Role of cellular wavelengths in self-acceleration of lean hydrogen-air expanding flames under turbulent conditions

An investigation is done upon the lean H-2-air flame under turbulent conditions to clarify the role of inherent instabilities and turbulence in self-acceleration of expanding flames. The result shows that, in weak turbulent flow fields, the two-stage self-acceleration feature still exists. As the turbulent intensity increases, the originally evident two-stage transition-saturation feature is weakened. When the Karlovitz number becomes greater than 1, the self-acceleration process no longer experiences the transition stage and performs a single-stage feature. These observations are correlated with the distribution and evolution of length scales in the cellular structure of the flamefront. A theoretical analysis is conducted to compare growth rates of disturbances induced by instability and turbulence, with consideration of their wavelength dependence. On this basis, interpretations are proposed on afore-mentioned phenomenal observations and response of quantitative parameters such as fractal excess and average cell wavelength. (c) 2020 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Automated summary

The investigation reveals that the lean H-2-air flame retains a two-stage self-acceleration feature in weak turbulent flow fields, which weakens as turbulent intensity increases; it transitions to a single-stage feature when the Karlovitz number exceeds 1. The observations are linked to the distribution and evolution of length scales in the cellular structure of the flamefront. Theoretical analysis comparing growth rates of disturbances induced by instability and turbulence provides interpretations for the observed phenomena and the response of quantitative parameters.