Etude de la combustion de gaz de synthèse issus d'un processus de ...

Chapter 6
motions within the cylinder, which in turn determines the extent of mixing between the
fresh charge and the residuals, as well as internal and external heat transfer rates. The
key to the premixed combustion modeling is the prediction of S te, the turbulent flame
speed normal to the surface of the flame. In turbulent flames, the flame speed depends
on both chemical kinetics and the local turbulence characteristics.
Many methods for describing and calculating the turbulent flame speed have been
developed (see for instance the excellent review of Lipatnikov and Chomiak, (2002)).
The goal of this work is to develop a fast simulation program for the combustion of
syngas in spark ignition engines. The main interest is the pressure development in the
engine cylinders, which is directly related to the power output and the efficiency.
Therefore, in this work the so-called DamkÖhler method is used and according to this
model turbulent flame speed is as follows (Blizard and Keck, 1974):
tel-00623090, version 1 - 13 Sep 2011
S = C u + S
(6.26)
te
2
'
Where, u’ is the root mean square (rms) turbulent velocity, C 2 a calibration constant
dependent of the engine geometry and S u the laminar burning velocity.
Obviously, proper in-cylinder turbulence modeling needs to be estimated. For this
propose, a simple turbulence model, firstly proposed by Hall and Bracco, (1987) and
used by several authors [Verhelst and Sierens, (2007); Farhad et al., (2009); Federico
et al., (2010)] has been considered:
⎛ θ − 360 ⎞
u' TDC
= 0.75up = 0.75(2 sn), u' = u' TDC ⎜1−0.5
45
⎟
(6.27)
⎝
⎠
u
where u’ TDC is the rms turbulent velocity at TDC, taken to be 0.75 times the mean
piston speed; θ is the crank angle and, s, is the stoke. A linear decay of the rms
turbulent velocity u’ from top dead center is imposed.
6.2. Numerical solution procedure
The basic concept of the model is the division of the burned gas region into several
distinct zones for taking into account the temperature stratification of the burned gas.
The multi-zone simulation model is applied throughout the closed part of the engine
cycle, between IVC and EVO, i.e. compression, combustion and expansion. Admission
phase is also included in the code in order to take into account the heating of the
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