CN117195436B - Method for determining length of exhaust manifold of multi-cylinder opposed-piston engine - Google Patents
Method for determining length of exhaust manifold of multi-cylinder opposed-piston engine Download PDFInfo
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- CN117195436B CN117195436B CN202311434299.7A CN202311434299A CN117195436B CN 117195436 B CN117195436 B CN 117195436B CN 202311434299 A CN202311434299 A CN 202311434299A CN 117195436 B CN117195436 B CN 117195436B
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Abstract
The invention discloses a method for determining the length of an exhaust manifold of a multi-cylinder opposed-piston engine, which belongs to the technical field of engines and comprises the following steps: step 1, determining an engine ignition interval according to the number of engine cylinders; step 2, calculating an exhaust continuous angle according to the radius of an engine crank, the length of a connecting rod and the height of an exhaust port; step 3, determining the exhaust overlapping period of the adjacent cylinders according to the exhaust continuous angle, the ignition interval and the engine speed; step 4, calculating the propagation speed of the exhaust pressure wave; step 5, calculating the shortest exhaust circulation path; and 6, calculating the length of the exhaust manifold. The invention provides a method for determining the length of an exhaust manifold of a multi-cylinder opposed-piston engine, which directly calculates the length of the exhaust manifold without exhaust interference through a plurality of steps and formulas based on given rotating speed, cylinder number, cylinder center distance, crank radius, connecting rod length, inlet and outlet heights and the gas property of exhaust.
Description
Technical Field
The invention belongs to the technical field of engines, and particularly relates to a method for determining the length of an exhaust manifold of a multi-cylinder opposed-piston engine.
Background
Compared with a common four-stroke engine, the two-stroke engine with the opposite pistons has the advantages that a valve mechanism is omitted, an air inlet and an air outlet are respectively arranged at two ends of the cylinder, and the opening and closing of the air inlet and the air outlet are controlled through the movement of the pistons, so that high-temperature and high-pressure waste gas generated by in-cylinder combustion is discharged out of the cylinder, fresh air is introduced into the cylinder at the same time, the next cycle combustion is participated, and the continuous operation of the engine is ensured. The exhaust passage of the opposed piston two-stroke engine has the function of ensuring that the exhaust gas in the cylinder is smoothly discharged out of the cylinder, and the pressure at the exhaust port is required to be as low as possible so as to form a certain intake-exhaust pressure difference to push fresh air into the cylinder, as shown in fig. 1. For a multi-cylinder opposed piston two-stroke engine, the distance between cylinders is short, when the exhaust port of one cylinder is opened, high-temperature and high-pressure exhaust gas in the cylinder is discharged, a strong positive pressure wave is generated and transmitted to the exhaust port of the adjacent cylinder, and at the moment, if the exhaust of the adjacent cylinder is not finished and the exhaust port is still opened, the positive pressure wave pushes the discharged gas back into the cylinder, so that the exhaust gas flows back, and the phenomenon is the exhaust interference phenomenon of the multi-cylinder engine. Therefore, a method for determining the length of the exhaust manifold of the multi-cylinder opposed-piston engine is needed to solve the problem in the prior art that when the exhaust of the adjacent cylinders is not finished and the exhaust ports are still open, the positive pressure wave pushes the exhausted gas back into the cylinders, so that the exhaust gas flows backwards.
Disclosure of Invention
The invention aims to provide a method for determining the length of an exhaust manifold of a multi-cylinder opposed-piston engine, which solves the problem that in the prior art, when the exhaust of an adjacent cylinder is not finished and an exhaust port is still open, positive pressure waves push the exhausted gas back into the cylinder, so that the exhaust gas flows backwards.
To achieve the above object, the present invention provides a method for determining the length of an exhaust manifold of a multi-cylinder opposed-piston engine, comprising the steps of:
step 1, determining an engine ignition interval according to the number of engine cylinders, forCylinder engine->The ignition interval of adjacent cylinders is +.>；
Step 2, according to the engineCrank radiusLength of connecting rod->And exhaust height +.>Calculating an exhaust gas sustaining angle;
step 3, determining the exhaust overlapping period of the adjacent cylinders according to the exhaust continuous angle, the ignition interval and the engine speed;
step 4, calculating the propagation speed of the exhaust pressure wave;
step 5, calculating the shortest exhaust circulation path;
and 6, calculating the length of the exhaust manifold.
Preferably, the exhaust gas duration angle in step 2 is calculated as follows:
;
wherein,for crank radius>For the length of the connecting rod->Crank-link ratio>，/>The crank angle is 0-360 DEG CA,>the exhaust sustaining angle is +.>。
Preferably, the specific process of determining the exhaust overlap period of the adjacent cylinders in the step 3 is as follows:
for the followingCylinder engine, when->The exhaust overlap period of adjacent cylinders is +.>No interference exists between the exhaust gases of the cylinders; when->The exhaust overlap angle of each cylinder is +.>The exhaust overlap angle of each cylinder is converted into time according to the engine speed, and the specific expression is as follows:
;
in the method, in the process of the invention,for the period of exhaust overlap>For engine speed>Is the exhaust sustaining angle.
Preferably, the calculation process of the propagation velocity of the exhaust pressure wave in step 4 is specifically as follows:
;
wherein,sound speed for engine exhaust->Is the exhaust specific heat ratio; />Is the gas constant of the exhaust gas->For the exhaust gas temperature, the gas constant of the exhaust gas +.>The calculation formula of (2) is as follows:
;
in the method, in the process of the invention,is the (th) in exhaust>Mass fraction of seed gas component, +.>Is the (th) in exhaust>The relative molecular mass of the seed gas component;
specific heat ratio of exhaust gasThe calculation formula is as follows:
;
in the method, in the process of the invention,、/>the constant pressure specific heat capacity and the constant heat capacity of the exhaust are respectively, wherein the constant pressure specific heat capacity of the exhaustThe calculation formula is as follows:
;
in the method, in the process of the invention,is the (th) in exhaust>The gas composition is->Constant pressure specific heat capacity at temperature, constant specific heat capacity of exhaust gasThe calculation formula of (2) is as follows:
。
preferably, the calculation formula of the shortest exhaust gas flow path in step 5 is as follows:
;
wherein,for the shortest exhaust gas flow path,/->Sound speed for engine exhaust->Is the exhaust overlap period.
Preferably, the calculation formula of the exhaust manifold length in step 6 is as follows:
;
wherein,for exhaust manifold length, +.>For the distance between cylinder centers>Is the shortest exhaust gas flow path.
Therefore, the method for determining the length of the exhaust manifold of the multi-cylinder opposed-piston engine has the following beneficial effects:
(1) The designed length of the exhaust manifold can effectively solve the problem of exhaust interference of the multi-cylinder opposed-piston two-stroke engine;
(2) A complex one-dimensional or three-dimensional simulation model of the engine is not required to be constructed, common formulas are adopted for calculation, and the calculation cost is low;
(3) The method does not need to provide a large number of engine parameters, and can be carried out in an early design stage of the engine only by the basic rotation speed, the number of cylinders, the cylinder center distance, the crank radius, the length of a connecting rod, the height of an exhaust port and the property of exhaust gas.
The technical scheme of the invention is further described in detail through the drawings and the embodiments.
Drawings
FIG. 1 is a schematic diagram of a multi-cylinder opposed-piston two-stroke engine breathing system in the background;
FIG. 2 is a schematic illustration of the exhaust duct configuration of a multi-cylinder OP2S engine of this invention;
FIG. 3 is an exhaust interference schematic diagram of a multi-cylinder engine of the present invention;
FIG. 4 is a flow chart of a method for determining the shortest exhaust manifold length of a multi-cylinder opposed-piston engine of the present invention.
Detailed Description
The following detailed description of the embodiments of the invention, provided in the accompanying drawings, is not intended to limit the scope of the invention, as claimed, but is merely representative of selected embodiments of the invention. All other embodiments, which can be made by those skilled in the art based on the embodiments of the invention without making any inventive effort, are intended to be within the scope of the invention.
Referring to fig. 2-4, a method for determining the length of an exhaust manifold of a multi-cylinder opposed-piston engine includes the steps of:
step 1, determining engine ignition interval according to the number of engine cylinders, wherein the cycle period of the two-stroke engine is 360 degrees CA (360 degrees CA is 360 degrees crank angle), each cylinder is ignited once in each cycle, and the engine is started to the following stepsCylinder engine->The ignition interval of adjacent cylinders is +.>. According to the invention, only the conditions of three, four and five-cylinder engines are considered, for a two-cylinder two-stroke opposed-piston engine, the ignition interval is 180 degrees CA and is larger than the exhaust continuous angle of the two-stroke engine (namely the angle of the crankshaft turning from the opening of the exhaust port to the closing of the exhaust port), and exhaust interference can not occur among cylinders; for a six-cylinder engine, three cylinders are generally divided into a group, so that the determination of the manifold length of the six-cylinder engine and above can be applied to the case of three, four and five-cylinder engines;
step 2, according to the radius of the engine crankLength of connecting rod->And exhaust height +.>Calculating exhaust gas continuous angle and calculating toolThe body is as follows:
;
wherein,crank radius in mm +.>The length of the connecting rod is in mm, < >>Crank-link ratio>，The crank angle is 0-360 DEG CA,>the exhaust sustaining angle is +.>。
And 3, determining the exhaust overlapping period of the adjacent cylinders according to the exhaust continuous angle, the ignition interval and the engine speed, wherein the specific process is as follows:
for the followingCylinder engine, when->The exhaust overlap period of adjacent cylinders is +.>No interference exists between the exhaust gases of the cylinders; when->The exhaust overlap angle of each cylinder is +.>The exhaust overlap angle of each cylinder is converted into time according to the engine speed, and the specific expression is as follows:
;
in the method, in the process of the invention,for the exhaust overlap period, the unit is s, < >>The unit is r/min for engine speed, < >>Is the exhaust sustaining angle.
And 4, calculating the propagation speed of the exhaust pressure wave, wherein the specific calculation process is as follows:
;
wherein,the sound velocity of the exhaust gas of the engine is expressed in m/s #>Is the exhaust specific heat ratio; />Is the gas constant of the exhaust gas, expressed in J/kg/K,/I>Is the exhaust gas temperature, in K, the gas constant of the exhaust gas +.>The calculation formula of (2) is as follows:
;
in the method, in the process of the invention,is the (th) in exhaust>Mass fraction of seed gas component, +.>Is the (th) in exhaust>The relative molecular mass of the seed gas component;
specific heat ratio of exhaust gasThe calculation formula is as follows:
;
in the method, in the process of the invention,、/>the constant pressure specific heat capacity and the constant heat capacity of the exhaust are respectively J/kg/K, wherein the constant pressure specific heat capacity of the exhaust is +.>The calculation formula is as follows:
;
in the method, in the process of the invention,is the (th) in exhaust>The gas composition is->Constant pressure specific heat capacity at temperature, constant specific heat capacity of exhaust gasThe calculation formula of (2) is as follows:
。
and 5, calculating the shortest exhaust circulation path, wherein a specific calculation formula is as follows:
;
wherein,for the shortest exhaust gas flow path in mm, & lt/EN & gt>Sound speed for engine exhaust->Is the exhaust overlap period.
Step 6, calculating the length of the exhaust manifold, wherein the specific calculation formula is as follows:
;
wherein,for exhaust manifold length, +.>The cylinder center distance is in mm, < >>Is the shortest exhaust gas flow path.
Examples
In this example, the object was a three cylinder opposed piston two stroke engine with a speed of 2800r/min, a crank radius of 29.5mm, a connecting rod length of 118mm, an exhaust port height of 13mm, and a cylinder center distance of 88.4mm. The firing interval is 120 CA, and the relation between the piston displacement and the crank angle is as follows:
;
solving two solutions of the following equation in the range of 0-360 ° CA:
;
obtaining°CA，/>°CA，/>CA of degree greater than->Calculate the exhaust overlap period to +.>. The engine exhaust temperature is 800K, and the gas components and the respective mass fractions in the exhaust are: o (O) 2 Mass fraction 0.099, CO 2 Mass fraction 0.119, N 2 Mass fraction 0.739, H 2 O mass fraction 0.043, relative molecular mass of four gases are respectively 32, 44, 28 and 18, and the gas constant of the exhaust gas is calculated as follows:
;
table look-up to obtain constant pressure specific heat capacity of four gases at 800K: o (O) 2 1016J/kg/K, CO 2 1085J/kg/K, N 2 1097J/kg/K, H 2 O is 2075 J/kg/K, the constant pressure specific heat capacity of the exhaust gas is calculated as follows:
;
the specific heat capacity is as follows:
;
the exhaust specific heat ratio is:
;
the propagation speed of the pressure wave in the exhaust gas is further calculated as:
;
the shortest exhaust gas flow path is calculated as:
;
the shortest exhaust manifold length required was calculated from the cylinder center distance 88.4mm as:
。
therefore, the method for determining the length of the exhaust manifold of the multi-cylinder opposed-piston engine is adopted, and the length of the exhaust manifold without exhaust interference is directly calculated through a plurality of steps and formulas based on given rotating speed, cylinder number, cylinder center distance, crank radius, connecting rod length, inlet and outlet heights and gas properties of exhaust.
Finally, it should be noted that: the above embodiments are only for illustrating the technical solution of the present invention and not for limiting it, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that: the technical scheme of the invention can be modified or replaced by the same, and the modified technical scheme cannot deviate from the spirit and scope of the technical scheme of the invention.
Claims (1)
1. A method for determining the length of an exhaust manifold of a multi-cylinder opposed-piston engine, comprising the steps of:
step 1, determining an engine ignition interval according to the number of engine cylinders, forCylinder engine->The ignition interval of adjacent cylinders is +.>；
Step 2, according to the radius of the engine crankLength of connecting rod->And exhaust height +.>Calculating an exhaust gas sustaining angle;
step 3, determining the exhaust overlapping period of the adjacent cylinders according to the exhaust continuous angle, the ignition interval and the engine speed;
step 4, calculating the propagation speed of the exhaust pressure wave;
step 5, calculating the shortest exhaust circulation path;
step 6, calculating the length of an exhaust manifold;
the exhaust gas sustaining angle in step 2 is calculated as follows:
；
wherein,for crank radius>For the length of the connecting rod->Crank-link ratio>，/>The crank angle is 0-360 DEG CA,>the exhaust sustaining angle is +.>；
The specific process of determining the exhaust overlap period of the adjacent cylinders in step 3 is as follows:
for the followingCylinder engine, when->The exhaust overlap period of adjacent cylinders is +.>No interference exists between the exhaust gases of the cylinders; when->The exhaust overlap angle of each cylinder is +.>The exhaust overlap angle of each cylinder is converted into time according to the engine speed, and the specific expression is as follows:
；
in the method, in the process of the invention,for the period of exhaust overlap>For engine speed>Is the exhaust sustaining angle;
the process of calculating the propagation velocity of the exhaust pressure wave in step 4 is specifically as follows:
；
wherein,sound speed for engine exhaust->Is the exhaust specific heat ratio; />Is the gas constant of the exhaust gas->For the exhaust gas temperature, the gas constant of the exhaust gas +.>The calculation formula of (2) is as follows:
；
in the method, in the process of the invention,is the (th) in exhaust>Mass fraction of seed gas component, +.>Is the (th) in exhaust>The relative molecular mass of the seed gas component;
specific heat ratio of exhaust gasThe calculation formula is as follows:
；
in the method, in the process of the invention,、/>the constant pressure specific heat capacity and the constant heat capacity of the exhaust are respectively, wherein the constant pressure specific heat capacity of the exhaustThe calculation formula is as follows:
；
in the method, in the process of the invention,is the first in the exhaust/>The gas composition is->Constant pressure specific heat capacity at temperature, constant specific heat capacity of exhaust gasThe calculation formula of (2) is as follows:
；
the calculation formula of the shortest exhaust gas circulation path in step 5 is as follows:
；
wherein,for the shortest exhaust gas flow path,/->Sound speed for engine exhaust->Is the exhaust overlap period;
the calculation formula of the exhaust manifold length in step 6 is as follows:
；
wherein,for exhaust manifold length, +.>For the distance between cylinder centers>Is the shortest exhaust gas flow path.
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| US11739701B2 (en) * | 2018-11-08 | 2023-08-29 | Marelli Europe S.P.A. | Method to determine the mass of air trapped in each cylinder of an internal combustion engine |
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| CN107480313A (en) * | 2016-08-29 | 2017-12-15 | 宝沃汽车（中国）有限公司 | Cylinder temperature computational methods, system and the vehicle of engine |
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