Plasma-assisted Combustion Research Articles

A novel machine learning based lumping approach for the reduction of large kinetic mechanisms for plasma-assisted combustion applications

The development of skeletal mechanisms has become essential for multi-dimensional simulations of plasma-assisted combustion (PAC). However, reduction tools developed for traditional combustion applications are not always applicable to PAC, due to the complex interplay between non-equilibrium plasma and combustion kinetics. Plasma direct relation graph with error propagation (P-DRGEP) is a recent plasma-specific reduction method developed in order to incorporate plasma energy branching in the reduction. In the first part of this work, the applicability of P-DRGEP to large kinetic mechanisms is investigated. A detailed isooctane/air plasma mechanism containing 2805 species and 18457 reactions is reduced to 415 species and 4716 reactions, keeping errors on ignition time within 3% for a wide range of initial conditions: from 750 K to 1200 K, 10 atm and equivalence ratios from 0.75 to 1.50. The second part focuses on isomer lumping, which is another reduction technique widely used in combustion. When applied to PAC, it is shown that the resulting lumped mechanism produces poor results. A novel plasma-specific isomer lumping strategy using machine learning is proposed instead. With the supervised algorithm of gradient boosting, predictive regression models are generated, which describe rate coefficients of lumped reactions adequately. These models are trained with simulation data. Leveraging this newly proposed lumping approach on the reduced mechanism, allows for an additional 28% reduction in the number of species and 19% reduction in the number of reactions. Two different versions are presented: in the first one the models are trained using one input feature (1D), while in the second one, two input features are selected (2D). The resulting lumped mechanism is shown to produce accurate predictions of PAC over the entire parameter space of interest, while significantly decreasing the computational time. Indicatively, with the 1D version the maximum error on ignition time in this range of conditions is 6%. The 2D approach produces even lower errors, which do not exceed 3%.Novelty and significance statementIn this work, a novel approach for isomer lumping, in plasma-assisted combustion mechanisms, is demonstrated. This plasma-specific approach, uses predictive machine learning regression models to describe the complex evolution of lumped reaction rate coefficients. Combining it with the plasma direct relation graph with error propagation, a powerful reduction framework is created, which is successfully demonstrated on a detailed isooctane/air plasma kinetic mechanism, via zero-dimensional ignition simulations. This framework constitutes a useful tool towards the creation of highly accurate skeletal mechanisms, which significantly reduce the computational costs of simulations.

Numerical study of exhaust chemical composition in a methane DBD plasma actuator under different operating conditions

In this paper, numerical simulations of a Dielectric-Barrier Discharge (DBD) plasma actuator are performed to predict its output chemical composition. The plasma actuator is cylindrical, with two coaxial electrodes and a quartz dielectric. The electrical discharge occurs in a pulsed manner around the quartz wall. This device is utilized for methane conversion in plasma-assisted combustion applications. The effects of voltage, frequency, temperature, and relative permeability parameters on methane conversion and some selected species concentrations were investigated. The results show that plasma discharging converts methane to hydrogen and heavier hydrocarbons such as C2H3, C2H4,C2H5, C2H6, and C3H8. Moreover, increasing the relative permeability coefficient and voltage had the greatest effect on methane conversion. Increasing the relative permeability from 2 to 6 increases the methane conversion by 43 % and also increases the H2 density by 57 %. The conversion rate of methane and the H2 density increase by 18 % with increasing the voltage from 6 to 8 kV. The partial conversion of methane to hydrogen and radical species benefits combustion applications in terms of flame stability and emissions reduction.

Adaptation of the Kinetical Scheme to Ethylene Combustion Conditions at Temperatures Above 1200 K

In the paper authors present original methods for analyzing the kinetic scheme and reaction rateconstants for calculation of the ignition delay time and the laminar velocity of the combustion wave forC2H4–O2–Ar and C2H4-air mixtures. The kinetic scheme under consideration will further be applied inproblems of plasma-assisted combustion in a supersonic flow using a discharge. After made changes to thereaction system, a good agreement between the calculation results and experimental data was obtained.

On the Influence of Discharge Parameters on the Kinetics of the Plasma-Assisted Combustion of Synthesis Gas in Air

On the Influence of Discharge Parameters on the Kinetics of the Plasma-Assisted Combustion of Synthesis Gas in Air

Numerical study of nitrogen oxides chemistry during plasma assisted combustion in a sequential combustor

Plasma Assisted Combustion (PAC) is a promising technology to enhance the combustion of lean mixtures prone to instabilities and flame blow-off. Although many PAC experiments demonstrated combustion enhancement, several studies report an increase in NOx emissions. The aim of this study is to determine the kinetic pathways leading to NOx formation in the second stage of a sequential combustor assisted by Nanosecond Repetitively Pulsed Discharges (NRPDs). For this purpose, Large Eddy Simulation (LES) associated with an accurate description of the combustion/NOx chemistry and a phenomenological model of the plasma kinetics is used. Detailed kinetics 0-Dimensional reactors complement the study. First, the LES setup is validated by comparison with experiments. Then, the NOx chemistry is analyzed. For the conditions of operation studied, it is shown that the production of atomic nitrogen in the plasma by direct electron impact on nitrogen molecules increases the formation of NO. Then, the NO molecules are transported through the turbulent flame without being strongly affected. This study illustrates the need to limit the diatomic nitrogen dissociation process in order to mitigate harmful emissions. More generally, the very good agreement with experimental measurements demonstrates the capability of LES combined with accurate models to predict the NRPD effects on both turbulent combustion and NOx emissions.

Kinetic roles of excited state species in the oxidation of n-pentane/air assisted by nanosecond-pulsed discharge

Despite the significant advancement in plasma assisted combustion recently, many of the underlying plasma/combustion interaction mechanisms remain unknown. Critical data such as cross sections for large hydrocarbons and reaction rate constants involving excited species are still limited. To address these issues, a detailed plasma chemistry mechanism governing the oxidation processes in a n-pentane/air combustion mixture was proposed and studied by including a complete set of e-n-pentane cross section and excited state chemistry of n-pentane. The concentrations of alkane (CH4, C2H6, C3H8), alkene (C2H4, C3H6), methanol, NO2 and NH3 were measured by GC and a small amount of liquid products are qualitatively characterized by GC-MS. The electron-scattering cross sections of n-pentane were obtained by the R-matrix method. The rate constants of excited species of n-pentane which involved the chemical reactions were calculated via Fridman α-model and MMVT method. A linear increase in reactants consumption with increased voltages was observed experimentally, suggesting that n-pentane excitation by plasma was decoupled from the low-temperature chemistry. The kinetic mechanism accurately predicted the generation of alkane and hydrogen and captured the overall trend. However, it underestimated the generation of NH3 and NO2, indicating certain reaction pathways in NH3 and NO2 generation were missed. The results showed that because of the introduction nitrogen in the system, the excited states of the oxidant molecules O(1D), O(1S), N2(B) and N2(C) reacted with n-pentane to form fuel radicals via H-atom abstraction reactions RH + X* → R + XH. The excited species of n-pentane reacted with O, H, OH to form n-pentane radicals via RH* + X → R + XH, accordingly enhancing the chain initial reactions. Importantly, ammonia was produced in a n-pentane/air mixture with plasma assistance through the pathway of N2 → N(2D) → NH → NH2 → NH3. These results highlight strong roles of excited species in a complex n-pentane/air plasma chemistry system.

A numerical investigation of plasma-assisted ignition by a burst of nanosecond repetitively pulsed discharges

Nanosecond repetitive pulse discharges (NRP) are a promising technology to promote the ignition of a lean reactive mixture. The success or failure of ignition results from complex interaction phenomena between the plasma generated by the discharge and the properties of the turbulent flow. This work presents two approaches for modeling plasma-assisted ignition scenarios resulting from NRP discharges. The first consists of a low-order model based on dimensionless analysis, while the second involves a Large Eddy Simulation (LES) of the reactive turbulent flow that requires high-performance computing. Both methods are presented and successfully applied to an experimental setup, which was specifically designed to study the influence of flow operating conditions and electrical discharge properties on plasma-assisted flame ignition.The simple dimensionless analysis can identify coupled and decoupled regimes, which always lead to ignition success or failure, respectively. However, the model is too crude to predict the fine interactions between plasma kinetics, combustion chemistry, and flow dynamics that control the formation of the reactive core in partially coupled regimes. The LES provides a means to capture these complex interaction mechanisms. A quantitative analysis of the reactive kernel growth has been performed by numerically reconstructing the OH-PLIF signal measured by the camera. A very good agreement is observed, validating the numerical strategy for plasma assisted combustion.

How pulse energy affects ignition efficiency of DBD plasma-assisted combustion

This work aims to find how coupled energy per pulse influences the ability of a pulsed dielectric barrier discharge (DBD) plasma to ignite fuel-lean methane–air flow. For that, experiments are performed on a custom-built DBD flow reactor with a variable dielectric thickness and the discharge is operated by bursts of 10 ns duration pulses at 3 kHz repetition rate. With an increase in dielectric thickness, we observe that the coupled energy per pulse decreases even though applied voltage conditions are similar and so more pulses are required to ignite the lean mixture. Interestingly, we observe a significant increase in the minimum ignition energy (MIE) with an increase in the thickness beyond 3 mm. Moreover, the ignition kernel growth rate is much slower in the thicker dielectric cases even though total energy coupling per burst is similar. This phenomenon is investigated further by evaluating plasma parameters using electrical and optical diagnostics. Effective dielectric capacitance, discharge current, and voltage drop across the gas gap are derived from an equivalent circuit analysis, whereas plasma gas temperature and effective reduced electric field ( E/N ) are estimated from optical emission spectroscopy. From these analyses, we conclude that a thicker dielectric limits the discharge current and so the plasma filament temperature. For more than 3 mm thick dielectric cases, the filament heating per pulse is too low to achieve strong enough plasma pulse-to-pulse coupling which eventually leads to higher MIE and slower ignition kernel growth rate or the inability to ignite at all.

Effect of a single nanosecond pulsed discharge on a flat methane–air flame

Successful implementation of plasma-assisted combustion in applied thermal processes heavily relies on how the plasma can be formed as it interacts with the reactive flow and what the effects are of such a plasma on the combustion process. The current study is an experimental investigation of a plasma-assisted lifted flat methane–air flame by a nanosecond pulsed discharge at atmospheric pressure. The nanosecond pulsed discharge, with a pulse duration of 4 ns and an amplitude of 30 kV to 50 kV, is used to stimulate the flame with a repetition rate of 1 Hz. The flame/plasma interactions are investigated with electrical and optical/laser diagnostics to study plasma-formation and its effect on the temperatures and formaldehyde formation. The flame speed seems to be accelerated for tens of milliseconds after the plasma stimulation, without noticeable gas temperature increase at the flame front and in the post-flame region. Formaldehyde is formed in the unburnt region while there is a slight increase in formaldehyde signal in the preheat zone. These results show that a volumetric effect of plasma-assisted combustion can be achieved with a short nanosecond plasma from a single excitation.

A Review of Current Advances in Ammonia Combustion from the Fundamentals to Applications in Internal Combustion Engines

The energy transition from hydrocarbon-based energy sources to renewable and carbon-free energy sources such as wind, solar and hydrogen is facing increasing demands. The decarbonization of global transportation could come true via applying carbon-free fuel such as ammonia, especially for internal combustion engines (ICEs). Although ammonia has advantages of high hydrogen content, high octane number and safety in storage, it is uninflammable with low laminar burning velocity, thus limiting its direct usage in ICEs. The purpose of this review paper is to provide previous studies and current research on the current technical advances emerging in assisted combustion of ammonia. The limitation of ammonia utilization in ICEs, such as large minimum ignition energy, lower flame speed and more NOx emission with unburned NH3, could be solved by oxygen-enriched combustion, ammonia–hydrogen mixed combustion and plasma-assisted combustion (PAC). In dual-fuel or oxygen-enriched NH3 combustion, accelerated flame propagation speeds are driven by abundant radicals such as H and OH; however, NOx emission should be paid special attention. Furthermore, dissociating NH3 in situ hydrogen by non-noble metal catalysts or plasma has the potential to replace dual-fuel systems. PAC is able to change classical ignition and extinction S-curves to monotonic stretching, which makes low-temperature ignition possible while leading moderate NOx emissions. In this review, the underlying fundamental mechanism under these technologies are introduced in detail, providing new insight into overcoming the bottleneck of applying ammonia in ICEs. Finally, the feasibility of ammonia processing as an ICE power source for transport and usage highlights it as an appealing choice for the link between carbon-free energy and power demand.

(Invited) Plasma-Assisted Ammonia Combustion and Flare Gas Reforming to Enhance Reactivity and Control Emission

Increasing emphasis on the de-carbonization of energy production has led researchers to consider carbon-free, renewable, and green fuels such as hydrogen (H2) and ammonia (NH3). While H2 suffers from the major challenges of production difficulties, transportation, and storage, NH3 is plagued with challenges of low flame speeds causing unstable flames, high autoignition temperatures resulting in longer ignition delays, narrow flammability limits, and higher levels of NOx emission. Among the different solutions to overcome these challenges of NH3 combustion, non-equilibrium plasma-based igniters are significant owing to the promotion of localized volumetric ignition kernel development by both thermal and chemical assistance. Computational investigation of plasma-assisted combustion of ammonia-air mixtures in constant volume and constant pressure reactors are conducted, to determine the impact of operating conditions on ignition delays and NOx emissions. A mechanism has been assembled in this work using well-validated plasma reactions of NH3 with O2 and N2, alongside plasma kinetics of air from the literature. Subsequently, the newly developed mechanism was used to investigate the plasma-assisted oxidation of NH3. In particular, the impact of the reduced electric field (E/N), equivalence ratio, pressure, pulse frequency, and energy density on the ignition delays and NOx emission were investigated. A Global Pathway-based Analysis algorithm for plasma-assisted systems (PGPA) is used to analyze the nanosecond pulsed nonequilibrium plasma-assisted combustion of NH3/air mixtures. Firstly, a faster ignition and lower production of NOx are observed in the case of plasma discharges compared to thermal energy deposition, owing to the enhanced production of OH radicals and the early reforming of NH3 to produce N2 and H2 with plasma, respectively. At lower reduced electric fields (E/N), PGPA analyses elucidated the significance of gas heating due to vibrational-translational cycles of NH3 and N2 on the increased reactivity of NH3/air mixtures as compared to ignition at a higher E/N. The fuel-lean mixture is observed to exhibit higher production of NOx than stoichiometric and fuel-rich mixtures, resulting from plasma chemistry involving oxygen radical and electronic excited states of N2. Higher rates of collisional quenching at higher pressures during the inter-pulse gaps are found to result in a lesser amount of electronically excited states of N2 and O2, resulting in lower production of air-bound NOx during the pulses.Complementing combustion enhancements, the study also considers the role of plasma-assisted systems in gas reforming, thereby imparting specific desired characteristics lacking in the original mixture. For instance, plasma-assisted reforming can be utilized to control emissions by reforming specific emission precursors or by improving the gas reactivity to promote clean combustion. Natural gas associated with oil wells and natural gas fields is a significant source of greenhouse gas emissions and airborne pollutants. Flaring/burning of the associated gas removes greenhouse gases like methane (CH4) and other hydrocarbons. Our study explores the possibility of enhancing the flaring of associated gas mixtures (C1 – C4 alkane mixture) using nanosecond pulsed non-equilibrium plasma discharges. A well-studied conventional combustion chemistry for small alkanes is 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 nonequilibrium plasma-assisted reforming and subsequent combustion of the flare gas mixture diluted with N2 at different conditions. The results indicate an enhanced production of H2 and C2H4 in the reformed gas mixture, owing to the electron-impact dissociations of alkanes and subsequent H-abstractions and recombination reactions, thereby resulting in a mixture of CH4, H2, C2H4, C2H2, and other unsaturated C3. The reformed mixture exhibits significantly high reactivity as exhibited by their increased flame speeds and shorter ignition delays. The reformed mixture is also observed to promote increased CH4 destruction levels and complete flaring, thereby reducing the emissions of CH4 and other hydrocarbons.

Plasma-Assisted Ammonia Combustion—Part 2: Combustion of Ammonia in Oxygen

Plasma-Assisted Ammonia Combustion—Part 2: Combustion of Ammonia in Oxygen

Numerical Studies on Hydrogen Production from Ammonia Thermal Cracking with Catalysts

To explore and optimize the process of hydrogen production from plasma-assisted ammonia-cracking, a tubular ammonia-cracking on-site hydrogen production device with plasma-assisted ammonia combustion flue gas as the heat source was developed. Using the Temkin–Pyzhev kinetic model and the local thermal equilibrium (LTE) hypothesis, the effects of operating conditions, such as combustion flue gas temperature and ammonia flow rates, on ammonia-cracking efficiency were investigated. The numerical results are quantitatively consistent with the experiment. Ammonia cracking efficiency is notably influenced by the initial combustion gas temperature. When the gas velocity of the cracking system is less than or equal to 0.03 m/s, the cracking rate increases by 63% when the inlet temperature of the heat pipe changes from 700 K to 800 K. The cracking rate of ammonia decreased with the increase of ammonia flow rate, and this trend reached the maximum and began to weaken when the flow rate was 0.3 m/s. Longer catalyst bed length does not always mean higher cracking efficiency; the length of the cracking tube over 0.6 m shows little effect on cracking efficiency. Response surface methodology was used to conduct multi-factor analysis of the three main factors affecting the cracking rate of the cracker, namely, the temperature of the heating tube, the flow rate of flue gas in the heating process, and the inlet flow rate of the catalytic bed. It was found that the flow rate of the catalytic bed was the most significant factor affecting the cracking rate, which could be used as the main control method. The numerical results would provide technical guidance for industrial applications of on-site hydrogen production devices from ammonia decomposition.

Plasma-based global pathway analysis to understand the chemical kinetics of plasma-assisted combustion and fuel reforming

The Global Pathway Analysis (GPA) algorithm helps analyze the chemical kinetics of complex combustion systems by identifying important global reaction pathways connecting a source species to a sink species through various important intermediate species (i.e., hub species). The present work aims to extend GPA algorithm to plasma-assisted combustion and fuel reforming systems to identify the dominant global pathways in such systems at various conditions. In addition, the present study extends the ability of GPA algorithm to identify reaction cycles involving the excitation of high-concentration species (e.g., O2, N2, and fuel) to their vibrational and electronic states and the subsequent de-excitation to their ground state, based on their significance on the reactivity of plasma-assisted systems in terms of gas heating and radical production. Provisions are made in the GPA algorithm to evaluate the reactivity of identified reaction pathways and cycles based on the element-flux transfer (i.e., dominance), heat release, and radical production rate. The newly developed Plasma-based Global Pathway Analysis (PGPA) algorithm is then used to analyze the plasma-assisted combustion of ammonia and reforming of methane. The PGPA analyses elucidated the significance of vibrational-translational cycles on the reactivity of NH3/air mixtures. Further, analyses on the production of NO ascribed the early reforming of NH3 to N2 and H2 in impeding the production of NO during plasma-assisted NH3 ignition. Lastly, the enhanced reforming of CH4/N2 mixtures using plasma has been attributed to electron impact dissociation of CH4 when compared to thermal reforming. In contrast, conventional path-Flux analysis (PFA) was found to require significant manual effort and pre-analysis intuitions from expert knowledge, making it arduous to provide valuable insights into plasma chemistry. The user-friendly and automated nature of PGPA thus provides a valuable tool for assessing the kinetics of plasma-assisted systems helpful in analyzing and, further, a foundation in reducing plasma-assisted chemistry, without the needs of expert knowledge.

Efficiency analysis of ignition by Nanosecond Repetitively Pulsed discharges using a low-order model

Plasma-assisted combustion is an interesting method to promote the ignition of a lean reactive mixture instead of conventional spark plugs. Especially, Nanosecond Repetitively Pulsed (NRP) discharges technique is an energy-efficient way to initiate and control combustion processes. Ignition success or failure results from the competition between the discharge energy accumulation, the gas residence time in the discharge region, and the combustion chemistry. Plasma-assisted ignition is modeled here by a Perfectly-Stirred Reactor (PSR) whose volume represents the one surrounding the interelectrode region. NRP discharges are applied inside the reactor to initiate the combustion of the injected mixture. This model numerically identifies a plasma-assisted ignition efficiency map in terms of the amount of energy per pulse and the pulse repetition frequency, at low CPU cost. A criterion based on the residence time, interpulse time, and chemical time is introduced to predict the successful formation of a reactive kernel. This criterion is successfully validated by analyzing the plasma-assisted PSR solutions.

Large-Eddy Simulation of swirled flame stabilisation using NRP discharges at atmospheric pressure

In this work, the use of Nanosecond Repetitively Pulsed (NRP) discharges is investigated numerically to improve the stabilisation of the flame in a swirl burner. The studied configuration is the PACCI burner test rig set up at KAUST, in which it was experimentally demonstrated that NRP discharges can effectively enhance flame stability. Simulations are performed with the reactive compressible Navier–Stokes solver AVBP, using a recently developed phenomenological model for plasma-assisted combustion of methane-air premixed flame. The ability of the numerical model to reproduce the main flow behaviours is first assessed by comparison with PIV measurements in cold flow conditions. Then, a lean atmospheric pressure case (ϕ=0.67) without plasma actuation is simulated and compared with OH* chemiluminescence image from experiment. Both numerical and experimental results reveal an unstable turbulent flame, with intermittent attachment to the burner exit. Finally, two operating conditions with NRP discharges are simulated. The NRP discharges correspond to 10 kV pulses applied at a frequency of 20 and 30 kHz, respectively corresponding to a discharge power 0.72 and 1.17% of the thermal flame power. First, a significant stabilisation effect is observed when applying the discharges, which efficiently mitigate the flame lifting. This effect is quantitatively demonstrated by tracking the flame centre of gravity, which shows that the flame moves upstream under the influence of the plasma, in good agreement with experimental observations. Results also show that a net power gain is obtained by applying NRP discharges to combustion by comparing the thermal flame power to the plasma power. In particular, an increase of plasma actuation efficiency from 4 to 6 as been observed in the cases studied by increasing the plasma power.

The backward problem in plasma-assisted combustion: Experiments of nanosecond pulsed discharges driven by flames

Plasma technologies are a promising way of addressing a number of challenges in combustion, ranging from stabilization and flame-holding for hypersonic vehicles, to enabling low-emissions propulsion and power. Whereas most works in the literature have centered on the forward problem: the impact of the plasma on different combustion metrics, including static and dynamic flame stabilization; fewer studies have been devoted to the backward problem: or the significance of having a strongly inhomogeneous environment, often unsteady in time, on the discharge characteristics. In this perspectives article, the backward problem is addressed in a hierarchical manner. First, the implications of the discharge proceeding in an inhomogeneous background gas, with gradients in density and composition, and nonuniform flows, are discussed. Next, these foundation experiments are used as elementary building blocks to explain experiments of nanosecond pulsed discharges in dynamic combustion environments, including a transient laminar flame and a combustor undergoing dynamics. Finally, the strong coupling between the forward and backward problem is illustrated with an imaging study, using transparent electrodes, of a mesoscale premixed flame and a nanosecond pulsed dielectric barrier discharge. The experiments demonstrate the importance of considering the pulse-to-pulse evolution due to changes in the background environment when using plasma assistance in unsteady combustion processes, including active control of combustion dynamics.

A review of recent studies and emerging trends in plasma-assisted combustion of ammonia as an effective hydrogen carrier

Recently, ammonia is getting more attractive as a potential alternative fuel for future power generation and transportation purposes due to its ability to reduce consumption of fossil fuels, soot, CO2 emissions, and hydrocarbon pollutants. In the recent past, several studies aimed to the development of ammonia combustion systems have been conducted. However, ammonia combustion systems face several challenges, such as poor ignition timings, lower burning velocity, low energy density, shorter flammability limits than hydrocarbons. These issues are compounded by the significant increase in NOx emissions, which makes practical application of ammonia challenging.Various conventional methods, such as blending ammonia with other hydrocarbons and hydrogen, have been employed to improve combustion performance and reduce NOx emission. Meanwhile, it increased the engine complexities and at the same time, it raised CO2 and NOx emissions. Recently, plasma-assisted combustion (PAC) has emerged as a promising technology to boost the ammonia combustion process by improving ignition delay timings, increasing flame speed, extending flammability limits, and reducing NOx emissions. In recent years, plasma-assisted combustion (PAC) has emerged as a promising technology to enhance the ammonia combustion process by improving ignition delay timings, increasing flame speed, extending flammability limits, and reducing NOx emissions. Nevertheless, only a few studies on plasma-assisted ammonia combustion (PAAC) are available in the literature.This review paper aims to summarize the latest advancements in the field of PAAC during the last years, including progress in the development of numerical models and experimental studies. The paper highlights the detailed procedure of PAAC numerical modeling and the limitations of numerical models. Finally, the latest numerical and experimental developments of PAAC have been discussed.

Plasma-Assisted Ammonia Combustion—Part 1: Possibilities of Plasma Combustion of Ammonia in Air and Oxygen

Plasma-Assisted Ammonia Combustion—Part 1: Possibilities of Plasma Combustion of Ammonia in Air and Oxygen

Numerical analysis of a nanosecond repetitively pulsed plasma-assisted counterflow diffusion flame

A computationally efficient model is proposed to analyze plasma-assisted combustion using nanosecond repetitive pulsed (NRP) plasmas. The NRP plasma discharge is placed in the oxidizer stream of a counter-flow diffusion flame. The effect of changing the flow rate and the pulse repetition frequency (PRF) of a continuous NRP plasma discharge on the temperature and species profiles of a counter-flow diffusion flame is investigated numerically. The results confirm that oxygen atom and nitrogen vibrational states are the most important species to enhance combustion. The results also show that kinetic effects are much more significant for higher PRF and lower pulse voltage. In addition, when steady plasma profiles are used instead of unsteady plasma profiles, the extinction strain rates increase by 25.8%, 21.1%, and 10.8% for PRF equal to 1, 2, and 4 kHz, respectively.