Investigation of the Heat Loss Effect on Cellular Flames via Proper Orthogonal Decomposition

ABSTRACT

For better control of a lean premixed combustion system, it is necessary to understand the mechanism of unsteady cellular flame. The objective of the present study is to investigate how heat loss influences the cellular instability of lean premixed flame. The lean premixed CH₄/H₂/air cellular flames generated on a McKenna burner were studied, and heat loss was responsible for the manifestation of unsteady cellular structure. A method of applying proper orthogonal decomposition in scale analysis is presented, which has proven helpful in characterizing the cellular flame. The multiple scale nature of unstable cellular flame was identified, and the small scales were found to act in the random movement of cells. The contribution of each scale is obtained. The energy distribution on modes indicates that the energy on higher-order modes, equivalently the contribution of smaller scales, is decreased with decreasing heat loss. Through analyzing the principal modes and temporal coefficients, heat loss is found to influence a flame’s unstable behavior by promoting the oscillation of large scales, and the wrinkling factor is estimated. It is found that there is a cut-off length scale, below which the wrinkles make little contribution to the enhancement of combustion intensity.

KEYWORDS:

• Cellular flame
• Heat loss
• McKenna burner
• OH-PLIF
• Proper orthogonal decomposition

Additional information

Funding

This study is supported by the National Natural Science Foundation of China (Nos. 51776164 and 91441203). The support from The State Key Laboratory of Engines, Tianjin University (K2017-03) and the State Key Laboratory of Laser Interaction with Matter (SKLLIM1508) is also appreciated. Wu Jin also acknowledges the Chinese Scholarship Council (CSC201606280217) for a joint PhD scholarship at the University of Sydney.