Characteristics of the Multiple Injection Diesel Spray Employed Common Rail System

Abstract

The multiple injection strategies have been widely employed in many new diesel applications, such as HCCI (Homogeneous Charge Compression Ignition) and LTC (Low Temperature Combustion), which are very effective in improving fuel-air mixture and entrainment. In this paper, using high injection pressure of common rail and high-speed camera system, the experimental studies on the spray characteristics of the single, double and triple injections are conducted. The spray average fuel/air equivalence ratio is employed to evaluate the overall effects of the fuel-air mixture, which is the ratio of the fuel/air mass ratio in the spray and the fuel/air stoichiometric mass ratio. It is shown that the spray average fuel/air equivalence ratio decreased with the increased injection pressure, indicating that increasing injection pressure could intensify fuel-air mixture. For double injections, spray tip penetrations and volumes increase with the increased injected volume percentage. It is also found that spray development rate of the second injection is higher than the first injection. Double injections lead to lower spray average fuel/air equivalence ratios than the single injections. For triple injections, the spray average fuel/air equivalence ratios are almost lower than stoichiometry. The triple injection of which the volume distribution of every injection time is evenly has the lowest spray average fuel/air equivalence ratio, and has the best effect of fuel-air mixture.

Near-nozzle microscopic characterization of diesel spray under cold start conditions with split injection strategy

“…The spray characteristics for split injection strategy are very complicated due to strong interaction between split injections and various involved mechanisms, for instance, fast transition of flow regimes in the nozzle, primary spray collision and induced air driving force [15]. The flow regime transition results in breakup regime transition, and the influence of temperature further complicates the breakup characteristics when split injection employed.…”