Optimization method for exhaust temperature non-uniformity of cylinders of engine

Abstract

The invention relates to the technical field of uniform exhaust temperature of each cylinder of an engine, and provides an optimization method for exhaust temperature non-uniformity of each cylinder of the engine, which adopts a mode of assisting a calculation model and an actual experiment to realize model verification, so as to ensure that the calculation model is correctly built, and improve the efficiency. The method for optimizing the exhaust temperature non-uniformity of the cylinders of the engine comprises the following steps that an engine real object rack of a pulse exhaust pipe and a constant-pressure supercharger is built, and the engine real object rack of the pulse exhaust pipe and the constant-pressure supercharger is built; a cylinder thermal process calculation model, an intercooler calculation model, an intake and exhaust system calculation model and a turbocharging system calculation model are built in cooperation with an engine entity, the accuracy of the calculation models is verified through comparison between recorded actual data and simulation data, and factor analysis of exhaust temperature nonuniformity of each cylinder of the engine is achieved through the calculation models. And forming an optimization strategy of exhaust temperature non-uniformity of each cylinder of the engine in combination with a factor relationship.

Description

Technical Field

[0001] The present invention relates to the technical field of uniform exhaust temperature of each cylinder of an engine, and in particular to a method for optimizing the non-uniformity of exhaust temperature of each cylinder of an engine. Background Art

[0002] As we all know, the uneven exhaust temperature of each cylinder of the engine refers to the phenomenon that there are differences in the temperature of the gas discharged from each cylinder of the engine during operation. It is not only related to the technical performance and service life of the engine, but also involves environmental protection and economic benefits. During the engine design and maintenance process, effective measures should be taken to reduce the uneven exhaust temperature and ensure stable and efficient operation of the engine.

[0003] After searching, Chinese patent publication number CN112943464B and Chinese patent publication number CN116044593A respectively disclose a method and device for compensating for uneven cylinder work performance and a method and related device for controlling a multi-cylinder engine. The former is roughly described as obtaining the engine speed and the exhaust temperature corresponding to each cylinder of the engine, judging whether the working condition of the engine is stable according to the speed, and if the working condition of the engine is stable, judging whether the non-abnormal condition is met according to the exhaust temperature of each cylinder, and if the non-abnormal condition is met, at least one cylinder is a cylinder to be compensated, and the average exhaust temperature is determined according to the exhaust temperatures of all normal cylinders, and the corresponding temperature difference is determined according to the exhaust temperature of the cylinder to be compensated and the average exhaust temperature, and the temperature difference corresponding to the cylinder to be compensated is determined according to the temperature difference of the cylinder to be compensated. , determine the compensation injection amount of the cylinder to be compensated. It uses the body exhaust temperature sensor of the high-power engine, combined with the temperature compensation algorithm, to realize the injection compensation of the uneven work of each cylinder of the high-power engine, and can realize long-term online monitoring and compensation. The latter can be roughly described as including obtaining the intake temperature of each cylinder in the multi-cylinder engine, determining the corrected injection amount of each cylinder according to the intake temperature of each cylinder, and controlling the injection pump of each cylinder to inject fuel with the corresponding corrected injection amount. This method directly collects the intake temperature of each cylinder, determines the corrected injection amount according to the intake temperature, and eliminates the difference in intake temperature of each cylinder by changing the injection amount of each cylinder, thereby improving the uniformity of exhaust temperature of each cylinder, and improving the working performance of the multi-cylinder engine without changing the existing structure of the engine.

[0004] Although the above-mentioned existing technical solution can reduce the temperature deviation between the cylinders of the engine, the way it reduces the temperature deviation is by controlling the injection amount. Although the injection control of the injection amount has a certain optimization effect on the uneven exhaust temperature of the engine cylinders, the injection amount directly determines the power output. Frequent adjustment of the injection amount can easily cause unstable power output, which in turn affects the stable power output of the engine. Summary of the Invention

[0005] In response to the shortcomings of the existing technology, the present invention provides a method for optimizing the unevenness of exhaust temperature in each cylinder of an engine. The method adopts a computational model and actual experiments to assist in model verification to ensure that the computational model is built correctly, and combines the correct computational model to further extend the analysis relative to the actual engine to form an optimization method for the unevenness of exhaust temperature in each cylinder of the engine.

[0006] To achieve the above object, the present invention provides the following technical solution: a method for optimizing the unevenness of exhaust temperature of each cylinder of an engine, comprising the following steps: S1. Build a diesel engine with a pulse dry-cooled exhaust pipe and a constant-pressure turbocharger. The engine is a physical model that includes a cylinder, intercooler, intake and exhaust pipes, and a turbocharger. S2, supporting cylinders, intercoolers, intake and exhaust pipes and turbochargers respectively build cylinder thermal process calculation model, intercooler calculation model, intake and exhaust system calculation model and turbocharger system calculation model; S3. Generate an engine operation simulation based on the calculation model and record the simulation data. After the simulation, generate actual data records by actually running the engine. S4. By comparing the recorded actual data with the simulation data, if the error is within an acceptable range, it is determined that the calculation model has sufficient accuracy, thereby achieving verification of the accuracy of the calculation model; S5. When the error between the calculation model and the actual data is within the allowable range, the calculation model establishment method is effective. The calculation model is used to analyze the factors causing the unevenness of the exhaust temperature of each cylinder of the engine, and the relationship between the factors is combined to optimize the unevenness of the exhaust temperature of each cylinder of the engine.

[0007] Preferably, the process of building the cylinder thermal process calculation model is as follows: assuming the cylinder as an adiabatic system, rationally setting the pressure, temperature, and flow state of the working fluid in the cylinder, and using the ideal gas state equation, mass conservation equation, and energy conservation equation to combine the cylinder working process to obtain the combustion heat release law and the cylinder heat transfer law: The ideal gas state equation is calculated as follows: The mass conservation equation is calculated as: The energy conservation equation is calculated as follows: Where: They are the total mass of the working fluid in the cylinder, the mass of the working fluid entering the cylinder, the mass of the working fluid discharged from the cylinder, and the mass of the working fluid injected into the cylinder, in kg / s; 、 、 They are the internal energy of the working fluid in the cylinder, the heat released by the combustion of the fuel in the cylinder, and the heat transferred to the outside through the cylinder wall, in kJ. 、 They are the specific enthalpy of the working medium entering the heat exchange and the specific enthalpy of the working medium discharged from the cylinder, in kJ / Kg; is the working medium pressure in the cylinder, unit is Pa; is the cylinder working volume, unit: m2; is the working medium temperature in the cylinder, unit K; The calculation formula for the instantaneous combustion heat release rate of fuel combustion in the cylinder is: Where: The cyclic injection volume of each cylinder, in kg / s; The lower calorific value of fuel combustion, unit is kJ / kg; is the combustion heat release rate, unit is kJ / ℃A; The percentage of fuel burned in the cylinder, that is, the mass of fuel burned in the cylinder and the amount of fuel injected in the cycle at a certain crankshaft angle The ratio of The combustion heat release process was calculated using Weber's semi-empirical formula: Where: is the combustion quality index; 、 、 and They are crank angle, combustion duration angle, combustion start angle, and combustion end angle, in units of / ℃A, where ; The calculation formula for the cylinder wall heat transfer per unit crankshaft angle is: Where: is the engine speed, in r / min; is the instantaneous average heat transfer coefficient; is the heat exchange area, unit is m³; are the instantaneous temperature of the working medium in the cylinder and the average temperature of the cylinder wall, in K, respectively. For the cylinder head; For the cylinder liner; For the piston top; The calculation formula of the instantaneous average heat transfer coefficient of the cylinder is: Where: They are respectively the in-cylinder pressure, the in-cylinder pressure when the crankshaft angle is at the bottom dead center, and the cylinder pressure when the engine is dragged backward, in Pa; They are respectively the in-cylinder temperature and the in-cylinder temperature when the crankshaft angle is at the bottom dead center, in K; D is the cylinder diameter, in mm; is the average piston speed, in m / s; Respectively, they are the cylinder working volume and the cylinder volume when the crankshaft angle is at the bottom dead center, in m³; They are air flow velocity coefficient and combustion chamber status coefficient respectively.

[0008] Preferably, the intercooler calculation model mainly involves the parameters of the intercooler outlet temperature and outlet pressure , is the turbocharger outlet air temperature, subscript " " stands for air," " stands for cooling water," " represents the intercooler inlet status," " represents the intercooler outlet status; Intercooler outlet gas temperature The calculation formula is: Intercooler outlet cooling water temperature The calculation formula is: Pressure loss of the charge air after passing through the intercooler The calculation formula is: Where: To calibrate the pressure loss of the intercooler under working conditions, the value is usually (0.3-0.5) kPa; They are the actual air flow of the intercooler and the air flow of the intercooler under the calibrated working conditions, respectively, in kg / s.

[0009] Preferably, in the process of generating the intake and exhaust system calculation model, it is necessary to consider that the engine's working process has a cyclical nature, and the gas flow process in the intake and exhaust pipes has typical unsteady flow characteristics. In the engine simulation calculation, the basic control equation of one-dimensional unsteady flow is used as follows: Continuity equation: Momentum equation: Energy equation: Where: is the gas flow rate, in m / s; is the gas density, unit is kg / m³; is the cross-sectional area of the pipe, unit: m2; 、 are the pipe diameter and the average circumference of the pipe section, in mm. ; is the friction coefficient inside the pipeline, usually taken as 0.005; is the heat transfer rate per unit mass of fluid; The conservation equations in the exhaust system calculated using the finite volume method are as follows: Where: is the conservative flow rate of the fluid; is the fluid density; To control body surface area; To control body volume; is the outer normal of the control body surface; is the fluid velocity; is the diffusion coefficient; To control the source term in the body; When using conservation control equations to perform numerical integration calculations, it is necessary to satisfy the CFL criterion to obtain a stable solution. Where: is the time step; is the step length along the length of the pipeline; is the gas flow rate; is the gas sound speed; When using one-dimensional thermodynamic simulation software to calculate internal combustion engine performance, the following discretization lengths are generally used: intake system discretization length ≈ 0.4xD; exhaust system discretization length ≈ 0.55xD. As gas flows through the intake and exhaust ducts, friction between the gas and the duct walls causes a loss of gas pressure. The magnitude of this friction coefficient is affected by the Reynolds number and the roughness of the duct walls. When the wall of the intake and exhaust duct is smooth, the calculation formula of the friction coefficient C is as follows: Where: is the Reynolds number.

[0010] When the wall surface of the intake and exhaust pipes is rough, the friction coefficient Increase, and use Nikuradse formula to correct the friction coefficient as follows: Where: is the equivalent diameter of the intake and exhaust pipes; is the height of the pipe wall roughness; When there are bends in the intake and exhaust pipes or the cross-section of the pipe is irregular, the airflow pressure in the pipe will be lost. The pressure loss coefficient is used to represent the degree of loss as follows: Where: is the total inlet pressure of the intake and exhaust pipes; is the total outlet pressure of the intake and exhaust pipes; is the inlet gas density of the intake and exhaust ducts; is the inlet gas velocity of the intake and exhaust ducts; In the intake and exhaust system, when the gas flows in the pipe, heat transfer occurs between the gas and the pipe wall. The heat transfer coefficient as follows: .

[0011] Preferably, the turbocharger system calculation model is as follows: the original turbocharger is composed of a centrifugal compressor and a radial turbine. In an exhaust gas turbocharger engine, the exhaust gas energy discharged from the engine cylinder is converted into mechanical work by the turbine, driving the compressor impeller coaxial with the turbine to rotate. In the compressor, the mechanical work is used to compress the fresh air, providing sufficient air density for combustion work in the engine cylinder. Therefore, the turbocharger system calculation model needs to meet the following three balance conditions: The power balance condition requires that the average output power of the turbine and the average power consumption of the compressor Equal, such as: Since the exhaust gas mass flow rate flowing through the turbine and the exhaust gas enthalpy difference before and after entering the turbine jointly determine the average output power of the turbine, and usually, the loss of the turbocharger is included in the average output power of the turbine, The relevant calculation formula is as follows: Where: is the exhaust gas mass flow rate passing through the turbine; is the mechanical efficiency of the turbocharger system; are the enthalpy values at the turbine inlet and outlet, respectively; is the isentropic efficiency of the turbine; is the average constant-pressure specific heat of the turbine; turbine inlet temperature; is the turbine expansion ratio; Since the mass flow of air flowing through the compressor and the enthalpy difference of air before and after entering the compressor jointly determine the average power consumption of the compressor, The relevant calculation formula is as follows: Where: is the air mass flow rate flowing through the compressor; are the enthalpy values at the compressor inlet and outlet respectively; is the isentropic efficiency of the compressor; is the average constant-pressure specific heat of the compressor; is the compressor inlet temperature; is the compressor pressure ratio; The overall efficiency formula for a turbocharger is as follows: Speed balance condition, requiring turbine speed and compressor speed equal: In the case of unstable engine operation, the moment of inertia of the turbocharger rotor must be Take into account, to obtain the turbocharger rotor angular velocity The specific calculation formula is: The mass balance condition requires that the gas mass flow rates in the turbine and compressor be equal: Where: is the mass flow rate of exhaust gas flowing through the wastegate valve; is the mass flow rate of fuel, which is generally negligible.

[0012] Preferably, the error range between the actual data and the simulation data should be less than 10%.

[0013] Compared with the prior art, the present invention provides a method for optimizing the unevenness of exhaust temperature in each cylinder of an engine, which has the following beneficial effects: The present invention combines theory with practice to form verification and judgment of the designed calculation model to determine the accuracy and feasibility of the calculation model, and then forms a causal relationship analysis of the unevenness of the exhaust temperature of each cylinder of the engine under the guidance of the calculation model, forming the necessary technical direction inspiration, and then conducts experimental verification again according to the simulation technology inspiration, forming a combination of theory and practice, and forming an optimization method for the unevenness of the exhaust temperature of each cylinder of the engine. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a process framework diagram of the present invention; Figure 2 This is a schematic diagram of the intermediate tube solution of the present invention; Figure 3 This is a schematic diagram of the constant pressure exhaust pipe solution of the present invention; Figure 4 This is a series of data comparisons between the actual experiment and simulation of the present invention Figure 1 ; Figure 5 This is a series of data comparisons between the actual experiment and simulation of the present invention Figure 2 ; Figure 6 This is a comparison chart of the operating data of the intermediate pipe solution, the constant pressure exhaust pipe solution and the original engine operation solution of the present invention; Figure 7 These are the extreme values of the temperature difference between the cylinders and the exhaust pipes when the intermediate pipe solution, the constant pressure exhaust pipe solution, and the original engine operation solution are operated. DETAILED DESCRIPTION

[0015] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0016] For examples, see Figure 1-Figure 7 A method for optimizing the unevenness of exhaust temperature of each cylinder of an engine comprises the following steps: S1. Build a diesel engine with a pulse dry-cooled exhaust pipe and a constant-pressure turbocharger. The engine is a physical model that includes a cylinder, intercooler, intake and exhaust pipes, and a turbocharger. S2, supporting cylinders, intercoolers, intake and exhaust pipes and turbochargers respectively build cylinder thermal process calculation model, intercooler calculation model, intake and exhaust system calculation model and turbocharger system calculation model, The process of building the cylinder thermal process calculation model is as follows: the cylinder is assumed to be an adiabatic system, and the pressure, temperature, and flow state of the working fluid in the cylinder are rationally set. The ideal gas state equation, mass conservation equation, and energy conservation equation are used to combine the cylinder working process to obtain the combustion heat release law and the cylinder heat transfer law: The ideal gas state equation is calculated as follows: The mass conservation equation is calculated as: The energy conservation equation is calculated as follows: Where: They are the total mass of the working fluid in the cylinder, the mass of the working fluid entering the cylinder, the mass of the working fluid discharged from the cylinder, and the mass of the working fluid injected into the cylinder, in kg / s; 、 、 They are the internal energy of the working fluid in the cylinder, the heat released by the combustion of the fuel in the cylinder, and the heat transferred to the outside through the cylinder wall, in kJ. 、 They are the specific enthalpy of the working medium entering the heat exchange and the specific enthalpy of the working medium discharged from the cylinder, in kJ / Kg; is the working medium pressure in the cylinder, unit is Pa; is the cylinder working volume, unit: m2; is the working medium temperature in the cylinder, unit K; The calculation formula for the instantaneous combustion heat release rate of fuel combustion in the cylinder is: Where: The cyclic injection volume of each cylinder, in kg / s; The lower calorific value of fuel combustion, unit is kJ / kg; is the combustion heat release rate, unit is kJ / ℃A; The percentage of fuel burned in the cylinder, that is, the mass of fuel burned in the cylinder and the amount of fuel injected in the cycle at a certain crankshaft angle The ratio of The combustion heat release process was calculated using Weber's semi-empirical formula: Where: is the combustion quality index; 、 、 and They are crank angle, combustion duration angle, combustion start angle, and combustion end angle, in units of / ℃A, where ; The calculation formula for the cylinder wall heat transfer per unit crankshaft angle is: Where: is the engine speed, in r / min; is the instantaneous average heat transfer coefficient; is the heat exchange area, unit is m³; are the instantaneous temperature of the working medium in the cylinder and the average temperature of the cylinder wall, in K, respectively. For the cylinder head; For the cylinder liner; For the piston top; The calculation formula of the instantaneous average heat transfer coefficient of the cylinder is: Where: They are respectively the in-cylinder pressure, the in-cylinder pressure when the crankshaft angle is at the bottom dead center, and the cylinder pressure when the engine is dragged backward, in Pa; They are respectively the in-cylinder temperature and the in-cylinder temperature when the crankshaft angle is at the bottom dead center, in K; D is the cylinder diameter, in mm; is the average piston speed, in m / s; Respectively, they are the cylinder working volume and the cylinder volume when the crankshaft angle is at the bottom dead center, in m³; They are air flow velocity coefficient and combustion chamber status coefficient respectively.

[0017] The main parameters involved in the intercooler calculation model are the outlet temperature of the intercooler and outlet pressure , is the turbocharger outlet air temperature, subscript " " stands for air," " stands for cooling water," " represents the intercooler inlet status," " represents the intercooler outlet status; Intercooler outlet gas temperature The calculation formula is: Intercooler outlet cooling water temperature The calculation formula is: Pressure loss of the charge air after passing through the intercooler The calculation formula is: Where: To calibrate the pressure loss of the intercooler under working conditions, the value is usually (0.3-0.5) kPa; They are the actual air flow of the intercooler and the air flow of the intercooler under the calibrated working conditions, respectively, in kg / s.

[0018] In the process of generating the intake and exhaust system calculation model, it is necessary to consider that the engine's working process is cyclical and the gas flow process in the intake and exhaust pipes has typical unsteady flow characteristics. In the engine simulation calculation, the basic control equation of one-dimensional unsteady flow is as follows: Continuity equation: Momentum equation: Energy equation: Where: is the gas flow rate, in m / s; is the gas density, unit is kg / m³; is the cross-sectional area of the pipe, unit: m2; 、 are the pipe diameter and the average circumference of the pipe section, in mm. ; is the friction coefficient inside the pipeline, usually taken as 0.005; is the heat transfer rate per unit mass of fluid; The conservation equations in the exhaust system calculated using the finite volume method are as follows: Where: is the conservative flow rate of the fluid; is the fluid density; To control body surface area; To control body volume; is the outer normal of the control body surface; is the fluid velocity; is the diffusion coefficient; To control the source term in the body; When using conservation control equations to perform numerical integration calculations, it is necessary to satisfy the CFL criterion to obtain a stable solution. Where: is the time step; is the step length along the length of the pipeline; is the gas flow rate; is the gas sound speed; When using GT-POWER software to calculate internal combustion engine performance, the following discretization lengths are generally used: intake system discretization length ≈ 0.4xD; exhaust system discretization length ≈ 0.55xD. As gas flows through the intake and exhaust ducts, friction between the gas and the duct walls causes gas pressure loss. The magnitude of this friction coefficient is affected by the Reynolds number and the roughness of the duct walls. When the wall of the intake and exhaust duct is smooth, the calculation formula of the friction coefficient C is as follows: Where: is the Reynolds number.

[0019] When the wall surface of the intake and exhaust pipes is rough, the friction coefficient Increase, and use Nikuradse formula to correct the friction coefficient as follows: Where: is the equivalent diameter of the intake and exhaust pipes; is the height of the pipe wall roughness; When there are bends in the intake and exhaust pipes or the cross-section of the pipe is irregular, the airflow pressure in the pipe will be lost. The pressure loss coefficient is used to represent the degree of loss as follows: Where: is the total inlet pressure of the intake and exhaust pipes; is the total outlet pressure of the intake and exhaust pipes; is the inlet gas density of the intake and exhaust ducts; is the inlet gas velocity of the intake and exhaust ducts; In the intake and exhaust system, when the gas flows in the pipe, heat transfer occurs between the gas and the pipe wall. The heat transfer coefficient as follows: .

[0020] The turbocharger system calculation model is as follows: The original turbocharger is composed of a centrifugal compressor and a radial turbine. In an exhaust gas turbocharger engine, the exhaust energy discharged from the engine cylinder is converted into mechanical work by the turbine, driving the rotation of the compressor impeller coaxial with the turbine. In the compressor, mechanical work is used to compress the fresh air, providing sufficient air density for combustion work in the engine cylinder. Therefore, the turbocharger system calculation model needs to meet the following three balance conditions: The power balance condition requires that the average output power of the turbine and the average power consumption of the compressor Equal, such as: Since the exhaust gas mass flow rate flowing through the turbine and the exhaust gas enthalpy difference before and after entering the turbine jointly determine the average output power of the turbine, and usually, the loss of the turbocharger is included in the average output power of the turbine, The relevant calculation formula is as follows: Where: is the exhaust gas mass flow rate passing through the turbine; is the mechanical efficiency of the turbocharger system; are the enthalpy values at the turbine inlet and outlet, respectively; is the isentropic efficiency of the turbine; is the average constant-pressure specific heat of the turbine; turbine inlet temperature; is the turbine expansion ratio; Since the mass flow of air flowing through the compressor and the enthalpy difference of air before and after entering the compressor jointly determine the average power consumption of the compressor, The relevant calculation formula is as follows: Where: is the air mass flow rate flowing through the compressor; are the enthalpy values at the compressor inlet and outlet respectively; is the isentropic efficiency of the compressor; is the average constant-pressure specific heat of the compressor; is the compressor inlet temperature; is the compressor pressure ratio; The overall efficiency formula for a turbocharger is as follows: Speed balance condition, requiring turbine speed and compressor speed equal: In the case of unstable engine operation, the moment of inertia of the turbocharger rotor must be Take into account, to obtain the turbocharger rotor angular velocity The specific calculation formula is: The mass balance condition requires that the gas mass flow rates in the turbine and compressor be equal: Where: is the mass flow rate of exhaust gas flowing through the wastegate valve; is the mass flow rate of fuel, which is generally negligible.

[0021] S3. Generate an engine operation simulation based on the calculation model and record the simulation data. After the simulation, generate actual data records by actually running the engine. S4. By comparing the recorded actual data with the simulated data, if the error is within an acceptable range, the calculation model is determined to have sufficient accuracy, achieving the verification of the accuracy of the calculation model. The error range between the actual data and the simulated data should be less than 10%; S5. When the error between the calculation model and the actual data is within the allowable range, the calculation model establishment method is effective. The calculation model is used to analyze the factors causing the unevenness of the exhaust temperature of each cylinder of the engine, and the relationship between the factors is combined to optimize the unevenness of the exhaust temperature of each cylinder of the engine.

[0022] In summary, combined with the establishment of the above calculation model, the data comparison between actual experiment and simulation is formed. Figure 3 and attached Figure 4 The comparison between the experimental and model parameters clearly shows that under the same load characteristic conditions, the air-fuel ratio obtained by the engine simulation is slightly lower than the experimental results, and the specific fuel consumption is slightly higher than the experimental results. The maximum relative error is less than 5%. However, with the increase of power, the specific fuel consumption characteristics are basically consistent with the experimental results. The comparison of other main parameters also has a good agreement. This shows that the constructed calculation model can well predict the changing trend of engine characteristics, and the simulation calculation results are true and credible.

[0023] Based on the calculation model parameters, it is obvious that controlling the exhaust gas mass flow rate can also optimize the exhaust temperature unevenness. Taking the Yuchai 16VC eight-cylinder diesel engine as an example, scheme 1: the intermediate pipe scheme is set. A connecting pipe is added between the original two pulse exhaust pipes to release the exhaust of the 4th and 5th cylinders, thereby reducing the impact of the exhaust of these two cylinders on the 1st and 8th cylinders. The corresponding principle diagram is as shown in the attached figure. Figure 2 As shown; Setting scheme 2: constant pressure exhaust pipe scheme, using relatively large cavity exhaust pipe to achieve uniform exhaust pressure of each cylinder. The corresponding principle diagram is as shown in the attached figure. Figure 3 shown.

[0024] Combined with attachment Figure 6 and attached Figure 7 The two sets of setting schemes are compared with the operating data of the original engine. It can be clearly judged that the two optimized exhaust pipe schemes show a high degree of consistency in engine specific fuel consumption, intake parameters and exhaust parameters. Replacing the optimized exhaust pipe will not significantly reduce the engine performance. However, under different working conditions, the exhaust temperature of each cylinder is extremely different. Figure 7As shown in the figure, with the increase of load, the exhaust temperature extremes of the three exhaust pipe schemes all show a significant increasing trend, but the exhaust temperature extremes of the intermediate pipe scheme and the constant pressure pipe scheme are significantly lower than that of the original machine's pulse exhaust pipe. At the overload operating point, the exhaust temperature extremes of the intermediate pipe scheme and the constant pressure pipe scheme are 25% and 41% lower than those of the original machine, respectively.

[0025] in conclusion: (1) The uneven ignition sequence leads to cylinder exhaust interference, affecting the residual exhaust gas coefficient, and further affecting combustion, which is the main reason for the uneven exhaust temperature; (2) The intermediate pipe and constant pressure pipe can effectively reduce exhaust fluctuations, thereby improving exhaust pressure uniformity; (3) Both the intermediate pipe and the constant pressure pipe schemes can improve the exhaust temperature consistency, and the constant pressure pipe scheme has a more obvious effect; (4) The experimental results show that the constant pressure pipe can improve the exhaust temperature range by about 20°C compared with the intermediate pipe under the same injection correction code, and has better adaptability to the exhaust temperature range adjustment; (5) The experimental results show that the performance and transient response of the engine using the constant pressure tube are basically the same as those of the original engine.

[0026] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for optimizing the non-uniformity of exhaust temperature of each cylinder of an engine, characterized in that: The steps include: S1. Build a physical engine test bench with a pulse exhaust pipe and a constant-pressure turbocharger. The physical engine test bench includes an engine with cylinders, intercoolers, intake and exhaust pipes, and a turbocharger, as well as an engine measurement and control system including a flow meter, pressure sensor, temperature sensor, data acquisition system, data storage system, and test bench control system. S2, supporting cylinders, intercoolers, intake and exhaust pipes and turbochargers respectively build cylinder thermal process calculation model, intercooler calculation model, intake and exhaust system calculation model and turbocharger system calculation model; S3. Generate an engine operation simulation based on the calculation model and record the simulation data. After the simulation, generate actual data records by actually running the engine. S4. By comparing the recorded actual data with the simulation data, if the error is within an acceptable range, it is determined that the calculation model has sufficient accuracy, thereby achieving verification of the accuracy of the calculation model; S5. When the error between the calculation model and the actual data is within the allowable range, the calculation model establishment method is effective. The calculation model is used to analyze the factors causing the unevenness of the exhaust temperature of each cylinder of the engine, and the relationship between the factors is combined to optimize the unevenness of the exhaust temperature of each cylinder of the engine.

2. The method for optimizing the non-uniformity of exhaust temperature of each cylinder of an engine according to claim 1, characterized in that: The process of building the cylinder thermal process calculation model is as follows: the cylinder is assumed to be an adiabatic system, and the pressure, temperature, and flow state of the working fluid in the cylinder are rationally set. The ideal gas state equation, mass conservation equation, and energy conservation equation are used to combine the cylinder working process to obtain the combustion heat release law and the cylinder heat transfer law: The ideal gas state equation is calculated as follows: The mass conservation equation is calculated as: The energy conservation equation is calculated as follows: Where: They are the total mass of the working fluid in the cylinder, the mass of the working fluid entering the cylinder, the mass of the working fluid discharged from the cylinder, and the mass of the working fluid injected into the cylinder, in kg / s; 、 、 They are the internal energy of the working fluid in the cylinder, the heat released by the combustion of the fuel in the cylinder, and the heat transferred to the outside through the cylinder wall, in kJ. 、 They are the specific enthalpy of the working medium entering the heat exchange and the specific enthalpy of the working medium discharged from the cylinder, in kJ / Kg; is the working medium pressure in the cylinder, unit is Pa; is the cylinder working volume, unit: m2; is the working medium temperature in the cylinder, unit K; The calculation formula for the instantaneous combustion heat release rate of fuel combustion in the cylinder is: Where: The cyclic injection volume of each cylinder, in kg / s; The lower calorific value of fuel combustion, unit is kJ / kg; is the combustion heat release rate, unit is kJ / ℃A; The percentage of fuel burned in the cylinder, that is, the mass of fuel burned in the cylinder and the amount of fuel injected in the cycle at a certain crankshaft angle The ratio of The combustion heat release process was calculated using Weber's semi-empirical formula: Where: is the combustion quality index; 、 、 and They are crank angle, combustion duration angle, combustion start angle, and combustion end angle, in units of / ℃A, where ; The calculation formula for the cylinder wall heat transfer per unit crankshaft angle is: Where: is the engine speed, in r / min; is the instantaneous average heat transfer coefficient; is the heat exchange area, unit is m³; are the instantaneous temperature of the working medium in the cylinder and the average temperature of the cylinder wall, in K, respectively. For the cylinder head; For the cylinder liner; For the piston top; The calculation formula of the instantaneous average heat transfer coefficient of the cylinder is: Where: They are respectively the in-cylinder pressure, the in-cylinder pressure when the crankshaft angle is at the bottom dead center, and the cylinder pressure when the engine is dragged backward, in Pa; They are respectively the in-cylinder temperature and the in-cylinder temperature when the crankshaft angle is at the bottom dead center, in K; D is the cylinder diameter, in mm; is the average piston speed, in m / s; Respectively, they are the cylinder working volume and the cylinder volume when the crankshaft angle is at the bottom dead center, in m³; They are air flow velocity coefficient and combustion chamber status coefficient respectively.

3. The method for optimizing the non-uniformity of exhaust temperature of each cylinder of an engine according to claim 2, characterized in that: The main parameters involved in the intercooler calculation model are the outlet temperature of the intercooler and outlet pressure , is the turbocharger outlet air temperature, subscript " " stands for air," " stands for cooling water," "Represents the intercooler inlet status," " represents the intercooler outlet status; Intercooler outlet gas temperature The calculation formula is: Intercooler outlet cooling water temperature The calculation formula is: Pressure loss of the charge air after passing through the intercooler The calculation formula is: Where: To calibrate the pressure loss of the intercooler under working conditions, the value is usually (0.3-0.5) kPa; They are the actual air flow of the intercooler and the air flow of the intercooler under the calibrated working conditions, respectively, in kg / s.

4. The method for optimizing the non-uniformity of exhaust temperature of each cylinder of an engine according to claim 3, characterized in that: In the process of generating the intake and exhaust system calculation model, it is necessary to consider that the engine's working process is cyclical and the gas flow process in the intake and exhaust pipes has typical unsteady flow characteristics. In the engine simulation calculation, the basic control equation of one-dimensional unsteady flow is as follows: Continuity equation: Momentum equation: Energy equation: Where: is the gas flow rate, in m / s; is the gas density, unit is kg / m³; is the cross-sectional area of the pipe, unit: m2; 、 are the pipe diameter and the average circumference of the pipe section, in mm. ; is the friction coefficient inside the pipeline, usually taken as 0.005; is the heat transfer rate per unit mass of fluid; The conservation equations in the exhaust system calculated using the finite volume method are as follows: Where: is the conservative flow rate of the fluid; is the fluid density; To control body surface area; To control body volume; is the outer normal of the control body surface; is the fluid velocity; is the diffusion coefficient; To control the source term in the body; When using conservation control equations to perform numerical integration calculations, it is necessary to satisfy the CFL criterion to obtain a stable solution. Where: is the time step; is the step length along the length of the pipeline; is the gas flow rate; is the gas sound speed; When using one-dimensional thermodynamic simulation software to calculate internal combustion engine performance, the following discretization lengths are generally used: intake system discretization length ≈ 0.4xD; exhaust system discretization length ≈ 0.55xD. As gas flows through the intake and exhaust ducts, friction between the gas and the duct walls causes a loss of gas pressure. The magnitude of this friction coefficient is affected by the Reynolds number and the roughness of the duct walls. When the wall of the intake and exhaust duct is smooth, the calculation formula of the friction coefficient C is as follows: Where: is the Reynolds number; When the wall surface of the intake and exhaust pipes is rough, the friction coefficient Increase, and use Nikuradse formula to correct the friction coefficient as follows: Where: is the equivalent diameter of the intake and exhaust pipes; is the height of the pipe wall roughness; When there are bends in the intake and exhaust pipes or the cross-section of the pipe is irregular, the airflow pressure in the pipe will be lost. The pressure loss coefficient is used to represent the degree of loss as follows: Where: is the total inlet pressure of the intake and exhaust pipes; is the total outlet pressure of the intake and exhaust pipes; is the inlet gas density of the intake and exhaust ducts; is the inlet gas velocity of the intake and exhaust ducts; In the intake and exhaust system, when the gas flows in the pipe, heat transfer occurs between the gas and the pipe wall. The heat transfer coefficient as follows: 。 5. The method for optimizing the non-uniformity of exhaust temperature of each cylinder of an engine according to claim 4, characterized in that: The turbocharger system calculation model is as follows: The original turbocharger is composed of a centrifugal compressor and a radial turbine. In an exhaust gas turbocharger engine, the exhaust energy discharged from the engine cylinder is converted into mechanical work by the turbine, driving the compressor impeller coaxial with the turbine to rotate. In the compressor, mechanical work is used to compress the fresh air, providing sufficient air density for combustion work in the engine cylinder. Therefore, the turbocharger system calculation model needs to meet the following three balance conditions: The power balance condition requires that the average output power of the turbine and the average power consumption of the compressor Equal, such as: Since the exhaust gas mass flow rate flowing through the turbine and the exhaust gas enthalpy difference before and after entering the turbine jointly determine the average output power of the turbine, and usually, the loss of the turbocharger is included in the average output power of the turbine, The relevant calculation formula is as follows: Where: is the exhaust gas mass flow rate passing through the turbine; is the mechanical efficiency of the turbocharger system; are the enthalpy values at the turbine inlet and outlet, respectively; is the isentropic efficiency of the turbine; is the average constant-pressure specific heat of the turbine; Turbine inlet temperature; is the turbine expansion ratio; Since the mass flow of air flowing through the compressor and the enthalpy difference of air before and after entering the compressor jointly determine the average power consumption of the compressor, The relevant calculation formula is as follows: Where: is the air mass flow rate flowing through the compressor; are the enthalpy values at the compressor inlet and outlet respectively; is the isentropic efficiency of the compressor; is the average constant-pressure specific heat of the compressor; is the compressor inlet temperature; is the compressor pressure ratio; The overall efficiency formula for a turbocharger is as follows: Speed balance condition, requiring turbine speed and compressor speed equal: In the case of unstable engine operation, the moment of inertia of the turbocharger rotor must be Take into account, to obtain the turbocharger rotor angular velocity The specific calculation formula is: The mass balance condition requires that the gas mass flow rates in the turbine and compressor be equal: Where: is the mass flow rate of exhaust gas flowing through the wastegate valve; is the mass flow rate of fuel, which is generally negligible.

6. The method for optimizing the non-uniformity of exhaust temperature of each cylinder of an engine according to claim 5, characterized in that: The error range between the actual data and the simulation data should be less than 10%.

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