Project Details
Projekt
Laminar burning velocity measurements of refrigerants under terrestrial and microgravity conditions
Applicant
Dr.-Ing. Joachim Beeckmann
Subject Area
Energy Process Engineering
Term
since 2023
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 497007546
Next-generation refrigerants with lower global warming potential for cooling and heating applications pose increased fire hazards due to their high flammability. Classification of a substance’s fire hazard potential includes not only flammability but also the evaluation of its laminar burning velocity, a quantity additionally representing reactivity and exothermicity. Conventional methods for determining laminar burning velocities measure a mixture's flame propagation speed, for instance, by assessing spherical flames. Due to the slow propagation speed of most refrigerant flames, the impact of two physical phenomena significantly increases: (1) The buoyancy-induced deformation of the flames, and (2) the radiation heat losses, invalidating the underlying assumptions required for experimental methods. Hence, standard data extraction assumptions, such as spherical flame shape, fail and accurate literature data on flame velocities for these refrigerants are rare. To obtain a fundamental understanding of the refrigerant’s combustion behavior and to provide accurate flame velocity data, the flame structure, propagation, and surrounding gas dynamics must be studied in detail using high-fidelity experiments. In this project, robust methods will be developed to reliably characterize the combustion behavior of refrigerants. First, the buoyancy deformation effects of slow-propagating refrigerants will be investigated using Particle Image Velocimetry (PIV). The flame front's local curvature and strain effects are key factors in determining burning velocities. Microgravity experiments, conducted in the drop tower facility of the Center of Applied Space Technology and Microgravity (ZARM) of the University of Bremen, will provide buoyancy-free flame propagation data, isolating the radiation heat loss effect. These heat losses will be quantified by the spatially and temporally resolved flame temperature fields obtained using the high-speed Rayleigh scattering. The findings will help develop and modify existing radiation correction models, that were developed for hydrocarbons but have not yet been validated for refrigerant flames. Finally, a flame structure analysis based on an asymptotic approach with a multi-step reaction scheme will be performed to reveal the underlying physicochemical processes involved in the ignition, extinction, and propagation of refrigerant/oxidant mixtures. The applicability of the existing asymptotic approaches will be studied, and modifications tailored explicitly for refrigerant flames will be applied. This will contribute to developing an accurate and robust simplified modeling approach with approximation formulas for the burning velocities of refrigerant flames.
DFG Programme
Research Units
