CN107092723B - Automatic calibration method for empirical parameters of double weber combustion rules - Google Patents
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Abstract
The invention aims to provide an automatic calibration method for empirical parameters of a double weber combustion rule. The method comprises the steps of firstly obtaining a combustion phase separation point by adopting a combustion phase separation point determining method, dividing burned fraction test data into two parts and carrying out corresponding processing, respectively obtaining a preliminary Weber parameter estimation value by adopting algebraic analysis on the two parts of data, and then obtaining a final estimation value by adopting a least square algorithm. The invention combines an algebraic analysis method and a least square algorithm, complements the advantages and disadvantages of the algebraic analysis method and the least square algorithm, realizes the automatic calibration of the empirical parameters of the combustion rule of the double weber (Wiebe), has better convergence and stability and higher accuracy during the parameter calibration, and can quickly and accurately build a zero-dimensional combustion model based on the combustion rule of the double weber (Wiebe).
Description
Technical Field
The invention relates to a method for acquiring a combustion rule of an internal combustion engine.
Background
In order to solve the increasingly serious environmental pollution problem, international emission regulations are increasingly strict, and harmful emissions of engines are limited, so that manufacturers are particularly important to control the emissions of the engines. The emission characteristic of the diesel engine is closely related to the combustion process in the cylinder, so that the realization of real-time control of the combustion process has important significance for the emission control of the engine. With the rapid development of computer technology, the computer simulation technology has vigorous vitality, a system model is abstracted through abstract simulation of a real system, and people carry out simulation test research on the model on a computer, so that the scientific research and production cost is reduced, the risk is reduced, and the scientific research efficiency is also improved. The reliability and accuracy of the system model directly determine the reliability and accuracy of the simulation result. In the field of internal combustion engines, a zero-dimensional combustion model based on a Weber (Wiebe) combustion rule is simple in form and small in modeling difficulty, and meanwhile, certain simulation accuracy is achieved within a certain working condition range. Based on the Weber Wiebe) combustion model, a plurality of researchers successfully predict the pressure and the temperature in a cylinder of a direct injection diesel engine, a non-direct injection diesel engine and a two-stroke diesel engine. Research shows that a single weber (Wiebe) combustion rule is only suitable for simulating a combustion process with one combustion phase or two slightly-mixed combustion phases, better simulation cannot be achieved for a combustion process with obviously two mixed combustion phases, and a double weber (Wiebe) combustion rule can better simulate a combustion process with two mixed combustion phases. Weber Wiebe) combustion rule empirical parameters directly influence the accuracy of a weber (Wiebe) combustion model, and there are documents which research how to calibrate the empirical parameters of the weber (Wiebe) combustion model, such as an algebraic analysis method and a least square algorithm, but the algebraic analysis method and the least square algorithm have advantages and disadvantages. The stability of the calibration parameter is good, an initial value does not need to be given, but the optimality of the calibration parameter cannot be guaranteed; the latter may guarantee local optimality of the calibration parameters, but convergence and calibration results depend on the given initial values. Therefore, the two methods are necessary to be considered to be combined, so that the advantages and the disadvantages of the two methods are complementary, and finally, the weber combustion rule empirical parameters are calibrated quickly and accurately. For the combustion process with obvious mixing of two combustion phases, how to automatically calibrate and obtain the double weber (Wiebe) combustion rule empirical parameters is very critical.
Disclosure of Invention
The invention aims to provide a double-Weber combustion rule empirical parameter automatic calibration method for accurately and automatically calibrating relevant parameters based on burned fraction test data.
The purpose of the invention is realized as follows:
the invention discloses a method for automatically calibrating empirical parameters of a double-Weber combustion rule, which is characterized by comprising the following steps of:
(1) performing combustion test on the diesel engine, collecting the burned fraction test data,is the angle of crankshaft rotation, xbIs a sum ofCorresponding fraction burned, combustion fitting start angleTaking a crank angle corresponding to 1% of burned fraction and a combustion fitting end point angleTaking the crank angle corresponding to 99% of the burned fraction and extractingExperimental data of (2) in (d)
(2) According toIs calculated to obtainAndpreliminary estimate of (2)Andwherein The corresponding crank angle when the burned fraction is zero, if the burned fraction test data is always greater than zero, the corresponding crank angle of the data starting point is taken asLinearize the simple Weber equationRealize the test data sequenceIs linearized, the linearized data sequence is
(3) For data sequenceDeriving the combustion phase separation point p by combustion phase separation point determination, i.e. finding a point p such that it is before and after this pointAndcomprehensive R for respectively carrying out linear fitting on data2The precision reaches the maximum;
(4) sequencing the fractional burn test data according to the separation point pDivided into two parts, i.e.Andwhereinx1b=[xb(1),xb(2),…,xb(p)],x2b=[xb(p+1),xb(p+2),…,xb(n)];α0=xb(p) as an initial value of premixed combustion ratio, and for x1bAnd x2bAnd (3) carrying out normalization treatment: order to Respectively realize thatAndlinearization, pairAndrespectively carrying out linear fitting on the two parts of data sequences to respectively obtain fitting slopes A1And A2From m10=A1-1、m20=A 21 gives m10And m20Wherein m10And m20Respectively setting a premixed combustion index initial value and a diffusion combustion index initial value; at alpha0、m10、m20、Andrespectively as alpha, m1,m2、Andthe initial iteration value of the method is fitted by adopting a nonlinear least square algorithm to obtain alpha, m1,m2、Andis estimated.
(5) And outputting a double weber equation parameter set, and automatically calibrating to obtain the empirical parameters of the double weber (Wiebe) combustion rule.
The present invention may further comprise:
1. the method for acquiring the combustion phase separation point p comprises the following steps:
suppose that the data separation point i separates the data sequenceDivided into two parts, the part before the ith data isSections following the ith dataIs divided intoTo pairAndrespectively carrying out linear fitting, wherein the linear fitting precision of the two parts of data is R2 1And R2 2Comprehensive accuracy R2Is defined as R2(i)=[R2 1×i+R2 2×(n-i)]N, where n is the total number of data, the data separation point i can be changed from 1 to n, and the comprehensive precision R can be respectively obtained in sequence2Then get the integrated precision R2The data separation point i at which the maximum value is reached is taken as the combustion phase separation point p.
The invention has the advantages that: the invention finally realizes a method for rapidly and accurately automatically calibrating to obtain the double-weber combustion rule empirical parameters by adopting an original double-weber (Wiebe) combustion rule empirical parameter automatic calibration method based on the weber (Wiebe) combustion rule and the burned fraction test data. The automatic calibration method for the combustion rule empirical parameters of the double weber (Wiebe) combustion rules determines the combustion phase separation point by adopting an original combustion phase separation method, combines an algebraic analysis method and a least square algorithm to complement the advantages and the disadvantages of the two methods, realizes the automatic calibration of the combustion rule empirical parameters of the double weber (Wiebe), has better convergence and stability and higher accuracy during parameter calibration, and provides great convenience for the researchers in the industry to calibrate the combustion rule empirical parameters of the double weber (Wiebe).
Drawings
FIG. 1 is a flow chart of the present invention.
Detailed Description
The invention will now be described in more detail by way of example with reference to the accompanying drawings in which:
referring to FIG. 1, first, the ignition start point test value is used as the estimated value of the combustion start pointTo be provided withAs duration of combustionThe estimated value of the fuel fraction test data is subjected to linear processing according to a Weber (Wiebe) equation; the method comprises the steps of firstly obtaining a combustion phase separation point by adopting a combustion phase separation point determining method provided by the invention for processed test data, secondly dividing the test data into two parts according to the combustion phase separation point, respectively carrying out corresponding processing on the two parts of data, then respectively obtaining a primary estimated value of combustion rule empirical parameters of the double weber (Wiebe) by adopting an algebraic analysis method for the two parts of data after processing, and finally obtaining a final estimated value of the combustion rule empirical parameters of the double weber (Wiebe) by adopting a nonlinear least square algorithm for calibration.
The method for automatically calibrating the combustion rule empirical parameters of double weber (Wiebe) comprises the following calculation processes:
the method comprises the following steps: introduction of measured fractional burn test data sequencesWhereinIs the angle of crankshaft rotation, xbIs a sum ofCorresponding fraction burned, combustion fitting start angleTaken to an as-burnt fraction x of slightly more than 0 (preferably 1%)bCorresponding crankshaft angle, combustion fitting end angleTaking the burned fraction x to be slightly less than 1 (preferably 99%)bCorrespond toAnd crank angle of (2), and extractingExperimental data of (2) in (d)
Step two: test data series based on fraction burnedFirst, it is calculated to obtainAndpreliminary estimate of (2)Andwherein The crank angle corresponding to zero burned fraction (for improving the applicability and stability of the method, if the burned fraction test data is always greater than zero, the crank angle corresponding to the data starting point is used as). Linearize the simple Weber equation Realize the test data sequenceIs linearized, the linearized data sequence is
Step three: for data sequenceAnd obtaining a combustion phase separation point p by adopting a combustion phase separation point determination method. Suppose that the data separation point i separates the data sequenceDivided into two parts, the part before the ith data isThe portion following the ith data isTo pairAndrespectively carrying out linear fitting, wherein the linear fitting precision of the two parts of data is R2 1And R2 2Comprehensive accuracy R2The definition is shown in the following formula, wherein n is the total number of data, the data separation point i can be changed from 1 to n, and the comprehensive precision R can be respectively obtained in turn2Then get the integrated precision R2The data separation point i at which the maximum value is reached is taken as the combustion phase separation point p.
R2(i)=[R2 1×i+R2 2×(n-i)]/n
Step four: fractional burn test data series based on combustion phase separation point pDivided into two parts, i.e.Andwhereinx1b=[xb(1),xb(2),…,xb(p)],x2b=[xb(p+1),xb(p+2),…,xb(n)]。 α0=xb(p) as an initial value of premixed combustion ratio, and for x1bAnd x2bAnd (3) carrying out normalization treatment:order to Respectively realize thatAndlinearization, pairAndrespectively carrying out linear fitting on the two parts of data sequences to respectively obtain fitting slopes A1And A2From m10=A1-1、m20=A 21 gives m10And m20Wherein m10And m20Respectively setting a premixed combustion index initial value and a diffusion combustion index initial value; both a1 and a2 are preferably constant values of 4.605 (not limited to 4.605) corresponding to a fractional burn period of 0% to 99% as a combustion efficiency factor. At alpha0、m10、m20、Andrespectively as alpha, m1,m2、Andthe initial iteration value of the method is fitted by adopting a nonlinear least square algorithm to obtain alpha, m1,m2、Andis estimated.
Step five: and outputting the double weber equation parameter set.
So far, according to the measured test data, the empirical parameters of the combustion rule of the double weber (Wiebe) can be automatically calibrated.
The specific principle of the automatic calibration method for the combustion rule empirical parameters of the double weber (Wiebe) is as follows:
the simple weber equation is shown in equation (3).
In the formula, xbAs a percentage of fuel burned; m is a combustion quality index; a is a combustion efficiency factor;-an instantaneous crank angle;-duration of combustion;-the start of combustion.
For theFrom xbDetermining the corresponding crank angle when the crank angle is 0; for theFrom xbThe crankshaft rotation angle period corresponding to 0-0.99 is determined.
Crank angle corresponding to 50% heat releaseAs the combustion center, corresponding to equation (3), is:
finishing to obtain:
converting formula (5) to:
from equation (6), m can be calculated by calculating the slopes of G and H.
Suppose the combustion fit starting point is xbsCorresponding to a crank angle ofCombustion fit endpoint of xbcCorresponding to a crank angle ofThis can be derived from equation (3):
when the combustion duration is selected to be a crank angle period corresponding to 0-99% of the burned fraction,
as can be seen from equation (7), a will be different for different combustion durations and m. The present invention a is preferably 4.605.
Converting the single weber combustion rule of formula (3) into:
for a direct injection diesel engine, a premixed combustion mode exists more or less in the combustion process except for a diffusion combustion mode, and it is very critical to find a separation point of the premixed combustion mode and the diffusion combustion mode for the convenience of parameter calibration of a double weber equation. The software takes an original approach to determining the combustion mode split point and the validation algorithm is described below.
From the formula (8) it can be seen that m isThe size may reflect how fast the combustion process is. For the premixed combustion mode, the combustion speed is higher, so m is smaller; for the diffusion combustion mode, the combustion speed is slow, so m is large. The combustion mode separation point is the integrated R which finds a point so that the G and K data before and after the point are respectively subjected to line fitting2The accuracy reaches the maximum. Assume that a linear fit of R is applied to G and K before this point (the p-th data point)2Accuracy is R2 1G and K after this point are R with a linear fit2Accuracy is R2 2Define the general formula R2(p) precision is:
then, take R2And (p) is the maximum value, and the corresponding p is the combustion mode separation point to be found.
The fractional burn test data is divided into two parts according to the data split point p,x1b=xb(1:p),x2b=xb(p+1:end), α0=xb(p) and x1bAnd x2bAnd (3) processing:respectively carrying out algebraic analysis on the processed two-dialing data to obtain m,Andas an initial value of the iteration of the least-squares algorithm.
The least squares algorithm is commonly used for the nonlinear equation fitting problem, the theory of which is described below.
Given n pairs of independent and dependent variablesi,yi) The parameter set to be determined is β, the fitting equation chosen is p (x, β), and therefore the sum of the squares of the errors is:
the least squares algorithm is to obtain a set of β such that S (β) is minimal.
The preferred least squares algorithm of the present invention is the Levenberg-Marquardt algorithm. The algorithm calculation starts with an initial value that requires a parameter set β to be calibrated to be given. Thereafter, the newly estimated value β + is substituted at each iteration step β. To determine, equation p (x)iβ +) was estimated linearly:
p(xi,β+)=p(xi,β)+Ji(11)
in the formulaIs a gradient with respect to β. When S (β) reaches the minimum, the gradient of the S (β) pair becomes 0. According to equation (11), the first order estimate of equation (10) is as follows:
expressed in vector form as:
S(β+)≈||y-f(β)-J||2(13)
equation (13) derives J and makes the derivative function zero, which yields:
(JTJ)=JT[y-f(β)](14)
the Levenberg-Marquardt algorithm improves upon equation (14) to the following equation:
(JTJ+λI)=JT[y-f(β)](15)
in the formula, I is an identity matrix, and λ is a damping coefficient, which is used to adjust the step length of each iteration. When lambda is zero, the formula (15) is reduced to the formula (14) which is a Gauss-Newton algorithm; when λ is large, equation (15) degenerates to the gradient descent algorithm.
For increasing the convergence rate of equation (15), J is used for equation (15)TJ instead of I, the final Levenberg-Marquardt algorithm is shown below:
(JTJ+λdiag(JTJ))=JT[y-f(β)](16)
the initial value of the parameter to be calibrated needs to be given when the least square algorithm starts to calculate, the convergence and iterative computation time of the least square algorithm are strong in dependence on the initial value, the final result cannot guarantee global optimality, and only local optimality can be guaranteed, so that the key point is to give a reasonable initial value. The invention adopts an algebraic analysis method to calculate the weber empirical parameters according to the test data as the initial values of the least square algorithm, and then carries out further iterative calculation, thus not only ensuring the optimality of the calibration result, but also improving the convergence of the least square method to a great extent and reducing the iterative calculation time.
Claims (2)
1. The automatic calibration method of the empirical parameters of the double weber combustion rule is characterized by comprising the following steps:
(1) performing combustion test on the diesel engine, collecting the burned fraction test data,is the angle of crankshaft rotation, xbIs a sum ofCorresponding fraction burned, combustion fitting start angleTaking a crank angle corresponding to 1% of burned fraction and a combustion fitting end point angleTaking the crank angle corresponding to 99% of the burned fraction and extractingExperimental data of (2) in (d)
(2) According toIs calculated to obtainAndpreliminary estimate of (2)Andwherein The corresponding crank angle when the burned fraction is zero, if the burned fraction test data is always greater than zero, the corresponding crank angle of the data starting point is taken asLinearize the simple Weber equationTo realize the testData sequenceIs linearized, the linearized data sequence is
(3) For data sequenceDeriving the combustion phase separation point p by combustion phase separation point determination, i.e. finding a point p such that it is before and after this pointAndcomprehensive precision R for respectively carrying out linear fitting on data2The maximum is reached;
(4) sequencing the fractional burn test data according to the separation point pDivided into two parts, i.e.Andwhereinx1b=[xb(1),xb(2),…,xb(p)],x2b=[xb(p+1),xb(p+2),…,xb(n)]; α0=xb(p) as an initial value of premixed combustion ratio, and for x1bAnd x2bAnd (3) carrying out normalization treatment: order to Respectively realize thatAndlinearization, pairAndrespectively carrying out linear fitting on the two parts of data sequences to respectively obtain fitting slopes A1And A2From m10=A1-1、m20=A21 gives m10And m20Wherein m10And m20Respectively setting a premixed combustion index initial value and a diffusion combustion index initial value; at alpha0、m10、m20、Andrespectively as alpha, m1,m2、Andthe initial iteration value of the method is fitted by adopting a nonlinear least square algorithm to obtain alpha, m1,m2、Andthe final estimate of (d);
(5) and outputting the double weber equation parameter set, and automatically calibrating to obtain the empirical parameters of the double weber Wieb combustion rule.
2. The method for automatically calibrating the empirical parameters of the dual weber combustion rule of claim 1, wherein: the method for acquiring the combustion phase separation point p comprises the following steps:
suppose that the data separation point i separates the data sequenceDivided into two parts, the part before the ith data isThe portion following the ith data isTo pairAndrespectively carrying out linear fitting, wherein the linear fitting precision of the two parts of data is R2 1And R2 2Comprehensive accuracy R2Is defined as R2(i)=[R2 1×i+R2 2×(n-i)]N, where n is the total number of data, the data separation point i can be changed from 1 to n, and the comprehensive precision R can be respectively obtained in sequence2Then get the integrated precision R2The data separation point i at which the maximum value is reached is taken as the combustion phase separation point p.
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