Soot Generation Research Articles

Multi-field coupling effect of injection on dynamics and thermodynamics of a linear combustion engine generator with slow compression and fast expansion

An asymmetric reciprocating engine (ARE) with slow compression and fast expansion is designed in this paper, which can improve combustion performance and energy conversion efficiency by optimizing piston motion. However, due to the particularity of piston motion, how to consider the multi-field coupling effect of injection position (IP) on dynamics and thermodynamics becomes a key issue. Therefore, this paper proposes a multi-dimensional coupled model including motion, gas exchange and combustion, and uses an iterative algorithm to solve the model. The results show that ARE has better gas exchange performance and higher acceleration near TDC than conventional engines because of its slow compression and fast expansion processes, which lead to its obvious advantages in gas organization and combustion heat release. Furthermore, increasing IP has a positive excitation effect on the operating frequency and the combustion performance of ARE because the changed motion results in a longer ignition delay and a better fuel atomization environment. However, increasing IP continuously will lead to weak turbulent motion, which will greatly reduce the combustion reaction rate. The results suggest that increasing the IP is beneficial to improve the thermal efficiency of ARE and reduce soot generation, but too large an IP is not supported.

Simulation Investigation on the Effects of EGR Ratio and Nozzle Angle on In-Cylinder Combustion and Pollutant Generation of PODE/Methanol Blends

ABSTRACT In order to explore effects of coal-based oxygenated fuels polyoxymethylene dimethyl ether (PODE) and methanol on pollutant emissions of diesel engines, in-cylinder combustion numerical model was developed by coupling PODE/methanol reaction mechanism with CONVERGE software. The influences of exhaust gas recirculation (EGR) and nozzle angle on in-cylinder combustion and pollutant generation of PODE/methanol blends were studied. Results show that with the increase of EGR ratio, the fuel-air equivalence ratio increases, the in-cylinder pressure decreases, and the ignition delay period is prolonged. The generation range and rate of NOx gradually decrease, and the final NOx generation decreases by 85.1% at EGR = 20%. However, the peak soot generation rate and the final soot generation increase. With the increase of nozzle angle, the peak in-cylinder pressure and the overall heat release rate increase. When the nozzle angle is adjusted from 148° to 164°, the rich area of fuel-air equivalent ratio in the piston pit decreases, the high temperature area in the piston pit almost disappears. The final in-cylinder NOx generation has been reduced by 29.3%. The soot distribution gradually moves to the upper layer of combustion chamber, and the peak soot generation rate decreases, while the final soot generation increases by almost 49.5%.

The Effect of Alcohol Compounds on Droplet Combustion Characteristics of Unsaturated Fatty Acid of Linoleic Acid

Alcohol compounds have become a popular choice as additives for improving the performance of biodiesel. However, given the complexity of biodiesel, which is composed of various components of vegetable oil, it requires intensive research to fully understand its behavior. This study aims to investigate the impact of alcohol compounds on the droplet combustion characteristics of linoleic acid, an unsaturated fatty acid. Four alcohol compounds, namely methanol, ethanol, propanol, and butanol, were utilized to evaluate their effects on the combustion properties of the fuel mixtures. The droplet combustion characteristics were observed under normal atmospheric pressure and temperature conditions, with the fuel mixture consisting of 80 % linoleic acid and 20 % alcohol compounds. Our findings indicate that the addition of alcohol compounds to linoleic acid significantly reduced the ignition delay time, although the droplet lifetime was slightly increased. Moreover, it was observed that alcohols with shorter carbon chains had a greater impact on reducing the ignition delay time. Additionally, the results demonstrated that the alcohol compounds could accelerate the rate of increasing combustion temperature, reduce soot formation, and shorten the duration of soot formation. Furthermore, it was found that alcohol with a short carbon chain had a more pronounced effect on the overall combustion characteristics of linoleic acid. Overall, our study sheds light on the effects of alcohol compounds on the droplet combustion characteristics of linoleic acid, providing valuable insights for the optimization of biodiesel performance. HIGHLIGHTS Alcohol has a significant impact on the properties of unsaturated fatty acids, specifically on factors such as ignition delay time, droplet lifetime, temperature, flame dimension, and soot production The addition of alcohol as an additive, results in a reduction in soot generation and a shorter duration of soot formation The length of the carbon chain in the alcohol additive plays a crucial role in the combustion properties of linoleic acid. Alcohols with shorter carbon chains have a greater impact on the overall combustion properties GRAPHICAL ABSTRACT

Experimental and numerical investigation of soot deposition on exhaust heat exchanger tube banks

The exhaust heat exchanger is widely used in waste heat recovery systems (WHR) to recover energy from exhaust gas. However, fouling of the exhaust heat exchanger due to the deposition of soot particles reduces the heat transfer efficiency. In this investigation, a deposition performance experimental system and an improved CFD-based soot deposition prediction model were proposed to investigate the deposition characteristics on tube banks in exhaust heat exchangers. Firstly, the test bench is introduced in detail, and the combination of air heater and soot generator was applied in the test bench to provide the particle flow with specified parameters. Then, considering the effect of thermophoresis, diffusion, inertial impaction, and removal mechanisms, an improved prediction model was proposed. Compared with the traditional two-fluid model (TFM), the thermal-hydraulic performance of exhaust heat exchangers is calculated by CFD software in this model, so it is suitable for all dividing wall type heat exchangers. Afterwards, the influence of particle diameter and tube spacing on the tube bank during the 4 h deposition process was experimentally or numerically investigated. It was found that the comprehensive performance of the tube bank is deteriorated by about 0.45%-1.85% after 4 hours of soot deposition. Besides, the deposition amount on the tube bank with smaller tube spacing (1.25D) is lower.

Size and light absorption of miniature-inverted-soot-generator particles during operation with various fuel mixtures

The Argonaut miniature inverted soot generator (MISG) serves as a convenient and stable source of soot black-carbon aerosol particles. The MISG performance has been previously characterized for ethylene and propane, in a simple two-flow setup of fuel and air. These fuels produce soot size distributions with geometric median diameters (GMDs) of 150–200 nm. These sizes are substantially larger than the soot particles emitted from typical internal-combustion and aviation gas turbine engines. Here, we sought to produce substantially smaller soot particles, representative of aviation gas turbine engine emissions, by using five different fuels (acetylene, methane, ethylene, propane, and dimethyl ether) and by enriching the combustion air with oxygen. We developed a rapid screening protocol for each fuel, to allow the full range of stable flame conditions to be explored. We monitored the size distribution, mass concentration, and mass absorption cross section (MAC) of denuded MISG soot in real time. We considered only operating conditions where stable soot mass concentrations above 3 μg/m3 were emitted, corresponding to a non-flickering and open-tipped flame. For virtually all operating conditions, the measured MAC was consistent with literature values for mature soot. The only exception was a propane-acetylene mixture, for which the measured MAC was much lower than literature values. The observed GMDs fell into two groups, and we did not identify any trends leading to the mixtures falling into either group. The two groups were at approximately 100 nm and 160 nm. Therefore, while this study identified conditions that reduced the soot particles to 100 nm, it did not identify conditions where even smaller soot particles could be produced. This study has demonstrated that the soot properties produced by the MISG are highly repeatable and relatively insensitive to fuel composition.

Soot and gaseous product formation characteristics of leached high-alkali lignite pyrolysis at a high temperature

The contents of alkali and alkaline earth metals (AAEMs) in Zhundong lignite are very high, which can affect the formation of soot during coal combustion process. In this study, the effect of leaching treatment on soot and gaseous product formation characteristics from the lignite pyrolysis at 1300 ℃ is investigated. The results show that water washing only removes a small amount of water-soluble AAEMs, which has little impact on the combustion characteristics of the coal, while acid washing pretreatment largely removes Na, Mg, Ca and other ash components, causing obvious ignition delay. The acid washing obviously leads to the deterioration of oxidation characteristics and increases the yield of pyrolytic soot, and the peak diameter of soot increases from 100 nm to 200 nm. Moreover, after both water- and acid-leaching, more CO2 is produced, while CH4, CO, and H2 are reduced. The yields of C2H4 are not changed before and after leaching. However, a certain amount of C2H2 is produced for acid-leached coal pyrolysis. These phenomena indicates that there may be different soot generation and evolution paths in three cases. To a certain extent, this provides a theoretical guidance for the research of effectively reducing soot emissions and improving coal utilization under high-temperature pyrolysis.

Numerical and experimental study on the performance of a hybrid draft biomass cookstove

Over 2 billion people worldwide rely on biomass for cooking and primarily use traditional cookstoves, causing 4 million casualties annually due to indoor air pollution. This can be minimised by improving the design and combustion characteristics of the stoves. The present study is an attempt to achieve these improvements by investigating numerically (3D) and experimentally the thermal and emission performance of a newly developed hybrid draft biomass cookstove (HDBC). The influence of secondary air mass flow rate on stove performance is analysed. A homogeneous combustion is modelled to evaluate thermal performance, and soot formation is studied using three soot models: one-step, two-step, and mass-brook. The numerical results are validated against Water Boiling Test (WBT) data. The HDBC achieved Tier 3 level in efficiency and Tier 4 level in CO and PM2.5 emission performance, both experimentally and numerically, thus outperforming standard natural draft stoves. The numerical results exhibited fair agreement with the experimental data, with an average deviation of 6%, 9%, and 26% for efficiency, CO, and PM2.5 emissions, respectively, compared to the experimental results. The soot generation predicted by a one-step soot model gives better results over the other two models and is in good agreement with the experimental results.

The impact of export tax rebate reform on industrial exporters’ soot emissions: Evidence from China

In this paper, we systematically explore the environmental effects of the export tax rebate rate reduction policy using the China Industrial Enterprise Database, the China Industrial Enterprise Pollution Database, and the China Customs Import and Export Database from 2005 to 2013. Our difference-in-difference (DID) estimates show that the reduction in the export tax rebate rate significantly reduces the intensity of corporate soot emissions, and this finding holds after a series of robustness tests. For every 1-unit reduction in export tax rebate rate, industrial exporters’ soot emission intensity decreases by 2.63%. The mechanism analysis shows that the decrease in soot generation, the decrease in coal use intensity, the increase in total amount and efficiency of soot treatment are important channels. Heterogeneity analysis shows that the reduction of export tax rebate rate has a more significant impact on the intensity of soot emissions of high pollution, high energy consumption and resource-based enterprises. This study may provide a reference for other developing countries that also rely on export tax rebates to adjust their policies to combine economic growth with pollution control.

Effects of Blended Biodiesel Coupled with Miller Cycle on Combustion and Emissions of Marine Diesel Engines

In order to study the effect of blended biodiesel coupled Miller cycle technology on the combustion and emission performance of diesel engine, the 4190 diesel engine was simulated by AVL-FIRE software. The Miller degree and different blending ratios of biodiesel are simulated and analyzed. The results show that: under the same Miller degree, with the increase of the blending ratio, the explosion pressure decreases significantly, the cylinder temperature decreases, the CO emission decreases significantly, and the NO emission increases. Soot emissions have dropped significantly. Under the same blending ratio, with the increase of Miller degree, the explosion pressure increases, the cylinder temperature decreases gradually but not obviously, the CO emission decreases, the NO emission increases first and then decreases, and the Soot emission decreases. Therefore, selecting the appropriate blending ratio and Miller degree can better reduce NO emissions, and at the same time have a better inhibitory effect on the generation of Soot and CO, and the power performance of the diesel engine is slightly improved. The results of this study provide a solution for the practical application of biodiesel.

Particulate Matter Emissions in Gasoline Direct-Injection Spark-Ignition Engines: Sources, Fuel Dependency, and Quantities

This study investigates sources of particulate matter (PM) from a direct-injected spark-ignition (DISI) engine, all of which are likely the result of poor mixture formation, although through varying mechanisms. Nine unique gasoline formulations, including both oxygenated and non-oxygenated fuels, with varying distillation curves and concentrations of different hydrocarbon classes were employed to investigate the effect of fuel on soot formation. The engine experiments were further supported by reacting and non-reacting experiments in a spray-chamber.The metal-engine experimental results indicated that engine-out PM emissions of the nine fuels generally conforms to their sooting tendency, here quantified by Particulate Matter Index (PMI). Discrepancies with the engine-out PM emissions and PMI were observed under transient operating condition, which is not reflective of the test conditions used to formulate the PMI. A diisobutylene surrogate blend and a high-olefin full-boiling range fuel were investigated further in the optically-accessible engine, showing soot generation from different sources. These differences came from the variation in their spray characteristics, as confirmed in the non-reactive spray-chamber experiments.While the earlier tests were conducted with a fouled injector, the injector was later cleaned and fuels were tested in the optical engine. High olefin fuel and diisobutylene blend showed significantly lower soot emissions with clean injector. E30 fuel exhibited spray impingement and subsequent diffusive combustion, known as pool fire, on the piston top characterized by a yellow flame due to soot luminosity. A final round of experiments in the spray-chamber mimic this pool fire mechanism. A stoichiometric flame was initiated after a spray has impinged on a wall and formed a film. Results showed a large time delay between the flame passing over the fuel film and the formation of soot mass. The slow soot formation via pyrolysis in spray-chamber suggest that pyrolysis may not be a dominating soot-production pathway in SI engines, even for conditions with significant wall wetting. The findings of this study highlight the many considerations which influence the effective design of a combustion system when the minimization of PM emissions is a goal, and the ways in which fuel formulation can change soot-production pathways in DISI engines.

Spray-wall interaction on n-dodecane spray combustion and soot formation under different wall temperatures

To investigate the effect of the wall on soot formation during spray combustion and to explain the existence of contradictory results, the vapor-phase, ignition, combustion, and soot formation of free- and impingement-spray with different wall temperatures were studied in comparison using optical diagnostic techniques. Results reveal that, compared to free spray, the impingement spray’s vapor-phase spray tip penetration is reduced, and its vapor-phase spray volume is increased by about three times. At conditions where only the vapor-phase impinges on the wall, the impingement spray has a shorter ignition delay time (IDT) for various wall temperatures. Furthermore, the soot formation of the impingement spray combustion is approximately one-third of the free spray, and the increase in air entrainment accounts for this phenomenon. In a comparison of different wall temperature conditions, the higher wall temperature facilitates the spray ignition process with a shorter IDT, and the ignition location is further away from the wall. However, the relationship between wall temperature and soot formation is not linear. The soot formation varies in a pattern of reducing and then increasing as the wall temperature increases due to the high wall temperature accelerating both the generation and oxidation rate of soot.

Experimental study on soot suppression efficiency of acetylene diffusion flames in a Rijke tube

• The soot suppression effect of acetylene diffusion flames in a Rijke-type combustor is reported for the first time. • Extremely high soot suppression efficiencies are only achieved at the tube’s naturally resonant frequencies (169 Hz and 346 Hz). • As the flow state turns into turbulence, soot is nearly completely suppressed. • With the generation of harmonics, different flame shapes are observed in adjacent periods. • Temperature downstream of the flame is increased from 1773 K to 2250 K. This work reports soot suppression effect of acetylene diffusion flames in a Rijke-type combustor for the first time. The soot generation and suppression from a laminar and turbulent diffusion flame in the Rijke tube by introducing an external acoustic forcing signal are investigated experimentally. A loudspeaker is applied at the bottom of the Rijke tube to induce resonance and control the frequency in the tube. The flame is fluctuated violently at the tube’s naturally resonant frequencies (169 Hz and 346 Hz), and extremely high soot suppression efficiencies are only achieved at these frequencies. Besides, the soot suppression efficiency gradually increases and the flame height gradually decreases with the increase of the acoustic pressure. Different flame shapes are observed in adjacent periods, which is the result of harmonics in the tube. The Reynolds number is calculated based on the velocity of the flame fluctuation. Results show that in laminar flow, the soot suppression efficiency is low. Differently, in turbulent flow, soot suppression efficiency (up to about 100 %) is extremely high. At turbulent condition, the mixing of fuel and air is enhanced, resulting in more soot to be oxidized. The flame temperature fluctuates periodically and the peak flame temperature shows a 96 degrees lag behind the peak acoustic pressure. Under the acoustic resonance, the temperature downstream of the flame gradually increases from 1773 K (without acoustics) to 2250 K.

Experimental study of the effect of physical and chemical properties of alcohols on the spray combustion characteristics of alcohol-diesel blended fuels

To reveal the effect of different long carbon-chain alcohols blended into diesel on combustion characteristics and soot emissions under different ambient temperatures, the spray combustion processes of diesel and four sets of blends (the volume ratio of propanol/diesel, butanol/diesel, pentanol/diesel, and hexanol/diesel being 20%/80%) were investigated in a constant volume combustion chamber (CVCC) using optical techniques. It was discovered that the physical (cooling effect, dilution effect, diesel evaporation inhibition) and chemical reaction properties of alcohols have a competitive effect on the spray combustion characteristics of alcohol-diesel blended fuels. The combustion pressures of alcohol-diesel blended fuels were lower than that of pure diesel due to lower heating values, and this difference became more obvious under higher ambient temperature. Alcohols blended into diesel fuel could improve the combustion efficiency. The ignition delay times (IDTs) of alcohol-diesel blended fuels decreased with increased carbon chain lengths of alcohols under low ambient temperature conditions. However, this trend was reversed with increasing ambient temperature, and the IDTs of alcohol/diesel blends became lower than that of pure diesel at higher ambient temperatures. Propanol or hexanol blended into diesel could significantly inhibit the generation of soot at low ambient temperatures, but other alcohols promoted it. Interestingly, all alcohol-diesel blend fuels inhibited the generation of soot under high ambient temperature conditions, and propanol was the most significant.

Numerical investigations of soot generation during wood-log combustion

• Particle-scale biomass combustion model with soot formation is established. • Virtual-particle-based thermally-thick model and two-equation soot model are integrated. • Improved prediction of soot volume fraction for a single-particle combustion experiment is achieved. • Soot generation during wood log combustion depends highly on flame structure and the packing of wood logs. Soot formation is an important challenge in the design of modern wood stoves, as soot not only deteriorates the combustion efficiency but also poses threats to human health. Although soot formation in biomass combustion has been studied previously, the investigation at wood stove level is still rare due to its complex nature. In this paper, numerical simulations are performed to uncover the basic trends of soot formation during wood log combustion. The soot formation model is developed based on a particle-resolved biomass combustion algorithm, where the intraparticle heat and mass transfer effect, soot mass fraction and particle size are all resolved. Besides, simplified tar and precursor models are used in solving the reaction kinetics of soot formation. The integrated model is first validated through the combustion simulation of a micron-sized coal particle in air, where the predicted flame temperature and the soot volume fraction show improved agreement with experimental data compared to a previous modeling work. Thereafter, the soot formation during wood-log combustion in a confined stove is studied. Different combustion behaviors are observed for varying numbers of wood logs and for variations in the wood-log stacking. Additionally, the flow field temperature, tar, soot, and oxygen concentrations during the combustion are analyzed. Finally, the influences of the air intake rate, the relative distance between wood logs, and temperature boundary condition on the soot formation are discussed. This work provides useful information for the design and the optimization of modern wood stoves.

Research on the Soot Generation of Diesel Surrogate Mechanisms of Different Carbon Chain Length

This paper studies the generation process and emission characteristics of soot from Marine diesel engine. On the basis of Particulate size mimic (PSM) detailed soot model, the parameters related to soot generation obtained from the reaction mechanism calculation of 3 surrogate of different carbon chain length: n-heptane, n-tetradecane and n-tetradecane-toluene were compared and analyzed including precursor of soot, quality and density of soot, particle size distribution of empirical soot model. The results show that the soot nucleation stage of n-tetradecane-toluene mechanism was slightly more consistent than that of n-tetradecane mechanism with the experimental results, far more consistent than that of n-heptane mechanism. The intensity of surface growth and aggregation stage is greater, which is reflected in the soot precursor: acetylene and A4, and leads to that the soot produced by the mechanism of n-tetradecane and n-tetradecane-toluene is small in quality but large in quantity. The particle size distribution calculated by n-tetradecane and n-tetradecane-toluene mechanism is closer to the experimental data than that calculated by n-heptane mechanism. Then combustion process of n-tetradecane and n-tetradecane-toluene mechanism is more suitable for marine engine, which is reflected in the higher temperature and the smaller equivalent ratio in the cylinder.

Detection of Polycyclic Aromatic Hydrocarbons in High Organic Carbon Ultrafine Particle Extracts by Electrospray Ionization Ultrahigh-Resolution Mass Spectrometry.

The detection of polycyclic aromatic hydrocarbons (PAHs) by electrospray ionization (ESI) without additional reagents or targeted setup changes to the ionization source was observed in ultrafine particle (UFP) extracts, with high organic carbon (OC) concentrations, generated by a combustion aerosol standard (CAST) soot generator. Particulate matter (PM) was collected on filters, extracted with methanol, and analyzed by ESI Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS). Next to oxygen-containing species, pure hydrocarbons were found to be one of the most abundant compound classes, detected as [M + Na]+ or [M + H]+ in ESI+ and mostly as [M - H]- in ESI-. The assigned hydrocarbon elemental compositions are identified as PAHs due to their high aromaticity index (AI > 0.67) and were additionally confirmed by MS/MS experiments as well as laser desorption ionization (LDI). Thus, despite the relatively low polarity, PAHs have to be considered in the molecular attribution of these model aerosols and/or fresh emissions with low salt content investigated by ESI.

Numerical study on the wall-impinging diesel spray soot generation and oxidation in the cylinder under cold-start conditions of a diesel engine

The combustion of wall-impinging diesel spray of heavy-duty diesel engines deteriorates combustion quality under cold-start conditions, making it difficult to control soot emissions. To investigate the causes of soot increase in the combustion of wall-impinging spray at low temperature and low speed starting conditions, the effect of the starting fuel mass on the soot formation and oxidation process was analyzed using a multidimensional computational fluid dynamics (CFD) model. The results show that the diesel spray is guided by the piston wall and the limited space, the spray impinged on the wall and the vapor-phase fuel flowed in the spray interaction zone. Thus, the soot mainly accumulates in the spray interaction zone, the region near the cylinder head and the bowl wall in the combustion chamber bowl. The soot from the vapor of deposited fuel film in the piston bowl wall and near wall region accumulates continuously in the after combustion stage, becoming the main source of soot emissions at the time of exhaust valve opening (EVO). Increasing the mass of starting fuel raises the mass of the rich mixture and wall-impinging fuel, which enhances the mismatch between fuel and air, resulting in higher soot generation, while soot is more difficult to be completely oxidized by OH radicals, and ultimately soot emissions increase significantly. It can be deduced that the engine-optimized injection strategy may mitigate the increase in soot emissions at high start-up fuel injection conditions.

Impact of PODE3 on soot oxidation reactivity at different stages in n-heptane/toluene diffusion flames

PODE3, with the molecular formula of CH3O(CH2O)3CH3, is considered a highly competitive alternative fuel due to the absence of CC bond and its high oxygen content, and have been shown to significantly reduce soot emission when applied as a diesel fuel additive. However, the effect of PODE3 addition on the oxidation reactivity of soot generated in the flame remains unclear which is of great importance for the optimal design of the post-treatment devices during its application. In this work, the impact of PODE3 (0 %, 10 %, and 20 % by volumetric fraction) addition on the oxidation reactivity of soot at different maturity and oxidation degrees in n-heptane/toluene co-flow diffusion flames was specially investigated combining information on thermogravimetric analysis, high-resolution transmission electron microscope, and Raman spectroscopy. Results showed that PODE3 substitution significantly shrank soot generation region, and increased the flame temperatures before height above burner (HAB) < 45 mm. The addition of PODE3 improved the soot oxidation reactivity, which had a strong ability to hinder the growth of the microcrystalline carbon layers and resulted in a high content of amorphous carbon in soot particles. Specifically, it had more significant impacts on the soot in the oxidation stage than the surface growth stage. These can be explained that with PODE3 addition, on the one hand, the “reliable carbon atom” for soot formation is significantly reduced and the amount of oxidizing species is increased, resulting in a smaller particle size and a higher content of disordered and amorphous carbon in soot particles. On the other hand, the flame temperatures increased where HAB < 45 mm, which would promote the soot formation reactions. The combined effects of these factors make PODE3 have more significant inhibitory impacts in reactivity of soot sampled at oxidation stage than that at surface growth stage. Therefore, the impact of PODE3 addition on soot nanostructures and oxidation reactivity is not only reflected in its chemical effect but also in temperature effect.

Controlled Laboratory Generation of Atmospheric Black Carbon Using Laser Excitation-Based Soot Generator: From Basic Principles to Application Perspectives: A Review

The mimicking of atmospheric soot with versatile chemophysical properties is a critical issue in many applications, starting from instrument calibration, through producing aerosol standards for academic research, and ending with the reduction of uncertainties associated to carbonaceous particulate matter in the atmosphere, just to name a few. The present study deals with laser ablation as a novel and interesting technique for the generation of soot with high elementary carbon (EC) content with microphysical features similar to diesel or atmospheric soot and for modelling biomass emission under well-controlled laboratory conditions. The operation of the laser-excitation-based soot generator and the characteristics of the produced particles are compared to the most widely used techniques like flame, spark discharge generators, and real combustion soot originating from diesel- and aircraft engines or from field measurement. The comparison shows that significant differences in the physicochemical features exist between the real combustion soot and the soot originating from different excitation mechanisms. Moreover, the soot produced by different techniques shown also significant differences. However, due to some inherent and favorable attributes of the laser ablation technique—such as the possibility of the independent variation of physical characteristics of the generated soot particles—the potential for modelling biomass burning or to produce soot particles even in the accumulation mode makes it a useful tool in many cases.

Numerical investigation of component coupling effect on soot forming under low temperature condition

The chemical reactions of each component of hydrocarbon fuels at low temperatures become more complex and the interactions become stronger, which is considered to potentially affect the soot formation characteristics. A 0-dimensional simulation was applied to analysis the component coupling effect on polycyclic aromatic hydrocarbon(PAH) forming process for diesel surrogate fuel, n-heptane/cyclohexane/toluene. The results show that, for the single component, the low temperature reaction of cyclohexane could contribute to the PAH formation while n-heptane inhibit it, and toluene is hardly involved in the soot generation at low temperature. Due to the component coupling effect of multi-component diesel surrogate fuels, the soot generation is significantly reduced at low temperatures, and the pyrene(A4) generation is reduced by 3 orders of magnitude compared to individual components weighted fuels. The generation of O radicals from n-heptane rapidly consumes C6H5O, which replaces its original reaction road to naphthalene(A2). As a result, the reaction time of A2 is shortened by 2 orders of magnitude, then, the generation of A4 and soot are reduced due to the reduction of A2. Therefore, the competition and consumption between the low temperature reaction products and the core radicals of soot generation are the key to reducing soot accumulation.