Particulate Characterization and Lubricating Oil Tribology Investigations of a Gasoline Compression Ignition Engine Using Low Octane Fuels

Abstract

High compression ratio and lean-burn operation of low-octane gasoline-fueled compression ignition engines lead to significantly higher thermal efficiencies. Hence, it has emerged as a potential technology to propel medium and heavy-duty vehicles. Gasoline compression ignition engines use advanced fuel injection timings and gasoline-like low-octane fuels, and their impact on the lubricating oil tribology and particulate emissions must be experimentally assessed. Hence, this experimental study compares these aspects for the gasoline compression ignition and baseline conventional diesel combustion engines. Extreme heat, moisture, contamination by particulate matter, corrosive gases, dirt, fuel dilution, wear debris, and depleted additives can degrade the lubricating oil, resulting in higher engine wear and eventual failure. The experiments were conducted on a medium-duty diesel engine at varying engine loads and speeds, and the effect of fuel injection timing on particulate emissions was investigated. The engine was operated for 20 hours, and lubricating oil samples drawn at fixed intervals were analyzed for changes in lubricating oil using spectroscopic techniques. Transmission electron microscopy and inductively coupled plasma-mass spectroscopy were used to analyze the soot and trace elements in the lubricating oil. Spray droplet distribution in the cylinder in a non-reactive computational fluid dynamics simulation environment was done to understand the fuel dilution to the lubricating oil. Results indicated that gasoline compression ignition emitted more particulates than baseline diesel combustion. The gasoline compression ignition engine's lubricating oil showed higher soot-in-oil and lower trace elements, ash, and carbon contents than baseline diesel combustion. Fuel dilution to the lubricating oil was observed in the simulations.