Effect of two halogenated olefins on combustion characteristics of Isobutane

To reduce the greenhouse effect, environmentally friendly working fluids such as unsaturated halogenated olefins and hydrocarbons have attracted much attention. This study focuses on the combustion characteristics of two binary mixtures of isobutane (R600a) and R1234ze(E) and R1233zd(E). The results indicate that the addition of R1234ze(E) and R1233zd(E) has different effects on the combustibility of R600a under rich and lean fuel conditions. From the perspective of flammability limit range, as the ratio of R1234ze(E) and R1233zd(E) increases, the flammability limit range of both mixtures first increases and then decreases. For R1233zd(E)/R600a containing chlorine (Cl), the maximum flammable limit range corresponds to (nF + nCl)/nH equal to 1/3, which is significantly smaller than the nF/nH ratio of 1 in R1234ze(E)/R600a. Secondly, through calculation and simulation, it was found that the flame retardancy of R1233zd(E) is stronger than that of R1234ze(E), as the Cl in the former has a stronger ability to capture active radicals. Finally, based on Chemical kinetics analysis, it is found that adding R1234ze(E) to R600a during oxygen enrichment will increase the concentration of active radicals H, O and OH during combustion. This leads to higher combustion temperature and smaller flame thickness, thereby promoting the combustion process. The results will have significant implications for the safe application of new mixed working fluids and the analysis of internal reaction mechanisms of the mixture flammability.