Effect Of Dimethyl Ether Addition Research Articles

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.

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.

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.

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...

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.

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.

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.

An experimental and numerical study of the effects of dimethyl ether addition to fuel on polycyclic aromatic hydrocarbon and soot formation in laminar coflow ethylene/air diffusion flames

The effects of dimethyl ether addition to fuel on the formation of polycyclic aromatic hydrocarbons and soot were investigated experimentally and numerically in a laminar coflow ethylene diffusion flame at atmospheric pressure. The relative concentrations of polycyclic aromatic hydrocarbon species and the relative soot volume fractions were measured using planar laser-induced fluorescence and two-dimensional laser-induced incandescence techniques, respectively. Experiments were conducted over the entire range of dimethyl ether addition from pure ethylene to pure dimethyl ether in the fuel stream. The total carbon mass flow rate was maintained constant when the fraction of DME in the fuel stream was varied. Numerical calculations of nine diffusion flames of different dimethyl ether fractions in the fuel stream were performed using a detailed reaction mechanism consisting of 151 species and 785 reactions and a sectional soot model including soot radiation, inception of nascent soot particle due to collision of two pyrene molecules, heterogeneous surface growth and oxidation following the hydrogen abstraction acetylene addition mechanism, soot particle coagulation, and PAH surface condensation. The addition of a relatively small amount of dimethyl ether to ethylene was found experimentally to increase the concentrations of both polycyclic aromatic hydrocarbons and soot. The synergistic effect on polycyclic aromatic hydrocarbons persists over a wider range of dimethyl ether addition. The numerical results reproduce the synergistic effects of dimethyl ether addition to ethylene on both polycyclic aromatic hydrocarbons and soot, though the magnitude of soot volume fraction overshoot and the range of dimethyl ether addition associated with the synergistic effect of soot are less than those observed in the experiment. The synergistic effects of dimethyl ether addition to ethylene on many hydrocarbon species, including polycyclic aromatic ones, and soot can be fundamentally traced to the enhanced methyl concentration with the addition of dimethyl ether to ethylene. Contrary to previous findings, the pathways responsible for the synergistic effects of benzene, polycyclic aromatic hydrocarbons, and soot in the ethylene/dimethyl ether system are found to be primarily due to the cyclization of l-C 6H 6 and n-C 6H 7 and to a much lesser degree due to the interaction between C2 and C4 species for benzene formation, rather than the propargyl self-combination reaction route, though it is indeed the most important reaction for the formation of benzene.