Assessment on Combustion and Emissions of Diesel Engine Fueled with Partially Hydrogenated Biodiesel

Via partial hydrogenation, polyunsaturated fatty acid methyl esters (FAMEs) in biodiesel were largely converted to monounsaturated and saturated FAMEs, which brought the following changes in fuel properties: lower iodine value, better oxidative stability, higher cetane number, and slightly increased kinematic viscosity. Experiments were conducted to evaluate the combustion and emission performance in a diesel engine using diesel, B20 (80% diesel and 20% biodiesel), PHB10 (90% diesel and 10% partially hydrogenated biodiesel), and PHB20 (80% diesel and 20% hydrogenated partially biodiesel). The aforementioned four fuels almost shared the same equivalent specific fuel consumptions, owing to the combined effects of oxygen content, cetane number, and kinematic viscosity. Because the high cetane number of hydrogenated biodiesel overweighed its incremental kinematic viscosity in ignition, the ignition timings for B20, PHB10, and PHB20 compared with diesel were advanced by 0.8° crank angle (CA), 0.6°CA, and 1.4°CA, respectively. Simultaneously, the heat release rate peaks and pressure peaks for B20, PHB10, and PHB20 were advanced but decreased accordingly. B20, PHB10, and PHB20 exhibited reduced hydrocarbon (HC), carbon monoxide (CO), and smoke emissions and increased nitrogen oxides (${\mathrm{NO}}_{\mathrm{x}}$) emission compared with diesel. Overall, among the four fuels, PHB20 presented the lowest emissions excluding ${\mathrm{NO}}_{\mathrm{x}}$ emissions.