IN-24-C032 - New Developments on Investigating the Ignition Propensity of Mildly-Flammable Refrigerants PDF

The introduction of mildly-flammable refrigerants into motor vehicle air conditioning (MVAC) systems has required rigorous evaluation, including system testing to ensure efficiency as well as flammability testing to ensure safety. In this study, we have conducted a literature review of standard test methods (e.g., ASTM E681) for evaluating refrigerant flammability as well as newer experimental methods. One of the objectives of flammability testing includes determining the lower flammability limit (LFL) and upper flammability limit (UFL) of the refrigerant-air mixture. Another important property of flammable refrigerants related to their safety classification is burning velocity. An experimental apparatus for measuring this parameter is presented and discussed in this study. Despite establishment of these flammability testing methodologies, there is still no current standard for an experimental apparatus that can simulate real-world conditions, in which a refrigerant leak in the vehicle passenger compartment or in the engine compartment occurs. We have designed and constructed a specialized apparatus for this purpose that will be introduced in this paper. The experimental facility includes a steel test chamber with an internal volume of approximately 1 m3 consisting of five rigid sides, a sixth side consisting of an aluminum foil blow-out panel, as well as instrumentation to measure temperature and pressure, and digital high-speed camera recording. In order to properly simulate conditions found in an incident, such as a vehicle collision, the test chamber can be equipped with a variety of ignition sources that can usually be found in a vehicle. Examples of these ignition sources include an electrical wire-to-wire short, a headlight filament bulb, and a blower motor wire resistor. A few case studies and selected flammability testing results will be presented, and the pros/cons and challenges with these flammability test methods will be discussed.