Dimethyl Ether Addition Research Articles

Effect of Dimethyl Ether Addition on Soot Formation Dynamics of Ethylene Opposed-Flow Diffusion Flames

Soot formation dynamics in C2H4/dimethyl ether (DME) opposed-flow diffusion flames was numerically studied in this paper, employing detailed gas-phase and dispersed-phase chemistries and transport models. A wide range of DME additions from pure C2H4 to pure DME was involved to systematically examine its impact on the soot formation process. It was found that the flow field had an important impact on the soot structure inside the flame. The soot volume fraction reached a maximum at the stagnation plane due to the infinite residence time, and then vanished abruptly on the fuel side of the stagnation plane. In the opposed-flow diffusion flames, enhancements of nucleation, H-abstraction–C2H2-addition (HACA) reaction, and polycyclic aromatic hydrocarbon (PAH) condensation rates in the near-stagnation region disappeared, such that the local particle size distribution function (PSDF) curve became unimodal, which was rather different from the burner-stabilized stagnation premixed flame. A synergistic effect of DM...

High-pressure pyrolysis and oxidation of DME and DME/CH4

The pyrolysis and oxidation of dimethyl ether (DME) and its mixture with methane were investigated at high pressure (50 and 100 bar) and intermediate temperature (450–900 K). Mixtures highly diluted in nitrogen with different fuel–air equivalence ratios (Φ=∞, 20, 1, 0.06) were studied in a laminar flow reactor. At 50 bar, the DME pyrolysis started at 825 K and the major products were CH4, CH2O, and CO. For the DME oxidation at 50 bar, the onset temperature of reaction was 525 K, independent of fuel–air equivalence ratio. The DME oxidation was characterized by a negative temperature coefficient (NTC) zone which was found sensitive to changes in the mixture stoichiometry but always occurring at temperatures of 575–625 K. The oxidation of methane doped by DME was studied in the flow reactor at 100 bar. The fuel–air equivalence ratio (Φ) was varied from 0.06 to 20, and the DME to CH4 ratio changed over 1.8–3.6%. Addition of DME had a considerable promoting effect on methane ignition as the onset of reaction shifted to lower temperatures by 25–150 K. A detailed chemical kinetic model was developed by adding a DME reaction subset to a model developed in previous high-pressure work. The model was evaluated against the present data as well as data from literature. Additional work is required to reconcile experimental and theoretical work on reactions on the CH3OCH2OO PES with ignition delay measurements in the NTC region for DME.

Modeling phase behavior of Poly(ɛ-caprolactone) solutions at high pressure

Poly(ɛ-caprolactone) (PCL) is a biocompatible and biodegradable polymer and is widely used in controlled drug-delivery applications. For the production of polymeric microspheres loaded with pharmaceutical products, the supercritical fluid technology using carbon dioxide (CO2) is favored because of its non-toxic nature. In this work, the phase behavior of PCL in various supercritical solvents such as CO2, CHClF2, dimethyl ether (DME), 1-butene, and propylene is described by the PC-SAFT model. The effects of the molecular weight of PCL, the type of solvent, pressure, temperature, and the concentration of the cosolvent are investigated. The solubility of PCL in supercritical solvents is accurately described over a wide range of temperatures (from 293.15 to 503 K) and for pressures up to 300 MPa. CO2 shows the poorest solubility, while CHClF2 shows the highest solubility. The predicted cloud-point pressures show an increasing tendency with an increase of the molecular weight of the PCL. The addition of cosolvents, i.e., DME and CHClF2, to the PCL/CO2 solution increases of the dissolving power of the mixed solvent. The results predicted with the PC-SAFT equation of state are in good agreement with the experimental data.

An experimental and modeling study of dimethyl ether/methanol blends autoignition at low temperature

New rapid compression machine (RCM) ignition delay data for dimethyl ether (DME), methanol (MeOH), and their blends are acquired at engine-relevant conditions (T = 600 K–890 K, P = 15 bar and 30 bar, and equivalence ratios of ϕ = 0.5, 1.0, and 2.0 in synthetic dry air). The data are then used to validate a detailed DME/MeOH model in conjunction with literature RCM and shock tube data for DME and MeOH. This detailed DME/MeOH model, constructed by systematically merging literature models for the combustion of the individual fuel constituents, is capable of accurately predicting the experimental ignition delay data at a wide range of temperatures and pressures. The experiments and simulations both show a non-linear promoting effect of DME addition on MeOH autoignition. Additional analyses are performed using the merged DME/MeOH model to gain deeper insight into the binary fuel blend autoignition, especially the promoting effect of DME on MeOH. It is found that the unimolecular decomposition of HO2CH2OCHO plays an essential role in low temperature DME/MeOH blend autoignition. The accumulation of HO2CH2OCHO before the first-stage ignition and later quick consumption not only triggers the first-stage ignition, but also causes the non-linear promoting effect by accumulating to higher levels at higher DME blending ratios. These analyses suggest the rate parameters of HO2CH2OCHO unimolecular decomposition are critical to accurately predict the first-stage and overall ignition delay times as well as the first-stage heat release profile for low temperature DME/MeOH oxidation.

Effect of dimethyl ether (DME) addition on sooting limits in counterflow diffusion flames of ethylene at elevated pressures

The effects of dimethyl ether (DME) addition to ethylene fuel on sooting tendencies with varying pressure were investigated in counterflow diffusion flames by using a laser scattering technique. Sooting limit maps were determined in the fuel (XF) and oxygen (XO) mole fraction plane, separating sooting and non-sooting regions. The results showed that when DME is mixed to ethylene, the sooting region was appreciably shrank, especially in the cases of soot formation/oxidation (SFO) flames as compared with the cases of soot formation (SF) flames. This indicated an inhibiting role of DME on sooting. An interesting observation was that the critical XO required for sooting initially decreased and then increased with the DME mixing ratio to ethylene β for the cases of SF flames, exhibiting a non-monotonic behavior. This implied a promoting role of DME on sooting when small amount of DME is mixed to ethylene. As the pressure increased, the sooting region generally expanded. Specifically, the range of β in promoting soot formation extended with pressure. This implies that a strategy in reducing soot by adding DME to ethylene at high pressures required a large amount of DME addition. To interpret the observed phenomena, kinetic simulations including reaction pathway and sensitivity analyses were conducted with the opposed-flow flames model using the KAUST-Aramco PAH Mech. The results showed that the thermal effect of DME addition on sooting tendency monotonically decreases with β. The chemical effect was found to be the main contributor to the DME addition effect on sooting tendency, resulting in the non-monotonic sooting limt behavior. The pathway analysis showed the role of methyl radicals generated from DME promoted incipient benzene ring formtion when small amount of DME was added, which can be attributed to the soot promoting role of DME addition for small β.

Effects of dimethyl ether addition on soot formation, evolution and characteristics in flame-wall interactions

In this study, the detailed effects of different levels of DME addition on soot formation, evolution and characteristics in flame-wall interactions are studied to improve the energy efficiency and develop soot reduction strategies. A quartz plate which is cooled by the circulating water is uprightly installed above the ethylene jet diffusion flames to generate the flame-wall interactions. The impinging flame propagates along the surface and a series of soot rings are formed. Soot particles from different regions which represent various combustion stages are sampled and analyzed. The nanostructure of soot is acquired by the high resolution transmission electron spectroscopy (HRTEM). The results of Raman spectroscopy reflect the soot graphitization degree and verify the HRTEM findings. The thermogravimetric analyzer (TGA) is adopted to evaluate the oxidation reactivity of soot particles. The results show that the flame impingement exhibits a significant impact on soot evolution and characteristics. The addition of DME performs well in suppressing soot formation and promoting energy efficiency. The addition of 20% DME suppresses the production of soot particles from post-impingement regions and promotes the oxidation reactivity. However, the promotion of soot formation and the reduction of oxidation reactivity are found in post-impingement regions with 5% DME addition.

A computational analysis of methanol autoignition enhancement by dimethyl ether addition in a counterflow mixing layer

To provide fundamental insights into the ignition enhancement of methanol (MeOH) by the addition of the more reactive dimethyl ether (DME), computational parametric studies were conducted in a one-dimensional counterflow fuel versus air mixing layer configuration with the incorporation of detailed chemistry and transport. Various computational analysis tools based on the computational singular perturbation (CSP) framework were employed for detailed identifications of complex chemical pathways. CSP tools were also used to develop a 43-species skeletal mechanism for efficient computation of ignition of methanol-DME blends at engine conditions. The overarching practical question was the extent to which the addition of DME improves the ignitability of the methanol. As a baseline analysis, the results of a uniform temperature condition at 850 K showed that the low temperature chemistry associated with the DME fuel was highly effective in promoting autoignition. The increase in the oxidizer side temperature was found to diminish the ignition enhancement by DME blending, as the overall reactivity increases and the dominant chemical pathways become shifted towards the high temperature reactions. Finally, the strain rate effect on the ignition delay time was found to be significant for the pure methanol case, and then the effect diminishes as the amount of DME addition increases. This behavior was explained by examining the spatial locations of the ignition kernels and the Damköhler number history for different strain rate conditions.

Experimental and kinetic study on ignition of DME/n-butane mixtures under high pressures on a rapid compression machine

Dimethyl ether (DME)/n-butane mixtures are ideal fuel for homogeneous charge compression ignition (HCCI) engine. Fundamental ignition delay data under engine-related conditions are essential to better understand HCCI combustion and to validate DME/n-butane models. However, there is a significant lack of ignition delay data of DME/n-butane mixtures under high-pressure and low-temperature conditions. Therefore, ignition delays of DME/n-butane mixtures at equivalence ratio of 0.5 were measured at different DME blending ratios (0, 20, 40, 60, 80 and 100%), pressures (12, 16, 24 and 30 bar), temperatures (622–929 K) and fuel concentrations (1.6 and 2.2%) using a rapid compression machine (RCM). A numerical analysis was performed using the NUI Aramco Mech 2.0, and a good agreement to experimental data was obtained. The results well indicate the two-stage ignition and negative temperature coefficient (NTC) behavior of DME/n-butane mixtures. With DME addition, system reactivity is enhanced and air-fuel mixtures can be ignited at lower temperatures. Meanwhile, DME addition promotes both the first-stage and total ignition, and the total ignition delay as a function of DME blending ratio decreases nonlinearly, especially at low pressures. In addition, the DME/n-butane mixtures ignite faster at higher fuel concentration and pressure conditions, which is more prominent in the NTC region. Kinetic analysis indicates that compared with slower internal H-atom isomerization rate of n-butane, DME has a more active chain branching path, which promotes the low-temperature oxidation of n-butane and overall fuel, thus faster development of total radical pool, increased concentration of radicals and decreased ignition delay. The addition of 20% DME results in a significant increase of free radicals and heat release rate while the DME chemistry becomes the most ignition-sensitive one in DME/n-butane mixtures when the DME blending ratio reaches 60%.

Chemical interaction of dual-fuel mixtures in low-temperature oxidation, comparing n-pentane/dimethyl ether and n-pentane/ethanol

With the aim to study potential cooperative effects in the low-temperature oxidation of dual-fuel combinations, we have investigated prototypical hydrocarbon (C5H12) / oxygenated (C2H6O) fuel mixtures by doping n-pentane with either dimethyl ether (DME) or ethanol (EtOH). Species measurements were performed in a flow reactor at an equivalence ratio of ϕ = 0.7, at a pressure of p = 970 mbar, and in the temperature range of 450–930 K using electron ionization molecular-beam mass spectrometry (EI-MBMS). Series of different blending ratios were studied including the three pure fuels and mixtures of n-pentane containing 25% and 50% of C2H6O. Mole fractions and signals of a significant number of species with elemental composition CnH2n+xOy (n = 1–5, x = 0–(n + 2), y = 0–3) were analyzed to characterize the behavior of the mixtures in comparison to that of the individual components. Not unexpectedly, the overall reactivity of n-pentane is decreased when doping with ethanol, while it is promoted by the addition of DME. Interestingly, the present experiments reveal synergistic interactions between n-pentane and DME, showing a stronger effect on the negative temperature coefficient (NTC) for the mixture than for each of the individual components. Reasons for this behavior were investigated and show several oxygenated intermediates to be involved in enhanced OH radical production. Conversely, ethanol is activated by the addition of n-pentane, again involving key OH radical reactions. Although the main focus here is on the experimental results, we have attempted, in a first approximation, to complement the experimental observations by simulations with recent kinetic models. Interesting differences were observed in this comparison for both, fuel consumption and intermediate species production. The inhibition effect of ethanol is not predicted fully, and the synergistic effect of DME is not captured satisfactorily. The exploratory analysis of the experimental results with current models suggests that deeper knowledge of the reaction chemistry in the low-temperature regime would be useful and might contribute to improved prediction of the low-temperature oxidation behavior for such fuel mixtures.

Soot formation characteristics of ethylene premixed burner-stabilized stagnation flame with dimethyl ether addition

Effect of dimethyl ether (DME) addition on PAH and soot formation mechanisms as well as particle-size distribution function (PSDF) behavior of C2H4 premixed burner-stabilized stagnation (BSS) flame was studied. A wide range of DME addition from pure C2H4 to pure DME was considered. The sectional aerosol dynamics model with detailed gas- and particle-phase kinetic mechanism was employed for the simulations. The results indicate that soot growth rate by nucleation, and especially the H-abstractionC2H2addition (HACA) mechanism and polycyclic aromatic hydrocarbons (PAH) condensation increased significantly inside the stagnation boundary layer, due to strong flame-wall interaction. The PSDF curve in the post-flame region was unimodal, while that in the stagnation boundary layer was bimodal. The first peak of the PSDF curve in the stagnation boundary was resulted from the enhanced nucleation rate, and the second peak was due to the intensified soot surface growth by HACA reaction and PAH condensation. The rich premixed C2H4 BSS flame did not exhibit the synergistic effect of DME addition on PAH and soot formations. Soot formation rate decreased monotonously with DME addition for the C2H4 premixed BSS flame. Topology of soot PSDF behavior of the C2H4 premixed BSS flame changed significantly when DME addition exceeded above 20%.

Probing the low-temperature chemistry of ethanol via the addition of dimethyl ether

Considering the importance of ethanol (EtOH) as an engine fuel and a key component of surrogate fuels, the further understanding of its auto-ignition and oxidation characteristics at engine-relevant conditions (high pressures and low temperatures) is still necessary. However, it remains difficult to measure ignition delay times for ethanol at temperatures below 850 K with currently available facilities including shock tube and rapid compression machine due to its low reactivity. Considering the success of our recent study of toluene oxidation under similar conditions [38], dimethyl ether (DME) has been selected as a radical initiator to explore the low-temperature reactivity of ethanol. In this study, ignition delay times of ethanol/DME/‘air’ mixtures with blending ratios of 100% EtOH, 70%/30% EtOH/DME and 50%/50% EtOH/DME mixtures were measured in a rapid compression machine and in two high-pressure shock tubes at conditions relevant to internal combustion engines (20–40 atm, 650–1250 K and equivalences ratios of 0.5–2.0). The influence of these conditions on the auto-ignition behavior of the mixture blends was systematically investigated. Our results indicate that, in the low temperature range (650–950 K), increasing the amount of DME in the fuel mixture significantly increases the reactivity of ethanol. At higher temperatures, however, there is almost no visible impact of the fuel mixture composition, whereas DME shows a lower reactivity. Furthermore, with the addition of DME, different kinetic regimes were observed experimentally: the reactivity is controlled by ethanol when the addition of DME is less than 30% while it is dominated by DME when the proportion of DME is over 50%. Literature mechanisms show reasonable agreement with the new experimental data for the 100% EtOH and the 70%/30% EtOH/DME mixtures but under-predict the reactivity of the 50%/50% EtOH/DME mixtures at temperatures below 850 K, suggesting that further refinement of the low-temperature chemistry of ethanol/DME is warranted. An updated binary fuel mechanism is therefore proposed by incorporating the latest experimental and/or theoretical work in the literature, as well as adding new reaction pathways. Results indicate that the proposed model is in satisfactory agreement with all of the mixtures investigated.

Isomer Identification in Flames with Double-Imaging Photoelectron/Photoion Coincidence Spectroscopy (i2PEPICO) using Measured and Calculated Reference Photoelectron Spectra

Abstract Double-imaging photoelectron/photoion coincidence (i2PEPICO) spectroscopy using a multiplexing, time-efficient, fixed-photon-energy approach offers important opportunities of gas-phase analysis. Building on successful applications in combustion systems that have demonstrated the discriminative power of this technique, we attempt here to push the limits of its application further to more chemically complex combustion examples. The present investigation is devoted to identifying and potentially quantifying compounds featuring five heavy atoms in laminar, premixed low-pressure flames of hydrocarbon and oxygenated fuels and their mixtures. In these combustion examples from flames of cyclopentene, iso-pentane, iso-pentane blended with dimethyl ether (DME), and diethyl ether (DEE), we focus on the unambiguous assignment and quantitative detection of species with the sum formulae C5H6, C5H7, C5H8, C5H10, and C4H8O in the respective isomer mixtures, attempting to provide answers to specific chemical questions for each of these examples. To analyze the obtained i2PEPICO results from these combustion situations, photoelectron spectra (PES) from pure reference compounds, including several examples previously unavailable in the literature, were recorded with the same experimental setup as used in the flame measurements. In addition, PES of two species where reference spectra have not been obtained, namely 2-methyl-1-butene (C5H10) and the 2-cyclopentenyl radical (C5H7), were calculated on the basis of high-level ab initio calculations and Franck-Condon (FC) simulations. These reference measurements and quantum chemical calculations support the early fuel decomposition scheme in the cyclopentene flame towards 2-cyclopentenyl as the dominant fuel radical as well as the prevalence of branched intermediates in the early fuel destruction reactions in the iso-pentane flame, with only minor influences from DME addition. Furthermore, the presence of ethyl vinyl ether (EVE) in DEE flames that was predicted by a recent DEE combustion mechanism could be confirmed unambiguously. While combustion measurements using i2PEPICO can be readily obtained in isomer-rich situations, we wish to highlight the crucial need for high-quality reference information to assign and evaluate the obtained spectra.

Combustion and emissions characteristics of a S.I. engine fueled with gasoline-DME blends under different spark timings

Dimethyl ether has high cetane number and low temperature reaction characteristics. These mean that blending small amount of dimethyl ether to the spark-ignited engine would be helpful for improving the performance under lean conditions. Spark timing is one of the important factors influencing the engine combustion. Thus, it is necessary to investigate performance of the dimethyl ether-blended gasoline engine under various spark timings. The engine was run at 1400rpm, a manifolds absolute pressure of 60kPa and a constant excess air ratio of 1.20. Test results showed that the addition of dimethyl ether resulted in the raised indicated mean effective pressure for the gasoline engine. Over increased and decreased spark timing tended to cause the dropped indicated mean effective pressure. The coefficient of variation in indicated mean effective pressure was diminished with the spark timing advances and dimethyl ether addition. NOx and HC emissions were dropped with the spark timing decrease. NOx emissions from the dimethyl ether-mixed gasoline engine are decreased with the decrease of spark angle.

Influence of dimethyl ether and diethyl ether addition on the flame structure and pollutant formation in premixed iso-octane flames

While the combustion reactions of many individual fuels in flames have been studied in detail, often providing numerous experimental species profiles in combination with the development and critical testing of kinetic models, similar work on fuel mixtures has remained scarcer, especially for blends of conventional and biogenic fuels. In the present study, we have thus chosen iso-octane, one of the primary reference fuels that determine octane number and knocking tendency of gasoline, as the base fuel, and dimethyl ether (DME) and diethyl ether (DEE) as potentially bio-derived fuel components. Premixed low-pressure flames of iso-octane without and with different amounts of DME or DEE, of up to 50% of the fuel in the mixture, have been investigated systematically to analyze the change of the flame structure and species composition upon blending. All flames were studied at a pressure of 40 mbar (4kPa) with 50% argon dilution and a cold gas velocity of 60 cms−1. The carbon-to-oxygen ratio was fixed at 0.47 while the equivalence ratio changed from 1.47 to 1.84. Up to 70 species in the range of C0–C9 were identified and quantified in each flame by electron ionization molecular-beam mass spectrometry (EI-MBMS). Moreover, about 300 experimental species profiles were provided.The aim of this study is thus threefold. First, a new species dataset for a pure iso-octane flame is reported, since speciation data under premixed flame conditions for this fuel is surprisingly scarce. Second, the effects of DME and DEE addition in increasing amounts to the iso-octane base flame are investigated with special attention to the flame structure and pollutant species formation. Third, a joint combustion model for iso-octane, DME, and DEE mixtures consisting of 379 species and 1931 reactions is proposed that was examined against the present data and reference experiments for a larger range of conditions. Key pathways of interesting species, including aldehydes, alkenes, and soot precursors were revealed with the present mixture model. DME and DEE addition were found to have a similar influence on the flame structure of iso-octane, except for some C2 and C3 intermediates. The addition of DME as well as of DEE decreases the formation of soot precursors while it enhances the production of formaldehyde.

A modified bisulfite conversion method for the detection of DNA methylation.

Our purpose is to improve the conventional procedures for bisulfite conversion used to detect 5-methylcytosine in DNA. Impacts of different bisulfite salts, bisulfite conversion temperature, antioxidants and denaturants on DNA conversion and degradation were assessed by methylation-sensitive melt curve analysis. The modified method was tested on different genes and the conversion efficiency was analyzed by bisulfite sequencing. We developed a modified bisulfite conversion method that completes this process within 2 h. We demonstrate that high temperature denaturation is the major cause for DNA degradation, and the addition of ethylene glycol dimethyl ether is an effective way to accelerate the bisulfite conversion. The conversion efficiency is comparable to many other commercial kits. Our modified bisulfite conversion method is simple, cost efficient and less time consuming and is compatible with different genes and samples, thus has a great potential for the future research and clinical applications.

Investigation on performance of a spark-ignition engine fueled with dimethyl ether and gasoline mixtures under idle and stoichiometric conditions

This study investigated effects of dimethyl ether addition on the gasoline engine combustion and emissions performance under idle and stoichiometric conditions. The engine was first modified to be fueled with gasoline and dimethyl ether simultaneously. The experimental results showed that, with the increase of dimethyl ether energy fraction in the total fuel, the total fuel energy flow rate was decreased, and the flame development and propagation periods were shortened. The cycle-to-cycle variation was reduced and the degree of constant volume combustion was increased after the dimethyl ether addition. The dimethyl ether blending was beneficial for reducing hydrocarbon and nitrogen oxide emissions from 1951 and 95 ppm of the original engine to 552 and 34 ppm of pure dimethyl ether, respectively. Meanwhile, with the increase of dimethyl ether addition level, the peak cylinder pressure and carbon monoxide emission were decreased at first, whereas increased when the dimethyl ether energy fraction exceeded 49%. Furthermore, heat release rate during the low temperature reaction was enhanced with the increase of dimethyl ether addition level. The maximum heat release rate was heightened and its relevant crank angle was advanced during the high temperature reaction period after the dimethyl ether enrichment.

Two-level Full Factorial Design for Selectivity Modeling and Studying Simultaneous Effects of Temperature and Ethanol Concentration in Methanol Dehydration Reaction

Using surface analysis, simultaneous effects of temperature (260-380oC) and ethanol concentration (0-1%) on dimethyl ether (DME) selectivity, yields of hydrocarbon and DME, and methanol conversion were investigated in methanol dehydration reaction over γ-Al2O3 catalyst. Methanol conversion and yield of hydrocarbon/DME were found to be significantly affected by temperature and the temperature-ethanol concentration interactions. In addition, DME selectivity and yield of DME were found to be influenced by the process temperature, and ethanol concentration as well as their interactions. BET surface area measurement and scanning electron microscopy technique (SEM) confirmed that the catalyst deactivation was intensified at higher temperatures by increasing ethanol concentration. Using statistical regression, a mathematical model was developed, and then validated, to describe simultaneous effects of temperature and feedstock ethanol concentration on DME selectivity. Although the model was statistically significant, curvature was not significant. Therefore, a two-level full factorial design of experiment approach was followed as a promising strategy for DME selectivity modeling and interpretation of data in this work.

Study on effect of dimethyl ether addition on combustion characteristics of turbulent methane/air jet diffusion flame

The kinetics and soot and NOx emission characteristics of the CH4/dimethyl ether (DME) jet diffusion flames (JDFs) are studied by experiments and simulations with a detailed chemical mechanism. The results showed that decomposition of DME in the pyrolysis zone generated massive CH3, which changed the local flame structure and soot-correlated chemistry to some extent. Due to reductions of the incipient species concentrations including benzene (A1), pyrene (A4), C3H3, and C2H2, soot loading of the CH4 JDF decreased by reducing margins with DME addition. A1 and thus soot formation rates due to DME addition were most sensitive to the recombination reaction of C3H3 (C3H3+C3H3=A1). With respect to the CH4/DME JDFs, NOx was emitted mainly through the thermal and prompt pathways. The thermally-generated EINOx increased exponentially with DME addition because of the increasing enhancement of OH concentration in the radical pool. By contrast, the promptly-generated EINOx decreased in reducing margins with DME addition because of the reducing decrease in CH concentration. The synergistic effect of DME addition on the total NOx emission, i.e. the overall EINOx decreased firstly and then increased with DME addition, was examined in this paper. Additionally, it is reported that the 40%CH4/60%DME case was comprehensively optimal in terms of soot and NOx emission reductions.

Influence of dimethyl ether addition on the oxidation of acetylene in the absence and presence of NO

Dimethyl ether (DME) is a promising diesel fuel additive for reducing soot and NOx emissions, because of its interesting properties and the possibility of a renewable production. An experimental and modeling study of the oxidation of acetylene (C2H2, considered as an important soot precursor) and DME mixtures has been performed under well-controlled flow reactor conditions. The influence of temperature, air excess ratio (λ) and presence of NO on the oxidation process has been analyzed. Under fuel-rich conditions, the presence of DME in these mixtures modifies the radical pool delaying the acetylene consumption. C2H2 and DME, and the radicals generated in their conversion, interact with NO achieving different levels of NO concentration diminution depending upon the operating conditions. Under fuel-lean conditions, the presence of DME in the mixtures increases the NO diminution, whereas for the other values of λ considered, the maximum NO decrease reached is lower than that obtained in the case of pure acetylene.

Effect of furanic biofuels on particles formation in premixed ethylene–air flames: An experimental study

Furanic fuels have been recently investigated because they are considered possible fossil fuel substituents due to their high energy density, their renewable origin and consequently low green-house gas emissions. Few data are available about the behaviors of these fuels in laboratory flame reactors. We have recently studied their sooting tendency in a counter-flow diffusion flame showing a different propensity to form particulate matter depending on the richness of the combustion conditions. In this paper, we explore their tendency in forming particulate matter in atmospheric pressure premixed flames burning mixtures of ethylene and furanic fuels at four different equivalence ratios, namely 2.01, 2.16, 2.31 and 2.46, thus covering the range from slightly sooting to fully sooting conditions. Liquid furan, 2-methylfuran and 2,5-dimethylfuran have been added to ethylene as 10% and 20% of the total carbon fed to the flame.In-situ spectroscopy, namely laser UV-induced emission, has been used as diagnostic tool to detected different classes of precursor nanoparticles by changing the detection wavelength from the UV to the visible. Laser induced incandescence has instead been used to detect soot particles. Equivalence ratios, the total carbon flow rate and cold gas velocity have been kept constant, allowing the combustion temperature to be almost the same also when furans were added.LII signal decreases significantly when furans are added showing a strong effect of furanic fuels in decreasing the amount of soot formed in atmospheric pressure premixed flames. Particularly the reduction increases as the equivalence ratio increases. On the other side, LIF UV and LIF VIS slightly decrease when furans are added. The absence of a significant reduction of the LIF UV signal when furans are added suggests that small particle formation is not effectively inhibited by these additives. This behavior is similar to what found for ethanol and dimethyl ether addition to ethylene premixed flames, showing a similarity in the behavior of these oxygenated fuels.