CERFACS CERFACS Scientific Activity Report Jan. 2010 – Dec. 2011

COMBUSTION
2.1.7 Two-phase reacting flows in aeronautical engines (G. Hannebique,
L. Esclapez, A. Neophytou, E. Riber, B. Cuenot)
LES is now currently used to help for the design of new combustor geometries for aeronautical engines.
Today’s preoccupations of engineers are to decrease the NOx and CO production, while keeping high
combustion efficiency and stability. This reflects in a number of past and present european projects,
such as TLC, TECC or LEMCOTEC. In these projects, LES of multi-point burners of Snecma (PhD
of G. Hannebique and L. Esclapez), and LPP (Lean Premixed Pre-vaporized) burners of Turbomeca (A.
Neophytou) are performed to characterize the two-phase flame structure, ignition behavior, pollutants
emission and combustion efficiency.
2.1.8 Piston engines (V. Granet, B. Enaux, A. Misdariis, O. Vermorel, T. Poinsot)
In piston engines, cycle-to-cycle variations (CCV) affect combustion efficiency, and must be understood and
controlled to optimize engines. The difficulty is that many different mechanisms can lead to CCV, and that
their importance and interactions can hardly be studied using only standard engine experiments based on
cylinder pressure analysis. Moreover the simulation of CCV remains a computing challenge today, which
only a few groups in the world have tried to tackle.
The multi-cycles LES performed during the PhD thesis of B. Enaux [CFD89, CFD88] and V. Granet
[CFD95] have confirmed the high potential of LES to reproduce cyclic combustion variability in spark
ignition engines (Fig.2.6). Thanks to the LES database, which includes more than 150 individual cycles,
and to the experimental database of IFPEN created during the SGEMAC ANR project, different scenarii
have been proposed to explain why and how a specific operating point can generate high CCV levels. In
the present case, it was shown that CCV are essentially due to aerodynamic fluctuations at the spark plug,
which induce variations of the early flame kernel growth and of the overall combustion duration.
FIG. 2.6: Combustion variability in a four-valve spark ignition engine : iso-surface of temperature for 4
consecutive LES cycles (same crank angle).
2.1.9 Explosion phenomena (P. Quillatre, O. Vermorel, T. Poinsot)
Accidents due to gas explosions are a major concern for oil or chemical industries. Being able to locate
precisely the hazardous areas in industrial buildings, typically offshore oil and gas producing platforms is
136 Jan. 2010 – Dec. 2011