A method for predicting scavenging volume of opposed piston engines considering boundary pressure

Abstract

The invention discloses a method for predicting the scavenging volume of an opposed piston engine considering boundary pressure, which belongs to the field of engine technology. Firstly, the exhaust port opening time, the intake port opening time, the exhaust port closing time and the intake port closing time are obtained; secondly, the cylinder pressure and temperature at the exhaust port opening time are obtained and a function of transient change quantity is constructed; then, the ventilation process is divided into three stages: the exhaust port opening stage alone, the intake and exhaust port simultaneous opening stage and the intake port opening stage alone; then, each micro-segment of the three stages is decomposed into constant volume heat transfer, volume change and constant volume flow process, and the cylinder volume, cylinder pressure, cylinder temperature, cylinder gas mass, exhaust flow rate and intake flow rate are iteratively calculated after each micro-segment is completed, and the constant volume specific heat capacity and specific heat ratio of the cylinder gas are updated according to the temperature and material state at this time; finally, the scavenging volume is obtained by summing calculation, and the intake and exhaust flow curve is obtained.

Description

Technical Field

[0001] The invention belongs to the technical field of engines, and in particular relates to a method for predicting the scavenging volume of an opposed piston engine taking boundary pressure into consideration. Background Art

[0002] The opposed-piston two-stroke engine uses the pressure difference between the intake and exhaust to perform scavenging. The amount of scavenging determines the degree of replacement of fresh air and residual exhaust gas in the cylinder. When the scavenging amount is sufficient, it can reduce the residual exhaust gas in the cylinder, increase the air charge and thus increase the engine power.

[0003] The scavenging volume is closely related to the intake and exhaust boundary pressure. For different ventilation requirements, corresponding pressure boundary conditions need to be set. The method for obtaining the scavenging volume of opposed piston two-stroke engines at different intake and exhaust pressures currently mainly adopts one-dimensional or three-dimensional simulation methods, which have problems such as complex model construction process, many required parameters, and long three-dimensional calculation time. At present, there is a lack of a method for predicting the scavenging volume of opposed piston engines under certain intake and exhaust boundary pressures. Summary of the invention

[0004] The purpose of the present invention is to provide a method for predicting the scavenging volume of an opposed piston engine taking into account boundary pressure, to perform differential processing on the coupled processes of flow, heat transfer and volume change in the cylinder, to iteratively calculate the transient changes of the gas state parameters in the cylinder, and to achieve the prediction of the scavenging volume under a certain intake and exhaust pressure boundary at a lower calculation cost.

[0005] To achieve the above object, the present invention provides a method for predicting the scavenging volume of an opposed piston engine considering boundary pressure, comprising the following steps:

[0006] Step 1, obtaining the exhaust port opening time, the air inlet opening time, the exhaust port closing time and the air inlet closing time;

[0007] Step 2: Obtain the in-cylinder pressure and temperature at the time when the exhaust port is opened; obtain them through experiments or simulation calculations, or estimate them based on engine parameters;

[0008] Step 3, constructing a function of transient variation, including exhaust piston position, intake piston position, exhaust port opening area, intake port opening area, constant volume specific heat capacity, and specific heat ratio;

[0009] Step 4: Divide the ventilation process into three stages: the exhaust port opening stage, the intake and exhaust port opening stage, and the intake port opening stage. Differentiate the crankshaft angle in each stage, select the crankshaft angle interval, and obtain the corresponding time interval. Take the differential to obtain the intake pressure and exhaust pressure of each differential segment;

[0010] Step 5: Decompose each micro-segment of the exhaust port opening stage into constant volume heat transfer, volume change, and constant volume flow processes, iteratively calculate the cylinder volume, cylinder pressure, cylinder temperature, cylinder gas mass, exhaust flow rate, and intake flow rate after each micro-segment is completed, and update the constant volume specific heat capacity and specific heat ratio of the cylinder gas according to the temperature and material state at this time;

[0011] Step 6: Decompose each micro-segment during the stage where the intake and exhaust ports are opened simultaneously into constant volume heat transfer, volume change, and constant volume flow processes, iteratively calculate the cylinder volume, cylinder pressure, cylinder temperature, cylinder gas mass, exhaust flow rate, and intake flow rate after each micro-segment is completed, and update the constant volume specific heat capacity and specific heat ratio of the cylinder gas according to the temperature and material state at this time;

[0012] Step 7, decompose each micro-segment of the air intake opening stage into constant volume heat transfer, volume change, and constant volume flow processes, iteratively calculate the cylinder volume, cylinder pressure, cylinder temperature, cylinder gas mass, exhaust flow rate, and intake flow rate after each micro-segment is completed, and update the constant volume specific heat capacity and specific heat ratio of the gas in the cylinder according to the temperature and material state at this time;

[0013] Step 8: Obtain the scavenging volume by summing up and obtaining the intake and exhaust flow curve.

[0014] Preferably, in step 1, the method for obtaining the exhaust port opening time, the air inlet opening time, the exhaust port closing time and the air inlet closing time is:

[0015] Solve the following equation:

[0016]

[0017] Get two solutions and , Exhaust port opening time , exhaust port closing time ;

[0018] Solve the following equation:

[0019]

[0020] Get two solutions and , air inlet opening time , air inlet closing time ;

[0021] In the formula, is the crank angle, is the crank radius, is the connecting rod length, is the air inlet height, is the exhaust port height, is the intake phase difference, is the exhaust phase difference.

[0022] Preferably, the method for estimating according to the engine parameters in step 2 is:

[0023] S21, calculate the maximum temperature in the cylinder :

[0024]

[0025] In the formula, is the calorific value of fuel, is the heat transfer loss, is the average constant volume specific heat capacity during the closed stage in the cylinder, is the average specific heat ratio during the closed stage in the cylinder, is the air-fuel ratio, is the intake air temperature, is the clearance volume, ,in is the mechanical compression ratio, is the cylinder diameter; is the cylinder volume when the air inlet is closed, calculated by the following formula:

[0026]

[0027] S22, calculate the maximum pressure in the cylinder based on the maximum temperature in the cylinder :

[0028]

[0029] In the formula, is the average intake pressure;

[0030] S23, calculate the cylinder pressure when the exhaust port is opened , and the cylinder temperature at the time the exhaust port is opened , the calculation expression is as follows:

[0031]

[0032]

[0033] In the formula, is the cylinder volume when the exhaust port is opened, calculated by the following formula:

[0034] .

[0035] Preferably, the method for constructing the function of transient variation in step 3 is:

[0036] First, construct the exhaust piston position , Intake piston position Crankshaft angle Functions between:

[0037]

[0038]

[0039] Then, construct the exhaust port opening area , Air inlet opening area Crankshaft angle Functions between:

[0040]

[0041]

[0042] In the formula, is the ratio of the exhaust port width to the circumference, is the ratio of the exhaust port width to the circumference;

[0043] Finally, the specific heat capacity at constant volume is constructed Specific heat ratio The gas temperature in the cylinder , Air mass fraction in cylinder The constant volume specific heat capacity and specific heat ratio are related to the temperature in the cylinder and the type of substance:

[0044] In the formula, represents the gas constant.

[0045] Preferably, the range of the iteration sequence number in step 5 is ; The range of iteration numbers in step 6 is ; The range of iteration numbers in step 7 is , Indicates crankshaft angle interval.

[0046] Preferably, in step 5, step 6, and step 7, the specific method for obtaining the pressure and temperature in the cylinder after the heat transfer is completed by calculating the constant volume heat transfer process is:

[0047] Calculate heat transfer :

[0048]

[0049] In the formula, is the heat transfer coefficient, For the The cylinder temperature at the end of each micro-segment is is the ambient temperature;

[0050] Calculate the cylinder temperature after heat transfer is completed :

[0051]

[0052] In the formula For the The gas mass in the cylinder at the end of each micro-segment, For the Specific heat capacity at constant volume at the end of each micro-segment;

[0053] Calculate the cylinder pressure after heat transfer is completed :

[0054]

[0055] In the formula, For the The cylinder pressure at the end of each micro-segment.

[0056] Preferably, in step 5, step 6, and step 7, the specific method for obtaining the cylinder volume, pressure, and temperature after the volume change is completed by calculating the volume change process is:

[0057] Calculate the The cylinder volume after the micro-segment piston movement is completed :

[0058]

[0059] In the formula, The crankshaft angle is The exhaust piston position at The crankshaft angle is The intake piston position at ;

[0060] Calculate the cylinder pressure after the volume change is completed :

[0061]

[0062] In the formula, For the The cylinder volume at the end of each micro-segment is For the Specific heat ratio at the end of each micro-segment;

[0063] Calculate the cylinder temperature after the volume change is completed :

[0064] .

[0065] Preferably, in step 5, the intake and exhaust flow rate, the gas mass, pressure, temperature, and exhaust mass flowing out of the cylinder are obtained by calculating the constant volume flow process, and the specific method is:

[0066] During the exhaust port opening stage, , For the The intake flow rate of the micro-segment; calculate the Micro-segmented exhaust flow ,when For supercritical flow, For subcritical flow:

[0067] In the formula, The crankshaft angle is The exhaust port opening area is is the exhaust port flow coefficient, For the The exhaust pressure at the end of each micro-segment; after the constant volume flow process is completed, the exhaust mass flowing out of the cylinder is The mass of gas in the cylinder is The pressure in the cylinder is The temperature in the cylinder is , Indicates The exhaust gas mass flowing out of the cylinder in each micro-segment.

[0068] Preferably, in step 6, the intake and exhaust flow rate, the mass of the gas in the cylinder, the pressure, the temperature, the mass of the exhaust gas flowing out of the cylinder, and the mass of the intake gas flowing into the cylinder are obtained by calculating the constant volume flow process. The calculation of the constant volume flow process includes the following four cases:

[0069] Situation 1: When and , both the inlet and outlet have positive flow, The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is , where For the The intake pressure at the end of each micro-segment, The crankshaft angle is The air inlet opening area is is the inlet flow coefficient, is the intake specific heat ratio; after the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is , Indicates The mass of intake air flowing into the cylinder in micro-segments, Indicates The air mass fraction in the cylinder after each micro-segment is completed;

[0070] Case 2: and , the exhaust port has a positive flow, the intake port has a reverse flow, The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is ; After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ;

[0071] Case 3: and , the air inlet flows forward, the exhaust port flows backward, The exhaust flow rate of each micro-segment is , where is the exhaust temperature, is the exhaust specific heat ratio, and the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is ; After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ;

[0072] Case 4: and , backflow occurs at both the inlet and outlet. The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is ; After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is .

[0073] Preferably, in step 7, the intake and exhaust flow rate, the gas mass in the cylinder, the pressure, the temperature, and the mass of the intake air flowing into the cylinder are obtained by calculating the constant volume flow process, and during the calculation process, a forward flow or a reverse flow occurs at the air inlet:

[0074] when The air inlet has a positive flow. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is After the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ;

[0075] when Backflow occurs at the air inlet. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is , after the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is .

[0076] Therefore, the present invention adopts the above-mentioned method for predicting the scavenging volume of an opposed piston engine considering the boundary pressure, which has the following beneficial effects:

[0077] (1) Decompose the complex coupled processes of flow, heat transfer and volume change, calculate the instantaneous values ​​of the gas state parameters in the cylinder, and realize the prediction of scavenging volume;

[0078] (2) Calculations are completed through programming, eliminating the need for one-dimensional and three-dimensional simulations, saving computing costs;

[0079] (3) It can complete the prediction of the scavenging volume under any intake and exhaust pressure boundary, and can design the intake and exhaust pressure and pressure difference required by the engine according to the scavenging volume demand.

[0080] The technical solution of the present invention is further described in detail below through the accompanying drawings and embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0081] Figure 1 It is an overall flow chart of a method for predicting the scavenging volume of an opposed piston engine considering boundary pressure of the present invention;

[0082] Figure 2A schematic diagram of the ventilation process according to an embodiment of the present invention;

[0083] Figure 3 is an intake air flow curve diagram of an embodiment of the present invention;

[0084] Figure 4 FIG. 4 is an exhaust flow curve diagram of an embodiment of the present invention. DETAILED DESCRIPTION

[0085] The following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0086] See also Figure 1-4 , a method for predicting the scavenging volume of an opposed piston engine considering boundary pressure, comprising the following steps:

[0087] Step 1: Get the exhaust port opening time , Air inlet opening time , Exhaust port closing time and air inlet closing time The specific method is:

[0088] Solve the following equation:

[0089]

[0090] Get two solutions and , Exhaust port opening time , exhaust port closing time .

[0091] Solve the following equation:

[0092]

[0093] Get two solutions and , air inlet opening time , air inlet closing time Where is the crank angle, is the crank radius, is the connecting rod length, is the air inlet height, is the exhaust port height, is the intake phase difference, is the exhaust phase difference.

[0094] Step 2: Obtain the cylinder pressure when the exhaust port is opened ,temperature , can be obtained through experiments or simulation calculations, or can be estimated based on engine parameters. The method for estimating based on engine parameters is:

[0095] Calculate the maximum temperature in the cylinder , where is the calorific value of fuel, is the heat transfer loss, is the average constant volume specific heat capacity during the closed stage in the cylinder, is the average specific heat ratio in the closed stage in the cylinder, is the air-fuel ratio, is the intake air temperature, is the clearance volume, ,in is the mechanical compression ratio, is the cylinder diameter; is the cylinder volume when the air inlet is closed, calculated by the following formula:

[0096]

[0097] Calculate the maximum pressure in the cylinder based on the maximum temperature in the cylinder , where is the average intake air pressure.

[0098] Calculate the cylinder pressure when the exhaust port is opened , and the cylinder temperature at the time the exhaust port is opened , where is the cylinder volume when the exhaust port is opened, calculated by the following formula:

[0099]

[0100] Step 3: During the ventilation period, the piston position and the gas state in the cylinder undergo transient changes. A function of the transient change is constructed, including the exhaust piston position , Intake piston position , Exhaust port opening area , Air inlet opening area Specific heat at constant volume Specific heat ratio .

[0101] First, construct the exhaust piston position , Intake piston position Crankshaft angle Functions between:

[0102]

[0103]

[0104] Then, construct the exhaust port opening area , Air inlet opening area Crankshaft angle Functions between:

[0105]

[0106]

[0107] In the formula is the ratio of the exhaust port width to the circumference, is the ratio of exhaust port width to circumference.

[0108] Finally, the specific heat capacity at constant volume and the specific heat ratio are related to the temperature in the cylinder and the type of material. Specific heat ratio The gas temperature in the cylinder , Air mass fraction in cylinder Function:

[0109] Gas constant It is only related to the type of substance. Since the relative mass fractions of air and exhaust gas in the cylinder are basically equal, the material exchange between air and exhaust gas during the ventilation process does not affect , so it is believed Is a constant.

[0110] Step 4: Divide the ventilation process into three stages according to the intake and exhaust timing: the exhaust port opening stage ( ), the stage where the intake and exhaust ports are opened simultaneously ( ) and the air inlet opening stage ( ), differentiate the crankshaft angle, and select the crankshaft angle interval , and get the corresponding time interval , is the engine speed, and the intake and exhaust transient pressures are calculated according to the time interval Take the differential to obtain the intake pressure and exhaust pressure of each differential segment.

[0111] Step 5: When the exhaust port is opened alone, the high-pressure gas in the cylinder flows out from the exhaust port in one direction, and each micro-segment of the flow process is decomposed into constant volume heat transfer, volume change, and constant volume flow process. For the moment before the start of the first micro-segment, the volume of the cylinder is:

[0112]

[0113] The temperature and pressure are and The mass of gas in the cylinder is , (Note: , Bring in the above Calculated in the function of Then the iterative calculation begins. is the iteration ordinal, so The value is taken from Start, increase to , each iteration includes the following steps:

[0114] 1. Constant volume heat transfer process: First calculate the heat transfer , is the heat transfer coefficient, For the The cylinder temperature at the end of each micro-segment (Note: hour, = ), is the ambient temperature. Calculate the temperature in the cylinder after the heat transfer is completed. , where For the The gas mass in the cylinder at the end of each micro-segment, For the The constant volume specific heat capacity at the end of each micro-segment. Calculate the cylinder pressure after the heat transfer is completed. , For the The cylinder pressure at the end of each micro-segment.

[0115] 2. Volume change process: Calculate the The volume of the cylinder after the micro-segmented piston movement is completed:

[0116]

[0117] In the formula The crankshaft angle is The exhaust piston position at The crankshaft angle is The intake piston position at the time. Calculate the cylinder pressure after the volume change is completed. , For the The cylinder volume at the end of each micro-segment is For the Specific heat ratio at the end of each micro-segment. Calculate the cylinder temperature after the volume change is completed. .

[0118] 3. Constant volume flow process: When the exhaust port is opened alone, Calculate the The exhaust flow rate of a micro segment is For supercritical flow, For subcritical flow:

[0119] In the formula, The crankshaft angle is The exhaust port opening area is is the exhaust port flow coefficient, For the The exhaust pressure at the end of each micro-segment. After the constant volume flow process is completed, the exhaust mass flowing out of the cylinder is The mass of gas in the cylinder is The pressure in the cylinder is The temperature in the cylinder is .

[0120] So far, we have obtained After the micro-segmentation is completed, the cylinder volume , cylinder pressure , cylinder temperature , Gas quality in cylinder , Exhaust flow , intake air flow , the mass of exhaust gas flowing out of the cylinder , and update the constant volume specific heat capacity and specific heat ratio of the gas in the cylinder according to the temperature and material state at this time, , .make The value of is increased by 1, and the above constant volume heat transfer, volume change and constant volume flow process are repeated until .

[0121] Step 6: In the stage where the inlet and exhaust ports are opened simultaneously, there is gas flow at the inlet and exhaust ports at the same time, and each micro-segment of the flow process is decomposed into constant volume heat transfer, volume change, and constant volume flow process. At the moment before the inlet and exhaust ports are opened simultaneously, the air mass fraction in the cylinder is . Start iterative calculation, so The value is taken from Start and increase to , each iteration includes the following steps:

[0122] 1. Constant volume heat transfer process: The heat transfer amount is , the temperature in the cylinder after the heat transfer is completed is , the cylinder pressure after heat transfer is completed is .

[0123] 2. Volume change process: The volume of the cylinder after the micro-segmented piston movement is completed is:

[0124]

[0125] After the volume change is completed, the pressure in the cylinder is After the volume change is completed, the temperature in the cylinder is .

[0126] 3. Constant volume flow process: When the inlet and exhaust ports are open at the same time, both the inlet and exhaust ports may have forward flow and reverse flow, so the constant volume flow process may have the following four situations:

[0127] Situation 1: When and , both the inlet and outlet have positive flow, The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is , where For the The intake pressure at the end of each micro-segment, The crankshaft angle is The air inlet opening area is is the inlet flow coefficient, is the intake specific heat ratio. After the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is .

[0128] Situation 2: and , the exhaust port has a positive flow, the intake port has a reverse flow, The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is .

[0129] Situation 3: and , the air inlet flows forward, the exhaust port flows backward, The exhaust flow rate of each micro-segment is , where is the exhaust temperature, is the exhaust specific heat ratio, and the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is .

[0130] Situation 4: and , backflow occurs at both the inlet and outlet. The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is .

[0131] After the constant volume flow process is completed, the pressure in the cylinder is The temperature in the cylinder is .

[0132] So far, we have obtained After the micro-segmentation is completed, the cylinder volume , cylinder pressure , cylinder temperature , Gas quality in cylinder , Exhaust flow , intake air flow , the mass of exhaust gas flowing out of the cylinder , the mass of air flowing into the cylinder , and update the constant volume specific heat capacity and specific heat ratio of the gas in the cylinder according to the temperature and material state at this time, , .make The value of is increased by 1, and the above constant volume heat transfer, volume change and constant volume flow process are repeated until .

[0133] Step 7: In the stage where the air inlet is opened alone, there is flow only at the air inlet. Each micro-segment of the flow process is decomposed into constant volume heat transfer, volume change, and constant volume flow process. Perform iterative calculations to make The value is taken from Increase to , each iteration includes the following steps:

[0134] 1. Constant volume heat transfer process: The heat transfer amount is , the temperature in the cylinder after the heat transfer is completed is , the cylinder pressure after heat transfer is completed is .

[0135] 2. Volume change process: The volume of the cylinder after the micro-segmented piston movement is completed is:

[0136]

[0137] After the volume change is completed, the pressure in the cylinder is After the volume change is completed, the temperature in the cylinder is .

[0138] 3. Constant volume flow process: When the air inlet is opened alone, the exhaust flow rate , forward flow and reverse flow may occur at the air inlet:

[0139] (1) When The air inlet has a positive flow. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is After the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is .

[0140] (2) When Backflow occurs at the air inlet. The intake flow rate of each micro-segment is , the mass of air flowing out of the cylinder from the air inlet is , after the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is .

[0141] After the constant volume flow process is completed, the pressure in the cylinder is The temperature in the cylinder is .

[0142] So far, we have obtained After the micro-segmentation is completed, the cylinder volume , cylinder pressure , cylinder temperature , Gas quality in cylinder , Exhaust flow , intake air flow , the mass of air flowing into the cylinder , and update the constant volume specific heat capacity and specific heat ratio of the gas in the cylinder according to the temperature and material state at this time, , .make The value of is increased by 1, and the above constant volume heat transfer, volume change and constant volume flow process are repeated until .

[0143] Step 8: Calculate the scavenging volume ,by ( ) is the horizontal axis, The intake flow curve is obtained as the ordinate, The exhaust flow curve is obtained by taking the ordinate as the coordinate.

[0144] Example

[0145] In this embodiment, the crank radius , connecting rod length , air inlet height , Exhaust port height , intake phase difference , exhaust phase difference , inlet width to circumference ratio , Exhaust port width to circumference ratio . Solution The exhaust port opening time is The exhaust port closing time is . Solution Get the air inlet opening time , air inlet closing time .

[0146] Estimate the in-cylinder pressure and temperature at the time when the exhaust port opens. Fuel calorific value of opposed piston two-stroke diesel engine , heat transfer loss , the average constant volume specific heat capacity during the closed stage in the cylinder , the average specific heat ratio of the closed stage in the cylinder , air-fuel ratio , intake air temperature , average intake pressure , mechanical compression ratio , cylinder diameter , and the clearance volume is obtained , cylinder volume when the air inlet is closed , cylinder volume when the exhaust port is opened , calculate the maximum temperature in the cylinder , maximum pressure in cylinder , and then get the cylinder pressure when the exhaust port is opened , and the cylinder temperature at the time the exhaust port is opened .

[0147] Select crankshaft angle interval , engine speed , and get the corresponding time interval .

[0148] Gas constant At the moment before the first micro-segment begins, the cylinder volume , cylinder pressure , cylinder temperature The mass of gas in the cylinder is , , .

[0149] The intake and exhaust boundary pressures are set to , And remain unchanged, the intake and air flow coefficient , are all 0.9. Use programming to perform iterative calculations in steps 5 to 7. First, let , in the constant volume heat transfer process, the cylinder temperature after the heat transfer is completed is calculated , cylinder pressure ; During the volume change process, the cylinder volume after the piston movement is completed is calculated , cylinder pressure , cylinder temperature ; Calculate the exhaust flow rate during constant volume flow , intake air flow , the mass flowing into the cylinder or flowing back out of the cylinder through the air inlet , the mass flowing out of the cylinder or back into the cylinder through the air inlet , Gas quality in cylinder , cylinder pressure and the temperature in the cylinder , and update the constant volume specific heat capacity of the gas in the cylinder and specific heat ratio ,make , repeat the iterative process until The final calculated scavenging volume is , and obtain the intake flow curve and exhaust flow curve.

[0150] Therefore, the present invention adopts the above-mentioned opposed piston engine scavenging volume prediction method considering the boundary pressure, performs differential processing on the coupled process of flow, heat transfer and volume change in the cylinder, iteratively calculates the transient changes of the gas state parameters in the cylinder, and realizes the scavenging volume prediction under a certain intake and exhaust pressure boundary with a lower calculation cost.

[0151] Finally, it should be noted that the above embodiments are only used to illustrate the technical solution of the present invention rather than to limit it. Although the present invention has been described in detail with reference to the preferred embodiments, those skilled in the art should understand that they can still modify or replace the technical solution of the present invention with equivalents, and these modifications or equivalent replacements cannot cause the modified technical solution to deviate from the spirit and scope of the technical solution of the present invention.

Claims

1. A method for predicting the scavenging volume of an opposed piston engine considering boundary pressure, characterized in that: The following steps are involved: Step 1, obtaining the exhaust port opening time, the air inlet opening time, the exhaust port closing time and the air inlet closing time; The method for obtaining the exhaust port opening time, the air inlet opening time, the exhaust port closing time and the air inlet closing time is: Solve the following equation: Get two solutions and , Exhaust port opening time , exhaust port closing time ; Solve the following equation: Get two solutions and , air inlet opening time , air inlet closing time ; In the formula, is the crank angle, is the crank radius, is the connecting rod length, is the air inlet height, is the exhaust port height, is the intake phase difference, is the exhaust phase difference; Step 2: Obtain the in-cylinder pressure and temperature at the time when the exhaust port is opened; obtain them through experiments or simulation calculations, or estimate them based on engine parameters; The method for estimating based on engine parameters is: S21, calculate the maximum temperature in the cylinder : In the formula, is the calorific value of fuel, is the heat transfer loss, is the average constant volume specific heat capacity during the closed stage in the cylinder, is the average specific heat ratio in the closed stage in the cylinder, is the air-fuel ratio, is the intake air temperature, is the clearance volume, ,in is the mechanical compression ratio, is the cylinder diameter; is the cylinder volume when the air inlet is closed, calculated by the following formula: S22, calculate the maximum pressure in the cylinder based on the maximum temperature in the cylinder : In the formula, is the average intake pressure; S23, calculate the cylinder pressure when the exhaust port is opened , and the cylinder temperature at the time the exhaust port is opened , the calculation expression is as follows: In the formula, is the cylinder volume when the exhaust port is opened, calculated by the following formula: ； Step 3, constructing a function of transient variation, including exhaust piston position, intake piston position, exhaust port opening area, intake port opening area, constant volume specific heat capacity, and specific heat ratio; The method to construct the function of transient change is: First, construct the exhaust piston position , Intake piston position Crankshaft angle Functions between: Then, construct the exhaust port opening area , Air inlet opening area Crankshaft angle Functions between: In the formula, is the ratio of the exhaust port width to the circumference, is the exhaust port width to circumference ratio; Finally, the specific heat capacity at constant volume is constructed Specific heat ratio The gas temperature in the cylinder , Air mass fraction in cylinder Function: In the formula, represents the gas constant; Step 4: Divide the ventilation process into three stages: the exhaust port opening stage, the intake and exhaust port opening stage, and the intake port opening stage. Differentiate the crankshaft angle in each stage, select the crankshaft angle interval, and obtain the corresponding time interval. Take the differential to obtain the intake pressure and exhaust pressure of each differential segment; Step 5: Decompose each micro-segment of the exhaust port opening stage into constant volume heat transfer, volume change, and constant volume flow process. Iteratively calculate the cylinder volume, cylinder pressure, cylinder temperature, cylinder gas mass, exhaust flow rate, and intake flow rate after each micro-segment is completed, and update the constant volume specific heat capacity and specific heat ratio of the cylinder gas according to the temperature and material state at this time; the range of the iteration sequence is ; The specific method of the pressure and temperature in the cylinder after the heat transfer is completed is: Calculate heat transfer : In the formula, is the heat transfer coefficient, For the The cylinder temperature at the end of each micro-segment is is the ambient temperature; Calculate the cylinder temperature after heat transfer is completed : In the formula For the The gas mass in the cylinder at the end of each micro-segment, For the Specific heat capacity at constant volume at the end of each micro-segment; Calculate the cylinder pressure after heat transfer is completed : In the formula, For the The cylinder pressure at the end of each micro-segment; The specific method of cylinder volume, pressure and temperature after the volume change is completed is: Calculate the The cylinder volume after the micro-segment piston movement is completed : In the formula, The crankshaft angle is The exhaust piston position at The crankshaft angle is The intake piston position at ; Calculate the cylinder pressure after the volume change is completed : In the formula, For the The cylinder volume at the end of each micro-segment is For the Specific heat ratio at the end of each micro-segment; Calculate the cylinder temperature after the volume change is completed : ； Through the calculation of the constant volume flow process, the intake and exhaust flow, the gas mass, pressure, temperature, and exhaust mass out of the cylinder are obtained. The specific method is: During the exhaust port opening stage, , For the The intake flow rate of the micro-segment; calculate the Micro-segmented exhaust flow ,when For supercritical flow, For subcritical flow: In the formula, The crankshaft angle is The exhaust port opening area is is the exhaust port flow coefficient, For the The exhaust pressure at the end of each micro-segment; After the constant volume flow process is completed, the exhaust mass flowing out of the cylinder is The mass of gas in the cylinder is The pressure in the cylinder is The temperature in the cylinder is , Indicates The exhaust gas mass flowing out of the cylinder in each micro-segment; Step 6: Decompose each micro-segment of the stage where the intake and exhaust ports are opened simultaneously into constant volume heat transfer, volume change, and constant volume flow processes. Iteratively calculate the cylinder volume, cylinder pressure, cylinder temperature, cylinder gas mass, exhaust flow rate, and intake flow rate after each micro-segment is completed, and update the constant volume specific heat capacity and specific heat ratio of the cylinder gas according to the temperature and material state at this time; the range of the iteration sequence is Through the calculation of the constant volume flow process, the intake and exhaust flow, the gas mass, pressure, temperature, the exhaust mass out of the cylinder, and the intake mass into the cylinder are obtained. The calculation of the constant volume flow process includes the following four cases: Situation 1: When and , both the inlet and outlet have positive flow, The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is , where For the The intake pressure at the end of each micro-segment, The crankshaft angle is The air inlet opening area is is the inlet flow coefficient, is the intake specific heat ratio; after the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is , Indicates The mass of intake air flowing into the cylinder in micro-segments, Indicates The air mass fraction in the cylinder after each micro-segment is completed; Case 2: and , the exhaust port has a positive flow, the intake port has a reverse flow, The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is ; After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ; Case 3: and , the air inlet flows forward, the exhaust port flows backward, The exhaust flow rate of each micro-segment is , where is the exhaust temperature, is the exhaust specific heat ratio, and the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is ; After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ; Case 4: and , backflow occurs at both the inlet and outlet. The exhaust flow rate of each micro-segment is , the mass of exhaust gas flowing out of the cylinder is ;No. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is ; After the constant volume flow process is completed, the gas mass in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ; Step 7: Decompose each micro-segment of the air inlet opening stage into constant volume heat transfer, volume change, and constant volume flow process. Iteratively calculate the cylinder volume, cylinder pressure, cylinder temperature, cylinder gas mass, exhaust flow rate, and intake flow rate after each micro-segment is completed, and update the constant volume specific heat capacity and specific heat ratio of the cylinder gas according to the temperature and material state at this time; the range of the iteration sequence is , Indicates crankshaft angle interval; Through the calculation of the constant volume flow process, the intake and exhaust flow, the gas mass in the cylinder, the pressure, the temperature, and the mass of the intake air flowing into the cylinder are obtained. During the calculation process, the intake port has a positive flow or a reverse flow: when The air inlet has a positive flow. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is After the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ; when The air inlet has reverse flow. The intake flow rate of each micro-segment is , the mass of air flowing into the cylinder is , after the constant volume flow process is completed, the mass of the gas in the cylinder is , the air mass fraction in the cylinder is The pressure in the cylinder is The temperature in the cylinder is ; Step 8: Obtain the scavenging volume by summing up and obtaining the intake and exhaust flow curve.

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