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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]

R1234yf has been considered as an alternative refrigerant with the low global warming potential (GWP), but it is flammable. Therefore, it is necessary to study the reduction or inhibition of flammability of R1234yf by different flame retardants. This paper mainly contributed to the influence of two kinds of flame retardants on the flammability of R1234yf. Firstly, the flammability limits of R1234yf and the mixtures of R1234yf/R227ea and R1234yf/R134a were tested out. Then the relationship between their flammability limits characteristics with the ratio of the flame retardants to R1234yf were evaluated by the fitted equations. The critical suppression ratios of R227ea/R1234yf and R134a/R1234yf were obtained. The results indicated that the inhibitory effect of R227ea on R1234yf was better than that of R134a by comparative analysis. Finally, the flame colors and flame propagation velocity characteristics of R1234yf before and after the addition flame retardants were researched and analyzed. The research achievement will be of universal guiding significance for the security application of R1234yf. [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]

Fluorine-containing refrigerants will still play an irreplaceable role in the process of research and development of new refrigerants. So it is critical to study the main toxic combustion product HF. This paper contributed to concentration characteristics of HF about R32 and R161 on particular concentrations when combustion reaction occurred. Firstly, a new enclosed test method of concentration of HF (C HF ) was presented through comparative analysis different existent methods and results. Then based on the original experimental system independently designed and built, actual C HF of 16.9%/16.89% R32 and 4.17%–4.74% R161 were measured respectively under the conditions of normal temperature and humidity. Moreover, an equation was obtained to estimate the relationship between the actual C HF and concentration of R161 (C R161 ), when C R161 was in the range of lower flammability limit (LFL) and stoichiometric concentration (C st ). And the possible affected factors of the actual C HF were analyzed. Finally it should be given sufficient attention that the risk of high C HF still exists. Therefore, the results will be of universal guiding significance for the security application of fluorine-containing refrigerants in this paper. [ABSTRACT FROM AUTHOR]

R1234ze (E) is regarded as one of the competitive candidates of refrigerants. However its flammability has not been detected out completely. This paper contributed to the fundamental flammable characteristics and influences of R1234ze (E) as well as its blends by mixed with refrigerant R161 (fluoroethane) and R152a (1,1-difluoroethane) theoretically and experimentally. Firstly, the possibility of using R1234ze (E) as a refrigerant was analyzed by means of a technical review. Secondly, the flammability limits of pure R152a, R161 and R1234ze (E) were tested out respectively basing on a new built experimental rig. Continued, the flame image of R1234ze (E) was presented, and which was obtained under the testing condition of higher relative humidity of the surrounding air. In addition, the influence reasons of the relative humidity on the flammability limits of refrigerants were analyzed. Finally, the flammability limits of R1234ze (E)/R161 and R1234ze (E)/R152a were tested out under the different concentration ratios. The results showed that R1234ze (E) possessed a slight flame suppression effect on both R161 and R152a but could not make it unburnt completely under the experimental concentration range. And the flammability limits can be estimated by some a third order polynomial with acceptable accuracy. [ABSTRACT FROM AUTHOR]

The combustion mechanism of trans-1,3,3,3-tetrafluoroprop-1-ene (R1234ze(E)) has been investigated theoretically and experimentally. Firstly, The theoretical model of R1234ze(E) combustion was revealed in unimolecular decomposition, collision with oxygen, and addition with radicals (hydrogen and hydroxyl radical). All the reaction pathways were calculated by density function theory method on M06-2X/6–311 + G (d, p) level. Then, combustion experiments were performed to verify the transformation law of volume fractions of R1234ze(E), CO, CO 2 and O 2 as the volume fractions of R1234ze(E) were changed from 8.4% to 13.6%. Combined with the theoretical calculation model, a mechanism map was established for the combustion reaction of R1234ze(E) into stable products (electric spark ignition, 298.15 K, 1 bar). Furthermore, new chemical reaction equations were proposed to describe the stoichiometric combustion of R1234ze(E) in different conditions. • A theoretical calculation model for the R1234ze(E)–air combustion system was established. • The combustion reaction measurement of R1234ze(E) were conducted. • The schematic mechanism for the combustion of R1234ze(E) were described. • The new chemical reaction equations for the stoichiometric combustion of R1234ze(E) were proposed. [ABSTRACT FROM AUTHOR]