Tuning pMDI Plume Geometry for Low-GWP Formulations via Orifice Length and Exit Cone Manipulation

The transition from current-generation metered dose inhaler propellants such as HFA134a to low global warming potential propellants such as HFA152a and HFO1234ze(E) introduces a range of challenges. One of these is that low-GWP formulations exhibit differences in spray plume geometry when compared to currently approved products, due to differences in the chemicophysical properties of the formulations. The aim of this study is to investigate the efficacy of making small modifications to the pMDI actuator orifice geometry as a means of manipulating spray plume geometry. High speed imaging was used to measure spray plume geometry with a modular pMDI facility using interchangeable orifice designs, and standard canister and valve hardware. Both propellant-only placebos and solution formulations of beclomethasone dipropionate in propellant and 8% w/w ethanol cosolvent were considered. Actuator orifice length, exit cone depth and angle are correlated with spray plume width at the nozzle exit. These data show that small variations in actuator geometry can be used to tune the width of the plume to compensate for the changes in propellant properties.