High Temperature Soot Research Articles

An optical study of the combustion and flame development of ammonia-diesel dual-fuel engine based on flame chemiluminescence

Under the background of the “carbon peak and carbon neutrality”, the development and utilization of zero-carbon fuels, represented by green ammonia and green hydrogen, has gained attention from all walks of life. Among them, the problems of transportation and storage of hydrogen restrict its industrial development, while ammonia has significant advantages as a suitable hydrogen energy carrier for the power systems. The ammonia-diesel dual-fuel engine enables the mixture to be stratified in a time-activated multi-point ignition mode to promote efficient and clean combustion of ammonia. To investigate the combustion and flame development of the ammonia-diesel dual-fuel engine, an optical diagnostic study was carried out on a self-refit dual-fuel optical engine. The results show that the combustion inertia and lower flame temperature of ammonia can inhibit combustion and lead to lower cyclic heat release in the ammonia-diesel dual-fuel combustion (ADDC) mode, which in turn reduces the indicated mean effective pressure (IMEP). Different from the yellow-white flame produced by the high-temperature soot radiation in pure diesel combustion (PDC) mode, the flame in the ADDC mode appears orange. The peak of flame area (FR) percentage and flame natural luminosity (FNL) of the 80% ammonia ratio ADDC mode decrease by 60% and 92%, respectively, compared to the peaks at PDC mode. The ammonia combustion flame is mainly concentrated around the diesel flame, and at the same time achieves good ignition performance at all ammonia ratios. In contrast to the PDC mode where the FR and FNL decrease rapidly as the diesel injection timing (DIT) advances, the flame pattern of the ADDC mode does not respond significantly to the DIT.

PPS ultrafine fiber enhanced aramid fiber filter with superior thermal stability and excellent chemical resistance for efficient PM2.5 removal

Polyphenylene sulfide (PPS) fiber is widely used in high-temperature soot filters owing to its high-temperature and chemical stability. However, PPS fiber undergoes a thermal cross-linking reaction in high-temperature environments, leading to a decline in its mechanical properties, and eventually leading to filter material damage and failure. In this work, short para-aramid (PPTA) fiber was introduced into homemade PPS ultrafine fiber by wet dissociation and dry thermal consolidation technologies. The prepared PPS/PPTA ultrafine fiber felt exhibited high filtration accuracy and long-term thermal stability. The filtration efficiency of PPS/PPTA ultrafine fiber felt for PM0.3, PM0.5, PM1.0, PM2.5, PM5.0, and PM10 reached 89.02, 97.34, 99.85, 99.99, 100.00, and 100.00%, respectively, and remained above 98% after 20 cycles. These results were largely consistent with the theoretical values from the filtration model analysis. The PM2.5 filtration efficiency of PPS/PPTA ultrafine fiber felt remained above 99.73% after being placed at 230 °C for 48 h or being soaked in strong acid and alkali solutions for 48 h, indicating its excellent thermal and chemical stability. PPS/PPTA ultrafine fiber felt also possessed structural stability, with a tensile strength and tear index of 32.93 N/cm and 22.77 mN·m2/g, respectively. Due to its excellent comprehensive performance, we believe this PPS/PPTA ultrafine fiber felt provides a new strategy for the refined governance of industrial high-temperature soot.

CO2 gasification of dry quenching dust ash catalyzed in situ by soot

It's imperative to reduce the CO2 emissions in iron and steel manufacturing and improve the reaction rate of the CO2 gasification of dry quenching dust ash (DQDA). In this study, a new technology is proposed in which the CO2 gasification of DQDA is catalyzed by high-temperature soot (HS) in the high-temperature flue gas of a converter. In the experiments, a composite catalyst (FeO: Fe2O3 = 5:2) was used to stimulate the main Components of HS. The influence of the main components of HS (FeO, Fe2O3) on DQDA gasification with CO2 was evaluated by thermodynamic simulation calculation (FactSage 6.1), thermo-gravimetric analysis, and drop-tube furnace experiments at high temperatures. In addition, the catalytic efficiency was quantitatively evaluated by the α and β values, LHVs, and kinetic analyses using homogeneous and shrinking-core models. The results indicated that the HS has significant catalytic effects on the CO2 gasification of DQDA, and exhibited differing characteristics. The catalytic efficiency increased with temperature. At 1200 °C, the consumption of CO2 was increased from 24.13% without a catalyst to 30.76% with the HS composite catalysts. As a result, Fe, FeO, and Fe3C were the most common solid products catalyzed by HS. Experiments proved the new technology's practicality.

Emission Spectra of Hydrocarbon Flames Doped with Phosphorus-Containing Compounds

Phosphorus-containing compounds, including organophosphorus substances, are valuable laboratory flame additives for understanding the combustion behavior of sarin. Chemiluminescence features of excited intermediate species are useful markers of combustion, but an effective chemiluminescence-based combustion diagnostic for phosphorus-based compounds is yet to be developed. In this study, chemiluminescence spectra of atmospheric-pressure flames doped with three phosphorus-containing compounds, namely, dimethyl methylphosphonate, diisopropyl methylphosphonate, and phosphoric acid (), were obtained in two flame configurations, namely, spherically expanding flames and piloted liquid-spray flames. The spectra are compared with those obtained from undoped flames fueled by methane and methanol, respectively. Spectra were recorded for the wavelength range of 200–800 nm and for three equivalence ratios (, 1.0, 1.2) of spherical flames. For both flame configurations, the intensity of the doped flame emission increased relative to the neat flames by over an order of magnitude, but no clear spectral features besides a broad, featureless continuum emission could be identified. No significant difference was observed between the spectra of the spray flames doped with and with diisopropyl methylphosphonate. The observance of a continuum emission for all the doped flames is attributed to blackbody emission, likely resulting from high-temperature soot particles in the flame originating from condensed, phosphorus-containing combustion products. However, unique, narrow chemiluminescence features specific to phosphorus combustion could not be identified at this time.

Research Progress on High Temperature Corrosion Mechanism of Waste Incineration Power Generation Boiler

Waste incineration power generation is a main method of waste disposal, and high temperature corrosion has always been a key issue restricting the development of this technology. This paper reviews the research progress of high temperature corrosion mechanism of waste incineration boilers. Based on the chemical reaction of high temperature corrosion of chloride, the mechanism of chloride corrosion of boiler metal fittings is discussed. The analysis results show that the high-temperature flue gas corrosion mainly includes HCl gas corrosion, molten salt corrosion and sulfide corrosion. In addition, the analysis of the high-temperature soot corrosion mechanism shows that the corrosion behavior of the heated surface in the presence of sintered ash is stress cracking corrosion. This is the result of the combined effect of the stress destruction of dense sintered ash and the ion diffusion corrosion reaction of chlorine in the ash.

Spatially resolved measurements of soot and gaseous precursors in ethylene counterflow diffusion flames up to 32 atm

We investigate the effect of pressure on both flame structure and soot formation in nitrogen diluted counterflow diffusion flames of ethylene in the 8–32atm pressure range. Capillary-probe gas sampling is performed to resolve spatially the profiles of gaseous species up to three-ring aromatics by GC/MS analysis and multi-color pyrometry is used to quantify the soot volume fraction and dispersion exponent. Self-similarity of flames is preserved by keeping constant mixture fraction and strain rate, so that profiles of concentrations and temperature, normalized with respect to their peak values, are unaffected by changes in pressure, once the axial coordinate is nondimensionalized with respect to the pressure-dependent diffusion length scale. When conditions are chosen so that the overall soot loading is approximately constant and compatible with the diagnostics, it is found that both the soot volume fraction and the profiles of key aromatics in the high-temperature nucleation region are virtually invariant. For it to happen, a twofold increase in pressure must be compensated by a ∼100 K decrease in peak flame temperature and, therefore, in the temperature across the soot forming region. The implication is that from the perspective of the chemical kinetics of soot formation these two actions counterbalance each other. As pressure increases (and temperature decreases) the peak production rate of the high-temperature soot mechanism decreases and, further downstream, towards the particle stagnation plane, a low-temperature soot mechanism sets in, yielding an increase in soot H/C content. This mechanism is enhanced as the pressure is raised, causing a higher overall soot volume production rate in the 16atm flame and, especially, in the 32atm one. The role of C4/C2 species in the formation of C6H6 increases with increasing pressure and dominates over the recombination of propargyl radical at sufficiently high pressures. A comprehensive database is established for soot models at high pressures of relevance to applications.

Diesel combustion in high load situations: a visual analysis of mixture formation and air utilization

As fuel injection pressures keep rising, questions focus on additional benefits to be gained from the considerable efforts to achieve and handle the fuel pressure increments. The aim of fuel injection processes is to support the mixing of fuel molecules with oxygen. The steps towards this goal include fuel atomization, evaporation, heat transfer from air into the liquid or vaporized fuel together with transport of fuel for best air utilization. Engineering degrees of freedom include the parameters of the fuel injection system and handling of in-cylinder gas conditions. The paper describes basic high pressure flow processes, spray propagation, evaporation and combustion and the mixing of flame clouds with in-cylinder air for oxidation of high temperature soot particles. Experimental evidence of such processes is derived from laboratory flow tests as well as from optically accessed engines operated under conditions relevant for todays passenger car and heavy duty engines.

Silicon carbide-based membranes with high soot particle filtration efficiency, durability and catalytic activity for CO/HC oxidation and soot combustion

We report here the solution coatings of Diesel Particulate Filter (DPF) with allylhydridopolycarbosilane (AHPCS)-based polymers leading to supported silicon carbide (SiC)-based membranes with high temperature soot particle filtration efficiency, durability and catalytic activity. In a first part of the present study, our objective was to reduce the pore size of DPF to filtrate finer particles without altering filtration efficiency by coating DPF with an additional fine porous AHPCS-derived SiC membrane. The latter is produced by dip-coating AHPCS on DPF following by a pyrolysis of the AHPCS membrane-modified DPF at 1000°C under argon. We investigated the influence of dip-coating parameters and viscosity of different AHPCS solutions on the SiC membrane-coated DPF by SEM, mercury porosimetry, XRD and high-temperature thermogravimetric analysis. The evolution of the filtration capacity has been determined with a synthetic gas bench. An additional fine SiC membrane (∼150nm in thickness) prepared from a 10vol% of AHPCS in THF deposited on DPF allowed maintaining filtration efficiency as high as the virgin DPF while the pore size of the SiC membrane coated-DPF decreased to filter finer particles. Results are confirmed using a commercially-available polysiloxane (Si–C–O precursor). Furthermore, the SiC membrane acted as a thermal barrier coating and provided a better durability to the DPF by preventing apparition of cracks after heat-treatment to 1500°C under argon. The use of mixed oxide and metallic phases formed in-situ in SiC constitutes one of the solutions to generate new and effective catalytic performances to membranes. Within this context, in a second part of the study, we applied a reverse AHPCS-based microemulsion to combine SiC and oxide phases in the same additional porous membrane. As a proof of concept, we have prepared catalytically active Ce–O–Fe–Pt/SiC membrane coated DPF after dip-coating and pyrolysis under argon. These materials have been characterized and tested with regard to CO/HC oxidation and soot combustion. Ce–O–Fe–Pt/SiC membrane coated DPF showed an activity for CO conversion reaching a light-off temperature T50=270°C and the presence of the catalytic phase allowed burning soot at 486°C.

액중 전기선 폭발법에 의한 Ni-free Fe계 나노 합금분말의 제조: 2. 용매의 영향 및 제조 방법에 따른 분말입자의 비교

This study investigated the effect of solvent on the fabrication of Ni-free Fe-based alloy nano powders by employing the PWE (pulsed wire evaporation) in liquid and compared the alloy particles fabricated by three different methods (PWE in liquid, PWE in Ar, plasma arc discharge), for high temperature oxidation-resistant metallic porous body for high temperature soot filter system. Three different solvents (ethanol, acetone, distilled water) of liquid were adapted in PWE in liquid process, while X-ray diffraction (XRD), field emission scanning microscope (FE-SEM), and transmission electron microscope (TEM) were used to investigate the characteristics of the Fe-Cr-Al nano powders. The alloy powder synthesized by PWE in ethanol has good particle size and no surface oxidation compared to that of distilled water. Since the Fe-based alloy powders, which were fabricated by PWE in Ar and PAD process, showed surface oxidation by TEM analysis, the PWE in ethanol is the best way to fabricate Fe-based alloy nano powder.

NO x Storage and High Temperature Soot Oxidation on Pt–Sr/ZrO2 Catalyst

NO x storage–release and soot oxidation have been studied using strontium promoted zirconia with different surface areas. It was found that the amount of the adsorbed NO x increases with the increase of the support surface and Sr concentration up to 20 wt% Sr. Introduction of platinum has no effect on the amount of NO x stored, but improve soot oxidation due to recycling of NO to NO2. A combination of oxidation catalyst with NO x storage materials enables to lower the temperature of 20% soot conversion up to 100 °C in comparison with un-catalyzed soot oxidation.

Application of NOX storage/release materials based on alkali-earth oxides supported on Al2O3 for high-temperature diesel soot oxidation

Alkali-earth oxides and nitrates supported on alumina were studied as model systems for NOX storage/release. Their impact on the high-temperature soot oxidation has been investigated. The stability of surface nitrates and temperature of NOX release increase parallel to the basicity of the cation. The presence of soot decreases the temperature of NOX release. The storage capacity depends on the several factors, such as basicity, dispersion of the cation, and pre-treating conditions. Adsorption of NO with O2 at 200°C leads to the formation of surface nitrates that mainly exist as ionic nitrates. Stored nitrates contribute to the soot oxidation and assist to lower the temperature of soot oxidation up to almost 100°C. In the presence of only NOX storage material the efficiency of NOX utilization is, however, quite low, around 30%. Therefore, the presence of an oxidation catalyst is essential to increase the efficiency of NOX utilization for soot oxidation up to 140% and selectivity towards CO2. A combination of oxidation catalyst with NOX storage materials enables to lower the temperature of soot oxidation more than 100°C for the Sr- and Ca-based systems.

Air oxidation of carbon soot generated by laser ablation

Carbon soot was generated by laser ablation under oxygen-free and regulated-temperature conditions at 300 K and 1500 K. The soot was significantly oxidised by being exposed to air in darkness. The degree of oxidation was determined to be 0.038±0.012 and 0.093±0.009 for the high temperature (HT) soot and the low temperature (LT) soot, respectively, on the basis of elemental analysis, XPS and Karl-Fischer titration. Water physically absorbs on the soot in proportion to the degree of oxidation. TG, TPD and 13C-NMR revealed that there were at least 2 kinds of oxidised states. One of them mainly contributes to CO and CO2 emissions at 420–970 K, while another contributes to CO emission above 770 K. The former is a dominant oxide in the LT soot. On the basis of FT-IR and 13C-NMR spectra, carbonyl groups were confirmed to be one of the major oxidised species in the soot. FT-IR and acid-base titration revealed that the LT soot adsorbed more CO2 than the HT soot did. The adsorbed CO2 contributes to the acidic property of the soot. The soot is paramagnetic as well as conductive. C1s and Auger photoelectron spectra of the soot were neither graphite-like nor diamond-like. The air oxidation is discussed in relation to unique structures and formation mechanisms of the soot.

Heat Transfer Processes in Diesel Engines

The heat transfer processes taking place in the combustion chamber of direct-injection diesel engines are reviewed based on experiments performed in an atmospheric test rig, where a diesel engine spray was impinging vertically and at an angle onto a heated plate with and without a cross-stream of air simulating swirl, and in a single-cylinder engine incorporating a variable swirl mechanism. The convective heat transfer associated with the impinging spray on the wall of the piston-bowl and the radiative heat transfer associated with the high temperature soot particles formed during combustion were estimated for two swirl ratios, based on the measured temperature of the gas and the piston wall by means of two-colour pyrometry and fast-response thermocouples, respectively.

The effect of temperature on soot inception in premixed ethylene flames

The temperature dependence of soot and related hydrocarbon formation was studied in fuel-rich, premixed C 2 H 4 /O 2 flames by changing the flame temperature but keeping a constant C/O ratio. Three flames with temperature levels between the low-and high-temperature soot threshold of the bell-shaped domain of soot formation were analyzed. In addition to the formation of pyrolytic species such as acetylene, benzene, polycyclin aromatic compounds (PAHs), and soot, the large formation of a tarlike material was revealed in the soot preinception region of the flames. The chemical analysis and spectroscopic characterization of these species showed that tar is made up of high-molecular-weight compounds in which aliphatic and aromatic functionalities coexist. The decrease in the concentration and the aromatic character of tar was found to correspond with soot inception, indicating that it could be responsible for soot nucleation. PAH molecules indirectly participate in soot inception, providing the building blocks of tar and/or participating in further soot surface growth. The influence of temperature on soot formation was found to be different at the extremes of the bell-shaped domain of soot. In the flame near the low-temperature soot threshold, benzene, PAHs and pyrolytic species are formed in larger amounts, but low temperatures hinder the reactive coagulation of PAH molecules and aliphatic radicals into tarlike material, hindering, in turn, soot production. The buildup of tarlike material and the process of aromatization occur too slowly to allow the massive soot inception if the flame temperature is not high enough. At higher temperatures, oxidation is very active in the secondary oxidation zone of the flame, thus destroying PAHs that are not then available for formation of tarlike species. Consequently, soot inception is reduced. In the intermediate-temperature flame, where maximum soot formation was found, the temperature level is ideal for the formation of both PAHs and tar and their transformation to soot particles.

Behavior of Diffusion on Flames in AC Electric Field and DC Magnetic Field. Electrical Mobility of Soot Particle in AC Electric Field and Flame Deformation in DC Magnetic Field.

A diffusion flame at a low flow rate of propane gas in still air was surrounded by a circular mesh electrode. A circular burner of 8 mm diameter was used as the other electrode. Alternating electric field of high frequency and high voltage was applied between these electrodes. The luminosity which radiated from high temperature soot particles was measured by a photomultiplier. The oscillating frequency of the luminosity changed proportionally up to 80 Hz with the frequency of the applied electric field. The electrical mobility and effective equivalence diameter of soot particles in the flame were estimated by means of the displacement of the luminous signal and the relaxation time of the soot particles. Average values were calculated to be about 0.15 m2/(V·s) and 40 μm respectively. The deformation of diffusion flames at low flow rate has been investigated numerically by the use of a rectangular nozzle in magnetic field. The deformation of the flame was independent of the direction of the magnetic field. The strength of the external force by the magnetic field was proportional to the value of two powers of magnetic field (=H2) . The force exerted upon the boundary between the flame and the air by the magnetic field was one induced by the difference of the volumetric susceptibility between the two gases. The deformation, tilt and turn of the flame are caused by the buoyancy and the induced force by the magnetic field. The numerical analysis of the turn of the flame was conducted using the value of the pressure difference at the boundary between the two gases.

Soot distribution and cars temperature measuremnts in axisymmetric laminar diffusion flames with several fuels

Measurements of internal flame temperature distributions, using CARS, and soot distributions, using 90° Mie scattering, have been made in axisymmetric, laminar, diffusion flame for several gaseous fuels. Such internal measurements are important in understanding flame structure and mechanistic effects on soot generation, and in assessing correlations with global parameters such as the adiabetic flame temperature (AFT). Temperature measurements with ethylene, butene, allen and acetylene fuel indicate that gas within the fuel zone, and particularly along the centerline, attains 1600–1800 K at the point that soot becomes detectable on the centerline. Calculations with the Mitchell flame sheet model for ethylene, which includes a burner fuel preheating effect for our geometry, support the rapid attainmental of high centerline temperatures and indicate that radial heat transport is significant. These results suggest that rapid insertion thermocouple techniques, which have tended to show much lower temperatures along the centerline within the soot zone, may have lower accuracy when probing high temperature soot zones where radiation corrections would be significant. The luminous tip temperature of all smoke-point flames falls in the narrow range 1500–1600 K. Maximum radial temperature results with all fuels show AFT and soot radiation loss trends similar to our prior results with ethylene, and are in agrement with the results of Kent and Wagner. Our results show quantitatively the limitations imposed on temperature similarity when a highly-sooting fuel, such as acetylene, has a smoke-point height as short as one burner diameter or less. Taller, lower-AFT, nitrogen-diluted smoke-point flames show greater temperature similarity in such cases. Some quantitative soot results obtained with angular dissymmetry Mie scattering are reported which compare peak soot volume fraction characteristics of the smoke-point flames studied.