Etude de la combustion de gaz de synthèse issus d'un processus de ...
Etude de la combustion de gaz de synthèse issus d'un processus de ... Etude de la combustion de gaz de synthèse issus d'un processus de ...
Numerical simulation of a syngas-fuelled engine Concerning hydrogen-air flames, the extensive experimental work done by Verhelst, (2005) has been chosen for including the dependence on the air-fuel ratio, temperature, pressure and residual burned gas content: α ⎛T ⎞ ⎛ P ⎞ Su = Su ⎜ ⎟ ⎜ ⎟ − f 0 T P ⎝ 0 ⎠ ⎝ 0 ⎠ β ( 1 γ ) (6.28) Here, the reference conditions T 0 and P 0 are 365K and 5 bar, respectively. The influence of the equivalence ratio at these conditions is embodied in S u0 and is estimated at: S φ φ φ u0 3 2 =− 4.77 + 8.65 −0.394 − 0.296 (6.29) tel-00623090, version 1 - 13 Sep 2011 The values for α, β and γ are the following: α = 1.232 β = φ − φ + φ − φ < 3 2 2.9 6.69 5.06 1.16, 0.6 β = 0.0246φ + 0.0781, φ ≥ 0.6 γ = 2.715 −0.5φ (6.30) Where γ expresses the effect of residual gases. Verhelst and Sierens, (2007) selected a residual mass fraction of 27% given the best correspondence for the pressure trace during compression and maximum combustion pressure. Concerning methane–air flames, the correlation expressing the laminar burning velocity of Muller et al., (1997) has been adopted, since it is reliable for a wide range of pressures and preheats temperatures: 0 0 m T ⎛ u Tb −T ⎞ Su = A( T ) yF, u 0 ⎜ ⎟ T ⎝Tb −Tu ⎠ 0 ⎛ G ⎞ AT ( ) = Fexp ⎜ − 0 ⎟ ⎝ T ⎠ n (6.31) Where, y F,u = (1+AFR s /φ) represents the mass fuel fraction in the unburned mixture, AFR s is the stoichiometric air–fuel ratio;T 0 =-E/ln(p/B) is a representative temperature of the inner layer, defined by Peters and Williams, (1987) as the thin layer within which the first oxidation of methane into CO, hydrogen and water occurs; p is pressure, and the fuel-dependent constants are equal to: B=3.1557×10 8 (bar), E=23873 (K), F=2.21760×10 1 (cm/s) ,G=-6444.27 (K), m =0.565175 and n=2.5158. 180
Chapter 6 The calibration coefficient C 2 in the DamkÖhler model was set equal 1.7 as reported by Verhelst and Sierens, (2007). 6.3.1.2 Results and discussion The simulations results, compared to the respective references, have been presented in figures 6.3 and 6.4. 50 40 Numerical Experimental (Bade and Karim, 2001) Pressure (bar) 30 20 tel-00623090, version 1 - 13 Sep 2011 10 0 240 270 300 330 360 390 420 450 480 Crank Angle (degrees) Figure 6.3 – In cylinder pressure validation for CFR engine fueled by methane: ε=8.5, 900 rpm, IT=20º BTDC, φ=0.99. Pressure (bar) 60 50 40 30 20 Numerical Experimental (Verhelst, 2005) 10 0 240 270 300 330 360 390 420 450 480 Crank Angle (degrees) Figure 6.4 – In cylinder pressure validation for CFR engine fueled by hydrogen: ε=9.0, 600 rpm, IT=20º BTDC, φ=0.59. As clearly visible from these figures, a very good agreement is found. This allows validate the developed model and applied it to typical syngas compositions. 181
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Chapter 6<br />
The calibration coefficient C 2 in the DamkÖhler mo<strong>de</strong>l was set equal 1.7 as reported by<br />
Verhelst and Sierens, (2007).<br />
6.3.1.2 Results and discussion<br />
The simu<strong>la</strong>tions results, compared to the respective references, have been presented<br />
in figures 6.3 and 6.4.<br />
50<br />
40<br />
Numerical<br />
Experimental (Ba<strong>de</strong> and Karim, 2001)<br />
Pressure (bar)<br />
30<br />
20<br />
tel-00623090, version 1 - 13 Sep 2011<br />
10<br />
0<br />
240 270 300 330 360 390 420 450 480<br />
Crank Angle (<strong>de</strong>grees)<br />
Figure 6.3 – In cylin<strong>de</strong>r pressure validation for CFR engine fueled by methane: ε=8.5, 900 rpm,<br />
IT=20º BTDC, φ=0.99.<br />
Pressure (bar)<br />
60<br />
50<br />
40<br />
30<br />
20<br />
Numerical<br />
Experimental (Verhelst, 2005)<br />
10<br />
0<br />
240 270 300 330 360 390 420 450 480<br />
Crank Angle (<strong>de</strong>grees)<br />
Figure 6.4 – In cylin<strong>de</strong>r pressure validation for CFR engine fueled by hydrogen: ε=9.0, 600 rpm,<br />
IT=20º BTDC, φ=0.59.<br />
As clearly visible from these figures, a very good agreement is found. This allows<br />
validate the <strong>de</strong>veloped mo<strong>de</strong>l and applied it to typical syngas compositions.<br />
181
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