Modeling of diesel sprays using an Eulerian-liquid Eulerian-gas two -fluid model

Venkatraman Ananthakrishnan Iyer, Purdue University

Abstract

This thesis presents an Eulerian-liquid Eulerian-gas model for full-cone Diesel sprays. Current multidimensional models for Diesel sprays and combustion employ the Lagrangian-droplet Eulerian-fluid (LDEF) approach. One of the main limitations of this approach is that adequate numerical resolution cannot be used because it is valid only when the volume fraction of the droplets in a computational cell is less than 10%. An Eulerian-liquid Eulerian-gas two-fluid model is developed in order to overcome the limitations of the LDEF approach. Eulerian field equations are solved for the liquid and the gas phases with interface transport terms coupling the two phases. Mass and energy transfer at the interface are modeled by equilibrium, whereby vaporization is assumed to be mixing-controlled, and non-equilibrium approaches. Momentum transfer is modeled either by a locally homogeneous flow (LHF) approximation or by a separated flow model where effects of drag and finite transfer rates are considered. Atomization is modeled either by specifying drop sizes at the orifice or by employing a model for liquid core break-up. Collisions and coalescence are modeled through a collisions rate and a coalescence efficiency. Changes in size of drops as a result of vaporization, break-up and coalescence are included by solving an equation for the interfacial surface area concentration. An implicit finite volume numerical procedure with staggered grids is employed. The liquid and the gas terms are solved simultaneously by linearization of the interfacial transfer terms. Comparisons of computed and measured results are presented for a wide range of conditions. It is shown that the two-fluid model reproduces measured liquid velocity and turbulent kinetic energy profiles in the spray with adequate accuracy. Measured entrainment characteristics are also reproduced. Comparisons with measurements of steady liquid penetration in a Diesel spray lead to the following conclusions: Vaporization is mixing controlled under Diesel conditions. At lower ambient densities drop size effects and separated flow effects may be important. In such conditions, the details of the intact core model become important. Above all, it is shown that the two-fluid computations are able to overcome the limitations of the LDEF computations by employing adequate numerical resolution.

Degree

Ph.D.

Advisors

Abraham, Purdue University.

Subject Area

Mechanical engineering|Automotive materials

COinS