Comparison of simple and complex methods for determining refrigerant/air laminar burning velocities from the pressure rise in constant-volume experiments

Abstract

Laminar burning velocity is currently one of the metrics for differentiating refrigerant flammability risk per ANSI/ASHRAE Standard 34-2019, Designation and Safety Classification of Refrigerants. Several methods exist for determining laminar burning velocity, and the HVAC&R industry is currently evaluating whether the constant-volume method (CVM) is appropriate for measuring the burning velocity of refrigerants. This study focuses specifically on the different data reduction techniques that can be applied to yield the laminar burning velocity from the pressure rise in CVM experiments. More specifically, simple analytical expressions and more complex numerical models are applied to estimate the mass fraction of burned gas from the pressure rise x(P), which is a requisite for determining burning velocity from the measure pressure. When following the experimental and post-processing recommendations outlined in this paper, one of the simpler methods of estimating x(P) yields R32/air burning velocities that are within 5% of those deduced using the more complex methods of estimating x(P). The method presented can be applied to experimental pressure rise data obtained in both normal gravity and microgravity.