the low-pressure EGR rate temporarily ignores the determination factor of the nitrogen oxide concentration.

[0018] 3) When the oxygen concentration C of the scavenging box mixed gas 2 ≥ the calibrated oxygen concentration C of the scavenging box mixed gas 2ref , the nitrogen oxide concentration C of the exhaust gas in the exhaust system 1 ≥ the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref , and (C 2 - C 2ref ) / C 2ref≤0.03, (C 1 -C 1ref ) / C 1 ≤(T 1 -T 1m ) / 2T 1 When:

[0019] The real-time opening V of the air bypass control valve 2act Remains unchanged, otherwise the real-time opening V of the air bypass control valve 2act Is appropriately increased until the above conditions are met;

[0020] Wherein, T 1 Is the emission calculation value of the load closest to the four loads of 25%, 50%, 75% and 100% of the diesel engine power at this time, and T 1m Is the maximum emission value specified in the emission document under this load.

[0021] Furthermore, in the case of 3), the parameter 0.03 in the formula (C 2 -C 2ref ) / C 2ref ≤0.03, and the (T 1 -C 1ref ) / C 1 ≤(T 1 -T 1m ) / 2T 1 In (T 1 -T 1m ) / 2T 1 Can be appropriately adjusted according to the actual situation.

[0022] Compared with the prior art, the present invention can dynamically fine-tune the EGR rate of the diesel engine during ship operation, ensure that the performance of the diesel engine is always in a better state, realize the dynamic regulation and performance optimization of the low-pressure EGR rate of the main engine, and avoid the situation of excessive diesel engine emissions or deterioration of the performance condition. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 Is a schematic diagram of the principle of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention will be further described below with reference to the drawings and specific embodiments.

[0025] The present invention is used for the dynamic regulation and performance optimization of the low-pressure EGR rate of a low-speed diesel engine.

[0026] During the diesel engine bench test, considering the performance and emission status of the diesel engine, calibrate the opening V of the exhaust gas bypass control valve for introducing the exhaust gas of the exhaust system into the scavenging system under each load condition 1, and the opening degree V of the air bypass control valve of the air inlet and exhaust manifold 2 . Among them, the air bypass control valve is generally installed after the outlet of the compressor end of the diesel engine supercharger and before the air cooler. Once the calibrated opening degrees of the exhaust gas bypass control valve and the air bypass control valve are determined, the calibrated EGR rate of the diesel engine is basically determined.

[0027] During the actual operation of the diesel engine, according to its rotational speed and torque signals, the calibrated opening degree V of the exhaust gas bypass control valve under this operating condition is obtained 1ref , and the calibrated opening degree V of the air bypass control valve 2ref . In this way, the EGR rate of the diesel engine at this time can basically be kept consistent with the initially experimentally calibrated EGR rate. However, considering the influence of the actual operating conditions of the diesel engine and environmental factors, etc., when adjusted according to the calibrated opening degree of the control valve, there may be a certain difference between the actual EGR rate of the diesel engine and the pre-calibrated one; in addition, due to the change of the environmental conditions, the proportion of other exhaust gas components of the diesel engine at this time may also change to a certain extent compared with the experimental calibration, such as the change of the content of gaseous water in the exhaust gas components being relatively large compared with the calibration. Then, even if the actual EGR rate at this time is exactly the same as that during calibration, the performance condition of the diesel engine may not be in an optimal condition at this time. In some extreme cases, there may even be a possibility that the emissions of the diesel engine exceed the standard or the fuel consumption condition deteriorates relatively significantly.

[0028] The method of the present invention includes the following content.

[0029] To avoid this situation from occurring, during the bench test of the diesel engine, the exhaust gas nitrogen oxide concentration C of the exhaust system is also calibrated simultaneously 1 , and the oxygen concentration C of the scavenging box mixed gas 2 . During the actual operation of the diesel engine, according to the power condition of the diesel engine, the calibrated concentration C of the exhaust gas nitrogen oxide in the exhaust system of the diesel engine at this time is obtained 1ref , and the calibrated oxygen concentration C of the scavenging box mixed gas 2ref . Then, according to the difference between the measured values of C 1 and C 2 and the differences between the measured values and C 1ref and C 2ref , the real-time opening degree V of the air bypass control valve 2act is finely adjusted to achieve dynamic regulation and performance optimization of the low-pressure EGR rate on the basis of meeting the emissions of the diesel engine, and to make the performance of the diesel engine be in an optimal condition as much as possible.

[0030] The reason for choosing to finely adjust the air bypass control valve is that the adjustment of the air bypass control valve to the EGR rate is relatively obvious. In addition, the air bypass control valve is relatively small, which is convenient for the dynamic regulation of the EGR rate.

[0031] To ensure that the air bypass control valve has a dynamic regulation function under various environmental conditions, it is generally required that during the calibration test of the air bypass control valve, its minimum opening should not be less than 10% of the total opening, and the maximum opening should not be greater than 90% of the total opening.

[0032] The dynamic regulation and performance optimization of the low-pressure EGR rate are based on the following strategies:

[0033] When C 2 ≥ C 2ref , C 1 ≥ C 1ref , and (C 2 - C 2ref ) / C 2ref ≤ 0.03, (C 1 - C 1ref ) / C 1 ≤ (T 1 - T 1m ) / 2T 1 , the real-time opening V 2act of the air bypass control valve will remain unchanged; otherwise, the real-time opening V 2act of the air bypass control valve will increase appropriately until the above conditions are met. Where T 1 is the calculated emission value of the load closest to one of the four loads of 25%, 50%, 75%, and 100% of the diesel engine power at this time, and T 1m is the specified maximum emission value at this load. Of course, the parameters 0.03 in the above judgment formula, and (T 1 - T 1m ) / 2T 1 can be adjusted appropriately according to the actual situation.

[0034] When C 2 ≥ C 2ref , in addition, the nitrogen oxide emission concentration of the diesel engine is relatively higher than that during the EGR rate calibration. Generally speaking, the combustion condition and fuel consumption condition of the diesel engine will be relatively better at this time. At this time, we focus on preventing the nitrogen oxide emission of the diesel engine from exceeding the standard. The real-time opening V 2act of the air bypass control valve increases appropriately, so that the oxygen content in the combustion chamber reaction will decrease relatively, the nitrogen oxide concentration will also decrease accordingly, and the EGR rate will increase relatively. According to the IMO emission regulations, the nitrogen oxide emission of the diesel engine is the weighted average of the emissions of the four loads of 25%, 50%, 75%, and 100%. Therefore, in the dynamic regulation control of the air bypass control valve, the calculated emission value of the load closest to one of the four loads of 25%, 50%, 75%, and 100% of this load is selected as the limiting condition, (C 1 - C 1ref ) / C 1 ≤ (T 1 - T1m ) / 2T 1 The purpose of this restriction is to ensure that the actual nitrogen oxide emissions of the load will not exceed the standard. 1 -T 1m ) / 2T 1 This restriction condition can be adjusted accordingly according to the actual situation during the actual application process. (C 2 -C 2ref ) / C 2ref The purpose of the restriction condition of ≤0.03 is to avoid interference with the dynamic adjustment of the EGR rate due to sensor measurement errors as much as possible. 2 -C 2ref ) / C 2ref The limiting condition of ≤0.03 can also be adjusted accordingly according to actual conditions during practical application.

[0035] When C 2 <C 2ref When the air bypass control valve opens V 2act will be reduced appropriately until C 2 ≥C 2ref until.

[0036] When C 2 <C 2ref In addition, the NOx emission concentration of diesel engine is lower than that of EGR rate calibration. Generally speaking, the combustion and fuel consumption of diesel engine will be relatively poor at this time. At this time, we should focus on optimizing the performance of diesel engine and improving the fuel consumption of diesel engine.

[0037] When C 2 ≥C 2ref , and at the same time C 1 <C 1ref This situation generally does not occur, but it is possible in some special cases. At this time, we will add another judgment condition. When (C 2 -C 2ref ) / C 2ref ≤0.03, real-time opening of air bypass control valve V 2act Will be reduced appropriately until at least C is met 1 ≥C 1ref , or (C 2 -C 2ref ) / C 2ref >0.03 until one of the conditions is met.

[0038] When C 2 ≥C 2ref , C 1 <C 1ref , (C2 -C 2ref ) / C 2ref When both > 0.03 occur, an exhaust gas NOx concentration sensor alarm signal will be emitted at this time. During this period, the dynamic regulation of the low-pressure EGR rate will temporarily ignore the determination factor of the NOx concentration. At the same time, it is required to calibrate or replace the exhaust gas NOx concentration sensor in a timely manner.

[0039] In order to avoid interference with the dynamic regulation of the EGR rate due to sensor errors, in terms of the measurement of the oxygen concentration in the scavenging box, we generally require 3 sensors to be installed here, and daily calibration and regular calibration with standard gas are required to ensure the accuracy of the oxygen concentration measurement and avoid interference caused by oxygen concentration sensor failures. In terms of the measurement of the NOx concentration, considering that the exhaust gas NOx concentration sensor mainly plays an auxiliary judgment function, we do not necessarily require 2 or more NOx concentration sensors to be installed, but regular calibration or replacement is also required. Especially when an alarm signal appears, it is necessary to calibrate or replace the exhaust gas NOx concentration sensor in a timely manner.

[0040] Thus, the dynamic regulation and performance optimization of the low-pressure EGR rate are achieved.

[0041] The scope of protection required by the present invention is not limited to the above embodiments. Any equivalent changes and modifications made based on the content of this specification shall fall within the technical scope required to be protected by this invention application.

Claims

1. A method for dynamically adjusting the low-pressure EGR rate and optimizing the performance of a low-speed diesel engine, Characterized in that, The method for dynamically adjusting the low-pressure EGR rate and optimizing the performance includes: During the diesel engine bench test, considering the performance and emission status of the diesel engine, calibrate the opening V of the exhaust gas bypass control valve for introducing the exhaust gas of the exhaust system to the scavenging system under each load condition 1 、the opening V of the air bypass control valve for introducing air to the exhaust manifold 2 、the concentration C of nitrogen oxides in the exhaust gas of the exhaust system 1 and the concentration C of oxygen in the mixed gas in the scavenging box 2 ; During the operation of the diesel engine, according to the main engine speed and torque conditions, the calibrated opening V of the exhaust gas bypass control valve under this operating condition is obtained 1ref , the calibrated opening V of the air bypass control valve 2ref , the calibrated concentration C of nitrogen oxides in the exhaust gas of the exhaust system 1ref and the calibrated concentration C of oxygen in the scavenging air box mixture gas 2ref , and according to the corresponding calibrated opening V of the exhaust gas bypass control valve 1ref and the calibrated opening V of the air bypass control valve 2ref correspondingly adjust the opening of the regulating control valve; According to the measured values of the exhaust gas nitrogen oxide concentration C in the exhaust system 1 and the oxygen concentration C of the scavenging box mixed gas 2 respectively compared with the calibrated concentration C of the exhaust gas nitrogen oxides in the exhaust system 1ref and the calibrated oxygen concentration C of the scavenging box mixed gas 2ref the real-time opening V of the air bypass control valve 2act is finely adjusted, so as to realize the dynamic regulation and performance optimization of the low-pressure EGR rate, and on the basis of meeting the diesel engine emission requirements, make the performance of the diesel engine in an optimal condition.

2. The method for dynamically adjusting the low-pressure EGR rate and optimizing the performance of a low-speed diesel engine according to claim 1, Characterized in that, The dynamic adjustment of the low-pressure EGR rate is based on the following strategy: 1) When the oxygen concentration C of the scavenging box mixed gas 2 <is less than the calibrated oxygen concentration C of the scavenging box mixed gas 2ref the real-time opening V of the air bypass control valve 2act is appropriately reduced until the oxygen concentration C of the scavenging box mixed gas 2 ≥ the calibrated oxygen concentration C of the scavenging box mixed gas 2ref ; 2) When the oxygen concentration C of the scavenging box mixed gas 2 ≥ the calibrated oxygen concentration C of the scavenging box mixed gas 2ref , and the nitrogen oxide concentration C of the exhaust gas in the exhaust system 1 < the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref : If (C 2 - C 2ref ) / C 2ref ≤ 0.03, then the real - time opening V of the air bypass control valve 2act is appropriately reduced until one of the conditions that the nitrogen oxide concentration C of the exhaust gas in the exhaust system 1 ≥ the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref or (C 2 - C 2ref ) / C 2ref > 0.03 is satisfied; If (C 2 - C 2ref ) / C 2ref > 0.03, an alarm signal for the exhaust gas nitrogen oxide concentration sensor is issued, requiring timely calibration or replacement of the exhaust gas nitrogen oxide concentration sensor. Meanwhile, during this period, the dynamic adjustment of the low-pressure EGR rate temporarily ignores the determination factor of nitrogen oxide concentration; 3) When the oxygen concentration C of the scavenging box mixed gas 2 ≥ the calibrated oxygen concentration C of the scavenging box mixed gas 2ref , and the nitrogen oxide concentration C of the exhaust gas in the exhaust system 1 ≥ the calibrated nitrogen oxide concentration C of the exhaust gas in the exhaust system 1ref , and (C 2 - C 2ref ) / C 2ref ≤ 0.03, (C 1 - C 1ref ) / C 1 ≤ (T 1 - T 1m ) / 2T 1 : The real-time opening degree V of the air bypass control valve 2act Remain unchanged, otherwise increase the real-time opening degree V of the air bypass control valve 2act Appropriately until the above conditions are met; Among them, T 1 is the calculated emission value of the load closest to one of the four loads of 25%, 50%, 75% and 100% of the diesel engine power at this time, and T 1m is the maximum emission value specified in the emission document for this load.

3. The method for dynamically adjusting the low-pressure EGR rate and optimizing the performance of a low-speed diesel engine according to claim 2, Characterized in that, In the third case described above, the parameter 0.03 in the formula (C 2 -C 2ref ) / C 2ref ≤0.03, and the (T 1 -C 1ref ) / C 1 ≤(T 1 -T 1m ) / 2T 1 in the formula (T 1 -T 1m ) / 2T 1 can be adjusted appropriately according to the actual situation.

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