Detailed Kinetic Model Research Articles

Fossil Diesel, Soybean Biodiesel and Hydrotreated Vegetable Oil: A Numerical Analysis of Emissions Using Detailed Chemical Kinetics at Diesel Engine Like Conditions

Nowadays, emissions from internal combustion engines are a relevant topic of investigation, taking into account the continuous reduction of emission limits imposed by environmental regulatory agencies around the world, obviously as the result of earnest studies that have pointed out the impact on the human health of high levels of contaminants released into the environment. Over recent years, the use of biofuels has contributed to attenuating this environmental issue; however, new problems have been raised, such as NOx emissions tend to increase as the biofuel percentage in the fuel used in engines increases. In this research, the emissions of a compression ignition internal combustion engine modeled as a variable volume reactor with homogeneous combustion were numerically investigated. To analyze the combustion process, a detailed kinetics model tailored specifically for this purpose was used. The kinetics model comprised 30,975 chemical reactions involving 691 chemical species. Mixtures of fuel surrogates were then created to represent the fuel used in the Brazilian fuel marketplace, involving (i) fossil diesel—“diesel A”, (ii) soybean diesel—“biodiesel”, and (iii) hydrotreated vegetable oil— “HVO”. Surrogate species were then selected for each of the aforementioned fuels, and blends of those surrogates were then proposed as mixture M1 (diesel A:biodiesel:HVO—90:10:0), mixture M2 (diesel A:biodiesel:HVO—85:15:0), and mixture M3 (diesel A:biodiesel:HVO—80:15:5). The species allowed in the kinetics model included all the fuel surrogates used in this research as well as the target emission species of this study: total hydrocarbons, non-methane hydrocarbons, carbon monoxide, methane, nitrogen oxides, carbon dioxide, soot, and soot precursors. When compared to experimental trends of emissions available in the literature, it was observed that, for all the proposed fuel surrogates blends, the numerical approach performed in this research was able to capture qualitative trends for engine power and the target emissions in the whole ranges of engine speeds and engine loads, despite the CO and NOx emissions at specific engine speeds and loads.

Experimental and kinetic study of methanol/ethanol assisted oxidative degradation of ammonia in supercritical water

Ammonia is a refractory intermediate during supercritical water oxidation (SCWO) of nitrogen-containing wastes, and alcohols are usually introduced as auxiliary fuels to accelerate its degradation. The kinetics of methanol/ethanol assisted oxidative degradation of ammonia in supercritical water have been investigated in a flow reactor, covering alcohol-to-ammonia ratios of 0.2–2.0. During SCWO of ammonia-methanol mixtures, ammonia was mostly converted to N2, with N2O as the main by-product. Increasing methanol concentration facilitated effectively the degradation of ammonia. For the cases with ethanol assistance, high concentrations of HCN were detected at the investigated temperature. Increase in ethanol concentration enhanced ammonia conversion, but had a non-monotonic influence on N2 production. A detailed chemical kinetic model was developed by integrating the nitrogen chemistry with methanol/ethanol mechanisms. The model performance was further validated by comparing to the present and literature data. The model reproduced the ammonia conversions at different conditions fairly well, but overpredicted the N2 yield and underpredicted the NO2 and HCN yields slightly. Based on the model, reaction mechanism was inferred and important elementary steps were identified through kinetic analyses. Finally, the influence of process parameters on ammonia degradation rate was numerically explored. This study is expected to facilitate the application of SCWO technology for N-containing wastes treatment.

Investigating the formation of soot in CH4 pyrolysis reactor: A numerical, experimental, and characterization study

Methane pyrolysis is a promising method for eco-friendly hydrogen production, but soot formation and carbon interaction pose challenges for scaling up. Therefore, understanding the dynamics of soot formation and carbon deposition is crucial. This study delves into the intricacies of soot formation in methane pyrolysis under industrially relevant conditions, namely operations at atmospheric pressure, employing a H2:CH4 ratio of 2 and exploring a range of hot zone temperatures (1473 K, 1573 K, 1673 K, and 1773 K) with a 5 s residence time. Utilizing a detailed gas-phase kinetic model with direct carbon deposition reactions, the research adopts the method of moments coupled with a one-dimensional plug flow reactor model to simulate soot formation. The model is validated by characterizing soot particles that were produced in a pyrolysis reactor by means of transmission electron microscopy, Dynamic light scattering (DLS), and Raman spectroscopy. Results show that lower temperatures lead to nucleation-dominated growth, whereas higher temperatures significantly restrain particle growth due to carbon deposition. DLS data indicate a complex balance between particle growth and deposition processes. These findings provide insights into operational parameters that can enhance reactor performance and sustainability in hydrogen production processes by mitigating soot and carbon deposition.

A detailed chemical kinetic model for methanol and ammonia co-oxidation under hydrothermal flames: Reaction mechanism and flame characteristics

A detailed chemical kinetic model for ammonia and methanol co-oxidation under hydrothermal flames was established with pressure and thermodynamic corrections. Simulation model was validated by comparing with experimental temperature rise, and methanol and ammonia removal efficiencies. Species evolutions, reaction paths, and reaction sensitivities for pure ammonia combustion, and ammonia and methanol co-oxidation under hydrothermal flames were analyzed. Ammonia concentration begins to decrease only when methanol is consumed in a certain amount in the ammonia and methanol co-oxidation under hydrothermal flames, indicating the addition of methanol promotes the degradation of ammonia. Moreover, reaction heat is more conductive to ignition and the conversion of ammonia to nitrogen than active free radicals provided from methanol. The ignition delay time presents a minimum as a function of ammonia/methanol concentration ratio, with the minimum values of ignition delay time present at approximately ωNH3/ωCH3OH = 1 for different methanol concentrations. Higher preheating temperatures favor more NOX but less N2O formation, while higher ammonia concentrations favor both NOX and N2O formations. The presence of ammonia increases the laminar flame speed and permits a lower extinction temperature, indicating the mixture of methanol and ammonia can improve the stability of hydrothermal flames.

Species selection for automatic chemical kinetic mechanism generation

AbstractMany important chemical kinetic systems require detailed chemical kinetic models to resolve. These detailed kinetic models can involve thousands of species and hundreds of thousands of chemical reactions, making them difficult to construct by hand. Modern automatic mechanism generation algorithms can mostly be divided into two classes: rule and rate based. Rule‐based generators choose species based on user defined constraints on species and reaction classes. Rate‐based generators generate a much larger set of potentially important species and reactions and then choose which ones to add based on running simulations of species and reactions deemed important and calculating the flux to potentially important species. In principle, the latter is preferable, as it requires the user to make far fewer assumptions about what is important in the system. However, while the effectiveness of the rate‐based approach has been demonstrated in a wide variety of systems, it has also been demonstrated to have difficulty picking up important low‐flux chemistries. Here we present a discussion of the challenges associated with rate‐based mechanism generation and new algorithms that are able to efficiently mitigate these challenges improving species selection during mechanism generation in a set of case studies.

Comparative Study of n-C5 Bond Dissociation Energies and H-Atom Abstraction via H for Alkane, Alcohol, Methyl Ether, Nitroso, Nitro, Nitrite, and Nitrate.

Energetic materials have a wide range of applications, for many of which new materials are constantly developed. For understanding how energetic materials are chemically converted, it is essential to systematically understand how relevant functional groups affect the stability and properties of such materials. Here, the impact of nitroso, nitro, nitrite, and nitrate functional groups on a pentyl moiety is studied theoretically, focusing on bond dissociation energies and H atom abstraction via Ḣ. The nitroso group is found to imply the strongest effects, while the nitro group appears to exert a stabilizing effect on the pentyl moiety. Importantly, the nitrogenated functional groups generally stabilize the pentyl moiety, in contrast to alcohol and methyl ether functional groups. Therefore, it is concluded that using analogies to the chemistries of the latter two functional groups for chemical kinetic modeling of nitrogenated functional groups is not adequate. Based on the presented bond dissociation energies and rate coefficients, it is to be expected that unimolecular bond fissions at the nitrogenated functional groups will dominate over a wide temperature range. Building on the provided data, future detailed chemical kinetic modeling efforts for nitroso, nitro, nitrite, and nitrate compounds can be aided or initiated.

Study of peak Laminar Burning Velocity of several syngas compositions at different temperatures

In the context of the current energy transition, the use of biomass-derived syngas (BDS) is often recognized as a fundamental path towards decreasing fossil fuel dependency and greenhouse gas emissions. However, hydrogen-containing BDS are prone to flame instability problems. More efforts are being carried out aiming at efficiently adopting BDS in industrial combustors with CH4 co-firing or inert gas dilutions by exploring accurate knowledge of burning velocity. To do so, a deeper knowledge of the syngas combustion behaviour is strictly necessary. The objective of this study fits in this framework: in particular, a computational study has been carried out to evaluate kinetic models and present fresh insights on the effects of varying syngas mixtures such as CO/H2, CO/H2/CO2 and CO/H2/CH4 on Laminar Burning Velocity (LBV) and peak LBV location (ΦLBV=max). In-detail chemical kinetic simulations of equimolar (CO: H2 = 1:1) forestry waste syngas were systematically carried out taking advantage of the open-source CANTERA solver. Three detailed kinetic models i.e., newly released FFCM-2, USC mech II, and modified GRI mech III were implemented to report accurate flame parameters at 1 bar and different temperature levels (from 300 K up to 450 K). On comparing the results with experiments, FFCM-2 proved to be a good kinetic model for the considered syngas mixtures CO/H2, CO/H2/CO2 and especially for CO/H2/CH4 for mixtures containing a limited share of 30 % methane at normal and moderately elevated temperature at 0.4 ≤ Φ ≤ 2.1. The USC mech II performed very well for CO/H2, and CO/H2/CO2, while the modified GRI mech III model also gave agreeable predictions for CO/H2/CH4 mixture having rich methane content. Additionally, when varying syngas composition analysis was conducted at different temperatures, the progressive CO2 dilution and CH4 addition of up to 30 % reduced the peak LBV and moved the peak LBV locations (ΦLBV=max) towards lean ER conditions with 9 % and 40 % reductions, respectively; however, only the latter effect was enhanced at the elevated initial temperature. Furthermore, sensitivity analysis of respective syngas mixtures is reported at normal and elevated temperatures to explore the most sensitive intermediate reactions relative to LBV. The shift of peak LBV locations and their enhancement at elevated temperatures also open the research path to study the underlying impacts on the flame modes/regimes and structure, especially CO emissions pathways in syngas with 30 % of CH4 and CO2 additions.

Kinetic modeling of carbonaceous particle morphology, polydispersity and nanostructure through the discrete sectional approach

Carbon nanoparticle (CNP) formation from hydrocarbons combustion is of high interest not only for the study of pollutant (soot) emissions, but, above all, in the area of advanced materials. CNP optical and electronical properties, relevant for practical applications, significantly change with their size, morphology, and nanostructure. This work extends a detailed soot kinetic model, based on the discrete sectional approach, to explicitly incorporate the description of CNP polydispersity, maintaining the CHEMKIN-like format. The model considers various nanosized primary particles, generated from liquid-like counterparts through the carbonization process, which successively grow or aggregate forming fractal structures. The model is validated against experimental measurements from the literature including CNP volume fraction, several morphological characteristics, number density and particle H/C ratio. Data are taken from 19 laminar flames, in different configurations (counterflow diffusion flames, premixed flat flames established on the McKenna-type burner and burner-stabilized stagnation flames) and over a wide range of operating conditions (P=1–10 atm, Tmax=1556-2264 K). The model captures the measured trends of all the analyzed CNP properties as a function of equivalence ratio, residence time and fuel type in premixed flames, and pressure and strain rate in counterflow flames. Model deviations from the experiments are discussed, also in comparison with other state-of-the-art soot models based on different approaches. Sensitivity analyses are performed on carbonization, coalescence, and aggregation rates, which have the largest impact on CNP morphology and are characterized by larger uncertainty compared to elementary chemical pathways.

The pronounced NTC behavior of 1,2,4-trimethylbenzene at high-pressure oxidation

This study presents experimental and modeling results of the 1,2,4-trimethylbenzene (T124MBZ) oxidation in a jet-stirred reactor at equivalence ratios of 0.4 and 2.0, temperature range of 450–1000 K, and pressure of 12.0 atm. Compared with the oxidation at atmospheric pressure, a pronounced negative temperature coefficient (NTC) behavior of T124MBZ was observed between 622 K and 773 K under fuel-lean condition. A detailed chemical kinetic model involving 865 species and 5092 reactions was developed. In addition, the model was validated against experimental results of laminar burning velocities and ignition delay times. The present model reasonably reproduces these experimental data. The dominant consumption channels for T124MBZ are H-abstraction reactions on methyl groups by OH radicals. The H-abstraction reactions on the 1- and 2- methyl sites by OH radicals are the most promoting in pre- and mid- NTC phases, and H2O2(+M) = 2OH(+M) is the most promoting in the post-NTC phase, while the reaction on the 4-methyl site is the most inhibiting across pre-, mid-, and post-NTC phases. This difference arises from the fact that the dominant consumption pathway for 2,4-dimethylbenzyl and 2,5-dimethylbenzyl involves H-transfer, while the 4-methyl site cannot undergo an H-transfer reaction due to the absence of adjacent methyl groups. The competition between the two consumption channels of ·QOOH radicals (decomposition and second O2 addition), resulting in the reduction of OH radicals as temperature increases, leads to diminished OH production. This causes the emergence of pronounced NTC behavior at high pressure.

An experimental and modeling study of propane oxidation kinetics in low temperature supercritical water

Propane oxidation in supercritical water was investigated at iso-thermal iso-baric conditions using a batch reactor facility. Mixtures were comprised of 0.014 % propane by volume with an equivalence ratio of 0.8 and a total density of 222 mg/mL or 610 mg/mL. Reaction times ranged from 8 to 30 min for a temperature of 375ºC at 220 or 400 bar, or 400ºC at 220 bar. Major reaction products were CO and CO2 and minor products were propene, acetone, ethene, ethanol, methane, methanol and hydrogen. New detailed chemical kinetic models were developed by combining and refining existing models using genetic optimization. Model predictions exhibited excellent agreement with experimental observations, and indicated that rates of H-abstraction and OH addition reactions involving alkanes and alkenes are affected by the supercritical water environment. Model accuracy was highly sensitive to the rates of CH3O2H = CH3O + OH and CH3 + H2O2 = CH4 + HO2.

Deep insights on the Co-pyrolysis of tea stem and polyethylene terephthalate (PET): Unveiling synergistic effects and detailed kinetic modeling

This study investigates the co-pyrolysis of tea stem (TS) and polyethylene terephthalate (PET), with an emphasis on their interactions during the pyrolysis process. The effects of heating rate and TS/PET ratio on synergy of TS with PET pyrolysis was examined using thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FT-IR) techniques. The experimental runs were conducted at three mixing ratios (i.e., 3:1, 1:1, and 1:3) of TS to PET and four heating rates (i.e., 10, 15, 20, and 25 °C/min). The results show that the TS/PET ratio is the main factor determining the synergy of the two components. In particular, the mixture of 25 % TS and 75 % PET exhibited the least antagonistic effects, while the mixture of 75 % TS and 25 % PET had strong synergistic positive and negative effects. Moreover, the FT-IR analysis of the co-pyrolysis process suggested the presence of oxygenated compounds, including hydroxyl and carbonyl groups, indicating the potential formation of aromatic hydrocarbons in the co-pyrolysis process. A new kinetic modeling approach including seven independent parallel reactions (IPR), was developed to illustrate the complex decomposition behavior of the TS-PET mixture. The outcome of kinetic modeling using nonlinear multivariate optimization resulted in a quality of fit ranging from 1.38 % to 3.55 %. These results accurately depict the experimental evidence and offer useful understanding of the reaction kinetics and the overall influence of the mixing ratio on the kinetic triplets.

Experimental and modeling investigation of the oxidation of n-hexylbenzene: Insight into the formation of low-temperature intermediates

As vital components in transportation fuels, an in-depth understanding of the oxidation mechanism of n-alkylbenzenes is pivotal for minimizing pollutant emissions during combustion processes. However, previous research was mostly focused on high-temperature oxidation, while investigations on low-temperature oxidation of long-chain n-alkylbenzenes remains scarce. In this work, n-hexylbenzene (C12H18) was selected to conduct low-temperature oxidation experiments in a jet-stirred reactor. A series of crucial intermediates and products were detected and then quantified by the synchrotron vacuum ultraviolet radiation photoionization mass spectrometry (SVUV-PIMS). In particular, characteristic aromatic oxygenated intermediates with compositions of C12H18Oy, C12H16Oy, C12H14Oy and C12H12Oy (0 ≤ y ≤ 3) were measured, which reveal the occurrence of first O2 addition, second O2 addition, and sequential oxidation reactions. To disclose the crucial reactions that control the fuel decomposition and formation of oxygenated intermediates, a detailed kinetic model of n-hexylbenzene was developed. This model was further utilized to explore the oxidation behaviors of C6 to C12n-alkylbenzenes. It was revealed that n-hexylbenzene exhibits the strongest low-temperature oxidation reactivity, while C6C10n-alkylbenzenes display little reactivity under present conditions. In conclusion, the reasonable performance of this model in predicting the oxidation behaviors of n-alkylbenzenes indicates its potential application in elucidating the low-temperature oxidation chemistry of heavier n-alkylbenzenes.

Development of Detailed and Reduced Chemical Kinetic Models for Ammonia Gas Turbines

Abstract The power generation sector has been recently moving towards decarbonization and there is an increased interest in replacing conventional fossil fuels with fuels that produce reduced/zero carbon emissions. One such fuel is ammonia (NH3). However, ammonia is hard to ignite, has a low flame speed, and produces a significantly large amount of nitrogen oxide (NOx) emissions. Hence, using 100% ammonia as fuel in gas turbines requires significant modifications and the development of novel combustors. Blending hydrogen with ammonia, however, helps in having better control over the combustion properties. Before utilizing hydrogen-blended ammonia in an actual gas turbine combustor, thorough simulation studies are required to evaluate its performance, possible hazards, and emissions. The literature lacks well-validated chemical kinetic models for the combustion of hydrogen-blended ammonia for undiluted mixtures at gas turbine-relevant conditions (~20 bar). Hence, in this work, we develop a detailed chemical kinetic model for hydrogen blended ammonia combustion and validate it with a wide range of experimental data for both dilute and undiluted mixtures relevant to gas turbine operating conditions. The detailed chemical kinetic mechanism was reduced to a smaller version (32 species mechanism) without significant loss in accuracy using the direct relation graph with error propagation (DRGEP) and full species sensitivity analysis. The resultant mechanism can predict a wide range of experimental results with the least cumulative error and will be a valuable tool in CFD simulations that will enable the development of gas turbines for zero-carbon power generation.

Enhanced methylene blue dye sequestration by carbon-embedded mesoporous zinc oxide nanoparticles fabricated utilizing Aloe barbadensis miller biowaste: Batch optimization, simulation modeling, and textile effluent feasibility

The present study reports novel carbon-embedded mesoporous zinc oxide nanoparticles (ZnO/C NPs) utilizing Aloe barbadensis miller (Aloe vera) biowaste extract as size-reducing agent and bio-stabilizer via a one-pot green fabrication approach. The fabricated nanoparticles were carbonized at 250 °C and characterized using FTIR, UV-Vis, ZPA, TEM, SEM/EDX, XRD, BET, and TGA techniques. Using Brunauer, Emmett, and Teller's theory, the ZnO/C NPs specific surface area was determined to be 63.25 m2/g, and the average pore diameter (3.46 nm) was in the mesoporous range. Fabricated ZnO/C NPs have an un-uniform size distribution, with an average crystallite size of 17.37 nm. The methylene blue (MB) dye adsorption of mesoporous ZnO/C NPs was studied in batch mode experiments at 37 °C using an aqueous solution. Detailed isotherms and kinetics modeling were performed, and it established that the Langmuir isotherm and Pseudo second order kinetic correctly fit the optimized MB dye adsorption data due to their higher correlation coefficients than other analyzed models. The Langmuir isotherm-based monolayer adsorption was found to be 105.26 mg/g. The pseudo second order kinetic best explains the adsorption reaction, indicating that the chemisorption mechanism is more likely to regulate the MB dye adsorption. Further, thermodynamics parameters showed that the MB dye adsorption onto ZnO/C NPs was spontaneous, endothermic, and accompanied by increased entropy. The ZnO/C NPs demonstrated remarkable MB dye sequestration from aqueous solution upto four reusability cycles, with regenerability of ≥84.52 %. Furthermore, feasibility study revealed an outstanding decolorization efficacy of MB dye upto 58.18 % from textile effluent, establishing mesoporous ZnO/C NPs as viable, environment-friendly, and cost-effective remedies for textile wastewater treatment.

Revisit the PAH and soot formation in high-temperature pyrolysis of methane

As the major component of natural gas, most basic and stable hydrocarbon molecule, methane (CH4) is an important source in industrial processing. The polycyclic aromatic hydrocarbons (PAHs) and the soot produced in the utilization of CH4 also attract particular attention. In this work, CH4 pyrolysis was studied with gas chromatographs (GCs) and a gas chromatography-mass (GC-MS) spectrometry within the temperature range of 1073–1623 K at atmospheric pressure. Mole fraction profiles of 11 species, including CH4, C2H2, C2H4, C2H6, aC3H4, pC3H4, C3H6, C4H6, C6H6, C10H8 (naphthalene) and C12H8 (acenaphthylene) were quantified. C10H8 and C12H8 were detected during the pyrolysis of CH4. A detailed kinetic model involving 300 species and 1840 reactions was proposed with reasonable prediction against the measured data. During pyrolysis, CH4 is mainly consumed by the H-abstraction reactions. 2CH3=C2H5+H and C9H7+C3H3=A2R5+H2 are the two major reactions controlling CH4 consumption according to sensitivity analysis. In addition, the soot generated in the reactor was analyzed by Raman spectroscopy and Scanning Electron Microscope (SEM), showing the morphology and structural characteristics of the soot. The detailed formation and consumption pathways of PAHs such as naphthalene and acenaphthylene were analyzed. This work will enrich the understanding of CH4 pyrolysis and promote experimental and theoretical studies on the formation of PAHs and soot.

Mechanism and kinetics study of the chemically initiated oxidative polymerization of hexafluoropropylene

AbstractChemically initiated oxidative polymerization stands out as the most suitable method for the large‐scale and controllable synthesis of perfluoropolyether (PFPE). However, the mechanism and related reaction kinetics of this synthesis reaction remain elusive. In this study, PFPE was synthesized through the copolymerization of hexafluoropropylene and oxygen, initiated by fluorine. Subsequently, the synthesis mechanism of this chemically initiated oxidative polymerization was first explored using density functional theory. Simulation results yielded a comprehensive reaction network of the synthesis process, including chain initiation, propagation, decomposition, transfer, and termination. Meanwhile, a detailed kinetic model was constructed based on theoretical reaction rates of relevant elementary reactions. The effects of reaction operating conditions on the molecular weight of PFPE were experimentally investigated, with results in good agreement with the kinetic model. This work stablishes a solid foundation for optimizing and controlling the PFPE synthesis process.

Prediction of Soot in an RQL Burner Using a Semi-Detailed Jeta-1 Chemistry

Abstract The present work proposes a methodology to include accurate kinetics for soot modeling taking into account real fuel complexity in Large Eddy Simulation of aeronautical engines at a reasonable computational cost. The methodology is based on the construction of an analytically reduced kinetic mechanism describing both combustion and gaseous soot precursors growth with sufficient accuracy on selected target properties. This is achieved in several steps, starting from the selection of the detailed kinetic model for combustion and soot precursors growth, followed by the determination of a fuel surrogate model describing the complex real fuel blend. Finally the selected kinetic model is analytically reduced with the code ARCANE while controlling the error on flame properties and soot prediction for the considered fuel surrogate. To perform all evaluation and reduction tests on canonical sooting flames, a Discrete Sectional Model for soot has been implemented in Cantera. The resulting code (Cantera-soot) is now available for the fast calculation of soot production in laminar flames for any fuel. The obtained reduced kinetic scheme is finally validated in a Rich-Quench-Lean burner of the literature in terms of soot prediction capabilities by comparison of LES coupled to the Lagrangian Soot Tracking model with measurements. Results show a significant improvement of the soot level prediction when using the reduced more realistic kinetics, which also allows a more detailed analysis of the soot emission mechanisms. This demonstrates the gain in accuracy obtained with improved reduced kinetics, and validates the methodology to build such schemes.

Kinetic insights into ammonia-hydrogen doped ignition and emission assisted by nanosecond pulsed discharge

Non-equilibrium plasma is applied for the first time to ignite the ammonium-hydrogen mixture and reduce the NOx/N2O emission with effect in this work. Gas chromatography (GC) experiments as well as a detailed kinetic model, including neutral molecules, free radicals, charged particles, vibratory excited states, and electron excited states, are integrated to investigate the kinetic process of ammonia-hydrogen doped ignition and NOx/N2O emission facilitated by nanosecond pulsed discharge. The numerical model closely matches the GC-measured values of NH3 consumption, H2 increase, and N2O production. Pathway fluxes of important species and sensitivity analysis of ignition delay time reveal that the addition of non-equilibrium plasma has an obvious promotion effect on ammonia and hydrogen-doped oxidation and ignition. The initial ignition temperature significantly impacts the ignition delay time, with a more pronounced plasma-promotion effect observed at lower temperatures. Conversely, as the hydrogen mixing ratio increases, the ignition delay time decreases, yet the generation of NO and N2O increases. This is attributed to the heightened production of H and NH through elementary reactions such as NH3+HNH2+ H2, H + O2O + OH, and OH + H2H + H2O. Nevertheless, NO and N2O emissions are reduced by 1-2 orders of magnitude with plasma assistance compared to auto-ignition. The reduction in NO emissions can be attributed to increased consumption in the pathway of NO + NH2N2 + H2O and decreased formation in the pathways of HNO + O2HO2 + NO and NH + NON2O + H. Additionally, it was discovered that the electron attachment dissociation reaction e + N2O → O− + N2 predominantly contributes to the reduction of N2O. These research findings significantly contribute to advancing our understanding of the kinetics involved in ammonia-hydrogen doped ignition and emissions, particularly with plasma assistance, for potential engine applications.

Piston reactor for chemical energy storage: Modeling study to explore electro-mechanical conversion route using propane feedstock

Within the context of renewables and chemical energy storage, this work aims to explore chemical reaction conversion through the electro-mechanical route which is different from the commonly employed electro-thermal and electro-chemical conversion methods. Piston reactor is a novel equipment concept that can couple the rotational movement from an electric motor to a reciprocating piston within an enclosed reaction chamber resembling the operation of an internal combustion engine. Exploration of a reactor technology still in the laboratory stage requires an assessment of reaction intermediate mixtures to identify potential leads. This work uses a systematic methodology to assess these intermediate mixtures beyond typical reactor yield metrics to include economic values as part of the decision-making toward identifying lead candidates. Rather than focusing on a specific target reaction or product, this work is carried out as a model-driven study to cover a wider range of conditions and product scenarios. Propane as the main feedstock is selected because it is easier to trigger in the piston reactor, it is not a complex feed, a detailed kinetic mechanistic model is available to study it, and most importantly it can generate a wide range of industrially relevant products to serve the purpose of this study. The study revealed that the highly endothermic propane pyrolysis reaction requires intake temperatures larger than 950 K which is impractical. Diluting the feed with argon is one way to lower this intake temperature and achieve desirable conversion. This however is impractical because of additional separation steps and reduced production capacity. Thermal coupling of propane pyrolysis with exothermic side reactions by co-feeding oxygen, water, or carbon dioxide are investigated and showed promising results. A diverse range of products are produced such as hydrogen, carbon monoxide, ethylene, and propylene, achieving high conversions (>90 %), while simultaneously generating useful work and process heat. Unconventional triggers such as using ozone to generate radicals and trigger ignition are investigated to further lower the intake temperature requirements. The explored solution space is then evaluated considering a new reactor metric as the value of products mixture stream. Regions of high-value products do not match those obtained using the traditional yield metrics. This shows the importance of what metrics to use for assessing reactors with wide range of reaction mixture intermediates as the piston reactor. Full economic analysis and optimization are the right direction in the future to properly assess the potential of piston reactor technology.

Experimental and numerical study of stabilized flame in inverse coflow turbulent jet using nanosecond repetitively pulsed discharges

Methane has become increasingly popular in rocket propulsion, but low stability and limited flammability range have always been a concern about methane-powered systems. Many stabilization methods have been developed to change the geometrical or flow characteristics of the burner. However, most of these efforts have yet to be practically successful due to cost and compatibility issues. Alternatively, other methods such as microwave, dielectric barrier, and nanosecond repetitive pulse (NRP) discharges have been proven to be efficient by modifying the kinetic and transport pathways. NRP discharges have shown promising results as one of the most effective low-temperature plasma (LTP) methods. In this paper, chemiluminescence imaging is used to study the effect of NRP discharge on liftoff and blowout, as the important stabilization parameters, by recording the liftoff height and liftoff/blowout velocities under a wide range of discharge (f=0–10 kHz and V=11–19 kV) and jet velocity (ν=2–60 m/s). Depending on these parameters, four different discharge regimes of corona, diffuse, filamentary, and arc were observed. The results have shown that high-intensity plasma in a filamentary discharge regime can provide a significant advantage in delaying the liftoff conditions, but no improvements in the blowout were observed. It was also found that NRP discharge can reduce the liftoff height. To explore the cause of the increased stability, a parametric numerical study is conducted using detailed plasma-assisted methane kinetic modeling coupled to a 1D opposed diffusion flame simulation. Results show that the extinction limits of diffusion flames can be dramatically enhanced by LTP due to the local formation of high radical and excited species concentrations, with subsequent recombination leading to increased temperature and higher reactivity in the flame zone. In addition, a 1D laminar flame speed evaluation shows that the plasma-generated active species can dramatically increase the flame speed, which, in turn, reduces the lifted flame height above the burner surface.