The present paper argues that the prediction of turbulent premixed flames under non-adiabatic conditions can be improved by considering the combined effects of strain and heat loss on reaction rates. The effect of strain in the presence of heat loss on the consumption speed of laminar premixed flames was quantified by calculations of asymmetric counterflow configurations (“fresh-to-burnt”) with detailed chemistry. Heat losses were introduced by setting the temperature of the incoming stream of products on the “burnt” side to values below those corresponding to adiabatic conditions. The consumption speed decreased in a roughly exponential manner with increasing strain rate, and this tendency became more pronounced in the presence of heat losses. An empirical relation in terms of Markstein number, Karlovitz Number and a non-dimensional heat loss parameter was proposed for the combined influence of strain and heat losses on the consumption speed. Combining this empirical relation with a presumed probability density function for strain in turbulent flows, an attenuation factor that accounts for the effect of strain and heat loss on the reaction rate in turbulent flows was deduced and implemented into a turbulent combustion model. URANS simulations of a premixed swirl burner were carried out and validated against flow field and OH chemiluminescence measurements. Introducing the effects of strain and heat loss into the combustion model, the flame topology observed experimentally was correctly reproduced, with good agreement between experiment and simulation for flow field and flame length.
Bibliographical noteKAUST Repository Item: Exported on 2020-10-01
Acknowledgements: Gaurav Bansal contributed to the development of ideas during the early stages of this work with clarifying comments on the nature of extinction events in strained counterflow flames. The support of Alstom, Bayerisches Staatsministerium fur Wirtschaft, Bayerische Forschungsstiftung, Forschung und Kunst and Bayerisches Staatsministerium fur Wirtschaft, Infrastruktur und Technologie and Siemens in the framework of KW21 and of the Deutscher Akademischer Austausch Dienst (DAAD) is gratefully acknowledged. The work by Hong G. Im was sponsored by King Abdullah University of Science and Technology. We also want to thank Bernhard Rogg for making available the RUN-1DL program.