A projection procedure to obtain adiabatic flames from non-adiabatic flames using heat flux method

Laminar burning velocity S-L at elevated temperature T-u and its temperature dependence coefficient alpha in S-L/S-L(0) = (T-u/T-u(0))(alpha) are important parameters for industrial applications. However, experimental systems with high unburned gas temperatures may encounter pre-dissociation, leading to significant data scattering in the measurements. To negate this, the present work proposes a projection procedure to obtain adiabatic flame parameters at various unburned gas temperatures using non-adiabatic flames on a heat flux burner, by which the preheating can be achieved within much shorter time scale than, e.g., in conventional spherical flame methods, and the advantage of good data consistency in the heat flux method is kept. Burning velocity experiments were carried out with CH4 +air atmospheric flames covering T-u = 298-473 K, and the results show good agreement with the proposed projection equations. OH* spontaneous emission profiles were measured, indicating that the projection may extend to other flame characteristics. Uncertainty of the projection process was evaluated and comparisons were made with six popular kinetic mechanisms: GRI-Mech, FFCM-1 mech, Konnov mechanism, Glarborg mechanism, San Diego mechanism and Aramco mechanism. It is found that the simulated coefficients alpha are higher than experimental data especially at rich conditions; this is also found for literature values of high unburned gas temperature experiments. Possible reasons for this divergence are discussed. (C) 2020 The Combustion Institute. Published by Elsevier Inc. All rights reserved.

Automated summary

The study proposes a projection procedure to obtain laminar burning velocity at different unburned gas temperatures, effectively addressing the issue of data scattering caused by high unburned gas temperatures. Experimental results show good agreement with the proposed equations, indicating the potential extension of the projection method to other flame characteristics.