Air Flow Surrounding Burning Transient Diesel Sprays

Airflow characteristics surrounding burning transient diesel sprays inside a constant volume chamber under temperatures around 900 K were investigated using a 6-hole injector and a single-hole injector. Particle Image Velocimetry (PIV) was used to measure the gas velocities surrounding a spray plume as a function of space and time. The results were directly compared with the results from evaporating spray conditions near 900 K and non-evaporating conditions at 293 K.

A conical control surface surrounding the spray plume was chosen as a representative side entrainment surface. The normal and tangential velocities of both for evaporating and burning sprays were higher than those of room temperature non-evaporating sprays. The velocities tangential to the control surface, toward the injector tip, for the single-hole injection sprays were lower than those of 6-hole injection sprays. An abrupt increase in tangential velocities near the chamber wall suggests that the recirculation of surrounding gas was accelerated by the spray wall impingement for all conditions investigated. The total energy transferred into the burning sprays by the side air entrainment appears to be larger for single-hole injectors than that of 6-hole conditions due to the larger side entrainment region for burning spray conditions. About 44 to 56 % of the energy transferred by side gas entrainment was delivered to vaporize and heat the fuel for evaporating spray conditions. An estimated flame lift-off length of around 45-50 mm for burning spray conditions suggests that the thermodynamic and physical conditions of the side entrainment region of burning sprays are almost the same with the evaporating sprays around 900 K.