Molecular structures in flames: A comparison between SNapS2 and recent AFM results

REF Qi Wang, Jacob C. Saldinger, Paolo Elvati, Angela Violi

In the past few years, we have developed an atomistic code, SNapS2, that models the formation of PACs in combustion conditions, providing information on the chemical and structural evolution of these compounds. In this paper, we present a detailed analysis of the compounds formed in a premixed ethylene-air flame that was previously characterized experimentally by AFM (Commodo et al. 2019).

Fuel surrogates are mixtures of simple compounds that emulate the combustion characteristics of more complex fuels, with the primary objective to enable detailed combustion modeling of very complex real fu- els. Current efforts in surrogate development aim at optimizing the compositions of pure hydrocarbons to emulate multiple combustion related properties. In doing so, weights are assigned when defining optimiza- tion problem to reflect the importance of each property. In this study, we report on the relative importance of species selection and their weights on the overall performance of the optimized surrogate. Using experimental data of a reference jet fuel as target, we designed a study using a surrogate optimizer that imposes orthog- onal perturbations on the surrogate components and weights and analyzed their impact on the optimized surrogate mixtures.

On the importance of species selection for the formulation of fuel surrogates

REF Doohyun Kim, Angela Violi

The results show that the selection of surrogate components nearly predefines the overall shape of the distillation curves regardless of the weight values. The current study quantitatively supports the idea that appropriate selection of surrogate components that capture the physical and chemical characteristics of actual constituents of target fuel will increase the possibility of successful surrogate formulation and will mitigate the impact from arbitrary weight assignment.

A wide variety of real life complex networks are prohibitively large for modeling, analysis and control. Understanding the structure and dynamics of such networks entails creating a smaller representative network that preserves its relevant topological and dynamical properties. While modern machine learning methods have enabled identification of governing laws for complex dynamical systems, their inability to produce white-box models with sufficient physical interpretation renders such methods undesirable to domain experts. In this paper, we introduce a hybrid black-box, white-box approach for the sparse identification of the governing laws for complex, highly coupled dynamical systems with particular emphasis on finding the influential reactions in chemical reaction networks for combustion applications, using a data-driven sparse-learning technique.

On sparse identification of complex dynamical systems: A study on discovering influential reactions in chemical reaction networks

REF Farshad Harirchi, Doohyun Kim, Omar Khalil, Sijia Liu, Paolo Elvati, Mayank Baranwal, Alfred Hero, Angela Violi

Reaction pathways for the formation of five-membered rings onto polyaromatic hydrocarbon framework

REF Xuetao Shi, Qi Wang, Angela Violi

In this work, we use ab initio G3-type electronic structure calculations to explore systematically possible reaction pathways leading to the formation of five-membered rings.

Oxidation of 2,6-dimethylheptane at low temperature: Kinetic modeling and experimental study

REF Tanjin He, Doohyun Kim, Tyler Dillstrom, Kaiyuan Cai, Peng Zhang, Changpeng Liu, Xin He, Zhi Wang, Angela Violi

Branched alkanes represent an important class of compounds in conventional fuels and some bio-derived fuels. This study is dedicated to the investigation of the low-temperature oxidation chemistry of 2,6-dimethylheptane using a combination of experimental and computational methods.

characterizing the diversity of aromatics in a coflow diffusion jet a-1 surrogate flame

REF Jacob C. Saldinger, Qi Wang, Paolo Elvati, Angela Violi

Understanding the formation of soot precursors requires properly taking into account their diverse structure and chemistry. To study the extent of this variety in a realistic combustion system, we simulated the growth of polycyclic aromatic compounds (PACs) in a diffusion coflow flame using a three-component Jet A-1 surrogate (n-decane/ propylbenzene/ propylcyclohexane) as fuel. We leveraged our simulations to identify a number of aromatic structures. Overall, our results suggest that there is a wide range of structures with different degrees of oxygenation and aromaticity that must be accounted for when modeling PACs’ growth in combustion environments.

Molecular Dynamics Study of Dehydrated Lipopolysaccharide Membrane

REF Changiang Liu, Paolo Elvati, Angela Violi

The outer membrane of bacteria is known to play an important role in the rapid response to desiccation, although the causes and the extent of these effects are still mostly unclear. For this reason, in this work we study the desiccation response of the Gram-negative lipopolysaccharide (LPS) bacterial outer membranes.

INSIGHTS ON THE EFFECT OF ETHANOL ON THE FORMATION OF AROMATICS

REF Qi Wang, Jacob C. Saldinger, Paolo Elvati, Angela Violi

Our simulations confirm that an increase in the ethanol content results in a reduction of the formation of acetylene, small aromatics, and large PAHs. At the same time, the number of oxygenated PACs reach a maximum at a height above burner around 2-3 mm where they constitute 45% of all PACs: most of the oxygenated structures are phenols, mixed with approximately 15% of furans, and a small amount of ethers. Overall, the results indicate that the formation pathways of oxygenated PACs can compete with pure hydrocarbon growth mechanisms in the rapid growth region up to a height above burner of 2-3 mm. The rate of PACs' growth then gradually slows down, with pure hydrocarbon growth mechanisms being the main contributors in this region of the flame.

Chemical pathways for the formation of benzofuran and dibenzofuran in combustion

REF Xuetao Shi, Qi Wang, Angela Violi

Understanding and predicting the formation of polycyclic aromatic compounds (PACs) and their role in the formation of high molecular mass compounds is still an unresolved topic in combustion. PACs characteristics, such as chemical composition, size, and presence of side chains, play an important role not only in terms of environmental and health impact, but also when developing models that describe the formation of nanoparticles and soot. In this paper, we report on a detailed analysis of the reaction pathways describing the chemistry of furan-embedded PACs using ab initio G3-type electronic structure calculations leading to the formation of benzofuran and dibenzofuran from benzene and biphenyl. The 82 elementary reactions, identified in this work, contain unexplored pathways involving triplet oxygen atom and hydroxyl radical addition reactions. A protocol for improving the calculations of reaction energetics from ab initio compound methods is proposed, which consists of the thorough usage of IRCmax scheme to identify the transition state structure and an energy correction ( ~ 0.2 kcal/mol) to the empirical term in G3 formula for systems with open-shell singlet type of electronic configurations. Results show that the newly discovered benzofuran formation pathways can play a relative important role when in presence of phenol or phenoxyl radicals at various locations in the flame.