Maximum Soot Research Articles

Large eddy simulation of soot formation in a turbulent lifted flame with a discretized population balance and a reduced kinetic mechanism

This article presents simulations of a turbulent lifted flame using the large eddy simulation-transport probability density function-discretized population balance equation approach. This approach takes into account the interaction between turbulent reacting flow and soot particle formation. A reduced chemical kinetics mechanism including a series of polycyclic aromatic hydrocarbons (PAHs) species linked to soot formation is generated employing the approach of the directed relation graph error propagation and is tested on a perfectly stirred reactor under varying equivalent ratio conditions and premixed flames. The soot kinetics model includes the PAH-based nucleation and surface condensation, the hydrogen abstraction acetylene addition surface growth and oxidation mechanism, and the size-dependent aggregation. The soot morphology considers the surface area and other geometrical properties for both spherical primary particles and fractal aggregates. The simulation results show, in general, reasonably good agreement with experimental measurements in terms of lifted height, flame shape, flow-field velocity, the hydroxyl radical, and soot volume fraction. A discussion of micromixing and its modeling in the context of the Interaction by Exchange with the Mean model is also presented. To investigate the effect of the soot micromixing frequency factor on soot particles, an additional simulation is conducted where this factor is reduced by a factor of 10 for the soot particles. The maximum soot volume fraction is observed to increase slightly. However, compared with the impact of kinetics on soot modeling, this effect is a minor one.

Effect of Hydrogen Addition on Soot Reduction in Diffusion Flames

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

Maturity characterization of soot in laminar coflow diffusion flames of methane/anisole under different oxygen indices

Anisole fuel has gained increased attention, since it is considered a biofuel, and its addition to gasoline increases the octane number, improving the engine performance. This study focuses on the comprehensive characterization of soot maturity and sooting propensity of a well-controlled laminar coflow diffusion flame fueled with anisole and using methane as the carrier gas. Four laminar non-premixed flames were established below the smoke point. The oxidizer composition ranged from a molar fraction of oxygen (oxygen index, OI) of 21% to 35% (doped with pure oxygen), while keeping constant the total volumetric flow rate of oxidizer stream. Multi-wavelength line-of-sight attenuation experiments were performed from visible to infrared wavelengths, and the measurements of the extinction coefficient and flame temperature were used to retrieve two dimensional fields of soot temperature, volume fraction, radiative intensity and degree of soot maturity. In general, the sooting propensity and radiative behavior of the anisole flames follows a similar trend than typical hydrocarbon fuels when increasing the OI. However, the spatial distribution of soot volume fraction is enhanced, particularly near the flame centerline. In contrast, the soot production is promoted by the OI, near the flame wings. The same effect can be observed for the soot temperature. Indeed, temperature increases, promoting formation and oxidation processes, specially at the locations near the maximum soot volume fraction. In general, the maturity of soot particles is affected as the OI is changed. Also, it is observed that the degree of maturity is enhanced by flame temperature. In order to support these local observations, a statistical analysis was carried out. Finally, the results obtained yield a curated database for validating detailed soot production models of oxygenated fuels, and to gain further insights on the evolution of soot maturity and propensity of these particular fuels under different oxidizer conditions.

Sooting behavior on a spreading flame over PMMA rods under different oxygen concentrations

The flame spread process over the surface of a solid combustible material is highly influenced by the radiative feedback from the flame, and the conditions under which the process takes place. Soot particles generated during the burn are a big contributor to flame radiation and can play a critical role in the radiative exchange between the flame and the solid. Thus, increased knowledge of the soot production processes involved in the spread of a flame can further promote the understanding of growth and development of fires. The main purpose of this work is to study the effect of oxygen concentration on the sooting behavior of cylindrical samples of polymethyl-methacrylate (PMMA) in an opposed flow configuration. Measured data shows that during downward/opposed flame spread the mass burning rate and soot volume fractions increase with higher oxygen concentrations. The data presented is correlated using a scaling analysis that provides correlations for the maximum soot volume fraction, and the maximum integrated soot volume fraction as a function of the oxygen concentration using similar residence times to establish comparable conditions. The data shows the correlations introduced here provide useful information of the sooting behavior of spreading flames in environments of varied oxygen concentrations that could be used to guide potential fire safety applications.

Quantitative investigation of sooting dynamics in droplet combustion using an automated image analysis algorithm

This paper reports an image analysis approach using a newly-developed open-source program to extract quantitative measurements of soot volume fraction (SVF) from digital video images of burning n-heptane droplets. The automated program developed in this work can analyze images of fixed and untethered droplets to quantify sooting dynamics. The images analyzed in the program were taken from experiments carried out in the Multi-user Droplet Combustion Apparatus (MDCA) onboard the International Space Station (ISS). In these experiments, video imaging of burning droplets was obtained using backlighting by a laser diode with a wavelength of 653 nm. The light was collimated before it passed through the droplet and soot-containing region, after which the light was then attenuated and projected onto the camera’s sensors. This technique facilitates the measurements of SVF based on the principles of the full field light extinction method (FFLEM). The measurements provide quantitative data that reveal the sooting dynamics of liquid fuels during droplet combustion processes.The analyses of a soot-attenuating image (ISS n-heptane, untethered droplet) at an instant during the burning show that the SVF distribution has a peak at the soot shell location. It then decreases due to soot oxidation when the location is further away from the burning droplet. Regarding temporal effects on the maximum SVF (SVFmax), results show that SVFmax first increases after the burning is initiated until a peak value is reached, after which SVFmax decreases. The SVFmax values identified in this study for n-heptane are quantitatively consistent with previously reported values for fiber-supported droplets and are reached relatively early in the burning history. n-Heptane images are also analyzed to show the effects of initial droplet sizes on the maximum soot volume fraction. Results show that SVFmax decreases with increasing initial droplet size, which is consistent with visual observations of less soot formed and dimmer flame brightness as Do increases.

Comparative study of soot properties and pressure sensitivity in n-dodecane and decalin laminar flames

The main objective of this study is to compare the soot properties and pressure sensitivity of the high-carbon-number n-alkane and cycloalkane in laminar diffusion flames at elevated pressures. As typical high-carbon-number components of aviation kerosene, n-dodecane and decalin have been used in surrogate fuel kinetic models for aviation kerosene such as Jet-A and Chinese RP-3. In this study, quantitative experiments on soot properties are conducted in nitrogen-diluted n-dodecane and decalin laminar diffusion flames at up to 5.0 atm, which has scarcely been reported in the literature. Soot morphology and detailed soot volume fraction distribution are studied by transmission electron microscopy analysis and laser extinction method. Based on the soot volume fraction results, the soot yield is evaluated to compare the pressure sensitivity of the soot propensity between the two fuels. The results show that from 1.0 to 5.0 atm, the primary soot particle diameter, maximum soot volume fraction and soot yield in decalin flames are higher than those in n-dodecane flames. However, with increasing pressure, the growth rates of these soot properties are higher for n-dodecane flames than for decalin flames. The ratio of maximum soot yield of decalin to n-dodecane decreases from 2.2 at 1.0 atm to approximately 1.2 at 5.0 atm. The quantitative results indicate that the pressure sensitivity of soot properties of n-dodecane is stronger than that of decalin. The quantitative experimental results of this work are helpful in understanding the relevant fuel kinetic mechanisms suitable for simulating soot formation at elevated pressures.

Investigation of soot suppression by ammonia addition to laminar ethylene flames at varying pressure

Blending ammonia with hydrocarbon fuels is a promising pathway to expedite its use in different industries, as it might offer a good compromise between energy output and minimizing the emissions of both NOx and carbonaceous combustion products, including soot. This work describes the effects of pressure on soot formation in ethylene/ammonia laminar co-flow diffusion flames. A high-pressure chamber was used to study the flames at pressures between 1 to 7 atm, and ammonia addition mole fractions between 0 and 50% (38% in mass fraction). Soot volume fraction and soot temperature measurements using a Spectral Soot Emissions technique show that adding a 50% mole fraction of ammonia at atmospheric pressure reduces soot concentration below the detection limit of the technique and between 70% and 80% for all the remaining studied pressures; that is, the ammonia soot suppression characteristics are demonstrated when increasing pressure. Maximum soot yield and total volumetrically integrated soot volume fraction results are investigated to reveal the contrasting effects of pressure and ammonia addition on the flame structure and the soot formation mechanisms. The results showcase the potential of NH3 in high-pressure applications when mixed with hydrocarbon fuels to reduce carbon emissions.

Effect of preheating air temperature on sooting tendency in laminar co-flow diffusion flame of n-heptane

This work investigates the effect of preheating air temperature on the sooting tendency in the laminar co-flow diffusion flames of n-heptane. A modified co-flow burner was employed to produce steady n-heptane laminar diffusion flames with the preheating temperatures of co-flow air varying from 344 K to 588 K. The planar laser-induced incandescence (LII) calibrated by the line-of-sight attenuation (LOSA) was performed to quantitatively measure the soot volume fraction and the soot yield in flames and an ICCD camera was used to capture the flame luminosity images. The results reveal that the visible flame height is decreased with the preheating co-flow air temperature, and it is hardly affected by the air velocity with a constant air temperature. As the co-flow air temperature increases, the soot inception and oxidation and the peak soot concentration initiate at the lower positions in flames, and the soot loading in flames has a remarkable increasing trend by assessing the evolution of the soot volume fraction and the soot yield. However, the enhancement rate of total soot loading in flames with the co-flow air temperature below the initial fuel temperature is lower than that for the co-flow air temperature above the initial fuel temperature. In addition, the temperature sensitivity of soot loading is assessed by the maximum soot volume fraction, which is in accordance with those of the alkane in previous research. According to the response of the maximum soot yield to the co-flow air temperature and adiabatic flame temperature, the temperature sensitivity of sooting tendency in n-heptane flames is further confirmed.

Effects of intramolecular oxygen and partial premixing on soot formation in ethane/ethanol flames

Detailed soot concentration and temperature fields were measured in coflow laminar diffusion flames of neat ethane and ethane/ethanol mixtures, and partially premixed flames of ethane/ethanol mixtures. Two-dimensional diffuse-light line-of-sight attenuation and spectral soot emission techniques were employed for soot volume fraction and temperature measurements, respectively. The choice of flow rates prioritized tractability and comparability between flames. To this end, the total carbon mass flow rate and the C/H ratio were kept constant for all ethane/ethanol mixture flames, i.e., oxygen was introduced into the fuel stream either as intramolecular oxygen in ethanol or both as intermolecular and molecular oxygen. Soot concentration was observed to decrease monotonically with an increasing ethanol content in ethane/ethanol mixtures without synergistic effects. Soot concentration was also measured in neat ethane flames with flow rates matching those of ethane in ethane/ethanol mixtures. A comparison of these flames with ethane/ethanol flames revealed a striking soot suppression effect by ethanol addition. Although the carbon flow rate was less in neat ethane flames than the total carbon flow rate of their corresponding ethane/ethanol flames, the peak soot volume fractions were significantly higher in neat ethane flames. This points to a chemical soot suppression effect beyond that can be explained by the lower sooting propensity of ethanol fuel. These results were discussed in light of the synergistic effect studies in the literature. Lastly, measurements from partially-premixed ethane/ethanol mixtures are reported. The increased oxygen content significantly increased the peak soot volume fraction in these flames. These results support that intermolecular oxygen in ethanol and molecular oxygen in the fuel tube behave drastically differently in an ethane base flame. Ethanol addition does not exhibit synergistic effects on soot formation, whereas molecular oxygen addition increases maximum soot concentration, indicating the activation of unique soot production pathways.

Chemical, radiative, and dilutive effects of CO2 addition on soot formation in jet A-1 kerosene co-flow diffusion flame

With the development of aviation industry, it is urgently to investigate the soot formation properties of aviation kerosene to better control the soot emissions. The dilutive, chemical and radiative effects of CO2 on the soot inception, condensation and hydrogen abstraction acetylene addtion (HACA) growth processes in laminar co-flow Jet-A1 kerosene diffusion flames were numerically investigated by employing detailed chemical mechanisms and soot sectional models. The results showed that the addition of CO2 dramatically decreased the maximum temperature (by 92 K) and soot volume fraction (by 41.0%). The dilutive effect of CO2 contributed the most to the decrease of temperature and soot volume fraction. It also was the main factor in the decrease of soot inception, condensation and HACA growth processes. The chemical effect of CO2 had little impact on the decomposition of fuels into light hydrocarbons, but obviously limited the growth of light hydrocarbons to A1. The radiative effect of CO2 decreased the maximum temperature and soot volume fraction by 13 K and 5.2% (from 1.92-1.82 ppm). It had little impact on the soot inception, condensation and HACA growth rates.

The effects of oxygen index on soot formation of ethylene, propane and their mixtures in coflow diffusion flames

Oxygen index (OI) effects on soot formation and oxidation of ethylene, propane and their mixtures were investigated in coflow diffusion flames. Experimental results show that the peak soot volume fraction (SVF) firstly increases and then reaches the plateau region as OI increases from 0.21 to 0.42 in ethylene and 90%ethylene/10%propane mixture flames. However, the peak SVF firstly increases and then decreases with the increase of OI in propane flame. All these three cases present a consistent trend in terms of maximum soot yield which increases first and then decreases as OI increases. Synergistic effect was captured in ethylene/propane mixtures while it was firstly enhanced and then mitigated when OI increases in the investigated OI range. Numerical simulations were also conducted. A significant relationship was found among flame temperature, O2 mole fraction and SVF in terms of their spatial gradients. The non-linear trends of SVF and soot yield with OI can be attributed to the competition between soot formation and oxidation. Such competition was also indicated from polycyclic aromatic hydrocarbons (PAHs) growth. Numerical analyses revealed that small radicals including O, CH2 and C6H5 contribute to the non-linear changes of PAHs in the synergistic effect.

Soot formation from n-heptane counterflow diffusion flames: Two-dimensional and oxygen effects

Soot formation of n-heptane is experimentally and numerically studied in low-strain rate (K = 50 s−1) counterflow soot formation (SF) flames. Flame temperatures and soot volume fractions at different oxygen mole fractions on the oxidizer stream (xO2=0.3–0.45) are measured by using thermocouple-calibrated OH two colors laser-induced fluorescence (2C-PLIF) and laser-induced incandescence (LII) calibrated by light extinction methods, respectively. Mono (MAHs) and polycyclic aromatic hydrocarbons (PAHs) are also qualitatively measured by using the PAHs-LIF technique. Good agreement between measured and predicted maximum flame temperature (Tmax) and peak soot volume fraction (fv,peak) is obtained. However, discrepancies in the shape of the entire soot volume fraction profiles along the axial centerline are observed between 1D and 2D simulations. This result is found to be primarily related to the thermophoretic and radial effects in the low strain rate flames investigated, which hamper neglecting the underlying 2D effects. MAH/PAH peak mole fractions and fv,peak increase from xO2=0.3 to xO2=0.45 due to the related increase of flame temperature, which fosters n-heptane pyrolysis near the fuel nozzle leading to higher concentrations of C1C4 hydrocarbons. The latter are found to grow to MAHs/PAHs and finally to soot particles through analogous pathways independently of xO2. However, the higher flame temperature in the sooting region at xO2=0.45 leads to soot particles and aggregates characterized by larger sizes and more dehydrogenated than those produced at xO2=0.3.

Utilization of waste-derived biodiesel in a compression ignition engine

Air pollution has been broadly concerned as a global issue in all regions. Particulate matter (PM) emission mainly originated from the combustion of diesel engine in transport sector is progressively solved for mitigation. The purpose of this study is to preliminary utilize biodiesel from different feedstock as an alternative fuel in a diesel engine. Waste-derived biodiesel was prepared from waste cooking oil (WCOME) and waste chicken oil (CKOME) by transesterification process. Palm oil-derived biodiesel (POME) was also prepared and used as a reference. Fatty acid profiles of the prepared biodiesel were characterized by a gas chromatography–mass​ spectrometer. The biodiesel was analyzed for fuel characteristics under ASTM standards. The engine test was carried out on a single-cylinder diesel engine at the engine speed of 1500 rpm with full engine load. The engine combustion and performance as well as exhaust emissions of waste-derived biodiesel were compared with palm oil biodiesel and diesel fuel. The PM oxidation temperature was indicated by a simultaneous thermal analyzer. The obtained results disclosed that main fatty acids of POME and CKOME were palmitic acid (C16:0) and oleic acid (C18:1) while that of WCOME were oleic acid (C18:1) and linoleic acid (C18:2). It was evident that kinematic viscosity, specific gravity and flash point of biodiesels were above the limit prescribed by the diesel fuel standard. Lubricity of all biodiesels was bounded by the limitation of diesel specification. CKOME possessed excellent lubricating properties among biodiesels tested. The combustion of WCOME lowered CO, HC and smoke emissions compared to POME while the combustion of CKOME produced similar CO, HC and smoke emissions with more benefit in NOx emissions compared to POME. PM emissions caused by the combustion of biodiesel derived from WCOME and CKOME tended to oxidize easier than those of diesel fuel because the lower temperature for maximum soot oxidation by thermo-gravimetric analysis was obtained. Consequently, biodiesel derived from waste cooking oil and waste chicken oil can be considered as potential candidates to replace the biodiesel derived from palm oil as main feedstock of biodiesel production in Thailand without any penalty in exhaust emissions.

Experimental investigation of soot and radiation characteristics in ethylene/propane buoyant diffusion flames

Experimental study was carried out on the soot and radiation characteristics of ethylene/propane buoyant diffusion flames. Characteristics reported include flame natural luminosity, average soot distribution, maximum soot volume fraction, probability density function, soot yield, radiation flux and flame radiation fraction. Results showed that for a constant burning rate of 1.0 kW, different soot and radiation levels of flames produced can be achieved by adjusting gas composition of fuel mixtures. Propane exhibited a synergistic effect on the soot formation, resulting in nonlinear relationship between the maximum soot volume fractions and blending ratios. Based on the analysis of characteristic lengths and characteristic mixture fractions, a correlation of characteristic soot volume fraction with blending ratio was proposed to predict the maximum soot volume fraction of buoyant diffusion flames. The skewed distribution of probability density function elucidates differences in the effect of blending ratio on soot intermittence in the flames. Flame radiation fraction was proportional related to maximum soot volume fraction and linear correlated with soot yield. The analysis provided new comprehensive understanding of relationship between soot formation and fuel mixture, and could further apply to establish flame radiation equivalence principles of real fire emulation in fire research, fire safety testing and fire-fighting training.

Impact of n-butanol substitution in ethylene on soot yields in laminar diffusion flames at pressures 3 to 10 bar

Bioalcohols are perceived to be cleaner burning fuels and generally are assumed to be soot suppressants when blended with hydrocarbon fuels. Butanol isomers display some superior physical and chemical properties as compared to methanol and ethanol, and could be blended with hydrocarbon based transportation fuels without substantial modifications in engine hardware. However, the controversy in the literature about the influence of lower alcohols on soot when blended with hydrocarbons at various proportions has not been resolved yet. Further, there is a lack of information on the dependence of soot production on pressure obtained from tractable flames of butanol-hydrocarbon blends. Such benchmark information on the behaviour of soot characteristics at elevated pressures would be helpful to facilitate a better interpretation of the soot emissions from engines fuelled with butanol-hydrocarbon blends as well as providing data that could be used for numerical simulation efforts. Soot volume fractions and temperature fields of laminar coflow diffusion flames of a nitrogen-diluted ethylene base fuel and of the base fuel doped with 10% n-butanol were measured at operating pressures of 3, 5, 8 and 10 bar in a high-pressure chamber with optical access. Radially resolved temperatures and soot volume fractions were inferred from spectrally resolved radiation emitted by soot from the flames, stabilized on a 3 mm diameter burner, in which carbon and nitrogen mass flow rates in the fuel stream were kept constant. Maximum soot yield decreased by about 25% to 45% when 10% of the carbon in the fuel stream is provided by n-butanol throughout the pressure range; although local enhancements in soot production were observed at 3 bar. However, increases in local soot production disappeared when the pressure is increased to 8 and 10 bar. Current results were compared to ethanol substitution in the same base fuel under identical conditions.

Activity of Catalytic Ceramic Papers to Remove Soot Particles—A Study of Different Types of Soot

Diesel soot particles are of concern for both the environment and health. To catalytically remove them, it is important to know their structure and composition. There is little described in the literature on how catalysts favor the combustion of different soot fractions. In this work, programmed temperature oxidation (TPO) experiments were carried out using Co,Ce or Co,Ba,K catalysts supported on ceramic papers. Soot particles were obtained by burning diesel fuel in a vessel (LabSoot) or by filtering exhaust gases from a turbo diesel engine in a DPF filter (BenchSoot), and compared with a commercial diesel soot: Printex U. Various characterization techniques were useful to relate the characteristics of both the soot particles and the catalysts with the TPO results. The maximum catalytic soot burn rate (TM) temperatures were in the range of diesel exhaust temperatures that would facilitate in-situ regeneration of the DPF. The Co,Ba,K catalyst showed a higher catalytic effect in LabSoot, as the latter exhibited the largest primary particles and the higher order of graphene layers, for which the potassium-containing catalyst improves the contact between soot and catalyst and favors the combustion of soot, while the Co,Ce catalyst preferentially enhanced the combustion of commercial soot by supplying active oxygen.

Effect analysis on pressure sensitivity performance of diesel particulate filter for heavy-duty truck diesel engine by the nonlinear soot regeneration combustion pressure model

In this paper, the nonlinear soot regeneration combustion pressure model (NSRCMP model) is established and employed for Diesel Particulate Filter (DPF) simulation study. The NSRCMP model is reliable and accurate under simulation and experimental conditions of the process of clean filter, soot loading and soot regeneration combustion. The DPF soot loading response time and pressure drop are investigated under the parameter changes of cell density, wall thickness and permeability. It is a new attempt to measure the DPF pressure sensitivity by the trend of different design parameters. Cell density and permeability affect the soot loading time dramatically and the maximum and minimum soot loading time ratio is 3. Cell density and permeability make a significant pressure drop change through the pressure sensitivity comparisons. The corresponding ratio of maximum pressure sensitivity parameter is 2.4 when the cell density is 100 cpsi. The comparison results of pressure sensitivity under different permeabilities show a fixed ratio of 1.4. The results show that cell density is the key parameter to affect the overall system pressure. The influence of wall thickness on pressure sensitivity is not sensitive to the change of configurations of DPFs.

In situ growth of ceria nanofibers on cordierite monoliths for diesel soot combustion

The direct in situ growth of CeO2 nanofibers was performed by hydrothermal synthesis on cordierite monoliths for the diesel soot combustion reaction. They were characterized by SEM (Scanning Electron Microscopy), XRD (X-Ray Diffraction), LRS (Laser Raman Spectroscopy), textural analysis and adherence test. The mechanical stirring during the synthesis was essential to obtain the desired nanofibers, as well as a homogeneous coverage throughout the monolith with a very good anchoring to the substrate. The CeO2 nanoarray monolithic catalyst exhibited a catalytic oxidation activity similar to that obtained for bare CeO2 fibers (temperature of maximum soot combustion rate, TM = 428 °C). Raman in situ experiments along with kinetic analysis indicated that the amorphous fraction of carbon burned more easily than the graphitic fraction. Successive reaction runs indicated that the nanoarray of CeO2 fibers partially deactivated, especially after 800 °C. However, TM was 477 °C, being this last value about 100 °C lower than the non-catalytic soot combustion temperature.

The effects of intake temperature on reactivity controlled compression ignition combustion under high load

AbstractIn order to improve of high loaded diesel engine with high ethanol substitution rate, the effects of intake temperature on the combustion characteristics and generation characteristics of pollutants in cylinder from reactivity controlled compression ignition (RCCI) engine under high load was studied numerically. RCCI experimental data were obtained from a four cylinder turbocharged diesel engine fuel modified to run with diesel/ethanol dual fuel in the study. The simulation was performed via converge computational fluid dynamics (CFD) code, and numerical results were validated with the experimental data. The parameters such as cylinder pressure, cylinder temperature, heat release rate (HRR), CA10, CA50, indicated thermal efficiency, maximum pressure rise rate, NOx, soot, HC and CO emissions were investigated at 2000 rpm engine speed and high engine load (80% full load). The results show that decreasing intake temperature reduces the peaks of cylinder pressure and cylinder temperature, the HRR profile changes from double peak to single peak; the CA10 and the CA50 is retarded; maximum pressure rise rate and indicated thermal efficiency decrease. In addition, with the decreasing of intake temperature, the peaks of NOx, soot and CO generated in cylinder decreases, while the peaks of unburned HC generated in cylinder almost remain constant. Thus it can be seen that using optimal intake temperature is an effective way to improve ethanol substitution rate of diesel engine under high load.

Modeling soot particles as stable radicals: a chemical kinetic study on formation and oxidation. Part I. Soot formation in ethylene laminar premixed and counterflow diffusion flames

Based on recent theoretical and experimental evidences, this work proposes a detailed discrete sectional soot model considering particles and aggregates behaving as stable radicals, paving the way for the implementation of a game-changing assumption in soot kinetic models. The concentration of large closed-shell and open-shell polycyclic aromatic hydrocarbons (PAHs) levels out with the increase of their aromatic structure and, contrary to conventional assumptions in existing soot models, their reactivity approaches that of persistent radical species. These findings were implemented in the model here proposed to describe soot formation (Part I) and oxidation (Part II). While the number of lumped pseudo-species involved is significantly reduced compared to previous discrete sectional soot models since no distinction between the kinetics of closed-shell and open-shell particles is taken into account, the physical meaning and consistency with recent evidences improves together with model performances. Rate parameters of gas-phase reactions involving resonantly stabilized radical PAHs were used as a reference for soot particle kinetics. The model was validated against 65 target ethylene laminar premixed flames and counterflow diffusion flames, with a general good agreement between experimental data and numerical simulations at different pressures (P = 1–8 atm), maximum flame temperatures (Tmax∼1500–2400 K) and soot yields (fv∼0.01 to ∼170 ppm). Parity diagrams allow to identify systematic deviations of the present model from the experiments, while the comparison between all the flames included in the database highlights the relative contribution to soot formation and growth of the main reaction classes constituting the soot model, spotting analogies and peculiarities of the two flame configurations considered. Similar kinetic patterns characterize most of the flames within the database, independently of flame configuration and sooting tendency of the specific case. Large PAH condensation dominates the formation of the first soot nuclei, while the condensation of smaller PAHs up to four aromatic rings is primarily responsible for the growth of larger soot particles and aggregates. Finally, the contribution of the different fluid dynamics in premixed and counterflow flames to particle evolution, resulting in a higher hydrogenation level of soot particles in the latter, is discussed.