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Accurate measurements of the laminar flame speed are useful to constrain the uncertainty of chemical models. However, for slowly propagating flames, buoyancy distorts the flame and measuring flame speeds accurately becomes challenging. This is relevant for novel hydrofluorocarbon refrigerants, preventing an accurate assessment of their flammability. Additionally, nitrogenated chemistry could be investigated by measurements of ammonia/air flames but the low laminar flame speeds also lead to similar issues. The only way to circumvent buoyancy-induced effects is to gather measurements in microgravity. In this study, an image processing technique was developed to accurately extract the radius of the spherical flame. This is required as the projection of a sphere on a plane leads to measurement error. A lab-scale drop tower was designed and built to achieve approximately 500 ms of free fall time. The direct imaging technique was combined with the drop tower to gather flame measurements in free fall. The methodology was applied to obtain the laminar flame speed of a lean, high-pressure methane/air flame. 

Hydrofluorocarbons (HFC), which are mildly flammable and pose potential fire risks, have received greater attention as a viable low global warming potential alternative to traditional refrigerant and fire-suppressant compounds. However, the reactivity of these compounds can be exacerbated under certain conditions, with buoyancy-induced instability growth promoting flame acceleration and substantially increasing flame speeds of HFC/oxidizer deflagrations. Therefore, the flame acceleration of HFC/oxidizer deflagrations must be investigated to properly assess the flammability characteristics of these compounds. This study investigates the effect of the Rayleigh-Taylor instability on instability growth rates during the linear regime. To this end, simulations were performed tracking the growth of instabilities caused by an initial disturbance in the flame front, from which dispersion relations were derived for R-32/air mixtures varying the gravitational acceleration. 

Hydrofluorocarbons (HFC), which are mildly flammable and pose potential fire risks, have received greater attention as a viable low global warming potential alternative to traditional refrigerant and fire-suppressant compounds. Therefore, there is a demand to accurately quantify their flammability and reactivity to establish proper safety metrics. This study investigates the effects of radiation heat loss on slowlypropagating HFC/air laminar flames. Planar 1-D simulations of R-32/air and R-1234yf/air flames show significant reductions in laminar flame speed due to radiative heat losses from the flame zone. Simulations of spherically expanding flames (SEF) revealed that the radiation-induced flow needs to be considered when interpreting data from experiments. To this end, a Spherical-flame RADiation-Induced Flow (SRADIF) model was developed to estimate the burned gas inward flow velocities in constant-pressure SEFs, utilizing the optically thin limit assumption to model radiation heat loss. The model was validated against results from detailed numerical simulations of SEFs, from which radiation-induced inward flow was derived using a new formulation considering both the radiation heat loss and convective flow effects. Results show that SRADIF accurately predicts the inward flow velocity for R-32/air mixtures over a range of conditions and performs significantly better compared to existing analytical models. However, the model was unable to accurately predict flow velocities for R-1234yf/air flames and the reason for this is discussed. 

Hydrofluorocarbons (HFC), which are mildly flammable and pose potential fire risks, have received greater attention as a viable low global warming potential alternative to traditional refrigerant and fire-suppressant compounds. Therefore, there is a demand to accurately quantify their flammability and reactivity to establish proper safety metrics. This study investigates the effects of radiation heat loss on slowly-propagating HFC/air laminar flames. Simulations of spherically expanding flames (SEF) revealed that the radiation-induced flow needs to be considered when interpreting data from experiments. To this end, a new spherical-flame radiation model was developed to circumvent the effects of radiation-induced inward flow in constant-pressure (CON-P) SEF experimental measurements, accounting for radiation heat loss using the optically thin limit model. The developed spherical-flame radiation model was validated against results from transient SEF simulations. 

Hydrofluorocarbons (HFC), which are mildly flammable and pose potential fire risks, have received greater attention as a viable low global warming potential (GWP) alternative to traditional refrigerant and fire-suppressant compounds. Therefore, there is a demand to accurately quantify their flammability and reactivity to establish proper safety metrics. This study investigates the effects of radiation in slow-propagating HFC/air laminar flames. Planar 1-D simulations of R-32/air and R-1234yf/air flames show significant reductions in laminar flame speed due to radiative heat losses from the flame zone. Simulations of spherically expanding flames revealed that the radiation-induced flow needs to be considered when interpreting data from experiments. To this end, a radiation model was developed to circumvent the effects of radiation-induced inward flow in constant-pressure (CON-P) SEF experimental measurements, accounting for radiation heat loss using the optically thin limit model. Validation of the radiation model is currently underway, but preliminary results show that the model better predicts the inward flow velocity for most conditions compared to existing analytical models.