| Overexploitation of traditional fossil energy and increasing pressure on environmental protection,burning clean alternative fuels has become one of the effective means for diesel engines to save energy and reduce emissions.China's sixth-stage pollutant discharge regulations have imposed stricter requirements on pollutants such as nitrogen oxides(NOx),carbon monoxide(CO),hydrocarbons(HC),and particulate matter(PM).Blended fuels help reduce diesel engine pollutant emissions and promote efficient energy use.Compared with diesel,biodiesel has a large cetane number and viscosity,and n-butanol has a low cetane number and viscosity.As a renewable oxygenated fuel,the two can be miscible with diesel in any proportion.Blending can achieve fuel performance.Complement each other to improve fuel quality.In this research,biodiesel/nbutanol/diesel blended fuel were prepared,the effects of different blending ratios of biodiesel and n-butanol on the combustion performance,emission performance,and economic performance of diesel engines were analyzed,and the microstructure and oxidation activity of mixed fuel combustion particles were studied.Activity provided a theoretical basis for optimizing combustion and reducing particulate emissions.In this research,three mixtures of B5N5,B5N10 and B5N15(biodiesel volume fraction of 5%,n-butanol volume fraction of 5%,10% and 15%,diesel volume fraction of 90%,85% and 80%,respectively)were prepared.Carried out biodiesel/n-butanol/diesel blended fuel miscibility test,measured and calculated main physical and chemical properties of blended fuel.The results showed that the mixed fuel still showed a clear and transparent stable system after standing at room temperature for 60 days,without obvious stratification.With an addition of biodiesel,an increase of n-butanol blending ratio,the latent heating value and oxygen content of the mixed fuel increased,and the cetane number,low heating value,density and viscosity decreased.Through the bench test,the combustion characteristics of the biodiesel/n-butanol/diesel blended fuel were studied at full load,maximum torque speed of 2700r/min,and rated speed of 3600r/min.At two speeds,10%,25 %,50%,75% and 100% load,emission characteristics and economic characteristics of the mixed fuel are analyzed.The results showed that with the addition of biodiesel and the increase of the n-butanol blending ratio,the peak burst pressure,maximum pressure increase rate and instantaneous heat release peak of the mixed fuel were all improved compared with diesel,and the peak phases were delayed.Under low load(10% and 25% load)operating conditions,the NOx emissions of mixed fuel were reduced and CO emissions were increased compared to diesel;while under high load(75% and 100% load)operating conditions,the mixed fuel NOx emissions increased,CO emissions decreased.Under all operating conditions,the soot emissions of mixed fuels were reduced.Among them,the largest reduction occurred at 100% load;the HC emissions of B5N5 and B5N10 mixed fuels were reduced,and the HC emissions of B5N15 mixed fuels increased;Fuel consumption rate and effective thermal efficiency increased.High Resolution Transmission Electron Microscope(HRTEM)and Raman Spectra(RS)were used to analyze the changes in the microscopic morphology and structure parameters of the particles.The results showed that,compared with diesel,the combustion particle stack of B5N5,B5N10,and B5N15 mixed fuel were more compact,the average particle size decreased,and the fractal dimension of particles increased.The average interlayer spacing of carbon particles increased,the average crystallite size decreased,and the average crystallite curvature increased.The chemical heterogeneity of particulate matter increased,the degree of graphitization decreased,and the amorphous carbon content increased.Thermogravimetric Analysis(TGA)was used to study the variation of oxidation activity of particulate matter.The results showed that,with an addition of biodiesel and the increase of the nbutanol blending ratio,compared with diesel,thermogravimetry and derivative thermogravimetry curves of the mixed fuel shifted to lower temperatures.The ignition temperature,the peak temperature of low-temperature weight loss rate,peak temperature of high-temperature weight loss rate and an end temperature all decreased,and the corresponding peak values of lowtemperature weight loss rate and high-temperature weight loss rate increased.The volatile matter in mixed fuel particles increased,the content of dry soot and inorganic salts decreased,the activation energy of particles decreased,and the oxidation activity increased. |
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