Doctoral Dissertations
Date of Award
12-2019
Degree Type
Dissertation
Degree Name
Doctor of Philosophy
Major
Energy Science and Engineering
Major Professor
Ramanan Sankaran
Committee Members
Derek Splitter, Charles Finney, Zhili Zhang
Abstract
Direct numerical simulation (DNS) of auto-ignition under turbulent conditions has played a very important role in improving the fundamental understanding and advancement of combustion technologies for practical applications. However, very little is known of the nature of combustion in a reactive fuel/air mixture that is conducive to both spontaneous ignition and premixed deflagration. As such, characterizing the precise nature of combustion and the relevant propagation speed remains a challenge. This study attempts to address these questions by performing fully resolved numerical simulations of preheated fuel/air mixtures at elevated pressures using a newly developed DNS code called KAUST Adaptive Reactive Flows Solver (KARFS). Unlike a periodic box setup that has been used in most of the previous DNS studies, an inflow-outflow configuration representing a statistically stationary reaction front has been employed to understand the unsteady flame dynamics at auto-ignitive conditions.The first part of the dissertation is devoted to a discussion on parametric mapping of propagation speeds of auto-ignitive dimethyl-ether/air as well as dimethyl-ether/methane/air mixtures at elevated pressures under the influence of monochromatic thermal and composition/reactivity stratification using a one-dimensional, statistically stationary configuration. Thereafter, the implementation and effectiveness of Weighted Essentially Non-oscillatory (WENO) schemes in performing DNS of turbulent reacting flows is demonstrated with various non-trivial model problems. In addition, the scalability and performance portability of KARFS is presented on heterogeneous (CPU + GPU) system architectures. Finally, as a more extensive parametric quantification of the effects of thermal and composition stratification on turbulent flame propagation, results from DNS of a turbulent premixed flame in an auto-ignitive dimethyl-ether/air mixture conducted at elevated pressure are presented and discussed. The outcomes of this dissertation are expected to provide a fundamental understanding of the combustion mode transition and relevant propagation speeds in modern engines utilizing mixed-mode combustion.
Recommended Citation
Desai, Swapnil, "Direct Numerical Simulations of Flame Propagation in Stratified Mixtures at Auto-ignitive Conditions Using Accelerated Computing. " PhD diss., University of Tennessee, 2019.
https://trace.tennessee.edu/utk_graddiss/5710