Effects of non-unity Lewis number of gas-phase species in turbulent nonpremixed sooting flames

详细信息    查看全文

• 作者：Antonio Attili ; ^a ; ^{antonio.attili@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; ^{antonio.attili@kaust.edu.sa" class="auth_mail" title="E-mail the corresponding author} ; Fabrizio Bisetti^a ; ^{fabrizio.bisetti@kaust.edu.sa" class="auth_mail" title="E-mail the corresponding author} ; Michael E. Mueller^b ; ^{muellerm@princeton.edu" class="auth_mail" title="E-mail the corresponding author} ; Heinz Pitsch^c ; ^{h.pitsch@itv.rwth-aachen.de" class="auth_mail" title="E-mail the corresponding author}
• 关键词：Direct numerical simulations ; Soot ; Lewis number effects ; Differential diffusion ; Turbulent flames
• 刊名：Combustion and Flame
• 出版年：2016
• 出版时间：April 2016
• 年：2016
• 卷：166
• 期：Complete
• 页码：192-202
• 全文大小：2108 K

文摘

Turbulence statistics from two three-dimensional direct numerical simulations of planar n-heptane/air turbulent jets are compared to assess the effect of the gas-phase species diffusion model on flame dynamics and soot formation. The Reynolds number based on the initial jet width and velocity is around 15, 000, corresponding to a Taylor scale Reynolds number in the range 100 ≤ Re_λ ≤ 150. In one simulation, multicomponent transport based on a mixture-averaged approach is employed, while in the other the gas-phase species Lewis numbers are set equal to unity. The statistics of temperature and major species obtained with the mixture-averaged formulation are very similar to those in the unity Lewis number case. In both cases, the statistics of temperature are captured with remarkable accuracy by a laminar flamelet model with unity Lewis numbers. On the contrary, a flamelet with a mixture-averaged diffusion model, which corresponds to the model used in the multi-component diffusion three-dimensional DNS, produces significant differences with respect to the DNS results. The total mass of soot precursors decreases by 20–30% with the unity Lewis number approximation, and their distribution is more homogeneous in space and time. Due to the non-linearity of the soot growth rate with respect to the precursors’ concentration, the soot mass yield decreases by a factor of two. Being strongly affected by coagulation, soot number density is not altered significantly if the unity Lewis number model is used rather than the mixture-averaged diffusion. The dominant role of turbulent transport over differential diffusion effects is expected to become more pronounced for higher Reynolds numbers.