Carbon particulate matter incineration in diesel engine emissions using indirect nonthermal plasma processing

One of the promising applications of nonthermal plasma (NTP) for environmental cleanup technology is low-temperature oxidation or incineration of carbon particulate matter (PM) in diesel engine emissions. In this process, NO₂ and activated radical species induced by NTP can incinerate carbon PM trapped by a diesel particulate filter (DPF) at low temperature (< 300 °C). In the present study, an experiment was carried out on indirect NTP DPF regeneration for real diesel engine emissions comprising CO₂ of several per cent, hydrocarbons of several hundreds of ppm and moisture of several tens of percentages. It was confirmed that DPF regeneration is possible for a real diesel emission at a low temperature of 280 °C. The removal energy efficiency was estimated to be 0.82 g/kW h. This electric power range is sufficient to meet the recently proposed long-term national regulation for diesel automobiles in Japan.     

柴油机过滤体逆向喷气再生系统的模拟与试验研究

进行了柴油机过滤体逆向喷气再生系统的模拟与试验研究。采用计算流体力学软件Star-Cd,利用当量连续方法,建立了微粒捕集器的数学模型,分析了反吹管结构对过滤体内反吹气流的流动均匀性和压力损失的影响,并进行了试验验证。计算结果与试验结果有较好的一致性,表明所建立的流动模型可用来预测不同捕集器结构的过滤体内部的流动特征;螺旋喷吹的双反吹管结构可使过滤体的再生更加均匀。     

DOC+DPF在防爆柴油机上的应用研究

在某型防爆柴油机加装DOC+DPF后处理装置上进行台架实验,结果表明,PY03型装置不会增大防爆柴油机系统的排气背压,对CO平均转化效率达96%,对颗粒物有较高的捕集和再生效率,不透光烟度平均转化效率为82.7%;PY02型装置因尺寸较小,热负荷较高,与该排放状况不匹配。为提高装置的利用率和使用寿命,通过对耦合的DOC+DPF孔道进行可燃性气体CO组分输运和颗粒物离散相数值模拟。结果表明:随着废气流速的增大,DOC+DPF出口废气中CO浓度升高,转化效率下降;15 m/s的气流速度是发动机该排放水平下转化效率最高的最大速度;孔道入口速度增大,颗粒物向孔道后端壁面沉积;DOC+DPF装置在防爆柴油机上实用可行。     

Experimental investigation of impact of diesel particulate filter on smoke and NO<Subscript>x</Subscript> emissions of a Euro-I compression ignition engine with active and off-board regeneration

Old engines (Euro III or earlier) produce more emissions, and it will be difficult to entirely stop their usage especially in developing and under-developed nations; hence, it is desired that appropriate emission reduction technologies are tested on such engines to analyze their feasibility and economical acceptability. While most such studies have been conducted on constant speed stationary engines and modern engines, this study tried to analyze the effectiveness of an uncoated wall-flow type ceramic diesel particulate filter on a Euro-I, water-cooled, direct injection, variable speed, compression ignition engine in a laboratory set-up in India. Also, this study focused on diesel particulate filter regeneration by two methods: active regeneration by diesel injection in the particulate filter using an electronic control unit and off-board regeneration by taking out and heating the diesel particulate filter in an electrical resistance furnace at 650 °C for 10 h. The results, in the form of smoke emission, NO_x emission and engine performance, obtained using both the regeneration methods were analyzed, and conclusions were drawn. It was found that using diesel particulate filter, particulate matter emissions (smoke) were almost entirely eliminated. It was also found that off-board regeneration had numerous advantages compared to active regeneration. Since a furnace would be needed for off-board regeneration, an exchange process for diesel particulate filter is suggested.     

Diesel emission control: Catalytic filters for particulate removal

The European diesel engine industry represents a vital sector across the Continent, with more than 2 million direct work positions and a turnover of over 400 billion Euro. Diesel engines provide large paybacks to society since they are extensively used to transport goods, services and people. In recent years increasing attention has been paid to the emissions from diesel engines which, like gasoline engine emissions, include carbon monoxide (CO), hydrocarbons (HC) and oxides of nitrogen (NO_x). Diesel engines also produce significant levels of particulate matter (PM), which consists mostly of carbonaceous soot and a soluble organic fraction (SOF) of hydrocarbons that have condensed on the soot.

Meeting the emission levels imposed for NO_x and PM by legislation (Euro IV in 2005 and, in the 2008 perspective, Euro V) requires the development of a number of critical technologies to fulfill these very stringent emission limits (e.g. 0.005 g/km for PM). This review is focused on these innovative technologies with special reference to catalytic traps for diesel particulate removal.     

Oxidation treatment of diesel soot particulate on CexZr1-xO2

Catalytic oxidation of diesel soot particulate on Ce(x)Zr(1-x)O(2) catalysts was investigated. Results indicated that Ce/Zr ratios had a significant influence on the catalytic activities. Compared with the ignition temperature (T(i)) of uncatalyzed soot combustion, T(i) of Ce(0.5)Zr(0.5)O(2) with the best catalytic behavior decreased by 80 degrees C. The reactant gas compositions (O(2), H(2)O and NO) affected the catalytic activities too. O(2)-TPD, TG-DTA and XPS characterization results showed that Ce(x)Zr(1-x)O(2) released lattice oxygen continuously to promote the soot combustion even no gas oxygen occurred in the reaction atmosphere. The mechanisms of spill-over and reduction/oxidation functioned synergistically for soot catalytic combustion.     

Multiwavelength Raman microspectroscopy for rapid prediction of soot oxidation reactivity

Multiwavelength Raman microspectroscopy (MWRM) analysis for characterization of soot structure and reactivity was developed. This new method is based on the dispersive character of carbon D mode in Raman spectra (i.e., red shift and increase in intensity at higher excitation wavelength, λ(0)). The approach was proven by investigating various diesel soot samples and related carbonaceous materials at different λ(0) (785, 633, 532, and 514 nm). In order to compare the behavior of the D mode for various samples and to derive a single parameter characterizing the soot structure, the difference of integrals for pairs of spectra collected at different λ(0) was calculated. MWRM analysis revealed substantial differences in the structural ordering which decreases from graphite, over Printex XE2 and various diesel soot samples, to spark discharge soot. To obtain the relation between structure and reactivity of soot, MWRM analysis was combined with temperature-programmed oxidation (TPO). TPO allowed us to characterize the oxidation behavior of soot in terms of the maximum emission (CO + CO(2)) temperature and reactivity index. The latter was calculated by introducing the reactivity limits: spark discharge soot containing a large amount of disorder represents the upper limit, whereas the lower limit is given by graphite powder with high structural order. The comparison of MWRM (viz., the observed Raman difference integrals) and TPO data revealed a linear correlation between soot structure and oxidation reactivity. Thus, we demonstrated for the first time the potential of MWRM for a robust and rapid prediction of diesel soot reactivity based on the structure-reactivity correlation.     

Sooting behavior of ethanol droplet combustion at elevated pressures under microgravity conditions

Liquid ethanol is widely used in practical fuels as a means to extend petroleum-derived resources or as a fuel additive to reduce emissions of carbon monoxide from spark ignition engines. Recent research has also suggested that ethanol and other oxygenates could be added to diesel fuel to reduce particulate emissions. In this cursory study, the combustion of small ethanol droplets in microgravity environments was observed to investigate diffusion flame characteristics at higher ambient pressures and at various oxygen indices, all with nitrogen as the diluent species. At the NASA Glenn Research Center 2.2-second drop tower, free ethanol droplets were ignited in the Droplet Combustion Experiment (DCE) apparatus, and backlit and flame view data were collected to evaluate flame position and burning rate. Profuse sooting was noted above 3 atm ambient pressure. In experiments performed at the Japan Microgravity Center 10-second (JAMIC) drop shaft with Sooting Effects in Droplet Combustion (SEDC) apparatus, the first data that displayed a spherical sootshell for ethanol droplet combustion was obtained. Because of the strong sensitivity of soot formation to small changes in an easily accessible range of pressures, ethanol appears to be a simple liquid fuel suitable for fundamental studies of soot formation effects on spherical diffusion flames. The results impact discussions regarding the mechanism of particulate reduction by ethanol addition to fuels in high-pressure practical combustors.     

洋葱状纳米碳烟颗粒在基础油中的摩擦学性能

在SRV IV摩擦磨损试验机上,采用球-盘接触方式考察了不同载荷下碳烟颗粒在150SN基础油中的摩擦学性能。借助三维表面形貌仪、扫描电子显微镜、能谱仪、X射线光电子能谱仪及拉曼光谱探讨了载荷诱导的碳烟颗粒的减摩作用机理。结果表明,载荷对碳烟颗粒在150SN基础油中摩擦学特性有较大影响。低载荷时,碳烟颗粒可以改善基础油的抗磨性能;高载荷时,碳烟能够改善基础油的减摩性。载荷诱导的碳烟颗粒的减摩机理与其洋葱状的纳米结构有关,高载荷下碳烟颗粒外层的石墨微晶被剥离,在摩擦副表面形成了减摩层,使摩擦系数下降。     

Comparison of the characteristics of double-pass erbium-doped superfluorescent fiber sources obtained from different flattening techniques

We investigate and compare the characteristics of erbium-doped superfluorescent fiber sources (SFS's) obtained from the use of different flattening techniques in double-pass forward (DPF) and double-pass backward (DPB) configurations. The intrinsic flattening technique consists of optimizing the length of the erbium-doped fiber. The extrinsic flattening methods include the addition of a samarium-doped fiber (SDF) and a fiber-Bragg-grating (FBG) notched filter at the output end separately to shape the SFS spectrum. Although intrinsically flattened DPF and DPB SFS's have a large output power of >34 mW, they are accompanied by an ~3-dB ripple. The FBG-flattened DPF and DPB SFS's can achieve a wide linewidth of 35 nm with a small ripple of ~1.7 dB and better pump-power-dependent mean-wavelength stability; SDF-flattened DPF and DPB SFS's are inferior because of the SDF's lossy spectrum.     

柴油车微粒捕集器过滤材料研究进展

论述了几种类型过滤材料的特性及在柴油车微粒捕集器中的应用状况，分析了过滤材料面临的几个主要问题，并展望了其应用前景。     

New alternative (partially homogeneous) combustion process as a method for reduction of concentrations of nitric oxides and soot in combustion products of diesel

A new alternative (partially homogeneous) combustion process in diesel engines is proposed that provides changes in local values of the excess air coefficient and the temperature of the working substance in ranges lying beyond the area of the formation of nitric oxides and soot. It is important that the process is realized without significant changes in the serial construction. Modeling of the alternative process and the traditional diesel engine process is carried out on the basis of fundamental equations of three-dimensional nonstationary transfer in combination with models of combustion and formation of harmful substances: nitric oxides and soot. The set of equations for the model of the diesel cylinder with moving boundaries (valves, piston) is used in the Reynolds form and is closed by means of the k-ξ-f turbulence model considering the near-wall anisotropy of turbulence. The developed 3D models of the diesel engine work process are realized in the CFD code of the AVL-FIRE software complex. It is found that transition from the classic diesel engine process to partially homogeneous combustion makes it possible to block practically completely the formation of nitric oxides and to decrease soot emission substantially.     

Persistent free radicals, heavy metals and PAHs generated in particulate soot emissions and residue ash from controlled combustion of common types of plastic

The production and use of polymeric materials worldwide has reached levels of 150 million tonnes per year, and the majority of plastic materials are discarded in waste landfills where are burned generating toxic emissions. In the present study we conducted laboratory experiments for batch combustion/burning of commercial polymeric materials, simulating conditions of open fire combustion, with the purpose to analyze their emissions for chemical characteristics of toxicological importance. We used common types of plastic materials: poly(vinyl chloride) (PVC), low and high density poly(ethylene) (LDPE, HDPE), poly(styrene) (PS), poly(propylene) (PP) and poly(ethylene terephthalate) (PET). Samples of particulate smoke (soot) collected on filters and residue solid ash produced by controlled burning conditions at 600-750 degrees C are used for analysis. Emissions of particulate matter, persistent free radicals embedded in the carbonaceous polymeric matrix, heavy metals, other elements and PAHs were determined in both types of samples. Results showed that all plastics burned easily generating charred residue solid ash and black airborne particulate smoke. Persistent carbon- and oxygen-centered radicals, known for their toxic effects in inhalable airborne particles, were detected in both particulate smoke emissions and residue solid ash. Concentrations of heavy metals and other elements (determined by Inductively Coupled Plasma Emission Spectrometry, ICP, method) were measured in the airborne soot and residue ash. Toxic heavy metals, such as Pb, Zn, Cr, Ni, and Cd were relatively at were found at low concentrations. High concentrations were found for some lithophilic elements, such as Na, Ca, Mg, Si and Al in particulate soot and residue solid ash. Measurements of PAHs showed that low molecular weight PAHs were at higher concentrations in the airborne particulate soot than in the residue solid ash for all types of plastic. Higher-ringed PAHs were detected at higher concentrations in the residue solid ash of PVC as compared to those from the other types of plastic. The open-air burning of plastic material and their toxic emissions is of growing concern in areas of municipal solid waste where open-fires occur intentionally or accidentally. Another problem is building fires in which victims may suffer severe smoke inhalation from burning plastic materials in homes and in working places.     

Size determination of diesel soot particles using flow and sedimentation field-flow fractionation

The applicability of field-flow fractionation (FFF) was investigated for determination of size and size distribution of diesel soot particles. A sample preparation procedure was developed for FFF analysis where soot particles are recovered from filters in an ethanol bath sonicator, and then they are dispersed in water containing 0.05% Triton X-100 and 0.02% NaN(3). Mean diameters obtained from sedimentation FFF (SdFFF) and flow FFF (FlFFF) agree well with each other and are in good agreement with diameters obtained from photon correlation spectroscopy (PCS) and scanning electron microscopy. The relative error was less than 11%. Data show diesel soot particles have broad size distributions ranging from 0.05 up to ～0.5 μm with the mean diameters between 0.1 and 0.2 μm. The use of FlFFF is more convenient as FlFFF fractograms can be converted directly to size distributions, while the conversion of the SdFFF fractogram needs the particle density information. The density needed for SdFFF analysis was obtained by combining the SdFFF retention data with the PCS size data. For samples whose density is known, SdFFF may be more useful as SdFFF provides a wider dynamic range than FlFFF under constant field strength.     

A calibration-independent laser-induced incandescence technique for soot measurement by detecting absolute light intensity

Laser-induced incandescence (LII) has proved to be a useful diagnostic tool for spatially and temporally resolved measurement of particulate (soot) volume fraction and primary particle size in a wide range of applications, such as steady flames, flickering flames, and Diesel engine exhausts. We present a novel LII technique for the determination of soot volume fraction by measuring the absolute incandescence intensity, avoiding the need for ex situ calibration that typically uses a source of particles with known soot volume fraction. The technique developed in this study further extends the capabilities of existing LII for making practical quantitative measurements of soot. The spectral sensitivity of the detection system is determined by calibrating with an extended source of known radiance, and this sensitivity is then used to interpret the measured LII signals. Although it requires knowledge of the soot temperature, either from a numerical model of soot particle heating or experimentally determined by detecting LII signals at two different wavelengths, this technique offers a calibration-independent procedure for measuring soot volume fraction. Application of this technique to soot concentration measurements is demonstrated in a laminar diffusion flame.     

Influence of ethanol-diesel blended fuels on diesel exhaust emissions and mutagenic and genotoxic activities of particulate extracts

This study was aimed at evaluating the influence of ethanol addition on diesel exhaust emissions and the toxicity of particulate extracts. The experiments were conducted on a heavy-duty diesel engine and five fuels were used, namely: E0 (base diesel fuel), E5 (5%), E10 (10%), E15 (15%) and E20 (20%), respectively. The regulated emissions (THC, CO, NOx, PM) and polycyclic aromatic hydrocarbon (PAH) emissions were measured, and Ames test and Comet assay, respectively, were used to investigate the mutagenicity and genotoxicity of particulate extracts. From the point of exhaust emissions, the introduction of ethanol to diesel fuel could result in higher brake specific THC (BSTHC) and CO (BSCO) emissions and lower smoke emissions, while the effects on the brake specific NOx (BSNOx) and particulate matters (BSPM) were not obvious. The PAH emissions showed an increasing trend with a growth of ethanol content in the ethanol-diesel blends. As to the biotoxicity, E20 always had the highest brake specific revertants (BSR) in both TA98 and TA100 with or without metabolizing enzymes (S9), while the lowest BSR were found in E5 except that of TA98-S9. DNA damage data showed a lower genotoxic potency of E10 and E15 as a whole.     

Physical characterization of fine particulate matter inside the public transit buses fueled by biodiesel in Toledo, Ohio

This study presents the physical characteristics of fine particulate matter (PM) collected inside the urban-public transit buses in Toledo, OH. These buses run on 20% biodiesel blended with ultra-low sulfur diesel (ULSD) (B20). For risk analysis, it is crucial to know the modality of the size distribution and the shape factor of PM collected inside the bus. The number-size distribution, microstructure, and aspect ratio of fine PM filter samples collected in the urban-public transit buses were measured for three years (2007-2009), using an environmental scanning electron microscope (ESEM) coupled with energy dispersive X-ray spectrometry (EDX). Only the reproducible results from repeated experiments on ESEM and size distribution obtained by the GRIMM dust monitor were used in this study. The size distribution was found bi-modal in the winter and fall months and was primarily uni-modal during spring and summer. The aspect ratio for different filter samples collected inside the bus range from 2.4 to 3.6 in average value, with standard deviation ranging from 0.9 to 7.4. The square-shaped and oblong-shaped particles represent the single inhalable particle's morphology characteristics in the air of the Toledo transit buses.     

Controlling automotive exhaust emissions: successes and underlying science

Photochemical reactions of vehicle exhaust pollutants were responsible for photochemical smog in many cities during the 1960s and 1970s. Engine improvements helped, but additional measures were needed to achieve legislated emissions levels. First oxidation catalysts lowered hydrocarbon and carbon monoxide, and later nitrogen oxides were reduced to nitrogen in a two-stage process. By the 1980s, exhaust gas could be kept stoichiometric and hydrocarbons, carbon monoxide and nitrogen oxides were simultaneously converted over a single 'three-way catalyst'. Today, advanced three-way catalyst systems emissions are exceptionally low. NOx control from lean-burn engines demands an additional approach because NO cannot be dissociated under lean conditions. Current lean-burn gasoline engine NOx control involves forming a nitrate phase and periodically enriching the exhaust to reduce it to nitrogen, and this is being modified for use on diesel engines. Selective catalytic reduction with ammonia is an alternative that can be very efficient, but it requires ammonia or a compound from which it can be obtained. Diesel engines produce particulate matter, and, because of health concerns, filtration processes are being introduced to control these emissions. On heavy duty diesel engines the exhaust gas temperature is high enough for NO in the exhaust to be oxidised over a catalyst to NO2 that smoothly oxidises particulate material (PM) in the filter. Passenger cars operate at lower temperatures, and it is necessary to periodically burn the PM in air at high temperatures.     

Conductive particulate films fabricated by electrospray deposition of candle soot suspensions with acid treatment

The electrical properties of carbon-based materials have attracted significant interest due to their wide range of potential applications. This study investigated the effect of nitric acid treatment on the electrical conductivity of candle soot particle films. Electrospray deposition was used to deposit the candle soot dispersion on a solid substrate. The electrical conductivity of the films increased as the concentration of nitric acid increased, with the highest conductivity of 27.65 S cm⁻¹ observed in the film treated with 5 M nitric acid. The increase in conductivity was attributed to the enhancement of interparticle bonding between soot particles after acid treatment. Functional groups such as carboxylic or nitro groups were observed in the films by Fourier transform infrared (FTIR) spectroscopy. Raman spectroscopy showed a broadening of the D bands, suggesting a defect in the crystalline structure due to the formation of functional groups on the soot structure. These results suggest that nitric acid treatment can be used to improve the electrical conductivity of candle soot particle films.     

柴油机油烟的燃烧:其可溶有机组分含量对动力学参数的影响

论述了两种可溶有机组分含量(8w %,25w %)的柴油机油烟的燃烧机理。采用加热速率5℃ min～20℃ min非等温条件下的热重分析(TGA),考察了其在空气中的燃烧。应用Ozawa Flynn Wall方法,研究了析出物质的数据资料,并由复变非线性回归方法获得了各动力学参数。两种油烟的析出可根据三段机理予以模定,即:(1)可溶有机组分(SOF)的蒸发,(2)SOF热裂解,(3)炭基质燃烧。由于两种油烟所得的动力学参数非常近似,表明SOF含量对基质燃烧的影响极其有限。