Soot Production Research Articles

Ethanol supplement increases soot yields in nitrogen-diluted laminar ethylene diffusion flames at pressures from 3 to 5 bar

In spite of widely use of ethanol, mostly as a fuel extender in ground transportation engines, its sooting propensity with pressure and with ethanol content in the base fuel has not been clarified. Although, information on ethanol’s sooting and other combustion characteristics at atmospheric conditions is extensive, scaling this information to elevated pressures is problematic. Information that could be gathered from tractable laminar diffusion flames on the soot formation of ethanol’s response to pressure would be beneficial in assessing the soot emissions from engines fuelled with hydrocarbons supplemented with ethanol. To address this lack of information at pressures above atmospheric, high pressure soot formation in laminar co-flow diffusion flames fuelled by ethanol was investigated using nitrogen-diluted ethylene as the base fuel on a burner of 3 mm diameter fuel nozzle. Base fuel nitrogen to ethylene mass ratio was kept fixed at 6 for all experimental cases. In terms of total carbon mass flow, which was kept constant at 0.41 mg/s, ethanol’s contribution was varied as 0%, 10%, 30% and 40%, and the experiments were conducted at 3, 4, and 5 bar pressures. The main aim of the investigation was to evaluate the soot production at elevated pressures with increasing ethanol fraction in the fuel stream treating nitrogen-diluted ethylene as the other fuel component. Flame heights defined by the luminous visible tips did not display any significant changes as the ethanol fraction or pressure was changed. Spectrally-resolved line-of-sight soot radiation collected along the radial distance from the flame centreline at various heights above the burner exit with 1 mm increments was converted to radial soot temperature and volume fraction distributions through an Abel-type inversion algorithm. Within the bounds of pressure considered, soot production increased with the amount of ethanol added to the fuel stream. Largest incremental increase in soot production over ethylene diluted with nitrogen was observed at the condition with 10% carbon from ethanol in the fuel blend; further increases in ethanol fractions kept increasing the soot but at relatively lower rates. This non-linear effect with ethanol addition was discussed and it was argued that one of the reasons for this behavior is the influence of methyl radical produced by radical-induced decomposition of ethanol enhancing soot production for 10% ethanol case. With further increases in ethanol amount, this effect seems to slow down because of reduction in ethylene fraction and the increase in hydrogen to carbon ratio in the fuel stream at fixed carbon flow rate.

Influence of multiple pre-injection on engine performance based on exhaust gas control

With the development of the society, the emission laws are increasingly strict, and EGR and multiple pre-injection strategy can effectively reduce emissions. In order to study the influence of EGR rate and pre-injection on the emission and performance of engine, a computational fluid dynamics (CFD) simulation model was established based on GT power. By changing the EGR rate, the number of pre-injection and the amount of pre-injection, the best technology coupling point is explored. The results show that EGR can effectively reduce the generation of NOx, but it will lead to the increase of soot production and the decrease of power; pre-injection can improve the trade-off relationship between NOx and power.

Soot formation in turbulent flames of ethylene/hydrogen/ammonia

This paper presents an experimental study of turbulent non-premixed jet flames of ethylene/nitrogen where the nitrogen is substituted with different proportions of hydrogen and/or ammonia. The focus is largely on the effects of hydrogen and ammonia on soot production in turbulent flames. A combination of pointwise, laser-induced fluorescence in the visible and UV bands (LIF-UV–visible), and laser-induced incandescence (LII) is used to measure soot precursors and soot along the flame centerline. All signals are collected at a repetition rate of 10 Hz with fast photomultiplier tubes to resolve the time decay. In a separate experiment, joint imaging of LIF-OH CH is also performed at a repetition rate of 10 kHz. Hydrogen substitution is found to increase the production of soot, whereas ammonia substitution inhibits soot formation. The peak mean soot volume fraction is almost a factor of 3 lower in the 25% ammonia case in comparison to the 25% nitrogen case. The mean signal decay time constant decreases with ammonia substitution, implying the formation of smaller soot nanoparticles. The mean signal decay time constant remains unaffected with hydrogen substitution. Measured peaks in LIF-CH and LIF-OH are reduced with ammonia substitution but only in regions upstream of where soot is formed. Further downstream in the sooting region, neither OH nor CH appear to be affected by the substitution of N 2 with H 2 or NH 3 .

Effects of CO/H2/N2 addition on the soot morphology and nanostructure in laminar co-flow ethylene diffusion flame

This study investigated the effect of CO/H2/N2 addition on the morphological evolutions and nanostructures of soot generated from a laminar co-flow ethylene diffusion flame through utilizing the method of thermophoretic sampling and transmission electron microscopy (TEM). The additions were introduced into the inner tube along with the fuel stream, and the volume fractions of the additions are 10%, 20% and 30%. Specifically, the parameters of soot production, primary particle diameter (Dp), fractal dimension (Df), fractal pre-factor (kg) and the nanostructures were determined and analyzed. A reduction in soot production was observed with increasing proportion of the additives, demonstrating the addition of these diluent gases could inhibit the soot formation. Among the three additives, N2 is the most effective in reducing soot yield. The size analysis of soot particles and aggregates indicated the addition of CO or N2 could diminish the primary particle diameter and fractal parameters. The addition of H2 could reduce the primary particle diameter at the bottom flame while yields greater primary particles at 40 mm HAB. This result demonstrated that H2 addition may weaken the oxidation occurring on soot particles. High resolution transmission electron microscopy (HRTEM) analysis was also developed and the results showed that the addition of CO or H2 results in greater fringe length, smaller fringe tortuosity and inter-fringe spacing for soot particles, demonstrating the more orderly and compact lattice structure. In particular, the nanostructure parameters of soot particles in H2 enriched flame vary more significantly than those in CO enriched flame, demonstrating the soot nanostructure is more graphitized in H2 enriched flame. Different from the case of CO or H2 addition, the lattice characteristics for soot in the flames with N2 addition present inverse variation tendency.

Effects of carrier gas on the properties of soot produced by ethylene pyrolysis

Herein, we investigate the mechanism of soot formation produced by controlled-temperature pyrolysis of ethylene in Ar, He, or N2 and analyze the size distributions of soot particles to understand soot aggregation and nucleation behavior. Additionally, we probe the reactivity of soot, revealing that soot particles were highly unlikely to react with molecules of the above carrier gases. The use of Ar is demonstrated to promote soot production, facilitate crystalline growth, and increase the diameter of primary soot particles, while the use of He has an opposite effect, which is ascribed to the large size of the former molecules and the small size of the latter ones. Consequently, the soot generation mechanism is found to be affected by carrier gas type.

Differences in pool-fire induced soot production between subcooled spray and flash boiling spray in a DISI engine

Pool fire and fuel-rich combustion have been considered the primary soot/particulate matter sources for gasoline direct injection (GDI) engines, which is a crucial issue for commercial and passenger vehicles. Flash boiling atomization, achieved by heating the fuel before injection, can notably improve spray atomization and reduce the occurrence of pool fire, thus reduce soot emission under extreme conditions. This investigation compared the performance of subcooled spray combustions and flash boiling spray combustions with the use of an optical engine facility. The optical engine was equipped with an optical liner so that side views of the combustion can be captured with a high-speed color camera. The high-speed measurement data from early injection conditions were then analyzed with the HSV color model to investigate the flame characteristics in the premixed, infrared, and diffusion flame regions. Indicated mean effective pressure (IMEP) and particulate number (PN) under different conditions were also analyzed under different conditions. It was found that the combustion performance using flash boiling sprays is superior to that using subcooled sprays, and the difference between the two combustion modes was discussed with the use of the flame model.

Endoscopic fuel film, chemiluminescence, and soot incandescence imaging in a direct-injection spark-ignition engine

In direct-injection spark-ignition engines, fuel films formed on the piston surface due to impinging sprays are a major source of soot. Previous studies investigating the fuel films and their correlation to soot production were mostly performed in model experiments or optical engines. These experiments have different operating conditions compared to commercial engines. In this work, fuel films and soot are visualized in an all-metal engine with endoscopic access via laser-induced fluorescence (LIF) and natural incandescence, respectively. Gasoline and a mixture of isooctane/toluene were used as fuel for the experiments. The fuel films were excited by 266 nm laser pulses and visualized by an intensified CCD camera through a modular UV endoscope. Gasoline yielded much higher signal-to-noise ratio, and this fuel typically took an order of magnitude longer to evaporate than isooctane/toluene. The effects of injection time, injection pressure, engine temperature, and combustion on the fuel-film evaporation time were investigated. This film survival time was reduced with higher engine temperature, higher injection pressure, and later injection time, with engine temperature being the most significant parameter, whereas skip-fired combustion had very little effect on the film survival time. In complementary experiments, LIF from fuel films and soot incandescence were simultaneously visualized by an intensified double-frame CCD camera. At lower engine temperatures the fuel films remained distinct, and soot formation was limited to regions above the films, whereas at higher temperatures, fuel films, and hence the soot, appeared to be spread over the whole piston surface. Finally, high-speed imaging showed the spray, chemiluminescence, and soot incandescence, with results broadly consistent with fuel-film LIF and soot incandescence imaging.

Sooting characteristics of ethanol-ethylene blends in laminar coflow diffusion flames up to 10 bar

Ethanol, being a renewable product, has been perceived for a long time as a fuel that burns clean and more complete than conventional hydrocarbons as well as being thought as a soot suppressant in blends with gasoline and diesel fuel. Some of the results from a wide-range of studies investigating soot-suppression potential of ethanol at atmospheric pressure, including Smoke Point measurements, have yielded occasionally contradictory conclusions. Further, scaling of soot studies conducted under atmospheric conditions to engine-relevant pressures has always been problematic because of the non-monotonic response of combustion events to pressure. Ethanol’s soot inhibiting characteristics at elevated pressures under tractable conditions have not been previously documented and may not be inferred easily from atmospheric pressure measurements. Information from benchmark investigations with ethanol-hydrocarbon blends at elevated pressures could help in understanding the soot aerosol emissions from practical engines fueled with ethanol blends. Soot production in ethanol/ethylene laminar diffusion flames at elevated pressures was investigated on a 3 mm diameter coflow burner mounted in a high-pressure combustion vessel. Ethanol was added to ethylene, which is diluted with nitrogen, in various quantities from 0% to 40% in terms of total carbon of the fuel stream keeping the carbon flow rate constant at 0.41 mg/s. Experiments were conducted at pressures from 3 to 10 bar, and in addition to keeping the mass flow of carbon constant, the ratio of mass flow of nitrogen to mass flow of carbon was also kept fixed at 6 at the fuel nozzle. The soot spectral emission spectroscopy technique was used to obtain line-of-sight intensities of soot radiation which were then converted to radial soot temperature and volume fraction distributions at a given axial height within the flame. Soot production increased by a small but measurable amount with the fuel mixture containing 10% carbon from ethanol at 5 and 8 bar pressure flames indicating synergistic interactions; while at 3 and 10 bar, no measurable change was observed. When the ethanol’s carbon contribution was increased to 30% and 40%, soot formation was suppressed and the soot yields decreased below the soot level of neat nitrogen-diluted ethylene at 3 to 10 bar pressures. Sensitivity of soot production to pressure in ethylene/ethanol flames is found to be similar to that of ethylene up to 8 bar.

Methanol and OMEx as fuel candidates to fulfill the potential EURO VII emissions regulation under dual-mode dual-fuel combustion

Recent investigations show that there are different combustion strategies that promise to achieve higher efficiencies in internal combustion engines. Advanced combustion modes such as reactivity controlled compression ignition (RCCI) and dual-mode dual-fuel (DMDF) have proven to be able to achieve low NOx and soot engine-out emissions while being able to operate over the complete engine map. On another front, intensive research has been done in the fuels field. Oxygenated fuels, like oxymethylene dimethyl ethers (OMEx) and methanol, are of special interest because of their potential to reduce the soot emissions, while allowing to adjust parameters, such as EGR, to higher values to also reduce NOx emissions and avoid other problems like excessive in-cylinder peaks of pressure. In this research, the effects of diesel-methanol and OMEx-gasoline fuels were studied on a dual-mode dual-fuel (DFDM) multi-cylinder engine at 1800 rpm for various loads (25, 50, 80 and 100%). To do so, a dedicated calibration to optimize the brake thermal efficiency while trying to maintain NOx and soot emissions under EURO VI limitations was applied. Then, the combustion characteristics, performance and emissions results are compared to a base diesel-gasoline case. Boundary conditions (intake pressure, temperature and air mass) for each fuel combination where similar, with the exception of the premixed energy ratio, which was on average 20% lower for diesel-methanol. Each fuel combination was, weighted against each other by means of an merit function, where the fuel combination with the lowest value has the closest approximation to ideal BSFCeq, BSNOx, BSSoot, BSCO and BSHC targets. Results show that diesel-methanol presents no significant differences with respect to diesel-gasoline in terms of equivalent BSFCeq and NOx, while the substitution of diesel by OMEx in the dual-mode dual-fuel combustion has the potential of, although penalizing HC and CO emissions, not only achieving the EURO VI NOx (0.4 g/kWh) limits but also the future potential EURO VII (0.2 g/kWh) as well because of a negligible soot production that allows using EGR levels of up to 50%.

Soot properties in ethylene inverse diffusion flames blended with different carbon chain length alcohols

This study was devoted to the characterization of soot properties in ethylene inverse diffusion flames with different carbon length alcohols, which mainly contained the soot morphology, soot nanostructure, and oxidation reactivity. Ethanol, n-butanol, n-hexanol, and n-octanol were selected as the fuel additives. For all blended flames, a 30% volume fraction of ethylene was substituted by different alcohol additives, and the flow rates of the alcohols were adjusted to achieve the same number of carbon atoms. A combination of the thermophoretic sampling technique and the quartz plate sampling method was applied to gain soot features. The transmission electron microscopy (TEM), high-resolution transmission electron microscopy (HRTEM), Raman spectroscopy, and thermogravimetric analysis (TGA) were used. The results showed that soot production was reduced with the addition of all alcohols, and the minimum soot yield was observed with ethanol addition. The soot-reducing ability gradually decreased as the alcohols move higher. The sizes of the primary particles and soot aggregates increased slightly faster with the increasing carbon chain length. Furthermore, the soot generated from higher alcohol-doped flame has a higher degree of graphitization with longer fringe length and smaller fringe tortuosity. The four different alcohol additives all could improve soot oxidation reactivity. There was a correlation between soot oxidation reactivity and the carbon chain length of the alcohols that the longer carbon chain of these alcohol additives led to lower soot reactivity.

Formation and characteristics of soot from pyrolysis of ethylene blended with furan fuels

As two renewable oxygenated biofuels, 2,5-dimethylfuran and 2-methylfuran (DMF and MF) have been considered to be two of the most potential fuels in the future due to the development of the second-generation biosynthetic technologies. The atmosphere pyrolysis experiments with 0%, 25%, 50%, 75% and 100% replacement of ethylene by DMF/MF at 1173 and 1273 K were conducted. Collected soot samples were characterized by high resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TGA) to acquire their internal structure and oxidation reactivity. Results showed that soot mass was positively related with DMF addition ratios and the reaction temperature. Soot production was also enhanced when the MF addition ratio gradually increased from 0% to 75%. The influences of DMF addition can promote soot formation more obviously than MF. Temperatures showed a more significant influence on soot morphology than fuel types and DMF/MF addition ratios. For a fixed addition ratio of DMF/MF, soot showed liquid-like substances at 1173 K. At 1273 K, approximately round particles formed and linked together in chains. Moreover, at 1273 K, the aggregates obtained by adding MF contained more single particles, longer carbon chains, and larger projection area compared with the aggregates by adding same MF. For nanostructures, as the addition ratios of DMF/MF increased, as well as the reaction temperature improved, the fringe length of the carbon layer increased, the average fringe tortuosity decreased, and the stacking arrangement of soot became more orderly, the soot oxidation reactivity was lower. Under a same addition ratio and reaction temperature, soot obtained by adding DMF possessed slightly longer fringe length, smaller fringe tortuosity and lower oxidation reactivity than those of the soot obtained by adding MF. High correlation between fringe parameters and soot oxidation reactivity was discovered. The more ordered soot nanostructure, the longer fringe length, and the smaller fringe tortuosity could make the oxidation reactivity of soot get lower.

Soot formation in turbulent swirl-stabilized spray flames in a model combustor fueled with n-butanol/Jet A-1 blends

Information on sooting characteristics of n-butanol/middle distillate fuels from well-described spray flames is lacking but desirable as a benchmark which could help in better interpretation of the reciprocating engine data and can be used in numerical simulation validation efforts. The effects of n-butanol addition to turbulent swirl-stabilized JetA-1 spray flames were studied experimentally in a model gas turbine combustor with 94 mm × 94 mm cross-section and 188 mm length. n-Butanol was added in concentrations of 10% and 20% by energy content such that the total thermal power output was maintained at 10 kW in the globally fuel lean flames. Spray droplet size distributions and velocity fields were obtained using a Fraunhofer diffraction based droplet sizer and stereoscopic particle image velocimetry, respectively. Spatially resolved soot volume fraction and mean primary particle sizes were measured with auto-compensating laser-induced incandescence. Measurable differences in droplet size distributions were observed with n-butanol addition. Flow fields were similar in all flames. Time-averaged soot volume fraction peaks were observed in all flames at radial positions of approximately 0 mm and 27 mm and axial heights of approximately 20 mm and 40 mm, respectively. Soot production decreased monotonically throughout the flames with n-butanol addition. Primary soot particle diameters were generally within the range of 25 to 50 nm. Potential mechanisms explaining the changes observed with n-butanol substitution in jet fuel are discussed.

Numerical study of characteristics of liquefied petroleum gas flames in coflow air

Liquefied Petroleum Gas (LPG) is a fossil fuel mixture, widely used in domestic and industrial burners for several applications. Non-premixed flames are commonly preferred in these burners owing to their stability and controllability. However, based on operating conditions, non-premixed flames emit emissions such as CO and soot. Several techniques, including supply of coflow air and partial premixing of air with fuel, are used to abate these emissions. Due to multicomponent nature of LPG and its complex oxidation pathway, numerical studies on LPG flames are scarce in literature. However, such studies are helpful in the analysis of flames in several burners. With this motivation, systematic numerical simulations of canonical non-premixed coflow flames of LPG and air, without and with partial premixing of air in the fuel stream, have been presented. A two-dimensional axisymmetric domain is used to represent coflow burner. The numerical model includes sub-models to account for soot formation and its oxidation, and radiation energy loss due to participating species and soot. A short kinetic mechanism with 43 species and 392 elementary reactions is used. Results from the numerical model have been validated for flames of propane, n-butane and LPG. Coflow air is varied as proportions of stoichiometric air. Partial premixing of air to the fuel stream results in a reactant mixture that is not flammable. Characteristics of flames in all these cases are presented systematically using the fields of temperature, flow and species mass fractions. A relative comparison of soot production between all these cases is made. Results reveal that in coflow flames, the net soot emissions increase initially, reach a local maximum and then decrease. In partially premixed flames, soot emissions continuously decrease with an increase in the primary air and become almost negligible after a specified air addition to the fuel stream.

On the use of PIV, LII, PAH-PLIF and OH-PLIF for the study of soot formation and flame structure in a swirl stratified premixed ethylene/air flame

Soot formation and oxidation are investigated in swirl stratified premixed ethylene/air flames at atmospheric pressure. The effects of both swirl and stratification are studied to understand the relationship between the flame structure, soot precursors and soot. The topology of the flame is obtained with particle image velocimetry (PIV) and planar laser-induced fluorescence (PLIF) on hydroxyl radical (OH). The production of polycyclic aromatic hydrocarbons (PAHs) is investigated using PLIF by mainly probing the aromatic compounds with two benzene rings (i.e. naphthalene) that are known to actively participate in soot nucleation and growth. Soot production is investigated using laser-induced incandescence (LII), giving quantitative data on the soot volume fraction. Extensive information on the flame structure and the mechanisms of formation/consumption of soot is gathered based on the coupling of these laser diagnostics. An image analysis of velocity, OH, PAHs and soot distributions enables us to propose a scenario that describes the link between the inception, growth, aggregation and oxidation processes. In particular, the data reveal the presence of distinct zones for these processes: a thermal decomposition region in which PAHs contributes to nascent soot formation, organised as filaments along the interface between the PAH region and the inner recirculation zone (IRZ); a mixing region controlled by large moving structures that favour the growth and aggregation of nascent soot into mature soot; and an oxidation region leading to the fast consumption of soot particles. These processes are impacted to varying extents by the intensities of swirl and stratification.

Influence of Doped H2O or H2 on Soot Production and Power Capability in the Fuel-rich Gas Generator

ABSTRACT Influence of doped H2O or H2 on both soot production and power capability in the fuel-rich gas generator has been studied together by using the program of chemical equilibrium with applications (CEA). The oxidant is LOX, and the fuel is composed of Jet-A and the additive. The parameters of the gas generator are as follows: the range of combustion temperature is 800–1700 K, combustion pressure is 0.1–5.0 MPa, oxidant/fuel ratio is 0.1–1.2, and the mass percent of the additive in fuel is 0–60%. The results indicate that the addition of either H2O or H2 can obviously reduce the mass percent of soot in combustion products, and the reasons are discussed on the base of the products distributions. Moreover, the minimum amounts of addition to surrender mass percent of soot less than 0.1% are present. The effects of combustion pressure on soot mass percent in combustion products appear turning appoints around 1100 K, no matter the additive is H2O or H2. The addition of H2 can obviously improve the power capacity of combustion products in the whole temperature range. The addition of H2O can also improve slightly the power capacity of combustion products, when the combustion temperature is less than 1400 K. Effective molar weight of combustion products is the main factor affecting power capacity.

On the relative contributions of soot to radiative heat transfer at different oxygen indices in ethylene – O2/CO2 laminar diffusion flames

Soot concentration measurements in ethylene-O2/CO2 diffusion flames (fuel Re 120) encompassing oxidizer oxygen mole fractions (oxygen index, OI) of 35% to 90% were employed to validate a methodology for modeling soot production. A skeletal 10-step reaction mechanism and modeling the soot nucleation parameter (Cα) in the Moss-Brookes soot model as a function of OI provided adequate agreement with measurements. Cross-validation of the OI based Cα model was ascertained through ethylene-O2/CO2 diffusion flame simulations in a different experimental configuration (fuel Re 43, 35%-50% O2) by ensuring that peak soot concentrations were in good agreement with previously published results. A mesh resolution of 0.0625 mm within the flame was deemed necessary to obtain grid independent results. Despite increases in peak soot volume fractions and flame temperatures with OI, the radiant fraction (χR) (in-flame) decreases due to decreasing flame lengths. Although in-flame radiation is dominated by gases, the spectrally-continuous soot radiation plays an important role on χR (when it is assessed across the entire domain) due to the attenuation of flame radiation by the cold, radiatively-participating, co-flow. Consequently, in-flame radiation show a strong sensitivity to gas-radiative property models whereas χR when assessed across the entire domain is impacted by the choice of soot radiative property model.

Burning characteristics and soot formation in laminar methyl methacrylate pool flames

This study presents careful measurements from lab-scale experiments and predictions from comprehensive numerical model for the burning characteristics of laminar flames over MMA pools of different diameters with varying ullages or lip heights. Lab-scale experiments for steady burning of MMA pool are conducted, and temperature and concentrations of major species, have been measured for 3 mm ullage case for pool diameters of 25 and 30 mm. A compact kinetic mechanism with 49 species and 376 reactions, and a soot model are used for numerical simulations. Steady burning of laminar flame over an MMA pool is modelled using coupling heterogeneous interface conditions. Variable thermo-physical properties and multi-component diffusion are used. Results from grid-independent numerical simulations compare with reasonable accuracy against experimental measurements. For 25 mm MMA pool, the mass burning rate decreases rapidly from zero to 2 mm ullage and drops relatively gradually with further increase in the ullage. The ratio of mass of soot in the domain to mass of fuel burnt, decreases rapidly with an increase in ullage from zero to 3 mm, remains in same order till 5 mm ullage and then decreases with increasing ullage. Increased flame stand-off from the pool interface and oxygen penetration into the ullage causing partial premixing, form the reasons for the reduction in mass burning rate and decrease in the production of soot. The effects of pool diameter on burning characteristics at three ullages have also been presented.

Pressure effects on the soot production and radiative heat transfer of non-buoyant laminar diffusion flames spreading in opposed flow over insulated wires

Abstract This paper investigates experimentally and numerically pressure effects on soot production and radiative heat transfer in non-buoyant opposed-flow flames spreading over wires coated by Low Density PolyEthylene (LDPE). Experiments, conducted in parabolic flights, consider pressure levels ranging from 50.7 kPa to 121.6 kPa and an oxidizer flowing parallel to the wire's axis at a velocity of 150 mm/s and composed of 20% O2/80% N2 in volume. The numerical model includes a detailed chemistry, a two-equation smoke-point based soot production model, a radiation model coupling the Full-Spectrum correlated-k method with the finite volume method and a simple degradation model for LDPE. An analysis of the experimental data shows that the spread rate, the pyrolysis mass flow rate, and the residence time for soot formation are independent of pressure whereas the soot formation rate is third-order in pressure. The model reproduces quantitatively the effects of pressure on soot production and captures the transition from non-smoking to smoking flames. The radiant fraction increases with pressure because of an enhancement in soot radiation whereas the contribution of radiating gases remains approximately constant over the range of pressures considered. In addition, gas radiation dominates at pressure lower than 75 kPa whereas soot radiation prevails at higher-pressure levels. Consistently with the data obtained at normal gravity, the smoke-point transition is found to occur for a radiant fraction of about 0.3 and the soot oxidation freezing temperature is estimated in the range 1350–1450 K. Eventually, whatever the pressure considered, the surface re-radiation from the wire is higher than the incident radiative flux from the flame to the surface along the entire wire. This shows that radiative heat transfer contributes negatively to the heating of the unburnt LDPE and to the heat balance along the pyrolysing surface.

Microplasma ball reactor for JP-8 liquid hydrocarbon conversion to lighter fuels

Non-equilibrium microplasma technology is used as a non-conventional processing tool to attain fuel conversion efficiency. The microplasma was generated in a reactor with metal balls bouncing between parallel electrodes allowing energy control in a discharge. The released energy, in the range of 20–100 μJ per discharge initiates chain scission reactions to generate shorter chain hydrocarbons. The system consists of 300 reactors and is scaled and optimized to maximize power density while maintaining high efficiency for applications to Jet Propellant 8 (JP-8) fuel. Experiments demonstrate the ability of controlled chemistry (JP-8 to lighter hydrocarbons fuel conversion) without allowing excessive heat and carbon production. Analysis of gas products produced by JP-8 processing with specific energy input of 1450 kJ/kg demonstrates product distributions of 20.9%, 39.4%, 31.7%, 2.5%, 3.5% 1.3% by mass of H2, CH4, C2H4, C2H6, C3H6, C3H8 respectively and is 1.64% of the initial JP-8 mass (24 g). Soot production is only 0.07% of the JP-8 mass that results in a 35:1 product selectivity of gaseous compounds to soot. Calculated gas product yields of 11.7, 2.2, 0.99, 0.07, 0.07 and 0.02 molecules/100 eV for H2, CH4, C2H4, C2H6, C3H6, C3H8 respectively were observed and are generally higher than existing non-equilibrium processing technology.

Simulation of Turbulent Combustion in a Large Pulverized Coal Boiler Based on Turbulent Radiation Interaction and the Modified Soot Model.

A combustion heat transfer model suitable for engineering combustion simulation was developed. Using the model, pulverized coal combustion and the soot generation process were simulated in a 300 MW tangentially fired pulverized coal furnace. Here, we proposed a soot evolution model which includes the nucleation, growth, agglomeration, and oxidation processes in the pulverized coal combustion process based on the population balance method. In the process of heat transfer, the absorption coefficient is refined by considering the coal particles and soot radiation. Furthermore, turbulent radiation interaction (TRI) was introduced to the combustion model. Then, pulverized coal combustion and soot and NOX generation processes in a 300 MW tangentially fired pulverized coal furnace under different loads were studied. The results show that the simulated temperature field considering the effect of TRI is lower than that without TRI, and the simulation results considering the effect of TRI are closer to results from the field test. The error between the simulation results and the field tests is within 0.56%. The soot fraction is negatively correlated with temperature. The higher the temperature, the smaller the soot fraction. Taking into account the impact of TRI, the predicted soot production increased.