Corrosion of copper exposed to water-in biodiesel-diesel emulsion fuel stabilized with polyglycerol polyricinoleate emulsifier

Abstract

Despite emulsification of water in-diesel can decrease harmful exhaust emissions, unstable emulsion can result in formation of free water which can accelerate metal corrosion in the fuel delivery system of a diesel engine. This study aimed to formulate and assess stability of 5 vol% water in 5 vol% biodiesel in diesel emulsion fuel (W5B5) and investigate its effects towards copper corrosion. Stable W5B5 was successfully prepared with 3 vol% polyglycerol polyricinoleate (PGPR). After 1200 h of storage, W5B5 remained stable, indicated by mean droplet diameter of 627.6 ± 7.5 nm, sedimentation index of ∼3 %, and absence of free water formation. Upon exposure to copper, mean droplet diameter of W5B5 increased by 2.7 times compared to prepared W5B5. Viscosity and total acid number (TAN) values of copper exposed W5B5 increased by 26 % and 270 %, respectively, indicating enlargement of water droplets and degradation of fuel during immersion. Corrosion rate of copper exposed to W5B5 decreased by 92 % between 240 and 1200 h of immersion. Corrosion rate of copper in W5B5 was 5.5 times and 3.0 times higher diesel and biodiesel, respectively. Higher initial TAN of W5B5 than other fuels, attributed to addition of PGPR to form stable water-fuel emulsion, influenced the higher corrosion rate observed in W5B5 compared to other fuels. To minimize corrosive nature of W5B5, future research should focus on developing stable formulation with low initial acidity value comparable to or even lower than biodiesel. The contribution to knowledge from the study yielded valuable insights into the stability of emulsion fuel, corrosion behaviour, and impact of emulsifier acidity on corrosion rates.