Pressure Measurements for Refrigerant Flammability Limit Testing Using ASTM E681 Apparatus
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Improvements to the ASHRAE 34 and ASTM E681 standard test apparatus and procedure have been identied to make the test more repeatable and reproducible. Currently, the test apparatus centers around a glass flask with visual flammability criteria that can be subjective and dependent on a wide variety of factors. Additionally, the current test apparatus vents close to the time where the visual criteria is evaluated which can impact flame propagation.
A high frequency pressure transducer was added to the testing apparatus to understand the pressure development in the test vessel throughout flame propagation. Initial test pressures below atmospheric were studied to reduce the likelihood of premature venting. Quenching effects from the electrode rods of the test apparatus were quantied as well. Ultimately, a fractional pressure rise of 40% from a mixture starting at 91.2 kPa was proposed as a new pressure-based flammability criteria to potentially replace the current visual criteria. This new criteria would result in an lower flammability limit of 14.0% for R32.