Experimental And Simulation Study On The Spray And Combustion Characteristics Of Blended Fuel

To meet the requirements of stringent vehicle emissions regulations and drastic reductions in fuel usage, new combustion concepts such as HCCI, PPCI and LTC have been studied widely. These new combustion modes have the potential to reduce the formation of particulate and NOx inside the cylinder simultaneously. However, these advanced combustion modes have suffered from uncontrollable ignition and combustion rates, narrow operating load ranges, high levels of CO and HC emissions, and difficulty in cold start and mode transitions. As one of the unique operating principles of these combustion modes is that the ignition and combustion are mainly dominated by the chemical kinetics of fuel/air/residual gas mixtures and are only moderately influenced by turbulence and mixing, fuel design and management strategy like blended fuel has become an important manner in which to resolve these difficulties and dilemmas.In this paper, the spray characteristics of gasoline–diesel blended fuel has been studied by CFD method. Firstly, a sensitivity analysis of classic KH-RT break-up model was made in different ambient conditions based on the Sandia laboratory experiment data on ECN website. Afterwards a discrete multiple-component evaporation model was used to compare the spray characteristics of single component fuel and blended fuel under different ambient conditions. Simulation results show that the spray characteristics of blended fuel G50, such as spray penetration, SMD and evaporation rate, are always in the middle of G0 and G100. Besides, increasing ambient temperature has a significant impact on the fuel spray characteristics, a higher ambient temperature causes to a faster fuel evaporation, especially when the ambient temperature is high above the droplet critical temperature, droplet evaporation rate increases dramatically to 90%.A visualization study of diesel spray & combustion processes have been done with the use of high speed photography and Laser-Induced Incandescence method. Blue flame, yellow flame and white flame can be observed during the combustion processes in chronological sequence, and premixed combustion developed to diffusion combustion. When injection pressure decreased from 100 MPa to 60 MPa, liquid penetration decreased slightly and ignition delay increased. What's more, when injector hole diameter increased from 0.15 mm to 0.25 mm, liquid penetration increased from 35 mm to 55 mm and ignition delay increased. Finally, a reduced mechanism of PRF(Primary Reference Fuel) mechanism is incorporated in turbulent flame to simulate the chemical process of blended fuel. Simulation results show that with the increase of gasoline in blended fuel, the ignition delay period and flame lift-off length increase.