Compatibility and long-term degradation of fuel supply system and selected engine components from a legacy SI engine in E20 ethanol-blended fuel: A 1500-h static immersion study

Abstract

India has been rapidly transitioning to E20 (20% ethanol-blended petrol), raising important questions regarding the long-term compatibility of fuel-system components typical of legacy BS4 and early BS6 Phase-1 spark-ignition (SI) engines. The material degradation of critical fuel system and selected engine components were evaluated in this study by a 1500-h static immersion test at room temperature (25 ± 2°C) per SAE J1747 and SAE J1748 requirements. A 1999 1.6 L MPFI petrol engine was used for this demonstration with its components including aluminium pistons, fully assembled fuel injector assemblies, carbon steel fuel lines, Nitrile (NBR) rubber O-rings/gaskets and phenolic resin-treated cellulose fuel filters exposed to laboratory-blended E20 fuel and commercial BS6 baseline E0 fuel. The results indicated a significantly higher corrosion rate for the metallic components and significant chemical degradation for the non-metallic components exposed to E20 than those exposed to E0. Swelling, loss of elasticity and embrittlement were observed in NBR elastomers and significant breakdown in phenolic resin bonds in fuel filter media with the release of fibres. Post-immersion analysis revealed higher fuel density, kinematic viscosity, lower calorific value and a significant increase in the total acid number (TAN) which is considered to be a surrogate for possible acetic-acid formation. The surfaces after exposure to E20 showed increased oxygen/carbon content, features suggestive of oxide-scale formation and pitting, as indicated by high-magnification optical microscopy at 1000× with EDS. The results show that E20 fuel causes more material degradation under conditions with no motion in legacy SI engine components. The observed degradation modes and the literature reviewed indicate the need for material improvements like FKM (Viton) elastomers and corrosion-resistant alloys. Major limitations of the study include the static-only immersion conditions, the indirect inference of acetic-acid formation from TAN without direct chemical identification, the absence of presented EDS spectra and the fact that all specimens originated from a single legacy engine.