Study On Spray Characteristics Of Biodiesel And Its Blended Fuel

The spray characteristics of the fuel in the engine are important factors influencing its combustion process and pollutant emissions.In this paper,different proportions of ethanol,diethyl carbonate and di-n-butyl ether were blended in biodiesel.On the experimental platform of constant volume combustion bomb,the electronically controlled high pressure common rail injection system was used to simulate the fuel injection process of diesel engine.Using the schlieren method,the spray characteristics of different experimental fuels(including spray tip penetration,spray cone angle,spray projection area,and spray tip velocity)were quantitatively measured,and the spray characteristics of the three blended fuels were investigated.Explore the feasibility of using biodiesel and alcohol,ester and ether oxygenated fuels to replace diesel in engines.The major work may be summarized as the follows:The spray characteristics of biodiesel and diesel were tested.The experimental results showed that the biodiesel spray tip penetration was larger and the spray area was smaller than that of diesel,mainly because the density and viscosity of biodiesel were large and the diffusion performance was poor.The experimental data of spray tip penetration of diesel and biodiesel were lower than those of Hiroyasu model,mainly because the Hiroyasu model was obtained under the condition of low inj ection pressure.The spray characteristics of biodiesel-ethanol blended fuel were studied experimentally.The experimental results showed that the spray tip penetration of biodiesel-ethanol blended fuel was less than that of pure biodiesel under the same working conditions,and the spray cone angle was larger than that of diesel.The peak tip velocity increased with the increase of the injection pressure,and the ambinet pressure increased.The experimental data of spray tip velocity was in good agreement with the Hiroyasu model;the experimental data of spray penetration was smaller than that of Dent and Arregle models,mainly because the Dent model considered the influence of ambient temperature on penetration.The spray characteristics of biodiesel-diethyl carbonate(DEC)blended fuel were studied experimentally.The results showed that the spray tip penetration of raw spray decreased with the increase of ambient pressure and increased with the increase of injection pressure.When the content of diethyl carbonate was 15%,the spray characteristics(including spray penetration,spray cone angle,spray area)were close to diesel;the experimental data of spray penetration in the initial stage of spray was in good agreement with the Kostas model;the amount of gas entrainment in the blended fuel spray process was greater than that of biodiesel.From the spray morphology,the fluctuation of the edge of the spray was also more severe.The spray characteristics of biodiesel-di-n-butyl ether(DBE)blended fuels were investigated experimentally.The results showed that the biodiesel-DBE blended fuel had a lower spray penetration than biodiesel,and the spray cone angle was close to that of diesel.In the same axial position,the blended fuel had a radial diffusion range larger than that of biodiesel.Under the same working conditions,the breakup time of the blended fuel was earlier than that of biodiesel.Based on the empirical model of Hiroyasu spray tip penetration,the density term and correction factor were introduced to obtain a modified model of biodiesel-DBE blended fuel spray penetration,compared with Hiroyasu model.This formula was more suitable for predicting the macroscopic spray characteristics of a blended fuel at high injection pressures.