Abstract

large number of pipelines in the petroleum industry simultaneously transport gas and liquid. Transient behaviour of multiphase flow is frequently encountered in these pipelines. A common example is severe slugging that can occur in multiphase flow systems where a pipeline segment with a downward or even horizontal inclination is followed by a riser segment with an upward inclination. Transient flow conditions associated with severe slugging are relatively slow. Therefore, a transient drift flux model consisting of one momentum balance equation might suffice to express the dynamics of severe slugging. We present a transient drift flux model to simulate severe slugging phenomenon in pipeline-riser systems. The present model contains recently published correlations by Shi et al. for the drift flux slip model which cover the complete range of flow conditions without introducing any discontinuities in the calculated flow parameters. Thus, the transient simulations are converging rapidly and efficiently without applying any form of smoothing. The present model is tested against experimental data for severe slugging showing a better performance than previously published models.

Abstract

Significantly reduced development times of today's powertrains as well as steadily increasing requirements regarding fuel consumption and pollutant emissions require a continuous refinement of the development methods for internal combustion engines. The presented simulation method focuses on the new and tightened approval cycles for passenger car engines; more particularly on the start-up phase as well as on sharp load changes, which lead to increased engine out emissions. The aim of this study is to create a simulation tool for the investigation and the evaluation of the emissions during the dynamic engine operation. Established simulation methods, such as Computational Fluid Dynamics (CFD), are bundled in such a way that transient processes can be simulated within a reasonable calculation time without significant loss of information. The tool is based on a 1D gas exchange simulation software. Herein, detailed reaction kinetics are used to simulate the combustion process, which also takes the thermal boundary conditions (wall temperatures) and the quality of the mixture formation into account. For this purpose, the gas exchange model is extended with a thermal network and the mixture formation process is assessed with CFD. Suitable test bench data serve to validate the whole process chain. In addition to the improvement of the CAE-based assessment for the development of virtual engines, the simulation tool should provide an understanding of the phenomena leading to emission formation under the transient engine operation. Furthermore, using such a tool can contribute to the development of alternative driving concepts like plug-in hybrid electric vehicles (PHEV) and exhaust aftertreatment systems.