Study On The Effect Of Alcohol Blend Fuel On The Performance And Emission Characteristics Of Diesel Engine

Because of its reliability,high thermal efficiency and large torque at low speed,diesel engine is widely used in the areas of high power demand such as road traffic,ships,agricultural machinery and railway locomotives.Compared with the gasoline engine,the compression ignition mode of the diesel engine determines there is always a localized fuel rich area during the combustion process,which results in more soot particles than the gasoline generated,and the PM particles can even reach ten times more than that of the gasoline engine.Nowadays,the control of diesel particulate emissions is mainly from the aspects of improving fuel quality,in-machine purification technology and out-of-plane purification technology,while the direct addition of bio-fuels to diesel fuel to improve the fuel quality does not require the engine structure modification,which aroused great interest of researchers.This paper adopts a different fuel mixture method,that is,under the condition of ensuring the same oxygen mass concentration of the whole mixed fuel（6%by mass）,the mass percentage of each fuel component is calculated firstly and then compare the combustion characteristics and emission difference of various alcohol blended fuels.In order to ensure the comparability of the final results,the percentage of biodiesel in all blended fuels are guaranteed at the same fraction（33%by mass）,and all the alcohol blended fuels have been conducted mixture check to ensure the rationality of the mixing ratio.Comparison of engine performance and combustion characteristics was made when several common alcohol fuels（methanol,ethanol,butanol,pentanol）mixed with diesel/biodiesel under different load conditions at the constant engine speed.The differences in the brake specific fuel consumption,brake thermal efficiency,combustion duration,and ignition delay time of diesel engine were analyzed.The composition and distribution of gaseous emissions of different blended fuels were analyzed,which focused on concentration of CO,HC,NOx,CO₂,as well as the concentration of particulate matter.The experimental results showed that the difference in the fuel combustion characteristics leaded to the difference in the final emissions.Because the combustion temperature and the heat release rate of the pentanol blend fuel were the lowest,the best BSCO and BSHC emissions were obtained.Since the methanol blends had the highest latent heat of vaporization,it produced the lowest NOx emissions.The alcohol blended fuels had a significant particle-reducing effect compared to the regular diesel.For the particulate matter concentration,the DBP blended fuel can reduce the concentration of particulate matter by 43.3%at 10%load.For the particulate matter concentration,the methanol blended fuel had the best inhibitory effect.Among alcohol blends,the CO₂ produced by the engine is related to the emission and the fuel consumption rate,because the low heating value is similar among various blended fuels,it also leaded to similar CO₂ emissions.Based on the above studies,samples of diesel particulates were sampled under both high and low loads,and the distribution characteristics of OC and EC in engine particulates under conditions of diesel,biodiesel,and different alcohol blended fuels were investigated.The thermo-gravimetric analysis method was used to study the oxidation activity of the particulate matter.Finally,the microscopic structure,particle size distribution,and morphology of the particulate matter when the diesel engine burned with different blended fuel under different operating conditions were investigated by high magnification electron microscopy.The effects of different types of alcohol fuels on the formation mechanism of particulate matter were investigated.The experimental results revealed that the inhibitory effect of alcohol blended fuels on EC was more obvious,and butanol blends corresponded to the lowest EC emissions.Compared with other blended fuels,ethanol blended fuel had the most obvious effect of reducing OC emissions.The oxidation activity of particulate matter was determined by the microstructure of the particulate matter,which has the longest carbon layer length and the lowest particle curvature,also corresponded to the lowest oxidation activity.Methanol blended fuels had shorter diffusion combustion time than other blended fuels,which also leaded to a lower carbon layer length and a greater degree of curvature,corresponding to an optimal oxidation activity.