阅读说明：本技术 一种两阶段压缩膨胀发电机发电效率的预测方法 (Prediction method for power generation efficiency of two-stage compression expansion generator ) 是由 韩笑 刘龙 刘俊杰 梅齐昊 赵豪 许智淳 唐元亨 安琛 于 2021-06-18 设计创作，主要内容包括：本发明提出了一种两阶段压缩膨胀发电机发电效率的预测方法,将发动机工作过程具体分为第一压缩、第二压缩、中冷、燃烧、膨胀、膨胀六个阶段,每个阶段取步长为0.1,与混合加热理想循环每个阶段相对应,进行迭代求解,将得到的压力进行积分计算,求出工作过程的有效功W,再根据有效功W与总投入热量Q-(total)的比值求出有效热效率,与所耦合电机的效率相乘,即为整个两阶段压缩膨胀发电机的发电效率；本发明不局限于某一特定运行工况,并且对发动机具体型号依赖相对较小,相比CFD模型计算速度相对较快,可广泛应用于工作过程仿真,进行发动机性能预测、故障诊断等方面的研究,为更广范围的发电机热效率优化设计提供了数值预测手段。(The invention provides a method for predicting the power generation efficiency of a two-stage compression-expansion power generator, which specifically divides the working process of the engine into six stages of first compression, second compression, intercooling, combustion, expansion and expansion, wherein step length is taken in each stage Is 0.1, corresponding to each stage of the mixed heating ideal cycle, carrying out iterative solution, carrying out integral calculation on the obtained pressure, solving the effective work W in the working process, and then obtaining the total input heat Q according to the effective work W total The effective thermal efficiency is obtained by the ratio, and the effective thermal efficiency is multiplied by the efficiency of the coupled motor, namely the generating efficiency of the whole two-stage compression-expansion generator; the invention is not limited to a specific operation condition, has relatively small dependence on the specific model of the engine, has relatively high calculation speed compared with a CFD model, can be widely applied to the work process simulation for the research on the aspects of engine performance prediction, fault diagnosis and the like, and is a wider power generation rangeThe machine thermal efficiency optimization design provides a numerical prediction means.)

1. A method for predicting the power generation efficiency of a two-stage compression-expansion generator, the method comprising the steps of:

the working process of the engine is divided into six stages of first compression, second compression, intercooling, combustion, first expansion and second expansion, and step length is taken in each stageThe values are the same, corresponding to each stage of the mixed heating ideal cycle, and iterative solution is carried out;

the method comprises the following steps: determining boundary conditions and initial conditions according to geometric parameters and initial parameters of an engine to be used, and setting an adiabatic index kappa; the adiabatic index refers to an index of a reversible adiabatic process of an ideal gas;

step two: in the first compression stage, the adiabatic index kappa is used for calculation, and the temperature T after the first compression stage can be obtained by utilizing an ideal gas reversible process calculation formula₂And pressure P₂And taking the initial parameter as the initial parameter of the second compression stage process;

wherein, P₁Pressure before the first compression stage, T₁For the first compression stageFront temperature, V₁ ^KVolume before the first compression stage in adiabatic index kappa regime, V₂ ^KVolume after the first compression stage in adiabatic index kappa regime; v₁Volume before the first compression stage, V₂The volume after the first compression stage, and epsilon is the volume ratio before and after the first compression stage;

step three: calculating the second compression process according to a step length of the compression processInternal heat transfer capacityVolume workMass m of working medium, specific heat capacity c of working medium in secondary compression process_v1The temperature change in one step length in the second compression process is solved through a first thermodynamic law

Wherein Q is_WThe heat transfer capacity in the second compression process, V is the volume in the second compression process, and T is the temperature in the second compression process;

according to the temperature T obtained in the second step after the first compression stage₂Solving the temperature T of the first step end point in the second compression process₃Will T₃Performing iterative calculation on the initial temperature serving as the next step to obtain the temperature of each step in the compression process; calculating the temperature of each step length to obtain the pressure of each corresponding step length through an ideal gas state equation pV (RT);

step four: to pairCalculating the intercooler process according to the intercooler outlet air temperature T_sThe calculation formula of (a) obtains the temperature after passing through the intercooler, and the pressure loss delta p caused by the air passing through the intercooler_sCalculating the pressure p of the outlet_sThe concrete formula is as follows:

p_s＝p_K-Δp_s

wherein T is time, T_KVolume before the first compression stage in adiabatic index kappa regime, T_woFor the temperature of the cooling water at the outlet of the intercooler, T_wiFor intercooler inlet cooling water temperature, C_swIs the heat transfer coefficient K and the heat transfer area A_KProduct of c_pwM is the specific heat capacity of cooling water at constant pressure_wFor cooling water mass, m_sIn order to be the quality of the air,for air mass flow, p_sThe density of air at the intercooler inlet, A_kIs the flow area, eta, of the intercooler_rIs the coefficient of resistance of intercooler, p_KThe pressure of the intercooler is in a state of an adiabatic index kappa;

step five: calculating the combustion process, setting the combustion process as constant volume heating and constant pressure heating in the mixed heating ideal circulation, and setting one step length according to the combustion processInternal heat transfer capacityVolume workMass m of working medium^*Specific heat capacity c of working medium in combustion process_v2Input heat of combustion g of fuel_f(H_uU) burning rateDetermining the temperature change in a step length in the combustion process by a first thermodynamic law

Wherein the content of the first and second substances,is the amount of heat transferred during combustion, V^*Is the volume in the combustion process; t is^*Is the temperature during combustion;

repeating the temperature iteration step in the step 3, and solving to obtain the temperature and the pressure of each step;

step six: calculating the two expansion processes, setting the expansion processes as adiabatic expansion in an ideal cycle of mixed heating, repeating the calculation process in the step 3, and substituting the calculation process into the working medium specific heat capacity c after the combustion process_v3Solving to obtain the temperature and pressure of each step length in the expansion process;

step seven: performing integral calculation on the pressure obtained in the steps 3, 4, 5 and 6 to obtain effective work W in the working process, and then calculating the total input heat Q according to the effective work W_totalThe effective thermal efficiency is obtained by the ratio, and the effective thermal efficiency is multiplied by the efficiency of the coupled motor, namely the generating efficiency of the whole two-stage compression-expansion generator:

η＝η₁·η₂。

2. the method of claim 1, further comprising: in the first step, when the temperature of gas in the compression process of the engine is 300-400 ℃;

when the variation amplitude of the initial state temperature and the final state temperature of the gas in the compression process of the engine is larger than 600K, the average constant entropy index kappa is adopted_avInstead of the given adiabatic index k.

3. The method of claim 1, further comprising: in step three, the environment of the second compression process is set to adiabatic compression in the ideal cycle of mixed heating.

4. The method of claim 1, further comprising: in the fourth step, the pressure loss of the intercooler under the design working condition is taken as delta p_s＝0.3～0.5kPa。

Technical Field

The invention relates to the field of optimization of a working process of a generator, in particular to a prediction method of the generating efficiency of a two-stage compression-expansion generator.

Background

In recent years, with the continuous development of society, the problem of energy shortage is increasingly highlighted. Among various forms of energy, electric energy is one of the most widely used energy, and electric energy is mainly provided by diesel engines in the industries of vehicles, ships and the like. Therefore, new free piston internal combustion engines (FPLA) are becoming a research focus with the negative effects caused by conventional diesel engines becoming increasingly more severe. The FPLA is a product of direct coupling of a free piston internal combustion engine (FPE) and a linear generator (LA), combines the advantages of the FPE and the linear generator, and directly converts chemical energy of fuel into electric energy. The existing double-free-piston generator adopts a four-stroke design, applies a new cycle of two-stage compression and two-stage expansion, can effectively eliminate vibration caused by the two-stroke generator, and has higher generating efficiency and economic performance compared with the traditional internal combustion engine generating process, so that the double-free-piston generator is receiving more and more attention.

Because the generating efficiency of the free piston generator is closely related to the thermal efficiency of the engine and the efficiency of the motor, and the efficiency of the motor generally adopted by us is between 90% and 95%, compared with the efficiency of the motor, the thermal efficiency of the engine plays a critical role in the generating efficiency of the whole free piston generator, and the prediction of the generating efficiency by adopting a two-stage compression-expansion generator predicting method is more significant.

At present, the simulation prediction of the effective thermal efficiency is mainly divided into a zero-dimensional model (single-zone model), a quasi-dimensional model (multi-zone model) and a multi-dimensional model. Although the complex quasi-dimensional and multi-dimensional models have the potential of reproducing the physicochemical reaction in the fuel injection combustion process, the complex quasi-dimensional and multi-dimensional models are still limited by the lack of accurate knowledge of certain processes, and have considerable calculation amount, too long time consumption and incapability of meeting the requirements of performance prediction, control analysis and real-time simulation. The zero-dimensional model is mainly applied to the control and simulation of the power plant, and the zero-dimensional model such as a volumetric model, an average value model and the like belongs to the zero-dimensional model. Therefore, the invention mainly applies a volumetric method model in a zero-dimensional model, takes a mixed heating ideal cycle (Sabade cycle) as a theoretical basis, and provides a prediction method of the power generation efficiency of the two-stage compression-expansion power generator based on the working process of the two-stage compression and two-stage expansion.

Disclosure of Invention

The invention provides a prediction method of the power generation efficiency of a two-stage compression-expansion power generator, realizes the rapid and steady prediction of the power generation efficiency of the two-stage compression-expansion power generator under any power generator operation condition, and provides a better numerical analysis method for the optimization of the working performance and the improvement of the power generation efficiency of the two-stage compression-expansion power generator.

The invention is realized by the following technical scheme:

a method of predicting the efficiency of a two-stage compression-expansion generator, the method comprising the steps of:

the working process of the engine is divided into six stages of first compression, second compression, intercooling, combustion, first expansion and second expansion, and step length is taken in each stageThe values are the same, corresponding to each stage of the mixed heating ideal cycle, and iterative solution is carried out;

the method comprises the following steps: determining boundary conditions and initial conditions according to geometric parameters and initial parameters of an engine to be used, and setting an adiabatic index kappa; the adiabatic index refers to an index of a reversible adiabatic process of an ideal gas;

step two: in the first compression stage, the adiabatic index κ is calculated using an ideal gas reversible process meterThe temperature T after the first compression stage can be obtained by calculation₂And pressure P₂And taking the initial parameter as the initial parameter of the second compression stage process;

wherein, P₁Pressure before the first compression stage, T₁Is the temperature before the first compression stage, V₁ ^KThe volume before the first compression stage in adiabatic index kappa regime,volume after the first compression stage in adiabatic index kappa regime; v₁Volume before the first compression stage, V₂The volume after the first compression stage, and epsilon is the volume ratio before and after the first compression stage;

step three: calculating the second compression process according to a step length of the compression processInternal heat transfer capacityVolume workMass m of working medium, specific heat capacity c of working medium in secondary compression process_v1The temperature change in one step length in the second compression process is solved through a first thermodynamic law

Wherein Q is_WThe heat transfer capacity in the second compression process, V is the volume in the second compression process, and T is the temperature in the second compression process;

according to the temperature T obtained in the second step after the first compression stage₂Solving the temperature T of the first step end point in the second compression process₃Will T₃Performing iterative calculation on the initial temperature serving as the next step to obtain the temperature of each step in the compression process; calculating the temperature of each step length to obtain the pressure of each corresponding step length through an ideal gas state equation pV (RT);

step four: calculating the intercooler process according to the intercooler outlet air temperature T_sThe calculation formula of (a) obtains the temperature after passing through the intercooler, and the pressure loss delta p caused by the air passing through the intercooler_sCalculating the pressure p of the outlet_sThe concrete formula is as follows:

p_s＝p_K-Δp_s

wherein T is time, T_KVolume before the first compression stage in adiabatic index kappa regime, T_woFor the temperature of the cooling water at the outlet of the intercooler, T_wiFor intercooler inlet cooling water temperature, C_swIs the heat transfer coefficient K and the heat transfer area A_KProduct of c_pwM is the specific heat capacity of cooling water at constant pressure_wFor cooling water mass, m_sIn order to be the quality of the air,for air mass flow, p_sThe density of air at the intercooler inlet, A_kIs the flow area, eta, of the intercooler_rIs the coefficient of resistance of intercooler, p_KThe pressure of the intercooler is in a state of an adiabatic index kappa;

step five: calculating the combustion process, setting the combustion process as constant volume heating and constant pressure heating in the mixed heating ideal circulation, and setting one step length according to the combustion processInternal heat transfer capacityVolume workMass m of working medium^*Specific heat capacity c of working medium in combustion process_v2Input heat of combustion g of fuel_f(H_uU) burning rateDetermining the temperature change in a step length in the combustion process by a first thermodynamic law

Wherein the content of the first and second substances,is the amount of heat transferred during combustion, V^*Is the volume in the combustion process; t is^*Is the temperature during combustion;

repeating the temperature iteration step in the step 3, and solving to obtain the temperature and the pressure of each step;

step six: to two forCalculating the secondary expansion process, setting the secondary expansion process as adiabatic expansion in the ideal cycle of mixed heating, repeating the calculation process in the step 3, and substituting the calculated process into the working medium specific heat capacity c after the combustion process_v3Solving to obtain the temperature and pressure of each step length in the expansion process;

step seven: performing integral calculation on the pressure obtained in the steps 3, 4, 5 and 6 to obtain effective work W in the working process, and then calculating the total input heat Q according to the effective work W_totalThe effective thermal efficiency is obtained by the ratio, and the effective thermal efficiency is multiplied by the efficiency of the coupled motor, namely the generating efficiency of the whole two-stage compression-expansion generator:

η＝η₁·η₂。

further, in the first step, when the temperature of the gas in the compression process of the engine is 300-400 ℃;

when the variation amplitude of the initial state temperature and the final state temperature of the gas in the compression process of the engine is larger than 600K, the average constant entropy index kappa is adopted_avInstead of the given adiabatic index k.

Further, in step three, the environment of the second compression process is set to the adiabatic compression in the ideal cycle of the hybrid heating.

Further, in step four, the pressure loss, Δ p, of the intercooler during the design condition_s＝0.3～0.5kPa。

The invention has the beneficial effects

(1) The method is based on the ideal cycle of mixed heating (Sabourde cycle) as a theoretical basis, and based on the working process of two-stage compression and two-stage expansion, the working process of the two-stage compression and expansion generator under any initial working condition is approximately calculated, so that the temperature and pressure of each step under different working conditions can be obtained, and the application range of the method is not limited to a certain specific operation working condition;

(2) the invention is based on a volumetric method model in a zero-dimensional model, has relatively small dependence on the specific model of the engine, has relatively high calculation speed compared with a CFD model, can be widely applied to working process simulation for the research on the aspects of engine performance prediction, fault diagnosis and the like, and provides a numerical prediction means for the optimal design of the thermal efficiency of the generator in a wider range.

Drawings

FIG. 1 is a flow chart of a prediction method of the present invention;

fig. 2 is a result of cylinder pressure calculation obtained by the prediction method of the present invention.

Detailed Description

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.

Examples

A method of predicting the efficiency of a two-stage compression-expansion generator, the method comprising the steps of:

the working process of the engine is divided into six stages of first compression, second compression, intercooling, combustion, first expansion and second expansion, and step length is taken in each stageThe value is 0.1, and the iterative solution is carried out corresponding to each stage of the mixed heating ideal cycle;

the method comprises the following steps: determining boundary conditions and initial conditions according to geometric parameters and initial parameters of an engine to be used, and giving an adiabatic index (constant entropy index) kappa; the adiabatic index refers to an index of a reversible adiabatic process of an ideal gas;

step two: in the first compression stage, the adiabatic index k is 1.4, and the temperature T after the first compression stage can be obtained by using an ideal gas reversible process calculation formula₂And pressure P₂And using it as the starting parameter of the second compression stage process；

Wherein, P₁Pressure before the first compression stage, T₁Is the temperature before the first compression stage, V₁ ^KThe volume before the first compression stage in adiabatic index kappa regime,volume after the first compression stage in adiabatic index kappa regime; v₁Volume before the first compression stage, V₂The volume after the first compression stage, and epsilon is the volume ratio before and after the first compression stage;

step three: calculating the second compression process according to a step length of the compression processInternal heat transfer capacityVolume workMass m of working medium, specific heat capacity c of working medium in secondary compression process_v1The temperature change in one step length in the second compression process is solved through a first thermodynamic law

Wherein Q is_WThe heat transfer capacity in the second compression process, V is the volume in the second compression process, and T is the temperature in the second compression process;

according to the temperature T obtained in the second step after the first compression stage₂Solving the temperature T of the first step end point in the second compression process₃Will T₃Performing iterative calculation on the initial temperature serving as the next step to obtain the temperature of each step in the compression process; calculating the temperature of each step length to obtain the pressure of each corresponding step length through an ideal gas state equation pV (RT);

step four: calculating the intercooler process according to the outlet air temperature of the intercooler_xsThe calculation formula of (a) obtains the temperature after passing through the intercooler, and the pressure loss delta p caused by the air passing through the intercooler_sCalculating the pressure p of the outlet_sThe concrete formula is as follows.

p_s＝p_K-Δp_s

Wherein T is time, T_KVolume before the first compression stage in adiabatic index kappa regime, T_woFor the temperature of the cooling water at the outlet of the intercooler, T_wiFor intercooler inlet cooling water temperature, C_swIs the heat transfer coefficient K and the heat transfer area A_KProduct of c_pwM is the specific heat capacity of cooling water at constant pressure_wFor cooling water mass, m_sIn order to be the quality of the air,for air mass flow, p_sIs inter-coolingDensity of air at the inlet of the apparatus, A_kIs the flow area, eta, of the intercooler_rIs the coefficient of resistance of intercooler, p_KThe pressure of the intercooler is in a state of an adiabatic index kappa;

step five: step five: calculating the combustion process, setting the combustion process as constant volume heating and constant pressure heating in the mixed heating ideal circulation, and setting one step length according to the combustion processInternal heat transfer capacityVolume workMass m of working medium^*Specific heat capacity c of working medium in combustion process_v2Input heat of combustion g of fuel_f(H_uU) burning rateDetermining the temperature change in a step length in the combustion process by a first thermodynamic law

Wherein the content of the first and second substances,is the amount of heat transferred during combustion, V^*Is the volume in the combustion process; t is^*Is the temperature during combustion;

repeating the temperature iteration step in the step 3, and solving to obtain the temperature and the pressure of each step;

step six: calculating the two expansion processes, setting the two expansion processes as adiabatic expansion in the ideal cycle of mixed heating, repeating the calculation process of the step 3, and substituting the calculation process into the combustion processSpecific heat capacity c of working medium_v3Solving to obtain the temperature and pressure of each step length in the expansion process;

step seven: performing integral calculation on the pressure obtained in the steps 3, 4, 5 and 6 to obtain effective work W in the working process, and then calculating the total input heat Q according to the effective work W_totalThe effective thermal efficiency is obtained by the ratio, and the effective thermal efficiency is multiplied by the efficiency of the coupled motor, namely the generating efficiency of the whole two-stage compression-expansion generator;

η＝η₁·η₂。

the results of the power generation efficiency of the two-stage compression-expansion generator are shown in table 1:

TABLE 1

In the first step, when the temperature of gas in the compression process of the engine does not exceed 300-400 ℃, kappa is approximately equal to 1.4;

when the variation amplitude of the initial state temperature and the final state temperature of the gas in the compression process of the engine is larger than 600K, the average constant entropy index kappa is adopted_avInstead of the given adiabatic index k.

In step three, the environment of the second compression process is set to adiabatic compression in the ideal cycle of mixed heating.

In step four, the pressure loss, Δ p, of the intercooler during the design condition_s＝0.3～0.5kPa。

The method for predicting the power generation efficiency of the two-stage compression-expansion generator provided by the invention is described in detail, numerical simulation examples are applied in the method for explaining the principle and the implementation mode of the invention, and the description of the examples is only used for helping to understand the method and the core idea of the invention; meanwhile, for a person skilled in the art, according to the idea of the present invention, there may be variations in the specific embodiments and the application scope, and in summary, the content of the present specification should not be construed as a limitation to the present invention.