Experimental and numerical investigation of the effects of engine oil on combustion and particulate formation in a renewable bioethanol-gasoline engine

Ethanol is a promising biomass-derived renewable biofuel for internal combustion engines, offering substantial potential for carbon-emission reduction and knock suppression. This study combines experiments and numerical simulations to investigate the effects of engine oil on ethanol-gasoline combustion and emissions. Experiments were conducted to evaluate the influence of new and waste engine oil on flame temperature and ash morphology. A simplified kinetic model of engine oil, using C30H58 as a surrogate, was developed based on the HyChem method and coupled with an ethanol-gasoline sub-mechanism to establish a three-component mechanism suitable for CFD simulations. Three-dimensional simulations were then performed to examine the effects of ethanol and engine-oil blending ratios on in-cylinder combustion and soot formation. Results show that oil aging markedly deteriorates combustion completeness. The ethanol blending ratio exhibits a non-monotonic effect on combustion intensity: ratios ≥95% create an oxygen-rich environment that enhances combustion efficiency, whereas ratios <88% reduce oxygen availability, resulting in lower in-cylinder pressure and temperature. Engine oil addition increases pressure and temperature, shortens combustion duration, and strongly promotes soot formation; adding 6% engine oil increases soot emissions by 108.46% compared with pure ethanol. These findings support particulate-emission mitigation and the broader application of high-percentage renewable bioethanol fuels.