CN104537142B - Calculation Method of Thermodynamic Parameters for Four-Stroke Diesel Engine's Ventilation Process - Google Patents

Abstract

The invention discloses a method for calculating thermodynamic parameters in the ventilation process of a four-stroke diesel engine. The invention is based on the fact that the intake air volume of the diesel engine system is equal to the sum of the air intake volume and the scavenging volume of the cylinder, and is related to the gas distribution phase angle and the closing time of the exhaust valve. The air intake volume in the cylinder at the time when the intake valve is closed, the calculation model of the intake air volume of the diesel engine system during the intake process of the four-stroke diesel engine is constructed; Gas volume, construct a calculation model for the thermal parameters of the exhaust pipe at the end of each exhaust process of the four-stroke diesel engine; use the constructed model to obtain the thermal parameters of the diesel engine's ventilation process. The invention is simple, has strong practicability and high precision, and the error with the actual thermal parameter is within 3%.

Description

Calculation Method of Thermodynamic Parameters for Four-Stroke Diesel Engine's Ventilation Process

technical field

The invention belongs to the technical field of thermal process simulation of diesel engine performance, and in particular relates to a calculation method for thermal parameters of a four-stroke diesel engine ventilation process.

Background technique

The research on the gas exchange process of diesel engine mainly includes test method and computer numerical simulation method. The test method is the use of relevant test technology to conduct research on simulation and test machines, which is the premise and basis of theoretical research. However, due to the limitations of its superficial data, a single test method has been difficult to meet the research needs. At present, the calculation models used in numerical simulation methods can be roughly divided into filling and emptying method, mean value modeling, linearized modeling, and quasi-steady modeling. Wait. "Volume method model" is a commonly used analysis method for the ventilation process of four-stroke diesel engines. It is mainly based on the solution of the differential equation about the crank angle of the mass and internal energy in the cylinder. It is very useful for the detailed experimental analysis of the engine, and its analysis results are rich. , Meticulous and accurate, but it requires a high-performance computer, a large calculation space, a long calculation time and a large number of parameter fittings.

Contents of the invention

Aiming at the deficiencies in the prior art, the present invention provides a calculation method for the thermodynamic parameters of the four-stroke diesel engine ventilation process that can realize rapid prediction based on the gas exchange characteristics during the intake and exhaust process of the four-stroke diesel engine, which is a four-stroke diesel engine Performance parameter checking provides a theoretical basis.

According to the characteristics of the gas exchange process of the four-stroke diesel engine, the invention proposes a method for calculating the gas exchange process of the four-stroke diesel engine, including the intake air volume of the system, the intake air volume in the cylinder, the scavenging air volume, and the free exhaust gas. The methods of thermodynamic performance parameters such as volume, forced exhaust volume, scavenging slip air volume, process temperature and cylinder exhaust temperature, etc., to realize rapid budget and check of thermal performance parameters in the ventilation process.

In order to solve the problems of the technologies described above, the present invention adopts the following technical solutions:

A method for calculating thermodynamic parameters of a four-stroke diesel engine ventilation process, comprising steps:

Construct the calculation model of the air intake volume of the diesel engine system during the air intake process, see formulas (1) to (7):

m _in =m _ind +m _sc (1)

π _sc ＝ P _c /P _d (7)

Among them, _mind is the intake air volume of the cylinder during the intake process, min is the intake air volume of the diesel engine system during the intake process, m _sc is the scavenging volume of the diesel engine scavenging process; i is the number of cylinders _in the diesel engine system; the subscript c indicates the intake air The state of the intake pipe during the process, R _c represents the gas constant in the intake pipe, T _c is the temperature of the cooling medium in the intake pipe, P _c is the pressure of the intake pipe; N is the speed of the diesel engine, V _S is the effective working volume of the cylinder of the diesel engine, and k is the stroke coefficient , for a four-stroke diesel engine, k=2; η _fill is the gas charge coefficient during the intake process of the diesel engine, V _IC is the effective volume of the cylinder when the intake valve of the cylinder is closed, V _EC is the effective volume of the cylinder when the exhaust valve of the cylinder is closed, and ε _INL is the cylinder Head heat exchange coefficient, T _INL is the air temperature at the outlet of the intercooler; A _sc,eff is the effective area of scavenging air, A _in and A _out are the areas of the intake valve and exhaust valve of the cylinder respectively, η _sc,eff is the area of the scavenging air gas efficiency; Ψ(π _sc ) is the dimensionless pressure ratio, P _d is the exhaust pipe pressure during the intake process;

Collect the gas state parameters of the intake pipe and exhaust pipe, input the gas state parameters of the intake pipe and exhaust pipe and the geometric parameters of the diesel engine body into the calculation model of the intake air volume of the diesel engine system, and then obtain the intake air volume of the diesel engine system and the air intake volume of the cylinder and scavenging volume.

The method of the present invention also includes the calculation of thermodynamic parameters of the exhaust process, including:

(1) Calculation of the thermal parameters of the exhaust pipe at the end of the free exhaust process, the specific steps are as follows:

Construct the calculation model of the thermal parameters of the exhaust pipe at the end of the free exhaust process, see formulas (8)-(10):

Among them, T _bld , T _bld-out , m _bld-out are the starting temperature, ending temperature and free exhaust volume of the free exhaust process respectively; T ₆ , P ₆ , m ₆ respectively represent the exhaust gas in the cylinder before the exhaust valve is opened γ is the adiabatic index of the flue gas in the free exhaust process, P _d is the exhaust header pressure at the end of the free exhaust process, R is the exhaust gas constant of the exhaust pipe, and V _EO is the opening of the cylinder exhaust valve Hourly cylinder working volume; N is the diesel engine speed, k is the stroke coefficient, for a four-stroke diesel engine, k=2;

Collect the gas state parameters in the cylinder before the exhaust valve is opened and the gas state parameters of the exhaust pipe, and input the collected parameters and the geometric parameters of the diesel engine body into the calculation model of the thermal parameters of the exhaust pipe at the end of the free exhaust process to obtain the free exhaust process The starting temperature, ending temperature and free exhaust volume.

(2) The thermal parameters of the exhaust pipe at the end of the forced exhaust process, the specific steps are as follows:

Construct the calculation model of the thermal parameters of the exhaust pipe at the end of the forced exhaust process, see formulas (11)-(13):

m _exp =m ₆ -m _bld-out -m _sc(0) (12)

Among them, T _exp and m _exp are the end temperature and forced exhaust volume of the forced exhaust process, respectively, m _sc(0) is the exhaust gas volume at the beginning of the scavenging process; m ₆ is the mass of the exhaust gas in the cylinder before the intake valve is opened , T _bld and T _bld-out are the starting temperature and end temperature of the free exhaust process respectively; P _d is the exhaust manifold pressure at the end of the forced exhaust process, and V _IO is when the intake valve is opened (that is, the forced exhaust process ends When) the working volume in the cylinder, R is the exhaust gas constant of the exhaust pipe at the end of the forced exhaust process; N is the diesel engine speed, k is the stroke coefficient, and for the four-stroke diesel engine, k=2;

Collect the gas state parameters of the exhaust pipe, input the starting temperature and end temperature of the free exhaust process, the gas state parameters of the exhaust pipe, and the geometric parameters of the diesel engine body into the calculation model of the thermal parameters of the exhaust pipe at the end of the forced exhaust process, and obtain the forced exhaust The end temperature and forced exhaust volume of the gas process and the exhaust gas volume at the beginning of the scavenging process.

(3) Calculating the thermal parameters of the exhaust pipe after the scavenging process, the specific steps are as follows:

Construct the calculation model of the thermal parameters of the exhaust pipe at the end of the scavenging process, see formulas (14)-(16):

m _sc-out = s·m _sc (14)

m _out ＝m _in +m _f ＝m _bld-out +m _exp +m _sc(0) -m _res +m _sc-out (15)

Among them, m _sc-out is the amount of air slipped out during the scavenging process, m _out is the amount of exhaust gas in the exhaust manifold at the end of the scavenging process, T _d is the temperature of the exhaust gas in the exhaust manifold at the end of the scavenging process; m _sc is the scavenging air process scavenging volume, s is the slip coefficient of the scavenging process; min is the air intake volume of the cylinder during the intake process, m _f is the fuel consumption; m _{bld -out} is the free exhaust volume during the free exhaust process, and m _exp is The forced exhaust volume of the forced exhaust process, m _sc(0) is the exhaust gas volume at the beginning of the scavenging process; m _res is the residual exhaust gas volume in the cylinder at the end of the forced exhaust process, c _p,sc-out is the scavenging gas The average specific heat of the flue gas in the process, c _{p, exh} is the average specific heat of the flue gas in the free exhaust process and the forced exhaust process, c _{p, d} is the average specific heat of the flue gas in the ventilation process; T _exp is the end point of the forced exhaust process Temperature, that is, the temperature of the flue gas in the exhaust pipe at the end of the forced exhaust process; T _sc-out is the starting temperature of the scavenging process, that is, the cylinder intake temperature;

Input the exhaust pipe thermal parameter calculation model at the end of the free exhaust process and the forced exhaust process, and the calculation results of the diesel engine system air intake calculation model into the exhaust pipe thermal parameter calculation model at the end of the scavenging process, and obtain The amount of air that slips out during the scavenging process, and the exhaust gas volume and exhaust gas temperature in the exhaust header at the end of the scavenging process.

Compared with prior art, the beneficial effect of the present invention is:

1. Based on the intake air volume min of the diesel engine system, it is equal to the sum of the intake air volume min _ind and the scavenging air volume m _{sc in} the cylinder, and is related to the distribution phase angle of the exhaust valve closing time (EC) and the intake valve closing time (IC) The calculation method of intake air volume and scavenging air volume in the four-stroke diesel engine cylinder is proposed. This method avoids the high complexity of the actual air intake solution, and at the same time introduces the calculation of the air charge coefficient to adjust the intake air volume. A good compromise has been achieved between the solution complexity and the solution accuracy of the gas process.

2. Using the characteristics of the four-stroke exhaust process (free exhaust, forced exhaust, and scavenging process), and at the same time according to the exhaust valve opening time (EO) and the intake valve opening time (IO) of the exhaust volume, the A calculation method for the exhaust volume, exhaust temperature and exhaust gas temperature of four-stroke diesel engine exhaust is proposed. This method is simple and practical. The error between the obtained exhaust parameters and the actual exhaust parameters is within 3%. The theoretical basis and calculation method are provided for the calibration of the performance parameters of the exhaust gas during the diesel engine ventilation process.

Description of drawings

Fig. 1 is a flow chart of the method of the present invention;

Fig. 2 is the mass flow relation diagram of the intake process of the four-stroke diesel engine;

Figure 3 is a diagram of the mass flow relationship in the exhaust process of a four-stroke diesel engine.

detailed description

The air exchange process of the diesel engine includes the intake process and the exhaust process, therefore, the method of the present invention includes the calculation of the intake amount min of the diesel engine system _in the intake process and the calculation of the thermal parameters in the exhaust process.

1. Calculation process of the intake air volume _min of the diesel engine system during the air intake process

During the air intake process, the total intake air volume min of the diesel engine system is equal to the sum of the cylinder intake air volume min _ind and the scavenging air volume m _{sc , so the calculation of the intake air volume min is shown in formulas} (1) to (2):

In formula (1)～(2):

min _ind is the intake air volume of the cylinder during the intake process, unit: kg/s;

m _in is the total intake air volume of the diesel engine system, unit: kg/s;

m _sc is the total scavenging volume of diesel engine scavenging process, unit: kg/s;

i is the number of cylinders in the diesel engine system;

The subscript c indicates the state of the intake pipe during the intake process, R _c indicates the gas constant in the intake pipe, that is, the specific heat capacity of the gas in the intake pipe, generally 287J/kg·K; _Tc is the temperature of the cooling medium in the intake pipe, about 353-473K ; P _c is the intake pipe pressure;

N is the engine speed, unit: r/s;

V _S is the effective working volume of the diesel engine cylinder, unit: m ³ , V _S = L _S × A _B , L _S is the stroke of the cylinder piston, and A _B is the cross-sectional area of the cylinder;

k is the stroke coefficient, for a four-stroke diesel engine, k=2;

η _fill is the gas filling coefficient of the diesel engine intake process, and its range is 0.7 to 0.85, V _IC is the effective volume of the cylinder when the intake valve of the cylinder is closed, and V _EC is the effective volume of the cylinder when the exhaust _valve of the cylinder is closed; In the range of ~0.85, the usual value is 0.167; T _INL is the air temperature at the outlet of the intercooler;

A _sc,eff is the effective area of scavenging, unit: m ² , A _in and A _out are the area of the intake valve and exhaust valve of the cylinder respectively, η _{sc, eff} is the scavenging efficiency, the value range is 0.5～0.75, and the usual value is 0.6;

Ψ(π _sc ) is the dimensionless pressure ratio, π _{sc =} P _c /P _d, P _c is the intake pressure of the intake pipe, and P _d is the pressure of the exhaust pipe during the intake process.

On the premise that the parameters of the intake pipe and the geometric parameters of the diesel engine body are known, the intake air volume of the cylinder during the intake process of the four-stroke diesel engine can be obtained through the formulas (1) and (2), so as to calculate the intake process of the diesel engine under different working conditions performance parameters.

2. Calculation process of thermal parameters in the exhaust process

The exhaust process of diesel engine includes free exhaust process, forced _exhaust process and _{scavenging process} . with.

(1) Calculation of the thermal parameters of the exhaust pipe at the end of the free exhaust process.

After the diesel engine expands and works, the exhaust valve opens, and the diesel engine system performs a free exhaust process. The starting temperature T _bld , end temperature T _bld-out , and free exhaust volume m _bld-out of the free exhaust process are calculated as follows:

In formula (3)～(5):

The subscript 6 indicates the state of the exhaust gas in the cylinder before the exhaust valve is opened (that is, after the expansion works), and T ₆ , P ₆ , and m ₆ respectively indicate the temperature, pressure and quality of the exhaust gas in the cylinder before the exhaust valve is opened;

γ is the adiabatic index of the flue gas during the free exhaust process, usually 1.334;

P _d is the pressure of the exhaust main pipe at the end of the free exhaust process, unit: MPa;

R is the exhaust gas constant of the exhaust pipe at the end of the free exhaust process, that is, the specific heat capacity of the exhaust gas in the exhaust pipe, which is usually taken as 295J/kg·K;

V _EO is the working volume of the cylinder when the cylinder exhaust valve is opened (that is, the beginning of the free exhaust process), unit: m ² ;

N is the engine speed, unit: r/s;

k is the stroke coefficient, for a four-stroke diesel engine, k=2.

(2) Calculate the thermal parameters of the exhaust pipe at the end of the forced exhaust process.

After the free exhaust process is over, the piston in the diesel engine cylinder moves _upwards , and the diesel engine system _performs a forced exhaust process before the intake valve is opened. The calculation formula of exhaust gas volume m _sc(0) is as follows:

m _exp =m ₆ -m _bld-out -m _sc(0) (7)

In formula (6)～(8):

_m6 is the mass of the exhaust gas in the cylinder before the intake valve is opened, unit: kg/s;

T _bld and T _bld-out are the starting temperature and ending temperature of the free exhaust process, unit: K;

P _d is the exhaust header pressure at the end of the forced exhaust process, unit: MPa;

V _IO is the working volume in the cylinder when the intake valve is opened (that is, when the forced exhaust process ends), unit: m ² .

R is the exhaust gas constant of the exhaust pipe at the end of the forced exhaust process, usually 295J/kg·K;

N is the engine speed, unit: r/s;

k is the stroke coefficient, for a four-stroke diesel engine, k=2.

(3) Calculate the thermal parameters of the exhaust pipe after the scavenging process is completed.

After the forced exhaust process is over, the diesel engine system performs the _{scavenging process} before the exhaust valve is closed. The formula for calculating the exhaust gas temperature T _d of the main pipe is as follows:

m _sc-out = s·m _sc (9)

m _out ＝m _in +m _f ＝m _bld-out +m _exp +m _sc(0) -m _res +m _sc-out (10)

In formula (9)～(11):

m _sc is the scavenging volume, calculated according to formula (2);

s is the slip coefficient during the scavenging process, that is, the ratio of the mass of gas that does not enter the cylinder to the total mass of the scavenging gas during the scavenging process, generally 0.6 to 0.9;

m _in is the intake air volume of the cylinder during the intake process;

m _f is fuel consumption;

m _bld-out is the free exhaust volume in the free exhaust process, calculated according to formula (5);

m _exp is the forced exhaust volume in the forced exhaust process, calculated according to formula (7);

m _sc(0) is the exhaust gas volume at the beginning of the scavenging process, which is calculated according to formula (6);

m _res is the amount of residual exhaust gas in the cylinder at the end of the forced exhaust process, unit: kg/s;

c _{p, sc-out} is the average specific heat of flue gas in the sweeping process, its value is about 1.08, unit: kJ/kg k;

c _p,exh is the average specific heat of flue gas in the process of free exhaust and forced exhaust, its value is about 1.11, unit: kJ/kg·k;

c _p,d is the average specific heat of flue gas in the whole ventilation process, its value is about 1.10, unit: kJ/kg k;

T _exp is the end temperature of the forced exhaust process, calculated according to formula (8);

T _sc-out is the temperature of the starting point of scavenging (that is, the temperature of the intake air of the cylinder).

On the premise that the state parameters in the cylinder before the exhaust process (namely, the waste temperature T ₆ , pressure P ₆ and mass m ₆ in the cylinder before the exhaust valve is opened) are known, use formulas (3) to (11) to calculate the four Performance parameters of stroke diesel engine exhaust process.

The present invention will be described in detail below in conjunction with accompanying drawings and examples.

See Figure 1, the specific steps of this embodiment are as follows:

a. Establish the intake model and exhaust model of the four-stroke diesel engine ventilation process, based on the law of mass conservation, energy conservation, gas steady-state equation, etc., to refine the model, see formulas (1) to (11) .

b. Based on the gas state parameters of the intake pipe, the closing angle of the intake and exhaust valves, and the geometric parameters of the diesel engine body, the calculation of the intake air volume and scavenging volume in the cylinder during the intake process of the diesel engine is carried out;

c. Using the characteristics of the four-stroke exhaust process (free exhaust, forced exhaust, and scavenging process), at the same time according to the exhaust valve opening time (EO), intake valve opening time (IO), energy conservation law, mass mixing According to the law and the mixing characteristics of exhaust gas, the exhaust volume, exhaust temperature, and exhaust gas temperature of each exhaust process are calculated;

d. Use the actual operating condition data of the diesel engine to check the model calculation data and revise the parameters.

Taking the four-stroke diesel engine MAN 7L16/24 (1200RPM) as an example, the specific calculation steps are as follows:

The mass flow relationship model of the diesel engine intake process is shown in Figure 2, the gas state parameters of the intake pipe P _c = 0.3532MPa, T _c = 316.15K, the number of cylinders i = 7, the diesel engine speed N = 20r/s, the cylinder bore d = 0.16m, Cylinder stroke L _s = 0.24m, intake valve diameter d _in = 0.025m, exhaust valve diameter d _out = 0.027m, cylinder intake valve closing angle IC = 205°CA, exhaust valve closing angle EC = 60°CA , the intake valve opening angle IO=150°CA, the exhaust valve opening angle EO=130°CA. It is thus determined that, under the rated operating conditions of the four-stroke diesel engine, η _fill =0.82, η _sc,eff =0.42, mind = _1.0413kg /s, m _sc =0.437kg/s. In addition, the calculation results under different working conditions of the intake process and the error analysis with the actual operating data are shown in Table 1.

The mass flow relationship model of the diesel engine exhaust process is shown in Figure 3. Before free exhaust, the gas state parameters in the cylinder are P ₆ =1.0606MPa, T ₆ =965.5K, m ₆ =1.177kg/s, the gas state of the exhaust pipe The parameter is P _d =0.332MPa, thus it is determined that the four-stroke diesel engine is under the rated working condition, T _bld =858.6K, T _bld-out =723.0K, m _bld-out =0.67kg/s, m _{sc(0 )} =0.36kg/s, m _exp =0.15kg/s, T _exp =811.6K, T _d =782.6K, m _out =1.512kg/s. In addition, the calculation results under different working conditions in the exhaust process and the error analysis with the actual operating data are shown in Table 1.

Table 1 Comparison table between the model value and the actual working condition operation value of the four-stroke diesel engine ventilation process in the embodiment

Operating point (unit: %) 100 90 80 70 60 50 Air intake volume of diesel engine system (calculated value) (unit: kg/h) 5322 4767 4244 3727 3220 2728 Air intake volume of diesel engine system (actual value) (unit: kg/h) 5300 4715 4207 3824 3312 2808 Error (unit: %) 0.42 1.10 0.88 2.54 2.78 2.85 Smoke emission of diesel engine system (calculated value) (unit: kg/h) 5443 4896 4359 3828 3307 2802 Smoke emission of diesel engine system (actual value) (unit: kg/h) 5500 5000 4421 3905 3392 2886 Error (unit: %) 1.04 2.08 1.40 1.97 2.51 2.91 Exhaust temperature of diesel engine system (calculated value) (unit: K) 783 775 767 751 733 710 Exhaust temperature of diesel engine system (actual value) (unit: K) 768 758 748 732 712 692 Error (unit: %) 1.90 2.24 2.54 2.60 2.95 2.60

The above is only the specific implementation of this type of diesel engine algorithm, and is not used to limit the scope of protection of the present invention. Any modifications, equivalent replacements, improvements, etc. within the principles and methods of the present invention should be Within the protection scope of the present invention.

Claims (4)

1. The thermodynamic parameter calculation method of four-stroke diesel engine ventilation process, it is characterized in that: Construct the calculation model of the air intake volume of the diesel engine system during the air intake process, see formulas (1) to (7): m _in =m _ind +m _sc (1) π _sc ＝ P _c /P _d (7) Among them: _mind is the intake air volume of the cylinder during the intake process, min is the intake air volume of the diesel engine system during the intake process, m _sc is the scavenging volume of the diesel engine scavenging process; i is the number of cylinders _in the diesel engine system; the subscript c indicates the intake air The state of the intake pipe during the process, R _c represents the gas constant in the intake pipe, T _c is the temperature of the cooling medium in the intake pipe, P _c is the pressure of the intake pipe; N is the speed of the diesel engine, V _s is the effective working volume of the cylinder of the diesel engine, and k is the stroke coefficient , for a four-stroke diesel engine, k=2; η _fill is the gas charge coefficient during the intake process of the diesel engine, V _IC is the effective volume of the cylinder when the intake valve of the cylinder is closed, V _EC is the effective volume of the cylinder when the exhaust valve of the cylinder is closed, and ε _INL is the cylinder Head heat exchange coefficient, T _INL is the air temperature at the outlet of the intercooler; A _sc,eff is the effective area of scavenging air, A _in and A _out are the areas of the intake valve and exhaust valve of the cylinder respectively, η _sc,eff is the area of the scavenging air Gas efficiency; Ψ(π _sc ) is the dimensionless pressure ratio, P _d is the exhaust pipe pressure during the intake process, π _sc is the dimensionless ratio, that is, the ratio of the intake pipe pressure to the exhaust pipe pressure during the intake process, Collect the gas state parameters of the intake pipe and exhaust pipe, input the gas state parameters of the intake pipe and exhaust pipe and the geometric parameters of the diesel engine body into the calculation model of the intake air volume of the diesel engine system, and then obtain the intake air volume of the diesel engine system and the air intake volume of the cylinder and scavenging volume. 2. the thermodynamic parameter calculating method of four-stroke diesel engine ventilation process as claimed in claim 1, is characterized in that, also comprises: Construct the calculation model of the thermal parameters of the exhaust pipe at the end of the free exhaust process, see formulas (8)-(10): Among them: T _bld , T _bld-out , m _bld-out are the starting temperature, end point temperature and free exhaust volume of the free exhaust process respectively; T ₆ , P ₆ , m ₆ respectively represent the exhaust gas in the cylinder before the exhaust valve is opened γ is the adiabatic index of the flue gas in the free exhaust process, P _d1 is the exhaust main pipe pressure at the end of the free exhaust process, R is the exhaust gas constant of the exhaust pipe, V _EO is the opening of the cylinder exhaust valve Hourly cylinder working volume; N is the diesel engine speed, k is the stroke coefficient, for a four-stroke diesel engine, k=2; Collect the gas state parameters in the cylinder before the exhaust valve is opened and the gas state parameters of the exhaust pipe, and input the collected parameters and the geometric parameters of the diesel engine body into the calculation model of the thermal parameters of the exhaust pipe at the end of the free exhaust process to obtain the free exhaust process The starting temperature, ending temperature and free exhaust volume. 3. the thermodynamic parameter calculating method of four-stroke diesel engine ventilation process as claimed in claim 2, is characterized in that, also comprises: Construct the calculation model of the thermal parameters of the exhaust pipe at the end of the forced exhaust process, see formulas (11)-(13): m _exp =m ₆ -m _bld-out -m _sc(0) (12) Among them, T _exp and m _exp are the end temperature and forced exhaust volume of the forced exhaust process, respectively, m _sc(0) is the exhaust gas volume at the beginning of the scavenging process; m ₆ is the mass of the exhaust gas in the cylinder before the intake valve is opened , T _bld and T _bld-out are the starting temperature and end temperature of the free exhaust process respectively; P _d2 is the exhaust manifold pressure at the end of the forced exhaust process, and V _IO is when the intake valve is opened (that is, the forced exhaust process ends When) the working volume in the cylinder, R _e is the exhaust gas constant of the exhaust pipe at the end of the forced exhaust process; N is the diesel engine speed, k is the stroke coefficient, and for the four-stroke diesel engine, k=2; Collect the gas state parameters of the exhaust pipe, input the starting temperature and end temperature of the free exhaust process obtained in claim 2, the gas state parameters of the exhaust pipe, and the geometric parameters of the diesel engine body into the calculation of the thermal parameters of the exhaust pipe at the end of the forced exhaust process The model is used to obtain the end temperature and forced exhaust volume of the forced exhaust process and the exhaust gas volume at the beginning of the scavenging process. 4. the thermodynamic parameter calculating method of four-stroke diesel engine ventilation process as claimed in claim 3, is characterized in that, also comprises: Construct the calculation model of the thermal parameters of the exhaust pipe at the end of the scavenging process, see formulas (14)-(16): m _sc-out = s·m _sc (14) m _out ＝m _in +m _f ＝m _bld-out +m _exp +m _sc(0) -m _res +m _sc-out (15) Among them, m _sc-out is the amount of air slipped out during the scavenging process, m _out is the amount of exhaust gas in the exhaust manifold at the end of the scavenging process, T _d is the temperature of the exhaust gas in the exhaust manifold at the end of the scavenging process; m _sc is the scavenging air process scavenging volume, s is the slip coefficient of the scavenging process; min is the air intake volume of the cylinder during the intake process, m _f is the fuel consumption; m _{bld -out} is the free exhaust volume during the free exhaust process, and m _exp is The forced exhaust volume of the forced exhaust process, m _sc(0) is the exhaust gas volume at the beginning of the scavenging process; m _res is the residual exhaust gas volume in the cylinder at the end of the forced exhaust process, c _p,sc-out is the scavenging gas The average specific heat of the flue gas in the process, c _{p, exh} is the average specific heat of the flue gas in the free exhaust process and the forced exhaust process, c _{p, d} is the average specific heat of the flue gas in the ventilation process; T _exp is the end point of the forced exhaust process Temperature, that is, the temperature of the flue gas in the exhaust pipe at the end of the forced exhaust process; T _sc-out is the starting temperature of the scavenging process, that is, the cylinder intake temperature; Input the calculation results of claims 1 to 3 into the exhaust pipe thermal parameter calculation model at the end of the scavenging process to obtain the amount of air slipped out during the scavenging process and the exhaust gas volume and exhaust gas temperature of the exhaust main pipe at the end of the scavenging process.