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Hydrogenation of CO2 represents a promising pathway for converting it into valuable hydrocarbons and clean fuels like dimethyl ether (DME). Despite significant research, several challenges persist, including a limited understanding of reaction mechanisms, thermodynamics, the necessity for catalyst design to enhance DME selectivity, and issues related to catalyst deactivation. The paper provides a comprehensive overview of recent studies from 2012 to 2023, covering various aspects of CO2 hydrogenation to methanol and DME. This review primarily focuses on advancing the development of efficient, selective, and stable innovative catalysts for this purpose. Recent investigations that have extensively explored heterogeneous catalysts for CO2 hydrogenation were summarized. A notable focus is on Cu-based catalysts modified with promoters such as Zn, Zr, Fe, etc. Additionally, this context delves into thermodynamic considerations, the impact of reaction variables, reaction mechanisms, reactor configurations, and recent technological advancements, such as 3D-printed catalysts. Furthermore, the paper examines the influence of different parameters on catalyst deactivation. The review offers insights into direct CO2 hydrogenation to DME and proposes paths for future investigation, aiming to address current challenges and advance the field. [ABSTRACT FROM AUTHOR]

The parent HZSM-5 was modified with oxide M (M = Fe, Cu, La, P) via the incipient impregnation method by using ferric nitrate, copper nitrate, lanthanum nitrate and diammonium hydrogen phosphate as precursors to prepare a series of oxide M modified HZSM-5 (M/HZSM-5). And the M/HZSM-5 used as solid acid was physically mixed with commercial Cu/ZnO/Al2O3 to obtain bifunctional catalysts for steam reforming of dimethyl ether (SRD) reaction. The samples were systematically characterized by XRD, FTIR, N2 adsorption–desorption, and NH3-TPD techniques. The results showed that HZSM-5 structure remained basically unchanged after it was modified by oxide M; however, its specific surface area, pore volume, total acid amount, especially strong acid amount was decreased, and then affecting the DME conversion, H2 yield and carbon-containing product selectivity of the corresponding bifunctional catalyst. Among them, the bifunctional catalyst composed of Cu/ZnO/Al2O3 and La/HZSM-5 with the larger specific surface area and lower strong acid sites showed best SRD performance, and the dimethyl ether conversion and H2 yield reached 90.4% and 73.9% at TOS of 10 h under the conditions of reaction temperature 300 °C, pressure 0.1 MPa, space velocity 5000 mL/(g h), respectively. [ABSTRACT FROM AUTHOR]

The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with a Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. In this work, different types of TiO2 were used as a support to study the effect of changes in the structure of the TiO2 support on the acidity and dispersion of HPW. Various TiO2 supports with different structural and surface characteristics have been studied and the results indicate that: (i) the crystallinity and crystallite size of the primary particles of the HPW units depend on the TiO2 support; (ii) the pore size distribution of the TiO2 support affects the surface segregation of the heteropolyacids; and (iii) changes in the supported HPW acid catalysts do not significantly alter the crystal structure of the CuO and ZnO phases after contact with CZA in bifunctional catalysts. The activity results indicate that the variation in the intrinsic activity of the Cu-ZnOx centers in the bifunctional catalysts for direct DME synthesis is minimal due to the limited alteration of the crystal structure of the centers. [ABSTRACT FROM AUTHOR]

The purpose of this work was to study the catalytic activity for the conversion of methanol into formaldehyde, dimethyl ether, methyl formate, dimethoxymethanane of zeolite catalysts - based on natural clinoptilolite and its modified Co2+, Cu2+, Mo2+, Cr2+ forms (Cl-X). The yield was 14.3% in the naturalclinoptilolite, 27.8% in the Co2+-modified sample, and 37.3% in the Cu2+-modified sample, correspondingly. The introduction of relatively small amounts of Co2+ and Cu2+ cations into the catalyst led to an increase in the activity of the catalysts. The effect of partial pressure of CH3OH on the yield of DME was studied (maximum yield of 37.3%, mol. DME is achieved at the ratio CH3OH:O2 = 3:1). The decrease in the reaction temperature from 523 to 423 K led to an increase in the yield of DMM, and the formation of dimethyl ether and methyl formate increased with an increase in temperature to 623 K. [ABSTRACT FROM AUTHOR]

The development of compression ignition combustion engines is focused on meeting many challenges, mainly related to growing ecological requirements. Currently, however, due to technological barriers, meeting them is very difficult and requires the use of additional exhaust gas treatment systems. The use of injection of a diesel and gas solution seems to be very promising. The article presents the results of engine tests involving the use of a solution of diesel fuel and dimethyl ether. The tests were performed on a single-cylinder research engine equipped with a common rail fuel system. The obtained results suggest that the use of the solution has a positive effect on the process of creating the fuel-air mixture, resulting in a reduction in the concentration of HC and CO while increasing the share of NOx, suggesting an improvement in the combustion process, as evidenced by the limiting injection dose. [ABSTRACT FROM AUTHOR]

Abstract This study aims to develop two models for thermodynamic data on hydrogen generation from the combined processes of dimethyl ether steam reforming and partial oxidation, applying artificial neural networks (ANN) and response surface methodology (RSM). Three factors are recognized as important determinants for the hydrogen and carbon monoxide mole fractions. The RSM used the quadratic model to formulate two correlations for the outcomes. The ANN modeling used two algorithms, namely multilayer perceptron (MLP) and radial basis function (RBF). The optimum configuration for the MLP, employing the Levenberg–Marquardt (trainlm) algorithm, consisted of three hidden layers with 15, 10, and 5 neurons, respectively. The ideal RBF configuration contained a total of 80 neurons. The optimum configuration of ANN achieved the best mean squared error (MSE) performance of 3.95e−05 for the hydrogen mole fraction and 4.88e−05 for the carbon monoxide mole fraction after nine epochs. Each of the ANN and RSM models produced accurate predictions of the actual data. The prediction performance of the ANN model was 0.9994, which is higher than the RSM model's 0.9771. The optimal condition was obtained at O/C of 0.4, S/C of 2.5, and temperature of 250 °C to achieve the highest H2 production with the lowest CO emission.

There is a looming global crisis owing to the increase in greenhouse gases and the escalating fossil fuel process. The issue is further compounded by the ongoing conflicts in different places in the world. Hence, there is an urgent need for a bouquet of alternative fuels suitable to power the incumbent internal combustion engine. Among various options available Dimethyl Ether (DME) is a friendly environment fuel, easy to liquefy, and suitable for use in diesel engines, while Liquefied Petroleum Gas (LPG) is another potential alternative fuel suitable for internal combustion engines. The present study is an endeavor to investigate the characteristics of a diesel engine powered with DME-diesel blends as pilot fuel while LPG was used as the main fuel. During engine testing, different blends of diesel-DME were used containing 0%, 25%, 50%, and 75% DME. The AVL Boost software was employed for modeling the engine performance and tailpipe emission. The test fuel combination was successful in running the engine sans any abnormality in sound or performance. The results showed carbon monoxide (CO) and hydrocarbon (HC) emissions were reduced using the test fuel combination while there was a marginal increase in the oxides of nitrogen (NOx) levels. In general, the combination of DME and LPG could be considered as a potential and promising solution to reducing pollutant emissions.

Herein, we present the production of either dimethyl ether (DME), methyl formate (MF) or dimethoxymethane (DMM), representing pivotal molecules for the green transformation of fuels and chemical industry, by the non‐oxidative gas‐phase conversion of methanol under the same reaction conditions. The product selectivity is optimized by tailoring the acidic and dehydrogenative sites of the bifunctional Cu/Hβ catalyst system by varying the SiO2/Al2O3 ratio of the Hβ zeolite (25 and 520) and the Cu loading (0.5 and 20 wt %). At 240 °C, >99 % (DME), 74.5 % (MF), and 77.3 % (DMM) selectivity is achieved with the respective catalysts 0.5 %Cu/Hβ(25), 20 %Cu/Hβ(520), and 0.5 %Cu/Hβ(520). High acidic site concentration catalyzes DME formation, while the presence of Cu+ species is crucial for DMM formation, and Cu0 species mainly catalyze MF formation. A highly dynamic reaction behaviour is observed, when the dehydrogenative functionality is dominant (i. e. in the production of MF or DMM), presumably due to the dynamic nature of the Cu oxidation state, which is in turn influenced by possible by‐products (H2 and H2O). While the catalytic activity in DME synthesis over 0.5 %Cu/Hβ(25) is remarkably stable over 1500 min TOS, the activity in MF and DMM production over 20 %Cu/Hβ(520) and 0.5 %Cu/Hβ(520), respectively, can be successfully regenerated. [ABSTRACT FROM AUTHOR]

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The Reynolds-averaged Navier–Stokes (RANS)-based stochastic multiple mapping conditioning (MMC) approach has been used to study partially premixed jet flames of dimethyl ether (DME) introduced into a vitiated coflowing oxidizer stream. This study investigates DME flames with varying degrees of partial premixing within a fuel jet across different coflow temperatures, delving into the underlying flame structure and stabilization mechanisms. Employing a turbulence k- ε model with a customized set of constants, the MMC technique utilizes a mixture fraction as the primary scalar, mapped to the reference variable. Solving a set of ordinary differential equations for the evolution of Lagrangian stochastic particles' position and composition, the molecular mixing of these particles is executed using the modified Curl's model. The lift-off height (LOH) derived from RANS-MMC simulations are juxtaposed with experimental data for different degrees of partial premixing of fuel jets and various coflow temperatures. The RANS-MMC methodology adeptly captures LOH for pure DME jets but exhibits an underestimation of flame LOH for partially premixed jet scenarios. Notably, as the degree of premixing escalates, a conspicuous underprediction in LOH becomes apparent. Conditional scatter and contour plots of OH and CH2O unveil that the propagation of partially premixed flames emerges as the dominant mechanism at high coflow temperatures, while autoignition governs flame stabilization at lower coflow temperatures in partially premixed flames. Additionally, for pure DME flames, autoignition remains the primary flame stabilization mechanism across all coflow temperature conditions. The study underscores the importance of considering the degree of premixing in partially premixed jet flames, as it significantly impacts flame stabilization mechanisms and LOH, thereby providing crucial insights into combustion dynamics for various practical applications. [ABSTRACT FROM AUTHOR]

Copyright of Journal of Xi'an Jiaotong University is the property of Editorial Office of Journal of Xi'an Jiaotong University and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The zeolite-catalyzed conversion of DME into chemicals is considered environmentally friendly in industry. The periodic density functional theory, statistical thermodynamics, and the transition state theory are used to study some possible parallel reactions about the hydrogen-bonded DME over zeolite ferrierite. The following are the key findings: (1) the charge separation probably leads to the conversion of a hydrogen-bonded DME into a dimethyl oxonium ion (i.e., DMO+ or (CH3)2OH+) with a positive charge of about 0.804 e; (2) the methylation of DME, CH3OH, H2O, and CO by DMO+ at the T2O6 site of zeolite ferrierite shows the different activated internal energy (∆E≠) ranging from 18.47 to 30.06 kcal/mol, implying the strong methylation ability of DMO+; (3) H-abstraction by DMO+ is about 3.94–15.53 or 6.57–18.16 kcal/mol higher than DMO+ methylation in the activation internal energy; (4) six DMO+-mediated reactions are more likely to occur due to the lower barriers, compared to the experimental barrier (i.e., 39.87 kcal/mol) for methyl acetate synthesis; (5) active intermediates, such as (CH3)3O+, (CH3)2OH+, CH3CO+, CH3OH2+, and CH2=OH+, are expected to appear; (6) DMO+ is slightly weaker than the well-known surface methoxy species (ZO-CH3) in methylation; and (7) the methylated activity declines in the order of DME, CH3OH, H2O, and CO, with corresponding rate constants at 463.15 K of about 3.4 × 104, 1.1 × 102, 0.18, and 8.2 × 10−2 s−1, respectively. [ABSTRACT FROM AUTHOR]

Non-premixed combustion often occurs in practical engines, and it is affected by the coupling effects of chemical kinetics and transport. This study aims to elucidate the individual effect of chemical kinetics, molecular diffusion, and convective transport on non-premixed combustion. To this end, three types of reactive systems are investigated by numerical simulations considering detailed chemistry and transport: (1) thermochemical system: 0D homogeneous autoignition, (2) thermochemical-diffusive system: 1D non-premixed ignition in a static diffusion layer, (3) thermochemical-diffusive-convective system: 1D non-premixed ignition in a counterflow and 2D lifted flame in a coflow. The simulations are carried out for diluted dimethyl ether and hot air under engine-relevant conditions with a pressure of 40 atm and hot air temperatures of 700∼1500 K. First, homogeneous ignition process of DME/air premixture is investigated. It is found that, apart from the low- and high-temperature chemistry which are essential in the typical two-stage ignition, the intermediate-temperature chemistry can also play an important role, especially for slow reaction process in fuel rich regions. Then, the effects of thermochemical conditions and molecular diffusion are assessed for non-premixed ignition process in the 1D diffusion layer. The results show that, the reaction front always initiates from local autoignition in most reactive regions; then it propagates either in sequential auto-ignition mode or in diffusion-driven mode as a deflagration wave. With various thermochemical conditions, the chemical kinetics behave differently and produce complex multibrachial (tetrabrachial, pentabrachial and hexbrachial) structures during the reaction front propagation. Decreasing the diffusion layer thickness generally delays the reaction front initiation but enhances its transition into a diffusion-driven flame. Finally, it is shown that 1D diffusion layer simulations can qualitatively reproduce the complex multibrachial structures in 1D counterflow and 2D coflow at certain conditions. A regime diagram is proposed to separate the effects of chemical kinetics, molecular diffusion, and convective transport. [ABSTRACT FROM AUTHOR]

This paper investigates the effect of blending dimethyl ether (DME) and ethanol on the soot transition periods in ethylene counterflow diffusion flames by using a novel optical diagnostic method. The soot critical transition point in different conditions is identified experimentally and numerically. Two kinds of flames are carried out to gain the soot critical transition point in counterflow diffusion flames by changing oxygen fraction (Xo) and changing volume flow rates of fuel and oxidizer (Qv). The red-green-blue (RGB) ratio method is used to precisely identify the soot critical transition point, and chemical kinetic simulations are performed to analyze the detailed reaction paths. The results show that compared to the ethylene flame, the soot critical transition point occurs at a higher Xo and a lower Qv when DME or ethanol is blended. The addition of DME and ethanol can inhibit soot formation, due to the degree of soot formation reaction being lower than the degree of the oxidation reaction in the blending flames. [ABSTRACT FROM AUTHOR]

Annually, a growing demand was noted for replacing petroleum fuels with second-generation eco-friendly fuels like dimethyl ether (DME). Methanol dehydration into DME process has been considered as one of the potential pathways for the manufacture of a clean fuel. However, stable, and active catalyst is exceedingly requisite for generation of DME particularly at reasonably low temperature. In the current study, zirconia incorporated AlPO4 tridymite microporous molecular sieve catalysts were fabricated by a hydrothermal method in the presence of triethylamine (TEA) as a structure directing agent. The catalysts were characterized by X-ray diffraction (XRD), energy dispersive X-ray (EDX), Fourier transform infrared spectroscopy (FTIR), transmission electron microscopy (TEM), thermogravimetric analysis (TGA), and N2-sorption assessments. Catalysts' acidity was estimated by decomposition of isopropanol, pyridine and dimethyl pyridine chemisorption, and pyridine-TPD. Results revealed that catalysts surfaces composed acid sites of Brønsted nature and of weak and medium strengths. Activity results showed that 1 wt% H2SO4 modified zirconia incorporated AlPO4-TRI catalyst calcined at 400 °C presented the best activity with a conversion of 89% and a 100% selectivity into DME at 250 °C. The significant catalytic activity is well-connected to the variation in BET-surface area, acidity, and activation energy of methanol dehydration. The catalysts offered long-term stability for 120 h and could be regenerated with almost the same activity and selectivity. [ABSTRACT FROM AUTHOR]

Copyright of Journal of South China Normal University (Natural Science Edition) / Huanan Shifan Daxue Xuebao (Ziran Kexue Ban) is the property of Journal of South China Normal University (Natural Science Edition) Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

The aim of this review is to summarize and comparatively analyze recent reports on studying carbon dioxide conversion to methanol, dimethyl ether, and C2+ hydrocarbons, in particular, olefins, by catalytic hydrogenation. It is shown that the main approaches to providing high activity and selectivity of these processes are the targeted design of catalysts and the selection of conditions for hydrogenation processes, in particular, the use of supercritical CO2 and procedures that are alternative to conventional physicochemical methods for CO2 activation (electrocatalysis, photocatalysis). [ABSTRACT FROM AUTHOR]

Under slurry reactor conditions, the products of condensation are generrally formed on strong Mg/HZSM-5 acid sites independently of the SiO2/Al2O3 molar ratio in the zeolite. The composition of condensation products remains virtually unchanged as the molar ratio grows and basically consists of trimethyl and tetramethyl benzenes, but their content falls as the volume of mesopores grows with increasing SiO2/Al2O3. This lowers the hindrances to diffusion and the contribution from secondary reactions to improve the removal of coke precursors from the zeolite's surface and favorably affect the catalyst's activity (DME conversion doubles). The composition of reaction products changes slightly with an increase in the SiO2/Al2O3 molar ratio, and the total selectivity toward lower olefins is ~70 wt %. A rapid loss in Mg/HZSM-5 activity upon extending the period of operation under slurry reactor conditions is not due to coking, but to the catalyst being clogged by dispersion medium (polydimethylsiloxane) decomposition products. [ABSTRACT FROM AUTHOR]

Alpha alumina (α‐Al2O3) catalysts synthesized by ball milling are investigated in the dehydration of methanol to dimethyl ether (DME). The activity and stability of the catalysts were studied in a fixed‐bed continuous‐flow reactor setup. The effect of water vapor in the feed was studied as well. Among different alumina polymorphs studied, γ‐ alumina has been known to be the most effective for this reaction; however, the high surface area α‐Al2O3, which had been synthesized by ball milling, resulted in a comparable rate of methanol conversion, while it revealed a more stable performance under the influence of water vapor. The surface area, the number, and the nature of the acidic sites were found to be relevant parameters for the conversion of methanol to DME. The selectivity was as high as 99 % towards DME. [ABSTRACT FROM AUTHOR]

Hydrogen serves as a renewable, clean energy carrier, and the critical development of technologies for safer and simpler storage and transportation is imperative for addressing global warming. There is also a growing demand for efforts to capture and utilize CO2 to tackle similar issues. Consequently, considerable attention has been drawn to carriers that chemically store hydrogen. Hydrogen can be stored and released through hydrogenation and dehydrogenation. Notably, the storage and release of hydrogen via CO2 hydrogenation and subsequent dehydrogenation of its hydrogenation product could potentially bolster the future hydrogen economy, rendering it an appealing option as a CO2 circulation hydrogen carrier (CCHC). To leverage CCHC for various applications, a catalytic process enabling the reversible storage and release of hydrogen is essential. This review focuses on CCHC candidates, such as methanol (MeOH), dimethyl ether (DME), and formic acid (FA), summarizing recent catalytic approaches for hydrogen production through pivotal dehydrogenation processes within the CCHC cycle. [ABSTRACT FROM AUTHOR]

The study aimed to present a fluidized bed reactor filled with 50% platinum catalytic beads and 50% quartz sand for syngas generation via the partial oxidation of dimethyl ether (DME). For obtaining useful information, experiments were carried out using Taguchi orthogonal array method, which cut test run by 75.3%, with the results being used for constructing the Kriging surrogate model. The model was then modified to reduce the mean square error. It is validated that the model can predict the results reasonably well. The outcome shows that the proposed reactor can self-sustain the syngas reforming reaction without incurring extra heat for reactants preheating. In the operation region, the results show that the start-up temperature is most negligible in hydrogen generation. The yield rate of hydrogen increases in sync with the increase of oxygen's molar ratio and DME, thanks to higher reaction temperature. The results also suggest that the higher the molar ratio of oxygen and DME, the more significant the reverse water shift reaction. Playing a key role in the fluidized bed in the proposed reactor for hydrogen generation, the normalized velocity must be at a proper level, in order to induce bubbling fluidization without causing a lower hydrogen yield, the latter due to the short residence time of reaction caused by excessive velocity. The sensitive analysis of independent variables also proved the inference from the measured results. By comparing with the literature, the performance of the proposed reactor in the present study shows a reasonably well performance. Given focused hydrogen generation, the study's findings can be used as a basis for evaluating DME as a hydrogen carrier and the proposed fluidized bed reaction. • A novel reactor filled with 50% quartz sand & 50% Pt catalytic beads is proposed. • The reactor does not need additional heat to sustain gas reforming reaction. • The surrogate model estimates the yield products of gas reforming fairly well. • The normalized velocity in the reactor dominates the syngas generation. • The demonstrated novel fluidized bed demonstrates a reasonably well performance. [ABSTRACT FROM AUTHOR]

Cu-Co/X-MMT (X = Na, SiO2) catalysts were prepared via impregnation method using Na-MMT and SiO2-MMT (montmorillonite pillared by SiO2) as the support and copper nitrate and cobalt nitrate as precursors. In addition, the citric acid was introduced during the preparation of Cu-Co/SiO2-MMT to obtain Cu-Co/SiO2-MMT-Ac catalyst. The catalysts were characterized by XRD, TEM, H2-TPR, XPS and N2 adsorption–desorption at low temperature. The results showed that the acidity and specific surface area of SiO2-MMT were larger than those of Na-MMT, thus resulting in dimethyl ether (DME) conversion and H2 yield of Cu-Co/SiO2-MMT higher than those of Cu-Co/Na-MMT during steam reforming of DME (SRD). However, for Cu-Co/SiO2-MMT, there was a large amount of methanol in the carbon-containing product due to the large particle size of Cu. The Cu particle size of Cu-Co/SiO2-MMT-Ac was decreased significantly due to the introduction of citric acid, thus accelerating the steam reforming of methanol reaction and enabling the timely conversion of the intermediate product methanol of SRD, resulting in the increasing DME conversion and H2 yield. Therefore, Cu-Co/SiO2-MMT-Ac was expected to be a potential catalyst for SRD. [ABSTRACT FROM AUTHOR]

The kinetics of thermocatalytic transformations of methanol into dimethyl ether (DME) in water–methanol waste from natural gas purification on the used ASM, ASM BC, BASF KC-Trockenperlen H, BASF KC-Trockenperlen WS, and NIAP-AOS silica gel adsorbents. The physicochemical characteristics of the adsorbents were studied by low-temperature nitrogen adsorption, X-ray phase and X-ray fluorescence analysis, and scanning electron microscopy. The kinetic reaction of the thermocatalytic conversion of methanol into dimethyl ether on the ASM, ASM BC, BASF KC-Trockenperlen H, and BASF KC-Trockenperlen WS adsorbents was of the first order with respect to methanol, and it was of second order on the aluminum-oxide-based adsorbent NIAP-AOS. The activation energy values for the conversion of methanol to DME on the most effective silica gel adsorbent ASM 1 were estimated in the temperature range 160–290°C at a gas flow rate of 400 mL/min, which according to the Arrhenius dependence were 27.8 kJ/mol with an Si/Al ratio of 50.5 kJ/mol. [ABSTRACT FROM AUTHOR]

Density and dielectric spectra have been measured in the liquid phase of dimethyl ether (DME)–ethanol by an oscillating U-tube densimeter and a complex dielectric spectrometer under 1.00 MPa. The density was measured at 303.15 and 313.15 K and converted to the excess molar volume. The excess molar volumes were no smaller than − 0.880 and − 0.909 cm3·mol–1 at 303.15 and 313.15 K, respectively. The mole fraction dependence can be correlated with the Redlich–Kister equation, whose minimum was found to be around 0.58 for the mole fraction of DME. The dielectric constant and the dielectric relaxation time were evaluated from the complex dielectric spectra in the frequency range from 0.5 to 18 GHz at (293.2–313.2) K and 1.00 MPa. The dielectric constants and the relaxation time were decreased with the mole fraction of DME, and the latter tended to be around 25 ps in the mole fraction range higher than 0.6. The logarithmic dielectric constants can be correlated with a similar function to the Hildebrand equation with the volume fraction. The effective Kirkwood g-factor was evaluated at 293.2–313.2 K and 1.00 MPa. The g-factors were given by two linear functions crossed around 0.6 for the mole fraction of DME. Considering an atomic composition (C2H6O), the molecular sizes are not so different for DME and ethanol. Then, the solution structure was thought to be microscopically changed around 0.6 for the mole fraction of DME. The mole fraction will be utilized to switch the solubility to extract amphipathic compounds. [ABSTRACT FROM AUTHOR]

The development of a stable and selective catalyst for CO hydrogenation is of utmost importance for the chemical industry. Single-atom materials have recently received attention owing to their distinct atomic and electronic properties compared with nanoparticle counterparts. Herein, we report a Zn-NC single-atom catalyst derived from the pyrolysis of ZIF-8, featuring a high loading of Zn in a N-doped amorphous carbon matrix, used for one-step transformation of CO to dimethyl ether (DME). The Zn-NC single-atom catalyst presents highly exposed active sites in favor of the overall activity, reaching a site time yield of 32.4 mmolCO/gZn/h during the reaction, 2–4 times higher than the common activated carbon-supported ZnO catalyst (ZnO/AC). With the Zn–N3 structure dominating in the catalyst demonstrated by EAXFS, the catalyst exhibits a DME selectivity of 95.6%, while the byproducts of methane/ethane are less than 5%. A comprehensive reaction mechanism has been put forward based on the active site of Zn–N3 by using DFT calculations, and the coupling reaction of CH3O + CHO has been found as the key step in the direct formation of DME. The terminal O atom is captured by CO to form CO2. The two-step route of methanol formation followed by dehydration is not favored kinetically in this catalyst, which accounts for the considerable release of CO2 instead of H2O as the byproduct. [ABSTRACT FROM AUTHOR]

This study deals with enhancing the energy efficiency with ultra-low emissions and extending the operating range (maximum load limit) of dimethyl ether (DME) fueled homogeneous charge compression ignition (HCCI) engine using hydrogen and exhaust gas recirculation (EGR). In the neat DME mode, the possible maximum load limit with controlled auto-ignition (CAI) was found as 24% (BMEP of 1.67 bar). Beyond 24% load, the knocking was observed with an advanced combustion phase, and shortened combustion duration resulted in uncontrolled auto-ignition (UAI) combustion. The addition of EGR extended the maximum load limit to 52% (BMEP of 3.62 bar) (60% EGR). Near-zero levels of NO x , zero smoke, and marginal CO and HC emissions reduction were observed with the optimized EGR rate (35%). The hydrogen fuel addition along with DME at an optimized EGR rate resulted in combustion phase retardation with the elimination of the low-temperature reaction (LTR) region. The energy efficiency (EE) and indicated thermal efficiency (ITE) increased along with zero smoke emission, ultra-low NO x , CO, and HC, and lower CO 2 emissions till 12% of hydrogen energy share (HES). Thus, the combined strategy of EGR and hydrogen could effectively extend the operating range with ultra-low emissions levels. • EGR extended the maximum load limit and control knock in DME HCCI engine. • Higher energy efficiency and indicated thermal efficiency with hydrogen. • Zero smoke emission with Ultra-Low NO x , CO, CO 2 , and HC emissions. • Elimination of cool-flame (LTR) region with hydrogen. • DME and hydrogen could be a dual fuel combination for HCCI combustion. [ABSTRACT FROM AUTHOR]

Microalgae are a sustainable source for the production of biofuels and bioactive compounds. This review discusses significant research on innovative extraction techniques using dimethyl ether (DME) as a green subcritical fluid. DME, which is characterized by its low boiling point and safety as an organic solvent, exhibits remarkable properties that enable high extraction rates of various active compounds, including lipids and bioactive compounds, from high-water-content microalgae without the need for drying. In this review, the superiority of liquefied DME extraction technology for microalgae over conventional methods is discussed in detail. In addition, we elucidate the extraction mechanism of this technology and address its safety for human health and the environment. This review also covers aspects related to extraction equipment, various applications of different extraction processes, and the estimation and trend analysis of the Hansen solubility parameters. In addition, we anticipate a promising trajectory for the expansion of this technology for the extraction of various resources. [ABSTRACT FROM AUTHOR]

This paper deals with the proposition of a kinetic model for the direct synthesis of DME via CO2 hydrogenation in view of the necessary optimization of the catalytic system, reactor design, and process strategy. Despite the fact that DME synthesis is typically treated as a mere combination of two separated catalytic steps (i.e., methanol synthesis and methanol dehydration), the model analysis is now proposed by taking into account the improvements related to the process running over a hybrid catalyst in a rational integration of the two catalytic steps, with boundary conditions properly assumed from the thermodynamics of direct DME synthesis. Specifically, the CO2 activation step at the metal–oxide interface in the presence of ZrO2 has been described for the first time through the introduction of an ad hoc mechanism based on solid assumptions from inherent studies in the literature. The kinetic modeling was investigated in a tubular fixed-bed reactor operating from 200 to 260 °C between 1 and 50 bar as a function of a gas hourly space velocity ranging from 2500 to 60,000 NL/kgcat/h, in a stoichiometric CO2/H2 feed mixture of 1:3 v/v. A well-detailed elementary mechanism was used to predict the CO2 conversion rate and identify the key reaction pathways, starting with the analysis of the implicated reactions and corresponding kinetic mechanisms and expressions, and finally estimating the main parameters based on an appropriate modeling of test conditions. [ABSTRACT FROM AUTHOR]

The comparisons between the cracked gas and DME addition with a certain proportion on combustion behaviors are studied. A mechanism for the prediction of ammonia/H 2 /DME is updated based on the previously developed one. Since it is important to use a simplified mechanism in 3D numerical simulations, mechanism simplification is conducted, resulting in one with 72 species and 459 reactions. The premixed laminar flame simulations indicate that both the fuel cracking with hydrogen production and DME addition with a small amount can enhance laminar burning velocity (LBV) and extend lean-burn limit. NO is increased with hydrogen or DME addition due to the chemical and thermal effects, and comparatively, adding cracked gas leads to lower NO generation for the same blending ratio. The 3D simulated results shows that a sudden increase of HNO for DME addition during the combustion induces a higher NO formation relatively to that for hydrogen addition. [Display omitted] • A simplified mechanism for NH 3 , H 2 , DME, CO and their blends was developed. • The effects of cracked gas of H 2 /N 2 and DME on combustion and NO were investigated. • Ammonia cracking leads to higher LBV due to more generation of free radicals. • Adding cracked gas leads to lower NO than adding DME in ammonia mixture. [ABSTRACT FROM AUTHOR]

Polyoxymethylene dimethyl ether (PODE) and methanol are important low-carbon substitutable fuels for reducing carbon emissions in internal combustion engines. In the research, the impacts of methanol ratio, injection timing, and intake temperature on HCHO generation and emission were investigated using both engine tests and numerical simulations. Results suggest that an increase in methanol ratio suppresses auto-ignition tendency of PODE, leading to the increase of ignition delay period, pressure peak, and heat release rate peak inside the cylinder. The decrease in in-cylinder combustion temperature contributes to an increase in HCHO emission due to partial oxidation of methanol in the cylinder and exhaust pipe. While the injection timing is gradually postponed from −10 °CA ATDC to 2 °CA ATDC, in-cylinder high-temperature area decreases, the quantity of unburned methanol increases, but part of HCHO is converted to HCO due to H radical influence, resulting in 72% increased HCHO emission. With the increment of intake temperature, the oxidation and decomposition of in-cylinder methanol accelerate, leading to an improvement in combustion stability, more uniform temperature distribution, and a decrease in unburned methanol, which results in lower HCHO emission. When the intake temperature is rose from 30 to 60 °C, HCHO emission decreases by 11.2%. [ABSTRACT FROM AUTHOR]

In this study, the combustion and exhaust emission characteristics of a single‐cylinder, water‐cooled, four‐stroke VCR engine at a fixed CR were evaluated using DME and diesel with timed manifold injections of 2, 3, 4, and 5 ms for DME and conventional diesel settings. The investigational trials showed that DME has the capability to reduce NOx and OP while used in an optimized range and to have clean combustion characteristics. Induction of DME under low to medium load conditions resulted in a reduction in NOx, OP, and BTE with an increase in HC, whereas at higher load settings, NOx increased with an increase in diesel energy share. The dual fuel combustion was characterized by a short ignition delay, an early start of combustion, and increased in‐cylinder pressure due to the increased compression work input during the cycle. The absence of carbon–carbon bonds in DME molecules caused low soot emissions during dual fuel combustion. After experimentation, RSM was applied to the results for parametric optimization and found to be a useful tool for reducing the error as well as minimizing the number of trials. The optimum settings were achieved at 2 kW load and 4 ms duration, where the desirability function reached a value of 0.94189. The regression equations developed by the model were validated by 9 random experiments, and the error is found to be acceptable. The engine should be operated at medium load to control NOx, and the DME energy share should be low and near 50%. [ABSTRACT FROM AUTHOR]

Katsuwonus pelamis is a tuna species mostly sold for canned fillets, its livers were lack of utilization. This study thus investigated an oil production method combining microwave (MW) pretreatment and subcritical dimethyl ether (SDME) in aim to reach improved efficiency and oil quality. The heating characteristics from different MW powers (400, 600, and 800 W) were evaluated, and SEM showed MW having hydrolysis effect on matrix lipoprotein, the fortified recovery rate was also found. Under the MW-SDME condition with 600 W power, 1:5 solid-to-liquid ratio, and 100 min, the recovery reached 93.21% in maximal (SDME ∼50%). To further improve quality, MW powers was noticed affecting lipid types, fatty acid composition, and oxidative stability of produced oils. 1286 lipid types (mostly glyceride and phospholipid-type) were identified, while higher MW lowered the emulsifying phospholipids prompting phase separation. Several oxidation indexes consistently increased with the rising MW power, GC–MS suggested 400 W for higher DHA.

Energy systems are currently transforming into configurations with a significant share of renewable energies to reduce greenhouse gas (GHG) emissions. One frequently discussed option to reduce CO2 and simultaneously provide temporary storage for fluctuating renewable energy is coupling the energy and the transport sector in a Power-to-Liquid (PtL) approach by producing synthetic fuels. The syntheses for methanol, 1-step and 2-step dimethyl ether and oxymethylene dimethyl ethers (OME3–5) are modeled using captured CO2 and hydrogen. Hydrogen is produced by electrolysis using German electricity mixes (2021, 2030) and wind power. To evaluate the environmental impacts of the different PtL pathways, a comparative well-to-tank Life Cycle Assessment (LCA) is conducted. Aspen process simulations are performed to provide material and energy balances for the LCA. The results show that the production of all PtL fuels is highly emission intensive, when using the current electricity mix and is – from an environmental point of view – not a viable option today. The GHG emissions are estimated to be between 9.3 – 16 kg CO2 equivalents/l diesel equivalent which is five to eight times that of a conventional diesel system. But already the electricity mix 2030 can drastically reduce the GHG emissions to 2.5 – 6 CO2 equivalents/l diesel equivalent. Wind will decrease these values further to 0.6 – 3.6 CO2 equivalents/l diesel equivalent. Dimethyl ether and methanol generate considerably lower impacts than OME3–5 as their production is less energy intensive. The conventional 2-step dimethyl ether synthesis and the more innovative 1-step process hardly differ.

Hydrogenation of CO2 represents a promising pathway for converting it into valuable hydrocarbons and clean fuels like dimethyl ether (DME). Despite significant research, several challenges persist, including a limited understanding of reaction mechanisms, thermodynamics, the necessity for catalyst design to enhance DME selectivity, and issues related to catalyst deactivation. The paper provides a comprehensive overview of recent studies from 2012 to 2023, covering various aspects of CO2 hydrogenation to methanol and DME. This review primarily focuses on advancing the development of efficient, selective, and stable innovative catalysts for this purpose. Recent investigations that have extensively explored heterogeneous catalysts for CO2 hydrogenation were summarized. A notable focus is on Cu-based catalysts modified with promoters such as Zn, Zr, Fe, etc. Additionally, this context delves into thermodynamic considerations, the impact of reaction variables, reaction mechanisms, reactor configurations, and recent technological advancements, such as 3D-printed catalysts. Furthermore, the paper examines the influence of different parameters on catalyst deactivation. The review offers insights into direct CO2 hydrogenation to DME and proposes paths for future investigation, aiming to address current challenges and advance the field.

The performance of bifunctional hybrid catalysts based on phosphotungstic acid (H3PW12O40, HPW) supported on TiO2 combined with a Cu-ZnO(Al) catalyst in the direct synthesis of dimethyl ether (DME) from syngas has been investigated. In this work, different types of TiO2 were used as a support to study the effect of changes in the structure of the TiO2 support on the acidity and dispersion of HPW. Various TiO2 supports with different structural and surface characteristics have been studied and the results indicate that: (i) the crystallinity and crystallite size of the primary particles of the HPW units depend on the TiO2 support; (ii) the pore size distribution of the TiO2 support affects the surface segregation of the heteropolyacids; and (iii) changes in the supported HPW acid catalysts do not significantly alter the crystal structure of the CuO and ZnO phases after contact with CZA in bifunctional catalysts. The activity results indicate that the variation in the intrinsic activity of the Cu-ZnOx centers in the bifunctional catalysts for direct DME synthesis is minimal due to the limited alteration of the crystal structure of the centers.

The adsorption, temperature-programmed desorption, and carbonylation of dimethyl ether (DME) in the presence of mordenite and ferrierite (SiO2/Al2O3 ≈ 20, Zeolyst International) is studied. The effect of introducing Cu, Co, and Mg cations by ion exchange is discussed. Dimethyl ether carbonylation is conducted at 200°С, a pressure of 3 MPa, and a space velocity of 8000 mL g–1 h–1 in the following mixture (vol %): DME, ⁓2.2; CO, 92.8–95.5; and the rest, N2. After an induction period, the methyl acetate content in the presence of mordenite is about 4–5 times higher than that in the presence of ferrierite. Water, methanol, and hydrocarbons are formed in trace amounts. The introduction of Cu, Co, and Mg cations into mordenite by ion exchange (single ion-exchange run, cation/Al ratio of no more than 35%) leads to an increase not only in stability, but also in activity in the DME carbonylation reaction. It is found that an increase in the content of copper (from 1.19 to 2.23 wt %) and magnesium (from 0.62 to 1.8 wt %) has different effects on activity. It increases in the case of copper and decreases in the case of magnesium. The prereduction of a copper-exchanged mordenite leads to the appearance of metallic copper particles on the surface of the mordenite crystallites and a decrease in activity. According to in situ diffuse reflectance infrared spectroscopy, the introduction of magnesium cations by three ion-exchange runs leads to a significant decrease in the number of Brønsted acid sites (BASes) in both the 12-MR and 8-MR channels of the mordenite. The catalytic characteristics of ferrierite hardly change upon the introduction of copper and magnesium by ion exchange. [ABSTRACT FROM AUTHOR]

The ignition and combustion of three-component methane–hydrogen biofuel mixtures, considered as prospective fuels, were experimentally and numerically studied. Ignition delays in argon-diluted methane–hydrogen mixtures partially substituted with methanol or dimethyl ether were measured behind reflected shock waves in a temperature range of 1050–1900 K at pressures of 3.5–5.5 bar. The obtained results were used for validation of modern kinetic mechanisms for hydrocarbons combustion. Numerical modeling of the combustion of the considered fuels in air at elevated pressures and temperatures was carried out, simulating typical engine compressed conditions, and the dependencies of key parameters such as flame velocity and temperature on fuel composition were obtained. The results of the study can be used in developing new energy technologies, reducing the environmental impact of hydrocarbon combustion. [ABSTRACT FROM AUTHOR]

The promising direct dimethyl ether (DME) production through CO2 hydrogenation was systematically analyzed in this research by synthesizing, characterizing, and testing several catalytic structures. In doing so, various combinations of precipitation and impregnation of copper- and zinc-oxides (CuO–ZnO) over a ZSM-5 zeolite structure were applied to synthesize the hybrid catalysts capable of hydrogenating carbon dioxide to methanol and dehydrating it to DME. The resulting catalytic structures, including the co-precipitated, sequentially precipitated, and sequentially impregnated CuO–ZnO/ZSM-5 catalysts, were prepared in the form of particle and electrospun fibers with distinguished chemical and structural features. They were then characterized using XRD, BET, XPS, ICP, TGA, SEM, and FIB-SEM/EDS analyses. Their catalytic performances were also tested and analyzed in light of their observed characteristics. It was observed that it is crucial to establish relatively small-size and well-distributed zeolite crystals across a hybrid catalytic structure to secure a distinguished DME selectivity and yield. This approach, along with other observed behaviors and the involved phenomena like catalyst particles and fibers, clusters of catalyst particles, or the whole catalytic bed, were analyzed and explained. In particular, the desired characteristics of a CuO–ZnO/ZSM-5 hybrid catalyst, synthesized in a single-pot processing of the precursors of all involved catalytically active elements, were found to be promising in guiding the future efforts in tailoring an efficient catalyst for this system. [ABSTRACT FROM AUTHOR]

Dimethyl ether has gained great attention by Indonesian Government since it will be used for the substitution for liquid petroleum gas. This work was aimed to study the effect of phosphorus addition on γ-Al2O3 catalyst for methanol dehydration to DME synthesis. The catalysts were prepared using sonication-assisted impregnation. The modified catalysts were characterized (XRD, BET, and NH3-TPR analysis), and their activity was tested in bench scale reactor. The results showed that the 5%P/γ-Al2O3 catalyst had medium acidity which was good for dehydration of methanol to DME. The surface area, pore volume, and pore diameter were measured as 132 m2/g, 0.42 mL/g, and 127 Å, respectively. The activity test was carried out at 240–280 °C, atmospheric pressure, and GHSV 2,142 h−1. The 5%P/γ-Al2O3 catalyst exhibited good performances at a temperature of 240 °C with 42% of methanol conversion, 18% of yield of DME, and 75% of selectivity of DME. Methanol dehydration using modified 5% P/γ-Al2O3 did not produce H2 by-products and other compounds which were produced during methanol dehydration with unmodified γ-Al2O3. [ABSTRACT FROM AUTHOR]

The present work reports experimentation and numerical simulations of laminar burning velocity, emission analysis, and flame structure of dimethyl ether-hydrogen mixtures. The volumetric hydrogen addition is considered into the DME fuel for a range of mixture equivalence ratios (0.6< ϕ < 1.7). The initial mixture temperature is raised to 373 K at constant atmospheric pressure of 1.0 bar. The heat flux method is utilized to investigate the laminar burning velocity in laminar premixed planar adiabatic flames. The laminar burning velocity (LBV), along with the flame position and emission measurements, are extracted from these flames. The computations were performed with freely propagating flames (LBV, species, sensitivity, etc. data), and the burner stabilizes flames (flame position and emission analysis) for the same mixture and initial conditions using various detailed mechanisms. An emphasis is paid to a newly developed Shrestha mechanism, which includes a radiation model and NO sub-mechanism. Both experimental data and competition results were validated against the pure DME air mixture data available in the existing literature, and further analysis was carried out. It is observed that planar flames can be stabilized only up to a hydrogen addition of 40%. Adding hydrogen enhanced the flame temperature, heat release rates, and burning velocity while reducing the CO and NO emissions. A slight shift of peak burning velocity on the rich side of the equivalence ratio (from 1.05 to 1.2) is observed with hydrogen addition (0–40%). The mixture temperature also enhances the flame temperature and laminar burning velocity. It is interesting to note that hydrogen-added mixtures show a relatively lower dependency on initial mixture temperature. The variation of dominant species and heat release rates are also discussed in detail. The sensitivity analysis is carried out to get information on dominant reactions participating in the combustion of DME hydrogen mixtures. • Influence of H2 content on the LBV of premixed laminar DME flames was measured. • Influence of H2 content on the NOx Emission and temperature was measured. • Study of the flame structure characterized by the HRR and species profiles. • Experimental data compared with simulation results of 5 reaction mechanisms. [ABSTRACT FROM AUTHOR]

The present research investigates the possibility of enhancing the stability of SO42−–ZrO2 catalyst by adding Cu (2–12 wt%) prepared via a simple one-pot synthesis method. The substantial changes in the structures of Cu are observed which can be classified into two different ranges of Cu loading: 2–8 wt% and 10–12 wt%. Cu2O is predominant phase at Cu loading of 2–8 wt%, which strongly interacts with ZrO2, resulting in a decrease of number of acid sites and thus lowering DME yield compared to bare SO42−–ZrO2. At Cu loading of 10–12 wt%, the predominant phase of Cu becomes CuSO4 and the SO42− from CuSO4 may be formed as bridging S–O–S bonds with another S–O bonded to Zr atom, resulting in the catalytic stability improvement. The optimum Cu loading is 10 wt% which attains the maximum DME yield of 3.2% at 260 °C and 20 bar. [ABSTRACT FROM AUTHOR]

Dimethyl ether (DME) is an environmentally friendly fuel and economical compound that can be synthesized through methanol (MeOH) dehydration or direct synthesis from syngas via the water-gas shift reaction. Catalysts such as Cu/ZnO/Al2O3 (CZA) for syngas conversion to MeOH and ferrierite (FER), a group of zeolites, or γ-Al2O3 for MeOH dehydration are necessary for these reactions. A hybrid catalyst, CZA/FER, can be used to directly convert syngas into DME via MeOH. While previous studies have developed kinetic models for these catalytic reaction systems using lumped or microkinetic models, differences in describing elementary reactions have led to variations in detail. In this study, we developed a microkinetic model for DME synthesis from syngas via MeOH over a CZA/FER hybrid bifunctional catalyst. We considered detailed reaction rates and site fractions to determine the dominance of DME synthesis path between the associative and dissociative paths. The model is based on a two-site fraction model for each catalyst, with 28 reactions over CZA and nine reactions over FER. Reaction parameters were determined using transition state theory (TST) and the UBI-QEP method for CZA and the second-order Møller-Plesset perturbation theory (MP2) for FER The pre-exponential factors of Arrhenius rate constants were estimated with experimental data at 250 °C which supported the model's accuracy. Our results show that the associative pathway is dominant for DME synthesis over a CZA/FER hybrid catalyst, which differs from our previous research on microkinetic modeling for MeOH dehydration to DME over an FER zeolite. We also suggest an operating condition range for converting CO2 in the feed. We compared the relative reaction rates of elementary reactions and site fractions in each catalyst to enhance the understanding of the catalytic reaction system. [ABSTRACT FROM AUTHOR]

CH4/DME mixtures can be used for engines and gas turbines, and have already been studied for many years. However, DME has a strong cool flame phenomenon, which will greatly influence the ignition and combustion characteristics of following hot flames. Therefore, the cool flame characteristics of CH4/DME mixture are very important for their utilization. Recently, the inhibition effect of CH4 on DME cool flames has been discovered, but the mechanisms of the inhibition effects lack further verification and research. In this study, the inhibition effects were investigated via both experiments and simulations. In order to validate the inhibition effects, a comparison fuel of CH3OH/DME was also used in this study. The extinction limits, flame temperatures and combustion products of the cool flames of the CH4/DME and CH3OH/DME mixtures were measured using a counterflow burner, and the reaction paths and heat release rate were derived from the HPMech-v3.3. The results indicate that CH4 and CH3OH will both inhibit the cool flame of DME via competing with DME for OH and O radicals, and CH3OH has stronger inhibition effects than CH4, because it is more competitive and produces more CH2O, which inhibits the oxidation of DME. The HPMech-v3.3 closely agrees with the experimental data, but still needs to be improved. [ABSTRACT FROM AUTHOR]

Ammonia (NH3) is considered a promising zero-carbon fuel and was extensively studied recently. Mixing high-reactivity oxygenated fuels such as dimethyl ether (DME) or dimethoxymethane (DMM) with ammonia is a realistic approach to overcome the low reactivity of NH3. To study the combustion characteristics of NH3/DMM and NH3/DME mixtures, we constructed a NH3/DMM chemical mechanism and tested its accuracy using measured laminar burning velocity (LBV) and ignition delay time (IDT) of both NH3/DMM and NH3/DME mixtures from the literature. The kinetic analysis of NH3/DMM flames using this mechanism reveals that the CH3 radicals generated from the oxidation of DMM substantially affects the oxidation pathway of NH3 at an early stage of flame propagation. We investigated the formation of nitrogen oxides (NOx) in NH3/DMM and NH3/DME flames and little difference can be found in the NOx emissions. Using NH3/DMM flames as an example, the peak NOx emissions are located at an equivalence ratio (φ) of 0.9 and a DMM fraction of 40% in the conditions studied. Kinetic analysis shows that NOx emission is dominated by NO, which primarily comes from fuel nitrogen of NH3. The addition of DMM at 40% significantly promotes the reactive radical pool (e.g., H, O, and OH) while the maintaining a high concentration of NO precursors (e.g., HNO, NO2, and N2O), which results in a high reaction rate of NO formation reaction and subsequently generates the highest NO emissions. [ABSTRACT FROM AUTHOR]

This study examines kinetic enhancement by nanosecond dielectric barrier discharge (ns-DBD) plasma on fuel-lean, Φ = 0.7, dimethyl ether (DME), oxygen (O 2), and argon (Ar) premixture during deflagration to detonation transition (DDT) experiments in a microchannel. Nonequilibrium plasma produces active species and radicals as well as fast and slow heating of a mixture to promote ignition due to energetic electrons, ions, and electronic and vibrational excitations. Experiments are conducted to examine the influence of the plasma discharge on the premixture and on the resultant deflagration to detonation transition (DDT) onset time and distance through the use of high-speed imaging and one-dimensional, two-beam, femtosecond/picosecond, coherent anti-Stokes Raman scattering (CARS). A high-speed camera is used to trace the time histories of flame front position and velocity and to identify the dynamics and onset of DDT. The results show that plasma discharge can nonlinearly affect the onset time and distance of DDT. It is shown that a small number of plasma discharge pulses prior to ignition result in reduced DDT onset time and distance by 60% and 40%, respectively, when compared to the results without pre-excitation by ns discharges. The results also show that an increase of number of the plasma discharge pulses results in an extended DDT onset time and distance of 224% and 94%, respectively. Time history of the deflagration wave speed of DME and the analysis of ignition timescale under the choking condition of the burned gas of the deflagration wave suggest low temperature ignition may play a role for DME near the isobaric choking condition of the burned gas and the DDT. Plasma-induced low temperature oxidation of the reactive mixture is assessed via the CO 2 to O 2 ratio as measured through fs/ps CARS during the gas excitation in discharges. CARS measurements also confirm negligible vibrational and rotational heating of the gas by discharge. The present experiments demonstrate the ability of nonequilibrium plasma to alter the chemistry of DME/O 2 /Ar premixtures in order to control DDT for applications in advanced propulsion engines. [ABSTRACT FROM AUTHOR]

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The Reynolds-averaged Navier–Stokes (RANS)-based stochastic multiple mapping conditioning (MMC) approach has been used to study partially premixed jet flames of dimethyl ether (DME) introduced into a vitiated coflowing oxidizer stream. This study investigates DME flames with varying degrees of partial premixing within a fuel jet across different coflow temperatures, delving into the underlying flame structure and stabilization mechanisms. Employing a turbulence k-ε model with a customized set of constants, the MMC technique utilizes a mixture fraction as the primary scalar, mapped to the reference variable. Solving a set of ordinary differential equations for the evolution of Lagrangian stochastic particles’ position and composition, the molecular mixing of these particles is executed using the modified Curl’s model. The lift-off height (LOH) derived from RANS-MMC simulations are juxtaposed with experimental data for different degrees of partial premixing of fuel jets and various coflow temperatures. The RANS-MMC methodology adeptly captures LOH for pure DME jets but exhibits an underestimation of flame LOH for partially premixed jet scenarios. Notably, as the degree of premixing escalates, a conspicuous underprediction in LOH becomes apparent. Conditional scatter and contour plots of OH and CH2O unveil that the propagation of partially premixed flames emerges as the dominant mechanism at high coflow temperatures, while autoignition governs flame stabilization at lower coflow temperatures in partially premixed flames. Additionally, for pure DME flames, autoignition remains the primary flame stabilization mechanism across all coflow temperature conditions. The study underscores the importance of considering the degree of premixing in partially premixed jet flames, as it significantly impacts flame stabilization mechanisms and LOH, thereby providing crucial insights into combustion dynamics for various practical applications.