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In modern diesel engines, the exhaust soot primarily comes from the main-injection combustion and post-injection combustion. Therefore, to reduce the diesel soot emissions, it is essential to better understand the soots generated from the main-injection combustion (main-soot) and from the post-injection combustion (post-soot). This work focused on the properties of the main-soot and post-soot during the combustion process, including the primary particle size, nanostructure and soot mass. The in-cylinder soot samples were obtained using a self-developed total cylinder sampling system, and the primary particle size and nanostructure were determined using high-resolution transmission electron microscopy. The isolation of the post-soot was achieved by adding dimethyl ether to the intake gas instead of the real main-injection to create a simulated main-injection combustion environment for post-soot formation. Combustion analysis and numerical simulation results showed that the simulated combustion environment for post-soot formation generated by the DME combustion was very similar to that generated by the real main-injection combustion. During the combustion process, although the main-soot and post-soot exhibit similar variations in the primary particle size, the maximum primary particle size of the post-soot is smaller than that of the main-soot (23.38 nm for the main-soot and 20.51 nm for the post-soot). The main-soot and post-soot show almost the same trends in the nanostructure, as characterized by the fringe length, separation and tortuosity, throughout the combustion process. The introduction of the post-injection accelerates the reduction of the primary particle size of the main-soot and the increase in the structural order of the main-soot. Because a large number of the main-soot particles are oxidized during the post-injection combustion, the post-soot accounts for a considerable proportion in the engine-out soot (i.e., 42%). [ABSTRACT FROM AUTHOR]

In this work, the role of volatile organic compounds (VOCs) in soot oxidation and fragmentation was investigated in a lean, premixed CH 4 flame. An aerosol generator was used to homogeneously disperse soot with and without VOCs (termed Soot-W and Soot-WO, respectively) into the flame. Because minimal soot was formed in the flame itself, information on the fragmentation of the Soot-W and Soot-WO during the oxidation process was readily captured to determine the role of VOCs in soot fragmentation. The integrated number concentration of fine mode particles and the degree of particle aggregation show that the presence of VOCs suppresses soot aggregate fragmentation, primarily by the mitigating consumption of the neck sites between primary particles due to the decreased specific surface area. The actual oxygen diffusion route and effective pore width between the crystallite structures were determined using the image analysis technique. To determine the characteristic regime of oxygen diffusion, the distribution of effective pore width was studied using high-resolution transmission electron microscopy and image analysis. The estimated effectiveness factor indicates that the presence of VOCs lowers the propensity of internal burning via intra-particle oxygen diffusion, and reduces the extent of primary particle fragmentation, as evidenced by a relatively smaller peak of ultrafine particles. The analysis of the nanostructure of neck sites vs. the bulk discovers significantly more disordered and thus reactive structure at neck sites, explaining the prevalence of aggregate fragmentation over primary particle fragmentation. The finding of the role of VOCs in oxidation-driven fragmentation is beneficial to the optimization of existing models for predicting the number concentration of fine and ultrafine particles. Furthermore, a better understanding of this role may aid in the control of the most harmful fine and ultrafine particle emissions. [ABSTRACT FROM AUTHOR]

This paper focuses on the correlation between the oxidative reactivity and electrical properties of soot particles. Soot particles were produced from an n -heptane inverse diffusion flame and were sampled at different heights above the burner (HAB) using a thermophoretic and probe sampling techniques. The electrical properties were characterized by the electrical conductivity and work function, which were evaluated by an atomic force microscopy. The soot reactivity was assessed in terms of activation energy (E a) and characteristic oxidation temperatures, including peak temperature (T P) and burnout temperature (T b), using thermogravimetric analysis. As the soot particles gradually age, they have various electrical conductivity distributions. The average electrical conductivity presents an increase by three orders of magnitude when increasing the HAB from 10 to 60 mm. The work function of bulk soot particles shows an increase with the soot maturation. The soot reactivity gradually reduces during the soot maturation process because the values of E a , T P , and T b show increases with the increase in HAB. For the soot particles, the E a and T p have strongly positive correlations with the work function and with the logarithm of the electrical conductivity. Thus, electrical properties can serve as an indicator of soot reactivity. [Display omitted] • The electrical properties and reactivity of soot particles were assessed. • The electrical conductivity and work function increase as soot particles mature. • Soot reactivity decreases with the increase in logarithm of electrical conductivity. • Soot reactivity decreases with the increase in work function. • Soot electrical properties can serve as an indicator of soot reactivity. [ABSTRACT FROM AUTHOR]

The properties and oxidation of in-cylinder soot from a diesel engine fueled with n -heptane were explored under the simulated exhaust gas recirculation (EGR) condition, via CO 2 addition to the intake air of the engine. A self-developed total cylinder sampling system was employed to obtain the soot samples at the EGR ratios of 0 and 25%, and this study only focused on the soot oxidation that occurred in the soot oxidation-dominated (SOD) phase. Computational fluid dynamics (CFD) simulations were performed to determine the local combustion characteristics related to soot oxidation. Soot oxidation rates were evaluated based on in-cylinder soot mass traces and CFD results. Soot properties were characterized in terms of nanostructure, carbon chemical state, and surface functional groups. Detailed analysis of the soot mass indicates that EGR addition enhances the mass-based specific rate of soot oxidation. However, CFD results show that EGR addition reduces the flame temperature and the concentrations of O 2 and OH, and consequently decreases soot surface oxidation rates by O 2 and by OH. The characterization of soot properties shows that EGR decreases the degree of structural ordering and results in the formation of more oxygenated and aliphatic C–H groups on the soot surface. This alteration in physico-chemical properties favors soot oxidation during the combustion process, and results in an increase in the mass-based specific rate of soot oxidation in the SOD phase. [ABSTRACT FROM AUTHOR]

Abstract Post injection has significant benefit in the reduction of diesel soot emissions. Therefore, there is a need to understand the effect of post-injection strategy on soot physicochemical properties and reactivity because they play an important role in soot oxidation process that governs the final soot emissions. This work focuses on the impact of post injection on the physicochemical properties and reactivity of diesel in-cylinder soot using a main plus post injection (M*P) and a single injection (M) strategy. The soot was sampled by a developed total cylinder sampling system, and the dividing points of soot formation-dominant and oxidation-dominant phases were used for studying the impacts of post injection on the characteristics of in-cylinder soot. The physicochemical properties of the soot samples, including primary particle size, nanostructure, carbon chemical state and surface functional groups, were characterized. The soot reactivity was evaluated in terms of peak temperature, burnout temperature and apparent activation energy. In the oxidation-dominant phase, the M*P soot initially possesses smaller primary particle size, shorter fringe length, larger tortuosity, lower sp2/sp3 hybridization ratio of carbon atoms and higher content of aliphatic C H groups than the M soot. The beneficial influence of physicochemical properties on soot reactivity when using post injection is validated by the thermogravimetric data, which shows that the M*P soot is more reactive than the M soot at the onset of the oxidation-dominant phase. In the M*P case, the soot generated from the main-injection combustion has lower reactivity than the soot from the post-injection combustion after they experience the soot formation-dominant phase. The results indicate that the use of post injection leads to in-cylinder soot with physicochemical properties that favor reactivity. The enhancement of reactivity means that the soot will be more readily oxidized in the subsequent combustion process, and consequently contributes to a reduction in final soot emissions. [ABSTRACT FROM AUTHOR]

Abstract In this study, we investigated the redox reaction between a hydrocarbon (HC) and adsorbed NO x over Cu Pt Ba/Al 2 O 3 lean NO x trap (LNT) catalyst. Experimental characterizations included temperature-programmed desorption (TPD), temperature-programmed reduction (TPR), in situ diffuse reflectance Fourier transform spectroscopy (in situ DRIFTs) and Raman spectroscopy. Density functional theory (DFT) calculations were also performed. The model C 3 H 6 first adsorbed to the catalyst surface, and the resulting C 3 H 6 -adsorbed species reacted with adsorbed NO x species to form various intermediates such as: carboxylates, enolic compounds, carbonato complexes, Pt-carbonyls, acid anhydrides, basic hydroxyls, nitrogen-containing organic species, acyl chlorides, and ammonium salts. These intermediates participated in subsequent reactions and finally produced the effluent gases CO 2 , N 2 , NH 3 , and H 2 O. The decomposition ability of adsorbed NO x species indicated that the NO x species participated in the C 3 H 6 oxidation in the order: adsorbed N 2 O 4 > monodentate nitrates > free ionic nitrates > bulk free ionic nitrates. Carbonaceous materials were generated during the C 3 H 6 oxidation process and were consumed as intermediates by gaseous NO x released upon decomposition of the adsorbed NO x species. In summary, the redox reaction between C 3 H 6 and adsorbed NO x followed the Langmuir–Hinshelwood mechanism, and three reaction routes were proposed for the redox process over the studied catalyst. The activation energy barriers determined by DFT + U calculations for the three routes indicated that the initial dissociation of NO 3 − species in R (2) occurred more easily than the oxidation of C 3 H 6 species in R (1) , delivering the active oxygen species that participated in R (1) and R (3). As the reactions proceeded, the higher energy barrier for the complete dissociation of NO 2 * indicated that the temperature determined the further decomposition of adsorbed NO x species, and R (1) and R (3) were constrained owing to the limited surface active oxygen species from R (2). [ABSTRACT FROM AUTHOR]

Abstract This paper studies the electrical properties of the soot particles generated from an n-heptane inverse diffusion flame and the relationship between the electrical properties and the nanostructure. The electrical conductivity of isolated soot particle and work function of soot particles were measured by a PeakForce tunneling atomic force microscopy and a Kelvin-probe force microscopy. The nanostructure of soot particles was evaluated using X-ray diffraction and X-ray photoelectron spectroscopy. Different electrical conductivity distributions were found as the soot particles gradually matured, and at the same time the mean electrical conductivity of soot particles exhibited a nearly exponential increase. There existed a percolation threshold at which the mean electrical conductivity sharply increased by approximately two orders of magnitude. Similarly, the work function of soot particles increased during soot maturation process, which implies that it becomes harder for the electrons to escape from the soot samples. The crystallite width had a positive correlation with the logarithm of electrical conductivity and the work function for soot particles, while the interlayer spacing presented a negative correlation with the logarithm of electrical conductivity and work function. These results suggest that the electrical conductivity and work function can serve as indicators of ordering degree of soot particles. Moreover, the dependence of electrical properties on the nanostructure demonstrates the potential of better controlled flame conditions for producing tailored soot particles for a variety of applications. [ABSTRACT FROM AUTHOR]

Atomic force microscopy (AFM) was used to characterize the attractive force, adhesive force and adhesion energy between an AFM probe tip and nanometric soot particle generated by a premixed methane/oxygen flame. Different attractive force distributions were found when increasing the height above burner (HAB), with forces ranging from 1.1–3.5 nN. As the HAB was increased, the average attractive force initially increased, briefly decreased, and then underwent a gradual increase, with a maximum of 2.54 nN observed at HAB = 25 mm. The mean adhesive force was 6.5–7.5 times greater than the mean attractive force at the same HAB, and values were in the range of 13.5–24.5 nN. The adhesion energy was in the range of 2.0–5.6 × 10 −17 J. The variations observed in the average adhesion energy with increasing HAB were different from those of the average adhesion force, implying that the stretched length of soot particles is an important factor affecting the average adhesion energy. The Hamaker constants of the soot particles generated at different HABs were determined from AFM force-separation curves. The average Hamaker constant exhibited a clear correlation with the graphitization degree of soot particles as obtained from Raman spectroscopy. [ABSTRACT FROM AUTHOR]

The mechanism for the C2H3+ CH3CH2OH reaction has been investigated by the CCSD(T)/cc-pVTZ method based on the geometries of stationary points optimised at the B3LYP/6-311++G(d, p) level of theory. Five reaction channels have been identified for the production of C2H4+ CH2CH2OH, C2H4+ CH3CH2O, C2H4+ CH3CHOH, C2H3OH + CH3CH2,and C2H3OCH2CH3+ H (denoted as channels (1)–(5), respectively). The potential barrier heights of the corresponding transition states TSR/P1, TSR/P2, TSR/P3, TSR/P4 and TSR/P5 were predicted to be 12.40, 8.50, 8.11, 38.38 and 42.21 kcal/mol at the CCSD(T)//B3LYP level of theory, respectively. The rate constants and branching ratios for the three lower energy H-abstraction channels were calculated using conventional transition state theory with Eckart tunnelling correction at the temperature range 300–2500 K. The predicted rate constants have been compared with the available literature data. Both the forward and reverse rate constants have positive temperature dependence, and the tunnelling effect is only important at low temperatures. The branching ratio calculation shows that channel (2) is predominant and channel (3) is less competitive, while channel (1) is almost neglectable at low temperatures. However, all three channels are important in high-temperature region. [ABSTRACT FROM PUBLISHER]

The mechanism for the hydrogen abstraction reaction C 2 H 3 + CH 3 CHO has been investigated by the CCSD(T)/cc-pVTZ method based on the geometries of stationary points optimized at the B3LYP/6-311++G(d,p) level of theory. Two abstraction channels have been identified for the production of C 2 H 4 + CH 2 CHO and C 2 H 4 + CH 3 CO. The potential barrier heights of the corresponding transition states TSR/P1 and TSR/P2 were predicted to be 9.47 and 5.95 kcal/mol at the CCSD(T)//B3LYP level of theory, respectively. The rate constants and branching ratios for the two H-abstraction channels were calculated using conventional transition state theory with Eckart tunneling correction at the temperature range 300–2500 K. The predicted rate constants have been compared with available literature data. Both the forward and reverse rate constants have positive temperature dependence and the tunneling effect is only important at low temperatures. The branching ratio calculation shows that the channel producing C 2 H 4 + CH 3 CO remains predominant throughout the entire studied temperature range. [ABSTRACT FROM AUTHOR]

ABSTRACT The mechanism for the C2H3 + CH3OH reaction has been investigated by the Gaussian-4 (G4) method based on the geometric parameters of the stationary points optimized at the B3LYP/6-31G(2df, p) level of theory. Four transition states have been identified for the production of C2H4 + CH3O (TSR/P1), C2H4 + CH2OH (TSR/P2), C2H3OH + CH3 (TSR/P3), and C2H3OCH3 + H (TSR/P4) with the corresponding barriers 8.48, 9.25, 37.62, and 34.95 kcal/mol at the G4 level of theory, respectively. The rate constants and branching ratios for the two lower energy H-abstraction reactions were calculated using canonical variational transition state theory with the Eckart tunneling correction at the temperature range 300-2500 K. The predicted rate constants have been compared with existing literature data, and the uncertainty has been discussed. The branching ratio calculation suggests that the channel producing CH3O is dominant up to about 1070 K, above which the channel producing CH2OH becomes very competitive. [ABSTRACT FROM AUTHOR]

The present study investigated the effects of adding 20 vol.% biodiesel to petroleum diesel (to produce a mixture termed B20) on the physical properties and reactivity of the resulting exhaust soot particles. Tests were performed at different engine loads of a constant speed, and the soot particles from the combustion of B20 and petroleum diesel fuel (DF) were collected from the engine exhaust stream. Transmission electron microscopy and Raman spectroscopy were employed for the analysis of soot morphology and nanostructure. The thermogravimetric analysis was used to determine the oxidative reactivity of the soot. For both the DF and B20 soot, increased engine loads result in soot aggregates with more compact morphology and primary soot particles with larger size and more organized structure. Compared to the DF soot, the B20 aggregates have a slightly more compact morphology and smaller primary particle size. No appreciable differences are observed in nanostructure between the DF and B20 soot. The thermogravimetric analysis demonstrates that the B20 soot is associated with lower peak temperature, burnout temperature and apparent activation energy, suggesting that it is more reactive than the DF soot. [ABSTRACT FROM AUTHOR]

In this study, programmed temperature vaporization in the solvent vent mode (PTV-SV) of gas chromatography-mass spectrometry was optimized and validated for the analysis of particle-phase and gas-phase polycyclic aromatic hydrocarbons from diesel engine combustion. Because of the large number of experimental and response variables to be studied, central composite inscribed design was used to optimize the PTV-SV injection factors, including initial inlet temperature, vaporization flow and time. The optimized PTV-SV method was validated by linearity, accuracy and sensitivity. For the 16 Polycyclic aromatic hydrocarbons (PAHs) studied, the correlation coefficients for the calibration plots of peak areas versus concentrations (0.5–300 ng mL−1) ranged from 0.9812–0.9998. Limits of detection ranged from 0.016–20,130.375 ng mL−1, and limits of quantification ranged from 0.055–1.25 ng mL−1. The optimized method was used for the analysis of real samples collected from a diesel engine, which included particle-phase and gas-phase PAHs. The results showed that the improved PTV-SV method was satisfying for simultaneously identifying and quantifying PAHs produced during diesel combustion. [ABSTRACT FROM AUTHOR]

This work aimed to optimize the washcoat slurry for hydrotalcite-based lean NOx trap (LNT) catalyst. The effects of the slurry properties including pH, solid content, binder and additive on the hydrotalcite-based slurry viscosity were investigated. The particle size distribution of the optimal hydrotalcite-based slurry was measured. A cordierite material was used to coat the optimal slurry, and the washcoat was characterized by X-ray diffraction, scanning electron microscopy and N2 adsorption. The optimal slurry containing Pt and Ba was coated on the cordierite for the preparation of hydrotalcite-based LNT catalyst, and the performances of this catalyst were evaluated by NOx storage test, temperature programmed desorption and NOx reduction. For comparison, the performance of the commercial LNT catalyst with Pt/BaO/Al2O3 was analyzed. After coating, the hydrotalcite-based washcoat was closely contacted with the support, being the main phase MgO and presenting a specific surface area of 86.3 m2/g. The hydrotalcite-based LNT catalyst had better NOx storage and desorption ability, selectivity to N2 and LNT efficiency than the Pt/BaO/Al2O3 catalyst. [ABSTRACT FROM AUTHOR]

The purpose of the present study is to better understand the reaction kinetics of diesel exhaust soot during oxidation process. A thermogravimetric analyzer was used to oxidize real diesel exhaust soot generated from a Euro VI diesel engine under non-isothermal conditions. The Friedman-Reich-Levi method and the Sestak-Berggren model were used to determine the oxidation kinetics. Raman spectroscopy and high-resolution transmission electron microscopy were employed to follow the changes of the soot structure during oxidation. The activation energy gradually increased with increasing conversion level during soot oxidation. The oxidation process of diesel exhaust soot could be described as three-step kinetics, and the calculated conversions fitted the experimental results very well. The kinetic predictions of diesel soot oxidation that were obtained using the proposed kinetic models were more accurate and precise than those with the common first-order model. The structural order increased as oxidation progressed, which was responsible for the increased activation energy. The structural ordering was principally caused by the preferential oxidation of the disordered fraction in the diesel soot, especially for the amorphous carbon, which was oxidized in the initial stage of the oxidation reaction. [Display omitted] • The oxidation reaction kinetics of diesel exhaust soot were studied. • The activation energy of soot gradually increases with conversion during oxidation. • The oxidation process of diesel soot can be described as three-step kinetics. • The developed kinetic models can reflect the soot oxidation process accurately. • The structural ordering of diesel soot causes the increase in activation energy. [ABSTRACT FROM AUTHOR]

The storage and reduction of NOx on a series of Fe-modified hydrotalcite-based lean NOx trap catalysts were assessed, together with the product selectivity. The crystal structures and micromorphologies of these materials were characterized using X-ray diffraction and scanning electron microscopy, while in situ diffuse reflectance Fourier transform infrared spectroscopy was used to evaluate the evolution of transition state species. The introduction of Fe was found to improve the synergistic interaction between the Mg and Fe in the hydrotalcite structure, allowing these catalysts to work efficiently at low temperatures. In addition, both Pt/BaO/MgAlO and Pt/BaO/MgFeO catalysts exhibited better NOx adsorption and reduction performance compared with Pt/BaO/Al 2 O 3. The superior performance of the former two materials was attributed to the enhanced adsorption of NOx in the form of nitrates and nitrites by Fe and Mg and to the ready decomposition of these nitrates at low temperatures. A Pt/BaO/MgFeO catalyst showed excellent low temperature activity and high selectivity for N 2 together with superior sulfur resistance compared with Pt/BaO/Al 2 O 3. [Display omitted] • This study prepared a series of hydrotalcite-derived lean NOx trap catalysts. • The introduction of Fe was found to increase the NOx removal efficiency at low temperature because of improving the synergistic interaction between the Fe and Mg in the hydrotalcite structure. • Pt/BaO/MgFeO has better sulfur resistance than traditional Pt/BaO/Al 2 O 3 catalysts. [ABSTRACT FROM AUTHOR]

Copper–cerium–zirconium catalysts loaded on TiO 2 prepared by a wet impregnation method were investigated for NH 3 -selective catalytic reduction of NO x , aiming to study the effects of the Ce/Zr molar ratio on the performance of Cu–Ce–Zr/TiO 2 catalysts. The Cu–Ce 0.25 –Zr 0.75 /TiO 2 sample exhibited nearly 100% NO x conversion over a wide temperature range (165–450 °C), which is strikingly superior to that of Cu/TiO 2 (210–389 °C) within the range of exhaust temperatures of diesel engines. The factors that govern the activity enhancement were extensively investigated by using a series of characterization techniques, namely X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS) and temperature-programmed reduction by hydrogen (H 2 -TPR). The results showed that the addition of zirconium and/or cerium refined the copper dispersion, prevented copper crystallization and partially incorporated the copper ions into the zirconia (ceira) lattice, which led to enhance the redox abilities of Cu–Ce–Zr/TiO 2 catalysts. [ABSTRACT FROM AUTHOR]

The impact of soot on NO x adsorption was studied over a Cu-modified hydrotalcite-derived lean NO x trap catalyst in a NO + O 2 atmosphere. Powder X-ray diffraction, scanning electron microscopy, Raman scattering spectroscopy, and X-ray photoelectron spectroscopy were used to characterize the surface properties of the pure catalyst and the soot/catalyst mixture. The adsorbed NO x species on the samples were evaluated by in situ diffuse reflectance Fourier transform spectroscopy. The soot coverage decreases the available adsorption sites on the surface of the catalyst, and a portion of active oxygen species are consumed by the soot oxidation during He pretreatment process. The NO x adsorption on two catalyst samples simultaneously undergoes two routes: the "nitrite route" and the "nitrate route". The "nitrite route" is more dominant than the "nitrate route". During NO x adsorption, the soot oxidation weakens the NO oxidation to NO 2 , and the released CO 2 competes with NO x on the adsorption sites. Moreover, the temperature-programmed desorption tests indicate that the presence of soot reduces the NO x storage capacity of the catalyst and shifts the NO desorption peak to the lower temperature range by 50 °C.

Objective: To investigate the clinical application of laparoscopy-assisted subtotal colectomy with transanal specimen extraction for slow transit constipation(STC)., Methods: Retrospective analysis was performed on the clinical data of 8 cases with STC undergoing the procedure mentioned above from February to November 2013. Pre-and post-operative constipation was assessed using Wexner Constipation and Incontinence Scales, and quality of life was assessed using Gastrointestinal Quality of Life Index., Results: All the operations were completely successful without postoperative complications, such as intestinal fistula, pelvic infection, anastomotic stricture, intestinal obstruction. The Operative time was (287.6 ± 21.5) min, blood loss was (109.7 ± 41.1) ml, time to first flatus was (2.5 ± 0.9) d. The proportion of postoperative constipation symptom index improvement was(77.6 ± 8.3)%. Postoperative quality of life score was 97.3 ± 15.7, significantly higher than that before operation(P<0.05). Postoperative Wexner constipation score was 8.8 ± 3.7, significantly lower than that before operation., Conclusion: Laparoscopy-assisted subtotal colectomy with transanal specimen extraction in the treatment of STC has good short-term efficacy with obvious improvement in quality of life.