Diesel engine low-temperature starting control method suitable for extremely-low-temperature working condition

Abstract

The invention relates to a diesel engine low-temperature starting control method suitable for an extremely-low-temperature working condition, and the method comprises the steps: collecting the in-cylinder pressure of each combustion cycle through an in-cylinder pressure sensor in the starting process of a diesel engine, and calculating an immediate indication average pressure IMEP and a combustion center position CA50 key combustion parameter; on the basis of CA50 feedback of each cycle, the fuel injection advance angle of the next cycle is adjusted and optimized, cycle-by-cycle control over the fuel injection advance angle is achieved, and it is ensured that CA50 is intensively distributed in an efficient combustion interval; the fuel injection advance angle is optimized, the IMEP and the rotating speed of the diesel engine are monitored to serve as real-time feedback of the combustion state, the combustion state of the diesel engine becomes poor, system judgment enters motor active torque compensation control, fuel injection and motor cycle-by-cycle coupling control based on combustion parameter feedback is achieved, and it is ensured that the pressure in a cycle cylinder is stable in the starting process of the diesel engine. Combustion parameter feedback is adopted for oil injection and motor cycle-by-cycle coupling control, poor combustion cycle in an extremely low temperature environment is reduced, and stability and energy efficiency in the starting process are improved.

Description

Technical Field

[0001] The present invention relates to the technical field of power supply for a marine power system, and in particular to a low-temperature starting control method for a diesel engine under extremely low-temperature working conditions. Background Art

[0002] When a diesel engine is started in an extremely low temperature environment, the combustion conditions are poor and poor combustion cycles are prone to occur, resulting in difficulty in starting or even starting failure. Conventional starting control methods mainly rely on fixed injection parameters and medium preheating technology, but in extremely cold environments, fixed parameter injection control cannot adapt to rapidly changing combustion conditions, and medium preheating consumes a lot of energy, and starting failure cannot be avoided when the preheating temperature is low. Some technical solutions improve starting performance by increasing the injection amount or raising the preheating temperature, but these methods have significant energy waste and limited effects at too low temperatures. In addition, during the starting process of traditional diesel engines, the speed fluctuates greatly, making it difficult to achieve precise control of the combustion state, resulting in the accumulation of multiple poor combustion cycles, which seriously affects the normal operation of the diesel engine. Summary of the invention

[0003] In view of the problem that diesel engines are prone to poor combustion cycles in extremely cold environments, which leads to starting difficulties or even starting failures, a low-temperature starting control method for diesel engines suitable for extremely low temperature conditions is proposed. The method uses combustion parameter feedback to perform cycle-by-cycle coupling control of injection and motor, reduces poor combustion cycles in extremely low temperature environments, and improves stability and energy efficiency during starting.

[0004] The technical solution of the present invention is: a low-temperature starting control method for a diesel engine under extremely low temperature conditions. During the starting process of the diesel engine, the cylinder pressure of each combustion cycle is collected through an in-cylinder pressure sensor, and the key combustion parameters of the immediate indicated average pressure IMEP and the combustion center position CA50 are calculated; based on the CA50 feedback of each cycle, the injection advance angle of the next cycle is adjusted and optimized to achieve cycle-by-cycle control of the injection advance angle, ensuring that CA50 is concentrated in the high-efficiency combustion range; while optimizing the injection advance angle, IMEP and the diesel engine speed are monitored as real-time feedback of the combustion state. When the combustion state of the diesel engine deteriorates, the system determines to enter the motor active torque compensation control, and realizes the injection and motor cycle-by-cycle coupling control based on the combustion parameter feedback, ensuring that the cylinder pressure of the diesel engine is stable during the starting process.

[0005] Furthermore, the injection advance angle is controlled in a cycle: first, preliminary control of combustion is performed according to a preset injection advance angle starting value; when it is detected that CA50 deviates from the high-efficiency combustion range, an injection advance angle adjustment value is obtained according to CA50 of the previous cycle, CA50 high-efficiency range, and the speed difference between the current cycle and the previous cycle, and correction is made in the current combustion cycle to optimize the combustion efficiency of each combustion cycle.

[0006] Furthermore, the injection and motor cycle-by-cycle coupling control based on combustion parameter feedback takes IMEP and diesel engine speed n as inputs to determine whether active motor torque compensation is needed. When the number of consecutive cycles when IMEP is lower than the set speed maintenance standard is less than 3, only injection advance competition cycle control is performed; when IMEP is lower than the set speed maintenance standard for 3 consecutive cycles, on the basis of injection advance competition cycle control, the motor actively provides compensation torque to ensure that the speed of the diesel engine is not lower than the minimum starting speed.

[0007] Furthermore, the motor active torque compensation calculates the required torque compensation value according to the current IMEP and the diesel engine speed n. The motor active compensation torque T motor is the resistance torque T of the current state c With diesel engine indicated torque T engine The difference:

[0008] T motor =T c -T engine

[0009]

[0010] Where i is the number of cylinders; V s is the engine displacement, in L; IMEP is the indicated mean effective pressure, in MPa; τ is the stroke coefficient;

[0011] The test data was fitted to obtain the test diesel engine resistance torque formula:

[0012] T c =41.2ν 0.25 n 0.34

[0013] Where ν is the kinematic viscosity of the lubricating oil at this temperature, m 2 / s; n is the diesel engine speed, in r / min.

[0014] The beneficial effects of the present invention are as follows: the present invention is applicable to a diesel engine low-temperature starting control method under extremely low temperature conditions, and by adopting combustion parameter feedback to perform cycle-by-cycle coupling control of fuel injection and motor, the adverse combustion cycles in extremely low temperature environments are reduced, and the stability and energy efficiency during the starting process are improved. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 This is a flow chart of a low-temperature starting control method for a diesel engine under extremely low-temperature conditions according to the present invention;

[0016] Figures 2A-2C This is a comparison diagram of the maximum pressure in the cylinder during the cold start process of a diesel engine under three cold start failure conditions of the present invention. DETAILED DESCRIPTION

[0017] The present invention is described in detail below in conjunction with the accompanying drawings and specific embodiments. This embodiment is implemented based on the technical solution of the present invention, and provides a detailed implementation method and specific operation process, but the protection scope of the present invention is not limited to the following embodiments.

[0018] like Figure 1 The flowchart of the low temperature starting control method of a diesel engine applicable to extremely low temperature conditions is shown, and the method specifically includes the following:

[0019] 1. The in-cylinder pressure sensor collects the in-cylinder pressure of each combustion cycle and calculates the key combustion parameters of the instant indicated mean pressure (IMEP) and the combustion center position (CA50);

[0020] 2. Based on the CA50 feedback of each cycle, adjust and optimize the injection advance angle of the next cycle to ensure that CA50 is concentrated in the efficient combustion range. Combining feedforward and feedback control, a CA50-based injection advance angle control cycle is proposed;

[0021] 3. Aiming at the problem of cold start failure caused by multiple bad combustion cycles due to low medium preheating temperature during starting, a cycle-by-cycle coupling control method of fuel injection and motor based on combustion parameter feedback is proposed by taking advantage of the high power and fast response of hybrid motors.

[0022] 4. Through real-time feedback of the combustion state, determine whether the motor active torque compensation is needed. When the combustion state is poor and the diesel engine speed is lower than the set starting speed, the motor starts the reverse drag mode. After successful starting, the motor enters the monitoring mode, continuously tracking the combustion state and speed of the diesel engine, and judging in real time whether the motor active torque compensation needs to be intervened.

[0023] like Figure 1 First, during the diesel engine startup process, the in-cylinder pressure sensor collects the in-cylinder pressure data of each combustion cycle in real time, and calculates the instant indicated mean pressure (IMEP) and the combustion center position (CA50) based on the collected data. These parameters are used to monitor the combustion state of the diesel engine in real time to determine the current combustion efficiency and engine power output.

[0024] Then, the injection advance angle of this cycle is adjusted based on the CA50 feedback value of the previous cycle and the feedforward amount of the relationship between the injection advance angle and CA50 under different environments, medium temperatures and speeds. The system first performs preliminary combustion control based on the preset injection advance angle starting value (e.g. 10°CA BTDC). When it is detected that CA50 deviates from the efficient combustion range (e.g. 8-10°CA after top dead center), the injection advance angle adjustment value is obtained based on the CA50 of the previous cycle, the CA50 efficient range, and the speed difference between this cycle and the previous cycle, and is corrected in this combustion cycle to ensure that CA50 is always concentrated in the efficient combustion range, thereby optimizing the combustion efficiency of each combustion cycle.

[0025] Next, while optimizing CA50, if multiple bad combustion cycles occur under extremely low temperature conditions (i.e., IMEP is lower than the set standard value), the combustion state of the diesel engine deteriorates, and the system determines that it has entered the motor active torque compensation stage. In this stage, the motor calculates the required torque compensation value based on the current IMEP and diesel engine speed n. The diesel engine indicated torque is calculated based on IMEP, the diesel engine speed obtained from the crankshaft signal, and the kinematic viscosity obtained from the lubricating oil temperature are used to calculate the cold start resistance torque. The motor actively compensates the torque T motor is the resistance torque T of the current state c With diesel engine indicated torque T engine The difference:

[0026] T motor =T c -T engine

[0027]

[0028] Where i is the number of cylinders; V s is the engine displacement, in L; IMEP is the indicated mean effective pressure, in MPa; τ is the stroke coefficient;

[0029] The test data was fitted to obtain the test diesel engine resistance torque formula:

[0030] T c =41.2ν 0.25 n 0.34

[0031] Where ν is the kinematic viscosity of the lubricating oil at this temperature, m 2 / s; n is the diesel engine speed, in r / min.

[0032] Specifically, IMEP and diesel engine speed n are used as inputs to determine whether the motor needs active torque compensation. When IMEP is lower than the set speed maintenance standard for less than 3 consecutive cycles, only injection advance competition cycle control is performed. When IMEP is lower than the set speed maintenance standard for 3 consecutive cycles, on the basis of injection advance competition cycle control, the motor actively provides compensation torque to ensure that the speed of the diesel engine is not lower than the minimum starting speed, avoiding starting failure due to excessive speed drop.

[0033] Then, after the diesel engine is successfully started and enters stable operation, the motor enters the monitoring mode. In the monitoring mode, the motor continuously tracks the speed and IMEP parameters of the diesel engine to determine the stability of the combustion state. If an abnormal decrease in IMEP or speed is detected for three consecutive cycles, the motor will automatically start torque compensation and intervene again to provide additional power support to ensure the continuous stability of the diesel engine speed and combustion process.

[0034] Take the specific experimental results of a diesel engine as an example. The experimental conditions are shown in Table 1: cold start failure test conditions.

[0035] Table 1

[0036]

[0037] After applying the control method of the present invention, the maximum pressure in the cylinder during the first 80 cycles of the cold start process is compared with the original control method. Figures 2A-2C , corresponding to the situations under three working conditions respectively. The upper part of each sub-graph shows the variation of the maximum pressure value in the cylinder with the cycle number under the cycle-by-cycle coupling control of the injection and the motor, and the lower part shows the variation of the maximum pressure value in the cylinder with the cycle number under the original control. Figures 2A-2C It can be seen from the figure that under the same working condition, after controlling the injection advance angle cycle by cycle, the maximum pressure curve in the cylinder can still rise and reach normal after experiencing multiple bad combustion cycles. Figure 2C It can be seen that, under the original control, bad combustion cycles continuously occurred from the 28th cycle to the 32nd cycle during the cold start process, which eventually led to cold start failure. With the control method of the present invention, the maximum cylinder pressure change during the diesel engine start process tends to be stable.

[0038] The above-mentioned embodiments only express the specific implementation of the present invention, and the description thereof is relatively specific and detailed, but it cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, several modifications and improvements can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A low temperature starting control method for a diesel engine under extremely low temperature conditions, characterized in that: During the diesel engine starting process, the cylinder pressure of each combustion cycle is collected through the cylinder pressure sensor to calculate the key combustion parameters of the instant indicated mean pressure IMEP and the combustion center position CA50; Based on the CA50 feedback of each cycle, the injection advance angle of the next cycle is adjusted and optimized to achieve cycle-by-cycle control of the injection advance angle, ensuring that CA50 is concentrated in the high-efficiency combustion range; while optimizing the injection advance angle, IMEP and diesel engine speed are monitored as real-time feedback of the combustion state. If the combustion state of the diesel engine deteriorates, the system determines that it enters the active torque compensation control of the motor, and realizes cycle-by-cycle coupling control of the injection and the motor based on the feedback of combustion parameters, ensuring that the pressure in the circulating cylinder is stable during the diesel engine starting process.

2. The diesel engine low temperature starting control method suitable for extremely low temperature conditions according to claim 1, characterized in that: The injection advance angle cycle control: first, preliminary control of combustion is performed according to a preset injection advance angle starting value. When it is detected that CA50 deviates from the high-efficiency combustion range, the injection advance angle adjustment value is obtained according to the CA50 of the previous cycle, the CA50 high-efficiency range, and the speed difference between the current cycle and the previous cycle, and is corrected in the current combustion cycle to optimize the combustion efficiency of each combustion cycle.

3. The diesel engine low temperature starting control method suitable for extremely low temperature conditions according to claim 1 or 2, characterized in that: The injection and motor cycle-by-cycle coupling control based on combustion parameter feedback takes IMEP and diesel engine speed n as inputs to determine whether active motor torque compensation is needed. When the number of consecutive cycles when IMEP is lower than the set speed maintenance standard is less than 3, only injection advance competition cycle control is performed; when IMEP is lower than the set speed maintenance standard for 3 consecutive cycles, on the basis of injection advance competition cycle control, the motor actively provides compensation torque to ensure that the speed of the diesel engine is not lower than the minimum starting speed.

4. The diesel engine low temperature starting control method applicable to extremely low temperature conditions according to claim 3 is characterized in that: The motor active torque compensation calculates the required torque compensation value according to the current IMEP and the diesel engine speed n. The motor active compensation torque T motor is the resistance torque T of the current state c With diesel engine indicated torque T engine The difference: T=TT motor c engine Where i is the number of cylinders; V s is the engine displacement, in L; IMEP is the indicated mean effective pressure, in MPa; τ is the stroke coefficient; The test data was fitted to obtain the test diesel engine resistance torque formula: T c =41.2ν 0.25 n 0.34 Where, ν is the kinematic viscosity of the lubricating oil at this temperature, m 2 / s; n is the diesel engine speed, in r / min.

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