Analysis of transient liquid and vapor phase penetration for diesel sprays undervariable injection conditions

Abstract

The objective of this study is to investigate liquid length and vapor penetration for diesel sprays under highly transient injection conditions. High-speed Mie-scattering and shadowgraphy imaging of the spray evolution in an ambient of nitrogen are performed in a slow rotational optically accessible engine. Liquid length and vapor penetration were obtained for both single- and multiple-pulse (pilot-main and pilot-main-post) cases in a seven-hole nozzle that performs real engine injection strategies. In-cylinder temperature and density were simulated to reproduce operating conditions of a real engine at low load. Results show that liquid and vapor penetration coincide at the beginning of each injection pulse. For long injection pulses, liquid length can stabilize after some time, while penetration keeps growing. However, for short pulses liquid length has a highly transient evolution. Measurements were compared to calculations from a one-dimensional spray model that can predict spray evolution under highly transient conditions. No significant differences compared to experimental data were found in terms of penetration. Regarding liquid length, major differences were found in the opening and closing transients. Multiple injection analysis of the interaction between pulses was performed by means of the model results; previously single-pulse cases were used to calibrate the model.