Investigation of the fuel effects on burning velocity and flame structure of turbulent premixed flames based on leading points concept

ABSTRACT

The measurements on flame structure and burning velocities of C₃H₈/air, CH₄/air and CO/H₂/air turbulent premixed flames were conducted. Various experimental conditions for these mixtures were considered to understand the molecular and thermal diffusion process in turbulent flame, which was referred to the fuel effects. The fuel effects are interpreted as local burning velocity variation caused by molecular and thermal diffusivity with stretch effect. Leading points concept is a promising scaling approach to incorporate the fuel effects in turbulent flames recently. In this article, data across a variety of equivalence ratio and hydrogen fractions were obtained using Bunsen burner. Flame front was detected with OH-PLIF technique and turbulent burning velocity S_T referred to leading edge was derived. A new leading points characteristic speed S_L,LP was presented invoking both negative and positive Markstein number mixtures, revising the previous model in literature which is only suitable for negative Markstein number fuels. The turbulent burning velocity S_T under relatively weak turbulence intensity in this study and data of high turbulence intensity, high pressure from literature were renormalized with S_L,LP instead of S_L,0 based on leading points concept, where S_L,0 is the unstretched laminar flame speed. The results show that all the data sets were collapsed well which validated the significance of S_L,LP in normalizing S_T of different mixtures. An empirical formula for turbulent burning velocity correlation was obtained as . This formula is similar to that of Kobayashi; however, it shows superiority in incorporating the fuel effects.

KEY WORDS:

• Turbulent burning velocity
• turbulent premixed flame
• leading points concept
• fuel effects

Additional information

Funding

This study is supported by National Natural Science Foundation of China (No. 51776164, 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.