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Mobility and Systems

LES moves to rapid transients for cleaner powertrains

Gasoline direct injection engines emit soot particles during rapid transients.
  
This still poorly understood phenomenon is taken into account during new WLTCsa, aimed at more accurately reproducing real vehicle use.
     
High-resolution, digital flow simulations in the combustion chamber, capable, in particular, of resolving cycle-to-cycle variations, can be used to gain a better understanding of the mechanisms behind this soot formation.
     
 However, these simulations, based on LESb, are mastered on stabilized operating points(1), where they give relevant results, but they have never been carried out for transients.
    
Research conducted by IFPEN(2-3) in the ANR Astridec project demonstrated the relevance of LES for tackling this problem, via the first ever calculations involving 1D-3D code coupling.
   
In particular, these simulations reproduced the impact of engine transients, i.e. engine speed variations (for example, acceleration between 1,000 rpm and 1,800 rpm in the figure):

  • on the acoustics in the intake line,
       
  • and thus on filling and aerodynamics in the combustion chamber.

Further work is now required to fine-tune the results, separating the average and fluctuating components of velocity ranges.
   
To do this, research is focusing on two areas:

  • obtaining a usable average based on several transients,
       
  • and the implementation of specific after-treatment analyses, such as EMDd (4).

 

a - Worldwide harmonized Light vehicles Test Cycles.
 
b - Large-Eddy Simulation.
  
c - Aerodynamics and Sprays during Transients of Gasoline Direct Injection Engines.
  
d - Empirical Mode Decomposition.
   

 

Scientific contact:  adele.poubeau@ifpen.fr

Published in Science@ifpen n° 32 - March 2018

Publications

  1. A. Robert, S. Richard, O. Colin, L. Martinez, L. de Francqueville et al, Proc. Combust. Inst. 35(3), 2015 
        
  2. B. Roux, IFPEN, Ph.D. thesis 2015 : Couplage entre simulation système et simulation aux grandes échelles pour la simulation multi-échelles de moteurs à combustion interne.
    >> https://tel.archives-ouvertes.fr/tel-01343306/document
       
  3. A. Poubeau, S. Jay, A. Robert, E. Nicoud et al., Large-Eddy Simulations of a Speed Transient Performed on a Motored Gasoline Engine, SAE Technical Paper 2017
    >> Doi: 10.4271/2017-24-0028
        
  4. M. Sadeghi, K. Abed-Meraim, F. Foucher, C. Mounaïm-Rousselle, Analysis of the Bivariate EMD Behavior for Separating Coherent Structures from Interference Fluctuations in Isotropic Homogeneous Turbulence : Proceedings of the iTi Conference on Turbulence, Bertinoro, Italie, sept. 2014
    >> Doi: 10.1007/978-3-319-29130-7
       
       

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