Study on the flame retarding mechanism of HFC-134a on hydrocarbon refrigerants.

Hydrocarbons (HCs) are ideal candidates for the long-term environmentally friendly refrigerants due to their excellent advantages in environmental protection and energy efficiency. But the flammability properties limit their wide application. To address it, this study focused on the inhibition mechanism of HFC-134a on the combustion processes of hydrocarbon refrigerants (HC-50, HC-170, HC-290 and HC-600a). A kinetic model of HCs/HFC-134a combustion was established to compared the effects of HFC-134a on the adiabatic flame temperature, laminar burning velocity, key species and radical reactions. The results showed that the addition of HFC-134a significantly reduced the adiabatic flame temperatures and laminar burning velocities of hydrocarbons. The concentration analysis of products and rate of production (ROP) revealed that HFC-134a promoted the productions of flame retarding groups CF, CF2, CF3, and CHF, while consumed the concentrations of flammable radicals H, O, and OH. Furthermore, sensitivity and reaction path analysis proved the suppressing actions of HFC-134a. It was concluded that HFC-134a not only changed the reaction paths and sensitivity coefficients, but also transformed the promotion path into inhibitory path in combustion. These effects achieved effective inhibition on the combustion processes of HCs. The results of this paper not only supported the safe application of hydrocarbon refrigerants, but also provided new ideas for the development of new efficient flame retardants.