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NUMERICAL INVESTIGATION OF THE NO FORMAING PATHWAYS IN TURBULENT DIFFUSION FLAME SING UNSTEADY FLAMELET MODELLING APPROACH

Rohit Saini
Indian Institute of Technology Kanpur, U.P, India

Swetha Prakash
Indian Institute of Technology Kanpur, U.P, India

Ashoke De
IIT Kanpur

Rakesh Yadav
ANSYS Inc., San Diego, CA, USA

DOI: 10.1615/IHMTC-2017.190
pages 125-135

摘要

The present work reports the numerical investigation of NOx forming pathways in the turbulent diffusion flames using multiple unsteady flamelet modelling. The study involves 2D axisymmetric modelling of combustion using mixture fraction based turbulence-chemistry interaction approach with detailed chemistry. The main focus of the study is to analyse the effect of two mechanisms with NOx chemistry: a) GRI with 53 species and 325 reactions, b) POLIMI with 115 species and 2141 reactions, in predicting the NOx forming pathways in a piloted natural gas jet flame (Delft Flame III). It is observed that the unsteady flamelet modelling is essential in predicting the accurate formation of slow kinetic species such as NOx and NO containing intermediates. The inability of flamelet models in capturing localized flame extinction is observed, which lead to an over-prediction of NOx at larger downstream locations. The effect of a number of unsteady flamelets in the accuracy of prediction and different methods of initializing the probability marker for unsteady flamelets are monitored to study their importance in NOx prediction. The results predicted are in good agreement with the experimental measurements and POLIMI mechanism proved to be slightly more accurate than the well validated GRI mechanism in predicting NO mass fractions due to more number of species and reactions that describe the NOx chemistry in an improved way. Further, prompt route, nitric oxide route and NNH routes for NO formation are studied comprehensively to differentiate the dominating route for NO formation.

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