Study and characterization of the instabilities generated in expanding spherical flames of hydrogen/methane/air mixtures

In the present work an analysis of the origin and nature of intrinsic instabilities in combustion processes with different hydrogen/methane mixtures is developed. These expanding spherical flame front experiments have been developed in a cylindrical constant volume combustion bomb, which allows recording the process through Schlieren photography method. The stability study in combustion processes has a great importance to assure their security and control, since the understanding of flame instabilities is necessary for improving the internal combustion engines performance. To carry out this mentioned study, a review of the concepts and parameters used in spherical flame front instabilities research is first proposed, as well as a physical explanation of each concept and the relations among them. Additionally, a methodology that aims to determine the influence of the fuel mixtures in the origin and development of the flame front instabilities is suggested. Moreover, the intrinsic effects of the combustion process, such as the thermal-diffusive and the hydrodynamic effect, are separately studied, including their individual contributions to the growth rate of instabilities which allows to determine combustion nature and to obtain the instability peninsula of each fuel mixture. Finally, this methodology includes a qualitative study of the cellularity phenomenon (when the instabilities develop all over the flame front), considering the parameters which influence on this phenomenon. (C) 2022 The Author(s). Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.

Automated summary

This study analyzes the origin and nature of intrinsic instabilities in combustion processes with different hydrogen/methane mixtures. By conducting experiments on expanding spherical flame fronts in a cylindrical constant volume combustion bomb and using the Schlieren photography method, the stability of combustion processes is studied to ensure safety and control. A methodology is proposed to determine the influence of fuel mixtures on the origin and development of flame front instabilities. The study also separately investigates the thermal-diffusive and hydrodynamic effects of the combustion process and their contributions to instability growth rate, aiming to understand the combustion nature and obtain the instability peninsula of each fuel mixture.