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Show 4 - it appears that the combustion is initiated too intensively in the mixing zones and, therefore, propagates too rapidly in the fresh gas jets, thus consuming part of the fuel that would normally serve to feed the reaction in the downstream part of the chamber. 5 - Finally, the combustion zone located in the dome is slightly more downstream than what is observed with C H radicals imagery. Figure 6 shows a comparison between numerical results of temperature fields from this work (Figure 6.b) and the experimental measurements (Figure 6.a) and numerical calculations (Figure 6.c) of Montazel [15]). The maximum gas temperature reached in the experimental measurements is 1860 K. The present model (Fig 6.b) gives 1883 K and the C F M model [15] gives 1890 K. Figure 7 is a flame surface density field comparison between calculations results from the present study (Figure 7.a) and numerical calculations (Figure 7.b) of Montazel [15]. In our calculations, two combustion zones separated by fresh gases are clearly apparent on each side of the injection slot. The fuel mass fraction distribution is presented in Figure 8. A comparison between calculations from this work (Figure 8.a) and numerical calculations (Figure 8.c) of Montazel [15] shows the ability of the model proposed in this paper to predict the two reaction zones. Combustion downstream from the injection ports is well reproduced in our calculations and is absent in the prediction of the C F M model. The influence of inlet velocity on heat release fields is displayed in Figure 9 which shows a comparison between numerical results and experimental measurements. In this case the inlet velocity is Vo = 20 m/s and <f> = 0.7. The present work predicts (Figure 9.a) a maximum of 8.8 107 W / m 3 against 8.1 107 W / m 3 for the experimental measurements (Figure 9.b) of Montazel [15]. CONCLUSION A numerical model based on the flame surface density has been developed to predict the evolution of turbulent premixed flames and has been applied to a propane-air ramjet combustor. Realistic comparisons between numerical calculations and experimental measurements are obtained. The good agreement between predicted and measured results shows clearly the capabilities of this model and its relevance for future development. More research effort is needed in order to include propagation and curvature effects on flame production/destruction mechanism and also to determine how these efects act as source or consumption term in the F S D balance equation. REFERENCES 1-Bilger, R.W. "Turbulent jet diffusion flames". Progress in Energy and Combustion Science, 1, 87, 109-130, 1976. 2- Blint, J. "The relationship of laminar flame width to flame speed" Combustion Science and technology, 49, p.79-92, 1986. 3- Borghi, R. "Turbulent combustion modelling". Progress in Energy and Combustion Science, 14, 245-292, 1988. 4- Bray, K.N.C. and Moss, J.B. " A closure model for the turbulent premixed flame with sequential chemistry". Combustion and Flame, 30, 125-131, 1977. 5- Candel, S.M. , and Poinsot, T. " Flame strech and the balance equation for flame area" Combustion Science and technology, 70, 1-15, 1990. 6- Candel, S., VeynanteJ)., Lacas, F., Maistret, E., Darabiha, N. and Poinsot, T. "Coherent Flame Model : applications and recent extensions". In Advances in combustion modelling, Larrouturou, B. Singapore : World Scientific, 19-64, 1991. 7- Cant, R.S., Pope, S.B. and Bray, K.N.C. "Modelling of flamelet surface to volume ratio in turbulent premixed combustion"23rti Symposium (International) on Combustion. Pittsburgh: The Combustion Institute, 809-815, 1990. 8- Duclos, J.M., Veynante, D., and Poinsot, T. "A comparison of flamelets models for premixed turbulent combustion" Combustion and Flame, 95, 101-107, 1993. 9- Gordon, S and M c Bride, B J., "Computer Program for calculation of Complex Chemical Equilibrium Compositions, Rocket Performance, Incident and Reflected Shocks and Chapman-Jouguet Detonation", N A S A SP-273, 1971. 10- Kollman, W . "The P D F approach to turbulent flow". Theoretical and Computational Fluid Dynamics, 1, 249-285, 1990. 8 |