Experimental Investigation on the Early Stage Spray Characteristics with Biodiesel and Diesel

Abstract

The early stage spray characteristics have a great impact on the secondary atomization progress, and thus affect the engine combustion and emission performances. The experimental investigation of the early stage spray behaviors with biodiesel and diesel was carried out by employing a laser-based Mie-scattering method. The results show that the spray tip penetration for biodiesel is higher than that for diesel at the early stage spray under the same injection pressure. Moreover, the early stage spray tip penetration can be longer under high injection pressures for two fuels. Besides, the early stage spray cone angle for biodiesel is narrower than that for diesel, and the spray cone angle is especially higher than biodiesel by 25.8% after start of injection time of 0.01ms. Furthermore, under the same injection condition, the difference of early stage spray area between diesel and biodiesel is not obvious, while the spray volume for biodiesel is larger than that for diesel, and also the spray volume can be enlarged by increasing injection pressure for both fuels. KeywordsSpray characteristics; Mie-scattering; Biodiesel; Diesel Introduction For modern diesel engines, soot and nitrogen oxide are the two main emissions which are mainly influenced by mixture quality of air and fuel, and the emission characteristics are largely governed by atomization and spray processes [1][2][3][4]. Biodiesel, derived from the waste cooking oil and a kind of renewable energy, has been widely used as an alternative fuel for diesel engines. It is clear that the use of biodiesel in diesel engine can improve favorable emissions performance [5][6][7][8][9]. Although the importance of biodiesel in reducing diesel engine emission performance has been acknowledged, the research on early stage spray characteristics of biodiesel is still far from sufficient. The early stage spray dominates the secondary spray progress and the mixture quality of fuel and air, and thus affects the atomization quality of biodiesel. Therefore, it is important to define the effects of biodiesel at the early stage spray characteristics. Wang et al. [10,11] studied the near-field primary spray characteristics of different split injection strategies by using ultra-high speed imaging method. Their results indicated that the second split injection cause smaller spray area and shorten penetration during the early stage spray, and also the larger late injection stage can increase the spray area and the penetration. Moreover, they found that the strong primary collision can be caused by improving the injection pressure and shortening dwell split injection, thus the spray area and the spray cone angle increase, while the spray tip penetration decreases at the same time. And they also found that the long duration of the first injection enhances the primary collision. Wang et al. [12] also studied the spray behaviors of emulsified diesel blended with water through schlieren technique. They concluded that the penetration increases as the magnitude of water increases, wh...