Comparison of Flammability of Low-GWP Refrigerants Using 1.76-m3 Combustion Chamber

ABSTRACT

The transition to low global-warming potential (GWP) refrigerants is ongoing. Since a large part of Low-GWP refrigerants is combustible, fundamental flammability parameters have been studied. However, the combustion behavior of accidentally released refrigerants is not fully understood. In this study, we studied the relationship between the flammability parameters such as lower flammability limit (LFL), the fundamental burning velocity (FBV) and the combustion behaviors of Low-GWP refrigerants including R290 (C3H8), R152a (CH3CHF2), R143a (CH3CF3), R142b (CH3CClF2), R41 (CH3F), and R32 (CH2F2).

We conducted tests using three experimental configurations: static configuration, laminar and turbulent flow configuration simulating realistic refrigerant leak. Under static conditions, the burning velocities for R290, R152a (CH3CHF2), and R32 were measured in a 1.76 m³ combustion chamber. The measured values of burning velocities were in a good agreement with available literature data. Laminar refrigerant leak was studied for R290, R152a, R41(CH3F), R142b (CH3CClF2), and R32 in a 1.76 m³ combustion chamber. Flammability of turbulent flow leak of R290, R152a, R143a (CH3CF3), and R32 was analyzed using a 237 L plastic container.

Experiments simulating laminar and turbulent flow refrigerant leak demonstrated a positive correlation between LFL and the time before ignition. The refrigerant concentration at ignition agreed with LFL. It was found that the combustion behavior of refrigerants under leak conditions corresponds two types of flame propagation. The first type corresponds to a flame which rapidly spreads horizontally on the floor surface from the ignition source. The second type corresponds to flame kernel irregularly appearing around the continuous spark source. The approximate boundary between two types of combustion behavior corresponds to R152a (FBV = 23.6 cm/s, unsupported flame propagation) and R143a（FBV = 7.1cm/s, combustion supported by the continuous ignition source). This result is consistent with ASHRAE 34, ISO 817 and the GHS classification revised in 2017 adopting the burning velocity of 10 cm/s as a boundary between “highly flammable” and “lower flammable” refrigerants.

KEYWORDS:

• Word
• low global-warming potential
• combustion test
• flame propagation
• R32
• R290

Acknowledgments

We would like to thank Mr. Yasushi Kobayashi of Kayaku Japan Co., Ltd. for the supports in experiments.