Experimental Study And Numerical Simulation On Spray Characteristics Of Different Fuels

The issues of environmental pollution and energy depletion become conspicuous as the vehicles possessing capacity increasing.Automobile exhaust,one of the main pollutants source,gain more and more prominence.To reduce the pollutant emission and improve the fuel consumption from the internal combustion engine become one of the research emphases due to the stringent emission regulation and fuel consumption regulation.Diesel engine is widely used for its good power output,fuel economy and durability.However,the feature of high temperature diffusion flame including short period time for fuel-air mixing process,the heterogeneous fuel-air mixture,the interfere between mixing and combustion process all lead to poor NOx and soot emission.Obviously,the in-cylinder fuel-air mixture mixing and combustion process is the key factor to influence the diesel engine fuel economy and pollutant emission.A number of studies show that the fuel spray properties is the most important factor among the parameters about fuel-air mixing and combustion process.Therefore,it is necessary to investigate the effect of fuel spray on the mixture formation,to improve fuel-air mixing process by optimizing the fuel ato mization and evaporation process.Oxygenate introduction is an effective method to break the trade-off relation between NOx and soot formation.The addition of oxygenate fuel into diesel changes physical and chemical properties of the fuel mixture such as the density and viscosity,thence,the fuel spray properties demonstrate new characteristics.In this thesis the experimental and numerical investigation is applied to study the difference of spray properties between diesel/butanol mixture and diesel/dimet hyl carbonate(DMC)mixture.A visible constant volume bomb is develop to perform optical measurement for fuel spray properties.A fuel spray CFD simulated model based on AVL-Fire is built to perform extreme operating condition and complement the unavailable spray parameters through optical measurement.The results indicate that fuel penetration length increases with increasing injection pressure,nozzle diameter and decreasing atmospheric density.The developmental curves of penetration length between diesel and B30 are almost the same while that of D30 is longer due to the augment of fuel density and initial momentum.However,the discrepancy decreases as injection pressure elevation.Nozzle diameter plays an important role in both near/far field cone angle especially to the preliminary stage of latter one.The impact of injection pressure on far field cone angle is more prominent than the near field cone angle that former increases 6~8° when the injection pressure augments from 50 MPa to 110 MPa while the latter increases 2~3°.Moreove r,the far field cone angle increment reach 4° when the fuel injection towards stability.The spray cone angle elevates as atmospheric density increase.Generally,both the spray cone angle of B30 and D30 are greater than the one of diesel,however,the differences of spray cone angle caused by various fuel types reduce as injection pressure increasing.Sauter mean diameter(SMD)increases as injection pressure elevation or nozzle diameter reduction.SMD decreases with butanol blending ratio because the butanol introduction improves fuel atomization.The velocity field color of fuel injection all tend to fade from inner to edge which indicates that the fuel spray velocity decreases gradually from inner to outer edge.The dark colored area extend and the color darken which indicate that the high velocity region extends and the fuel injection velocity enhances as injection pressure increasing or atmospheric density decreasing.The area of darken region,namely the area of high velocity region,shrinks as atmospheric temperature increasing.The area of high concentration field decreases as increasing injection pressure or decreasing atmospheric density among diesel,DME,butanol and their mixture.The high concentration region decreases significantly even dimin ishes as atmospheric temperature increasing especially during the late injection period.The area of concentration field of both B30 and B45 all smaller than the one of pure diesel which demonstrates that the butanol introduction promotes homogeneous charge formation.