Publikationsserver der RWTH Aachen University
Validierung eines 1D-Spraymodells zur Simulation der Gemischbildung in direkteinspritzenden Dieselmotoren
Abstract
dc:descriptionModelling of Diesel sprays plays a crucial role for the calculation of performance and emissions (NOx and Soot) of Diesel engines since simulation of subsequent processes like ignition, heat release and pollutant formation strongly depends on the spray. In spite of existing detailed submodels 3D simulation of Diesel sprays is usually not even able to predict global quantities like penetration length of liquid and vapour. With the typically used stochastic spray model strong mesh dependency is observed. Reasons are insufficient numerical resolution of the flow near the orifice and non-converged statistical properties of the spray. In the present thesis, a universal concept for the simulation of Diesel sprays is presented. Near the nozzle orifice the ICAS technique (Interactive Cross-sectionally Averaged Spray) is used to overcome the spatial resolution problem. In order to improve statistical convergence, a two-fluid formulation is applied. Close to the nozzle exit the Diesel spray is substantially a 1D phenomenon. Therefore the governing equations are integrated over the cross-section of the spray and then solved separately in a one-dimensional code. The transport processes take place in a prescribed spray cone, in which the orifice is automatically resolved. Hence the interaction between liquid and gas is calculated in a correct way. In the 1D code several droplet classes are used. For each class, conservation equations are solved for droplet diameter, droplet temperature as well as for continuity and momentum of the liquid and the gaseous phase. The source terms between the phases are embedded conservatively into the spray region of the 3D code. In the 3D code only the gaseous phase is calculated. Chemical source terms as well as local gas temperatures and mixture compositions are interactively returned to the 1D code as boundary conditions. In the presence of swirl, the deflection of the spray region is modelled by a simple momentum balance. At a prescribed position the description of the spray is switched from the 1D model to the stochastic particle technique. Very good quantitative agreement is obtained between computed and measured penetration lengths of liquid and vapour phase for orifice-resolving meshes. Of course, the vapour phase propagation calculated by the 3D code on coarse meshes is still dependent on the discretization mesh. However, the spray structure in the 3D code converges with successive mesh refinement and becomes independent of the initial values of ambient turbulence. The mesh dependency of typical used relatively coarse engine meshes is considerably reduced by the use of a length scale limiter, whereby the calculated integral length scale is limited to the maximal physical length scale - the spray diameter. Combining ICAS + length scale limiter spray structures similar to the spray structure on orifice-resolving mesh are obtained on relatively coarse meshes suited for 3D engine calculations. Applicability of the ICAS technique for 3D engine calculations with moving boundaries is demonstrated by a homogenous Diesel combustion strategy. Good agreement between spray structure in 3D simulation and diagnostics in a single cylinder engine with optical access has been found.
Degree
thesis:*- Grantor dc:publisher
- Publikationsserver der RWTH Aachen University
- Year dc:date
- 2001
Author and committee
dc:creator, dc:contributor.*- Author dc:creator
-
- Krüger, Christian
- Contributors dc:contributor
-
- Peters, Norbert
Subjects
dc:subject × 8Rights
dc:rights- Statement dc:rights
-
- info:eu-repo/semantics/openAccess
- Language dc:language
- ger