Development of an aqueous surrogate for the spray performance evaluation of viscous bioliquids

Abstract Motivated by the importance of spray evaluation of viscous bioliquids prior to their deployments in combustion devices for heat and power generation, an aqueous surrogate was developed using water, glycerol, and a surfactant for nozzle design and optimization purposes. It provides a safe, clean, and transparent alternative for the spray characterization of bioliquids in a laboratory environment, compatible with different diagnostic methods. The relative proportions of the surrogate components were determined so that the spray-related physical properties of the developed surrogate solutions, namely kinematic viscosity and surface tension, at room temperature resemble those of fast pyrolysis bio-oil (FPBO) at different fuel temperatures up to 80 °C. The rheological characteristics of both FPBO and its surrogate were measured in detail. They were then atomized using a twin-fluid nozzle at different co-flowing airflow rates, 6 Q a 16 L/min, to compare their atomization and spray performances. Similar breakup mechanisms and flow patterns were observed for them as a function of Q a . Furthermore, the number- and volume-based distributions of various sizes of droplets within the sprays exhibited similar behaviour, along with a higher uniformity at the fiber-type breakup regime in comparison with the non-axisymmetric Rayleigh and membrane-type breakup modes. The global Sauter mean diameter (SMD) and standard deviation (STD) of their sprays also showed similar trends based on Q a , albeit with some differences within 10% for the cases with proper atomization conditions. The discrepancies, which mainly stemmed from both the multiphase nature of FPBO and the dynamic behaviour of surfactant solutions, diminished at large values of the co-flowing air inertial forces. The practicality of the present approach in developing surrogates for the spray evaluation of viscous bioliquids is verified using the present study’s measurements and analyses.