Experimental stability investigation of different water-in-jojoba biodiesel emulsions

Abstract

Investigating the stability of water in biodiesel emulsion fuels during storage and engine operation is crucial to consider for marketing processes. This study examines the stability of water-in-Jojoba biodiesel (WJBD) emulsion that is stabilized using three commercially available surfactants, Span-80 (HLB 4.3), Tween-80 (HLB 15), Triton X-100 (HLB 13.5). The investigation involves varying the composition of the emulsions by adjusting factors such as the hydrophile lipophile balance (HLB), surfactant concentration, water concentration, mixing speed, and mixing duration, and study their effects through a bottle test. Stable emulsions are studied by bright field optical microscopy, constant shear test, and thermal loop rheology test. The research reveals that Tween-80 (HLB 15) and Span-80 (HLB 4.3) effectively yield emulsions with high relative stability. Specifically, at 5 (v%) water concentration, emulsions prepared with Tween-80 (HLB 15) demonstrate the formation of water droplets as small as 3.88 µm. Additionally, emulsions at various water concentrations are thoroughly studied. Over time, phase separation is studied by microscopic images and showed minimal coalescence after the first day for the emulsions that showed promising stability in the bottle test. To further assess the stability, the stable emulsions undergo continuous shear test, wherein a consistent pattern of stable viscosity is observed as time passed. Moreover, the thermal loop test showed minimal change in the relative microstructure of the emulsion, where the difference in the storage modulus and the loss modulus didn’t exceed 15 % and 5 %, respectively. Understanding the change in microstructure, droplet sizes, and how the emulsions behave under certain shear stresses is critical for practical applications of this fuel. Through comprehending the factors that influence the emulsion stability, this study contributes valuable insights for the successful storage and engine operation of the WJBD.