Soot Formation Research Articles

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.

Conversion of boiler houses to alternative fuel

THE PURPOSE. To justify the need to transfer boiler houses from fuel oil to furnace domestic fuel. METHODS. Comparative studies of the main indicators of the quality of fuel oil and domestic heating oil (DHO) (heat of combustion, kinematic viscosity, flash point, pour point, ash content, humidity, sulfur content) were carried out. The environmental parameters of pollutants formed during the combustion of fuel oil and domestic stove fuel are calculated and compared with the values regulated by the EkoNiP 17.01.06-001-2017 "Environmental protection and nature management. Requirements of environmental safety" and TCU 17.02-XX-2019 "Environmental protection and nature management". RESULTS. As a result of comparative studies of the main indicators of the quality of fuel oil and furnace household fuel (PBT), it was shown that combustion in PBT boilers in comparison with fuel oil is preferable in terms of environmental consequences in terms of emissions into the atmosphere. As a result of the comparative analysis, it was found that during the transition from fuel oil to furnace household fuel, compliance with the basic environmental standards regulated by these regulatory documents is ensured by reducing by 70 times the amount of sulfur dioxide released into the atmospheric air during 10 days of burning furnace household fuel, as well as reducing the concentration of this type of emission by 72.5 times. When switching from fuel oil to furnace household fuel, pollution and equipment wear are also reduced due to the ash content index for furnace household fuel being 7 times lower than that of fuel oil, as well as a 2-fold reduction in the formation of soot and 70-fold reduction in sulfur dioxide during ten-day use of a new reserve type of fuel. CONCLUSION. Thus, as a result of experimental and calculated studies, it was shown that combustion in DHO boilers in comparison with fuel oil is preferable in terms of environmental consequences in terms of emissions into the atmosphere, reducing corrosion, stopping boilers for repairs, reducing fuel heating costs to facilitate transportation, reducing steam and fuel costs. When switching from fuel oil to furnace household fuel, pollution and equipment wear are also reduced due to the ash content index for furnace household fuel that is 7 times lower than that of fuel oil, as well as a 2-fold reduction in the formation of soot and 70-fold reduction in sulfur dioxide during ten-day use of a new reserve type of fuel.

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

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

Effects of pressure on soot formation in laminar coflow kerosene diffusion flames at pressures between 1 and 20 atm

Effects of pressure on soot formation in laminar coflow kerosene diffusion flames at pressures between 1 and 20 atm

Reaction path identification and validation from molecular dynamics simulations of hydrocarbon pyrolysis

AbstractCreation of complex chemical mechanisms for hydrocarbon pyrolysis and combustion is challenging due to the large number of species and reactions involved. Reactive molecular dynamics (RMD) enables the simulation of thousands of reactions and the discovery of previously unknown components of the reaction network. However, due to the inherent imprecision of reactive force fields, it is necessary to verify RMD‐obtained reaction paths using more accurate methods such as Density Functional Theory (DFT). We demonstrate a method for identification and confirmation of reaction pathways from RMD that supplement an established mechanism, using the example of benzene formation from n‐heptane and iso‐octane pyrolysis. We establish a validation workflow to extract reaction geometries from RMD and optimize transition states using the Nudged‐Elastic‐Band method on semi‐empirical and quantum mechanical levels of theory. Our findings demonstrate that the widely recognized ReaxFF parameterization, CHO2016, can identify known pathways from a established soot formation mechanism while also indicating new ones. We also show that CHO2016 underestimates hydrogen migration barriers by up to as compared to DFT and can lower activation barriers significantly for spin‐forbidden reactions. This highlights the necessity for validation or potentially even reparametrization of CHO2016.

Numerical study on the temperature dependence of soot formation in acetylene pyrolysis blended with methane, formaldehyde, methanol, and dimethyl ether

Abstract This paper addresses the combined effects of varying C/H and C/O ratios as well as of the molecular structure of the fuels selected on the normalized soot volume fraction f V. For the simulations, an already existing and validated reaction mechanism for the pyrolysis of C2H2 in argon, Aghsaee et al. (Combust. Flame 2014, 161, 2263–2269), was used in the current work. It was extended with PAH reactions from coronene (C24H12) up to ovalene (C32H14), whereas general principles for the rapid build-up of large PAHs were presented. Soot formation was modeled according to Appel et al. (Combust. Flame 2000, 121, 122–136) by applying the method of moments. A validation of the extended reaction model was carried out for shock-wave-induced O2/C2H2 mixtures from literature. In the following, the influence of blends of methane (CH4), formaldehyde (CH2O), methanol (CH3OH), and dimethyl ether (CH3)2O on soot formation during C2H2 pyrolysis diluted in Ar was studied. Special emphasis was laid on the inception chemistry of soot formation. The role of intermediates, such as the propargyl radical (C3H3), leading towards benzene and polyaromatic hydrocarbon (PAH) formation and their interplay with hydrogen molecules (H2) to H atoms (H) ratio was examined. All blends increased the ratio of the concentrations of H2 and H leading thus to reduced soot inception and soot formation. However, soot suppressing effects were overrun by supporting ones when the additives provided suitable molecular groups, such as methyl radicals (CH3), in sufficient high concentrations for early aromatic ring formation. Thus, a prominent synergistic effect on soot formation was found for the CH4/C2H2 mixture only. Besides, species able to mirror characteristics of the soot formation process, such as the peak value of the normalized soot volume fraction, are presented. The findings of this work indicate the synergistic effect of H2/H and C/O ratios as well as of methyl radicals on the PAHs’ production of appropriate size able to initiate soot inception process in an aliphatic fuel.

STUDY OF CATALYSTS BASED ON MESOPOROUS ALUMINOSILICATE IN THE DEAROMATIZATION PROCESS OF A MODEL MIXTURE: PHYSICO-CHEMICAL CHARACTERISTICS AND CATALYTIC ACTIVITY

The limitation on the content of aromatic hydrocarbons and sulfur is associated with environmental requirements according to Euro-5 standards. Upon combustion, these substances release highly toxic compounds into the atmosphere, adversely affecting human health and the surrounding environment. Additionally, a high concentration of aromatic hydrocarbons in diesel fuel significantly degrades its quality, leading to soot formation and reducing its cetane number. According to Euro-5 standards, the content of polycyclic aromatic hydrocarbons and sulfur compounds should not exceed 8% and 10 mg/kg, respectively. To address the challenge of producing high-quality diesel fuels, the hydrotreatment process is employed in the presence of heterogeneous catalysts.The article presents the synthesis of mesoporous aluminosilicates and bifunctional catalysts based on them to study the activity of the hydrotreatment process for a model mixture. The obtained samples were investigated using various physico-chemical methods such as SEM, low-temperature nitrogen adsorption/desorption, XRD, and FT-IR. It was established that the Ni/MAS-H-bentonite and Mo/MAS-H-bentonite catalysts exhibit high activity and selectivity in the hydrotreatment process under optimal conditions (240°C, 3 MPa, and 0.5 h-1).

Effect of horizontal insertion of metal wire mesh into the flame on the formation and suppression of soot in acetylene diffusion flame

A simple and efficient strategy to suppress soot from acetylene diffusion flames is reported for the first time. Horizontally insertion of metal wire mesh into the acetylene diffusion flame is found to greatly suppress the soot emission. The effects of experimental parameters such as acetylene flow rate, wire mesh height above nozzle (WHAN), material of wire mesh, mesh number, and inner diameter of the burner nozzle on soot suppression in acetylene diffusion flames are investigated. In addition, the collected soot samples are characterized by TEM, HRTEM, XRD, BET and Raman. The soot suppression efficiency can reach 100 % by horizontal insertion of the metal wire mesh in the acetylene diffusion flame. The WHAN has a great influence on the effect of soot suppression. In the first 210 s of horizontally inserting the metal wire mesh into the flame, the total mass of collected soot first decreases and then increases with the increase of WHAN. The minimum total mass of soot is achieved when the normalized WHAN (obtained by dividing the wire mesh height above nozzle by flame height without insertion of the wire mesh) is at 0.1. This position corresponds to the soot particle inception zone of the acetylene diffusion flame. The flame is divided into two parts when the metal wire mesh is horizontally inserted into the flame. The temperature of the flame below the metal wire mesh decreases from 1770 K to 1480 K. The temperature of the flame above the metal wire mesh increases from 1590 K to 1780 K. The soot collected on the metal wire mesh grows into a volcano-shaped carbon (VSC) structure. The results of the schlieren imaging experiments show that this structure can promote the mixing of air and fuel in the lower region of the flame thereby suppressing the formation of soot particles. The soot analysis shows that the horizontal insertion of metal wire mesh into the flame leads to high amorphous feature and low degree of structural order of the soot, which means that the oxidation reactivity of the soot increases.

Exploring electric field forces and polarization influence on combustion in Fe-additive fuel droplets

The application of electrical techniques such as electric field, polarization, and ionization in the field of combustion makes many positive developments possible. The electric field effect offers significant advantages in controlling flame stability and reducing soot formation during the combustion of fuels. Also, the conditioning effect can improve particle oxidation during combustion for hydrocarbon fuels containing metal particle inclusions with high calorific value. This study focuses on investigating the combustion and atomization behavior of Fe additive diesel fuel droplets at electric field strengths of E = 5 V/m, E = 6.7 V/m, and E = 10 V/m and in positive (↑) and negative (↓) electric field directions. The experiments were carried out by igniting a fuel droplet suspended on a ceramic wire with an arc at the center of the electric field between two conductive plates in a combustion chamber with optical apertures. The combustion processes were recorded with an optical system consisting of a high-speed camera and a thermal camera. Combustion and atomization behavior were characterized by sequential flame and droplet atomization images, respectively. The droplet shape change and flame behavior results were comparatively evaluated according to the d2-law. Ignition delay and extinction times were determined by processing threshold technique and maximum flame temperatures were determined by processing thermal camera images. The results showed that increasing the electric field intensity in the negative electric field direction resulted in improved soot oxidation, and Fe particles burnt efficiently. Ignition delay times showed a decreasing trend with an electric field effect and an increasing trend with the addition of Fe particles. The highest maximum flame temperature and lowest extinction time were recorded as 785 K and ∼ 578.34 ms for Diesel/Fe/100(↓) fuel droplet, respectively and Fe particles did not exhibit microexplosion phenomena at E = 10 V/m. In this study, it has been shown that an effective oxidation can be achieved for Fe particles by increasing the mobility of ionized species in the flame zone under the effect of electric field and a homogeneous thermal field can be created in the flame zone even in fuels with particle addition at increasing electric field intensities.

A combined combustion and conjugate heat transfer analysis of a hybrid draft biomass cookstove

A cookstove comprises both fluid and solid regions, with combustion gases representing the fluid domain and the combustion chamber wall and insulation forming the solid regions. These solid regions are made of different materials and make significant contributions to stove performance. So far, most studies conducted on biomass stoves have only analysed the fluid domain, neglecting solid regions. The current study integrates combustion and conjugate heat transfer analysis, encompassing both fluid and solid domains, to investigate the fluid flow and heat transfer behaviour of a hybrid draft biomass cookstove (HDBC) using CFD. This analysis aims to gain insights into the impact of stove materials on its performance. The study analysed six cases of HDBC, testing different combinations of materials: two for the combustion chamber (ceramic-cement and stainless-steel) and three for insulation (ceramic wool, perlite, and vermiculite). The combustion of biomass and the formation of soot are modelled using reaction kinetics and a one-step soot model, respectively. The CFD findings for thermal efficiency, CO, and PM2.5 emissions derived using combustion and soot model demonstrated closed alignment with the experimental result with variations of 3%, 19%, and 23%, respectively. It was observed that stoves with stainless-steel combustion chamber material exhibit better thermal and emission performance compared to ceramic-cement stoves, with perlite taking the edge over other insulation materials. The success of these materials is attributed to their superior thermophysical properties, which play a significant role in material selection.

Numerical Study of Premixed PODE3-4/CH4 Flames at Engine-Relevant Conditions

Polyoxymethylene dimethyl ether (PODEn, n ≥ 1) is a promising alternative fuel to diesel with higher reactivity and low soot formation tendency. In this study, PODE3-4 is used as a pilot ignition fuel for methane (CH4) and the combustion characteristics of PODE3-4/CH4 mixtures are investigated numerically using an updated PODE3-4 mechanism. The ignition delay time (IDT) and laminar burning velocity (LBV) of PODE3-4/CH4 blends were calculated at high temperature and high pressure relevant to engine conditions. It is discovered that addition of a small amount of PODE3-4 has a dramatic promotive effect on IDT and LBV of CH4, whereas such a promoting effect decays at higher PODE3-4 addition. Kinetic analysis was performed to gain more insight into the reaction process of PODE3-4/CH4 mixtures at different conditions. In general, the promoting effect originates from the high reactivity of PODE3-4 at low temperatures and it is further confirmed in simulations using a perfectly stirred reactor (PSR) model. The addition of PODE3-4 significantly extends the extinction limit of CH4 from a residence time of ~0.5 ms to that of ~0.08 ms, indicating that the flame stability is enhanced as well by PODE3-4 addition. It is also found that NO formation is reduced in lean or rich flames; moreover, NO formation is inhibited by too short a residence time.

Experimental and numerical studies of the evaporation and combustion characteristics of large-angle impinging sprays

To achieve a large fuel injection mass per cycle, using one injector will need a large nozzle, which may lead to combustion deterioration in high power density (HPD) engines. Therefore, two-injector method was adopted and then impinging sprays by two injectors were developed to promote the air/fuel mixing and combustion performance. This study investigated the spray, evaporation, ignition and soot emission characteristics of twin injectors at different impinging angles (90°, 120°, 150°, and 180°) using various high-speed imaging techniques in a constant volume chamber. Further, CFD simulations were performed to analyze the impinging sprays under HPD condition. Innovatively, a kinetic energy loss model for impinging sprays was proposed to quantify the effect of spray impingement. The results showed that the turbulent kinetic energy increased with the impinging angle, and the kinetic energy loss at any angle could be predicted by the kinetic energy loss of 180° impinging spray. The kinetic energy loss model better characterized the spray impingement process, and then more accurately predicted the atomization quality and mixing capacity compared with spray volume. Spray impingement changed fuel and soot distributions, the peak soot mass decreased with the impinging angle, which was reduced by 36.8 %, 39.8 %, 44.4 % and 45.9 % at 90 ∼ 180° impinging sprays, respectively, comparing to the single spray. These findings recommended that using a large impinging spray angle in real HPD engines can promote spray atomization and reduce soot formation.

Radiating biofuel-blended turbulent nonpremixed hydrogen flames on a coaxial spray burner

The low radiant intensity and luminosity of hydrogen flames can be enhanced by the addition of a small portion of sooting biofuels. To achieve higher effectiveness, the impact of blending turbulent nonpremixed hydrogen flames with liquid biofuels, by gas-assist atomisation, is investigated and compared with the introduction methods of prevapourisation and ultrasonic spray. The flame appearance, luminosity, radiant fraction, centreline temperature, and the near-field spray characteristics of four biofuel surrogates (eucalyptol, D-limonene, guaiacol, and anisole) blended into hydrogen flames are measured experimentally. Radiating biofuel/hydrogen flames are achieved on a coaxial needle spray burner by the addition of 0.1–0.3 mol% biofuel surrogates. Compared with the unblended hydrogen flame, the luminosity and radiant fraction are enhanced by 30%–500% and 2%–15%, respectively, with the addition of biofuel surrogates. The results show that adding the biofuel surrogates by gas-assist atomisation is more effective than prevapourisation and ultrasonic atomisation in luminosity and radiant fraction enhancement. It is found that the local fuel-rich conditions, which are beneficial for soot formation, are further facilitated by the larger droplets and spray objects generated by gas-assist atomisation. Of the additives tested, anisole is the most effective for luminosity and radiant fraction enhancement of a hydrogen flame while exhibiting the largest flame temperature drop due to the enthalpy of vapourisation and the radiative loss from the promoted soot formation. The viscosity and surface tension greatly influence the spray characteristics which in turn impacts the flame characteristics. Guaiacol, the representative of lignin, appears to have the lowest effectiveness in radiant fraction enhancement due to the presence of a hydroxy group, a higher bond dissociation enthalpy, and a coarser spray ascribed to higher viscosity and surface tension.

Insights into the pyrolytic coking process of RP-3 fuel from ReaxFF molecular dynamics

Active cooling technology serves as one of the promising and effective methods for addressing the thermal protection strategy for hypersonic aircraft. While the coke generated through pyrolysis, dehydrogenation and coking reactions of fuel will reduce the heat transfer efficiency, even clog the heat exchange channel. In this work, three-component RP-3 aviation fuel was adopted as model compounds to investigate the cracking coking reaction mechanism and explore the method of inhibiting coking. It is found that the three-component RP-3 molecules generate an intermediate system dominated by C2 products through bond breaking, reforming and bimolecular reactions (mainly hydrogen abstraction reactions) under supercritical state, in which the ·H radicals, as represented radicals, play a crucial role in the opening of benzene rings. The coking process is analyzed in details furtherly, and detailed soot formation mechanisms are revealed. Additionally, a suitable “core-shell structure” model is proposed to describe the coke formation process. Meanwhile, it is found that the addition of a small number of addition agents can effectively inhibit the formation of coke and thus prolong the residence time of fuel molecules in the heat transfer channel for the coking process mainly consisted of addition reaction. The study attempts to provide a theoretical basis for the high-temperature pyrolytic coking mechanism of endothermic hydrocarbon fuel, as well as the significance to understanding the inhibition of coke formation.

Contrail formation on ambient aerosol particles for aircraft with hydrogen combustion: a box model trajectory study

Abstract. Future air traffic using (green) hydrogen (H2) promises zero carbon emissions, but the effects of contrails from this new technology have hardly been investigated. We study contrail formation behind aircraft with H2 combustion by means of the particle-based Lagrangian Cloud Module (LCM) box model. Assuming the absence of soot and ultrafine volatile particle formation, contrail ice crystals form solely on atmospheric background particles mixed into the plume. While a recent study extended the original LCM with regard to the contrail formation on soot particles, we further advance the LCM to cover the contrail formation on ambient particles. For each simulation, we perform an ensemble of box model runs using the dilution along 1000 different plume trajectories. The formation threshold temperature of H2 contrails is around 10 K higher than for conventional contrails (which form behind aircraft with kerosene combustion). Then, contrail formation becomes primarily limited by the homogeneous freezing temperature of the water droplets such that contrails can form at temperatures down to around 234 K. The number of ice crystals formed varies strongly with ambient temperature even far away from the contrail formation threshold. The contrail ice crystal number clearly increases with ambient aerosol number concentration and decreases significantly for ambient particles with mean dry radii ⪅ 10 nm due to the Kelvin effect. Besides simulations with one aerosol particle ensemble, we analyze contrail formation scenarios with two co-existing aerosol particle ensembles with different mean dry sizes or hygroscopicity parameters. We compare them to scenarios with a single ensemble that is the average of the two aerosol ensembles. We find that the total ice crystal number can differ significantly between the two cases, in particular if nucleation-mode particles are involved. Due to the absence of soot particle emissions, the ice crystal number in H2 contrails is typically reduced by more than 80 %–90 % compared to conventional contrails. The contrail optical thickness is significantly reduced, and H2 contrails either become visible later than kerosene contrails or are not visible at all for low ambient particle number concentrations. On the other hand, H2 contrails can form at lower flight altitudes where conventional contrails would not form.

Experimental study of peripheral fuel injection for higher performance in diesel engines

In conventional diesel combustion (CDC), a centrally located multi-hole injector supplies fuel radially outwards. This study introduces and explores the concept of peripheral fuel injection (PeFI) to supply fuel from multiple locations on top of the combustion chamber using several single-hole injectors. The PeFI concept is designed to eliminate flame-wall and jet-wall interactions, and, ideally, to produce independent flames without any interference. PeFI is also intended to increase air entrainment in the near field and thus, reduce equivalence ratio at the lift-off length and subsequent soot formation. PeFI reduces wall heat transfer compared to CDC although this feature is not considered in the present study. The two methods of fuel injection are compared in a non-reacting optical chamber via high-speed imaging of the jets. N-heptane fuel at 1500 bar supply pressures is injected into a test chamber filled with nitrogen at engine relevant ambient densities of 23.0 and 18.5 kg/m3. Four configurations are trialed including a six-hole central injector and six, single-hole PeFI injectors with holes oriented at a layout angle, defined as the angle between the center of the fuel jet and chamber radius, of 0°, 15°, and 30°. Flow visualizations show jet-to-jet interactions at small layout angles for PeFI, but little to no jet-to-jet (or jet-wall) interference as the layout angle increases to 30°. Image analysis reveals that PeFI provides faster rate of injection, longer jet penetration length, greater width near the jet tip, and larger jet volume compared to those for the central injector. Overall, results demonstrate the potential of PeFI to simultaneously improve fuel efficiency and reduce emissions in diesel engines.

On the intricacies of soot volume fraction measurements in counterflow diffusion flames with light extinction: Effects of curtain flow

Counterflow diffusion flame is an attractive platform for fundamental research on kinetics of soot formation. Accurate determination of soot volume fraction in the flame is a prerequisite for in-depth analysis of the sooting characteristics and assessment of predictive soot models. Light extinction has been proven to be an efficient technique for measuring soot volume fraction thanks to its non-intrusiveness and its simple optical setup. Nevertheless, tomographic inversion needs to be performed if spatially resolved soot volume fraction is to be obtained from the measured light extinction data which is essentially a projection along the line-of-sight. In this regard, radial distribution of soot volume fraction would affect the accuracy of the measurement through its influences on the inversion processes. In this work, we show that the curtain flow, which is necessary to avoid the formation of the undesired secondary diffusion flame and to keep the core counterflow from ambient disturbances, has notable effects on spatially resolved soot volume fraction measurements with line-of-sight measurements. In particular, different flow rate settings of the curtain flow can result in different soot distributions at the edges of soot fields: upwards curved, outwards extended, and downwards curved, which may influence the measurement of centerline soot volume fraction distribution. The necessity of tomographic inversion, the minimal region of the projection image necessary for tomographic inversion (when necessary), the quasi-one-dimensional feature of soot distribution, and the sensitivity of measurement to slight flame asymmetry were investigated where possible to determine the most suitable curtain flow configuration for soot volume fraction measurements by light extinction. Recommendations on curtain flow setting are finally made.

Experimental study of the effect of hydrogenated catalytic biodiesel-Ethanol blends on combustion and soot formation process within an optical engine

The utilization of Ethanol in compression ignition engines has demonstrated great potential for reducing greenhouse gas emissions and breaking the NOX-soot trade-off relationship. However, it is usually necessary to burn ethanol with high-reactivity fuels to address its problem of high resistance to autoignition and low power output, especially during cold-start or low-load conditions. However, this combustion of high-reactivity fuels can lead to high soot emissions. This paper examines the characteristics of in-cylinder soot formation throughout two-color pyrometry in an optical engine operated in partially premixed low-temperature combustion mode, focusing on hydrogenated catalytic biodiesel/ethanol/n-octanol blends with two different proportions (75%/15%/10% and 60%/30%/10% by volume) and varying injection strategies. The results indicate that both blends exhibit a typical two-stage heat release process, with the highest cylinder pressure, earliest soot onset and the highest integrated KL factor occurring at an injection timing of −25°CA. By slightly compensating for power output, a higher proportion of ethanol in the blends leads to a significant in-flame soot reduction and a more uniform soot distribution within the cylinder.

An experimental and molecular simulation study on the soot formation characteristics and mechanism in hydrogen-ammonia blended ethylene combustion

Extinction measurement and thermophoretic sampling techniques were employed to investigate the soot formation characteristics in H2-NH3 blended C2H4 combustion. And the formation mechanism of benzene (A1) was analyzed using reactive molecular dynamics simulation (ReaxFF MD), unveiling the chemical coupling effects on soot formation at the molecular level. As the hydrogen/ammonia (H2/NH3) ratio decreases, the flame height decreases gradually, the flame brightness noticeably darkens, and the dark non-sooting core continuously increases. The maximum of soot volume fraction (fvmax) gradually decreases and shifts from the flame wing towards the flame centerline. Addition of H2-NH3 leads to an increase in the proportion of small-sized fringes and fringe tortuosity, resulting in an increase in the oxidation activity and a decrease in the fv. The largest soot particle contains a small amount of nitrogen atom (N). Some of these N atoms replace hydrogen atom (H) to bond with carbon ring, while others substitute for carbon atom (C) to form nitrogen ring, ultimately resulting in nitrogen-containing polycyclic aromatic hydrocarbons (PAHs) and nitrogen-containing soot. The reduction in the H2/NH3 ratio leads to a reduction in C in the largest soot particle, which more effectively inhibits soot formation and graphitization. On the other hand, it increases the N and nitrogen ring in the largest soot particle. It is possible that the increase in NH3 proportion favors N in competition with H for active sites on soot particles. A1-+H↔A1 is the most crucial reaction pathway of A1 formation. As the H2/NH3 ratio increases, H2 concentration significantly rises, leading to an enhancement in the forward reaction rate. Furthermore, the competition for H between H2 and NH3 by NH3+H↔NH2+H2 results in a chemical coupling effect on soot formation.

Effect of modifying bowl geometry for IC engine fueled with diesel and Biofuels - Review

Bio-fuels are one of the most prominent, emerging, and promising fuels, which are aimed to replace diesel in the next decade. Though bio-fuels may not give the same performance as conventional diesel due to certain issues related to both technical and economic aspects, this fact leads to the need for alterations that are supposed to incorporate either changes in the shape of the combustion chamber or other critical factors that affect the performance of the engine. The shape of the top surface, which is known as the "bowl," in the piston plays a major role, and any slight modification in that shape leads to amplified effects on various combustion, emission, and performance parameters. This article shows the valid reason for accepting bio-fuels as fuel for CI engines by considering outcomes derived from experiments and numerical analysis with changes in the shape of the piston bowl. The results obtained are based on the attainment of various parameters, which leads to higher turbulence velocity distribution, better mixture fraction values, and lower soot formation distribution that can be obtained by modifying the shape of bowl. The pressure, temperature and heat release in the combustion chamber found to be changed due to the modification in bowl geometry.