<b>An Investigation of Flammability in Low GWP Refrigerant Blends</b>

<p dir="ltr">Refrigerants employed in thermal management systems of next-generation military transport vehicles need to be efficient and safe for use in harsh environments. Currently, refrigerants are categorized as either high global warming potential (GWP) and low flammability (e.g., hydrofluorocarbons (HFCs)), or low GWP but higher flammability. The flammability aspect of low GWP refrigerants poses significant challenges for military applications due to varied extreme environments and battlefield threats. The primary concern is that the supply chain issues associated with HFCs will limit the availability of low flammable options for military refrigeration needs. The goal of this study is to create new test methodology to evaluate the flammability of selected pure refrigerants and their blends to determine their performance under various military-relevant threats, ultimately aiming to identify the optimal low GWP refrigerant for use in military mobile air conditioning (MAC) systems. This study examines a suggested refrigerant blend based on thermodynamic simulations under multiple ignition sources to study their ignition and combustion behavior. The resulting rankings are compared with expected flammability limits of pure refrigerants as established in ASHRAE Standard 34 (Designation and Safety Classification of Refrigerants). The ignition sources considered include hot nichrome wire, a 4 kV electric spark, and a burning solid propellant. Each ignition source was selected to mimic potential threats these refrigerants could be exposed to in a battlefield setting. The blend consisted of R-134a(0.125)/R-1234ze(E)(0.55)/R-1336mzz(E) (0.325) and when exposed to each of the ignition sources, no combustion behavior was seen. This indicates that it is a good candidate to replace existing refrigerants in military MAC systems.</p>