Large Eddy Simulation of Diesel Engine In-cylinder Flow

Abstract

The numerical simulation of the in-cylinder flow of a realistic Diesel engine is presented. Over the past three decades most of the CFD research for internal combustion engines (ICE) has been carried out using the Reynolds Averaged Navier Stokes (RANS) approach. Despite the achievements obtained in engine design, numerical investigations with RANS models can only give insight into the mean behaviour of the in-cylinder flow. By contrast, Large-Eddy Simulation (LES) allows a better description of the in-cylinder flow motion and gives access to the cycle-tocycle variations. Multi-cycle simulations of a motored case using LES and a hybrid LES/RANS approach are compared against experimental data and results obtained with a RANS methodology. The cycle-to-cycle variations in global in-cylinder characteristics such as pressure, swirl number and tumble number are reported and an analysis of the in-cylinder flow for each stroke of the engine cycle is presented. The interaction between spray and turbulence is also analysed with closed-chamber simulations. The effects of the hybrid RANS/LES approach on mixing of the vapour phase of the fuel is described and compared to the results obtained with a standard RANS approach. This work gives an insight into the numerical simulation of Diesel engine and illustrates some of the advantages of the LES methodology over RANS. The trade-off between computational cost and details in the flow description using a hybrid RANS/LES approach is discussed.

Scale-resolving simulations in engine combustion process design based on a systematic approach for model development

“…SRSs of realistic engines under motored conditions have recently been published by several groups. 11,18,[52][53][54][55][56][57] Especially, Yang et al 58 emphasized the significant benefits of SRSs by comparing them directly to URANS results.…”

Global reaction mechanism for the auto-ignition of full boiling range gasoline and kerosene fuels

“…The latter constitutes another important control factor in HCCI operation, since ignition can be either advanced (hot EGR) or delayed (cooled EGR dilution). State of the art modelling for such set-ups is presently carried out by means of large eddy simulation (LES), which is computationally very demanding since for reliable results, roughly 70% of the turbulent energy spectrum must be resolved [15,16]. As a consequence, the combination of such multi-dimensional models with the currently proposed detailed chemical kinetics required for HCCI combustion is therefore presently prohibitively expensive.…”

Influence of swirl, tumble and squish flows on combustion characteristics and emissions in internal combustion engine-review

“…The results showed that the swirl ratio of the swirl chamber increased linearly as the passage hole area decreased and magnitude of kinetic energy depended on air flow velocity changed based on different shape of passage hole. On the other hand, Bottone et al [37] studied Reynolds Averaged Navier-Stokes (RANS), Detached eddy simulations (DES) and Large-Eddy Simulation (LES) methods for multi-cycle simulations of incylinder flow with a realistic engine geometry by using STAR-CD CFD code. They demonstrated that the intensity of the cycle-tocycle variations in the swirl and tumble number was comparable to the DES and LES solutions.…”