An investigation of the effect of temperature on the oxidation processes of metallic diesel engine fuel system materials and B100 biodiesel from used cooking oil in exposure testing

Biodiesel is increasingly being used in automotive and other engine applications because of its potential to contribute to the reduction of CO₂ and other harmful emissions. However, biodiesel is known to be more corrosive in contact with metallic components than petroleum diesel. This work explores the corrosion of aluminium, steel, brass and copper metallic coupons exposed to B100 biodiesel at 25, 80, 90, 100, 110 and 120 °C. The metals that were chosen are commonly found in automotive engines. The B100 in each experiment was sampled at 48, 100, 150, 200 and 270 h and examined by GCMS to determine compositional changes. It was found that corrosion rates for copper were 10x faster than brass and approximately 100x faster than for mild steel, Al7075 and Al1050. Activation energies for corrosion were calculated from mass loss and ICP, with good correlation between the two methods for Cu containing samples. By mass loss, the activation energies for Cu, Brass, Al7075 and Al1050 were calculated to be −47.9 kJ mol⁻¹, −85.4 kJ mol⁻¹, −86.7 kJ mol⁻¹ and −54.4 kJ mol⁻¹, respectively. By ICP analysis, the activation energies for Cu, Brass, and Al7075 were calculated to be −57.9 kJ mol⁻¹, −90 kJ mol⁻¹ and −140 kJ mol⁻¹, respectively. Corrosion rates in brass and copper samples were faster owing to the direct reaction of copper with the fatty acid. The copper was found to cause chain scission and greater degradation of the biodiesel.