Study on flammability limit and combustion reactions behaviors of R744/R152a environmentally friendly mixed working fluid by experiments and molecular dynamic simulation

R744/R152a mixture has broader application prospects. However, its thermodynamic and safety characteristics need to be fully considered. This paper presents the flammability characteristics and reaction mechanism of R744/R152a mixture by experimental and ReaxFF MD. Firstly, the flammable zones of the mixture with different ratios were tested on a high-precision experimental setup. Using a high-speed camera and an infrared thermographic record flame evolution characteristics and relative flame temperature of the mixture both lean and rich limits. The flammable zones of R152a are 0.386–0.685 (Φ) at y = 0. R744 was able to narrow the flammability zones of R152a. As the inert gas increases, the lean and rich limits merge, is 0.542 (Φ). Based on experimental studies, the inhibitory effect of R744 on the oxidation mechanism of R152a was investigated from the atomic level using ReaxFF MD. The results showed that the R744 increased the activation energy of the system from 52.08 kcal/mol to 55.73 kcal/mol, 52.18 kcal/mol, 57.04 kcal/mol, 52.93 kcal/mol, 52.98 kcal/mol, respectively. Reaction pathways and the rates of elementary reaction are significantly suppressed. The simplified mechanism of the oxidation can reveal the macroscopic phenomenon that R744 inhibits flame propagation. The results of this study provide safety guidance for R744/R152a applications.