Abstract
A multidimensional Eulerian mathematical model has been developed for computing the behaviour of liquid sprays injected into combustion chamber of direct-injection diesel engines in modular, transparent manner suitable for parallel computing and for necessary model changes during future development.
Basic laws of conservation (mass, momentum and energy) formulated on finite volumes with arbitrary movable boundaries have been used for description of liquid phase and compressible gas flow. The equation set has been derived using integral approach in the form of ordinary differential equations. To ensure amount of computations at reasonable level the continuous droplet size distribution has been split in a number of classes. Droplets presented in each class are assumed to be identical, which enables us to describe them using average values. The propagation of liquid spray is based on the spherical droplet dynamics with changing mass due to evaporation.
Corresponding source terms for liquid fuel interactions with gaseous environment are included.
Boundary condition for fuel injection rate has been obtained from numerical simulations of injection process in electronically controlled common-rail injection system. A one-dimensional hydrodynamic model describing unsteady flow in high-pressure piping and injector with multi-hole nozzle has been used. The model is capable of calculating both single and multiple injection patterns. The combination of both models is targeted to direct injection optimisation in both spark and compression ignition engines.
Results of several computations are presented. Numerical tests has been performed under simplified conditions of partially-coupled flows to explore numerical features of the proposed techniques. Considerable care has been taken for the investigation of numerical errors associated by the numerical techniques used. The comparison of results achieved be means of different numerical methods is presented. The results shown provide some interesting details about the impact of numerical dissipation on the results of computations. The flow situation of some practical importance is presented considering the fully-coupled flows in the cylindrical combustion chamber of constant volume. It illustrates qualitative features of propagation of nonevapourating hollow-cone sprays.