CN111006872A - Engine combustion isochoricity calculation method and device and engine combustion analyzer - Google Patents
Engine combustion isochoricity calculation method and device and engine combustion analyzer Download PDFInfo
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Abstract
The invention discloses a combustion isochoric degree calculation method and device of an engine and an engine combustion analyzer, belonging to the technical field of enginesnThe heat is equally divided into a plurality of sections of constant-volume heat release at different crank angles, and the heat release sections are considered as an adiabatic process, so that an actual combustion cycle is divided into a plurality of sections of Otto cycles, the average thermal efficiency of the divided sections of Otto cycles is higher than the theoretical thermal efficiency of the combustion cycle of the engine, and the constant-volume degree of the actual combustion cycle is obtained and output. The invention can display the isochoricity of the combustion cycle of the engine in real time, provides direct and objective reference data for the combustion analysis and diagnosis in the actual engineering, and provides reference data for the automatic calibration work of the engine.
Description
Technical Field
The invention relates to the technical field of engines, in particular to a combustion isocapacity calculation method and device of an engine and an engine combustion analyzer.
Background
Constant volume combustion, also known as isochoric combustion, refers to combustion of fuel and oxygen under conditions in which the volumes are kept constant. In the actual combustion cycle, the proportion of the constant volume combustion in the whole combustion process is the constant volume of combustion, and the higher the constant volume of combustion is, the closer the whole combustion process is to the top dead center, so that the higher the thermal efficiency of the cycle is, the better the fuel economy of the engine is. Therefore, the isochoric degree is taken as a reference parameter, which has important guiding significance for indicating the quality of the circulating combustion and judging the ignition timing. However, in practical engineering applications, because quantification of the isochoricity has certain difficulty, development of a combustion analysis system based on isochoricity feedback calculation has certain challenges.
Disclosure of Invention
In view of the above, the present invention provides a combustion isochoric calculation method and device for an engine, and an engine combustion analyzer, which are intended to implement quantitative analysis and output of combustion isochoric, provide direct and objective reference data for combustion analysis and diagnosis in practical engineering, and provide reference data for automatic calibration of an engine.
In order to achieve the above object, the following solutions are proposed:
a combustion isochoricity calculation method of an engine includes:
obtaining a relational expression between the in-cylinder volume and the in-cylinder pressure of the engine in one combustion cycle;
calculating a relational expression between the heat release rate and the crank angle in the combustion period according to the relational expression between the cylinder volume and the cylinder pressure;
according to the relational expression of the heat release rate and the crank angle, carrying out integral operation on the heat release rate to obtain the total heat release quantity of the combustion period;
dividing the total heat release into i sub-heat releases, wherein i is a positive integer greater than 1;
calculating to obtain a heat release gravity center crank angle corresponding to each sub-heat release according to the relation between the heat release rate and the crank angle;
calculating to obtain the corresponding equivalent compression ratio of each sub-heat release quantity according to the corresponding heat release gravity center crank angle;
and calculating to obtain the isochoricity according to an isochoricity formula, wherein the isochoricity formula is as follows:
wherein, ηVIs of equal capacity, gamma is specific heat ratio of working medium, epsilon is compression ratio of enginemThe equivalent compression ratio corresponding to the mth sub-heat release quantity;
and outputting the calculated isocapacity.
Optionally, the heat release gravity center crank angle corresponding to each sub-heat release amount is calculated according to the relational expression between the heat release rate and the crank angle, and specifically:
calculating to obtain a heat release gravity crank angle corresponding to each sub-heat release quantity by using a heat release gravity crank angle formula, wherein the heat release gravity crank angle formula is as follows:
wherein, Q isnIs the total heat release, the
To start a crank angle, said
A heat release gravity center crank angle corresponding to the m-th partial heat release quantity
Is a relation of the heat release rate and the crank angle, the
Is the crank angle.
Optionally, for each sub-heat release quantity, the corresponding equivalent compression ratio is calculated according to the corresponding heat release gravity center crank angle, specifically:
according to the inherent parameters of the engine, calculating to obtain the in-cylinder volume when the crank angle of the engine is equal to the crank angle of the heat release gravity center;
calculating to obtain the equivalent compression ratio corresponding to each sub-heat release by using an equivalent compression ratio formula, wherein the equivalent compression ratio formula is as follows:
wherein, the epsilonmIs the equivalent compression ratio corresponding to the m-th sub-heat release, VmThe m-th sub-heat release corresponds to the cylinder internal volume corresponding to the heat release gravity center crank angle, and V ishIs the displacement of the engine.
Optionally, i is greater than or equal to 30.
A combustion isochoricity calculation apparatus of an engine, comprising:
an acquisition unit configured to acquire a relational expression between an in-cylinder volume and an in-cylinder pressure of the engine in one combustion cycle;
the first processing unit is used for calculating a relational expression between the heat release rate and the crank angle in the combustion period according to the relational expression between the in-cylinder volume and the in-cylinder pressure;
the second processing unit is used for carrying out integral operation on the heat release rate according to a relational expression between the heat release rate and a crank angle to obtain the total heat release quantity of the combustion period;
the average unit is used for averaging the total heat release into i parts of sub-heat release, wherein i is a positive integer greater than 1;
the third processing unit is used for calculating and obtaining a heat release gravity center crank angle corresponding to each sub-heat release quantity according to the relational expression of the heat release rate and the crank angle;
the fourth processing unit is used for calculating and obtaining the corresponding equivalent compression ratio of each sub-heat release quantity according to the corresponding heat release gravity center crank angle of each sub-heat release quantity;
the fifth processing unit is used for calculating and obtaining the isochoricity according to an isochoricity formula, wherein the isochoricity formula is as follows:
wherein, ηVIs of equal capacity, gamma is specific heat ratio of working medium, epsilon is compression ratio of enginemThe equivalent compression ratio corresponding to the mth sub-heat release quantity;
and the output unit is used for outputting the calculated isocapacity.
Optionally, the third computing unit is specifically configured to:
calculating to obtain a heat release gravity crank angle corresponding to each sub-heat release quantity by using a heat release gravity crank angle formula, wherein the heat release gravity crank angle formula is as follows:
wherein, Q isnIs the total heat release, the
To start a crank angle, said
A heat release gravity center crank angle corresponding to the m-th partial heat release quantity
Is a relation of the heat release rate and the crank angle, the
Is the crank angle.
Optionally, the fourth processing unit is specifically configured to:
according to the inherent parameters of the engine, the cylinder volume when the crank angle of the engine is equal to the crank angle of the heat release gravity center is calculated, and the equivalent compression ratio corresponding to each sub-heat release quantity is calculated by using an equivalent compression ratio formula, wherein the equivalent compression ratio formula is as follows:
wherein, the epsilonmIs the equivalent compression ratio corresponding to the m-th sub-heat release quantity, VmThe m-th sub-heat release corresponds to the cylinder internal volume corresponding to the heat release gravity center crank angle, and V ishIs the displacement of the engine.
Optionally, i is greater than or equal to 30.
An engine combustion analyzer comprises a display and a combustion isochoric degree calculation device of the engine;
the display is connected with the output unit and used for displaying the isochoricity in real time.
Compared with the prior art, the technical scheme of the invention has the following advantages:
the method and the device for calculating the combustion isochoricity of the engine and the engine combustion analyzer provided by the technical scheme enable the total heat release quantity Q of an actual combustion cyclenThe heat is equally divided into a plurality of sections of constant-volume heat release at different crank angles, and the heat release sections are considered as an adiabatic process, so that an actual combustion cycle is divided into a plurality of sections of Otto cycles, the average thermal efficiency of the divided sections of Otto cycles is higher than the theoretical thermal efficiency of the combustion cycle of the engine, and the constant-volume degree of the actual combustion cycle is obtained and output. The invention can display the isochoric degree of the combustion cycle of the engine in real time, can help engineers intuitively diagnose whether the engine is in the cycle combustion and judge and calibrate the ignition timing in the actual development and calibration work of the engine, and compared with the traditional method for carrying out complex comprehensive evaluation on the combustion diagnosis by using parameters such as combustion phase, oil consumption and the like, the invention realizes the quantitative analysis and output of the combustion isochoric degree, provides direct and objective reference data for the combustion analysis and diagnosis in the actual engineering, and simultaneously provides reference data for the automatic calibration work of the engine.
Drawings
In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the embodiments or the prior art will be briefly described below, it is obvious that the drawings in the following description are only embodiments of the present invention, and for those skilled in the art, other drawings can be obtained according to the provided drawings without creative efforts.
FIG. 1 is a flow chart of a combustion isochoric calculation method for an engine according to an embodiment of the present invention;
FIG. 2 is a schematic diagram of the averaging of the total heat release provided by the embodiment of the present invention;
FIG. 3 is a schematic diagram of a heat release center of gravity crank angle corresponding to a sub-heat release provided by an embodiment of the invention;
fig. 4 is a schematic logical structure diagram of a combustion isochoricity calculation apparatus of an engine according to an embodiment of the present invention.
Detailed Description
The existing engine combustion analyzer mainly detects cylinder pressure parameters, combustion phase parameters, knock index parameters, corresponding cylinder pressure curves, heat release curves and the like, and is lack of a device for calculating combustion isochoricity. The invention provides a method for calculating combustion isochoric degree and outputting and displaying, and originally provides a quantitative method for the combustion isochoric degree, provides direct and objective reference data for combustion analysis and diagnosis in actual engineering, and provides reference data for automatic calibration work of an engine.
The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the drawings in the embodiments of the present invention, and it is obvious that the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments, which can be derived by a person skilled in the art from the embodiments given herein without making any creative effort, shall fall within the protection scope of the present invention.
The combustion isochoric calculation of the invention realizes quantification based on the isochoric model angle of the Otto cycle. The otto cycle gives the maximum thermal efficiency that can be achieved by the engine absorbing all the heat at top dead centre, providing the maximum thermal efficiency of the isochoric model. As the actual working cycle of the gasoline engine involves a plurality of unequal-volume processes, the energy released by the fuel can not be completely absorbed by the working medium at the top dead center, thus weakening the work-doing capability of total released heat.
ηV＝ηr/ηotto
In the formula, ηrTheoretical thermal efficiency modeled for a multi-stage Otto cycle for an actual duty cycle, ηottoIs the theoretical thermal efficiency of the Otto cycle.
To handle this unequal course of the actual cycle, the system will sum the actual cycle total heat absorption QnThe more the segments are, the more the multi-segment Otto cycle reflects the isochoric condition of the actual working cycle, the average thermal efficiency η of the multi-segment Otto cycleiComprises the following steps:
in the formula, ηiIs the average thermal efficiency of a multi-stage otto cycle.
Finally, the equal capacity η is obtainedVComprises the following steps:
where ε is the compression ratio of the enginemIs the m-th molecular exotherm QmCorresponding equivalent compression ratio, gamma is specific heat ratio of working medium, i is total heat release quantity QnTotal number of aliquots.
Based on the principle, during the test, the compression ratio epsilon of the engine and the real-time circulating cylinder pressure P-V or P-V on an engine combustion analyzer are obtained
The curve data can obtain real-time isochoric degree, and then the real-time display monitoring can be realized by utilizing single chip microcomputer software and the like. The combustion isochoricity calculation method of the engine provided by the embodiment of the invention is described in detail below, and referring to fig. 1, the method comprises the following steps:
s11: a relational expression V-P between an in-cylinder volume V and an in-cylinder pressure P of an engine in one combustion cycle is obtained.
The existing engine combustion analyzer can display an engine P-V curve in real time in the fuel combustion process, namely a relational expression of the in-cylinder volume V and the in-cylinder pressure P of the engine in the fuel combustion process. Step S11 is executed to acquire a relational expression between the in-cylinder volume V and the in-cylinder pressure P from a conventional engine combustion analyzer.
The combustion process of fuel in an engine is also called a four-stroke cycle, and one combustion cycle is composed of four strokes, namely an air suction process, a compression process, an expansion work process and an exhaust process. Firstly, the piston moves downwards to enable a mixture of fuel and air to enter the cylinder through one or more air valves, an air inlet valve is closed, the piston moves upwards to compress mixed gas, then the mixed gas is ignited by a spark plug when the piston is close to the top of a compression stroke, thrust generated by explosion of combustion air forces the piston to move downwards to complete a power stroke, and finally the combusted gas is discharged out of the cylinder through an exhaust valve.
S12: according to a relational expression V-P of the in-cylinder volume V and the in-cylinder pressure P, calculating to obtain the heat release rate q and the crank angle in the combustion period
Is a relational expression of
Step S12 is executed to calculate the heat release rate curve by using the actually measured relation V-P (i.e. indicator diagram) and using thermodynamic method
The existing method for calculating and obtaining the heat release rate curve chart by utilizing indicator diagram
The methods described above are all applicable to this embodiment, and the present invention is not limited thereto.
After the engine leaves factory, the compression ratio epsilon, the length l of the connecting rod, the cylinder diameter d, the stroke s and the displacement VhEtc. are fixed values and can be calculated according to these basic parameters of the engineCalculating the crank angle
Relation with in-cylinder volume V of engine
And combining the relation P-V of the cylinder volume V and the cylinder pressure P to obtain the cylinder pressure P and the crank angle
Is a relational expression of
Relation formula
The engine is also an indicator diagram of the engine, that is, the in-cylinder pressure P and the crank angle can be calculated according to a relational expression V-P between the in-cylinder volume V and the in-cylinder pressure P
Is a relational expression of
Then calculating to obtain a heat release rate curve chart
S13: according to the heat release rate q and the crank angle
Is a relational expression of
Performing integral operation on the heat release rate Q to obtain the total heat release Q of the combustion periodn。
Step S13 is executed to obtain a heat release rate curve chart through integral operation
The area enclosed by the coordinate axes is the total heat release Qn。
S14: the total heat release QnThe average is i sub-exotherms.
The number of segments i is a positive integer greater than 1. The heat release per molecule is QnAnd i is carried out. The number i of the segments is a preset value, the larger the value i is, the more accurate the obtained isochoricity is, and the result is obtained through experimental analysis, when the number i of the segments is greater than or equal to 30, the accuracy of the calculation result of the isochoricity tends to be stable, and the value i can be preset according to the actual required condition under the condition of considering both precision and reflecting sensitivity. FIG. 2 shows the total heat release QnThe heat release Q of each divided sub-heat1、Q2、……、Qi-1、QiCondition (2) of (B), Q1＝Q2＝……＝Qi-1＝Qi。
S15: according to the heat release rate q and the crank angle
Is a relational expression of
And calculating to obtain the heat release gravity center crank angle corresponding to each sub heat release quantity.
In one embodiment of the invention, the heat release gravity crank angle corresponding to each sub-heat release quantity is calculated by using a heat release gravity crank angle formula.
The heat release gravity center crank angle formula is as follows:
wherein the content of the first and second substances,
in order to start the crank angle of rotation,
is the m-th molecular exotherm QmThe corresponding heat release gravity center crank angle,
m is a relation between the heat release rate and the crank angle, and is a closed interval [1, i]An integer in between.
With reference to figure 3 of the drawings,
is the m-th molecular exotherm QmThe corresponding half of the corresponding crank angle is solved by the formula of the heat release center crank angle to obtain the integral upper limit, namely
S16: and calculating the corresponding equivalent compression ratio of each sub-heat release quantity according to the corresponding heat release gravity center crank angle of each sub-heat release quantity.
The invention releases every molecule of heat QmSimplified to heat-releasing gravity center crankshaft angle
The equivalent volume of the part is absorbed, and then the corresponding equivalent compression ratio epsilon is calculatedm. In one embodiment of the invention, the in-cylinder volume is calculated when the crank angle of the engine is equal to the crank angle of the heat release center of gravity based on the intrinsic parameters of the engine. Different crank angles
The position of the piston movement can be determined, and the intrinsic parameters of the engine include the connecting rod length l, the cylinder diameter d, the stroke s, and the displacement VhEtc. calculating the crank angle based on the intrinsic parameters of the engine
Internal cylinder volume V of timem。
And calculating to obtain the equivalent compression ratio corresponding to each sub-heat release by using an equivalent compression ratio formula.
The equivalent compression ratio formula is:
wherein epsilonmIs the m-th molecular exotherm QmCorresponding equivalent compression ratio, VmIs the m-th molecular exotherm QmCorresponding heat release gravity center crankshaft angle
Corresponding in-cylinder volume, VhIs the displacement of the engine. VhAnd/epsilon represents the volume in the cylinder when the piston moves to the top dead center, i.e. the clearance volume.
S17: and calculating to obtain the isochoric degree according to an isochoric degree formula.
The formula of the isochoricity is as follows:
wherein, ηVThe specific heat capacity is equal, gamma is the specific heat ratio of the working medium, and epsilon is the compression ratio of the engine. Length l of connecting rod, diameter d, stroke s and displacement VhThe values are the design parameters of the engine and are all constants. The specific heat ratio gamma of the working medium is a constant, the value of the specific heat ratio gamma depends on the working medium of in-cylinder combustion circulation, and for the traditional automobile and diesel engine, the value of gamma is 1.4.
S18: and outputting the calculated isocapacity.
In the method for calculating the combustion isochoricity of the engine provided by the embodiment, the total heat release quantity of an actual combustion cycle is divided into QnAre equally divided into different crank angles
The heat is released in multiple stages with equal capacity, and the heat release stages are regarded as adiabatic process, so that an actual combustion cycle is divided into multiple stages of Otto cycle, the average thermal efficiency of the divided multiple stages of Otto cycle is higher than the theoretical thermal efficiency of the engine combustion cycle, and the equal capacity of the actual combustion cycle is obtained and output.The invention can display the isochoric degree of the combustion cycle of the engine in real time, can help engineers to intuitively diagnose whether the engine is in the cycle combustion and judge and calibrate the ignition timing in the actual development and calibration work of the engine, and compared with the traditional method for carrying out complex comprehensive evaluation on the combustion diagnosis by using parameters such as combustion phase, oil consumption and the like, the invention realizes the quantitative analysis and output of the combustion isochoric degree, provides direct and objective reference data for the combustion analysis and diagnosis in the actual engineering, and simultaneously provides reference data for the automatic calibration work of the engine.
While, for purposes of simplicity of explanation, the foregoing method embodiments have been described as a series of acts or combination of acts, it will be appreciated by those skilled in the art that the present invention is not limited by the illustrated ordering of acts, as some steps may occur in other orders or concurrently with other steps in accordance with the invention.
The following are embodiments of the apparatus of the present invention that may be used to perform embodiments of the method of the present invention. For details which are not disclosed in the embodiments of the apparatus of the present invention, reference is made to the embodiments of the method of the present invention.
The present embodiment provides a combustion isochoric degree calculation apparatus of an engine, which, referring to fig. 4, includes: an acquisition unit 11, a first processing unit 12, a second processing unit 13, an averaging unit 14, a third processing unit 15, a fourth processing unit 16, a fifth processing unit 17, and an output unit 18.
An acquisition unit 11 configured to acquire a relational expression between an in-cylinder volume and an in-cylinder pressure of the engine in one combustion cycle;
a first processing unit 12, configured to calculate a relational expression between a heat release rate and a crank angle in the combustion cycle according to the relational expression between the in-cylinder volume and the in-cylinder pressure;
the second processing unit 13 is configured to perform an integral operation on the heat release rate according to a relational expression between the heat release rate and a crank angle to obtain a total heat release amount of the combustion cycle;
an averaging unit 14 for averaging the total heat release into i sub-heat releases, i being a positive integer greater than 1;
the third processing unit 15 is configured to calculate a heat release gravity center crank angle corresponding to each sub-heat release amount according to the relational expression between the heat release rate and the crank angle;
the fourth processing unit 16 is configured to calculate, for each sub-heating capacity, an equivalent compression ratio corresponding to the sub-heating capacity according to a corresponding heating center crank angle;
a fifth processing unit 17, configured to calculate and obtain an isochoric degree according to an isochoric degree formula, where the isochoric degree formula is:
wherein, ηVIs of equal capacity, gamma is specific heat ratio of working medium, epsilon is compression ratio of enginemThe equivalent compression ratio corresponding to the mth sub-heat release quantity;
and the output unit 18 is used for outputting the calculated isocapacity.
In the combustion isochoricity calculation device for an engine according to the present embodiment, the averaging unit 14 averages the total heat release quantity of one actual combustion cycle by QnAre equally divided into different crank angles
The heat is released in multiple stages in an equal volume way, and the heat release stages are regarded as an adiabatic process, so that an actual combustion cycle is divided into multiple Otto cycles, the fifth processing unit 17 compares the average thermal efficiency of the divided multiple Otto cycles with the theoretical thermal efficiency of the actual combustion cycle to obtain the equal volume of the combustion cycle of the engine, and the output unit 18 outputs the equal volume. The invention can display the isochoricity of the combustion cycle of the engine in real time, can help engineers to visually diagnose whether the engine is in the cycle combustion and judge and calibrate the ignition timing in the actual development and calibration work of the engine, compared with the traditional method for carrying out complex comprehensive evaluation on the combustion diagnosis by using parameters such as combustion phase, oil consumption and the like, the invention realizes the quantitative analysis and output of the combustion isochoricity, provides direct and objective reference data for the combustion analysis and diagnosis in the actual engineering, and simultaneously provides the engine with the direct and objective reference dataThe automatic calibration work of (2) provides reference data.
Optionally, the third calculating unit 15 is specifically configured to:
calculating to obtain a heat release gravity crank angle corresponding to each sub-heat release quantity by using a heat release gravity crank angle formula, wherein the heat release gravity crank angle formula is as follows:
wherein, Q isnIs the total heat release, the
To start a crank angle, said
A heat release gravity center crank angle corresponding to the m-th partial heat release quantity
Is a relation of the heat release rate and the crank angle, the
Is the crank angle.
Optionally, the fourth processing unit 16 is specifically configured to:
according to the inherent parameters of the engine, the cylinder volume when the crank angle of the engine is equal to the crank angle of the heat release gravity center is calculated, and the equivalent compression ratio corresponding to each sub-heat release quantity is calculated by using an equivalent compression ratio formula, wherein the equivalent compression ratio formula is as follows:
wherein, the epsilonmIs the equivalent compression ratio corresponding to the m-th sub-heat release quantity, VmThe m-th sub-heat release corresponds to the cylinder internal volume corresponding to the heat release gravity center crank angle, and V ishIs a bank of enginesAmount of the compound (A).
Preferably, i is equal to or greater than 30.
The embodiment also provides an engine combustion analyzer, which comprises a display, the combustion isochoric degree calculating device of the engine, and a controller, wherein the display is used for displaying the combustion isochoric degree of the engine; the display is connected with the output unit and used for displaying the isochoricity sent by the output unit in real time.
The above-described embodiments of the apparatus are merely illustrative, and the units described as separate parts may or may not be physically separate, and parts displayed as units may or may not be physical units, may be located in one place, or may be distributed on a plurality of network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the solution of the present embodiment. One of ordinary skill in the art can understand and implement it without inventive effort.
In this document, relational terms such as first and second, and the like may be used solely to distinguish one entity or action from another entity or action without necessarily requiring or implying any actual such relationship or order between such entities or actions. Also, the terms "comprises," "comprising," or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but may include other elements not expressly listed or inherent to such process, method, article, or apparatus. Without further limitation, an element defined by the phrase "comprising an … …" does not exclude the presence of other identical elements in a process, method, article, or apparatus that comprises the element.
The embodiments in the present description are described in a progressive manner, each embodiment focuses on differences from other embodiments, and the same and similar parts among the embodiments are referred to each other.
The previous description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the present invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other embodiments without departing from the spirit or scope of the invention. Thus, the present invention is not intended to be limited to the embodiments shown herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.
Claims (9)
1. A combustion isochoricity calculation method of an engine, characterized by comprising:
obtaining a relational expression between the in-cylinder volume and the in-cylinder pressure of the engine in one combustion cycle;
calculating a relational expression between the heat release rate and the crank angle in the combustion period according to the relational expression between the cylinder volume and the cylinder pressure;
according to the relational expression of the heat release rate and the crank angle, carrying out integral operation on the heat release rate to obtain the total heat release quantity of the combustion period;
dividing the total heat release into i sub-heat releases, wherein i is a positive integer greater than 1;
calculating to obtain a heat release gravity center crank angle corresponding to each sub-heat release according to the relation between the heat release rate and the crank angle;
calculating to obtain the corresponding equivalent compression ratio of each sub-heat release quantity according to the corresponding heat release gravity center crank angle;
and calculating to obtain the isochoricity according to an isochoricity formula, wherein the isochoricity formula is as follows:
wherein, ηVIs of equal capacity, gamma is specific heat ratio of working medium, epsilon is compression ratio of enginemThe equivalent compression ratio corresponding to the mth sub-heat release quantity;
and outputting the calculated isocapacity.
2. The method according to claim 1, wherein the heat release gravity crank angle corresponding to each sub-heat release is calculated according to the relation between the heat release rate and the crank angle, and specifically comprises:
calculating to obtain a heat release gravity crank angle corresponding to each sub-heat release quantity by using a heat release gravity crank angle formula, wherein the heat release gravity crank angle formula is as follows:
wherein, Q isnIs the total heat release, the
To start a crank angle, said
A heat release gravity center crank angle corresponding to the m-th partial heat release quantity
Is a relation of the heat release rate and the crank angle, the
Is the crank angle.
3. The method according to claim 1, wherein for each sub-heat release, the corresponding equivalent compression ratio is calculated according to the corresponding heat release gravity crank angle, specifically:
according to the inherent parameters of the engine, calculating to obtain the in-cylinder volume when the crank angle of the engine is equal to the crank angle of the heat release gravity center;
calculating to obtain the equivalent compression ratio corresponding to each sub-heat release by using an equivalent compression ratio formula, wherein the equivalent compression ratio formula is as follows:
wherein, the epsilonmIs the equivalent compression ratio corresponding to the m-th sub-heat release quantity, VmThe m-th sub-heat release corresponds to the cylinder internal volume corresponding to the heat release gravity center crank angle, and V ishIs the displacement of the engine.
4. The method according to any one of claims 1 to 3, wherein i is equal to or greater than 30.
5. An apparatus for calculating a combustion isochoricity of an engine, comprising:
an acquisition unit configured to acquire a relational expression between an in-cylinder volume and an in-cylinder pressure of the engine in one combustion cycle;
the first processing unit is used for calculating a relational expression between the heat release rate and the crank angle in the combustion period according to the relational expression between the in-cylinder volume and the in-cylinder pressure;
the second processing unit is used for carrying out integral operation on the heat release rate according to a relational expression between the heat release rate and a crank angle to obtain the total heat release quantity of the combustion period;
the average unit is used for averaging the total heat release into i parts of sub-heat release, wherein i is a positive integer greater than 1;
the third processing unit is used for calculating and obtaining a heat release gravity center crank angle corresponding to each sub-heat release quantity according to the relational expression of the heat release rate and the crank angle;
the fourth processing unit is used for calculating and obtaining the corresponding equivalent compression ratio of each sub-heat release quantity according to the corresponding heat release gravity center crank angle of each sub-heat release quantity;
the fifth processing unit is used for calculating and obtaining the isochoricity according to an isochoricity formula, wherein the isochoricity formula is as follows:
wherein, ηVIs of equal capacity, gamma is specific heat ratio of working medium, epsilon is compression ratio of enginemThe equivalent compression ratio corresponding to the mth sub-heat release quantity;
and the output unit is used for outputting the calculated isocapacity.
6. The apparatus according to claim 5, wherein the third computing unit is specifically configured to:
calculating to obtain a heat release gravity crank angle corresponding to each sub-heat release quantity by using a heat release gravity crank angle formula, wherein the heat release gravity crank angle formula is as follows:
wherein, Q isnIs the total heat release, the
To start a crank angle, said
A heat release gravity center crank angle corresponding to the m-th partial heat release quantity
Is a relation of the heat release rate and the crank angle, the
Is the crank angle.
7. The apparatus according to claim 5, wherein the fourth processing unit is specifically configured to:
according to the inherent parameters of the engine, the cylinder volume when the crank angle of the engine is equal to the crank angle of the heat release gravity center is calculated, and the equivalent compression ratio corresponding to each sub-heat release quantity is calculated by using an equivalent compression ratio formula, wherein the equivalent compression ratio formula is as follows:
wherein, the epsilonmIs the equivalent compression ratio corresponding to the m-th sub-heat release quantity, VmThe m-th sub-heat release corresponds to the cylinder internal volume corresponding to the heat release gravity center crank angle, and V ishIs the displacement of the engine.
8. The device according to any one of claims 6 to 8, wherein i is equal to or greater than 30.
9. An engine combustion analyzer comprising a display, characterized by further comprising a combustion isochoric calculation device of the engine according to any one of claims 5 to 8;
the display is connected with the output unit and used for displaying the isochoricity in real time.
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