Influence Of Hydrogenated Biodiesel-ethanol-diesel On Combustion And Emission Performance

Biodiesel as a renewable fuel has several advantages over conventional diesel.However,the inferior cold flow properties and poor oxidation stability of biodiesel limit its applications in diesel engines.To alleviate these limitations,cottonseed and soybean biodiesel were partially hydrogenated to alter their chemical compositions.Moreover,on account of the high viscosity and the low volatilization effect of the hydrogenated biodiesel,ethanol was added in various proportions to prepare the hydrogenated biodiesel-ethanol-diesel fuel blend.Thermogravimetric analysis was employed to analyze the oxidation and thermal decomposition of the blends.The blended fuel samples were then combusted in a high-pressure common-rail direct ignition diesel engine to investigate engine performance,combustion and emissions(regulated and unregulated)characteristics.The definite content and conclusions obtained from the research work are presented as follows.(1)The catalytic transfer hydrogenation(CTH)method was employed to achieve the partial hydrogenation of soybean methyl ester(SME)and cottonseed methyl ester(CME).Biodiesel,isopropanol(hydrogen donor)and water(reaction medium)with a mass ratio of 7:32:100 were put in the flask.A Raney nickel catalyst was weighed as 13wt% of biodiesel.The hydrogenation reaction was performed at 85 ? with a constant stirring rate of 600 r/min.After hydrogenation,most of the polyunsaturated fatty acid esters were converted to monounsaturated and saturated fatty acid esters.The unsaturation of CME and SME was reduced by 35.3% and 40.7% respectively.The cetane number and kinematic viscosity of biodiesel were significantly increased,while a minute change occurred in the low heating value and the oxygen content.(2)The oxidation characteristics of the fuel blends of hydrogenated biodiesel,ethanol and diesel were investigated by thermogravimetry.Compared to PHB-diesel binary blend,the weightlessness temperature of PHB-ethanol-diesel ternary blend advanced due to its improved volatilization performance affected by ethanol.(3)The combustion characteristics of PHB fuel blends were performed on a common-rail direct-injection diesel engine.A 25%,50%,75%,and 100% of n = 2400r/min were considered as the test conditions.The low heating value of the PHB fuel blend contributed to its higher equivalent specific fuel consumption(ESFC)than diesel.The high cetane number of binary blend advanced the ignition timing,which reduced the combustible fuel mixture in the ignition delay.Thus,it contributed to the lower cylinder pressure and heat release rate of the binary blend at the main injection stage,compared to diesel.The low cetane number of ternary blend postponed its ignition timing,and its minute kinematic viscosity also lowered the difficulty to form mixture,which resulted in the more formation of the combustible mixture.Meanwhile,the highest oxygen content of ethanol promoted the combustion degree.The aforementioned reasons resulted in the higher cylinder pressure and heat release rate of the ternary blend,compared to diesel.(4)The regulated emission characteristics of PHB fuel blends were studied.Regulated emissions such as CO,HC,and smoke decreased while NOx increased for the PHB fuel blends,compared to diesel.The CO and HC emissions for the ternary blends were higher than those for the binary blends since the high latent heat of vaporization of ethanol reduced the cylinder temperature and lowered the degree of combustion.The NOx emission of the ternary blend was lower than that of the binary blend,affected by the latent heat of volatilization of ethanol,which contributed to the lower cylinder temperature.The lower smoke emission of the ternary blend compared to diesel was attributed to the high oxygen content of ethanol,which repressed the thermal cracking of the fuel.(5)The unregulated emissions of PHB fuel blends were investigated.For PHB fuel blends,NO2 emissions increased whilst H2 CO,SO2,CO2,CH4,and C2H4 emissions decreased,compared to diesel.The NO2 emission of the ternary blend was higher when compared to the binary blend,which was explained by the lower temperature of the cylinder resulted from the high latent heat of volatilization of ethanol,and its high oxygen content.The low cetane number and the high latent heat of volatilization of ethanol resulted in the decrease of cylinder temperature which in turn resulted to incomplete combustion.This exhibited the higher H2 CO emission of the ternary blend compared to the binary blend.The higher SO2 emission of the ternary blend was attributed to the higher oxygen content,which could extremely oxidize the sulfur contents in diesel.The low heating value of the ternary blend increased the fuel consumption,which consequently increased its CO2 emission.The cooling effect of ethanol supressed the combustion degree of the ternary blend,thus the CH4 emission of the ternary blend was higher than the binary blend.The high oxygen content of ethanol is prone to oxide the low-carbon molecules in diesel,which reduced the C2H4 emission of the ternary blend.This study explored the partial hydrogenation of biodiesel and the characteristics of PHB fuel blends.The combustion and emissions(regulated and unregulated)characteristics of fuel blends were outlined.This study could provide a reference for the utilization of the hydrogenated biodiesel-ethanol-diesel blends in industrial applications.