Search

The issue of global warming prompts us to consider some questions related to energy supply and use. Organic Rankine Cycles (ORC) is a suitable technology for converting low-grade thermal energy into electrical energy, vital for conserving energy and mitigating emissions. Currently, most environmentally friendly working fluids are characterized by their flammability. Analyzing the minimum ignition energy (MIE) of these working fluids is crucial in guaranteeing secure utilization. This paper introduced a novel approach to predicting the MIE of flammable working fluids using microscopic molecular structure analysis. Firstly, the bond energy of molecules was derived by optimizing the microscopic molecular structure of prevalent combustible agents based on the density functional theory (DFT), which was employed to calculate the heat of combustion. Secondly, a mathematical model for predicting the MIE of combustible working fluids was constructed, drawing inspiration from the energy relationship during combustion. Then, the newly formulated model was used to predict the MIE of propane and nine other combustible working fluids, and the results were compared with the existing data. The results show that the predicted values of the MIE exhibit an impressive accuracy rate exceeding 95%. Finally, the MIE prediction model has been modified to provide higher prediction accuracy. This study is of great significance to ensure the safe application of combustible working fluids and to explore environmentally friendly alternatives. [Display omitted] • A new method for predicting the MIE based on molecular structure was proposed. • The molecular structure was optimized based on density functional theory. • The mathematical model has a prediction accuracy of more than 95 %. • The model can predict the ignition energy of substances outside the database. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle (ORC) is an effective way to improve energy efficiency, and 2,3,3,3-tetrafluoropropene (R1234yf) is considered as a promising working fluid for ORC. However, the development of R1234yf in ORC is limited by its flammability, and the addition of 1,1,1,2-tetrafluoroethane (R134a) is an effective method to inhibit its flammability. In this paper, the combustion and interaction mechanism of R1234yf/R134a were investigated. Firstly, the combustion products of R1234yf/R134a were measured using an improved experimental device, the results showed a substantial reduction in the concentrations of CO, CO 2 , and HF with an increasing proportion of R134a. Then, the combustion mechanism of R1234yf/R134a was studied by ReaxFF-MD simulation. The initial decomposition time of R134a was found to be later than that of R1234yf, and a reduction in the production rate of combustion products was achieved with the addition of R134a. Furthermore, the combustion reaction was promoted by the increase in temperature. Finally, the main reaction pathways of working fluids were analyzed. The abstraction reaction of R134a with radicals and the scavenging of active radicals by flame retardant radicals were the key to inhibit the combustion reaction. The results have universal guiding significance for the safe application of R1234yf/R134a. • The combustion and interaction mechanism of R1234yf/R134a was investigated. • The combustion products of R1234yf/R134a with different proportions were measured. • The inhibitory effect of R134a on the combustion of R1234yf was studied. • The main reaction pathways of R1234yf/R134a were analyzed. [ABSTRACT FROM AUTHOR]

Organic Rankine cycle (ORC) is an effective way to utilize low-grade energy. 2,3,3,3-tetrafluoropropene (R1234yf) has attracted extensive attention due to its good environmental protection performance and is considered as an alternative working fluid in ORC. However, its thermodynamic, environmental and safety characteristics need to be fully considered. In this paper, the combustion mechanism and product characteristics of R1234yf were investigated by ReaxFF molecular dynamics simulations. The reaction temperature and equivalence ratio have important effects on the combustion of R1234yf. The early stage of the combustion process is mainly the unimolecular decomposition reaction of R1234yf, and then O 2 participates in the reaction, the consumption rate of R1234yf increases rapidly, the radicals O, H, OH, CF 3 , CF 2 , and CFO play important roles in the combustion reaction. The main combustion products include CO, CO 2 , HF, and COF 2. In addition, the combustion product concentration and yield of R1234yf were tested by an improved method. The results showed that the change law of combustion product yield with equivalence ratio was in good agreement with the simulation results, and the risk of high CO and HF concentrations still exists. The research results have practical significance for the safe application of R1234yf in ORC system. • The combustion mechanism of R1234yf was studied by ReaxFF-MD simulations. • The reaction conditions have important effects on the combustion of R1234yf. • The concentration and yield of combustion products were measured and analyzed. • The variation law of combustion products of R1234yf was obtained. [ABSTRACT FROM AUTHOR]