Основи забезпечення еколого-енергетичної ефективності суднових дизелів стабілізацією температури палива сумішами холодоагентів

Abstract

Dissertation for the Doctoral Degree in Technical Sciences, Specialty 05.05.03 – Engines and power plants (142 – “Power engineering”). – Odesa national maritime university, Odesa, 2023. The object of research is thermodynamic processes in diesel engines and in refrigeration plants of fuel temperature stabilization systems. The subject of research are features of the thermodynamic behavior of promising refrigerants when used in the fuel temperature stabilization system to improve the environmental and energy efficiency of the marine diesel engines and their systems workflow. The dissertation is devoted to solving the problem of improving the environmental and energy efficiency of marine diesel engines by using new environmentally friendly refrigerants as working substances of the fuel temperature stabilization system. The scientific novelty of the results obtained is that, based on the research performed by the applicant for the first time: - a solution to the problem of improving the environmental and energy efficiency of marine diesel engines when operating on ultra-low sulfur fuels is proposed by using promising mixtures of ozone-friendly and natural refrigerants in the fuel temperature stabilization system, the global warming potential of which is 30-40 % lower than formost pure and mixture fluorocarbons; - a methodology for compiling state models of mixtures based on the procedure of stepwise regression analysis, which allows for reliable approximation of experimental data with moderate amounts of calculations, has been developed. The proposed method, unlike most previous ones, allows for a more efficient formation of the structure and number of coefficients of the state model; - a method of calculating the thermodynamic properties of mixtures using the function of interaction of components, which, unlike the classical method of combining the coefficients of models of the state of components, allows to increase the accuracy of calculating the thermodynamic properties of substances in the supercritical region at high density values by 1.5-2 times, which is sufficient for calculating heat exchange processes in ship refrigeration units in order to improve their environmental performance in operation; - scientific and methodological basis for the development of automated systems for calculating the thermophysical properties of new promising refrigerants and their mixtures was created, for which state models were first obtained that allow obtaining the necessary values of refrigerant properties for their use in fuel temperature stabilization systems in order to comply with international environmental requirements; - the regularities of thermodynamic behavior of mixtures of ozone-safe and natural refrigerants in a state of phase equilibrium, which consist in the presence of azeotropic compositions for them, were revealed; when using azeotropic mixtures as refrigerants, it is possible to reduce losses from external irreversibility of heat transfer processes by 20-30% compared to non-azeotropic mixtures and significantly increase the energy efficiency of the cycle of refrigeration units of ship refrigeration and air conditioning systems; - a mathematical model was created for the ecological and thermo-economic analysis of refrigeration units of fuel temperature stabilization systems for diesel engines of transport vessels, which, unlike existing methods of thermodynamic and exergy analysis, allows estimating the total equivalent greenhouse gas emissions over the entire service life of the equipment; It was further developed and improved: - a method for determining the coefficients of state models of refrigerant mixtures by stepwise regression analysis to calculate their thermodynamic properties, which, unlike previous methods, allows the most significant ones to be consistently selected from the full array of coefficients; previous methods of compiling state models were based on the group exclusion of insignificant coefficients, which is not correct due to correlations between the coefficients; - a method for determining the thermodynamic properties of mixtures in the state of phase equilibrium of saturated vapor and liquid based on the use of the condition of equality of partial volatilities of mixtures of the same composition at constant temperatures instead of the less accurate Maxwell's rule, according to which the pressure values of saturated vapor and liquid at constant temperature were determined through the equality of areas under the real and calculated isotherms between the values of the specific volume of saturated vapor and liquid in the coordinates pressure - specific volume; - a method for taking into account the weight of experimental data on the pressure and density of mixtures by adding to the expression for calculating the variance of the compressibility coefficient in the case of mixtures an additive that takes into account the error in obtaining experimental values of the composition of the mixture; - a methodology for calculating the thermodynamic properties of refrigerants in an automated information system by introducing the obtained models of the state of new refrigerant mixtures into it and using updated software algorithms compiled taking into account the methods proposed and improved in this work for studying the thermodynamic behavior of refrigerant mixtures. The practical significance of the results obtained is that: 1. The state models and tables of thermodynamic properties of R32/R125, R125/R290 and R134a/R290 mixtures developed in this thesis are recognized by the State Standard of Ukraine as standard reference data recommended for use in the design and operation of refrigeration units of refrigeration and air conditioning systems. Natural refrigerants are recommended for use in terms of the requirements of the Montreal and Kyoto protocols, as they have negligible ozone depletion and global warming potential (3 for propane). Therefore, mixing alternative refrigerants, most of which have a significant impact on global warming, with natural substances and using them in ship refrigeration systems will significantly reduce the harmful impact on the environment. 2. A method of compiling state models based on stepwise regression analysis is proposed, which, unlike most existing methods, allows, in the process of performing the regression procedure, to effectively regulate the structure and number of its coefficients in order to increase the accuracy of the model 3. An automated information system has been developed that allows to calculate the thermodynamic properties of refrigerant mixtures under different combinations of independent variables, as well as to determine the parameters of the efficiency of refrigeration cycles. The automated information system and tables of thermodynamic properties of the three mixtures were implemented at Sistemar and Transship when modernizing refrigeration units for ship comfort air conditioning systems. The developed automated system is used at the Odesa National Maritime University in research and education. The introduction of the dissertation substantiates the relevance of the dissertation topic, shows its connection with existing research programs and topics. The purpose and tasks of the research are formulated. The scientific novelty and practical significance of the obtained results are considered. Data on the practical significance of the results, personal contribution of the applicant, approbation of the work, publications, structure and scope of work are given. In Chapter 1 the main ways of reducing harmful emissions from ship power plants are described and the choice of the most acceptable from the point of view of operation of ship low-speed engines, namely the use of diesel fuels with ultra-low sulfur content, is determined. The main difficulties that arise when using the indicated fuels are also analyzed, most of which are caused by low viscosity values at ambient temperature values that usually occur in the engine room. As one of the recommended methods of increasing the viscosity of fuels with ultra-low sulfur content, the use of a fuel temperature stabilization system based on a Freon refrigeration unit is proposed. The use of a refrigeration unit in the fuel temperature stabilization system leads to the need to solve another problem related to environmental protection when using different refrigerants. As part of the solution to this problem, an analysis of global trends in the transfer of ship refrigeration units to new environmentally safe refrigerants due to the ban on the production and use of ozone-depleting refrigerants and substances with an increased greenhouse effect was performed. At the moment, there is still an urgent need for new refrigerants, which would not be inferior to prohibited ones in terms of efficiency and meet international environmental requirements. As part of the search for new substances, it is proposed to use promising mixtures of ozone-safe and natural refrigerants, which combine the positive properties of each of the components, for the fuel temperature stabilization system. Among such substances, the most studied mixtures are R32/R125, R125/R290 and R134a/R290. In Chapter 2 the form of the model of state is chosen to calculate the thermodynamic properties of mixtures. There are many models of state that are used to describe the thermodynamic properties of not only pure substances but also mixtures. They are converted into the equation of state of an ideal gas if the values of density and pressure of the substance tend to zero. The simplest are cubic models of state, which are the modifications of the known van der Waals equation. In order to increase the accuracy of calculations of the thermodynamic properties of real gases, models of state with a larger number of coefficients than in cubic ones were proposed. The exact calculation of the thermodynamic properties of mixtures is provided by methods in which, in addition to data on the components of the mixture, the functions of intermolecular interaction of the components are also used. The mixtures considered in this paper consist of components for which there are reliable equations of state. Based on this and taking into account the presence of a number of experimental p,ρ,T,x-data for these mixtures, it can be argued that a generalized Lemmon model is quite suitable for compiling their models of state. It is well tested in practice and is quite easy to implement for binary mixtures. In Chapter 3 on the basis of available experimental data, uniform models of state are compiled to calculate the thermodynamic properties of mixtures R32/R125, R125/R290 and R134a/R290. After compilation, a detailed comparison was made with the available experimental and additionally obtained reference data. The comparison showed that the compiled models of state quite satisfactorily describe the available data and can be used to calculate the thermodynamic properties for design and operation of ship refrigeration systems. In Chapter 4 the created automated information system describes. For the design and study of refrigeration plants and units of industry and transport, reliable data on the thermophysical properties of working substances on different combinations of independent variables and in wide ranges of values of these variables are required. Important sources of information about the properties of substances and materials are data banks and automated information systems. Data banks in electronic form contain archives of available data, and in automated information systems thermophysical properties are calculated using models of state and equations for transfer properties. The automated system developed in the work calculates the properties of the 21st substance in gaseous and liquid states: monoatomic gases, air and its main components, carbon dioxide, ammonia, five hydrocarbons and six alternative refrigerants, as well as 11 mixtures (including investigated in the work of substances). In Chapter 5 an analysis of the features of the thermodynamic behavior of the mixtures in the state of phase equilibrium was performed and the efficiency indicators of the refrigerating plant cycle were calculated on the basis of the studied mixtures and their components. Tables of thermodynamic properties of mixtures in the single-phase region, in the saturated state, and for wet steam were compiled based on the obtained equations of state using known differential relations of thermodynamics. A detailed comparison of tabulated values of thermodynamic properties with data for the same temperature and pressure values obtained using the well-nown automated system REFPROP was also made. In Chapter 6 carrying out a study of the working process of the engine when working on fuels with an ultra-low sulfur content. It is known that when working on such fuel at the usual temperature in the engine compartment, which often exceeds 40°C, its viscosity takes a value below the minimum permissible limit for low-speed diesel engines. At the same time, the stability of the fuel equipment is disturbed and the quality of the work process deteriorates significantly. Therefore, it is necessary to control the temperature of the fuel before the PNVT, and for this purpose it is quite effective to use a fuel temperature stabilization system based on a freon refrigeration unit. In order to analyze the efficiency of the refrigerating unit when using new mixtures of refrigerants, an ecological and thermo-economic analysis of the studied mixtures was carried out when they were used in the fuel temperature stabilization system of a diesel engine of a transport vessel. In a comprehensive analysis of the efficiency of refrigeration equipment, it is necessary to take into account all the negative factors thataffect the environment during the operation of refrigeration equipment. This is possible by performing a TEWI analysis (TEWI is the full equivalent of global warming). The TEWI criterion takes into account both the direct contribution to the increase in total radiative forcing from the emission of refrigerants, and the indirect contribution from CO₂ emissions during the production of electricity necessary for the operation of refrigeration equipment.