Dimethyl Ether Addition Research Articles

Enhancing and assessing ammonia-air combustion performance by blending with dimethyl ether

As a hydrogen energy carrier and carbon-free fuel, ammonia (NH3) is being growingly considered as an alternative fuel for combustion systems in an effort to reduce carbon emissions. Unlike conventional fossil fuels, its relatively low flame speed hinders its widespread use in practice. Utilizing the 1D freely propagating flame model in Chemkin-Pro 2019, this work numerically evaluates the impact of blending ammonia with dimethyl ether (DME) on the laminar burning velocity of NH3/air flames. For this, the reaction mechanism is first validated by comparing predictions to experimental data available in the literature. The addition of DME is found to significantly enhance the laminar burning velocity (SL) of NH3 flames, which can be comparable to that of hydrocarbon fuels. This enhancement is a result of the combined thermal and chemical effects. Reaction pathway and sensitivity analyses reveal that adding DME enables the major reaction steps and the sensitivities to be altered, thus positively affecting the overall reaction rate. Furthermore, the SL of NH3/air flames is weakly dependent on the inlet thermodynamic pressure, but becomes stronger with more DME blended. The explanation behind this phenomenon is that the relative importance of the termination versus branching reactions is more significant in binary flames. The overall reaction order characterizing the importance of the chain branching and the terminating reactions shows a decreasing trend with increasing inlet pressure. In general, the present work provides a design guideline on the selection of fuel flexibility and sheds light on the fundamental NH3-DME-fueled flame enhancement mechanisms.

Experimental and kinetic study on laminar flame speeds of ammonia/dimethyl ether/air under high temperature and elevated pressure

Laminar flame speeds of ammonia mixed with dimethyl ether (DME) under elevated pressure and high temperature at different equivalence ratios were measured. Several kinetic models (Dai model, DTU model, Shrestha model, Mei model, Zhang model and Han model) are compared and validated with experimental data. Models with best performance were combined together for NH3/DME laminar flame speed validation and Dai-Zhang model was obtained. Simulations from Dai-Zhang model match well with experimental data. Pathway, sensitivity and key radicals’ mole fraction analysis were conducted to find out the deep kinetic insight on ammonia oxidation with and without DME addition. With DME addition, the oxidation of NH2 radical is dominated by carbon-containing species, with roughly NH2 50% reacting via NH2 + CH2O = NH2 + CHO and NH2 + CH3 = CH3NH2. In NH3/air flame, NH2 and NH radicals’ recombination reactions are more dominant than that in NH3/DME/air flame. Abstraction of NH2 by OH and H radicals forming NH becomes more important while branching ratio of HNO formation decreases. The directly oxidization of NH yielding NO can be neglected. Thus, NO formation decreases remarkably and the laminar flame speed is lower than co-firing with DME.Comparison was also conducted in NH3/DME/air, NH3/DMM/ air and NH3/syngas/air flames. SL of NH3/DME/air is slightly lower than NH3 blended with DMM. SL of syngas/NH3/air flame is firstly lower and then higher than DME/NH3/air. The position of cross point is around xNH3=0.4.

Particulate number and size distribution of dimethyl ether/gasoline combined injection spark ignition engines at medium engine speed and load

The understanding of particulate matter emissions from Dimethyl ether (DME)/gasoline combined injection engine is crucial for the application of DME in engines. In this study, the particulate number (PN) and the size distribution of particles from a combined injection spark ignition DME/gasoline engine are studied experimentally. The results show that the addition of DME can effectively reduce both the accumulation and nucleation mode particle numbers for the DME/gasoline engines compared with pure gasoline engines. The distribution of the particle sizes follows a single peak distribution pattern, and the size of the most of particles from DME/gasoline engine are in the nucleation mode, peaking at around 17.8 nm for different ignition timing and DME ratios. Both the nucleation particle numbers (NPN) and accumulation particle numbers (APN) are dependent on the operating conditions investigated in this study and the affecting degree depends on the DME ratios. The accumulation particle numbers (APN) fractions are almost the same for pure gasoline, but the APN fraction increased with the increase of engine load after DME additions.

Dimethyl ether (DME) and dimethoxymethane (DMM) as reaction enhancers for methane: Combining flame experiments with model-assisted exploration of a polygeneration process

The potential of dimethyl ether (DME) and dimethoxymethane (DMM), representatives of the attractive oxymethylene ether (OME) alternative fuel family, are explored here as reactivity enhancers for methane-fueled polygeneration processes. Typically, such processes that can flexibly generate power, heat, or chemicals, operate under fuel-rich conditions in gas turbines or internal combustion engines. To provide a consistent basis for the underlying reaction mechanisms, it is recognized that speciation data for the DME/CH4 fuel combination are available for such conditions while such information for the DMM/CH4 system is largely lacking. In addition, it should be noted that a detailed speciation study in flames, i.e., combustion systems involving chemistry and transport processes over a large temperature range, is still missing in spite of the potential of such systems to provide extended species information. In a systematic approach using speciation with electron ionization molecular-beam mass spectrometry (EI-MBMS), we thus report, as a first step, investigation of six fuel-rich premixed flames of DME and DMM and their blends with methane with special attention on interesting chemicals. Secondly, a comprehensive but compact DME/DMM/CH4 model (PolyMech2.1) is developed based on these data. This model is then examined against available experimental data under conditions from various facilities, focusing preferentially on elevated pressure and fuel-rich conditions. Comparison with existing literature models is also included in this evaluation. Thirdly, an analysis is given on this basis, via the extensively tested PolyMech2.1 model, for assumed polygeneration conditions in a homogeneous charge compression ignition (HCCI) engine environment. The main interest of this model-assisted exploration is to evaluate whether addition of DME or DMM in a polygeneration process can lead to potentially useful conditions for the production of syngas or other chemicals, along with work and heat. The flame results show that high syngas yields, i.e., up to ∼78% for CO and ∼35% for H2, can be obtained in their burnt gases. From the large number of intermediates detected, predominantly acetylene, ethylene, ethane, and formaldehyde show yields of 2.1−4.4% (C2 hydrocarbons) and 3.4−8.7% (CH2O), respectively. Also, methanol and methyl formate show comparably high yields of up to 0.6−6.7% in the flames with DMM, which is 1–2 orders of magnitude higher than in those with DME as the additive. In the modeling-assisted exploration of the engine process, the PolyMech2.1 model is seen to perform at significantly reduced computational costs compared to a recently validated model without sacrificing the prediction performance. Promising conditions for the assumed polygeneration process using fuel combinations in the DME/DMM/CH4 system are identified with attractive syngas yields of up to 77% together with work and heat output at exergetic efficiencies of up to 89% with DME.

Alkaline aerobic oxidation of native softwood lignin in the presence of Na+-cyclic polyether complexes

Alkaline aerobic oxidation is a promising way to convert lignin to low molecular weight phenols, especially 4-hydroxybenzaldehydes. Our previous studies reported that oxidation of softwood lignin samples with a bulky cation, Bu4N+, facilitates selective production of vanillin (4-hydroxy-3-methoxybenzaldehyde). This study presents vanillin production from native softwood lignin in Japanese cedar (Cryptomeria japonica) in NaOH aq. in the presence of cyclic polyethers, with our expectation that Na+-polyether complexes exhibit effects similar to those of Bu4N+. Oxidation of wood flour (10 mg) in 4.0 M NaOH aq. (2.0 mL) at 120 °C under air gave vanillin with 6.2 wt% lignin-based yield, which was raised to 15.2 wt% by the addition of 15-crown-5 (1,4,7,10,13-pentaoxacyclopentadecane). On the other hand, such effect was not observed with the addition of tetraethylene glycol dimethyl ether, a non-cyclic analog of 15-crown-5. Mechanistic study with a lignin model compound revealed that stabilization of a vanillin precursor by the complex cation was a reason for the increased vanillin yield exhibited by the crown ether. This is similar to the influence of Bu4N+ reported previously, suggesting effective control of aerobic oxidation by large size cationic species.

Enhancement of Lipid Extraction from Soya Bean by Addition of Dimethyl Ether as Entrainer into Supercritical Carbon Dioxide.

Soya beans contain a variety of lipids, and it is important to selectively separate neutral lipids from other lipids. Supercritical carbon dioxide extraction has been used as an alternative to the selective separation of neutral lipids from soya beans, usually using non-polar hexane. However, supercritical carbon dioxide extraction has a high operating pressure of over 40 MPa. On the other hand, liquefied dimethyl ether extraction, which has attracted attention in recent years, requires an operating pressure of only 0.5 MPa, but there is concern about the possibility of an explosion during operation because it is a flammable liquefied gas. Therefore, this study aims to reduce the operating pressure by using a non-flammable solvent, supercritical carbon dioxide extraction mixed with liquefied dimethyl ether as an entrainer. The extraction rate and the amount of neutral lipids extracted increased with increasing amounts of added liquefied dimethyl ether. In the mixed solvent, the amount of neutral lipids extracted was higher at an operating pressure of 20 MPa than in pure supercritical carbon dioxide extraction at 40 MPa. The mixing of liquefied dimethyl ether with supercritical carbon dioxide allowed an improvement in the extraction of neutral lipids while remaining non-flammable.

Experimental Study on Explosion Characteristics of Ultra-Low Concentration Methane Mixed with Dimethyl Ether

ABSTRACT Low-concentration methane accounts for the most massive percent of coal mine methane (CMM). Reasonable utilization of low-concentration methane, especially the ultra-low concentration methane (less than 5%), is of great significance for resource conservation and environmental protection. Therefore, a reasonable utilization method of ultra-low concentration methane (ULCM) was proposed. The main idea is to add combustible substances, such as dimethyl ether (DME), into ULCM to promote its combustion and explosion. The experimental investigations on the explosion parameters of ULCM mixed with DME were conducted in a horizontal explosion pipeline. The results suggested that the addition of DME can promote the combustion and explosion of ULCM. The maximum values of v and Pmax appear in the equivalence ratio of 1.1–1.3, which are slightly higher than the values at stoichiometric concentration because of the transient effect of the explosion pipeline. The results provide a reference for selecting optimum mixing concentration in the utilization process of ULCM mixed with combustion supporting agent. The researches offer a feasible method for the utilization of ULCM, which is of great significance for energy conservation and emission reduction of CMM.

Study on methane oxidation affected by dimethyl ether oxidation at low temperatures using a micro flow reactor with a controlled temperature profile

The present study aims to identify cross-reactions of methane and dimethyl ether (DME) at low temperatures. A weak flame in a micro flow reactor with a controlled temperature profile (MFR) for a stoichiometric methane/DME/air mixture with 90% CH 4 and 10% DME (hereinafter expressed as 90%/10% CH 4 /DME) was used and analyzed. The weak flame structure was investigated by chemiluminescence observation and laser-induced fluorescence (LIF) measurements of OH and CH 2 O. Measured chemiluminescence and fluorescence intensity profiles were compared to computations with five detailed chemical kinetic mechanisms. Both experimentally and computationally obtained results showed the weak flame position of 90%/10% CH 4 /DME shifted to lower temperature in MFR compared to that of 100% CH 4 reported earlier, indicating methane reactivity enhancement by the small DME addition. CH 2 O-LIF showed extensive formation of CH 2 O at low temperatures. Each mechanism predicted different levels of CH 2 O formation. The four mechanisms among five which include intermediate-temperature oxidation chemistry for methane , CH 3 → CH 3 O 2 → (CH 3 O 2 H) → CH 3 O → CH 2 O, predicted two-staged formation of CH 2 O at 650 and 730 K, whereas another mechanism predicted single-stage formation of CH 2 O at 650 K. Rate-of-production analysis revealed that OH radicals formed from low-temperature oxidation of DME initiate H-atom abstraction from methane; then intermediate-temperature oxidation chemistry for methane proceeds even at low temperatures. The contribution of intermediate-temperature oxidation chemistry for methane to CH 2 O formation at 730 K is stronger than that at 650 K, causing two-stage formation of CH 2 O.

Ignition delay times of iso-butane activated by DME under various equivalence ratios in the shock tube

The ignition delay time of the high cetane number dimethyl ether (DME), high octane number i-butane, and their binary blends were investigated in a shock tube over the temperature range of 1091–1797 K, pressures of 2–10 atm, and equivalence ratios of 0.5–2.0. The LLNL iso-Octane Model and the DME sub-set of the Aramco3.0 Model were assembled together to reproduce the ignition delay behavior of the binary blends. Chemical kinetic analyses were conducted to understand the interplay between DME and i-butane at high temperatures. The ignition delay of DME and i-butane show the opposite equivalence ratio dependence under the current conditions. The promoting effect of DME addition on the ignition delay of i-butane becomes more significant as the equivalence ratio increases. The research result shows that there is no significant fuel to fuel interactions between DME and i-butane in the present conditions. The high reactivity of DME and its rapid accumulation of the free radicals lead to the promoted auto-ignition of i-butane.

Explosion characteristics and energy utilisation of coal mine ultra-lean methane

Reasonable recycling low concentration methane, especially the ultra-lean methane (the concentration lower than 5%), is significant to resource saving and environment protection. Nowadays, low concentration gas power generation technology is well developed. Notwithstanding this, ultra-lean methane has not been applied in large scale mainly due to the high utilisation costs. Therefore, to address this issue, we break through the empirical thinking to make ultra-lean methane combustion by blending with combustible substances other than only increasing the methane concentration. Its feasibility was analysed from theoretical analysis, especially the cost analysis. Dimethyl ether (DME) was selected as the additive from a range of combustible substances. Then experimental study on the explosion parameters of coal mine ultra-lean methane blending with DME was carried out in a standard 20-L explosion spherical vessel; the lower explosion limits (LEL) at different initial temperatures (ambient temperature, 40°C, 60°C and 80°C) were tested at methane concentration of 0.5%, 1%, 2%, 3% and 4%, respectively. The experimental results indicate that the addition of DME can significantly reduce the minimum explosion concentration of methane, and both P max and (dP/dt)max increase with an increase of DME content in the total fuel. The overall trend of P max and (dP/dt)max increases first and reaches to the maximum. In addition, both CO and CO2 in explosion tail gases are consistent with the decrease trend with increasing in gas mixture. The explosion solid product contained a large number of aromatic hydrocarbon structures, and the solid particles were mainly two types of spherical and blocky with the diameter between 30 and 50 µm. The explosion phenomenon and data provide a reference for assessing the hazards of practical energy system, and guiding the designs of fuel formula and engine safety.

The role of DME addition on the evolution of soot and soot precursors in laminar ethylene jet flames

Dimethyl ether (DME) has received considerable attention as a fuel additive to reduce the emission of particulate matter (PM) due to its low-temperature chemistry, molecularly bound oxygen atom and the absence of CC bonds. However, the effect of DME addition on the evolution of soot and particularly soot precursors is not entirely understood. This study aims to shed light on this issue by blending different proportions of DME with diffusion, E60, and partially premixed, PP12, base cases of laminar ethylene flames using the Yale benchmark burner. Laser-induced fluorescence (LIF) intensity and decay time are used to characterize the structure and evolution of soot precursors, while laser-induced incandescence (LII) is utilized to determine the soot volume fraction (SVF) and the effective primary particle diameter (Dp). For the diffusion flames, the addition of 10% DME increases the concentrations of both soot and soot precursors. With the further addition of DME to 20%, the SVF decreases to levels similar to those of E60 and then decreases further with 30% DME addition. All diffusion flames with DME addition exhibit higher concentrations of soot precursors than those of the reference E60 case. For PP12, the addition of 10% DME shows similar concentrations of soot precursors and a slight reduction in the SVF which continues to decrease with further increases in DME additions to the PP12 flame. The addition of DME seems to have little effect on the soot particle diameters for all the studied flames. Overall, the PP flames result in smaller mean particle diameters than the diffusion flame counterparts.

Experimental and numerical study on the ignition delay times of dimethyl ether/ethane/oxygen/carbon dioxide mixtures

The ignition delay times (IDTs) of dimethyl ether (DME)/ethane/O2/CO2 mixtures were measured in a shock tube at pressures of 0.8, 2, and 10 atm; temperatures within the range of 1126–1449 K; equivalence ratio of 0.5; and DME proportions within the range of 0–100%. Four chemical kinetic models named OXYMECH, AramcoMech 3.0, San-Diego 2016 and Wang-DME were validated using the IDTs measured in this work. The results indicate that the OXYMECH predicts well the experimental data under O2/CO2 and O2/N2 atmospheres. At P = 0.8 and 2 atm, T = 1300 K, the increase of the DME proportion inhibits the ignition of the mixtures under O2/N2 and O2/CO2 atmospheres. At P = 10 atm, T = 1300 K, the IDTs of the mixtures firstly decrease when DME proportion increases from 0 to 20%, and then increase when DME proportion increases from 20 to 100% under O2/CO2 atmosphere, while the IDTs of the mixtures increase as the DME proportion increases under O2/N2 atmosphere. The valley-values of the IDTs of the mixtures appear at the certain DME proportion at P = 10 atm, T = 1100 K and 1200 K under O2/N2 and O2/CO2 atmospheres. The analyses of sensitivity and the rate of production were conducted to interpret the effect of DME addition and the properties of CO2 on the ignition of the DME/C2H6/O2/CO2 mixtures.

Combustion, performance, and emissions of safflower biodiesel with dimethyl ether addition in a power generator diesel engine

ABSTRACT In this study, the effect of dimethyl ether (DME) addition to diesel (ultralow sulfur diesel fuel) and biodiesel fuels on the combustion, performance, and emissions of a diesel-powered generator was investigated. For this purpose, fuel samples of the ternary blend that volumetrically composed of 10% safflower biodiesel–10% dimethyl ether–80% ultralow sulfur diesel fuel (B10DME10), the ternary blend that volumetrically composed of 25% safflower biodiesel–25% dimethyl ether–50% ultralow sulfur diesel fuel (B25DME25), the binary blend that volumetrically composed of 25% safflower biodiesel–75% ultralow sulfur diesel fuel (B10DME10) B25, and pure safflower oil biodiesel (B100) and standard ultralow sulfur diesel (D2) were prepared. The test engine was loaded by power drawing from the generator by the usage of equivalent powered electrical heating resistances. Generally, using DME with biodiesel improved the combustion properties of biodiesel blends that can be attributed to the lower viscosity of DME. The maximum cylinder pressure was obtained for B10DME10 in general and sometimes for B25DME25. When test fuels are compared, DME blends showed higher and earlier peaks of heat release compared to diesel and biodiesel blend fuels especially. It was found that combustion is more efficient from mass fuel consumption (MFC) and brake specific fuel consumption (BSFC) values in the use of DME than biodiesel. BSEC values of using DME in the blends considerably decreased that it is the proof of improved combustion and energy efficiency. The highest average efficiency values were obtained for B25DME25 as 28.3% although it has a lower calorific value than D2 due to the considerably improved combustion properties of DME, while the average efficiency values were 23.1%, 23.3%, and 20.7% for D2, B25, and B100 fuels, respectively. Highest carbon monoxide (CO) emissions were obtained in the use of pure biodiesel, while the lowest CO emissions were obtained in the use of DME. The addition of DME is seen to increase the nitrogen oxides (NOx) and CO emissions.

Effect of DME addition on flame dynamics of LPG/DME blended fuel in tail space of closed pipeline

In order to recognize and reveal the explosion characteristics and hazards of LPG blended fuel with active fuel additions, flame dynamics of liquefied petroleum (LPG)/dimethyl ether (DME) blended fuel in the tail space of a closed pipeline was experimentally investigated. A high-speed camera and a pressure transducer were used to acquire the flame structure and explosion overpressure, and the displacement and speed were further calculated by MATLAB programming. The research results show that the flame under the conditions of stoichiometric and lean-fuel concentration presents a more remarkable local suppressive propagation compared with the rich-fuel condition. In the vicinity of stoichiometric concentration, the increase of equivalence ratio leads to the increase of flame front temperature, meanwhile, the process also improves the molecular diffusion coefficient and heat transfer efficiency. The reverse propagation of flame brings obvious temperature loss to fuel system. The existence of reflected reverse flow makes it difficult for the flame to propagate to the end of the closed space. The increase of equivalence ratio and DME blended ratio is helpful for the improvement of flame suppressive mechanism and flame acceleration mechanism, and the effect of the latter is more obvious. The knowledge obtained about flame dynamic characteristics can improve the assessment and recognition of explosion hazards of blended fuel.

Role of dimethyl ether in incipient soot formation in premixed ethylene flames

Emissions of soot particles exert crucial impact on human health and the environment. Previous researches show that a partial replacement of fossil fuels with oxygenated fuels is supposed to reduce soot emission. However, the crucial information of soot size distributions is unclear, although small particles are more dangerous than large particles. In this paper, dimethyl ether (DME) is selected among the oxygenated fuels for the investigation of the doping effect on nascent soot formation. DME was doped in the burner-stabilized rich premixed ethylene/oxygen/argon flames at various mixing ratios. Flame temperature profiles were measured using R-type thermocouples with radiation correction. A scanning mobility particle sizer (SMPS) with a sampling system was used to determine particle size distributions (PSDs) of soot-containing combustion products with immediate dilution. Thermo-gravimetric analysis (TGA) complemented with elemental analysis (EA) was conducted to detect the chemical properties of formed soot particles. Additionally, species profiles of the experimental flame conditions were provided from simulations. The experimental PSDs showed that DME addition could slow down soot evolution process, while lead to a slight increase in incipient soot with size below 4 nm. When DME added, the production of benzene was suppressed due to the reduced concentrations of acetylene and propargyl, and thus soot nucleation. Meanwhile, soot oxidiation was enhanced because the OH radical and the oxidizability of soot particles are both increased. Considering the slight increase of sub-4 nm soot, the effect of oxygenated-PAHs (OPAH) was emphasized. The production of OPAH suppressed soot surface growth, which leading to the relatively lower consumption of sub-4 nm soot in DME added flames.As a result, DME cannot be simply regarded as a clean fuel due to the enhanced formation of sub-4 nm soot particles. When applying oxygenated fuels into practice, it is necessary to pay more attention to the size distributions of the emitted particles, and conduct appropriate post-processing techniques to reduce the emissions of small particles.

Shock wave evolution and overpressure hazards in partly premixed gas deflagration of DME/LPG blended multi-clean fuel

In order to reveal the shock wave propagation and overpressure hazards of DME (dimethyl ether)/LPG (liquefied petroleum gas) blended fuel in the process of partly premixed gas deflagration, both experimental apparatus and numerical model for multiple-gas explosion and propagation are established. The results show that the overpressure in the sharp-dropping overpressure hazards zone are generally more than 200 kPa, and the distribution range was 5.75–6.75 times of the maximum overpressure hazards zone. The overpressure in the gentle-dropping overpressure hazards zone is the smallest, but its propagation and influence distance is the largest, which can cause certain damage to people and buildings in the far field. The participation of DME at lean-fuel concentration had the greatest effect on the increase of overpressure hazards in the original premixed zone, which could reach 306.6%. The increase of equivalence ratio and the addition of DME fuel both accelerate the superposition of multiple pressure waves. High overpressure risk is always accompanied by high overpressure evolution speed. As equivalence ratio increases, the relationship between the average shock wave velocity and the DME blended ratio was linear, quadratic and cubic, also the flame acceleration mechanism by high burning rate and the flame deceleration mechanism by low combustion heat successively dominates.

Laminar premixed and non-premixed flame investigation on the influence of dimethyl ether addition on n-heptane combustion

Several different ether components have been proposed as renewable replacements for diesel fuel in compression ignition engines. From a fundamental point of view, blends of n-heptane and dimethyl ether (DME) have been considered in this study, where n-heptane is a single-component diesel surrogate and DME acts as a representative for oxymethylene ethers. n-Heptane and n-heptane / DME blends have been investigated experimentally under laminar premixed low-pressure and non-premixed atmospheric-pressure counterflow flame conditions. For the premixed case, a series of three fuel-rich flames was studied with oxygen as the oxidizer, at a constant C/O ratio of 0.47, pressure of 4 kPa, with 50% argon dilution, and an equivalence ratio ϕ near 1.5, burning pure n-heptane and mixtures of n-heptane with DME in the ratios 1:1 and 1:4. In the non-premixed counterflow configuration, two fuel/oxygen/argon flames were studied with pure n-heptane and a 1:1 DME–n-heptane mixture as the fuel. Electron ionization molecular-beam mass spectrometry was used for both flame configurations to investigate the flame structure and determine quantitative mole fraction profiles of stable and reactive species formed in the combustion process. Particular attention was given to the changes caused by partial replacement of n-heptane by DME.Notwithstanding the experimental focus of this work, the experimental results were compared with predictions from a model suitable for both n-heptane and DME that was combined for this case from recent mechanisms available in the literature for these fuels. While the overall flame structure was not significantly altered upon DME addition, with some smaller differences mainly due to temperature effects, more prominent changes and interactive effects were found for a number of primary decomposition products, oxygenated species, and higher-molecular hydrocarbon compounds. In most cases, experimentally observed trends, but not always quantitative changes, could be satisfactorily reproduced and explained by the model.

Effect of dimethyl ether addition on flame stability of premixed methane/air in a micro-planar quartz combustor

Blended combustion has a potential to promote flame stability under micro-scale condition. For this, the effect of dimethyl ether (DME) addition on the flame stability of premixed methane/air confined within a quartz combustor is explored through experimental approach. Seven flame propagation modes are observed for pure methane-air combustion. Experimental results indicate that flame stability could be remarkably enhanced, especially under fuel-lean conditions, and the flame is able to sustain stable combustion for some extreme circumstances with DME addition. To further understand the underlying mechanism of enhanced flame stability, detailed analyses regarding flame shape range and flame transition point as a function of blended ratio are also conducted. The existence range of various flame shapes can be generally broadened to some degree as increasing blended ratio, which is due to the increased value of flame transition point. Furthermore, it is found that variation frequency of weak flame decreases with an increase in blended ratio and inlet velocity. For sufficiently high blended ratio under fuel-lean condition, oscillating flame disappears, which indicates that flame is much more stable in this case. The reason for enhanced flame stability could be related to the increased flame speed and large extinction strain rate with DME addition.

Investigation on the chemical effects of dimethyl ether and ethanol additions on PAH formation in laminar premixed ethylene flames

This paper presents a comparative study focusing on the chemical effects of dimethyl ether (DME) and ethanol (EtOH) on PAH formation in fuel-rich laminar premixed ethylene flames using laser-induced fluorescence (LIF) diagnostic. To investigate the chemical effects, the equivalence ratios, dilution ratios, and temperature profiles were kept nearly constant while DME and EtOH were separately blended into the ethylene-base flame. The LIF testing data showed that the PAH formation was observably suppressed by the DME and EtOH additions, and DME was much more effective at suppressing the PAH formation than EtOH. To reveal the mechanism of the inhibiting effects of oxygenated fuels on PAH formation, chemical kinetic analysis was conducted. The model results captured the variation tendency of PAHs observed in experiments and indicated that the decreased concentration of carbon which was available to form the first aromatic ring (benzene) is the main reason for PAH reduction with EtOH and DME additions. Moreover, during the growth process from benzene to PAHs, the C2H2-addition reactions, which played a key role in the formation of new aromatic rings, were suppressed due to less C2H2 formed in EtOH and DME addition flames. There was less C2H2 produced from DME than that from EtOH, therefore, DME had a stronger inhibiting effect than EtOH on PAH formation in laminar premixed ethylene flames.

Impacts of dimethyl ether enrichment and various injection strategies on combustion and emissions of direct injection gasoline engines in the lean-burn condition

As an alternative fuel, dimethyl ether (DME) improves the combustion and reduces emissions of gasoline engines. Moreover, the control of injection strategies of direct injection (DI) gasoline engines could form the preferable stratified charge, enhancing the performance characteristics, especially under lean burning conditions. Thus, the co-effects of injection strategies and DME addition on the performance of a DI gasoline engine were investigated under the lean-burn condition. Results showed that the appropriate injection ratio (IR) during the two-stage injection strategy could exhibit a higher brake thermal efficiency (BTE), a lower cyclic variation and HC emissions compared to the single injection mode. Moreover, the cyclic variation was decreased firstly then increased, the BTE and heat release rate were raised firstly then reduced with the increase of IR. Furthermore, NOx emissions were increased firstly and then decreased, HC emissions were decreased firstly and then increased and the trend of CO emission was increased constantly. In addition, the DI gasoline engine blended with DME raised BTE, shortened the combustion phase, eased cyclic variation, increased CO emission and dropped HC emissions under tested conditions. The use of DME with optimum IR could be a practical way to improve the trade-off between BTE and NOx emissions.