Air ingestion and entrapment is prevalent in the lubricant circulating around internal combustion engine and can lead to formation of two-phase flow system referred to as bubbly oil which affecting the oil viscosity and overall damping capability. Experimental work is conducted to study the effective viscosity of bubbly oil in a simple shear rheometer with the aim of gaining a general understanding of the two-phase mixture flow and developing lubrication models to be used in subsequent analysis. A laboratory simulator is used to produce bubbly oil by controlling the system pressure, temperature, and gas content entrained from atmosphere and an enclosed rheometer is employed to measure the mixture viscosity. A new detailed design is incorporated into the commercial rheometer with the purpose of maintaining the distribution of bubbles within the lubricant. The transparent test chamber is initially pressurized with air to control the bubbly oil level and the bubbly oil viscosity is tested over a wide range of shear rates. Under shearing motion, the viscosity of bubbly oil varies with time and the results obtained are compared to that of single-phase oil.

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