Parametric analysis of commercial fuel sprays in a test bench with controlled temperature

Abstract

A novel setup using a modular test bench with independent control of gas-phase velocity, temperature, injection pressure, and nozzle geometry was employed to perform a comprehensive parametric analysis of commercial ethanol and gasoline sprays under non-reactive conditions. High-speed imaging and Phase Doppler Interferometry quantified integral and pointwise spray characteristics across divergent and convergent nozzles, varying pressures (50–70 bar) and gas-phase temperatures (25–40 °C). Divergent nozzles produced narrow and stable plumes with rapid momentum decay, whereas convergent nozzles yielded wider sprays with delayed velocity peaks and sustained dispersion. Elevated temperatures and pressures strongly influence spray characteristics, markedly reducing smaller diameter class populations and shifting secondary breakup downstream. Ethanol sprays exhibited higher values of the Ohnesorge numbers than gasoline and a more constant projected area variance (PAV), resulting in consistent spray formation across all tested conditions. Fuel volatility governed the evolution of droplet size distribution throughout the sprays, with gasoline sprays displaying bimodal size distributions and ethanol maintaining its size distribution pattern. Dimensionless parameter analysis (Weber and Ohnesorge numbers) highlighted the transition from aerodynamic to oscillation-dominated breakup regimes and their influence in the formation of new droplets and consequently the rate of droplet size reduction between measurement points. These findings provide valuable insights for injector design and commercial fuel spray applications, highlighting the potential of ethanol (a renewable fuel in Brazil) due to its stable and regular spray structure. This characteristic makes it particularly suitable for use in narrow operational windows, potentially enhancing overall process efficiency