Soot Combustion Research Articles

Ce-Mn oxides synthesized with citric acid on ceramic papers used as diesel particulate filters

Diesel Particulate filters are considered one of the most efficient technologies to reduce particulate matter emitted by diesel engines. In this paper we study the development of catalytic ceramic papers based on Mn-Ce and their applications as soot particle filters in bench scale tests. Ceramic papers were prepared by a dual polyelectrolyte papermaking method and were impregnated with Mn and Ce precursors through a wet-spray procedure using a commercial fogger. Catalytic ceramic papers were tested as catalysts for the combustion of soot, which was obtained both from the burning of diesel fuel and directly from a bench test. In addition, the filtering capacity of catalytic ceramic papers was tested through opacity measurements by placing the ceramic papers in a suitable case at the end of the engine. Mn-Ce based catalysts were active in the soot combustion. The addition of citric acid considerably improved the catalytic performance of all the systems studied. This beneficial effect of citric acid is related to an improvement in the distribution of the catalytic material onto the ceramic fibers, being the mixed equimolar oxide Mn-Ce the most active catalyst.

Thermocouple Temperature Measurements in Metalized Explosive Fireballs

AbstractThe detonation of a metalized explosive generates a fireball that has a spatially non‐uniform distribution of particle concentration and gas temperature. The transient gas temperature field must be probed with ruggedized spatially‐ and temporally‐resolved diagnostics. The use of in‐situ thermocouples for temperature measurements within multiphase fireballs is demonstrated. Although the thermocouple temperature lags behind the local gas temperature, the transient gas temperature is assessed by modeling the sensor assuming first‐order response and using two analysis methods: (1) when the thermocouple temperature trace reaches a local extrema, the thermocouple temperature is instantaneously equal to the local gas temperature, and (2) reconstructing the gas temperature trace using multiple co‐located thermocouples of different lag responses. The temperature history within the fireball at various distances is presented for charges consisting of packed beds of particles saturated with liquid nitromethane. The results for reactive particles (Al, Ti, Zr) are compared with non‐reactive particles (Fe), as well as homogeneous NM charges. For NM charges, a maximum gas temperature of about 1100 K occurs at times on the order of 100’s of milliseconds, less than the temperature of the burning soot in the fireball (∼1900 K). With Al particles, the gas temperature is spatially non‐uniform due to particle jetting and non‐uniform particle combustion, but gas temperatures up to about 1800 K are recorded for times up to 0.5 s, less than the temperature of the burning particles (∼2700 K). Inert particles act as a heat sink and the thermocouple temperatures recorded did not exceed 400 K.

Investigations on a new C-GPFs with electric heating for enhancing the integrated regeneration performance under critical parameters

In order to improve the uneven flow of exhaust in traditional catalytic gasoline particulate filter system (C-GPFs) and improve the regeneration performances under low-temperature conditions, the new C-GPFs integrated regeneration model is established and explored. In this work, firstly, the NO catalytic rate and soot combustion rate are defined as the evaluation indicators of the new C-GPFs integrated regeneration performances. Secondly, based on the numerical simulation software, the regeneration performances of the new C-GPFs with and without electric heating are compared and analyzed, and the calculation model is verified based on the engine experiments. Then, the effects of four different structure parameters on the regeneration performances of the new C-GPFs are studied. Finally, through the orthogonal experiments, the influence weights of the four parameters on NO catalytic rate, soot combustion rate, and pressure drop are explored, and the new C-GPFs are optimized under simulation conditions. The results show that after optimization, the NO catalytic rate is enhanced by 2.1%, the soot combustion rate is enhanced by 11.9%, and the pressure drop is increased by 3%. This work provides an important reference value for improving the integrated regeneration performance of the C-GPFs in a gasoline engine.

A nanorod-like KTi8O16 catalyst for soot combustion

A nanorod-like KTi8O16 catalyst was successfully prepared by combustion method and applied for removing hazardous diesel soot. The cryptomelane structure of KTi8O16 is confirmed by X-ray powder diffraction (XRD). The straight and smooth crystalline nanorods with the diameter of 180 nm are identified by transmission electron microscopy (TEM) and (200) facet is observed to be preferentially exposed. K cations are not freely present in cryptomelane structure of KTi8O16 derived from X-ray absorption fine-structure (XAFS) results, possibly due to the confinement or interaction of K with Ti element. By temperature-programmed oxidation (TPO) experiments, its catalytic soot combustion performance was evaluated, with T 10 and T m of 435°C and 511°C, which are decreased by 19°C and 45°C respectively compared with pure anatase TiO2. K+ species are deduced to serve as the active sites in the catalytic soot oxidation reaction, which are confined in the channels of the nanorod-like KTi8O16.

Metallic Ag Confined on SnO2 Surface for Soot Combustion: the Influence of Ag Distribution and Dispersion on the Reactivity

AbstractTo unravel the surface confinement effect of SnO2 for Ag, and find an effective way to design practical soot combustion catalysts, an XRD extrapolation method has been adopted for the first time to analyze the distribution and dispersion of metallic Ag on SnO2 surface. Ag addition can generate more surface oxygen vacancies on SnO2, thus forming richer amount of surface O2− and O22− anions. However, the amount of soot reactive oxygen sites is significantly influenced by the distribution of Ag. It is quantified that 1.86 mmol Ag/100 m2 SnO2 surface, which is equal to 5.2 wt% loading, is a threshold value for Ag distribution. Below the threshold, Ag is nearly in amorphous state, and has strong interaction with the SnO2 support, thus producing more soot reactive surface oxygen sites. Furthermore, the redox property of SnO2 lattice oxygen is enhanced by Ag addition. Therefore, metallic Ag in nearly amorphous state plays a critical role for the reaction. Ag crystallites formed on the surface above the threshold have negative influence on the activity. The best Ag/SnO2 catalyst can be fabricated by loading the threshold amount of Ag over SnO2 surface to get the maximum quantity of amorphous Ag species.

An investigation on early evolution of soot in n-dodecane spray combustion using large eddy simulation

Numerical simulations using large eddy simulation (LES) and Unsteady Reynolds Averaged Navier–Stokes (URANS) are carried out to identify the underlying mechanisms that govern the early soot evolution process in an n-dodecane spray flame at 21% O2 by molar concentration. A two-equation phenomenological soot model is used here to simulate soot formation and oxidation. Both ignition delay time (IDT) and lift-off length (LOL) are found to agree with experimental measurements. The transient evolution of soot mass, in particularly the soot spike phenomenon, is captured in the present LES cases, but not in the URANS cases. Hence, a comparison of numerical results from LES and URANS simulations is conducted to provide a better insight of this phenomenon. LES is able to predict the rapid increasing soot mass during the early stage of soot formation due to having a large favorable region of equivalence ratio (ϕ>1.5) and temperature (T>1800K) for soot formation. This favorable region increases and then decreases to reach a quasi-steady state in the LES case, while it continues to increase in the URANS simulation during the early time. In addition, the soot spike is a consequence of the competition between soot formation and oxidation rates. The time instance when the total soot mass reaches peak value coincides with the time instance when the total mass of soot precursor reaches a plateau. The soot spike is formed due to the continuous increase of oxidizing species in the LES case which leads to a more dominant oxidation process than the formation process.

The Effect of Synthesis Methods on Active Oxygen Species of MnOx-CuO in Soot Combustion

The activity of the catalyst is closely related to the synthesis method. Hereon, we prepared a series of XMn1Cu (X = 2, 4, 6, 8) catalysts by hydrolysis driven redox, co-precipitation and hydrothermal synthesis approaches, respectively. The effect of XMn1Cu synthesized by different strategies on soot combustion activity were compared. The results show that the catalysts fabricated by hydrolysis driven redox have excellent performance than the other two methods in soot removal, and the activity follows r-XMn1Cu > h-XMn1Cu > cop-XMn1Cu. The Mn/Cu = 4:1 is the optimal ratio of Cu-Mn composite oxide. Among the materials, the r-4Mn1Cu sample has the best catalytic activity due to the uniform distribution of Mn and Cu, high specific surface area, enhanced content of Mn4+, promoted concentration of lattice defects and oxygen vacancies, and T10, T50 and T90 are 303, 355 and 386 °C, respectively. The repeated experiments present that r-4Mn1Cu has high activity and stability in soot oxidation. Combined with experimental results and characterization, oxygen vacancies and reactive oxygen generation mechanism of XMn1Cu catalyst in soot combustion were further discussed.

Investigation into the Anticoking Performances of Sol–Gel-Derived SiO2 and SiO2–CeO2 Coatings during Thermal Pyrolysis of Light Naphtha

CeO2-based materials are widely applied in a three-way catalyst framework for catalytic combustion of diesel soot. For the application of CeO2 in coking inhibition during thermal cracking of hydroc...

Interface interaction induced oxygen activation of cactus-like Co3O4/OMS-2 nanorod catalysts in situ grown on monolithic cordierite for diesel soot combustion

Herein, Co3O4 decorated manganese oxide octahedral molecular sieve (OMS-2) catalysts with cactus-like nanorod morphology are in situ constructed on industrial cordierite monoliths for soot combustion. The specific structure of the catalysts provides sufficient macroporous space to improve the soot-catalyst contact efficiency. Compared with traditional powder-coated catalysts, the consumption of the as-synthesized catalyst is saved by ∼13 times with the same thickness, and the contact area is enlarged by ∼4 times with the same weight. Our findings show that the interface interaction between Co3O4 and OMS-2 promotes the generation of oxygen vacancies. The isotopic 18O2 results reveal that the number of active sites for soot combustion on the Co3O4 modified catalyst is 3 times larger than that on OMS-2 alone. Additionally, this interaction accelerates the activation of gaseous oxygen, and especially enhances the intrinsic activity, as well. The above advantages improve the apparent soot oxidation activity by ∼11 times.

Soot combustion over CeO2 catalyst: the influence of biodiesel impurities (Na, K, Ca, P) on surface chemical properties.

This work assessed the impact of biodiesel impurities on CeO2 catalyst for soot combustion via soot-TPO experiments. The results showed that Na- and K-doped catalysts were assisted for soot combustion, while Ca- and P-doped catalysts had a negative effect. N2 adsorption-desorption and XRD results indicated that doping biodiesel impurities led to smaller surface area by blocking small pores. Surface chemical properties are suggested as major reasons for promoting soot combustion by means of XPS, H2-TPR, and O2-TPD. Na- and K-doped catalysts showed stronger redox ability and surface lattice oxygen mobility, poorly for Ca- and P-doped catalysts. Interestingly, a large number of surface oxygen species were observed on P-doped catalyst and it enhanced the ignition of bio soot. In the presence of NO, surface chemical properties including NOx storage/release capacity and NO oxidation ability were characterized by NO-adsorption DRIFTS, NO-TPO and NOx-desorption DRIFTS, alkali-doped catalyst with excellent NOx storage capacity that can release active oxygen species and gaseous NO2 accelerate heterogeneous soot combustion, and the poor NO conversion ability to NO2 that weakens the promotion effect of soot combustion. Particularly in the existence of P, the promotion effect of soot elimination in NO + O2 was further weakened by the reason of poor NOx storage capacity and NO oxidation ability.

Chemical synthesis and evaluation of Co3O4/Ce0.9Zr0.05Y0.05O2-δ mixed oxides for the catalytic-assisted combustion of soot

Soot is one of the primary atmospheric pollutants coming from incomplete combustion in diesel engines. Therefore, its mitigation is mandatory to preserve air quality and to diminish the already known harmful effects on human health. In the present work, it is studied the chemical synthesis of nanocrystalline powders of CeO2-based oxides and their catalytic performance on the combustion of soot at low temperatures. Specifically, cerium oxide co-doped with zirconium and yttrium was successfully synthesized via hydrothermal synthesis and subsequently loaded with an active phase of Co3O4. The obtained catalysts were physicochemical, structural, and microstructurally characterized. Different samples were tested by thermogravimetric analysis looking forward to elucidating both the effect of the composition and other features of the catalyst on the soot combustion's kinetic and temperature. Results showed the obtaining of a high activity catalyst by reaching values of 255.4 and 327.2 °C for the T10 and T50, respectively. It is discussed the role of the Co3O4 acting as a promoter phase in the catalyst.

Tuning the oxygen mobility of CeO2 via Bi-doping for diesel soot oxidation: Experimental and DFT studies

The oxygen mobility of BixCe1−x (x = 0, 0.1, 0.2, 0.3, 1) has been experimentally and theoretically investigated. The catalysts were synthesized by a simple co-precipitation method and used for soot combustion. As shown in Raman results, Bi0.2Ce0.8 has the largest amount of oxygen vacancies. The interaction of the Bi-Ce system is also presented in the outcomes of XPS, H2-TPR and O2-TPD, as well as the increased active oxygen species caused by the weakening of the metal-oxygen bond resulting from the oxygen mobility. Additionally, the electronic transfer between the Bi and Ce and the elongation of the Ce-O reported in the DFT studies support the synergism of Bi-Ce and the tuned mobility of oxygen. Further, the decrease of formation energy of oxygen vacancies presented in Bi0.2Ce0.8 in agreement with the experimental results. Moreover, the optimal adsorption capacity demonstrates excellent activity. Finally, we have well verified our previous proof that Bi0.2Ce0.8, which has a higher oxygen ion mobility, has the best catalytic performance under tight and loose conditions. Our work deepens the understanding of oxygen mobility over Bi-doped CeO2 and provides a strategy to promote the catalytic activity by tuning the oxygen mobility.

Surface acid etching for efficient anchoring of potassium on 3DOM La0.8Sr0.2MnO3 catalyst: An integration strategy for boosting soot and NOx simultaneous elimination

The emission of soot and NOx is one of the most severe environmental issues, and the key factor is the development of catalysts in after-treatment systems. In this study, an innovative non-noble metal catalyst, named HKLSM, was fabricated by etching 3DOM La0.8Sr0.2MnO3 with citric acid and synchronously anchoring potassium salt, for soot and NOx simultaneous removal. The citric acid could not only slightly erode the 3DOM skeleton, thereby beneficial to the dispersion of potassium, but also react with high-valence state Mn to generate abundant coordination unsaturated Mn3+ sites, which could produce more active oxygen species. Moreover, HKLSM showed a higher NOx adsorption capability than the samples that were not subjected to acid etching. This adsorbed NOx could be stored as NO3− species, which could facilitate soot combustion. Among all the as-prepared catalysts, HKLSM demonstrated a competitive soot combustion activity with a T50 value of 368 °C, a TOF value of 3.24 × 10−4 s−1, a reaction rate of 1.87 × 10−7 molg−1s−1, a total NOx to N2 yield of 42.0% and favorable reusability and water-resistance. This integration strategy can rationalize an alternative protocol to soot and NOx simultaneous elimination or even other catalysis systems.

Ethanol supplement increases soot yields in nitrogen-diluted laminar ethylene diffusion flames at pressures from 3 to 5 bar

In spite of widely use of ethanol, mostly as a fuel extender in ground transportation engines, its sooting propensity with pressure and with ethanol content in the base fuel has not been clarified. Although, information on ethanol’s sooting and other combustion characteristics at atmospheric conditions is extensive, scaling this information to elevated pressures is problematic. Information that could be gathered from tractable laminar diffusion flames on the soot formation of ethanol’s response to pressure would be beneficial in assessing the soot emissions from engines fuelled with hydrocarbons supplemented with ethanol. To address this lack of information at pressures above atmospheric, high pressure soot formation in laminar co-flow diffusion flames fuelled by ethanol was investigated using nitrogen-diluted ethylene as the base fuel on a burner of 3 mm diameter fuel nozzle. Base fuel nitrogen to ethylene mass ratio was kept fixed at 6 for all experimental cases. In terms of total carbon mass flow, which was kept constant at 0.41 mg/s, ethanol’s contribution was varied as 0%, 10%, 30% and 40%, and the experiments were conducted at 3, 4, and 5 bar pressures. The main aim of the investigation was to evaluate the soot production at elevated pressures with increasing ethanol fraction in the fuel stream treating nitrogen-diluted ethylene as the other fuel component. Flame heights defined by the luminous visible tips did not display any significant changes as the ethanol fraction or pressure was changed. Spectrally-resolved line-of-sight soot radiation collected along the radial distance from the flame centreline at various heights above the burner exit with 1 mm increments was converted to radial soot temperature and volume fraction distributions through an Abel-type inversion algorithm. Within the bounds of pressure considered, soot production increased with the amount of ethanol added to the fuel stream. Largest incremental increase in soot production over ethylene diluted with nitrogen was observed at the condition with 10% carbon from ethanol in the fuel blend; further increases in ethanol fractions kept increasing the soot but at relatively lower rates. This non-linear effect with ethanol addition was discussed and it was argued that one of the reasons for this behavior is the influence of methyl radical produced by radical-induced decomposition of ethanol enhancing soot production for 10% ethanol case. With further increases in ethanol amount, this effect seems to slow down because of reduction in ethylene fraction and the increase in hydrogen to carbon ratio in the fuel stream at fixed carbon flow rate.

Synthesis of superficially modified Ce1−x(Zr + Y)xO2−δ solid solutions and thermogravimetric analysis of their performance in the catalytic soot combustion

In this work, solid solutions of general formula Ce1−x(Zr + Y)xO2−δ were chemically synthesized through the so-called citrate-EDTA complexing method, wherein the doping cations Zr and Y were substituted in the ceria lattice with an equimolar amount of 0.05 ≤ x ≤ = 0.25. The ternary oxides were heat-treated, and those that showed the best textural properties were superficially impregnated with Fe2O3 particles by the thermal decomposition method using a metalorganic precursor. The X-ray diffraction results suggest that co-doping with Zr4+ and Y3+ promotes a slight distortion of the CeO2 cubic cell. Nevertheless, the fluorite cubic structure of the oxides remains stable after being exposed to heat treatments. Furthermore, using scanning electron microscopy and Raman techniques, the presence of deposited Fe2O3 and the formation of extrinsic vacancies in the materials could be corroborated. Finally, the oxides’ catalytic evaluation in the soot oxidation reaction was carried out using the thermogravimetry technique. The ternary oxide with cerium molar content equal to 0.9 and impregnated with Fe2O3 presented excellent catalytic behavior for soot oxidation. T10, T50, and T90 temperatures were 310, 383, and 416 °C, respectively.

Enhancement Effect of Soot Combustion Over CeO <sub>2</sub> Catalysts Obtained from Ce-BTC-MOF

Enhancement Effect of Soot Combustion Over CeO <sub>2</sub> Catalysts Obtained from Ce-BTC-MOF

Hydrothermally prepared Ag-CeZrO2 nanocomposite for efficient diesel soot oxidation

Air pollution caused by diesel soot emission, is a serious environmental issue. In order to prevent the soot being released into the atmosphere, the catalyzed combustion of the soot trapped in diesel particulate filter (DPF) is performed, normally at high temperature. Among different noble metal dopants, Ag is effective in decreasing the active temperature, which can catalyze graphitic oxidation by penetrating into bulk graphite. The optimum 5 wt% Ag loading in Ag-ZrO2NPs were reported earlier. In our previous study, we demonstrated the catalytic properties of Ag-ZrO2 nanoparticles (NPs) with optimum 0.9 wt% Ag loading, which showed its cost effectiveness when compared with the high cost of Ag noble metal. The catalytic oxidation peak position declined gradually 455 °C to 399 °C with corresponding sintered temperature from 400 °C to 800 °C respectively.In this study, further decrease in soot oxidation temperature (387 °C) was achieved by incorporating ceria into the Ag-ZrO2 system (Ag-CeZrO2). A facile hydrothermal synthesis method was utilized for preparation of Ag-CeZrO2 nanocomposites. After the incorporation of ceria to Ag-ZrO2 system, the tetragonal phase of ZrO2 was observed instead of multi phases (tetragonal and monoclinic) ZrO2. In the present study, the soot combustion behavior of Ag-ZrO2 and Ag-CeZrO2 catalysts is described in details..

Electrospinning synthesis and characterization of nanofibers of Co, Ce and mixed Co-Ce oxides. Their application to oxidation reactions of diesel soot and CO

Co, Ce and Co-Ce nanofibers were synthesized by the electrospinning method. To obtain mixed fibers, Co was incorporated in two ways: one step synthesis and sequential synthesis. Nanofibers were applied to two reactions: gas-solid (CO oxidation) and solid-solid-gas (combustion of diesel soot). Different activity trends were observed in both reactions. For soot combustion, Co-Ce nanofibers were more active either than Co or Ce nanofibers. For CO oxidation instead, the activity order was Co > Co-Ce > Ce. Moreover, in the case of soot combustion, for all samples the temperature of maximum combustion rate occurred at a relatively narrow range (350−390 °C). On the contrary, for CO oxidation the temperature range for T50 was notably wider (150−325 °C). The high activity shown for all the samples for soot oxidation is related to the multiple contact points between the fibers and the soot particles, and the trend observed for CO oxidation related to the higher redox capacity of Co, as observed from CO-TPR experiments.

Experimental study on in-flame soot formation and soot emission characteristics of gasoline/hydrogenated catalytic biodiesel blends

Gasoline compression ignition engine is one of the most promising low-temperature combustion strategies using gasoline as fuel due to its high thermal efficiency and low emission characteristics. While the ignition difficulty under low loads and knocking combustion under high loads limit its practical applications. To solve these problems low reactive gasoline fuel blending with high reactive hydrogenated catalytic biodiesel was proposed. However, soot characteristics of large hydrocarbons are not yet known. In order to understand the relationship between the in-flame soot formation and soot emission for these blending fuels and to find an optimum ratio for GCI engines. Fundamental study on in-flame soot formation in a constant volume combustion chamber is studied using a diffused background-illumination extinction method. The results show that the in-flame soot mass and soot combustion duration was found to be reduced with increasing the ratio of gasoline. Lower ratios of hydrogenated catalytic biodiesel blends are tested in a gasoline compression ignition engine and the experimental results reveal that the increase of hydrogenated catalytic biodiesel ratio increased the total number of soot particle emission. The total number of particle emission showed a positive relationship with soot formation. But there is a weak relationship between the particle size distribution and in-flame soot formation under the same working loads. The results also demonstrated that the particle diameter was mainly depending on working conditions rather than soot formation. The blend ratio of hydrogenated catalytic biodiesel and the injection strategies were mainly contributed to the concentration of particle size.

Effects analysis on soot combustion performance enhancement of an improved catalytic gasoline particulate filter regeneration system with electric heating

The soot combustion performance of catalytic gasoline particulate filter regeneration system (C-GPFs) can be significantly improved by increasing the temperature of gasoline exhaust gas at low-temperature conditions. In this paper, firstly, the soot oxidation rate is introduced as an evaluation index for the combustion performance of C-GPFs, and a suitable electric heating power is defined. Secondly, based on the computational fluid dynamics software, the traditional and improved electric heating C-GPFs combustion performance is compared and analyzed, and the accuracy of the improved electric heating C-GPFs model is verified through experiments. Finally, the effects of critical exhaust parameters on the soot combustion performance and electric energy consumption of the electric heating C-GPFs is studied by numerical simulation. The results of the study show that: the electric energy consumption under the suitable electric heating power is reduced by 49.6% as the exhaust flow rate decreases from 0.023 kg/s to 0.017 kg/s. The electric energy consumption under the suitable electric heating power is reduced by 50.4% as the exhaust temperature increases from 558 K to 588 K. The electric energy consumption under the suitable electric heating power is reduced by 31.6% as the exhaust oxygen concentration increases from 1.6% to 2.4%. The electric energy consumption under the suitable electric heating power is reduced by 34.7% as the exhaust NO concentration increases from 0.08% to 0.12%. Finally, this work provides a direction for improving the soot combustion performance in gasoline engines at low-temperatures.