CN104376215A - Method for calculating thermal performance of working process of air cylinder of marine main engine - Google Patents

Abstract

The invention discloses a method for calculating thermal performance of the working process of an air cylinder of a marine main engine. The method is based on a mean value model and a seiliger model, an isovolumetric supercharge ratio a and an isobaric pre-expansion ratio b serve as loop parameters of the seiliger model, the isovolumetric supercharge ratio a and the isobaric pre-expansion ratio b are fitted on the basis of a large number of measured data and correlation theories, and the method is applied to simulation of the working process of the air cylinder of the marine main engine. The method can be used for steady-state calculation of the working process in the air cylinder of the marine main engine, computational accuracy can be improved, and the number of parameters needed for calculation is reduced.

Description

Marine main engine cylinder operation process performance calculation method

Technical field

The invention belongs to Engineering Thermodynamics technical field, particularly relate to a kind of marine main engine cylinder operation process performance calculation method.

Background technology

Marine main engine in-cylinder process comprises the change procedure of the various complexity such as machinery, physics, chemistry, heattransfer and fluid flow, accurate computation host in-cylinder process to raising main frame dynamic property and economy significant.At present, the normal mean value model that adopts calculates diesel engine in-cylinder process.Large-sized low-speed two stroke diesel engine mean value model is proposed in 1989 by E.Hendricks, is mainly used in diesel engine nonlinear Control and state observation.J.P.Jensen is that research object establishes mean value model with small diesel engine, and after this, mean value model is widely used in control and the emulation of diesel engine.

Domestic a series of research and apply is also carried out to mean value model.Duan Shulin achieves the dynamic simulation of turbo-charged diesel based on mean value model.Handsome Ying Mei etc. studies turbo-charged diesel mean value model, and gives the method calculating turbosupercharger.Feng Guosheng etc. carry out simulation study based on mean value model to diesel engine and electric-control system thereof.But mean value model have ignored the cyclic fluctuation of gas in the jar temperature and pressure, calculate the indicated power of diesel engine entirety according to indicated thermal efficiency, thus calculate the average indication torque of diesel engine.In addition, also have some scholars based on softwares such as GT-Power, Fire, KIVA, numerical simulation calculation is carried out to in-cylinder process, but in real-time Shortcomings.The present invention carries out refinement in conjunction with mean value model and Seiliger model to in-cylinder process, can improve calculating real-time.

The initial stage seiliger model that Seiliger proposed in nineteen twenty-two contains three combustion phases, i.e. isochoric combustion, isobaric combustion and constant-temperature combustion.And main frame in-cylinder process calculates general employing two combustion phases, i.e. isochoric combustion and isobaric combustion now.Owing to waiting appearance pressure ratio and isobaric cut-off ratio as important seiliger loop parameter, the accuracy of its numerical value has important impact to cylinder internal procedure.

Summary of the invention

For the deficiency that prior art exists, the invention provides a kind of marine main engine cylinder operation process performance calculation method improving real-time and accuracy.

The present invention is based on mean value model and seiliger model, pressure ratio a and isobaric cut-off ratio b is held for seiliger mold cycle parameter to wait, hold pressure ratio a and isobaric cut-off ratio b based on a large amount of measured data and correlation theory matching etc., and be applied to marine main engine cylinder operation process simulation.

For achieving the above object, the present invention adopts following technical scheme:

A kind of marine main engine cylinder operation process performance calculation method, comprises step:

Step 1, holds pressure ratio a according to marine main engine load acquisition etc., and described camshaft main control system etc. hold pressure ratio a=2.46557-4.51929x+6.34422x ²-3.16267x ³, 0.4≤x≤1, described automatically controlled main frame etc. hold pressure ratio $a=\left\{\begin{array}{cc}1.64592-0.82439x+0.40848x^2,& 0.4\&le;x<0.9\\ 2.32103-1.204x,& 0.9\&le;x\&le;1\end{array}\right.,$ X represents marine main engine load;

Step 2, calculates isobaric cut-off ratio wherein, Q _infor the circulation thermal discharge in cylinder operation process, according to formula Q _in=m _fh _uobtain, m _fmarine main engine fuel delivery per cycle, H _uit is fuel oil low heat value; c _pthe specific heat at constant pressure of cylinder interior gas, c _vit is the specific heat at constant volume of cylinder interior gas; A holds pressure ratio a for waiting; t ₁for the temperature of changeable compression process initial point, r _ceffective compression ratio, n _cit is polytropic compression exponent;

Step 3, holding pressure ratio a and isobaric cut-off ratio b according to waiting, being used in the thermodynamic performance that mean value model obtains changeable compression process, isochoric combustion process, isobaric combustion process and polytropic expansion process respectively;

Step 4, obtains the heat of each process generation of cylinder according to the thermodynamic performance of each process and done work.

The thermodynamic performance of above-mentioned changeable compression process, isochoric combustion process, isobaric combustion process and polytropic expansion process adopts following formulae discovery:

$\frac{V_1}{V_2}=r_c;\frac{V_3}{V_2}=1;\frac{V_4}{V_3}=b;\frac{V_5}{V_4}=r_e;$

$\frac{p_2}{p_1}={r_c}^{n_c};\frac{p_3}{p_2}=a;\frac{p_4}{p_3}=1;\frac{p_4}{p_5}={r_e}^{n_e};$

$\frac{T_2}{T_1}={r_c}^{n_c-1};\frac{T_3}{T_2}=a;\frac{T_4}{T_3}=b;\frac{T_4}{T_5}={r_e}^{n_e-1};$

Wherein, p ₁, V ₁, T ₁the in-cylinder pressure of changeable compression process initial point, volume and temperature respectively, p ₂, V ₂, T ₂the in-cylinder pressure of changeable compression course end, volume and temperature respectively, p ₃, V ₃, T ₃the in-cylinder pressure of isochoric combustion course end, volume and temperature respectively, p ₄, V ₄, T ₄the in-cylinder pressure of isobaric combustion course end, volume and temperature respectively, p ₅, V ₅, T ₅the in-cylinder pressure of polytropic expansion course end, volume and temperature respectively; r _c, r _eeffective compression ratio and effective die swell ratio respectively; A, b hold pressure ratio and isobaric cut-off ratio; n _c, n _epolytropic compression exponent and polytropic expansion index respectively.

The heat that each process of above-mentioned cylinder produces and do work and be:

Changeable compression process done work isochoric combustion W that process is done work ₂₃=0, isobaric combustion W that process is done work ₃₄=c _vt ₃m ₄(γ-1) (b-1), polytropic expansion process done work $W_{45}=c_v\&CenterDot;T_4\&CenterDot;m_5\&CenterDot;\frac{\mathrm{\&gamma;}-1}{n_e-1}\&CenterDot;(1-\frac{1}{{r_e}^{n_e-1}});$

The heat that each process of cylinder produces is:

The heat that changeable compression process produces the heat Q that isochoric combustion process produces ₂₃=c _vt ₂m ₃(a-1), the heat Q of isobaric combustion process generation ₃₄=c _vt ₃m ₄γ (b-1), the heat that polytropic expansion process produces $W_{45}={-c}_v\&CenterDot;T_4\&CenterDot;m_5\&CenterDot;(1-\frac{\mathrm{\&gamma;}-1}{n_e-1})\&CenterDot;(1-\frac{1}{{r_e}^{n_e-1}});$

Wherein, T ₁, T ₂, T ₃, T ₄be respectively the cylinder temperature of changeable compression process initial point, changeable compression course end, isochoric combustion course end, isobaric combustion course end, m ₁changeable compression process gas in the jar quality, m ₃, m ₄, m ₅be respectively isochoric combustion process, isobaric combustion process, polytropic expansion process cylinder in mixed gas quality, r _ceffective compression ratio, n _cpolytropic compression exponent, c _vbe the specific heat at constant volume of air, γ is the specific heat ratio of air; A waits to hold pressure ratio, and b is isobaric cut-off ratio.

Compared to the prior art, tool of the present invention has the following advantages and beneficial aspects:

The present invention can be used for marine main engine gas in-cylinder process steady-state simulation, can improve computational accuracy, reduces computation complexity.

Accompanying drawing explanation

Fig. 1 is that the p-ψ in cylinder Seiliger cyclic process schemes.

Embodiment

Technical solution of the present invention is further illustrated below in conjunction with embodiment.

The present invention is based on mean value model, utilize seiliger to circulate and marine main engine cylinder is divided into changeable compression process, isochoric combustion process, isobaric combustion process and polytropic expansion process as process, and calculate the thermodynamic performance of each process respectively.

Fig. 1 is Seiliger circulation p-ψ, and in figure, horizontal ordinate ψ represents crank angle, and ordinate p represents inner pressure of air cylinder, BDC is lower dead center, and TDC is top dead centre, and IC is transfer port close moment, EC is the exhaust valve closure moment, and EO is that vent valve opens the moment, and 1-2 is changeable compression process, 2-3 is isochoric combustion process, 3-4 is isobaric combustion process, and 4-5 is polytropic expansion process, and 5-1 is that scavenging period starts, point 1 represents in-cylinder process initial point, i.e. the exhaust valve closure moment.Seiliger circulation thermodynamic performance calculates in table 1, and air original pressure, temperature are known parameters.The calculating of in-cylinder process heat and merit is in table 2.

In table 1Seiliger circulation, thermal parameter calculates

The calculating of table 2 in-cylinder process heat and merit

In table 1 ~ 2, p ₁, V ₁, T ₁the in-cylinder pressure of in-cylinder process initial point, volume and temperature respectively, p ₂, V ₂t ₂the in-cylinder pressure of changeable compression course end, volume and temperature respectively, p ₃, V ₃, T ₃isochoric combustion course end in-cylinder pressure, volume and temperature respectively, p ₄, V ₄, T ₄the in-cylinder pressure of isobaric combustion course end, volume and temperature respectively, p ₅, V ₅, T ₅the in-cylinder pressure of polytropic expansion course end, volume and temperature respectively.R _c, r _ebe effective compression ratio and effective die swell ratio respectively, a, b hold pressure ratio and isobaric cut-off ratio, n _c, n _epolytropic compression exponent and polytropic expansion index respectively, and n _c< γ, n _c=1.35 ~ 1.38, n _e> γ, n _e=1.30 ~ 1.35.M ₁changeable compression process gas in the jar quality, m ₃, m ₄, m ₅mixed gas quality in isochoric combustion, isobaric combustion and polytropic expansion process cylinder respectively.

(1) pressure ratio a is held according to marine main engine carry calculation etc.:

Camshaft main control systems etc. hold pressure ratio a:

a＝2.46557-4.51929x+6.34422x ²-3.16267x ³,0.4≤x≤1 (1)

Automatically controlled main frames etc. hold pressure ratio a:

$a=\left\{\begin{array}{cc}1.64592-0.82439x+0.40848x^2,& 0.4\&le;x<0.9\\ 2.32103-1.204x,& 0.9\&le;x\&le;1\end{array}\right.---\left(2\right)$

In formula (1) ~ (2), x represents marine main engine load.

(2) calculating of isobaric cut-off ratio b:

In isobaric combustion process, isobaric cut-off ratio b affects the combustion heat release situation in whole cylinder.In isochoric combustion process and isobaric combustion process, the caloric receptivity of air is as follows:

$Q_{23}=c_v\&CenterDot;T_2\&CenterDot;m\&CenterDot;(a-1)=c_v\&CenterDot;T_1\&CenterDot;{r_c}^{n_c-1}\&CenterDot;m\&CenterDot;(a-1)---\left(3\right)$

$Q_{34}=c_v\&CenterDot;T_3\&CenterDot;\mathrm{\&gamma;}\&CenterDot;m\&CenterDot;(b-1)=c_v\&CenterDot;T_1\&CenterDot;{r_c}^{n_c-1}\&CenterDot;m\&CenterDot;\mathrm{\&gamma;}\&CenterDot;a\&CenterDot;(b-1)---\left(4\right)$

$Q_{\mathrm{in}}=Q_{23}+Q_{34}=c_v\&CenterDot;T_1\&CenterDot;{r_c}^{n_c-1}\&CenterDot;m\&CenterDot;(a-1)+c_v\&CenterDot;T_1\&CenterDot;{r_c}^{n_c-1}\&CenterDot;m\&CenterDot;\mathrm{\&gamma;}\&CenterDot;a\&CenterDot;(b-1)---\left(5\right)$

Due to so have:

$Q_{\mathrm{in}}=c_v\&CenterDot;T_1\&CenterDot;{r_c}^{n_c-1}\&CenterDot;m\&CenterDot;(a-1)+c_p\&CenterDot;T_1\&CenterDot;{r_c}^{n_c-1}\&CenterDot;m\&CenterDot;a\&CenterDot;(b-1)---\left(6\right)$

Order $T_1\&CenterDot;{r_c}^{n_c-1}\&CenterDot;m=M,$ Then:

Q _in＝c _v·M·(a-1)+c _p·M·a·(b-1) (7)

$b=\frac{Q_{\mathrm{in}}-c_v\&CenterDot;M\&CenterDot;(a-1)}{c_p\&CenterDot;M\&CenterDot;a}+1---\left(8\right)$

Q _infor the circulation thermal discharge in main frame in-cylinder process, Q _in=m _fh _u.

Formula (9) is adopted to revise isobaric cut-off ratio b:

$b=[\frac{Q_{\mathrm{in}}-c_v\&CenterDot;M\&CenterDot;(a-1)}{c_p\&CenterDot;M\&CenterDot;a}+1]/1.1---\left(9\right)$

In formula (3) ~ (9), Q ₂₃represent the caloric receptivity of air in isochoric combustion process, Q ₃₄represent the caloric receptivity of air in isobaric combustion process; γ is specific heat ratio, c _pspecific heat at constant pressure, c _vspecific heat at constant volume, m _fmarine main engine fuel delivery per cycle, H _ube fuel oil low heat value, m is gas in the jar quality.

Adopt said method Ship ' main frame 6S50MC-C8 in-cylinder process (100% operating mode), marine main engine 6S50MC-C8 basic parameter is in table 3.

Table 36S50MC-C8 basic parameter

The exhaust valve closure moment, (115 DEG C of A) was cylinder internal procedure initial point, was then changeable compression process, isochoric combustion process, isobaric combustion process and polytropic expansion process.Pressure, temperature, heat and merit in each process cylinder are calculated, the results are shown in Table 4.

Under table 4 marine main engine 100% operating mode, cylinder intrinsic parameter calculates

Claims (3)

1. a marine main engine cylinder operation process performance calculation method, is characterized in that, comprise step:

Step 1, holds pressure ratio a according to marine main engine load acquisition etc., and described camshaft main control system etc. hold pressure ratio a=2.46557-4.51929x+6.34422x ²-3.16267x ³, 0.4≤x≤1, described automatically controlled main frame etc. hold pressure ratio $a=\left\{\begin{array}{cc}1.64592-0.82439x+0.40848x^2,& 0.4\&le;x<0.9\\ 2.32103-1.204x,& 0.9\&le;x\&le;1\end{array}\right.,$ X represents marine main engine load;

Step 2, calculates isobaric cut-off ratio wherein, Q _infor the circulation thermal discharge in cylinder operation process, according to formula Q _in=m _fh _uobtain, m _fmarine main engine fuel delivery per cycle, H _uit is fuel oil low heat value; c _pthe specific heat at constant pressure of cylinder interior gas, c _vit is the specific heat at constant volume of cylinder interior gas; A holds pressure ratio a for waiting; t ₁for the temperature of changeable compression process initial point, r _ceffective compression ratio, n _cit is polytropic compression exponent;

Step 3, holding pressure ratio a and isobaric cut-off ratio b according to waiting, being used in the thermodynamic performance that mean value model obtains changeable compression process, isochoric combustion process, isobaric combustion process and polytropic expansion process respectively;

Step 4, obtains the heat of each process generation of cylinder according to the thermodynamic performance of each process and done work.

2. marine main engine cylinder operation process performance calculation method as claimed in claim 1, is characterized in that:

The thermodynamic performance of described changeable compression process, isochoric combustion process, isobaric combustion process and polytropic expansion process adopts following formulae discovery:

$\frac{V_1}{V_2}=r_c;\frac{V_3}{V_2}=1;\frac{V_4}{V_3}=b;\frac{V_5}{V_4}=r_e;$

$\frac{p_2}{p_1}={r_c}^{n_c};\frac{p_3}{p_2}=a;\frac{p_4}{p_3}=1;\frac{p_4}{p_5}={r_e}^{n_e};$

$\frac{T_2}{T_1}={r_c}^{n_c-1};\frac{T_3}{T_2}=a;\frac{T_4}{T_3}=b;\frac{T_4}{T_5}={r_e}^{n_e-1};$

Wherein, p ₁, V ₁, T ₁the in-cylinder pressure of changeable compression process initial point, volume and temperature respectively, p ₂, V ₂, T ₂the in-cylinder pressure of changeable compression course end, volume and temperature respectively, p ₃, V ₃, T ₃the in-cylinder pressure of isochoric combustion course end, volume and temperature respectively, p ₄, V ₄, T ₄the in-cylinder pressure of isobaric combustion course end, volume and temperature respectively, p ₅, V ₅, T ₅the in-cylinder pressure of polytropic expansion course end, volume and temperature respectively; r _c, r _eeffective compression ratio and effective die swell ratio respectively; A, b hold pressure ratio and isobaric cut-off ratio; n _c, n _epolytropic compression exponent and polytropic expansion index respectively.

3. marine main engine cylinder operation process performance calculation method as claimed in claim 1, is characterized in that:

The heat that each process of described cylinder produces and do work and be:

Changeable compression process done work isochoric combustion W that process is done work ₂₃=0, isobaric combustion W that process is done work ₃₄=c _vt ₃m ₄(γ-1) (b-1), polytropic expansion process done work $W_{45}=c_v\&CenterDot;T_4\&CenterDot;m_5\&CenterDot;\frac{\mathrm{\&gamma;}-1}{n_e-1}\&CenterDot;(1-\frac{1}{{r_e}^{n_e-1}});$

The heat that each process of cylinder produces is:

The heat that changeable compression process produces the heat Q that isochoric combustion process produces ₂₃=c _vt ₂m ₃(a-1), the heat Q of isobaric combustion process generation ₃₄=c _vt ₃m ₄γ (b-1), the heat that polytropic expansion process produces $Q_{45}=-c_v\&CenterDot;T_4\&CenterDot;m_5\&CenterDot;(1-\frac{\mathrm{\&gamma;}-1}{n_e-1})\&CenterDot;(1-\frac{1}{{r_e}^{n_e-1}});$

Wherein, T ₁, T ₂, T ₃, T ₄be respectively the cylinder temperature of changeable compression process initial point, changeable compression course end, isochoric combustion course end, isobaric combustion course end, m ₁changeable compression process gas in the jar quality, m ₃, m ₄, m ₅be respectively isochoric combustion process, isobaric combustion process, polytropic expansion process cylinder in mixed gas quality, r _ceffective compression ratio, n _cpolytropic compression exponent, c _vbe the specific heat at constant volume of air, γ is the specific heat ratio of air; A waits to hold pressure ratio, and b is isobaric cut-off ratio.