Soot Production Research Articles

Evaluation of soot emission and wall heat loss for the fuels with high aromatic contents using the coupled analysis of chemical luminescence images with heat flux

The stricter regulations on the sulfur content of marine fuel oil in the general sea area that came into effect in January 2020 have led to a prediction of the increase of light cycle oil with high aromatic contents. The higher aromatic content is expected to result in higher soot in the exhaust gas. During combustion, soot emits radiant heat because of blackbody radiation, some of which passes through the walls of the combustion chamber and is released outside. Therefore, the exhaust emission characteristics and wall heat loss are affected if soot formation during combustion differs depending on the aromatic content of the fuel oil. This study developed an analytical method that combines the temporal and spatial distributions of C2 and OH radicals (these species contribute to soot formation and oxidation) to evaluate the emission and wall heat loss characteristics of different aromatics in fuel oils via combustion and heat flux analysis. The method was applied to test fuels containing different aromatic contents. Two test fuels containing 60 vol% each of toluene (monocyclic) and 1-methylnaphthalene (bicyclic) were evaluated in a rapid compression machine with a 100 mm wall-to-wall distance combustion chamber. The results suggested that the differences in soot emissions were observed because of differences in aromatics, and no differences in the wall heat flux were observed. The distributions of C2 and OH radical luminescence intensities between the walls were examined, and the differences in soot production were attributed to differences in the C2 radical production upstream of the flame in the region of low air entrainment. The lack of difference in the heat flux between the test fuels can be attributed to the the differences in the C2 and OH luminescence intensities, which are related to the heat release rate and heat flux, being almost nonexistent near the walls.

Application of scalable sensor-assisted multi-scale computational methods in the simulation of micro mechanical behavior of composite materials

Micro mechanics involves the examination of the mechanical behavior of heterogeneous materials, taking into account inhomogeneities such as voids, fractures, and inclusions, and building on mathematical models developed. Composites bring engineering design barriers despite their strengths. Composite manufacturing and processing need specialized equipment, strategies, and labor, ensuring they are challenging and expensive. Mechanical behavior deals with how a composite material performs if faced with mechanical effects and action. Scalable sensor-assisted multi-scale computational Methods (SS-MSCM) are used to investigate topics ranging from the molecular basis of soot production in combustion to how molecule-level flaws influence macroscopic mechanical qualities. Carbon fiber reinforced polymers (CFRP) are generated by mixing graphene fiber with a resin, like vinyl ester and epoxy, to render a composite material with superior performance to the component ingredients. Hence, SS-MSCM-CFRP has Improved mechanical qualities achieved by incorporating nano-reinforcements, including carbon nanofibers and graphene nanoplates, into the CFRP matrix: enhanced flexural and compressive strengths, energy absorption upon impact, toughness to fracture, and interlaminar bonding. Composite materials feature excellent mechanical qualities like high strength and stiffness, fatigue resistance, and durability. It is possible to insert scalable sensors throughout the manufacturing process, which enables real-time monitoring of structural health, strain, and other factors. Scalable sensor-assisted multi-scale computational methods offer enhanced accuracy, real-time monitoring, and cost-effectiveness by integrating sensor data with computational models, improving predictions and failure mechanism insights. However, they face limitations like sensor dependency, computational complexity, data integration challenges, and high implementation costs, leading to potential discrepancies between simulation and experimental results. Important qualities include corrosion resistance, thermal conductivity, and electrical conductivity. As the composite materials develop to satisfy the established mechanical stress and temperature conditions, they offer high durability and strength.

Review of Some Methods of CO2 Utilization

Abstract Protecting the environment from harmful substances (carbon oxides, nitrogen oxides, soot products, etc.) is one of the pressing issues of our time. This article discusses specific topics related to the need to reduce carbon dioxide emissions into the atmosphere, which are generated during biomass gasification, Fischer-Tropsch synthesis, and other processes. The article also identifies alternative methods for producing valuable petrochemical products, which significantly reduce gas emissions into the atmosphere.

Experimental study on the effects of n-butanol and n-propanol on the spray and combustion characteristics of diesel/biodiesel blends in a constant volume combustion chamber

The depletion of fossil fuel resources and the escalating environmental impact of greenhouse gas emissions have intensified the global exploration of renewable and sustainable energy sources. Biodiesel produced from vegetable oils and animal fats has become a promising alternative to conventional diesel fuel due to its renewability and lower carbon emission. This study investigates the differences in spray, combustion and flame characteristics between soybean-based biodiesel blended with propanol and butanol at various ratios. The results indicate that the liquid spray penetration length of biodiesel mixed with propanol and butanol exceeds that of soybean-based biodiesel. And the increase of spray penetration is accompanied by a longer flame lift-off length, which indicates the improvement of spray characteristics. Regarding combustion, alcohol-fuel blends exhibit a reduction in peak combustion pressure but an increase in peak apparent heat release rate. Additionally, these fuels show a shorter ignition delay and combustion duration. The peak natural flame luminosity is lower for alcohol fuels, suggesting their potential to reduce carbon soot production and support low-carbon combustion. These experimental results contribute to advancing research on cleaner, more efficient and renewable fuels, thereby reducing reliance on conventional fossil fuels.

Catalytic performance of Cs-V-based non-noble soot oxidation catalyst used for DPF and its enhancement by cerium addition

Non-noble metal catalysts have great potential for controlling soot emissions due to their effective oxidation properties and low cost. This study investigated the characteristics of Cs-V-based non-noble metal soot catalyst and Ce doping enhancement effect through comprehensive characterization of physicochemical properties, catalytic activity evaluation, and density functional theory (DFT) theoretical calculations. The results demonstrate that Ce doping improves the degree of surface particle aggregation and the spatial distribution morphology of Cs-V-based catalyst, with a 36.7 % increase in the specific surface area. Additionally, Ce doping enhances the probability of oxygen adsorption and dissociation activation on the Cs-V-based catalyst, accelerating the soot-oxidation process, improving the soot-oxidation activity, with a decrease in the characteristic temperature T10 (temperature at 10 % conversion rate of soot) from 349.7 ℃ to 281.1 ℃, and decreases the activation energy for soot-oxidation to 5.8 kJ/mol. DFT calculations reveal that Ce doping strengthens the pulling effect of interatomic chemical bonds, facilitating the removal of oxygen atoms and dissociated reactive oxygen (Oasd), resulting in an increase in the adsorption energy of C4 molecules and a shorter bond length between C4 molecules and the catalytic surface, facilitating the desorption of post-oxidation soot products.

Assessment of a PAH-based soot production model in laminar coflow methane diffusion flames doped by gasoline surrogate fuels

This article assesses the capability of the PAH-based soot model developed by the authors and validated in ethylene non-premixed flames to predict soot production in flames fueled with gasoline surrogates. The soot model was coupled to a flamelet model and the Rank-Correlated Full-Spectrum k model to simulate laminar coflow nitrogen-diluted methane/air diffusion flames doped with n-heptane/toluene and iso-octane/toluene mixtures. Consistent with our previous studies, the simulation was conducted using the Kaust Mechanism 1, pyrene as soot precursor, and the same set of model parameters. The model reproduced reasonably-well the peak soot volume fraction. However, the soot production onset was predicted much earlier than measurements owing to the early formation of pyrene induced by the presence of toluene. These discrepancies can be partially corrected by selecting a larger PAH than pyrene with a similar level of concentrations as soot precursor. For the present mechanism, anthanthrene was found to be the best candidate. Model results show that different mechanisms dominate the soot mass growth in ethylene and gasoline surrogate flames. While the HACA is more important in the former, PAH condensation largely prevails in the latter. This suggests that ethylene may be not the most relevant reference fuel for developing semi-empirical soot models for fires. Further investigations are required to confirm this conjecture.

Permissible Extrapolation Justification of the Multiplicative Multifactorial Model and Its Application to the White Soot Production Technology

The solution to a specific technological problem is combined with the methodological development of a nonlinear multifactorial relationship to justify the boundaries of its extrapolation beyond the experimental range used. White soot was produced through two-stage carbonization of a silicate solution (composition, g/l: Na2O = 126.5, SiO2 = 107.7, Al2O3 = 3.1), obtained after processing waste tailings with carbon dioxide in a recirculation system. The influence of the deposition duration, temperature, and final pH value of the pulp on the formation of the specific surface area (Ssp, m2/g) of white soot was studied. The specific surface area was calculated from the average diameter of the white soot particles measured using an electron microscope. A multifactorial experiment was designed, and the experimental results were processed using a probabilistic deterministic method for experiment design (PDED) to obtain a nonlinear multiplicative combined model. A new interpretation of the subordination of the nonlinear multiple correlation coefficient R and the R2 value was given as relating to the structural and adaptive components of complex self-organizing systems. This determines their use for assessing the ratio of the basic R and extrapolated R2ranges of variation for each factor and any combinations thereof and multifactorial dependence in general. The results are presented in the form of multifactor tabular nomograms measured by the number of multifactor cells in localized areas of optimal sets that allow isolation by one or another combination of factors. The technological object of extrapolation of the ‘white soot’ production is linked to the solution of emerging methodological problems and illustrates the accessibility of the engineering application of the proposed method for combining nonlinear and linear approaches to mathematical experimental design. Doi: 10.28991/HIJ-2024-05-03-08 Full Text: PDF

Soot volume fraction measurements in aero-engine model combustor outlet using two-color laser-induced incandescence

Quantitative measurement of Soot Volume Fraction (SVF) is an essential prerequisite for controlling soot particle emissions from aero-engine combustors. As an in-situ and non-intrusive optical diagnostic technique, Laser-Induced Incandescence (LII) has been increasingly applied for soot concentration quantification in various combustion environments such as laminar flame, vehicle exhaust, internal combustion chamber as well as aero-engine combustor. In this work, we experimentally measured the spatial and temporal distribution of SVF using two-color LII technique at the outlet of a single-sector dual-swirl aero-engine model combustor. The effect of inlet pressure and air preheat temperature on the SVF distribution was separately investigated within a pressure range of 241–425 kPa and a temperature range of 292–500 K. The results show that soot production increases with the inlet pressure but generally decreases with the air preheat temperature. Qualitative analysis was provided to explain the above results of parametric studies. The LII experiments were also conducted under 3 designed conditions to evaluate soot emission under practical operations. Particularly, weak soot emission was detected at the outlet under the idle condition. Our experimental results provide a valuable benchmark for evaluating soot emission in the exhaust plume of this aero-engine combustor during practical operations.

Modeling of Soot Emission in Turbulent Diffusion Flames Impinging on a Cold Surface

ABSTRACT A hydrocarbon flame impinging on a cold surface produces an enhanced soot emission compared to the identical free flame. Cooking with biomass fuels is one practical process where soot emissions due to flame impingement has important environmental and health consequences. This problem was examined in a simplified system in which a turbulent non-premixed ethylene flame impinged on a cold surface. Previous experiment on this configuration examined the influence of a number of parameters on soot emission. The present paper uses numerical modeling to investigate the mechanism of soot emission enhancement in this configuration. Variations in the height of the surface above the fuel jet inlet showed going through a maximum, replicating the data. Since soot behavior can be affected by both thermal quench and flow field disruption, we decoupled the processes by replacing the cold surface with an adiabatic surface. These results indicated that most of the emission enhancement was due to the flow field disruption and not due to thermal quench. The modeling suggests that the presence of the surface changes the scalar dissipation rate, which influences C2H2 concentration, a key species in the soot surface growth process. Specifically, the surface causes a spike in the scalar dissipation rate adjacent to the surface, which significantly influences C2H2 concentration and results in increased soot production. The surface also forces the flame to spread radially, allowing more O2 to penetrate the flame immediately, enhancing the soot oxidation process. The combination of the enhanced soot production and oxidation produces the observed behavior.

Prediction of Soot in an RQL Burner Using a Semi-Detailed Jeta-1 Chemistry

Abstract The present work proposes a methodology to include accurate kinetics for soot modeling taking into account real fuel complexity in Large Eddy Simulation of aeronautical engines at a reasonable computational cost. The methodology is based on the construction of an analytically reduced kinetic mechanism describing both combustion and gaseous soot precursors growth with sufficient accuracy on selected target properties. This is achieved in several steps, starting from the selection of the detailed kinetic model for combustion and soot precursors growth, followed by the determination of a fuel surrogate model describing the complex real fuel blend. Finally the selected kinetic model is analytically reduced with the code ARCANE while controlling the error on flame properties and soot prediction for the considered fuel surrogate. To perform all evaluation and reduction tests on canonical sooting flames, a Discrete Sectional Model for soot has been implemented in Cantera. The resulting code (Cantera-soot) is now available for the fast calculation of soot production in laminar flames for any fuel. The obtained reduced kinetic scheme is finally validated in a Rich-Quench-Lean burner of the literature in terms of soot prediction capabilities by comparison of LES coupled to the Lagrangian Soot Tracking model with measurements. Results show a significant improvement of the soot level prediction when using the reduced more realistic kinetics, which also allows a more detailed analysis of the soot emission mechanisms. This demonstrates the gain in accuracy obtained with improved reduced kinetics, and validates the methodology to build such schemes.

Effect of Hydrogen Addition on Soot Reduction in Diffusion Flames

This study explores the effects of hydrogen addition on soot reduction in methane-air diffusion flames, employing computational analysis coupled with chemical equilibrium and k-epsilon combustion turbulence models. By varying the fuel mixture with hydrogen mass percentages ranging from 0% to 11%, alterations in flame behaviour were observed. Results revealed a notable increase in maximum flame temperature at 1.3% hydrogen addition, attributed to enhance combustion efficiency, while subsequent additions led to temperature decrements due to dilution effects. Concurrently, soot production exhibited a general decrease, with reductions quantified up to 96.7% compared to baseline conditions, primarily due to improved oxidation and decreased carbon content. Additionally, the position of maximum flame temperature and soot mass fraction shifted along the axial direction owing to hydrogen's higher flammability compared to methane-air diffusion. These findings offer insights into optimizing flame characteristics for reduced particulate matter emissions, emphasizing the potential of hydrogen addition in mitigating soot formation in diffusion flames.

Experimental and numerical investigations of soot formation in propane laminar coflow flames in O2/N2 and O2/CO2 atmospheres

Oxygen-rich combustion is a new type of clean combustion technology with important application prospects. At present, there are few detailed analyses on the mechanism changes of soot formation under oxygen enrichment of propane. In this paper, the effects of oxygen-rich (O2/N2, O2/CO2) combustion on soot formation in the propane laminar flow coaxial jet diffusion flame were investigated by using the experiment and numerical simulation. The flame image was taken by a color (CCD) camera in the visible band, and the two-dimensional distribution of temperature and soot volume fraction in the flame was reconstructed. In numerical simulation, the soot production model considers a detailed description of nucleation via collisions among heavy polycyclic aromatic hydrocarbons, particle aggregation, polycyclic aromatic hydrocarbons condensation, surface growth and oxidation through the hydrogen abstraction acetylene addition mechanism. The results show that the experimental results were compared with the numerical simulation results, and the numerical simulation results predict the temperature and soot change of oxygen-rich flame well. With the increase in oxygen concentration, the peaks of soot and temperature in the two oxygen-rich atmospheres gradually increased. With the increase in oxygen concentration, the peaks of soot and temperature in the two oxygen-rich atmospheres gradually increased. Comparing the combustion mechanism changes of the two oxygen-rich combustion systems, it was found that the hydrogen abstraction acetylene addition mechanism was the main cause of soot generation. The OH oxidation is dominated near the fuel nozzle side, and O2 oxidation is dominant downstream. With the substitution of CO2 for N2, the chemical effect of CO2 reduces the flame temperature and inhibits the formation mechanism and oxidation mechanism of soot to some extent. This in turn leaded to a reduction in the amount of soot produced.

Investigation of the chemical mechanism of pollutant formation in co-firing of ammonia and biomass lignin

Ammonia (NH3) and biomass are recognised as renewable energy carriers with substantial promise for reducing carbon emissions. However, the issue of nitrogen oxides (NOX, including NO and NO2) and nitrous oxide (N2O) emissions from ammonia combustion and soot from biomass combustion, remains a pressing concern due to their detrimental impacts on the environment and human health. This study investigated the mechanism of pollutant formation during ammonia-lignin co-firing through reactive molecular dynamics (RMD) simulations. The results indicate that co-firing a certain amount of ammonia with lignin can reduce the formation of soot. This is mainly due to NH2 radicals converting a portion of polycyclic aromatic hydrocarbon (PAH) precursors into C–N compounds. However, it is necessary to maintain higher ammonia concentrations. Adding a small quantity of ammonia would decrease the extent of oxidative reactions within the system and fail to generate enough NH2 radicals to consume the carbon atoms forming PAH precursors, ultimately resulting in increased soot production. The impact of lignin on the formation of NOX and N2O during ammonia combustion has two main aspects: Firstly, the oxidising radicals formed during the initial decomposition of lignin promote the generation of N–O bonds, leading to an increase in the quantities of NOX and N2O during the initial reaction stage. Secondly, the carbon-containing products produced from lignin decomposition consume nitrogen atoms by forming N–C bonds, thereby diminishing available nitrogen atoms for nitrogen oxides formation. This study provides new insights into the formation of primary pollutants of ammonia and biomass co-firing on an atomic scale, which can help develop pollutant mitigation measures.

Numerical investigation of mixing and heat transfer in a 7.9 m JP-8 pool fire

The response of objects engulfed in, and adjacent to, large-scale pool fires is of interest in accident and safety assessments. In this study, Fuego, a low-Mach turbulent reacting flow code was used to study conjugate heat transfer in a 7.9 m diameter JP-8 pool fire. Simulations were designed to replicate past experimental measurements (Blanchat et al., 2006) of incident heat flux to three cylindrical calorimeters in and around the pool fire. Two turbulent combustion models were compared directly - the eddy dissipation concept and a more recently developed unsteady flamelet model. First and second order spatial and temporal discretization schemes were also compared to assess the performance of low-dissipation numerical operators. Heat flux predictions to the transportation size calorimeter outside the fire were within experimental uncertainties. Inside the fire, experimental measurements were higher than predicted values and may have been a consequence of soot deposition and augmented participating media radiation from soot and fuel vapor. Simulation predictions improved in cases where turbulent kinetic energy and mixing were more resolved. This work, and others referenced herein, suggest that spatial resolution on the order of 0.5–1.0 cm may be required to fully resolve fluid instabilities, vortex production between fire plumes and crosswind, soot production, and fuel-air mixing. This presents a substantial computational challenge for safety assessments of engulfed objects in fully turbulent pool fires.

An experimental study on in-cylinder soot formation and flame oscillation of renewable fuel blends in an optical engine

Methanol has been widely recognized as a promising alternative fuel for mitigating greenhouse gas emissions. However, its application in internal combustion engines often necessitates blending with a high-reactivity fuel to address challenges related to ignitability and combustion stability. In this study, a two-color method was employed in a single-cylinder optical engine to investigate the characteristics of soot formation and flame oscillation of methanol blended with a high-reactivity fuel, hydrogenated catalytic biodiesel (HCB), under partially premixed combustion (PPC) modes. The blended fuels include M15 (15% methanol, 60% HCB, and 25% n-octanol) and M25 (25% methanol, 60% HCB, and 25% n-octanol), with pure hydrogenated catalytic biodiesel M0 (100% HCB) serving as the reference fuel. N-octanol was utilized as the co-solvent to enhance the stability of the mixture. The results indicate that, employing double-injection strategies, as the methanol content increases in the blended composition, leading to a postponed peak cylinder pressure and heat release rate during combustion. Thanks to the high-level premixed combustion and higher oxygen content, the increases of alcohol blending significantly reduced in-cylinder soot formation. Double-injection strategies reduced soot production effectively and resulted in a more uniform soot distribution compared to single-injection strategies. In terms of flame oscillation, its amplitude primarily correlates with the rate of cylinder pressure rise, while the methanol content within the blends exerts a minor impact on flame oscillation. Double-injection strategies contributes to a more uniform fuel distribution, ensuring a smoother heat release process and significantly reducing flame oscillation amplitudes compared to single-injection strategies.

Planar laser-induced incandescence for the study of soot production in a multi-sector RQL Jet A combustor

Understanding the production of non-volatile particulate matter (nvPM), which is composed primarily of soot, is critical not only for reducing emissions but also for improving engine performance. While there has been significant prior work studying the fundamentals of soot formation, there is significantly less work that investigates soot formation with realistic aeroengine geometries, injectors, and fuels in high pressure conditions. In this work, soot production in a three-sector rich-quench-lean (RQL) aeroengine combustor is studied with Jet A fuel. Global equivalence ratios ranging of 0.10 to 0.20 and pressures ranging from 2.7 to 6.9 bar absolute (40 to 100 psia) are tested. In order to characterize in-situ soot production near the fuel injectors, two-dimensional laser-induced incandescence is utilized to estimate single-shot and average soot volume fractions. Time-resolved laser-induced incandescence is then used to create single camera and single laser-shot incandescence decay time images in order to infer how soot particle sizes evolve. Results show a significant increase in soot production at higher global equivalence ratios and higher pressures. Incandescence decay times, however, do not change significantly over the same range of conditions. These measurements can not only help understand soot distributions in practical RQL systems but also help improve future aeroengine combustor designs.

Thermal runaway and soot production of lithium-ion batteries: Implications for safety and environmental concerns

Global energy shortages are becoming increasingly severe, and lithium-ion batteries are becoming an important substitute for fossil fuels. However, thermal runaway of a battery is a significant factor impacting battery industry development. Here, we conducted tests on battery thermal runaway using a combustion test chamber, analysing the effects of natural aging and state of charge (SOC) on battery thermal runaway. Additionally, EDS and XPS were used to analyse the soot particles formed during thermal runaway. Four stages in thermal runaway, e.g., battery bulge, smoke release, jet fire, and fire extinction. LiFePO4 with a higher SOC is more likely to cause thermal runaway. In addition, natural aging has an obvious impact on the intensity of thermal runaway. The gas products generated during a battery fire are identified as C1–C4 hydrocarbons. The soot generated by battery combustion presents a typical “core-shell” structure. The soot surface exhibits C–C, C–O, and O–H bonds, while the soot from early manufactured batteries also contains O–CO and π bonds. Soot contains not only C and O but also trace amounts of Li, F, P and Fe. These results reveal the characteristics of soot emission during thermal runaway of batteries, providing valuable insights for evaluating their toxicity and environmental impact.

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.

On ammonia/diesel dual-fuel combustion in optical engine

Ammonia-diesel dual-fuel combustion mode is one of the potential ways to achieve lower carbon emissions in compression ignition engines. In this work, the effects of ammonia addition on diesel combustion characteristics were experimentally investigated in an optical CI engine. The gaseous ammonia is introduced to the engine through a port injection while diesel is directly injection into the cylinder. A color high-speed camera was utilized to detect and differentiate between diffusion burning and lean-premixed ammonia combustion. Additionally, computational models were conducted and the findings were coupled with the experimental data. According to optical investigations, the lift-off distance is created during the diesel spray and progressively grows as the ammonia energy ratio (AER) rises. The findings indicate that, in comparison to pure diesel combustion mode, combustion in an ammonia environment exhibits prolonged ignition delay duration and lesser flame luminosity. Secondly, a multi-injection strategy for diesel fuel was used where the diesel pre-injection timing (SOPI) values adjusted from −30 °CA ATDC to −60 °CA ATDC). Advancing SOPI is an effective approach to suppress diesel diffusion flame and reduce soot production in the cylinder. For advanced SOPI, findings reveal that rich pockets have decreased drastically as the combustion progresses. With the advancement of SOPI, there is a notable a connection between the flame speed and the peak heat release rate, where a high flame speed correlates to a greater heat release rate peak. Finally, the ratio of pre-injection of diesel fuel (ROPI) varied from 0 to 100% as a mean to improve flame propagation. There is a crucial threshold of pre-injection (ROPI) mass ratio of 45%, at which the initial flame features alter considerably. As the ROPI exceeds 45%, the flame kernel appears as a visible flame near to the main injection timing (SOMI), indicating that the ignition delay duration is decreasing.

Role of the Equivalence Ratio on Soot Formation in a Perfectly Premixed Turbulent Swirled Flame: A Combined Experimental and Large Eddy Simulations Study

Abstract The understanding of processes that govern soot production in aero-engines is fundamental for the design of new combustion systems with low environmental impact. Many combustors, more specifically those used in aero-engines, feature rich flame regions typically exploited in the so-called rich-quench-lean (RQL) technology. Thus, it is important to consider rich turbulent flames operating in the premixed mode. To this purpose, a model scale swirled combustor, called EM2Soot, was designed at the EM2C laboratory to analyze soot production under perfectly premixed rich conditions. In this work, the effect of the equivalence ratio on soot production in this burner is experimentally characterized and numerically simulated. Measurements of Planar Laser Induced Fluorescence of polycyclic aromatic hydrocarbons (PLIF-PAH) were performed to examine soot precursors presence, whereas soot volume fraction is measured with planar laser-induced incandescence (LII). Large Eddy Simulations (LES) are carried out using models already established in literature. By considering a range of equivalence ratios, the soot volume fraction from the experiments was found to reach a maximum near 1.8, whereas a lower level of soot volume fraction was measured for lower and for higher equivalence ratios. The large eddy simulations are found to be in qualitative agreement with experimental data in terms of polycyclic aromatic hydrocarbons (PAHs) and soot location. The soot volume fractions fv are notably overestimated with respect to the LII measurements. However, the numerical results correctly retrieve a reduction of soot production for the highest considered equivalence ratio value and can be used to explain the experimental behavior.