Engine durability and lubricating oil tribology study of a biodiesel fuelled common rail direct injection medium-duty transportation diesel engine

Abstract

Biodiesel has emerged as a viable alternative to mineral diesel in the transport sector to replace fossil fuels partially. However, long-term compatibility with engine hardware must be evaluated to ensure a smooth transition. Long-term material compatibility studies of Karanja oil methyl ester (biodiesel) blends with the hardware of a modern common rail direct injection system equipped diesel engine used in sports utility vehicles have been carried out in this investigation. A long-term endurance test was carried out in two phases, each lasting 274 h and utilizing (i) baseline mineral diesel and (ii) a 20% v/v Karanja biodiesel blended with mineral diesel (KB20). After completing the first phase, the engine was dismantled, and essential engine components were investigated for carbon deposits and physical wear using several techniques. Before proceeding with the next phase of the endurance test KB20, new engine components were installed in the engine, and then the test was executed. The KB20-fuelled engine exhibited lower wear on the valves and crankpins but higher wear of liners, piston rings, pistons, gudgeon pin, small and big end bearings of the connecting rod, and the main bearings. Fuel chemistry affected the lubricating oil efficacy and its residual useful life. Lubricating oil from the KB20-fuelled engine exhibited a higher increase in density and ash content. KB20 fuelled engine's lubricating oil underwent higher oxidation and polymerization. The surface roughness characteristics of the cylinder liner were measured before and after the endurance test for comparative wear evaluation during both phases of the endurance test. Carbon deposits on the cylinder head, piston top, and injectors were compared, and the pistons of the KB20 fuelled engine exhibited higher carbonaceous deposits. Biodiesel blends harmed the CRDI engine's fuel injection system. Biodiesel harms the fuel injection equipment (FIE) of the CRDI engine. Various tribological tests were performed on the lubricating oil samples collected regularly to examine the compatibility of KB20 vis-à-vis mineral diesel. This series of tribological tests on the lubricating oil samples assessed the effect of fuel chemistry on the lubricating oil's performance and residual useful life. Tests included variations in lubricant density, viscosity, flash point temperature, moisture content, pentane and toluene insoluble, and copper corrosion with time. The study summarily concluded that Biodiesel blends could be utilized in a CRDI engine without causing major engine durability or lubricating oil degradation issues.