Opposite effects of R1234yf on the flammability limits of R600a refrigerant: experimental and kinetic insight.

R1234yf/R600a refrigerants blends are regarded as a compromise solution to replace high-GWP refrigerants. They possess excellent thermodynamic properties compared to pure refrigerants. However, R1234yf refrigerants exhibit completely opposite influences on the lower (LFL) and upper flammability limits (UFL) of hydrocarbon refrigerants. In this study, the representative HFOs refrigerant R1234yf was selected to experimentally investigate its influence on the flammability limits (FLs) of R600a, a typical hydrocarbon refrigerant. The LFL and UFL of R600a converge when the volume fraction of R1234yf in mixture reaches 0.92. The UFL and LFL of R600a are reduced by 93.7 % and 71.9 %, respectively. Secondly, oxidation experiments of R600a were conducted using synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) technology, and a kinetic model for R600a was selected based on the experimental data. The hydrocarbon mechanism was coupled with the optimized NIST2021 mechanism, and for the first time, a kinetic model applicable to R1234yf/R600a refrigerants blend was proposed. The proposed kinetic model reveals the mechanisms driving the contrasting effects of R1234yf on the FLs of R600a refrigerants. Simulation results indicate that R1234yf significantly influences the flame structure of R600a in both lean and rich combustion, owing to pronounced variations in the mole fractions of radicals H, OH, and O. Among them, H radicals have a greater influence on the reaction pathways than OH and O radicals. These findings help to identify the potential risks associated with promoting the use of R1234yf/R600a refrigerant blends.