Effect of High-Pressure Split Injection on Mixture Formation and Combustion of Fuel Spray in Diesel Engine

Paper #:
  • 2018-01-0241

  • 2018-04-03
Increasing the injection pressure and splitting the injection stage are the major approaches for a Diesel engine to facilitate the fuel-air mixture formation process, which determines the subsequent combustion and emission formation. In this study, a two-dimensional (2-D) piston cavity that has the same shape as a small-bore diesel engine was employed to form the impinging spray, which was injected into a constant volume vessel by a single-hole nozzle with a hole-diameter of 0.11 mm. The tracer Absorption Scattering (LAS) techique was adopted to observe the spray mixture formation process. The injection process comprised a pre-injection followed by the main injection. The main injection was carried out either as a single injection of injection pressure 100 MPa (Pre + S100) or split injection of injection pressure 160 MPa itself was either of two types defined by mass fraction 50 : 50 and 75 : 25 (Pre + D160_50-50, Pre + D160_75-25). The ignition delay/location and the soot formation in the spray flame were analysed by the two color method. Two ambient gas strategies, 20% O2 and 15% O2 were adopted in the combustion process to investigate the O2 concentration effect on the combustion. The experimental results revealed that the vapor distribution of split injection was significantly more homogeneous than that of single injection. High soot concentration and low temperature appeared near the cavity wall region under the three injection strategies. The second main injection caught up with the previous injection’s flame, which deteriorated the combustion and resulted in higher soot generation. Low O2 concentration increase the soot mass because of lean O2. The combustion duration of low O2 concentration is longer than that of high O2 concentration. The low O2 concentration has an obviously positive effect on the soot mass of split injection strategies than that of single injection strategy.
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