Soot Formation Research Articles

Effect of 2-butanone addition to ethylene fuel on soot formation in counterflow diffusion flames using newly proposed soot model

An improved consistent soot model is proposed and applied to evaluate the effect of 2-butanone addition (10 % to 50 % on a volume basis represented as case 1 to case 5) to ethylene fuel on soot formation using a counterflow burner configuration. The predictive capability of the suggested soot model is verified by assessing its performance against existing experimental data on soot formation (SF) configuration-type ethylene counterflow flames at diverse strain rates and various fuel additives. The proposed soot model comprises 55 inception reactions with temperature-dependent collision efficiency and 10 condensation reactions from 10 PAH species (from naphthalene to larger PAHs up to coronene), including modified HACA surface growth and oxidation reactions. 2-butanone is produced as a byproduct during the pyrolysis of biomass and the microbiological fermentation of agricultural waste. It holds various benefits as a prospective biofuel for spark ignition (SI) engines. Limited information exists regarding its sooting characteristics due to a lack of available soot measurements. The simulations are conducted for the soot formation (SF) type counterflow flames with a fixed fuel and oxidizer jet velocity. The proposed soot model can effectively replicate both the qualitative and quantitative aspects of the experimental trends and shows a better agreement than the existing models available in the literature. The soot volume fraction (SVF) and the particle number density (PND) decrease with increasing the 2-butanone concentration in the binary fuel mixture. The PAH concentration decreases with increasing 2-butanone addition in the fuel mixture. The peak SVF and the maximum temperature are reduced by ∼22.7 % and ∼3.6 %, with a 40 % increase in the 2-butanone portion in the fuel mixture from case 1 to case 5. Increasing the 2-butanone content in the fuel mixture decreases the inception rate, HACA rate, and condensation rate while it increases the oxidation rate.

Numerical investigation of diesel spray combustion characteristics in the ammonia/air atmosphere

Ammonia/diesel dual-fuel combustion mode is a promising strategy for decarbonizing internal combustion engines. However, the impact of a premixed ammonia/air atmosphere on diesel spray combustion characteristics is not fully understood. This study analyzes the effects of premixed ammonia/air atmosphere, including premixed equivalence ratio, the cooling effect of liquid ammonia vaporization, and ambient oxygen concentration on the ignition and combustion characteristics and soot yield potential of diesel spray. Numerical simulations using n-heptane as a single-component diesel surrogate reveal that increasing the premixed ammonia equivalence ratio and lowering ambient oxygen concentration extend the ignition delay times and flame lift-off length of n-heptane spray. Liquid ammonia vaporization further prolongs the ignition delay by lowering the ambient temperature during n-heptane auto-ignition. Moreover, there is a trade-off between ignition delay and soot yield potential as longer ignition delays allow more thorough mixing of diesel and premixed gas, reducing soot formation. Given the substantial extension of ignition delay in ammonia/air atmospheres, it is recommended that ammonia/diesel dual-fuel engines operate with higher charged gas temperatures to ensure stable and repeatable ignition events. The negative effects of increased soot yield could be mitigated by using ammonia to reduce soot precursors. Overall, these results underline the need for further fundamental studies on ammonia/diesel co-combustion to facilitate the commercial adoption of ammonia/diesel dual-fuel engines.

Simultaneous improvements of thermal efficiencies and smoke emissions in semi-premixed diesel combustion with dual-injectors and a spatially divided combustion chamber

To simultaneously establish the high thermal efficiencies and the low smoke emissions in the semi-premixed diesel combustion with a twin peaked heat release consisting of the first-stage premixed combustion and the second-stage spray diffusive combustion, a combination of dual-injectors and a newly designed divided combustion chamber was proposed and the combustion characteristics were investigated. The divided chamber with a lip at the middle of the side wall can prevent the second fuel spray from entering the burned region of the premixture from the first-stage injection, realizing a suitable spatial distribution of spray flames and suppressing the soot formation. The dual-injectors can independently provide the fuel sprays into the upper and the lower layers of the divided chamber with the optional quantities and timings for the first and second injections, establishing the optimum combustion phasing. The distributions of the equivalence ratios and the soot formation characteristics in the divided chamber as well as in an ordinary re-entrant chamber as a reference were analysed with CFD simulations, showing that the soot formation is smaller in the divided chamber. The second-stage spray diffusive combustion is improved as well as the late afterburning and the combustion duration are reduced with the suppression of interference between the spray flames in the divided chamber. The cooling loss in the divided chamber is smaller due to the weaker gas motion and the lower heat transfer coefficient. The experiments also showed that the thermal efficiencies are better and the smoke emissions are lower in the divided chamber at medium loads. However, at higher loads, the smoke emissions increase due to the offset injector arrangement, and the CFD analysis showed that lower smoke emissions can be expected with optimization of the injector arrangement to locate the injector for the second fuel injection at the centre of cylinder.

CLIMATE AND ENVIRONMENTAL BACKGROUNDS OF FUEL UTILIZATION, INFLUENCING UPON ALTERATION THE EUROPEAN AND UKRAINIAN TRENDS OF GAS SUPPLY. PART 2. PROVIDING THE EFFICIENCY OF FUEL USE IN CONDITIONS OF DECARBONIZATION OF ENVIRONMENT

The paper is dedicated to power and environmental aspects of option the most appropriate types of fuel for supplying the economics of European countries and Ukraine. Accordingly notions about influence of C-containing fuels on greenhouse effect and on warming of environment, the existing tendency of substitution the fossil fuels — generally — and the natural gas — particularly — for methane-hydrogen mixtures is discussed as a controversial point. The problem of advancement the national fuel complexes is under consideration and has been studied with approach based upon the example of Ukrainian pre-war state of economics. An attention has been paid up on reduction of production and consumption of all types of the fossil fuels in the last decades, mainly due lowering the industrial using constituent. An enhancement of fuel using efficiency due improvement of furnace equipment basis provides an successive solution the fuel problems. The thermodynamic background for evaluation the efficiency of fuel using with account of the furnace’s non-ideality has been developed. The problem of “wet combustion” takes of special significance by the reason of weather and climate conditions’ account, on the one hand, and an opportunity to control the efficiency of fuel using, on the other hand, with new combined technique. The contemporary approach consists in combination the direct method of decrease the CO2 emission due exclusion of using the C-containing fuels (firstly — the fossil fuels) and with enhancement the efficiency of using the fossil fuels, for example due erection the recuperative heat recovery facilities with preliminary preheating of combustion air, in some advanced cases by combination with an air, humidification. The perspective ways of provision the decarbonization of environment consists in substitution the fossil fuels (mainly the natural gas NG) for hydrogen or H2-containing gas mixtures. The thermodynamic analysis of relevant technique has been carried out to estimate the opportunities of control the efficiency of hydrogen admixture to NG. Taking into account the variety of technologies of hydrogen production, the engineering method with giving of conditional coloration of hydrogen as a fuel has been considered. The “green” H2 makes the most valuable type of fuel (compared with “blue”, “turquoise”, “yellow”, “rose” colored and especially to the “grey” H2) as a substituting fuel from the standpoint of H2 fitness to process and plant. Particularly for high-temperature melting furnaces a provision of maximum emissivity of flame requires an using of carbon containing fuels to organize thermal pyrolysis of gas and soot formation within the combustion zone. Ref. 44, Fig. 5, Tab. 3.

Effects of different ammonia energy ratio on soot formation and oxidation in an ammonia diesel dual-fuel engine

Due to environmental pollution and energy crises, zero‑carbon fuel ammonia (NH3) has attracted extensive attention as an alternative fuel for engines. In this paper, the effects of ammonia energy ratio (AER) and injection strategy on particulate emission characteristics of an ammonia diesel dual-fuel engine were examined by merging experimental and simulation results; additionally, soot formation and oxidation mechanism were investigated. Results showed that the reduction in particulate emission was substantially higher than the increase in AER. When AER increased to 60 %, the reduction in particulate mass concentration reached 97.5 %. The initial soot formation area gradually moved to the bottom of the piston bowl with increasing AER. When the piston reached the top dead center, the high-soot-concentration area was shifted to the center of the piston bowl as AER increased. The contents of acetylene (C2H2) and methyl (CH3) reduced considerably, which restricted the formation of soot precursors. With AER increasing, the contents of nitric oxides (NOx) and other nitrogen-containing species increased and reacted with CH3 and other carbon-containing species, which effectively reduced the number of C in soot formation pathway, thereby lowering particulate emissions. As AER increased, hydroxyl (OH) involved in soot formation gradually decreased, and only 14 % of OH was involved in the oxidation of n-heptane at 60 % AER, which was favorable for reducing the soot formation rate. Furthermore, OH is a substantial species in soot oxidation. The introduction of ammonia caused an increase in OH, which facilitated the removal of soot. The decrease in hydrogenium (H) hindered the hydrogen–abstraction–acetylene–addition (HACA) reaction, further limiting the soot surface growth. By optimizing the injection timing and AER, particulate emission was lowered to 4.31 × 10−5 μg/cm3, and particle size was reduced by 64.2 % when AER was 60 %, injection timing was −20° CA ATDC, and injection pressure was 60 MPa.

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.

Experimental and numerical investigation of the synergistic effect on soot formation in ethanol/n-heptane laminar diffusion flames at elevated pressures

As a carbon-neutral fuel, ethanol is commonly used as a partial replacement for gasoline, but its impact mechanism on the soot formation of gasoline remains unclear, especially under elevated-pressure conditions. In this work, the soot formation of ethanol/n-heptane was experimentally and numerically investigated in laminar diffusion flames in the pressure range of 1.2–5 bar. For all experimental conditions, the total carbon flow rate in the fuel was maintained at 0.353 mg/s with 0%, 10%, 20%, and 30% ethanol contributions. The soot volume fraction and flame temperature were obtained by laser-induced incandescence coupled with light extinction and color-ratio soot pyrometry technique. In the considered pressure range, the synergistic effect on the soot formation was observed with 10% ethanol addition and became more pronounced at higher pressures. The soot formation was suppressed when the amount of ethanol was increased to 20% or 30%. Numerical simulations are performed using a reduced n-heptane/ethanol chemical mechanism and a soot model based on the bivariate Hybrid Method of Moments. The synergy effect was successfully predicted by the model. The simulation results indicate that the reason for the synergistic effect is the increase in acetylene and methyl caused by ethanol pyrolysis, which increases the mass fraction of soot precursor species and consequently promotes PAH condensation.

Computational assessment of soot models in ethylene/air laminar diffusion flames

To improve the accuracy of soot formation and evolution predictions, several physical and chemical models have been developed over the last decades. These models include (i) detailed chemical kinetic mechanisms describing both gas-phase chemistry related to combustion processes and reaction pathways leading to large-sized aromatic molecules, which are needed for modelling soot formation, and (ii) soot models providing a comprehensive description of soot particle dynamics and interactions with gas-phase chemical species. Accordingly, in this work, two detailed soot models, the method of moments (MOM) and the discrete sectional method (DSM), are evaluated in ethylene/air laminar diffusion flames, and their corresponding results are compared with experimental measurements. Furthermore, the NBP and KM2 chemical kinetic mechanisms are assessed and compared with each other by examining key chemical species related to soot formation and evolution. To compute gas mixture’s radiative properties, the weighted sum of grey gases model considering a grey medium is also utilised. Finally, the contributions of the soot precursors known as PAH (polycyclic aromatic hydrocarbon) to soot formation are also analysed. The main results show that the discrepancies in PAH concentrations obtained with different chemical kinetic mechanisms can be significant. In addition, compared to MOM ones, DSM results obtained here show a better agreement with experimental data. Finally, the analysis of PAH shows that those with two (A2) to four (A4) aromatic rings impact the most on soot modelling. Specifically, contributions of A4 were found to be more significant at lower heights above the burner, whereas A2 was found to be more impactful downstream as the flame develops. Maximum contributions of A2 and A4 to the soot inception rate were 66% and 85%, respectively, whereas the maximum summed contribution of PAH with five (A4R5) to seven (A7) aromatic rings accounted for only 13% of the inception rate.

Effect of H2/CO addition on soot formation in ethylene diffusion flame

Coupling the San Diego gas phase reaction mechanism and the Moss Brookes soot model using FLUENT14.0 software, the effect of adding H2/CO on the fuel side on soot formation in an ethylene/air laminar diffusion flame was studied. A specific analysis was conducted on the effects of H2, CO and its chemical effects on flame temperature, soot volume fraction, mole fractions of important intermediate products OH, H, and C2H2, as well as rate of soot mass nucleation, surface growth, and oxidation. In the numerical calculation, the virtual substances FH2 and FCO are set to separate the chemical effect of H2 and CO and to analyze the chemical effect of adding H2 and CO on soot formation. The results show that the flame temperature increases slightly, and the soot volume fraction decreases monotonically with adding H2 and CO. The chemical effect of H2 increases the temperature, the mole fraction of C2H2 and H, the soot nucleation rate, and the surface growth rate, and finally, it promotes soot formation. The chemical effect of CO increases the temperature and H mole fraction, reduces the OH mole fraction, and then increases the soot surface growth rate and reduces the soot oxidation rate. The higher soot nucleation, surface growth rate, and lower oxidation rate jointly promote soot formation.

Unraveling the impact of acrylonitrile on naphthyl radical during the growth process of polycyclic aromatic hydrocarbons

The introduction of ammonia effectively inhibits soot formation through its chemical interactions, partly attributable to the effects exerted by CN species. This study aims to investigate the influence of larger CN species, specifically acrylonitrile (C3H3N), identified in NH3-doped flames, on the growth process of polycyclic aromatic hydrocarbons (PAHs). The potential energy surfaces (PESs) governing the reaction between C3H3N and the naphthyl radical were explored utilizing G3(MP2, CC)//B3LYP/6-311G++(d,p) level theory. The formed C3H3N adducts exhibit the potential to generate PAHs featuring CH=CHCN side chain or nitrogen-containing PAHs (N-PAHs). The Rice-Ramsperger-Kassel-Marcus (RRKM) theory was employed to calculate temperature- and pressure-dependent rate coefficients, enabling the assessment of yield distribution across the temperature range of 300–2500 K. In the 1-naphthyl + C3H3N reaction at 1 atm, the preferential formation of acenaphthylene-1-carbonitrile occurs at 300–1600 K, shifting towards PAHs with CH=CHCN side chains at temperatures exceeding 1600 K. The predominant production of PAHs with CH=CHCN side chains occurs in the 2-naphthyl + C3H3N reaction across all temperature ranges. These findings enhance our understanding of the mechanisms involving CN species and PAHs, significantly advancing the study of how intricate mechanisms influence PAH growth in NH3-doped flames.

EFFECT OF DIESEL ENGINE DECARBONISATION ON SELECTED EXHAUST VALUES

In this article, the authors refer to the measurement of acoustic emission, where they found that this methodology can determine the combustion characteristics in the combustion chamber of the engine and thus it is possible to confirm a better combustion process and overall reduction of engine noise after decarbonization. The formation of diesel exhaust soot is also supported by the authors' paper, in which they describe how such soot is formed and what effect the addition of special mixtures to the combustion process has on the formation of such carbon deposits. The article uses BG technologies for deep engine decarbonization, including intake and exhaust parts. This technology is one of many on the market, but it was only with this technology that the authors managed to achieve the relevant results that this article will introduce to. For the test, we selected vehicles that had a problem to pass at the emission control.

Spray combustion characteristics and soot formation potential of Nano-Al2O3 diesel at low ambient temperatures

Nanoparticle additives have the potential to enhance combustion efficiency and reduce emissions in liquid combustion processes. This study thoroughly investigates the spray evaporation, ignition, and combustion characteristics of nanoparticle/fuel blends, especially under challenging environmental conditions, to improve combustion efficiency and reduce emissions. Employing diffused background illumination, shadowgraph, Mie scattering, high-speed natural luminosity, and two-color method, the spray combustion dynamics of thermally stable nano-Al2O3/diesel (NAD) blends were examined within a constant volume combustion chamber. Diesel, a prevalent primary or auxiliary fuel, represents other highly volatile renewable fuels, while Al2O3, a significant component in combustion fly ash, is noted for its specific catalytic properties and ability to re-burn, eliminating organic toxic elements. The results indicated that NAD blends exhibit a faster evolution rate for both liquid and vapor sprays compared to pure diesel, attributed to the increased kinetic energy of breakup droplets. Under most experimental conditions, incorporation of nano-Al2O3 slightly reduced the ignition delay time due to enhanced heat transfer. Notably, nano-Al2O3 altered the ignition mechanism of the diesel spray, transitioning it from partially premixed to diffusion combustion and relocating the ignition point nearer to the injector. The combustion flame of NAD blends demonstrated increased luminosity, a shorter flame lift-off length, and variations in start-of-injection and total-injection-nozzle-lift-off. However, due to a high equivalence ratio mixture between the liquid phase spray and combustion region, the soot concentration in NAD blends was higher than that in diesel. Additionally, the elevated flame temperature in NAD blends significantly increased the soot concentration. Overall, nano-Al2O3 markedly enhances diesel combustion, especially in low ambient temperatures, suggesting its impressive potential for the high-efficiency and low-emission utilization of renewable fuels or the combustion of recycled waste solvents.

Soot formation and its hazards in battery thermal runaway

As an increasingly important solution for the energy industry, batteries are widely used in electric vehicles and energy storage systems. However, thermal runaway of batteries is a serious safety hazard. In this process, the materials in the battery undergo thermal decomposition and combustion, resulting in the formation of soot and other harmful byproducts and posing a significant threat to the environment and human health. In this work, LiFePO4 and ternary lithium batteries are selected as experimental subjects to comprehensively evaluate the soot hazard in the thermal runaway process. The LiFePO4 and ternary lithium battery soot samples exhibited a typical "core-shell" structure, with lattice spacings ranging between 0.36-0.46 and 0.35–0.46 nm, respectively. The surfaces of these materials are covered with functional groups, including C–C, C–O, and O–H bonds. Soot samples taken from the thermal runaway of ternary lithium batteries also contain O–CO and π bonds, consistent with the functional groups in wood soot. Through EDS and XPS characterization, it is evident that the LiFePO4 battery soot contains C, O, Li, F, P, and Fe, while the ternary lithium battery soot, in addition to these elements, also contains Ni, Co, and Mn. The battery soot samples exhibited significant cytotoxicity to human cells, such as lung cells (MRC-5) and neural cells (SH-SY5Y). With high concentrations of soot, the survival rate of lung cells and nerve cells is low. Compared to wood soot, battery soot causes greater damage to human lungs and neural cells. The research in this work contributes to a better understanding of the hazardous characteristics of soot in battery thermal runaway and its potential threats to human health, offering a crucial reference for enhancing battery safety and emergency responses.

Developing a New Skeletal Mechanism for Propane, Butane, and LPG Fuels

ABSTRACT This study aimed at developing a new skeletal mechanism for LPG fuel capable of predicting combustion in a wide range of engine operating conditions with high fidelity. A novel reduction schematic was developed and applied to the Lawrence Livermore National Laboratory (LLNL) detailed mechanism (980 species, 4972 reactions) concerning NOx and soot formation as well. A two-level reduction method was used in which each level included Direct Relation Graph Error Propagation (DRGEP), DRGEP with isomer lumping, and DRGEP with sensitivity analysis. As a result, the skeletal mechanism was obtained with 88 species and 727 reactions and was successfully verified by comparing the results of the ignition delay/temperature and laminar flame speed/equivalence ratio for the combustion of propane, butane, and fuel mixture (90% propane/10% butane) with the experimental data. The obtained discrepancy of the ignition delay/temperature curves for the fuel mixture was around 5%. Additionally, a zero-dimensional engine calculation was conducted, and the results indicated that the mechanism was successful in predicting the engine combustion pressure with an error of around 5%.

Physical and Chemical Effects of Ammonia on Gas Emissions and Soot Formation in Laminar Coflow Ethylene Diffusion Flames

Physical and Chemical Effects of Ammonia on Gas Emissions and Soot Formation in Laminar Coflow Ethylene Diffusion Flames

Effects of inorganic sodium on the soot generation of coal particle: Insights with PLIF and DFT calculation

Inorganic sodium in low rank coal exerts significant influence on the soot generation in the early stage of combustion. The effect of inorganic sodium on the PAHs, soot formation and OH generation of coal particle was investigated on a concentrating light heating platform using Planar Laser Induced Fluorescence (PLIF) of OH radicals and PAHs. The generation characteristics of PAHs during coal particles pyrolysis with the temperature of 500 °C and 800 °C were also investigated. Raw coal, acid-washed (AW) coal and AW impregnated with different mass ratio of NaCl (1 %, 3 % and 5 % NaCl-loaded) were studied. Theoretical calculations using density functional theory was performed to explore the effect of sodium on the conversion of small molecule to macromolecular substances during early coal combustion. The results showed that the NaCl addition inhibited the OH radical and soot generation in the early stage of coal combustion, as demonstrated by the reduced OH intensity, and decreased soot intensity by observing the flame luminosity for the NaCl-loaded coals, compared with AW coal. Simultaneously, the PAHs generation was significantly reduced for NaCl-loaded coals, both at the early stage of coal combustion and under pyrolysis conditions, compared with AW coal. The quantum chemistry calculation revealed that the formed C-Na structure enhanced coal structural stability, making the chemical bonds less prone to cleavage, thereby inhibiting the volatile and PAHs release during the early stage of coal combustion. On the other hand, the released Na+ can catalyze the addition reactions of small ring PAHs (naphthalene, naphthalene derivatives) to larger ring PAHs (phenanthrene, pyrene), which would promote the PAHs and soot generation in homogeneous reactions, explaining the highest PAHs with 3-to-5 rings for 5 % NaCl-loaded coal among NaCl-loaded coals. The above two kings of reaction pathways were related to soot formation, but considering the results of reduced soot yield after NaCl addition, the former dominated. Furthermore, the results from the two pathways also illustrated that the Na inhibit the OH formation, which was corresponding to the decreased OH intensity for NaCl-loaded coals, as detected by OH-PLIF, and thus was detrimental to soot consumption. Therefore, the presence of Na in the early stage of combustion inhibited the release of volatiles and PAHs, which was the main reason for the decreased soot generation amount of NaCl-loaded coal.

Numerical study on soot formation in ammonia/ethylene laminar counterflow diffusion flame

The ammonia addition can significantly inhibit soot formation in hydrocarbon fuel flames. However, due to the complexity of the interaction between nitrogen and hydrocarbon, the inhibiting effect of NH3 addition on soot formation has not been fully understood yet. In this study, a mechanism is constructed through mechanism comparison, reduction, and merging. The constructed mechanism includes ammonia, polycyclic aromatic hydrocarbons (PAHs), and nitrogen-containing aromatic compounds (NACs) sub-chemistry. Then the constructed mechanism is coupled with a soot model to conduct a series of simulations of ammonia/ethylene laminar counterflow flames with various ammonia doping ratios. The results show that the constructed model can reproduce the suppression effect of ammonia addition on soot formation well. To explain the chemical inhibiting effect, the rate of production (ROP) and reaction pathway are analyzed. It can be concluded that the main formation pathway of benzene is C2H4 → C2H3 → C2H2 → C3H3 → A1. The decomposition of ammonia consumes H radical which is necessary for the conversion of C2H4 to C2H3, leading to a decrease in the reaction rates along the benzene formation pathway. Moreover, the N-containing species react with the small hydrocarbon molecules/radicals to form hydrogen cyanide (HCN), in which the reaction between C2H2 and N radical is the largest contributor. Compared to the reactions between C1-C2 species and nitrogen-containing species, the reactions between C3 species and nitrogen-containing species contribute less to the chemical effect of NH3 addition. All these reactions reduce the carbon flux of the benzene formation path. In addition, the impact of reactions between HCN and aromatic hydrocarbons which produce NACs is also investigated. The reactions of HCN addition to benzene and naphthalene compete with the C2H2 addition reactions, resulting in a slightly enhanced inhibiting effect of ammonia addition on soot formation.

Visualization study the cross spray and combustion characteristics of diesel and methanol in a constant volume combustion chamber at cold and flare flash boiling regions

To optimize the performance of diesel/methanol dual fuel engine, fundamental research on the spray and combustion characteristics of diesel/methanol dual direct injection was conducted in a constant volume combustion chamber. The injection pressures were set as at 60 MPa, 80 MPa, 100 MPa, while the ambient pressures were set as 4 MPa and 0.01 MPa, corresponding to cold and flare flash boiling regions, respectively. The results showed that diesel/methanol cross-collision accelerated the droplet interaction, promoting more uniform mixing. Compared to the cold region, the diesel/methanol collision spray had a larger axial and radial diffusion rate and evaporation rate in the flare flash boiling region. In addition, in the flare flash boiling region, the collision length, collision width, and spray projected area of both the liquid and gas phases were significantly greater than those in the cold region. With the increase in injection pressure, the spray obtained more kinetic energy, leading to a more intense collision process and more homogeneous fuel-gas mixing. Besides, a higher injection pressure shortened the mixing time of the fuel-air mixture before collision, resulting in a smaller equivalent ratio, a smaller ignition delay, a larger flame lift-off length, and a lower soot formation.

Design and modeling of a co-flow reactor for turquoise hydrogen production

This work focuses on the design of a reactor for producing clean hydrogen from methane pyrolysis in the form of the so-called “turquoise hydrogen”. In addition to its simple geometry, the fundamental concept and the main novelty of the proposed method rely on using part of the methane to produce the required heat needed for the thermal decomposition of methane (TDM). The reactor configuration for hydrogen production is shown to produce significant advantages in terms of greenhouse gas (GHG) emissions. A reactive flow CFD model incorporating also soot formation mechanism has been first developed and validated with experimental results available in the literature and then used to design and characterize the performances of proposed reactor configuration. 3D CFD simulations have been carried out to predict the behavior of the reactor configuration; a sensitivity analysis is used for clearing the aspect related to key environmental parameters, e.g., the global warming impact (GWI). The real potential of the proposed design resides in the low emissions and high efficiency with which hydrogen is produced at the various operating conditions (very flexible reactor), albeit subject to the presence of carbon by-product. This suggests that this type of methane conversion system could be a good substitute for the most common hydrogen production technologies.

A comparative investigation of the operating performance and emission characteristics of various diesel engines driving the firefighting pump

The investigation of engines with different performances driving the same load-consuming device is necessary for practical applications. In this paper, three diesel engines with varying capacities for driving the same firefighting pump for high-rise residential buildings were studied and compared for their performance, combustion parameters, and emissions by the simulation method. The AVL BOOST software is utilized to establish theoretical combustion models for these engines. The operating balance point of each engine is determined, and the appropriate transmission ratio of the drive train system is proposed to be applied. The results show that the working partial load modes of Model 1 at 91 % engine load and 2970 rpm, Model 2 at 74 % engine load and 2960 rpm, and Model 3 at 57 % engine load and 2490 rpm. The engine works in its higher load mode, producing higher brake specific fuel consumption (BSFC), higher NOx and CO emissions, lower soot formation, and vice versa. The engine operates at its lower load, resulting in decreased BSFC, less NOx and CO emissions, and more soot generation. The results suggest that Model 2 in the present work is the option that can balance the factors of engine power, initial investment cost, fuel consumption economics, and emissions. The findings obtained from this work are the scientific foundations to support the design of the firefighting pump systems when considering comprehensive factors of technical technology, investment cost, and environmental consideration.