Dynamic working condition based on quantitative relationship analysis of thermal management method for vehicle diesel engine

Abstract

The present application relates to a kind of dynamic working condition based on quantification relation analysis of diesel engine thermal management method for vehicle, based on the actual control and operating parameter in the dynamic running process of diesel engine for vehicle to predict the in-cylinder combustion process of diesel engine, working medium pressure and temperature variation history, heat load and exhaust temperature of combustion chamber, to define the cooling demand of combustion chamber under dynamic working condition, exhaust temperature to obtain the cooling demand of EGR, the cooling demand of supercharged air, and the cooling demand of oil, combustion chamber cooling medium;Again based on the heat flow between in-cylinder working medium and the inner wall of combustion chamber, the change between combustion chamber wall temperature and inflow, outflow heat flow, the quantification relation between cooling medium temperature rise and flow, based on the cooling demand of each subcooling system, the heat load of generalized thermal management system including combustion chamber and traditional subcooling system and the precise intelligent management of cooling medium flow are accurately managed.

Description

Technical Field

[0001] This invention relates to the field of diesel engine technology, and in particular to a thermal management method for automotive diesel engines based on quantitative relationship analysis under dynamic operating conditions. Background Technology

[0002] The matching and optimization of various subsystems of a diesel engine, including the in-cylinder combustion and heat conversion system, and the cooling and lubrication systems, are achieved on a diesel engine test bench when the engine is operating under hot and steady-state conditions, with each control and operating parameter at its optimal matching state. When the in-cylinder combustion and heat conversion process deviates from this state due to some factor, the amount of heat exchange between the working fluid and the combustion chamber wall, the exhaust temperature, the in-cylinder pressure, and the piston force (as well as the piston ring / cylinder liner friction) will all change accordingly. If the control and operating parameters of the cooling and lubrication systems are still controlled according to the test bench hot-engine and steady-state calibration results without adaptive adjustments, the thermal load between various components of the diesel engine will often deviate from its optimal value, leading to performance degradation. For example, when the diesel engine is in the cold start hot-engine process, the temperature of the working fluid in the cylinder and the combustion chamber wall temperature are very different from the hot-engine and steady-state calibration conditions. At this time, the control strategy for the combustion chamber coolant flow rate must be adjusted accordingly. Another example is that under vehicle-mounted variable operating conditions, even if the diesel engine speed and the cyclic injection quantity (load) are the same as the hot-engine and steady-state conditions, if the actual excess air coefficient or EGR rate is different, the temperature and pressure of the working fluid in the cylinder are often very different from the test bench hot-engine and steady-state conditions at the same speed and load. At this time, the control strategy for the combustion chamber coolant should also be adjusted accordingly, otherwise it will lead to over-cooling or under-cooling of the combustion chamber. The heat load in the EGR cooler, turbo intercooler, and vehicle radiator will vary due to the different temperatures of the working fluid in the cylinder. If the coolant flow of these components is not adjusted accordingly, the cooling of these components will deviate from the steady-state calibration results, resulting in over-cooling or insufficient cooling capacity.

[0003] Therefore, the heat load and cooling requirements of traditional diesel engine cooling system components largely depend on the combustion and heat-to-work conversion process within the cylinder. In other words, the combustion and heat-to-work conversion process within the diesel engine cylinder is the heat source for all relevant components of the cooling system. However, under dynamic vehicle operating conditions, the key control and operating parameters that play a crucial role in the combustion and heat-to-work conversion process within the diesel engine cylinder often cannot be operated entirely according to the calibration results under the same speed and load (cycle injection quantity) under steady-state test conditions. For example, the EGR flow rate and turbocharger pressure under dynamic conditions often change before reaching steady-state conditions. That is, the diesel engine's operating state under vehicle operating conditions, especially the in-cylinder process, often differs significantly from the calibrated state under steady-state conditions. This necessitates real-time adjustments to some key control and operating parameters based on the actual operating conditions of the diesel engine.

[0004] Current intelligent thermal management methods refer to those targeting different operating conditions (cycles) and application scenarios (environmental conditions and diesel engine hot / cold states), using bench steady-state calibration results as the tracking target. However, due to the numerous and interdependent control and operating parameters of diesel engines, multi-parameter optimization based on detailed diesel engine mechanism models requires significant computational power and long execution time, failing to meet the control requirements of rapidly changing automotive diesel engine operating conditions. Consequently, current "intelligent" thermal management technologies are limited to smaller subsystems within the diesel engine thermal management system, such as the cooling subsystem composed of fans and water pumps, and are based on a "quasi-static" matching method using bench steady-state calibration map interpolation. Since the actual control and operating parameters of diesel engines under dynamic conditions often deviate from the steady-state calibration map, this "quasi-static" matching method using bench steady-state calibration map interpolation often deviates from the optimal matching state of each subsystem. Currently, no intelligent thermal management method has been developed that can meet the needs of a generalized diesel engine thermal management system—that is, one that includes both combustion and cooling subsystems and is adaptable to dynamic vehicle operating conditions. Summary of the Invention

[0005] This invention provides a thermal management method for automotive diesel engines based on quantitative relationship analysis under dynamic operating conditions, characterized in that the method includes the following steps:

[0006] Step 1: Input the engine's cylinder bore, stroke, displacement, valve timing, and other structural and design parameters required for simulation, as well as the thermal management objectives for this experiment;

[0007] Step 2: Read the engine control parameters and operating parameters required for in-cylinder process calculations under this operating condition from the ECU;

[0008] Step 3: Based on the obtained engine design parameters, actual parameters, and operating parameters, update the characteristic parameters of the engine's in-cylinder combustion process and the combustion heat release rate-crankshaft angle curve; and predict the changes in working fluid pressure and temperature in a complete cycle to calculate the engine's in-cylinder indicated performance.

[0009] Step 4: Calculate the cumulative heat flow between the working fluid and the combustion chamber wall, and the cumulative heat flow between the outer wall of the combustion chamber and the cooling medium in the cycle, based on the full-cycle pressure and temperature curve of the working fluid in the cylinder.

[0010] Step 5: After calculating and defining the in-cylinder heat load, heat flow, wall temperature, and cooling requirements, the heat load, cooling medium flow, and power consumption of each sub-cooling system of the engine are defined with the in-cylinder as the heat source.

[0011] Step 6: Input the control parameters required for the engine thermal management system obtained from the above matching and optimization steps into the engine ECU to implement control, and repeat steps 2-6 to implement control for the next operating condition.

[0012] Furthermore, step 3 also includes the following steps:

[0013] Step 31: Define the control equation for the internal combustion engine cylinder pressure rise and temperature rise, use the Weber function to describe it based on the crankshaft angle position, and generate the combustion heat release rate-crankshaft angle curve;

[0014] Step 32, Calculation of characteristic parameters of the in-cylinder combustion heat release process;

[0015] The characteristic parameters of the in-cylinder combustion heat release process include RGF, CA50 and CA10-90;

[0016] Step 33: Establish a cycle with the crankshaft rotating 720°, and update the characteristic parameters of the in-cylinder combustion process corresponding to each crankshaft angle in the cycle, as well as the instantaneous pressure and temperature of the working fluid in the cylinder, through the combustion heat release rate-crankshaft angle curve.

[0017] Furthermore, in step 31, the governing equations include:

[0018] The cylinder pressure change rate of the diesel engine is:

[0019]

[0020] Instantaneous pressure rise rate of gas inside the cylinder, This refers to the specific heat ratio of the gas inside the cylinder. Instantaneous cylinder volume, This refers to the cylinder pressure when the intake valve is closed. This refers to the cylinder volume when the intake valve is closed. This refers to the cylinder temperature when the intake valve is closed. Let be the gas state constant. The air-fuel ratio of fuel. The excess air coefficient of the air-fuel mixture. This refers to the ratio of the combusted gas from the previous cycle remaining in the cylinder when the intake valve is closed, relative to the total gas volume. The calorific value of fuel oil. In-cylinder combustion efficiency Dimensionless combustion heat release rate The heat exchange rate between the gas inside the cylinder and the walls of the combustion chamber;

[0021] Instantaneous cylinder pressure can be calculated by sequentially increasing the crankshaft angle:

[0022]

[0023] The dynamic pressure inside the cylinder increases to ( ) at the crankshaft angle. The instantaneous pressure corresponding to the position. For the dynamic pressure inside the cylinder at the crankshaft angle of The instantaneous pressure corresponding to the location. This represents the change in crankshaft rotation angle.

[0024] Integrating the high-pressure and low-pressure cycles of the diesel engine yields the average indicated pressure and indicated thermal efficiency of the high-pressure cycle:

[0025]

[0026]

[0027]

[0028] This refers to the average indicated pressure of the engine's high-pressure cycle. Here, PMEP represents the average indicated pressure of the engine's low-pressure cycle, and PMEP represents the pumping losses during the engine's low-pressure cycle. This refers to the displacement of a single engine cylinder. The indicated thermal efficiency of the engine's high-pressure cycle. This refers to the amount of fuel injected during the cycle.

[0029] The instantaneous temperature rise rate inside the cylinder can also be calculated:

[0030]

[0031] Instantaneous temperature rise rate of the gas inside the cylinder, Total mass of gas inside the cylinder;

[0032] Instantaneous cylinder temperature can also be calculated by progressively increasing the crankshaft angle:

[0033]

[0034] The in-cylinder dynamic temperature increases to ( ) at crankshaft angle. The instantaneous cylinder temperature corresponding to the position.

[0035] Furthermore, in step 31, the dimensionless combustion heat release rate is expressed using a Weber function as follows:

[0036]

[0037] The crankshaft angle corresponding to the start of combustion; The combustion duration is the difference between the initial and final crankshaft rotation angles. Combustion quality parameters used to characterize the shape of the combustion heat release rate curve; This refers to the crankshaft rotation angle.

[0038] Furthermore, step 32 also includes the following steps:

[0039] Step 321: Determine the combustion duration and the combustion efficiency corresponding to the combustion start point;

[0040] Among them, the crankshaft rotation angle corresponding to the combustion start point Combustion duration as a function of the difference between the initial and final crankshaft rotation angles. The relationship is:

[0041]

[0042]

[0043]

[0044] The crankshaft angle corresponding to the end of combustion. The combustion duration is from 10% to 90% combustion. This represents the crankshaft angle position when 50% of the heat released during combustion.

[0045] The 10-90% combustion duration and 50% combustion point of a gasoline engine can be further expressed as functions of engine speed, in-cylinder residual exhaust gas coefficient, excess air coefficient, and ignition advance angle.

[0046] Crankshaft angle position when combustion releases 50% of its heat for:

[0047]

[0048] This refers to the advance angle for ignition or fuel injection. The duration of combustion from the moment of ignition until 50% of the fuel is burned;

[0049]

[0050] - These are the coefficients representing the relationship between CA50 and each parameter after linear fitting. It is a constant representing 50% of the combustion duration, and this constant is related to the engine's structural parameters;

[0051] Combustion duration from 10% to 90% combustion for:

[0052]

[0053] - After linear fitting The coefficients relating to each parameter It is a constant representing 10%-90% of the combustion duration, and this constant is related to the engine's structural parameters;

[0054] Step 322: Determine the RGF within the diesel engine cylinder;

[0055]

[0056] RGF is the ratio of the burned gas from the previous cycle remaining in the cylinder when the intake valve is closed, and EGR is the exhaust gas recirculation rate. This refers to the exhaust pressure of the diesel engine. This refers to the intake pressure of the diesel engine. This refers to the diesel engine speed. The overlap angle between the intake and exhaust valves.

[0057] Furthermore, step 4 also includes the following steps:

[0058] Step 41: Calculate the heat exchange between the in-cylinder gas and the combustion chamber cooling medium, as well as the heat load of the combustion chamber;

[0059] Step 42: Calculate the combustion chamber wall temperature and the heat flow carried away by the combustion chamber coolant by the surface temperature change of the combustion chamber wall in adjacent cycles, and calculate the change of combustion chamber wall temperature and update the wall temperature for calculating the next operating condition;

[0060] In step 41, the thermal conductivity between the combustion chamber and the outer wall surface is calculated:

[0061]

[0062] K represents the thermal conductivity between the inner and outer walls of the combustion chamber, where K is the thermal conductivity of the combustion chamber wall material. The thickness of the combustion chamber wall. The instantaneous heat conduction area between the combustion chamber and the outer wall surface. The temperature of the combustion chamber wall. The temperature of the outer wall of the combustion chamber;

[0063] Calculate the convective heat transfer rate between the outer wall of the combustion chamber and the cooling medium:

[0064]

[0065] The heat exchange rate between the outer wall of the combustion chamber and the cooling medium. The heat transfer area of ​​the outer wall of the combustion chamber. The liquid-solid convection heat transfer coefficient between the outer wall of the combustion chamber and the coolant can be expressed as a single-valued function of the coolant flow rate. The specific quantitative relationship must be based on the specific cooling channel design and solved through CFD simulation calculations.

[0066]

[0067] This refers to the volumetric flow rate of the cooling medium.

[0068] In step 42, the heat transferred from the outer wall of the combustion chamber to the cooling medium within a cycle:

[0069]

[0070] in, The liquid-solid convective heat transfer coefficient between the outer wall of the combustion chamber and the coolant. For heat exchange contact area, To reduce the outdoor wall temperature of the combustion chamber, The average temperature of the coolant on the outer wall of the combustion chamber;

[0071] The heat flow carried away by the combustion chamber coolant is:

[0072]

[0073] Heat flow carried away by the combustion chamber coolant (W); n: diesel engine speed (r / min).

[0074] Combustion chamber coolant outlet temperature:

[0075]

[0076] In the formula, The temperature of the coolant at the combustion chamber outlet. This refers to the temperature of the coolant at the combustion chamber inlet. The density of the coolant, This refers to the specific heat at constant pressure of the coolant.

[0077] Furthermore, in step 4, the heat exchange between the working fluid in the cylinder and the combustion chamber wall is divided into two types: convective heat release and radiative heat release, and the heat exchange is the sum of the two:

[0078]

[0079] The convective heat transfer rate between the gas inside the cylinder and the wall of the combustion chamber; The radiative heat transfer rate between the gas inside the cylinder and the wall of the combustion chamber;

[0080] Convective heat transfer between the in-cylinder gas and the combustion chamber walls:

[0081]

[0082] The heat transfer area between the gas inside the cylinder and the combustion chamber wall. The temperature of the combustion chamber wall, This is the heat transfer coefficient between the gas inside the cylinder and the combustion chamber wall;

[0083] The heat released by the gas radiating to the combustion chamber wall can be expressed by the following formula:

[0084]

[0085] In the formula, The emissivity is the heat transfer coefficient between the gas and the combustion chamber wall. For the Stef-Boltzmann constant, This represents the instantaneous contact area between the working fluid and the combustion chamber. The instantaneous temperature of the working fluid. The temperature of the combustion chamber wall;

[0086] Given the diesel engine speed and load, the FMEP value is obtained from the table, thereby estimating the frictional heat generated between the piston rings and the cylinder wall:

[0087]

[0088] In the formula, FMEP represents the heat flux generated by friction between the engine piston rings and cylinder walls, while FMEP represents the mean effective pressure of frictional losses and accessory losses of the moving parts of the diesel engine. Cylinder displacement;

[0089] The convective heat transfer between the working fluid in the cylinder and the combustion chamber wall in one cycle is:

[0090]

[0091] The convective heat transfer from the working fluid in the cylinder to the combustion chamber wall during a cycle;

[0092] The amount of heat released by the radiative reaction between the working fluid in the cylinder and the combustion chamber wall during one cycle is:

[0093]

[0094] This refers to the heat released by the gas through radiation to the combustion chamber wall during one cycle. This represents the average contact area between the working fluid and the combustion chamber in the cycle. The average temperature of the gas in the cycle. This refers to the average wall temperature of the combustion chamber during the cycle.

[0095] The heat generated by friction between the piston rings and the cylinder wall during one cycle is:

[0096]

[0097] This refers to the heat generated by friction between the piston rings and the cylinder wall during one cycle.

[0098] The net heat absorbed by the combustion chamber wall material in this cycle:

[0099]

[0100] The change in combustion chamber wall temperature during this cycle:

[0101]

[0102] Combustion chamber wall temperature at the start of the next operating condition:

[0103]

[0104]

[0105] The combustion chamber wall temperature for the next operating condition. The combustion chamber wall temperature under current operating conditions. The combustion chamber outer wall temperature for the next operating condition. This represents the temperature of the outer wall of the combustion chamber under the current operating conditions.

[0106] Furthermore, in step 5, the sub-cooling system includes a turbocharger intercooler, an EGR cooler, an oil cooler, and a vehicle radiator;

[0107] The heat load and required coolant flow rate of the turbocharged intercooler are as follows:

[0108]

[0109] The volumetric flow rate of the cooling medium in the intercooler. The mass flow rate of fresh air. The specific heat at constant pressure of fresh air. The density of the cooling medium in the intercooler. The specific heat at constant pressure of the cooling medium in the intercooler. This refers to the outlet temperature of the cooling medium in the intercooler. This refers to the inlet temperature of the cooling medium in the intercooler. This refers to the inlet temperature of the fresh air to the intercooler. The outlet temperature of the fresh air in the intercooler;

[0110] The heat load and required coolant flow rate of the EGR cooler are as follows:

[0111]

[0112] In the formula, The mass flow rate of EGR gas. The specific heat at constant pressure of EGR fuel gas. This refers to the volumetric flow rate of the cooling medium in the EGR cooler. The density of the cooling medium in the EGR cooler. The specific heat at constant pressure of the cooling medium in the EGR cooler. The outlet temperature of the cooling medium in the EGR cooler. The inlet temperature of the cooling medium for the EGR cooler. The inlet temperature of the gas for the EGR cooler. The outlet temperature of the gas in the EGR cooler;

[0113] The heat load and required coolant flow rate of the oil cooler are as follows:

[0114]

[0115] This refers to the mass flow rate of the engine oil. The specific heat at constant pressure of engine oil. This refers to the volumetric flow rate of the cooling medium in the oil cooler. The density of the cooling medium in the oil cooler. The specific heat at constant pressure of the cooling medium in an oil cooler. This refers to the outlet temperature of the cooling medium in the oil cooler. This refers to the inlet temperature of the engine oil in the oil cooler. This refers to the outlet temperature of the engine oil in the oil cooler. This refers to the inlet temperature of the cooling medium in the oil cooler.

[0116] Furthermore, in step 5, the vehicle radiator is used to dissipate heat for the turbocharger intercooler, EGR cooler, oil cooler, and combustion chamber cooler, and the volumetric flow rate of the cooling air required by the radiator fan is:

[0117]

[0118] The mass flow rate of the medium being cooled in the radiator. The specific heat at constant pressure of the medium cooled by the radiator; The volumetric flow rate of cooling air required by the radiator fan. The density of the cooling air supplied to the radiator fan. The specific heat at constant pressure of the cooling air supplied to the radiator fan. The outlet temperature of the radiator air. The temperature of the cooled medium at the radiator inlet. The temperature of the medium to be cooled at the radiator outlet. This is the inlet temperature of the air in the radiator.

[0119] The beneficial effects achieved by this invention are:

[0120] This invention predicts the in-cylinder combustion process based on the actual control and operating parameters of a diesel engine under dynamic vehicle conditions, and then predicts the pressure and temperature changes of the working fluid in the cylinder. Based on this, it updates the heat flow between the working fluid in the cylinder and the combustion chamber wall and the exhaust temperature in real time, achieving more precise intelligent management.

[0121] This invention uses the heat load and heat transfer of the diesel engine combustion chamber wall as a heat source to define the heat load and cooling requirements of various related components of the diesel engine. For example, the cooling requirement of the combustion chamber comes from the heat flow between the working fluid in the cylinder and the inner wall of the combustion chamber and the wall temperature of the combustion chamber; the heat load and cooling requirement of the EGR cooler depends on the EGR flow rate and the exhaust temperature of the diesel engine; the cooling requirement of the turbocharger intercooler depends on the turbocharger pressure of the diesel engine, the compressor efficiency, and the desired temperature after intercooling; the cooling requirement of the outer wall of the combustion chamber comes from the heat flow between the working fluid in the cylinder and the inner wall of the combustion chamber, and the friction loss between the piston rings and the cylinder wall; the heat load and cooling requirement of the vehicle radiator are related to the above items, thus linking the heat load and cooling requirements of the diesel engine combustion chamber and related sub-cooling systems to the in-cylinder process to obtain more accurate cooling requirements.

[0122] After defining the heat load and cooling requirements of each relevant subsystem of the diesel engine in this invention, the flow control target of the cooling medium in each cooling / heat dissipation component is accurately calculated based on the quantitative equation between the flow rate of the cooling medium in each cooler and radiator, the heat flow rate carried away, and the inlet and outlet temperatures.

[0123] The calculation methods proposed in this invention for in-cylinder pressure, temperature, heat flow, cooling medium flow, and temperature rise rate are based either on energy and mass conservation equations or on empirical equations derived from measured parameters through induction, summarization, and refinement, ensuring calculation accuracy. Since most numerical models are based on explicit formulas and do not require iterative calculations, the calculation speed is fast, making it applicable to the dynamic control and dynamic simulation and optimization of operating parameters of diesel engine thermal management systems under real vehicle conditions. Attached Figure Description

[0124] Figure 1 This is a flowchart of the thermal management method for automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis provided in an embodiment of the present invention;

[0125] Figure 2 This is a flowchart illustrating the calculation of the performance of the in-cylinder heat-work conversion process, combustion chamber heat load, and cooling requirements of a vehicle diesel engine in a dynamic operating condition-based thermal management method based on quantitative relationship analysis, provided in an embodiment of the present invention.

[0126] Figure 3 This is a flowchart of the thermal load and flow control of a diesel engine cooling system sub-component in the dynamic operating condition-based quantitative relationship analysis method for automotive diesel engine thermal management provided in this embodiment of the invention. Detailed Implementation

[0127] The technical solution of the present invention will be described in more detail below with reference to the accompanying drawings. The present invention includes, but is not limited to, the following embodiments.

[0128] This invention proposes a dynamic operating condition-based thermal management method for automotive diesel engines, using the actual in-cylinder combustion and heat-work conversion process as the heat source. It requires memory and processing speed suitable for on-board use, encompassing a broad diesel engine thermal management system covering both in-cylinder combustion and external cooling systems, and is characterized by dynamic matching optimization. The technical approach is as follows: First, based on the analysis, refinement, and secondary development of numerous diesel engine bench performance benchmark test results, clear quantitative relationship equations are derived between the characteristic parameters of in-cylinder combustion heat release and gas-wall heat exchange processes and diesel engine control and operating parameters, such as engine speed, intake pressure, excess air coefficient, in-cylinder residual exhaust gas coefficient, and injection advance angle. Second, based on in-cylinder energy conservation, mass conservation, and gas state equations, quantitative relationship equations are developed between in-cylinder working fluid pressure and temperature and in-cylinder combustion, heat transfer, and control and operating parameters. On this basis, based on the diesel engine... The control and operating parameters of the diesel engine obtained during actual operation are used to predict the combustion and heat transfer processes in the cylinder, as well as the pressure and temperature of the working fluid. Based on this, the heat flow rate through the combustion chamber and the exhaust temperature are calculated to define the heat load and cooling requirements of the combustion chamber, the EGR cooling system, the turbocharger intercooler system, the oil cooling system, and the cooling medium heat dissipation system. After obtaining the heat load and cooling requirements of the combustion chamber and each heat dissipation subsystem, the flow control target of the cooling medium can be accurately obtained based on the quantitative relationship equation between the heat dissipation of each subsystem and the flow rate and temperature rise of the cooling medium.

[0129] The diesel engine generalized thermal management system involved in this invention includes heat dissipation components such as a combustion chamber, a diesel engine combustion chamber cooling system, a turbocharger intercooler, an EGR cooler, an oil cooler, and a vehicle radiator;

[0130] The pre-set heat load and temperature control targets for the cooling system include the combustion chamber wall temperature, the fresh air outlet temperature of the turbocharger intercooler, the EGR gas outlet temperature, and the outlet temperature of the cooling medium for each cooler and radiator. The control parameters for the thermal management system include the flow rate and power consumption of the coolant pump, oil pump, and cooling fan.

[0131] The main control and operating parameters of the diesel engine operation process that need to be measured or read from the ECU include boost pressure, excess air coefficient, fuel injection quantity, injection timing, EGR rate, exhaust gas turbine bleed valve opening or VNT position, etc.

[0132] As attached Figure 1 As shown, to achieve the above functions, the present invention includes the following steps:

[0133] Step 1: Input the engine's cylinder bore, stroke, displacement, valve timing, and other structural and design parameters required for simulation, as well as the thermal management objectives for this experiment.

[0134] The system pre-sets whether the diesel engine uses a cold start, full MAP equivalent cooling, or on-board dynamic operating conditions for intelligent matching of the thermal management system; it defines the parameters that need to be controlled or optimized during engine operation, including the maximum wall temperature limit of the combustion chamber, the outlet temperature target of the cooled medium in each cooling subsystem, and the outlet temperature limit of the coolant in each cooling subsystem.

[0135] Step 2: Read the engine control and operating parameters required for in-cylinder process calculations under this operating condition from the ECU, including: engine speed, boost pressure, actual excess air coefficient, actual EGR rate, cyclic injection quantity, injection advance angle, intake valve closing time, etc. Each operating condition includes multiple cycles with the same parameters and an engine crankshaft angle of 720°.

[0136] Step 3: Based on the acquired actual control and operating parameters of the engine, first update the characteristic parameters of the in-cylinder combustion process and the combustion heat release rate-crankshaft angle curve; then predict the change law of working fluid pressure and temperature in a complete cycle, and calculate the in-cylinder indicated performance of the engine accordingly; since the heat exchange rate between the working fluid and the combustion chamber wall affects the cylinder pressure and cylinder temperature of the working fluid, but the pressure and temperature of the working fluid in turn affect the heat transfer coefficient and thermal radiation rate between the working fluid and the combustion chamber wall, iterative calculations are required between the pressure, temperature and heat exchange rate between the working fluid and the cylinder wall;

[0137] Step 31: Define the control equations for the increase in cylinder pressure and temperature of the internal combustion engine;

[0138] A diesel engine is a heat-to-work conversion device that converts the chemical energy of fuel into heat energy by burning an air-fuel mixture in the cylinder. This heat energy heats the gas, increasing its temperature and pressure, which in turn drives the piston to expand and perform work. The heat-to-work conversion process within the diesel engine cylinder can be described based on the conservation of energy and mass within the cylinder, as well as the equation of state for an ideal gas.

[0139] The rate of change of cylinder pressure in a diesel engine can be solved by simultaneously applying the laws of conservation of in-cylinder energy, conservation of mass, and the ideal gas law:

[0140] (1)

[0141] Instantaneous cylinder pressure can be obtained by successively increasing the crankshaft angle:

[0142] (2)

[0143] Integrating the high-pressure and low-pressure cycles of a diesel engine yields the average indicated pressure of the high-pressure cycle and the indicated thermal efficiency of the high-pressure cycle.

[0144] (3)

[0145] (4)

[0146] (5)

[0147] Similarly, the instantaneous temperature rise rate inside the cylinder can also be solved:

[0148] (6)

[0149] Instantaneous cylinder temperature can also be obtained by progressively increasing the crankshaft angle:

[0150] (7)

[0151] In the above formulas: Instantaneous pressure rise rate of gas in cylinder (Pa / °CA); Instantaneous pressure of gas inside the cylinder (Pa); Instantaneous cylinder volume ( ); This is the cylinder pressure (Pa) when the intake valve is closed. The cylinder volume when the intake valve is closed ( ), The cylinder temperature (K) when the intake valve is closed; : Dimensionless combustion heat release rate (1 / °CA); : Heat exchange rate between in-cylinder gas and combustion chamber wall (J / °CA); Cylinder volume change rate ( / °CA); : Specific heat ratio of the gas inside the cylinder (-); Instantaneous temperature rise rate of the gas inside the cylinder (K / °CA); Instantaneous temperature of gas inside the cylinder (K); : Total mass of gas in cylinder (kg); R: Gas state constant (J / kgK); : The average indicated pressure (Pa) of the engine high-pressure cycle; PMEP: Mean Indicated Pressure of Engine Low-Pressure Cycle and Pumping Loss (Pa) of Engine Low-Pressure Cycle; Indicated thermal efficiency of engine high-pressure cycle (-); : Calorific value of fuel oil (J / kg); : Circulating fuel injection quantity (kg); Engine single-cylinder displacement ( ); In-cylinder combustion efficiency (-); : Excess air coefficient of the mixture (-); AFR0: Equivalent air-fuel ratio of the fuel (-).

[0152] As can be seen from the above equations, by obtaining the instantaneous pressure rise and temperature rise rate in the cylinder, and by progressively increasing the crankshaft angle position, the cylinder pressure and cylinder temperature at each crankshaft angle position in the entire cycle can be obtained. Integrating these values ​​yields the in-cylinder performance parameters such as indicated work, average indicated pressure, and indicated thermal efficiency for the entire cycle. It also provides the parameters that characterize in-cylinder NVH and source emissions, including the highest combustion pressure, maximum pressure rise rate, highest combustion temperature, and average temperature during combustion.

[0153] However, as can be seen from equations (1) and (6), in order to solve the pressure and temperature of the working fluid in the cylinder, in addition to accurately obtaining relevant operating parameters such as the cylinder pressure, temperature, cylinder volume, total mass of gas in the cylinder, residual exhaust gas coefficient, excess air coefficient, etc. when the intake valve is closed, it is also necessary to know the combustion heat release rate of the working fluid in the cylinder and the heat flow between the working fluid and the combustion chamber wall.

[0154] The following focuses on describing the combustion heat release rate of the working fluid in the cylinder and the calculation method of the heat flow between the working fluid and the combustion chamber wall.

[0155] For the purpose of in-cylinder performance simulation, the combustion heat release process in the cylinder of an internal combustion engine can be described by the Weber function, which updates the combustion heat release rate based on the crankshaft angle position.

[0156] For homogeneous mixture spark-ignition gasoline or gas engines, a single Weber equation can usually be used to describe them; while for heterogeneous mixture compression ignition internal combustion engines (diesel engines belong to this category), a three-stage Weber function of pre-combustion, main combustion, and aftercombustion is usually required to describe them.

[0157] The basic form of the Weber function is:

[0158] (8)

[0159] In the formula: : Crankshaft rotation angle (°CA·BTDC) corresponding to the combustion start point; : The combustion duration (°CA) is the difference between the initial and final crankshaft rotation angles. : Combustion quality parameters characterizing the shape of the combustion heat release rate curve (-). For homogeneous air-fuel spark-ignition gasoline engines, The value is around 2.0; for heterogeneous mixture compression ignition diesel engines, the values ​​for the three stages of pre-combustion, main combustion, and aftercombustion are different, and are usually determined based on the analysis results of the measured cylinder pressure curves in the bench test of the diesel engine.

[0160] Step 32, Calculation of characteristic parameters of the in-cylinder combustion heat release process;

[0161] The characteristic parameters of the in-cylinder combustion heat release process include combustion parameters such as RGF, CA50 and CA10-90, combustion duration and combustion efficiency corresponding to the combustion start point, and combustion heat release rate.

[0162] Step 321: Determine the combustion duration and the combustion efficiency corresponding to the combustion start point;

[0163] The crankshaft angles corresponding to the absolute start and end points of combustion in an internal combustion engine are often difficult to determine. In practice, the crankshaft angle at 10% heat release during combustion is often used to represent the actual start point of combustion, and the crankshaft angle at 90% heat release is used to represent the actual end point of combustion. That is, the combustion duration from 10% to 90% (CA10-90) is usually used instead of the combustion duration from 0% to 100% (CA0-100); simultaneously, the crankshaft angle position at 50% heat release (CA50), rather than the combustion start point (CA0), is used as the characteristic value of the combustion process phase. The conversion relationships between these characteristic parameters are as follows:

[0164] (9)

[0165] (10)

[0166] (11)

[0167] This is the crankshaft angle corresponding to the end of combustion.

[0168] Equations (9) and (10) express the combustion duration and combustion start point required to solve the Weber combustion function as a relationship with the typical and general 10-90% combustion duration and 50% combustion point position.

[0169] The team's preliminary research shows that the 10-90% combustion duration and 50% combustion point of a gasoline engine can be further expressed as functions of parameters such as engine speed, in-cylinder residual exhaust gas coefficient, excess air coefficient, and ignition advance angle, as shown in equations (12), (13), and (14). Similarly, the characteristic parameters of each stage of the three-stage combustion of a diesel engine can also be expressed in a similar form. The value of the constant term in the equation needs to be obtained based on regression analysis of a large number of combustion heat release rate curves measured in bench steady-state tests.

[0170] The crankshaft angle at the 50% combustion point is equal to the crankshaft angle corresponding to the ignition (or injection) moment, plus the combustion duration from the ignition (or injection) moment until 50% of the fuel is burned, i.e.:

[0171] (12)

[0172] In the formula, CA50: 50% ignition point position (°CA·ATDC); : Ignition or injection advance angle (°CA·BTDC); The combustion duration (°CA) from the moment of ignition (or injection) until 50% of the fuel is burned can be expressed by the following equation:

[0173] (13)

[0174] Similarly, the 10-90% combustion duration can also be expressed as a function of parameters such as engine speed, in-cylinder residual exhaust gas coefficient, excess air coefficient, and ignition or injection advance angle.

[0175] (14)

[0176] Of the parameters that affect the crankshaft angle position at 50% of the combustion point and the duration of combustion from 10% to 90%, all except the residual exhaust gas coefficient in the cylinder are control and operating parameters that can be directly read from the ECU or obtained through direct testing.

[0177] Step 322: Determine the RGF within the diesel engine cylinder;

[0178] The residual exhaust gas coefficient within an internal combustion engine cylinder can be measured relatively accurately based on parameters such as the external EGR rate, the intake and exhaust pressure difference, the timing and overlap of the intake and exhaust valves, and the engine speed.

[0179] (15)

[0180] In the above formula, RGF: the ratio of the burned gas from the previous cycle remaining in the cylinder when the intake valve is closed (-); EGR: exhaust gas recirculation rate (-). Diesel engine exhaust port pressure (Pa); Diesel engine intake pressure (Pa); Diesel engine speed (rpm); : Intake and exhaust valve overlap angle (°CA).

[0181] Step 33: Establish a cycle with the crankshaft rotating 720°, and update the characteristic parameters of the in-cylinder combustion process corresponding to each crankshaft angle in the cycle, as well as the instantaneous pressure and temperature of the working fluid in the cylinder, through the combustion heat release rate-crankshaft angle curve.

[0182] Step 4: After obtaining the full-cycle pressure and temperature curve of the working fluid in the cylinder, the cumulative heat flow between the working fluid and the combustion chamber wall, and the cumulative heat flow between the outer wall of the combustion chamber and the cooling medium in this cycle can be calculated. Based on this, the heat load of the combustion chamber wall and the wall temperature change pattern can be predicted. The relevant formulas involved in this calculation are detailed below, along with the appendix. Figure 2 ;

[0183] Step 41: Calculate the heat exchange between the in-cylinder gas and the combustion chamber cooling medium, as well as the heat load of the combustion chamber;

[0184] Equations (1) and (7) show that the instantaneous pressure rise and temperature rise rate in the cylinder are directly related to the instantaneous heat transfer rate between the working fluid in the cylinder and the combustion chamber wall: the more heat is lost from the working fluid to the combustion chamber wall, the lower the pressure rise rate and temperature rise rate of the engine, and vice versa. The heat exchange between the working fluid in the cylinder and the combustion chamber wall is divided into two types: convective heat release and radiative heat release, and the heat exchange is the sum of the two:

[0185] (16)

[0186] In the formula, : Convective heat transfer rate between the gas inside the cylinder and the wall of the combustion chamber (J / °CA); Radiative heat transfer rate between the gas inside the cylinder and the wall of the combustion chamber (J / °CA).

[0187] Calculate the convective heat transfer between the in-cylinder gas and the combustion chamber walls:

[0188] Convective heat transfer rate between in-cylinder gas and combustion chamber walls It is usually described using the formula: heat transfer coefficient * heat transfer area * temperature difference, i.e.:

[0189] (17)

[0190] In the formula, The heat transfer area between the gas inside the cylinder and the combustion chamber wall ( ); : Combustion chamber wall temperature (K); The heat transfer coefficient between the gas inside the cylinder and the combustion chamber wall (J / *K*°CA).

[0191] The convective heat transfer coefficient between the gas inside the cylinder of an internal combustion engine and the combustion chamber wall is usually calculated using the Woschni formula:

[0192] (18)

[0193] In the formula, B: Constant; Cylinder diameter (m); : A parameter characterizing the velocity of airflow within the cylinder, usually replaced by the average velocity of the piston (m / s).

[0194] Equations (17) and (18) show that the heat transfer coefficient and convective heat transfer rate between the gas in the cylinder and the combustion chamber wall are closely related to the instantaneous pressure and temperature of the gas in the cylinder. In order to accurately describe the heat loss of the gas in the cylinder and the heat load and cooling requirements of the combustion chamber, the changes in cylinder pressure and cylinder temperature must be updated in real time. The changes in cylinder pressure and cylinder temperature are related to the heat loss rate in the cylinder. Therefore, equations (17) and (18) need to be solved iteratively with equations (1) and (6).

[0195] Calculate the radiative heat transfer between the in-cylinder gas and the combustion chamber wall:

[0196] For diesel engines that produce particulate matter during combustion, in addition to the aforementioned convective heat transfer, radiative heat transfer also occurs between the gas and the combustion chamber wall. The amount of heat released radiated from the gas to the combustion chamber wall can be expressed by the following formula:

[0197] (19)

[0198] In the formula, : Emissivity of heat released by radiation between the gas and the combustion chamber wall (-); : Stef-Boltzmann constant: =5.67x10⁻⁸ (W / *K4); Instantaneous contact area between the working fluid and the combustion chamber ( ); : Instantaneous temperature (K) of the working fluid; : Temperature of the inner wall of the combustion chamber (K).

[0199] Calculate the heat generated by piston ring / cylinder liner friction:

[0200] Another portion of the heat transferred to the outside through the combustion chamber cylinder liner is the frictional heat generated between the piston rings and the cylinder liner. This portion of heat is generally considered to account for approximately 50% of the frictional and accessory losses (FMEP) of moving parts. To calculate the magnitude of this heat, the value of FMEP must first be determined. The FMEP of an engine is usually determined based on actual measurements and expressed as a function or graph of diesel engine speed and load. Therefore, given the diesel engine speed and load, the FMEP value can be obtained from a table, thereby estimating the frictional heat generated between the piston rings and the cylinder wall.

[0201] (20)

[0202] In the formula: Heat flow generated by friction between engine piston rings and cylinder wall (J / °CA); FMEP: Average effective pressure (Pa) of friction loss and accessory loss of moving parts in diesel engine. Cylinder displacement ( ).

[0203] Calculate the thermal conductivity between the inner and outer walls of the combustion chamber:

[0204] (twenty one)

[0205] In the formula: K: Thermal conductivity between the inner and outer walls of the combustion chamber (J / °CA); K: Thermal conductivity of the combustion chamber wall material (J*m / K*°CA); Combustion chamber wall thickness (m); Instantaneous heat transfer area between the combustion chamber and the outer wall surface ( ); : Combustion chamber wall temperature (K); : Temperature of the outer wall of the combustion chamber (K).

[0206] Calculate the convective heat transfer rate between the outer wall of the combustion chamber and the cooling medium:

[0207] (twenty two)

[0208] In the formula, : Heat exchange rate between the outer wall of the combustion chamber and the cooling medium (J / °CA); : Liquid-solid convective heat transfer coefficient between the outer wall of the combustion chamber and the coolant (J / *K*°CA), can be expressed as a single-valued function of coolant flow rate. The specific quantification relationship must be based on the specific cooling channel design and solved through CFD simulation calculations.

[0209] (twenty three)

[0210] The pressure difference generated by the cooling medium flowing through the combustion chamber is a square relationship with the volumetric flow rate (which also needs to be determined by CFD):

[0211] (twenty four)

[0212] The driving work of the combustion chamber cooling medium can be determined by the following formula:

[0213] (25)

[0214] In the formula, : The flow rate of the cooling medium through the outer wall of the combustion chamber ( / s); : Differential pressure of cooling medium flow on the outer wall of the combustion chamber (Pa); Heat transfer area of ​​the outer wall of the combustion chamber ( ); : Temperature of the outer wall of the combustion chamber (K); : Average temperature (K) of the coolant on the outer wall of the combustion chamber; : Drive power of cooling medium on the outer wall of the combustion chamber (W).

[0215] Calculate the overall heat transfer rate between the working fluid in the cylinder and the cooling medium in the combustion chamber, as well as the heat load on the combustion chamber walls:

[0216] Solving the above equations simultaneously, the overall heat exchange rate between the cylinder gas and the cooling medium on the outer wall of the combustion chamber can be expressed as:

[0217] (26)

[0218] Equation (23) shows that the actual heat flow rate transferred from the gas in the cylinder to the cooling medium is not only proportional to the temperature difference between the gas and the cooling medium, but also depends on the heat transfer coefficient between the gas in the cylinder and the combustion chamber wall. The thermal conductivity K of the combustion chamber wall and the heat transfer coefficient between the outer wall of the combustion chamber and the cooling medium. And the minimum value among the three plays a major role. Of the three: the heat transfer coefficient between the in-cylinder gas and the combustion chamber wall... It depends on the gas temperature, pressure, and relative velocity, as shown in equation (18); the thermal conductivity K / ΔX of the combustion chamber wall is a constant, and for metal combustion chamber wall materials, its value is much greater than and and Therefore, its influence on the heat transfer process between the gas and the cooling medium can be ignored. The size mainly depends on the flow rate of the cooling medium: the larger the flow rate of the cooling medium, the greater the... The larger the flow rate, the lower the resistance of the outer wall of the combustion chamber to the heat transfer process, the greater the heat carried away by the outer wall, and the lower the outer wall temperature of the combustion chamber. Conversely, the smaller the flow rate of the cooling medium, the lower the resistance of the outer wall. The smaller the flow rate, the greater the resistance of the outer wall of the combustion chamber to the heat transfer process, the less heat is carried away from the outer wall of the combustion chamber, and the higher the outer wall temperature of the combustion chamber. Therefore, by controlling the flow rate of the cooling medium on the outer wall of the combustion chamber, the combustion chamber wall temperature and the heat loss from the gas to the cooling medium can be controlled.

[0219] Step 42: Calculate the combustion chamber wall temperature by measuring the surface temperature change of the combustion chamber wall in adjacent cycles;

[0220] When the sum of the heat flows from the gas to the inner wall of the combustion chamber, i.e., the sum of equations (17) + (19) + (20), is not equal to the heat flows from the outer wall of the combustion chamber to the cooling medium, as shown in equation (22), the wall temperature of the combustion chamber will change. The rate of change of the combustion chamber wall temperature can be expressed as:

[0221] (27)

[0222] In the formula, : Temperature rise rate of combustion chamber wall (K / °CA); Mass of combustion chamber wall material (kg); Specific heat at constant volume of combustion chamber wall material (J / kg*K); : The rate of radiative heat release from the in-cylinder gas to the combustion chamber wall (J / °CA); : Rate of heat generation from friction between piston rings and cylinder liner (J / °CA).

[0223] Because the temperature and pressure of the working fluid in the cylinder change significantly within a working cycle, the temperature difference, heat transfer coefficient, and radiative heat release rate between the working fluid and the combustion chamber wall also change considerably. Solving for the wall temperature change using the difference form shown in equation (27) would be computationally intensive. Although the temperature change of the gas in the cylinder can reach over 1500K within a cycle, the surface temperature change of the combustion chamber wall is only around tens of K, and the temperature change of the outer wall is even smaller. Therefore, the inner and outer wall temperatures of the combustion chamber can be considered constant within a cycle. Thus, the combustion chamber wall temperature can be calculated over a single cycle, rather than using each degree of crankshaft rotation as the time scale, i.e.:

[0224] The convective heat transfer between the working fluid in the cylinder and the combustion chamber wall during one cycle:

[0225] (28)

[0226] The radiative heat released by the working fluid in the cylinder and the combustion chamber wall during one cycle:

[0227] (29)

[0228] The heat generated by friction between the piston rings and the cylinder wall during one cycle:

[0229] (30)

[0230] In the formula, : Convective heat transfer from the working fluid in the cylinder to the combustion chamber wall during one cycle (J); Heat released by radiation from the gas to the combustion chamber wall during one cycle (J); Heat generated by friction between the piston rings and the cylinder wall during one cycle (J); The average contact area between the working fluid and the combustion chamber in the cycle ( ); : The average temperature (K) of the gas in the cycle; : Average wall temperature of the combustion chamber during the cycle (K).

[0231] The heat transferred from the outer wall of the combustion chamber to the cooling medium in this cycle:

[0232] (31)

[0233] The net heat absorbed by the combustion chamber wall material in this cycle:

[0234] (32)

[0235] The change in combustion chamber wall temperature during this cycle:

[0236] (33)

[0237] Combustion chamber wall temperature at the start of the next operating condition:

[0238] (34)

[0239] (35)

[0240] Heat flow carried away by the combustion chamber coolant:

[0241] (36)

[0242] In the formula, : Heat flow carried away by the combustion chamber coolant (W); n: Diesel engine speed (r / min).

[0243] Combustion chamber coolant outlet temperature:

[0244] (37)

[0245] In the formula, : Temperature of the coolant at the combustion chamber outlet (K); : Temperature of the coolant at the combustion chamber inlet (K); Density of coolant (kg / ); Specific heat at constant pressure of coolant (J / kg*K).

[0246] Equations (1) to (37) above express the in-cylinder combustion and heat-work conversion process of the internal combustion engine, the in-cylinder pressure rise rate, temperature rise rate, cylinder pressure, cylinder temperature change, in-cylinder indicated performance, and the heat transfer between the working fluid and the combustion chamber wall, the cooling medium and the combustion chamber outer wall, the temperature rise process of the combustion chamber material, and the heat load as simple functional relationships of engine control and operating parameters that can be directly read from the ECU or directly or indirectly measured. Based on these parameters, various in-cylinder indicated performances of the diesel engine can be predicted according to the above equations. The calculation process is attached. Figure 2As shown. Since the above quantitative relationships are explicit, most steps do not require iteration, resulting in very fast computation speed. This makes it suitable for online testing, analysis, and intelligent control of diesel engine performance and thermal management systems.

[0247] Step 5: After calculating and defining the in-cylinder heat load, heat flow, wall temperature, and cooling requirements, the heat load, coolant flow rate, and power consumption of each engine sub-cooling system are defined using the in-cylinder process as the heat source. The reason for using the in-cylinder process as the "heat source" is to ensure that the engine cooling system's heat load and cooling requirements are updated promptly due to the influence of the in-cylinder process. The calculation methods and formulas for the heat load, coolant flow rate, and power consumption of each engine cooling subsystem are detailed in the following calculations, and the calculation process is detailed in the appendix. Figure 3 The cooling subsystem includes the turbocharger intercooler, EGR cooler, oil cooler, and vehicle radiator.

[0248] Step 51, Determining the heat load and required coolant flow rate of the booster intercooler:

[0249] The relationship between the outlet temperature of the pressurized fresh air and the pressurizer pressure ratio, inlet temperature, and compressor efficiency is as follows:

[0250] (38)

[0251] In the formula, : Inlet temperature (K) at the fresh air end of the turbocharger; : Fresh air outlet temperature of the turbocharger (K); : Inlet pressure of fresh air to the booster (Pa); : Fresh air outlet pressure of the booster (Pa); The isentropic efficiency of the turbocharger is -.

[0252] Gas temperature after intercooling:

[0253] (39)

[0254] In the formula, : Inlet temperature of the cooling medium in the intercooler (K); The inlet temperature (K) of the fresh air to the intercooler is typically equal to or close to the outlet temperature of the compressor. ; : Fresh air outlet temperature (K) of the intercooler; Intercooler efficiency (-).

[0255] Equation (39) shows that the outlet temperature of fresh air after intercooling depends not only on its inlet temperature, but also on the inlet temperature of the intercooler's cooling medium and the efficiency of the intercooler. Usually, the inlet temperature of the intercooler's cooling medium is a known constant or varies only within a very narrow range. Therefore, the outlet temperature of fresh air depends on the inlet temperature of fresh air and the efficiency of the intercooler. If the outlet temperature of the air after intercooling is to be kept at a certain value (usually the control target) or vary with a preset curve, then the efficiency of the intercooler (usually proportional to the flow rate of the cooling medium) needs to be adjusted to keep the air inlet temperature from changing.

[0256] The heat removed by the intercooler:

[0257] (40)

[0258] The flow rate of the cooling medium in the intercooler is determined based on the energy balance within the intercooler.

[0259] (41)

[0260] Volumetric flow rate of the medium in the intercooler:

[0261] (42)

[0262] In the formula, Mass flow rate of the cooling medium in the intercooler ( / s); : Cooling medium volumetric flow rate of intercooler ( / s); : Mass flow rate of fresh air (kg / s); Specific heat at constant pressure of fresh air (J / kgK); Density of the cooling medium in the intercooler (kg / ); Specific heat at constant pressure of the cooling medium in the intercooler (J / kgK); : Outlet temperature (K) of the cooling medium in the intercooler : Inlet temperature (K) of the cooling medium in the intercooler.

[0263] Intercooler power consumption:

[0264] (43)

[0265] In the formula, Power loss of the intercooler (W); The pressure loss (Pa) of the intercooler is usually the volumetric flow rate. The square relationship can be obtained by interpolation from the pre-stored measured map of the intercooler.

[0266] In equation (42), the specific heat at constant pressure of air and the cooling medium of the intercooler are known parameters that vary with temperature, while the inlet and outlet temperatures of the cooling medium of the intercooler and the outlet temperature of the fresh air are known parameters or preset parameters to be controlled. Therefore, based on the inlet temperature of the fresh working fluid of the intercooler and the flow rate of the fresh air, the flow rate of the cooling medium of the intercooler can be determined by equation (42), and the power consumption of the intercooler can also be calculated by equation (43).

[0267] Step 52, Determining the heat load and required coolant flow rate of the EGR cooler:

[0268] Temperature of EGR gas after cooling:

[0269] (44)

[0270] In the formula, : Inlet temperature of the cooling medium in the EGR cooler (K); : Inlet temperature (K) of the gas in the EGR cooler; : Outlet temperature (K) of EGR cooler gas; Efficiency of EGR cooler (-).

[0271] Equation (44) shows that the outlet temperature of the EGR cooler gas depends not only on its inlet temperature, but also on the inlet temperature of the EGR cooler cooling medium and the efficiency of the EGR cooler. Usually, the inlet temperature of the EGR cooler cooling medium is a constant or varies only within a very narrow range. Therefore, the outlet temperature of the EGR cooler gas depends on the inlet temperature of the EGR cooler gas and the efficiency of the EGR cooler. If the outlet temperature of the cooled gas is to be kept at a certain value or vary according to a certain preset curve, then the change of the EGR cooler gas inlet temperature (which depends on the in-cylinder process) requires adjusting the efficiency of the EGR cooler (which is usually proportional to the flow rate of the cooling medium).

[0272] The heat removed by the EGR cooler:

[0273] (45)

[0274] The flow rate of the cooling medium in the EGR cooler:

[0275] (46)

[0276] Volumetric flow rate of cooling medium in EGR coolers:

[0277] (47)

[0278] In the formula, : Mass flow rate of EGR gas (kg / s); Specific heat at constant pressure of EGR fuel gas (J / kgK); Mass flow rate of the cooling medium in the EGR cooler (kg / s); Volumetric flow rate of the cooling medium in the EGR cooler ( / s); Density of the cooling medium in the EGR cooler (kg / m³) ); Specific heat at constant pressure of the cooling medium in an EGR cooler (J / kgK); : Outlet temperature (K) of the cooling medium in the EGR cooler;

[0279] EGR cooler power consumption:

[0280] (48)

[0281] In the formula, Power loss (W) of EGR cooler; The pressure loss (Pa) of an EGR cooler is typically the volumetric flow rate. The square relationship can be obtained by interpolation from the pre-stored measured map of the EGR cooler.

[0282] In equation (47), the specific heat at constant pressure of the fuel gas and the cooling medium in the EGR cooler are known parameters that vary with temperature, while the inlet and outlet temperatures of the cooling medium in the EGR cooler and the outlet temperature of the fuel gas are known parameters or preset parameters to be controlled. Therefore, based on the inlet temperature of the fuel gas in different EGR coolers (which depends on the in-cylinder process of the diesel engine) and the flow rate of the EGR gas, the flow rate of the cooling medium in the EGR cooler can be determined by equation (47), and the power consumption of the EGR cooler can also be calculated by equation (48).

[0283] Step 53: Determining the heat load of the oil cooler and the required coolant flow rate;

[0284] Temperature and heat load in the oil cooler:

[0285] (49)

[0286] In the formula, : Inlet temperature of the oil in the oil cooler (K); : The outlet temperature (K) of the oil in the oil cooler; : Inlet temperature (K) of the cooling medium in the oil cooler; : Efficiency of the oil cooler (-).

[0287] Heat removed by the oil cooler:

[0288] (50)

[0289] The volumetric flow rate of the cooling medium in the oil cooler:

[0290] (51)

[0291] In the formula, : Mass flow rate of engine oil (kg / s); Specific heat at constant pressure of engine oil (J / kgK); : Volumetric flow rate of the cooling medium in the oil cooler ( / s); Density of the cooling medium in the oil cooler (kg / m³) ); Specific heat at constant pressure of the cooling medium in an oil cooler (J / kgK); : The outlet temperature (K) of the cooling medium in the oil cooler.

[0292] Accessory power consumed by the oil cooler:

[0293] Oil side:

[0294] (52)

[0295] Coolant side:

[0296] (53)

[0297] In the formula, The pressure loss (Pa) on the oil side of the oil cooler is usually the volumetric flow rate. The square relationship can be obtained by interpolation from the pre-stored measured map of the oil cooler; The pressure loss (Pa) on the coolant side of the oil cooler is usually the volumetric flow rate. The square relationship can be obtained by interpolation from the pre-stored measured map of the oil cooler.

[0298] Equation (53) shows that the specific heat at constant pressure of the engine oil and the cooling medium in the oil cooler are known parameters that change with temperature, while the inlet and outlet temperatures of the cooling medium in the oil cooler and the outlet temperature of the engine oil are known parameters or preset parameters to be controlled. Therefore, based on the different inlet temperatures of the engine oil and the oil flow rate (which depends on the operating conditions of the diesel engine), the flow rate of the cooling medium in the oil cooler can be determined by equation (51), and the power consumption of the oil cooler can also be calculated by equations (52) and (53).

[0299] Step 54, Determining the heat load of the vehicle radiator and the speed of the cooling fan:

[0300] The outlet temperature of the cooled medium in the radiator and the heat load of the radiator:

[0301] (54)

[0302] In the formula, Temperature of the cooled medium at the radiator inlet (K); : Temperature (K) of the medium to be cooled at the radiator outlet; : Inlet temperature of the radiator air (K); : Radiator efficiency (-).

[0303] Heat removed by the radiator:

[0304] (55)

[0305] The volumetric airflow rate that the radiator fan needs to provide:

[0306] (56)

[0307] In the formula, : Mass flow rate of the cooling medium to the radiator (kg / s); : The specific heat at constant pressure of the cooling medium in the radiator (J / kgK); The volumetric airflow rate that the radiator fan needs to provide ( The flow rate ( / s) is usually proportional to the fan speed. Given the fan volumetric flow rate, the corresponding fan speed (control target) can be found through a measured curve of fan speed versus volumetric flow rate. Density of cooling air provided by the radiator fan (kg / m³) ); Specific heat at constant pressure (J / kgK) of the cooling air provided by the radiator fan. : Air outlet temperature of the radiator (K).

[0308] The power consumed by the radiator fan:

[0309] (57)

[0310] In the formula, The pressure difference (Pa) generated by cooling air flowing through the radiator is usually related to the volumetric flow rate. It is proportional to the square of the value. Given the flow rate through the radiator, the corresponding pressure difference can be found through the measured curve of the radiator flow rate versus pressure difference.

[0311] In equation (56), the specific heat at constant pressure of the medium to be cooled in the radiator and the cooling air are known parameters that vary with temperature, while the inlet and outlet temperatures of the cooling air in the radiator and the outlet temperature of the medium to be cooled in the radiator are known parameters or preset parameters to be controlled. Therefore, based on the inlet temperature and flow rate of different media to be cooled (depending on the operating conditions of the diesel engine), the volumetric flow rate of the cooling air is determined by equation (56), and the power consumption of the radiator cooling fan is calculated based on equation (57) by finding the control target of the fan speed and the pressure difference loss based on the performance map of the fan and radiator.

[0312] Based on the above: Under dynamic operating conditions, the definition of the quantitative relationship between the control and operating parameters of the diesel engine based on the actual operating state, including the in-cylinder and cooling system, has been completed.

[0313] Step 6: Input the control parameters required for the engine thermal management system obtained from the above matching and optimization steps into the engine ECU and implement control.

[0314] This invention is not limited to the specific embodiments described above. Those skilled in the art can implement this invention using various other specific embodiments based on the disclosed content of the embodiments and accompanying drawings. Therefore, any design that adopts the design structure and concept of this invention and makes some simple changes or modifications falls within the protection scope of this invention.

Claims

1. A thermal management method for automotive diesel engines based on quantitative relationship analysis under dynamic operating conditions, characterized in that, The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis includes the following steps: Step 1: Input the engine's bore, stroke, displacement, valve timing, and thermal management objectives for this test; Step 2: Read the engine control parameters and operating parameters required for in-cylinder process calculations under this operating condition from the ECU; Step 3: Based on the obtained engine design parameters, actual parameters, and operating parameters, update the characteristic parameters of the engine's in-cylinder combustion process and the combustion heat release rate-crankshaft angle curve; and predict the changes in working fluid pressure and temperature in a complete cycle to calculate the engine's in-cylinder indicated performance. Step 4: Calculate the cumulative heat flow between the working fluid and the combustion chamber wall, and the cumulative heat flow between the outer wall of the combustion chamber and the cooling medium in the cycle, based on the full-cycle pressure and temperature curve of the working fluid in the cylinder. Step 5: After calculating and defining the in-cylinder heat load, heat flow, wall temperature, and cooling requirements, the heat load, cooling medium flow, and power consumption of each sub-cooling system of the engine are defined with the in-cylinder as the heat source. Step 6: Input the control parameters required for the engine thermal management system obtained from the above matching and optimization steps into the engine ECU to implement control, and repeat steps 2-6 to implement control for the next operating condition.

2. The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis according to claim 1, characterized in that, Step 3 also includes the following steps: Step 31: Define the control equation for the internal combustion engine cylinder pressure rise and temperature rise, use the Weber function to describe it based on the crankshaft angle position, and generate the combustion heat release rate-crankshaft angle curve; Step 32, Calculation of characteristic parameters of the in-cylinder combustion heat release process; The characteristic parameters of the in-cylinder combustion heat release process include the ratio of the burned gas from the previous cycle remaining in the cylinder to the total gas volume when the intake valve is closed (RGF), the crankshaft angle position when 50% of the combustion heat release occurs (CA50), and the combustion duration from 10% to 90% (CA10-90). Step 33: Establish a cycle with the crankshaft rotating 720°, and update the characteristic parameters of the in-cylinder combustion process corresponding to each crankshaft angle in the cycle, as well as the instantaneous pressure and temperature of the working fluid in the cylinder, through the combustion heat release rate-crankshaft angle curve.

3. The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis according to claim 2, characterized in that, In step 31, the governing equations include: The cylinder pressure change rate of the diesel engine is: ； Instantaneous pressure rise rate of gas inside the cylinder, This refers to the specific heat ratio of the gas inside the cylinder. Instantaneous cylinder volume, This refers to the cylinder pressure when the intake valve is closed. This refers to the cylinder volume when the intake valve is closed. This refers to the cylinder temperature when the intake valve is closed. Let be the gas state constant. The air-fuel ratio of fuel. The excess air coefficient of the air-fuel mixture. This refers to the ratio of the combusted gas from the previous cycle remaining in the cylinder when the intake valve is closed, relative to the total gas volume. The calorific value of fuel oil. In-cylinder combustion efficiency Dimensionless combustion heat release rate The heat exchange rate between the gas inside the cylinder and the walls of the combustion chamber; Instantaneous cylinder pressure can be calculated by sequentially increasing the crankshaft angle: ； The dynamic pressure inside the cylinder increases to ( ) at the crankshaft angle. The instantaneous pressure corresponding to the position. For the dynamic pressure inside the cylinder at the crankshaft angle of The instantaneous pressure corresponding to the location. This represents the change in crankshaft rotation angle. Integrating the high-pressure and low-pressure cycles of the diesel engine yields the average indicated pressure and indicated thermal efficiency of the high-pressure cycle: ； ； ； This refers to the average indicated pressure of the engine's high-pressure cycle. Here, PMEP represents the average indicated pressure of the engine's low-pressure cycle, and PMEP represents the pumping losses during the engine's low-pressure cycle. This refers to the displacement of a single engine cylinder. The indicated thermal efficiency of the engine's high-pressure cycle. This refers to the amount of fuel injected during the cycle. The instantaneous temperature rise rate inside the cylinder can also be calculated: ； Instantaneous temperature rise rate of the gas inside the cylinder, Total mass of gas inside the cylinder; Instantaneous cylinder temperature can also be calculated by progressively increasing the crankshaft angle: ； The in-cylinder dynamic temperature increases to ( ) at crankshaft angle. The instantaneous cylinder temperature corresponding to the position. This represents the instantaneous temperature of the gas inside the cylinder.

4. The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis according to claim 3, characterized in that, In step 31, the dimensionless combustion heat release rate is expressed using the Weber function as follows: ； The crankshaft angle corresponding to the start of combustion; The combustion duration is the difference between the initial and final crankshaft rotation angles. Combustion quality parameters used to characterize the shape of the combustion heat release rate curve; This refers to the crankshaft rotation angle.

5. The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis according to claim 1, characterized in that, Step 4 also includes the following steps: Step 41: Calculate the heat exchange between the in-cylinder gas and the combustion chamber cooling medium, as well as the heat load of the combustion chamber; Step 42: Calculate the combustion chamber wall temperature and the heat flow carried away by the combustion chamber coolant by the surface temperature change of the combustion chamber wall in adjacent cycles, and calculate the change of combustion chamber wall temperature and update the wall temperature for calculating the next operating condition; In step 41, the thermal conductivity between the combustion chamber and the outer wall surface is calculated: ； K represents the thermal conductivity between the inner and outer walls of the combustion chamber, where K is the thermal conductivity of the combustion chamber wall material. The thickness of the combustion chamber wall. The instantaneous heat conduction area between the combustion chamber and the outer wall surface. The temperature of the combustion chamber wall. The temperature of the outer wall of the combustion chamber; Calculate the convective heat transfer rate between the outer wall of the combustion chamber and the cooling medium: ； The heat exchange rate between the outer wall of the combustion chamber and the cooling medium. The heat transfer area of ​​the outer wall of the combustion chamber. The liquid-solid convection heat transfer coefficient between the outer wall of the combustion chamber and the coolant can be expressed as a single-valued function of the coolant flow rate. The specific quantitative relationship must be based on the specific cooling channel design and solved through CFD simulation calculations. ； This refers to the volumetric flow rate of the cooling medium. In step 42, the heat transferred from the outer wall of the combustion chamber to the cooling medium within a cycle: ； in, The liquid-solid convective heat transfer coefficient between the outer wall of the combustion chamber and the coolant. For heat exchange contact area, To reduce the outdoor wall temperature of the combustion chamber, The average temperature of the coolant on the outer wall of the combustion chamber; The heat flow carried away by the combustion chamber coolant is: ； The heat flow rate carried away by the combustion chamber coolant is expressed in W; n is the diesel engine speed, expressed in r / min. Combustion chamber coolant outlet temperature: ； In the formula, The temperature of the coolant at the combustion chamber outlet. This refers to the temperature of the coolant at the combustion chamber inlet. The density of the coolant, This refers to the specific heat at constant pressure of the coolant.

6. The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis according to claim 5, characterized in that, In step 4, the heat exchange between the working fluid in the cylinder and the combustion chamber wall is divided into two types: convective heat release and radiative heat release, and the heat exchange is the sum of the two: ； The convective heat transfer rate between the gas inside the cylinder and the wall of the combustion chamber; The radiative heat transfer rate between the gas inside the cylinder and the wall of the combustion chamber; Convective heat transfer between the in-cylinder gas and the combustion chamber walls: ； The temperature of the combustion chamber wall, This is the heat transfer coefficient between the gas inside the cylinder and the combustion chamber wall; The heat released by the gas radiating to the combustion chamber wall can be expressed by the following formula: ； In the formula, The emissivity is the heat transfer coefficient between the gas and the combustion chamber wall. For the Stef-Boltzmann constant, This represents the instantaneous contact area between the working fluid and the combustion chamber. The instantaneous temperature of the working fluid. The temperature of the combustion chamber wall; Given the diesel engine speed and load, the FMEP value is obtained from the table, thereby estimating the frictional heat generated between the piston rings and the cylinder wall: ； In the formula, FMEP represents the heat flux generated by friction between the engine piston rings and cylinder walls, while FMEP represents the mean effective pressure of frictional losses and accessory losses of the moving parts of the diesel engine. Cylinder displacement; The convective heat transfer between the working fluid in the cylinder and the combustion chamber wall in one cycle is: ； The convective heat transfer from the working fluid in the cylinder to the combustion chamber wall during a cycle; The amount of heat released by the radiative reaction between the working fluid in the cylinder and the combustion chamber wall during one cycle is: ； This refers to the heat released by the gas through radiation to the combustion chamber wall during one cycle. This represents the average contact area between the working fluid and the combustion chamber in the cycle. The average temperature of the gas in the cycle. This refers to the average wall temperature of the combustion chamber during the cycle. The heat generated by friction between the piston rings and the cylinder wall during one cycle is: ； This refers to the heat generated by friction between the piston rings and the cylinder wall during one cycle. The net heat absorbed by the combustion chamber wall material in this cycle: ； The change in combustion chamber wall temperature during this cycle: ； For the quality of the combustion chamber wall material, The specific heat at constant volume of the combustion chamber wall material; Combustion chamber wall temperature at the start of the next operating condition: ； ； The combustion chamber wall temperature for the next operating condition. The combustion chamber wall temperature under current operating conditions. The combustion chamber outer wall temperature for the next operating condition. This represents the temperature of the outer wall of the combustion chamber under the current operating conditions.

7. The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis according to claim 1, characterized in that, In step 5, the sub-cooling system includes a turbocharger intercooler, an EGR cooler, an oil cooler, and a vehicle radiator; The heat load and required coolant flow rate of the turbocharged intercooler are as follows: ； The volumetric flow rate of the cooling medium in the intercooler. The mass flow rate of fresh air. The specific heat at constant pressure of fresh air. The density of the cooling medium in the intercooler. The specific heat at constant pressure of the cooling medium in the intercooler. This refers to the outlet temperature of the cooling medium in the intercooler. This refers to the inlet temperature of the cooling medium in the intercooler. This refers to the inlet temperature of the fresh air to the intercooler. The outlet temperature of the fresh air in the intercooler; The heat load and required coolant flow rate of the EGR cooler are as follows: ； In the formula, The mass flow rate of EGR gas. The specific heat at constant pressure of EGR fuel gas. This refers to the volumetric flow rate of the cooling medium in the EGR cooler. The density of the cooling medium in the EGR cooler. The specific heat at constant pressure of the cooling medium in the EGR cooler. The outlet temperature of the cooling medium in the EGR cooler. The inlet temperature of the cooling medium for the EGR cooler. The inlet temperature of the gas for the EGR cooler. The outlet temperature of the gas in the EGR cooler; The heat load and required coolant flow rate of the oil cooler are as follows: ； This refers to the mass flow rate of the engine oil. The specific heat at constant pressure of engine oil. This refers to the volumetric flow rate of the cooling medium in the oil cooler. The density of the cooling medium in the oil cooler. The specific heat at constant pressure of the cooling medium in an oil cooler. This refers to the outlet temperature of the cooling medium in the oil cooler. This refers to the inlet temperature of the engine oil in the oil cooler. This refers to the outlet temperature of the engine oil in the oil cooler. This refers to the inlet temperature of the cooling medium in the oil cooler.

8. The method for thermal management of automotive diesel engines under dynamic operating conditions based on quantitative relationship analysis according to claim 7, characterized in that, In step 5, the vehicle radiator is used to dissipate heat for the turbocharger intercooler, EGR cooler, oil cooler, and combustion chamber cooler. The volumetric flow rate of the cooling air that the radiator fan needs to provide is: ； The mass flow rate of the medium being cooled in the radiator. The specific heat at constant pressure of the medium being cooled by the radiator. The volumetric flow rate of cooling air that the radiator fan needs to provide. The density of the cooling air supplied to the radiator fan. The specific heat at constant pressure of the cooling air supplied to the radiator fan. The outlet temperature of the radiator air. The temperature of the cooled medium at the radiator inlet. The temperature of the medium to be cooled at the radiator outlet. This is the inlet temperature of the air in the radiator.

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