Diesel jet impingement on small cylindrical obstacles for mixture homogenization by late injection strategy

Abstract

The paper deals with ‘destroying’ a high-velocity diesel fuel jet by impingement on small cylindrical obstacles. This process permits very quick jet distribution in the volume. Essential is a process of impingement on a first obstacle: its diameter, distance from the nozzle outlet, and injection pressure play a dominant role in characterizing jet distribution in space. This spatial distribution is based on a multijet model, initially observed by diesel jet impingement on a porous structure. In diesel jet impingement on a single obstacle with a smaller diameter (d=1 mm), the distribution angle decreases with an increase of injection pressure. For bigger obstacle diameters (d = 2 mm) the angle between both jets increases almost independently with regard to injection pressure. This angle does not change with time after initial impact. It decreases, however, with an increasing distance between nozzle and obstacle. For diesel jet impingement on more than one single obstacle, jet distribution depends on the obstacle's geometrical configuration but not necessarily on the number of obstacles. Quite similar distribution has been obtained for configurations with four and eight obstacles. It is possible to design a configuration of small obstacles such as to permit very good charge homogenization within a defined space (combustion chamber). Such an example of five-obstacle configuration has also been investigated in the paper. A multijet structure also permits higher air entrainment as compared with a free jet configuration. All these effects would promote fast spatial distribution of diesel jets and, under hot conditions, faster vaporization and better mixing with air.