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

Experimental and numerical laminar syngas combustion
tel-00623090, version 1 - 13 Sep 2011
They stated that as the H 2 concentration in the H 2 –CO mixture increased, the mixture
started behaving similarly to the H 2 –air mixture and the effect of flame stretch on
burning velocity also became more pronounced. Sun et al., (2007) measured stretchfree
burning velocities for CO–H 2 –air mixtures at different mixing ratios (the values of
the CO/H 2 ratio used were 50:50, 75:25, 95:5, and 99:1), equivalence ratios and
pressures using expanding spherical flames at constant pressure. They used artificial
air with helium instead of nitrogen to have stable flames at higher pressures. Burke et
al., (2007) studied the effects of CO 2 on the burning velocity of a 25% H 2 –75% CO
mixture with 12.5%O 2 –87.5%He oxidizer under stoichiometric conditions and they
varied the CO 2 concentration in the fuel from 0 to 25% using spherically expanding
flames. They stated that the largest flame radius for calculation of unstretched burning
velocity should be less than 30% of the radius wall in a cylindrical chamber. Natarajan
et al., (2007) investigated the effects of CO 2 on burning velocities of H 2 –CO mixtures
for different H 2 /CO ratios, varying the CO 2 mole fraction in the fuel (0% and 20%), the
equivalence ratio (0.5–1.0), the initial temperature (300–700K), and pressure (1–5
atm). Two measurement techniques were used: one using flame area images of a
conical Bunsen flame and the other based on velocity profile measurements in a onedimensional
stagnation flame.
No extensive combustion study is available in the literature for typical syngas
compositions like the ones expressed in chapter 2. This motivated the present work to
choose three typical compositions of syngas and to study the laminar burning velocity
and flame stability. These typical syngas compositions were selected from Bridgwater,
(1995) and are shown in the Table 4.1.
Table 4.1 – Syngas compositions (% by volume)
Gasifier
Gas composition
(% by volume) HHV
(MJ/m 3 )
H 2 CO CO 2 CH 4 N 2
Updraft 11 24 9 3 53 5.5
Downdraft 17 21 13 1 48 5.7
Fluidized bed 9 14 20 7 50 5.4
There are also gaps in the fundamental understanding of syngas combustion
characteristics, especially at elevated pressures that are relevant to practical
combustors. In this chapter, constant volume spherically expanding flames are used to
determine a burning velocity correlation valid for engine conditions.
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