A STUDY OF DROPLET COLLISION MODELLING FOR SPRAY FORMATION AND MIXING WITH A TWO-ROW GROUP-HOLE INJECTION NOZZLE FOR DIESEL ENGINES

Improvement of the diesel engine and optimization of the combustion process continues to be an important aspect of efforts to meet new emissions regulations. The most important factors which directly influence the performance of a diesel engine are related to the spray formation and vaporization of the liquid fuel upon injection into the cylinder. Therefore in order to improve diesel engines, new studies need to be undertaken to further develop the injection system and, in particular, the nozzle layout and subsequent spray formation. This paper describes the computational modelling process of spray formation and atomization from a novel type of diesel injector with a nozzle layout that consists of a group of upper and lower sets of holes. A version of the KIVA-3V open-source code with extended capability of large eddy simulation (LES) was utilized for this work. Particular attention was paid to modelling droplet collision processes as the two rows of sprays were at converging angles to each other, promoting spray interactions. The simulated results were compared against experimental data in terms of spray penetration length and curvature for the vapor and liquid phases of the fuel. The experiments were conducted in an optical compression machine using high-speed schlieren and Mie scattering imaging techniques. Significant improvement in the simulation process and better agreement with experimental data was observed when additional modes of droplet collisions were coded, namely, reflexive and stretching separation. The methodology was also tested with different injection pressures of 1200 and 1800 bar. The use of additional modes of droplet collisions was also found beneficial for a typical single-row injector whose results were compared against the two-row injector and benchmarking experiments under the same conditions.