Numerical study of the internal flow and initial mixing of diesel injector nozzles with V-type intersecting holes

Abstract

A V-type intersecting hole nozzle, in which each hole is formed by the coalescence of a pair of sub-holes, has been developed to improve fuel-air mixing for diesel engines. In this paper, a numerical study has been conducted to examine the effects of the V-type intersecting hole structure on the internal flow of a nozzle and the initial stage of the fuel-air mixing processes. With this aim, a multi-phase flow calculation has been implemented on seven V-type intersecting hole nozzles with impact angles ranging from 20° to 50° and a referenced cylindrical hole nozzle under injection pressures varying from 60MPa to 240MPa. The comparison was made in terms of mass flow, momentum flux, effective velocity, discharge coefficient, area coefficient and velocity coefficient. The three-fluid model, which was validated using X-ray experimental data of an Engine Combustion Network (ECN) Spray A injector, was employed to calculate the associated multi-phase flow. The main results show that use of a V-type intersecting hole in a nozzle eliminates cavitation, leading to higher mass flow and momentum flux. Correspondingly, for these V-type intersecting hole nozzles, the discharge coefficients are insensitive to injection pressure, but decrease with an increasing impact angle, and are 20–30% higher than those of the cylindrical hole nozzle. These higher discharge coefficients mainly result from very high area coefficients that are approximately 0.98 at all injection pressure conditions because of the non-cavitating nature of the in-nozzle flow. Moreover, the impact effect of a V-type intersecting hole results in a fan-shaped jet with a very large spreading angle (25–40°) at the dispersion plane and a relatively narrower angle (approximately 12°) at the impact plane. The jet spreading angles at both planes are wider than that of the cylindrical hole nozzle (approximately 7°), indicating a noticeable improvement in the initial fuel-air mixing. Additionally, an increase in the impact angle of a V-type intersecting hole nozzle promotes initial mixing in terms of yielding a wider jet spreading angle, in spite of a slightly lower effective velocity.