Fringe Length Research Articles

Development of graphitic and non-graphitic carbons using different grade biopitch sources

The growing demand for bio-renewable alternatives to fossil fuels in the production of sustainable carbon materials, aimed at reducing environmental impact, is crucial for advancing a greener future. This research explores an innovative approach for producing biopitches from bio-oils, which are subsequently utilized as a sustainable precursor for developing advanced graphitic carbons (GC) and non-graphitic carbons (NGC) through carbonization and graphitization processes. The study emphasizes the impact of the chemical composition of bio-oils and biopitches, including heteroatom structures, aromatic/aliphatic ratio, and oxygen content with oxygen-bearing functional groups, on the production of GC and NGC. The research also examines their structural parameters at various heating temperatures using characterization techniques such as X-ray diffraction (XRD), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. XRD analysis revealed that GC samples have lower interplanar spacing (d002) and larger crystallite size than NGC, while Raman shows more short-range order and defects in NGC. Furthermore, HRTEM images and fringe analysis demonstrated differences in lamellae structures, tortuosity, and fringe length. These observations, unveiling differences in crystallite size and degree of graphitization between GC and NGC, underscore the influence of temperature on structural order and defect annealing, which is crucial for optimizing material properties.

Investigation on nanostructure, surface functional groups, and oxidation activity of particulate along the exhaust after-treatment of a diesel engine fueled with waste cooking oil biodiesel blends.

In this study, the nanostructure, surface functional groups, and oxidation activity of soot particulate along the exhaust after-treatment system of a heavy-duty diesel engine fueled with waste cooking oil (WCO) biodiesel blends are investigated by TEM, XPS, and TGA respectively. The main findings are as follows: Along the exhaust after-treatment system, fringe length of primary particles of soot particulate emitted from tested heavy-duty diesel engine fueled with B0, B10, B20, and B100, i.e., 0%, 10%, 20%, and 100% ratio of WCO biodiesel blended into petroleum diesel in volume respectively increases, while fringe tortuosity and separation distance of primary particles reduces. The fringe length of B10, B20, and B100 is smaller, but the fringe tortuosity and separation distance are larger than that of B0. The O/C ratio of soot particulate tends to increase firstly and then decrease as the exhaust passes through DOC+cDPF and SCR+ASC in sequence. The O/C ratio of B10, B20, and B100 are also higher than that of B0. Soot particulate at cDPF outlet contains carborundum and biuret is found at SCR+ASC outlet. The sp3/sp2 ratio decreases along the exhaust after-treatment system, and B10, B20, and B100 tend to get higher sp3/sp2 ratio than B0. The C-OH and C=O content of soot particulate from different WCO biodiesel blends show generally similar trends along the exhaust after-treatment system, while the activation energy of soot particulate keeps increasing along the exhaust after-treatment system, but decreases with the increasing of blend ratio. These findings can provide useful references for optimizing the after-treatment system for WCO biodiesel blends.

Plasma treatment on flame soot: view from nanostructure and reactivity of soot

In recent years, the use of plasma for pollutant emission control has an expected potential. In this study, soot particles from flames were sampled from an ethylene inverse diffusion flame, which were placed in a self-designed dielectric barrier discharge plasma device for reaction treatment. The nanostructure and oxidation reactivity of soot particles after plasma treatment were evaluated by transmission electron microscopy, Raman spectroscopy, X-ray diffraction analysis and X-ray photoelectron spectroscopy. With 16 kV, 2.5 kHz as an example, with the treatment of plasma, the fringe length decreases (1.3% and 9.6%), and the fringe tortuosity increases (1.1% and 8.7%) in both high-maturity and low-maturity soot particles, which means that the oxidation activity of soot is enhanced after plasma discharge. Raman spectra, X-ray diffraction analysis spectra and X-ray photoelectron spectroscopy spectra have confirmed this phenomenon, especially the oxidation activity of soot particles under the action of plasma at high maturity is more obvious. It is worth noting that the enhancement of soot oxidation activity after plasma discharge has certain limitations, that is, the oxidation activity will not continue to increase after it is enhanced to a certain intensity, which may be related to the selection of Ar as the atmosphere gas.

Experimental investigation of kerogen structure and heterogeneity during pyrolysis

Kerogen in shale microstructure plays a vital role in hydrocarbon generation, retention and accumulation. However, characterization of kerogen structure is challenging arguably due to a complex microporous structure and chemical heterogeneity. Thus, the role of kerogen molecular structure in controlling porosity and its heterogeneity, as well as its evolutionary processes, remains unclear. In this study, we investigate the chemical and pore structure of heated kerogen samples by employing a range of characterization tools including gas adsorption experiments, high-resolution transmission electron microscopy (HRTEM), Fourier transform infrared (FTIR) spectroscopy, and laser Raman experiments for a broad range of pyrolysis temperatures (420–850 °C). Multifractal theory and peak fitting techniques were used to evaluate the controlling mechanisms of kerogen pore structure and heterogeneity. The results suggest that with increasing thermal maturity, the content of oxygen functional groups and long-chain aliphatic groups in kerogen significantly decreases, while the length of aromatic fringes increases and gradually becomes oriented. Furthermore, with increasing thermal maturity, the pore volume of kerogen exhibits a non-monotonic trend, i.e., a decrease, followed by an increase, and then finally a decrease. This is primarily influenced by processes such as hydrocarbon production weakening, secondary hydrocarbon cracking, and carbonization. The heterogeneity and dispersion of meso to macro-sized pores in kerogen increase with temperature, while the connectivity gradually decreases. The chemical structure and spatial distribution of kerogen significantly affect the heterogeneity, connectivity, and dispersion of meso to macro-sized pores. Specifically, high aromaticity, structural disorder, and short aliphatic chains result in enhanced heterogeneity and dispersion of meso to macro-sized pores, reducing pore connectivity. This study thus contributes to a deeper understanding of the evolution of organic matter pores.

Molecular structure and evolution mechanism of shale kerogen: Insights from thermal simulation and spectroscopic analysis

During thermal evolution, the kerogen in shale formation undergoes significant chemical, structural and compositional changes, continuously influencing the shale storage capacity, hydrocarbon generation potential, and gas occurrence state. This study systematically examines the chemical structural changes during the thermal evolution of Longmaxi shale kerogen using hydrothermal laboratory experiments from 420 to 850 °C. Additionally, a range of characterization techniques, including Fourier Transform Infrared (FTIR) spectroscopy, Raman spectroscopy, High-Resolution Transmission Electron Microscopy (HRTEM), X-ray Diffraction (XRD), and Solid-state 13C Nuclear Magnetic Resonance (13C NMR), were employed to systematically investigate the kerogen structure and its evolution patterns. Results indicate that Longmaxi Formation kerogen comprises a large molecular carbon framework with aromatic structures, long-chain aliphatic components, and oxygen-containing functional groups. As thermal maturity reaches 2.6 %, the alignment of aromatic fringes gradually increased, with over 60 % aligning in the main direction. Throughout thermal evolution (1.9–3.2 %), fringes in the 5–10 Å range within aromatic structures peak at over 20.45 %, with fringes over 50 Å rapidly increasing from 3 % to over 15 %. Early in the thermal evolution, the long-chain aliphatic component of the kerogen decreases rapidly and part of the structure forms small aromatic rings through aromatisation. The mature to over-mature stage can be divided into three phases: 1) 1.7–2.4 % (loss of oxygen-containing functional groups), 2) 2.4–3.5 % (formation of larger aromatic structures via condensation reactions), 3) over 3.5 % (continued aggregation of aromatic rings, resulting in an increase in the length of aromatic fringes). At a macroscopic level, this induces changes in kerogen pore structure and carbonization features. This study thus provides new insights into the thermal evolution of shale kerogen, which in turn improve understanding of shale reservoirs for hydrocarbon exploitation.

Impacts of Fuel Stage Ratio on the Morphological and Nanostructural Characteristics of Soot Emissions from a Twin Annular Premixing Swirler Combustor.

Soot particles emitted from aircraft engines constitute a major anthropogenic source of pollution in the vicinity of airports and at cruising altitudes. This emission poses a significant threat to human health and may alter the global climate. Understanding the characteristics of soot particles, particularly those generated from Twin Annular Premixing Swirler (TAPS) combustors, a mainstream combustor in civil aviation engines, is crucial for aviation environmental protection. In this study, a comprehensive characterization of soot particles emitted from TAPS combustors was conducted using scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM), and Raman spectroscopy. The morphology and nanostructure of soot particles were examined across three distinct fuel stage ratios (FSR), at 10%, 15%, and 20%. The SEM analysis of soot particle morphology revealed that coated particles constitute over 90% of the total particle sample, with coating content increasing proportionally to the fuel stage ratio. The results obtained from HRTEM indicated that average primary particle sizes increase with the fuel stage ratio. The results of HRTEM and Raman spectroscopy suggest that the nanostructure of soot particles becomes more ordered and graphitized with an increasing fuel stage ratio, resulting in lower oxidation activity. Specifically, soot fringe length increased with the fuel stage ratio, while soot fringe tortuosity and separation distance decreased. In addition, there is a prevalent occurrence of defects in the graphitic lattice structure of soot particles, suggesting a high degree of elemental carbon disorder.

Effect of nano-graphene lubricating oil on particulate matter of a diesel engine

Nano-graphene lubricating oil with appropriate concentration shows excellent performance in reducing friction and wear under different working conditions of diesel engines, and has been widely concerned. Lubricating oil has a significant impact on particulate matter (PM) emissions. At present, there are few studies on the impact of nano-graphene lubricating oil on the physicochemical properties of PM. In order to comprehensively evaluate the impact of nano-graphene lubricating oil on diesel engines, this paper mainly focused on the effects of lubricating oil nano-graphene additives on the particle size distribution and physicochemical properties of PM. The results show that, compared with pure lubricating oil, the total number of nuclear PM and accumulated PM of nano-graphene lubricating oil is significantly increased. The fractal dimension of PM of nano-graphene lubricating oil increases and its structure becomes more compact. The average fringe separation distance of basic carbon particles decreases, the average fringe length increases. The degree of ordering and graphitization of basic carbon particles are higher. The fringe tortuosity of basic carbon particles decreases, and the fluctuation of carbon layer structure of basic carbon particles decreases. Aliphatic substances in PM are basically unchanged, aromatic components and oxygen functional groups increase. The initial PM oxidation temperature and burnout temperature increase, the maximum oxidation rate temperature and combustion characteristic index decrease, and the activation energy increases, making it more difficult to oxidize. This was mainly caused by the higher graphitization degree of PM of nano-graphene lubricating oil and the increased content of aromatic substances.

Oxidation-induced variations in the physical and fragmentation characteristics of exhaust soot from DMC-diesel blend: Effect of NO presence in the air atmosphere

This study investigated the changes in physical properties (including morphology, primary particle diameter, fractal dimension, and nanostructure) and fragmentation characteristics of exhaust soot from a modern direct injection diesel engine fueled with diesel (D100) and its blend with 7 vol% of dimethyl carbonate (DMC7) during oxidation processes in air and air-NO atmospheres. Soot particles (D100 soot and DMC7 soot) with specific oxidation degrees (0%, 20%, 50%, and 80%) were produced using a thermogravimetric analyzer, then applied to a high-resolution transmission electron microscopy to generate images. The results exhibited that the morphology for D100 soot and DMC7 soot transformed similarly through oxidation, experiencing an increase in fractal dimension, and a decrease in primary particle diameter, while the introduction of NO to the air accelerated these transformations. Additionally, the nanostructure of both soot particles was gradually ordered through oxidation, as evidenced by longer fringe length, narrower separation distance, and lower tortuosity, while DMC7 soot showed lower order degree compared to D100 soot. Interestingly, the ordering processes of soot nanostructure were decelerated as NO was involved in the oxidation process. Furthermore, the aggregate fragmentation rate for both soot particles declined over the oxidation process, while the possibility for primary particle fragmentation increased overall. Moreover, DMC7 soot exhibited significantly lower aggregate fragmentation rate and higher possibility for primary particle fragmentation than D100 soot at the same oxidation stage. This suggests that DMC7 soot is more susceptible to internal oxidation compared to D100 soot. Furthermore, the presence of NO in the air promoted aggregate fragmentation, while reducing the possibility of primary particle fragmentation.

Effects of ammonia addition on the soot nanostructure and oxidation reactivity in n-heptane/toluene diffusion flames

Co-firing NH3 with conventional hydrocarbon fuels is an important approach for reducing CO2 emissions in existing combustion systems. Besides CO2, the blending of NH3 would also notably affect soot formation and its oxidation behaviors. In the present study, we focus on the effects of NH3 on the nanostructure and oxidation characteristics of soot produced in diffusion flames of n-heptane/toluene mixtures. Two configurations of laminar co-flow diffusion flame, including both normal and inverse diffusion flames (NDF and IDFs), were used for investigation. High-resolution transmission electron microscopy (HRTEM), Raman spectroscopy (Raman), and Thermogravimetric analysis (TGA) were employed for soot characterization. The HRTEM and Raman spectra showed that with the increase of NH3 blending ratio, the fringe length (La) and the degree of graphitization decreased while the microcrystal tortuosity (Tf) increased. The results are in consistent with TGA analysis which suggests the promoting effects of NH3 on the soot oxidation reactivity. Difference between NDF and IDF with respect to the soot nanostructure and oxidation activity were discussed. It is our hope that the present results could deepen our understanding on the effects of NH3 on soot nanostructure and oxidation behavior and benefit the design of particulate filters for combustion devices fueled with hydrocarbon/NH3 mixtures.

Effects of polyoxymethylene dimethyl ethers (PODEn) on soot characteristics in isooctane inverse diffusion flames

Polyoxymethylene dimethyl ethers (PODEn, n = 1–3) such as dimethoxymethane (DMM) and PODE3 are considered highly promising alternative fuels due to their lack of C–C bonds and significant oxygen contents. Particularly, PODE3-blends with diesel have been proven to substantially reduce soot emissions and fuel consumption rates under optimized engine conditions, although the impact on soot nanostructure properties remains unclear. This study explored the effects of DMM and PODE3 on soot characteristics in isooctane (i-octane) inverse diffusion flames, focusing on soot morphology, soot nanostructure, soot nanocrystallite, and soot spectral features. To compare soot particles behavior, DMM and PODE3 blended as the isooctane substitute (by 20% and 40% volumetric fractions) were examined with various diagnostic techniques, including high-resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS).The results showed that DMM and PODE3 contributed to a reduction in sooting tendency from i-octane flames, whereas the average soot mass decreased significantly as the PODE3 ratio increased, consistent with a higher oxygen concentration. Therefore, 20% PODE3/i-octane exhibited growing disorganized arrangements of soot particles with shorter fringes, smaller crystallite sizes, and a relatively lower degree of graphitization than 20% and 40% DMM additions. However, XPS analysis indicated that soot produced from PODE3/i-octane mixtures had less oxygen atoms because PODE3 has multiple –CH2O- chain groups that can convert oxygen into carbon monoxide with little soot production. Moreover, HRTEM, XRD, and Raman spectra analyses of 40% PODE3-doped flames confirmed an exceptional correlation with turbostratic soot structure, as manifested by the shortest fringe length, longest fringe tortuosity, more amorphous soot with the smallest crystallite dimensions, and least degree of graphitization.

Quantitative Analysis of the Impacts of Ash from Lubricating Oil on the Nanostructure of Diesel Particulate Matter

Microscopic analyses of the effects of ash on particulate matter oxidation are rather scarce. In this study, three different lubricating oils with varying ash contents were used to investigate their effects on the nanostructure of diesel particulate matter. The nanostructure and nanostructure parameters, including fringe length, fringe separation distance, and fringe tortuosity, were studied using high-resolution transmission electron microscopy. The results show that all samples obtained from blending with different lubricant oil present typical core–shell structures. The inner cores remain relatively unchanged, whereas the thickness of the outer shells increases with the increasing ash content in the lubricant oil under the same working conditions. The fringe length increases and the fringe separation distance decreases with the rising ash content in the lubricant oil operating in the same working conditions. The fringe tortuosity decreases when the ash content in the lubricant oil increases from 0.92% to 1.21%, but shows little change when the ash content in the lubricant oil increases from 1.21% to 1.92%. Based on the effects of ash on the nanostructure parameters, it can be inferred that the oxidation activity of particles decreases with increasing ash content in the lubricant oil.

Study on the morphology, nanostructure and fragmentation properties of diesel and diesel-DMM soot particles oxidized in the air/air-NO environment

As an alternative fuel for diesel engines, dimethoxymethane (DMM) has attracted wide attention in recent years, but its impact on the post-treatment process of diesel exhaust particles has been rarely studied. To get a better understanding of the oxidation kinetics of soot in diesel particulate filters (DPFs), the oxidation process of soot emitted from a modern compression ignition (CI) fueled by diesel (D100) and its blend with 11 vol% dimethoxymethane (DMM11) at the same working conditions were investigated by a thermogravimetric analyzer in the air and air-NO atmospheres in this study, respectively. Soot samples at different oxidation degrees (0 %, 20 %, 50 % and 80 % mass loss) were tested by a high-resolution transmission microscopy to characterize the variations of physical properties (morphology, fractal dimension, primary particle diameter and nanostructure) and oxidation-induced fragmentation properties over the oxidation process. The results showed that DMM11 soot had higher oxidation reactivity than D100 soot, and the oxidation reactivity of soot was enhanced by NO involved in the air atmosphere. During the oxidation process, the fractal dimension of D100 and DMM11 soot aggregates gradually increased, and the number and diameter of the primary particles in an aggregate became smaller. This variation trends became more obvious with the presence of NO in the air environment. The nanostructures of D100 and DMM11 soot particles gradually become ordered (characterized by longer fringe length, narrower separation distance and less tortuosity) as the oxidation proceeds. While, when NO added in the air atmosphere the possibility of microcrystals oxidation inside the particles decrease to slow down the getting-ordered rate of soot. Moreover, the fragmentation probability of D100 and DMM11 soot aggregates decreases gradually as oxidation proceeds. During the oxidation process, the probability of primary particle fragmentation for D100 soot increases continuously, while the probability of DMM11 primary soot particles fragmentation showed an increase-then-decrease trend. Compare with D100 soot, DMM11 soot are more likely to occur the fragmentation behavior over the oxidation process. It is worth noting that the addition of NO to the air atmosphere increases the possibility of aggregate fragmentation, while it decreases the possibility of primary particle fragmentation. This work can provide theoretical basis for the development of high efficiency purification technology for diesel exhaust particles.

Effect of ammonia addition on nanostructure of soot in laminar coflow diffusion flames of ethylene diluted with nitrogen

The effect of ammonia addition on the nanostructure of soot particles was studied experimentally for ethylene diffusion flames. To compensate the thermal effect and nitrogen-containing species production when ammonia was added, the total mole fraction of ammonia and nitrogen was fixed in the fuel stream. Soot particle size, fringe length, and fringe tortuosity were measured through transmission electron microscopy (TEM) and high-resolution transmission electron microscopy (HRTEM). A complementary X-ray photoelectron spectroscopy (XPS) analysis provided information about the chemical bonding of soot. A significant delay in soot growth was observed and the particle size increased with the addition of ammonia. While there was no obvious correlation between the fractal dimension of soot and ammonia mole fraction (XNH3) or sampling location. With the addition of ammonia, the mean fringe length increased reasonably linearly with XNH3 and the fringe tortuosity increased up to XNH3 ≈ 0.17 and then decreased with XNH3, which suggested that ammonia addition led to higher graphitization and lower oxidative activity. The soot from ammonia diluted flame exhibited lower reactivity, implying the delay of soot surface growth. With the addition of ammonia, the value of sp2/sp3 (indication of the graphitization degree of soot particles) did not change much for XNH3 from 0 to 0.17 then increased significantly, which indicated the degree of graphitization of soot particles significantly increased with ammonia addition. The intensity of the N1s peak (indication of the N-containing species in soot) increased with the addition of ammonia. This study confirmed that the addition of NH3 promotes the graphitization of soot.

Study of soot microscopic characteristics in hydrogen/methane/ethylene co-flow diffusion flame

Hydrogen (H2) has been regarded as a highly competitive alternative fuel that does not produce CO2 and soot during combustion. However, the effect of hydrogen addition on soot formation and emission is questionable. The purpose of this paper is to study the influence of hydrogen/methane on the morphology of soot and the evolution of nanoparticle structure in laminar flame of ethylene. In this study, the soot morphology and nanostructure in H2/CH4/C2H4 laminar co-flow diffusion flames were investigated with thermophoretic sampling and high-resolution transmission electron microscopy (HRTEM). The results showed that the average primary particle diameters (Dp) of pure ethylene flame gradually decreased along the flame height direction, showing the competition between soot surface growth and soot oxidation. When the hydrogen is added into the fuel flow of ethylene, the Dp decrease at most sample points. Methane affects the inhibitory effect of hydrogen doping on soot, and with the increase of methane mixing ratio, the change trend of Dp of each hydrogen mixture with flame height is becoming more and more consistent. The nanostructure analysis showed that hydrogen doping made soot particles shorter, more tortuous and denser fringes. There is a synergistic effect to promote the growth of primary soot particles at low methane ratio, but it disappears after mixing 20 % hydrogen. The fringe length and tortuosity of soot particles gradually increase with the methane ratio.

Assessment of magnetic effects on soot characteristics in inverse diffusion ethylene flames

The magnetic effect on soot properties in ethylene inverse diffusion flames (IDF) was investigated in this study. The investigation involved the use of high-resolution transmission electron microscopy analysis (HRTEM), Raman spectroscopy analysis, X-ray photoelectron spectroscopy (XPS) and X-ray diffraction spectroscopy (XRD) to examine the nanostructure and graphitization degree of soot collected from flame exhaust gas at various height above burner surface (HAB) under both magnetic and non-magnetic conditions. Increasing the magnetic flux density resulted in modifications to soot properties. When the sampling height was HAB = 4 cm, increasing magnetic flux density resulted in longer fringe lengths, lower fringe tortuosity, less amorphous carbon content and surface oxygen content for the collected soot from flame exhaust gas. These results indicated higher graphitization degrees, which may be attributed to longer residence time and oxidation of soot particle in flames. Moreover, when the sampling height increased from HAB = 4 cm to 6 cm under non-magnetic condition, the nanostructure of soot in the flame exhaust gas was more organized, possible due to the oxidation of soot at the region between HAB = 4 and 6 cm region. However, with the magnetic field on, the crystalline structure of soot in the flame exhaust gas became increasingly disordered as the sampling height increased. This suggested that the soot may also be affected by the magnetic effects in addition to oxidation at the region between HAB = 4 and 6 cm region. The magnetic effect could trigger the transformation of graphitic carbon to amorphous carbon in soot particles as they passed through the magnetic field. With more elaborated magnetic fields, the magnetic effect on soot could contribute to strategies controlling soot emissions and removal.

Effect of a retrofitted metallic microfiber partial flow diesel particulate filter on a light duty diesel vehicle particle emission characteristics

This study was conducted two distinct experiments, using a light-duty diesel vehicle at various engine speeds and loads as well as the new European driving cycle (NEDC) comparing commercial diesel fuel (B7) and pure biodiesel (B100). The NEDC involves a combination of urban and extra urban driving conditions. It aims to study a diesel vehicle's thermal efficiency as well as its gaseous and particulate matter (PM) emissions. This involves comparing results with and with no diesel oxidative catalyst (DOC) and a partial flow diesel particulate filter (PDPF) system. The surface morphology, micro- and nanostructure of a diesel vehicle's PM were also examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffraction (XRD) and thermogravimetric analysis (TGA) to determine nanostructural and dimensional changes after mounting a DOC-PDPF system. Comparison of B7 and B100 combustion showed that B100 had around 1 % increase in brake thermal efficiency (BTE) at 1500 and 2000 rpm compared to B7 since B100 is a more oxygenated biofuel. At 2500 rpm, similar BTE values were observed. Introduction of a DOC-PDPF system resulted in an approximately 1 % BTE reduction for both fuels. This was due to greater friction losses caused by backpressure from the DOC-PDPF system. Increased exhaust backpressure was progressive, ranging from 1 kPa at idle speed to 6 kPa at high engine speeds for both tested fuels. The DOC-PDPF system respectively minimized PM emissions and particle numbers (PNs) by more than 50 % and 35 % for B7 and 71 % and 31 % for B100. These results are average values under the various phases of NEDC testing. A 30 % decrease in PM and a 44 % reduction in PNs under the overall test cycle were found when B100 was tested compared to B7. The soot primary particle size was reduced from 34.69 to 29.08 nm and the carbon fringe length diminished from 1.25 to 0.949 nm at different pre- and post-DOC-PDPF locations. This was due to partial oxidation on the surfaces of the PDPF metallic microstructure. PM undergoes simultaneous partial oxidation after passing through the DOC-PDPF system, as confirmed by TGA analysis.

Enhancement of energy, exergy and soot characteristics with the utilization of MEK in diesel engine

This study investigated the effects of methyl ethyl ketone (MEK) on a diesel engine’s energy, exergy and emissions. The evaporation of a bi-component droplet of MEK and heptane was modeled. Furthermore, the soot morphology and nanostructure were quantified. Different blends were examined at other engine conditions. Running the engine under idle conditions and optimum speed considerably reduced engine emissions. MEK noticeably decreased the maximum reachable load of the diesel engine. Both specific fuel consumption and thermal efficiency increased with MEK. The exergetic efficiency increased while the fuel exergy decreased at the same work exergy. The effects of MEK on combustion characteristics were insignificant. However, a stronger premixed combustion phase was obtained where MEK evaporated first and caused a slightly longer droplet lifetime. Low percentages of MEK reduced CO emissions, while NOx emissions increased consistently with the MEK addition. The engine conditions noticeably influenced the unburned hydrocarbon emissions with MEK. Both smoke opacity and primary particle diameter decreased. The fringe analysis emphasized that MEK decreased fringe length, soot intensity, and alignment, increasing fringe tortuosity and spacing. Clearly, methyl ethyl ketone suppressed soot formation in a diesel engine and decreased its reactivity.Graphical abstract

Effect of ammonia addition on the morphology and nanostructure evolution of soot particles in ethylene co-flow diffusion flames

Carbon-free ammonia (NH3) fuel blending hydrocarbon fuel is a viable option to overcome the drawbacks of pure NH3 combustion, but will lead to soot formation. In this study, the effects of NH3 addition (0–40 vol%) on soot morphology and nanostructure evolution in ethylene (C2H4) co-flow diffusion flames were investigated by using thermophoretic sampling particle diagnostic-transmission electron microscopy and lattice-fringe algorithm. The results showed that under the same carbon flow rate, NH3 addition has little effect on the flame height, but great effect on the flame structure and soot formation. With the increase of NH3 blending ratio, the soot volume fraction (SVF), the fractal dimension of the soot aggregates and the average primary particle size showed a gradual decrease. Among them, with 40% NH3 addition, the SVF decreased by 76.7% and the peak average particle size decreased by 34.3% at HAB = 30 mm. Moreover, many particles with multi-core core-shell structure appear in the A40 flame. In terms of nanostructure parameters, the mean fringe length of particle fringes shows a gradually increasing trend, while the mean tortuosity and mean inter-fringe spacing show a gradually decreasing trend with the increasing HAB. NH3 addition causes the fringe length to decrease, the tortuosity and inter-fringe spacing to increase. The soot particles formed in the doped NH3 flames have more disordered structure.

Response of anthracite microcrystalline structure due to multi-phase CO2 injection

CO2 injection in coal causes permeability reduction, but also affects the microcrystalline structure. To quantify the different response of microcrystalline structure of anthracite after multi-phase CO2 injection, anthracite samples from the Qinshui basin, the samples were demineralized by HF-HCl before CO2 injection, then subjected dry, demineralized samples to CO2 injection experiments at 4 MPa (gaseous), 6 MPa (subcritical) and 8 MPa (supercritical) pressure, the microcrystalline quantification was obtained using X-ray diffraction and image analysis of HRTEM micrographs, the morphological characteristics of ultramicropore were quantitatively characterized by HRTEM image analysis. With increasing injection pressure, the interplanar spacing (d002) and aromaticity (fa) of the coal gradually increased, while the average number of aromatic layers (Nc) and unit stacking height (Lc) gradually decreased; the variation in the unit lateral size (La) also became more complex. Thus, the coal crystal structure was altered after CO2 treatment and the degree of damage increased with pressure. Further, the average length of coal lattice fringes becomes shorter with the increase of pressure, while the length, width and area of ultra-micropores in subcritical and supercritical SH and ZZ coal increase. In addition, the average curvature of the lattice fringes became larger, and the directional ordering decreased after CO2 intrusion. Thus, CO2 injection led to the transformations of crystal structure, generating intermolecular structural defects, and a reduction in order in the striation direction. This study presents the microcrystalline structure and ultra-micropore response of anthracite due to CO2 injection, which also helps with in-depth understanding of the impact of CO2-ECBM.

Experimental investigation of metallic partial-flow particulate filter on a diesel engine's combustion pressure and particle emission

The study aims to present the combustion and exhaust behaviors of a 3 L, four-cylinder common rail diesel engine with three different kinds of conventional B7 diesel fuels with and without a platinum diesel oxidation catalyst (DOC) system and non-catalytic partial flow through a diesel particulate filter (P-DPF). Testing is performed under the three different operating conditions, idle to medium engine loading at 1000, 1500, and 2000 engine revolutions per minute with four different engine torques of 84, 112, 140 and 160 Nm. The surface morphology and agglomerate size of particulate matter (PM), single primary particle analysis as well as the fringe length of the carbon crystallite structure were also examined using scanning electron microscopy (SEM), transmission electron microscopy (TEM) and energy dispersive x-ray spectroscopy (EDS) to achieve a better understanding through image processing. The P-DPF system does not have a significant effect on an engine's in-cylinder combustion characteristics and brake thermal efficiency. The diesel engine's particle emissions are reduced by trapping them on the metallic micro-fibers of a P-DPF. CO2, NO, and O2 levels show that the carbonaceous particle emissions on the micro-structure of the P-DPF passively react with NO2 and O2. Consequently, diesel engine particle emissions can be reduced by around 50% using a P-DPF system under the experimental conditions of the current study.