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1. Experimental Investigation of the Combustion Properties of an Average Thermal Runaway Gas Mixture from Li-Ion Batteries.

   Olivier Mathieu, Claire M. (February 2022, Energy fuels)

   To assess the fire hazard associated with venting gases coming from a lithium-ion battery during a thermal runaway, a mixture representative of such venting gas was determined by averaging 40 gas compositions presented in the literature. The final mixture is composed of C3H8, C2H6, C2H4, CH4, H2, CO, and CO2. The combustion properties of this mixture were determined using various combustion devices: shock tubes for ignition delay time measurements in air and for H2O time histories in very dilute mixtures (99% Ar), as well as a closed bomb to measure the laminar flame speeds. Experiments were performed at around atmospheric pressure and for several equivalence ratios in all cases. Several detailed kinetics models from the literature were assessed against the data generated with this very complex mixture, and it was found that modern detailed kinetics mechanisms were capable of appropriately predicting the combustion properties of thermal runaway gases from a battery in most cases, with the NUIGMech 1.1 model being the most accurate. A numerical analysis was conducted with the two most modern models to explain the results and highlight the most important reactions. 

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2. 1. Experimental study of the formation of CO during ethanol pyrolysis and dry reforming with CO2.

   Olivier Mathieu, Claire M. (July 2022, Applications in energy and combustion science)

   To use piston engines and their pressure and temperature histories as a chemical rector to produce valuable chemicals, accurate chemical kinetics models are necessary so the engine parameters and mixtures can be designed. Using piston engines in such a way could lead to the production of target chemicals with net-negative CO2 emissions. This benefit is especially true for ethanol, a very common biofuel. To validate models, the dry reforming of ethanol and CO2 was investigated experimentally in a shock tube (50/50 ethanol/CO2 in 99.75% dilution) by following the formation of CO with a laser absorption setup. The effect of the presence of CO2 in the mixture was also investigated by comparing the results of the 50/50 ethanol/CO2 mixture with those from the pyrolysis of ethanol (without CO2) at various concentrations (99.75 and 98% dilution). The 98% dilution results compare extremely well with results from the literature, whereas the other conditions had never been investigated prior. The experimental data were compared to modern detailed kinetics mechanisms, and the experimental CO profiles were poorly predicted overall. Recent literature developments on ethanol pyrolysis were incorporated into the models, and the predictions were improved in some cases and conditions, although further improvements are still necessary. A numerical analysis (rate of production and sensitivity) was performed for the most accurate modified model to highlight the most important reactions involved in the formation of CO under our conditions. 

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3. Plasma Assisted Emission Control of Hydrocarbon Gas Flares: A 0D Feasibility Study

   https://doi.org/10.2514/6.2023-2060  

   Johnson, Praise Noah; Taneja, Taaresh Sanjeev; Yang, Suo (January 2023, AIAA SCITECH 2023 Forum)

   Natural gas associated with oil wells and natural gas fields is a significant source of greenhouse gas emissions and airborne pollutants. Flaring of the associated gas removes greenhouse gases like methane and other hydrocarbons. The present study explores the possibility of enhancing the flaring of associated gas mixtures (C1 – C4 alkane mixture) using nanosecond pulsed non-equilibrium plasma discharges. Starting with a detailed chemistry for C0 – C4 hydrocarbons (Aramco mechanism 3.0 – 589 species), systematic reductions are performed to obtain a smaller reduced mechanism (156 species) yet retaining the relevant kinetics of C1 – C4 alkanes at atmospheric pressure and varying equivalence ratios (φ = 0.5 – 2.0). This conventional combustion chemistry for small alkanes is then coupled with the plasma kinetics of CH4, C2H6, C3H8, and N2, including electron-impact excitations, dissociations, and ionization reactions. The newly developed plasma-based flare gas chemistry is then utilized to investigate repetitively pulsed non-equilibrium plasma-assisted reforming and subsequent combustion of the flare gas mixture diluted with N2 at different conditions. The results indicate an enhanced production of hydrogen, ethylene and other species in the reformed gas mixture, owing to the electron-impact dissociation pathways and subsequent H-abstractions and recombination reactions, thereby resulting in a mixture of CH4, H2, C2H4, C2H2, and other unsaturated C3 species. The reformed mixture shows an enhanced reactivity as exhibited by their shorter ignition delays. The reformed mixture is also observed to undergo increased methane destruction and higher equilibrium temperatures compared to the original mixture as the gas temperature increases, thereby exhibiting a potential for reducing the unburnt emissions of methane and other hydrocarbons. 

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4. Mapping the performance envelope and energy pathways of plasma-assisted ignition across combustion environments

   https://doi.org/10.1016/j.combustflame.2024.113793  

   Dijoud, Raphael J; Laws, Nicholas; Guerra-Garcia, Carmen (January 2025, Combustion and Flame)

   Nanosecond pulsed plasmas have been demonstrated, both experimentally and numerically, to be beneficial for ignition, mainly through gas heating (at different timescales) and radical seeding. However, most studies focus on specific gas conditions, and little work has been done to understand how plasma performance is affected by fuel and oxygen content, at different gas temperatures and deposited energies. This is relevant to map the performance envelope of plasma-assisted combustion across different regimes, spanning from fuel-lean to fuel-rich operation, as well as oxygen-rich to oxygen-vitiated conditions, of interest to different industries. This work presents a computational effort to address a large parametric exploration of combustion environments and map out the actuation authority of plasmas under different conditions. The work uses a zero-dimensional plasma-combustion kinetics solver developed in-house to study the ignition of CH4/O2/N2 mixtures with plasma assistance. A main contribution of the study is the detailed tracking of the energy, from the electrical input all the way to the thermal and kinetic effects that result in combustion enhancement. This extends prior works that focus on the first step of the energy transfer: from the electrical input to the electron-impact processes. Independent of the composition, four pathways stand out: (i) vibrational-translational relaxation, (ii) fast gas heating, (iii) O2 dissociation, and (iv) CH4 dissociation. Results show that the activated energy pathways are highly dependent on gas state, composition, and pulse shape, and can explain the observed range in performance regarding ignition enhancement. The approach can be used to calculate the fractional energy deposition into the main pathways for any mixture or composition, including new fuels, and can be a valuable tool to construct phenomenological models of the plasma across combustion environments. 

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5. Plasma Chemistry and Applications of Atmospheric Pressure Transient Electrical Discharges

   Dhali, Shirshak K (July 2025, Springer Series on Atomic, Optical, and Plasma Physics; Springer: Berlin/Heidelberg, Germany.)

   Guharay, S; Wada, M (Ed.)

   At or near atmospheric pressure, overvolted gas breakdown results in a streamer formation. In many applications of non-thermal plasma where efficient excited species generation is critical, the streamers are quenched to prevent it from reaching the arc phase. This can be achieved by repetitive nano second pulsing or dielectric barrier discharges were the dielectric charging quenches the arc formation. In such discharges, the plasma characteristics such as electron and ion densities and the production of excited species is determined by the streamer properties. Over the past five decades, a vast amount of experimental and computational work has been accumulated to establish a well-accepted theory of streamer formation and propagation. In this article we discuss the fluid models for streamers and quantify some macroscopic properties which can inform specific applications. We discuss in detail the fluid equations needed to model streamers and several schemes of parametrization of the transport and electron collisional processes. From an application point of view, the steamer simulations are used to quantify the excited species production by electron impact. This information is used to predict the specific outcomes via the plasma chemical conversion pathways. We present results of streamer discharges for three applications which are of technological importance to illustrate this approach: Plasma-assisted combustion, remediation of toxic gases, and plasma medicine. For plasma-assisted combustion the results of hydrogen ignition are discussed since non-hydrocarbon-based fuels such as hydrogen and ammonia are potential fuel candidates to reduce greenhouse gases. For the remediation of toxic gases, we discuss the removal of SOX/NOx from flue gas. Plasma medicine is a relatively new field and repetitive nano-second pulsed discharges in a helium gas carrier shows promise as a reactive plasma source for treating biological material. We discuss the helium metastable production in a streamer discharge since this species leads to the production of OH radicals which plays an important role. 

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