HOT SURFACE IGNITION OF R-32 AND R-410A REFRIGERANT MIXTURES WITH LUBRICATING OIL

This study examines the flammability of refrigerant and oil mixtures. The flammability risk associated with refrigerants is an important property to consider prior to their use in residential and commercial HVAC systems. This research was conducted to compare the ignition characteristics of R-32 with R-410A, and the effects of lubricating oil. Unpiloted hot-plate ignition tests were carried out to determine ignition temperatures and quantify the flammability risks associated with these refrigerants. Additionally, computational fluid dynamic (CFD) methods were used to model the vapor temperatures and concentrations of an R-32 jet impinging on a hot-surface. The laboratory results indicate that R-32 will ignite upon contact with a 764oC surface. This is higher than the reported 648oC autoignition temperature of R-32. R-410A was found to ignite upon contact with a 790oC surface. Results with mixtures of refrigerant and polyolester (POE) oil were found to ignite at temperatures close to that of oil alone, 645oC. CFD predictions show that ignition is likely to occur along the edges of the apparatus, where the fuel vapor concentrations and temperatures are within the limits of combustion

Autoignition of R32 and R410 Refrigerant Mixtures with Lubricating Oil

Refrigerant R32 (difluoromethane, formula CH2F2) is a working fluid with favorable environmental and performance properties. However, it can be slightly flammable under certain conditions (13 – 30% by volume in air), with a flammability classification of 2L. The risks of ignition, fire, and hazardous decomposition products are being assessed in our laboratories using experiments, risk analysis, and computational fluid dynamics simulations. R32 has entered service in Japan and is being considered for service in the US. Its adoption is being hindered by its slight flammability in air. Past research has examined the flammability of pure refrigerants without considering the effects of the presence of lubricating oil. The concentration of oil released in a refrigerant leak can vary depending on the location of the leak and the operating state of the equipment. In this study, mixtures of R32 and R410 with lubricating oil are impinged onto a hot horizontal metal surface to examine autoignition behavior. The tests simulate a leak in a cooling system that impinges on a heating element. The hypothesis of this research is that the autoignition behavior of these mixtures is dominated by the presence of lubricating oil, not by differences in the refrigerant flammability. Only preliminary results are available at the time of abstract preparation, but extensive results will be included in the presentation at Purdue