双燃料发动机缸内分层激光诱导荧光实验及化学动力学模拟研究

双燃料压燃（RCCI）是一种很有前景的发动机新型燃烧方式,能在小负荷到中高负荷范围内实现发动机高效清洁燃烧,为了将RCCI拓展到更高负荷,需要对其缸内燃油分层和燃烧过程开展更深入研究。本文在一台双燃料光学发动机上采用燃油-示踪剂平面激光诱导荧光法（PLIF）,对RCCI着火前缸内燃油分层进行定量测量,选用甲苯作为示踪剂,利用266 nm脉冲激光激发甲苯荧光,发动机转速1200 r·min^-1,平均指示压力6.9×10⁵ Pa,气道喷射异辛烷,缸内在上止点前10°喷射正庚烷。采用燃油-气体绝热混合假设,对PLIF测量结果进行温度不均匀性修正,以上止点后5°曲轴转角下的测量结果为例,不修正相比修正测试区域内的最大当量比高估15%。根据实验结果,利用Chemkin软件分析了活性、浓度和温度分层对燃烧滞燃期的影响,结果显示燃料活性分层和浓度分层共同决定RCCI的着火滞燃期,其中活性分层影响要大于浓度分层,而温度分层对着火滞燃期影响很小。RCCI燃烧过程自发光的高速成像结果表明,着火过程首先出现在燃烧室边缘的高活性区域,随后火焰向燃烧室中心处的低活性区域发展,碳烟辐射光图像显示碳烟主要形成于燃烧室边缘的高活性区域。     

Efficient reduction of NOx emissions from waste double-base propellant in co-pyrolysis with pine sawdust

Co-pyrolysis technology containing biomass offers remarkable advantages in reducing NO_x emissions economically and efficiently. In this work, it was innovatively introduced to solve the problem of excessive NO_x emission during the incineration of waste energetic materials (EMs). The kinetics and NO_x emission characteristics of waste double-base propellant (DP), pine sawdust (PS), and their mixtures with different ratios during pyrolysis were investigated by thermogravimetric analysis and fixed-bed experiments. The results showed that there was a significant interaction between DP and PS. Kinetic analysis by Friedman and Kissinger-Akahira-Sunose (KAS) methods demonstrated that the average activation energies of the mixtures with different ratios were smaller than that of DP, indicating that the addition of PS improved the reactivity of co-pyrolysis. In addition, the fixed-bed experiment determined that the lowest NO_x emission was achieved during DP pyrolysis alone at 900 ℃. Co-pyrolysis at this temperature was found to have synergistic effects of reduced NO_x emissions for different ratios of mixtures. The best synergistic effect was achieved at the mixing ratio of 60 wt% DP and 40 wt% PS, resulting in a 72.11 % reduction in actual NO_x emissions compared to the expected value. This study provides a new direction and powerful data support for the clean, efficient and economic treatment of waste EMs, especially for practical engineering strategies.     

Pilot-Scale Aftertreatment Using Nonthermal Plasma Reduction of Adsorbed NOx in Marine Diesel-Engine Exhaust Gas

Regulations governing marine diesel engine NO_x emissions have recently become more stringent. As it is difficult to fulfill these requirements by combustion improvements alone, effective aftertreatment technologies are needed to achieve efficient NO_x reductions. In this study, we develop an effective NO_x-reduction aftertreatment system for a marine diesel engine that employs combined nonthermal plasma (NTP) and adsorption. Compared with selective catalytic reduction, the proposed technology offers the advantages of not requiring a urea solution or harmful heavy-metal catalysts and low operating temperatures of less than 150 °C. The NO_x reduction comprises repeated adsorption and desorption flow processes using NTP combined with NO_x adsorbents made of MnO_x–CuO. High concentrations of NO_x are treated by NTP after NO_x adsorption and desorption, and this aftertreatment system demonstrates excellent energy efficiencies of 161 g(NO₂)/kWh, which fulfills the most recent International Maritime Organization emission NO_x standards in the Tier II–III regulations for 2016 and requires only 4.3 % of the engine output power.     

Experimental comparison of performance and emission characteristics of 4-stroke CI engine operated with Roselle and Jatropha biodiesel blends

The environmental degradation, combined with the continuous depletion of the world's fossil fuel reserves, has forced the search for alternative fuels. This study was performed to investigate the performance of novel biodiesels in the CI engine. The experiments were performed at three different compressions ratios (16:1, 17:1, 18:1) and four loading conditions (25%, 50%, 75%, 100%). Different types of fuels such as jatropha biodiesel (JB), roselle biodiesel (RB), and ternary biodiesel (TB) were prepared and analyzed. The thermal performance of different fuels was analyzed in terms of brake thermal efficiency (BTE), brake specific fuel consumption (BSFC), and exhaust gas temperature (EGT). The emission characteristics such as CO₂ emission, NO_x emission, and smoke emission were analyzed for all types of fuels. The results of these fuels in the engine were compared with mineral diesel (MD). The BTE was increased with increasing compression ratios and loads for all types of fuels. The BSFC was increased with increasing compression ratios but decreased with increasing loads. The increase in emission of NO_x was observed at higher compression ratios and loads. However, the CO₂ emission was decreased at higher loads and lower compression ratio. The performance curves achieved with a 20% jatropha biodiesel blend showed results that were approximate to those obtained with pure MD. The comparative analysis between different fuels showed that JB exhibit higher thermal performance as compared to other biodiesels. Therefore, JB can be a better alternative to conventional fuel.     

凹凸棒黏土对燃煤PM2.5排放及团聚捕集特性影响

在固定床反应系统上考察凹凸棒黏土对燃煤可吸入颗粒物PM_2.5的排放及团聚捕集特性影响,分析凹凸棒黏土添加量以及添加凹凸棒黏土情况下燃烧气氛、燃烧温度和钙硫物质的量比等参数对燃煤PM_2.5的数量浓度、质量浓度以及团聚捕集率的影响规律。结果表明,煤燃烧过程中添加凹凸棒黏土可以显著降低PM_2.5排放浓度,凹凸棒黏土的添加量不宜超过3%(质量分数);空气气氛下燃烧产生的PM_2.5多于O₂/CO₂气氛;随着钙硫物质的量比的增大,PM₁的质量浓度减小,但PM_1~2.5的质量浓度增大,颗粒物的粒径有向更大粒径转移的趋势;燃烧温度的升高会促进PM_2.5各粒径范围颗粒物的生成,降低了凹凸棒黏土对PM_2.5团聚捕集率。     

Oxygen storage capacity of substituted YBaCo4O7+δ oxygen carriers

Depletion of non-renewable energy sources are at elevated manner due to the rapid growth of industrialization and transportation sector in last few decades and leads to further energy demand. Biodiesels especially second-generation fuels from non-edible oil resources are alternate sources for replacement of diesel fuel in CI engines due to their considerable environmental benefits. In the present work, non-edible feedstock of Calophyllum inophyllum seed oil (tamanu oil) is used for biodiesel production. Transesterification method is used for preparation of biodiesel in the existence of methanol with NaOH as catalyst. The copper nanoparticles are synthesized by electrochemical method, and it is characterized by using X-ray diffraction analysis (XRD) and scanning electron microscopy (SEM). XRD and SEM results confirm the presence of copper nanoparticle and size of around 30 nm. This paper aims to investigate the effects of the copper additive nanoparticles with biodiesel blends on the engine performance, combustion and emission characteristics of single-cylinder direct-injection diesel engine and compared that with diesel fuel. The results showed that the addition of nano-additives enhances brake thermal efficiency and reduces specific fuel consumption compared to biodiesel blends but slightly lower than diesel. Combustion characteristics also are enhanced by improved oxidation reaction inside the combustion chamber which resulted in higher heat release rate. The emissions of HC, NO_x and O₂ are significantly reduced for nano-additive blends compared to diesel but increased CO₂ emission was observed. It is noticed that higher CO₂ emission and substantial reduction of unused O₂ emissions from engine fueled with nano-additive are evident for enhanced oxidation and better combustion. Energy and exergy analysis of the diesel engine is carried out to estimate the effect of using nanoparticle additive with biodiesel.

     

Role of nitrogen dioxide in the oxidation of diesel soot on promoted mixed catalysts with fluorite and perovskite structures

The oxidation of soot on catalysts with the perovskite and fluorite structures (including platinum-promoted catalysts) in the presence and in the absence of NO₂ was studied using in situ IR spectroscopy and temperature-programmed techniques (TPR, TPD, and TPO). It was found that, as a rule, the temperature of the onset of soot oxidation considerably decreased upon the addition of NO₂ to a flow of O₂/N₂, whereas the amount of oxygen consumed in soot oxidation considerably increased. To explain these facts, we hypothesized that the initiation of soot combustion in the presence of NO₂ was related to the activation of the NO₂ molecule through the formation (at a low temperature) and decomposition (at a high temperature) of nitrate structures on the catalyst. Superequilibrium amounts of NO₂ resulted from the decomposition of nitrate complexes immediately on the catalyst for soot combustion. Based on a comparison between catalyst activities and data obtained by TPR and the TPD of oxygen, a conclusion was drawn that the presence of labile oxygen in the catalyst is a necessary but insufficient condition for the efficient occurrence of a soot oxidation reaction in the presence of NO₂. The introduction of platinum as a constituent of the catalyst increased the amount of labile oxygen and, as a consequence, increased the amount of highly reactive nitrate complexes. As a result, this caused a decrease in the temperature of the onset of soot combustion.     

Study of combustion intermediates in fuel‐rich methyl methacrylate flame with tunable synchrotron vacuum ultraviolet photoionization mass spectrometry

A fuel‐rich premixed laminar methyl methacrylate (MMA)/O₂/Ar flame at low pressure (30 Torr) with the equivalence ratio (?) of 1.60 is studied in this work. Synchrotron vacuum ultraviolet photoionization combined with molecular beam mass spectrometry is employed to identify the combustion intermediates including isomeric intermediates. The observed combustion intermediates can be classified as four types: radicals, non‐cyclic hydrocarbons, cyclic hydrocarbons and oxygenates. Benzene is the unique aromatic hydrocarbon detected in this work, and several oxygenates with two oxygen atoms are identified. Mole fraction profiles of most intermediates are evaluated, which can help understand the MMA combustion mechanism under fuel‐rich conditions. The similarities among rich flames of MMA and other oxygenated fuels, as well as the characteristics of rich MMA flame, are also discussed. The results show that combustion of MMA not only reduces soot emissions, but also has low concentrations of some potential toxic by‐products. Copyright © 2008 John Wiley & Sons, Ltd.     

NO2 measurement artifacts in the presence of soot

Nitrogen dioxide is a regulated pollutant, which is measured routinely. Since it can be formed during combustion processes, it is often measured in the presence of soot. This study investigates the possible artifact formation due to the interaction of soot and NO₂ in the sampling lines and instrument prefilters. The transfer of varying NO₂ concentrations through filters and tubes coated with different kinds of soot was investigated by using a dedicated photoacoustic soot and NO₂ analyzer (TwinPAS). The effects of flow rate, temperature, relative humidity, tubing respectively filter material, soot reactivity, and passivation on the NO₂ measurement artifacts have been investigated. We found significant lags (up to 2 min) of the NO₂ transfer as well as total NO₂ losses of up 10 %.     

Easy synthesis of three‐dimensionally ordered macroporous CuO–CeO2 mixed oxide catalysts and their high activities for the catalytic combustion of soot

Three‐dimensionally ordered macroporous (3DOM) Cu_xCe‐M (x denote the mole ratio of Cu/[Ce + Cu]) oxide catalysts with large pore sizes and interconnected macroporous frameworks were successfully synthesized using a polymethyl methacrylate template method. The 3DOM structure improves the contact efficiency between catalyst and soot, which benefits soot elimination in the low temperature range. The low redox barriers of the 3DOM Cu–Ce solid solution also facilitate the elimination of the soot. The 3DOM Cu_0.1Ce catalysts exhibit the highest catalytic activity with maximum soot oxidation rate temperatures at 375 and 351 °C in the air and NO _x atmosphere, respectively. The NO _x‐TPD results demonstrate that the NO₂ produced in the Ce_0.1Cu‐M sample plays a curial role in improving the soot oxidation performance. Meanwhile, the NO‐DRIFTs reveal that the nitrates stored in the Cu_0.1Ce‐M sample also had a promotional effect on the soot elimination.     

Emission profile of rapeseed methyl ester and its blend in a diesel engine

Fatty acid methyl esters, also known as biodiesel, have been shown to have a great deal of potential as petro-diesel substitutes. Biodiesel comprise a renewable alternative energy source, the development of which would clearly reduce global dependence on petroleum and would also help to reduce air pollution. This paper analyzes the fuel properties of rapeseed biodiesel and its blend with petro-diesel, as well as the emission profiles of a diesel engine on these fuels. Fuels performance studies were conducted in order to acquire comparative data regarding specific fuel consumption and exhaust emissions, including levels of carbon monoxide (CO), carbon dioxide (CO₂), smoke density, and NO_x, in an effort to assess the performance of these biodiesel and blend. The fuel consumption amount of oil operations at high loads was similar or greater than that observed during petro-diesel operation. The use of biodiesel is associated with lower smoke density than would be seen with petro-diesel. However, biodiesel and its blend increased the emission of CO, CO₂, and nitrogen oxides, to a greater degree than was seen with petro-diesel. The above results indicate that rapeseed biodiesel can be partially substituted for petro-diesel under most operating conditions, regarding both performance parameters and exhaust, without any modifications having to be made to the engine.     

Effects of Magnetic Nanofluid Fuel Combustion on the Performance and Emission Characteristics

Although the compression ignition engines are a significant source of power, their detrimental emissions create considerable problems to the environment as well as to humans. The objective of the present experimental investigation is to examine the effects of the magnetic nanofluid fuels on combustion performance characteristics and exhaust emissions. In this regard, the Fe₃O₄ nanoparticles dispersed in the diesel fuel with the nanoparticle concentrations of 0.4 and 0.8 vol% were employed for combustion in a single-cylinder, direct-injection diesel engine. After a series of experiments, it was demonstrated that the nanoparticle additives, even at very low concentrations, have considerable influence in diesel engine characteristics. Furthermore, the results indicated that the nanofluid fuel with nanoparticle concentration of 0.4 vol% shows better combustion characteristics in comparison with that of 0.8 vol%. Based on the experimental results, NO _x and SO₂ emissions dramatically reduce, while CO emissions and smoke opacity noticeably increase with increasing the dosing level of nanoparticles.     

Computed Potential Energy Surfaces and Minimum Energy Pathways for Chemical Reactions

Computed potential energy surfaces are often required for computation of such observables as rate constants as a function of temperature, product branching ratios, and other detailed properties. We have found that computation of the stationary points/reaction pathways using CASSCF/derivative methods, followed by use of the internally contracted CI method with the Dunning correlation consistent basis sets to obtain accurate energetics, gives useful results for a number of chemically important systems. Applications to complex reactions leading to NO_x and soot formation in hydrocarbon combustion are discussed.     

An Analysis of Exhaust Emission of the Internal Combustion Engine Treated by the Non-Thermal Plasma

Industries’ air pollution causes serious challenges to modern society, among them exhaust gases from internal combustion engines, which are currently one of the main sources. This study proposes a non-thermal plasma (NTP) system for placement in the exhaust system of internal combustion engines to reduce the toxic contaminants (HC, CO, and NO_x) of exhaust gases. This NTP system generates a high-voltage discharge that not only responds to the ion chemical reaction to eliminate NO_x and CO, but that also generates a combustion reaction at the local high temperature of plasma to reduce HC. The NTP system was designed on both the front and rear of the exhaust pipe to analyze the difference of different exhaust flow rates under the specified frequency. The results indicate that the NTP system can greatly reduce toxic contaminants. The NTP reactor placed in the front of exhaust pipe gave HC and CO removal efficiency of about 34.5% and 16.0%, respectively, while the NTP reactor placed in the rear of exhaust pipe gave NO_x removal efficiency of about 41.3%. In addition, the voltage and material directly affect the exhaust gases obviously. In conclusion, the proposed NTP system installed in the exhaust system can significantly reduce air pollutants. These results suggest that applying NTP to the combustion engine should be a useful tool to simultaneously reduce both emissions of NO_x and CO.     

Experimental simulation of the relative contribution of volatile-N and char-N to NO X formation from a low-capacity bituminous coal-fired industrial boiler

The conversion of fuel-N to NOx is the main contribution of NOx from coal-fired industrial boilers and is the least-studied modelling problem arising from coal combustion. This paper summarises the current understanding of the mechanisms that account for the formation of NOx from fuel-N during coal combustion. Further experimentation on NOx emissions during bituminous coal combustion was simulated with attention focused on the contribution of char-N and volatile-N to fuel-NOx through the Coal/Char combustion method. The critical analysis of this issue allowed for the identification of uncertainties and produced well-founded conclusions. The results indicated that fuel-NOx formation was a very complex physical-chemical process involving many competing mechanisms. These mechanisms included chemical reactions, convective mass transfer, heat transfer, adsorption and desorption. The contribution of char-N in this experiment varied between 30% and 70%. There may be a slight question as to the exact identity of the main contributor to fuel-NOx , and no definitive conclusion can be made as of yet. This uncertainty is because the contribution of char-N to fuel-NO x was heavily affected by the combustion conditions and the contribution of char-N increased monotonically as temperature increased. There was a critical point in the relationship between particle size, air flow, O2 concentration and the contribution of char-N. The contribution of char-N increased with the increase of particle size and air flow initially when less than the critical value, and decreased when more than thecritical value. The contribution of char-N initially decreased when the O2 concentration was increased from 10% to 15% and increased more with the further increase in O2 concentration.     

Simultaneous soot combustion and NOx reduction over a vanadia-based selective catalytic reduction catalyst

Simultaneous NO_x reduction and soot combustion over a commercial vanadia-based selective catalytic reduction (SCR) catalyst were investigated. Carbon black was used as model soot. The impact of the contact intensity between carbon and catalyst was studied. The experiments appeared as promising results for the utilization of vanadia-based SCR catalysts in SCR on filter system as, in the SCR operating temperature range (250–400 °C), no significant impact of the presence of carbon black on NO_x reduction was observed. However, a decrease in the specific carbon oxidation rate was highlighted. This latter increases with the contact between carbon and catalyst and is attributed to a lack of NO₂, consumed by the fast SCR reaction. At temperatures greater than 400 °C, the contact between carbon particles and the SCR catalyst partially inhibits the NO_x reduction, whereas it exhibits a catalytic effect on the carbon oxidation rate. The tighter the contact between the two materials, the more significant is this behavior. A redox mechanism, which competes with the redox cycle of the SCR mechanism, was proposed. The impregnation of a V-based SCR catalyst with 2 wt % of calcium was also performed. A drastic loss of DeNO_x activity was observed, whereas the effect of the contact between carbon and catalyst was reduced.     

Sulfur impact on diesel emission control- A review

The effect of sulfur on diesel emission control is reviewed in this paper. Diesel exhaust differs from that of petrol engine exhaust in two major characteristics. Firstly, diesel exhaust contains a far higher amount of particulate matter, and secondly, the exhaust is far leaner, that is, far more oxidizing than a typical exhaust from petrol engines. Under these conditions, the conventional three-way catalysts are not effective in reducing NO_x . Emission from diesel engines is a complex phenomenon. The composition, the properties and the amount of these emissions depend on strictly technical parameters such as engine design and engine operation characteristics and on fuel and lube oil composition. Diesel fuel contains a small amount of sulfur which has an adverse effect even on the raw particulate emissions. The investigations on the effect of sulfur on hydrocarbons, CO and NO_x abatement in diesel exhaust gas is reviewed together with the newest technologies to avoid catalyst deactivation by unwanted SO₂ reactions.     

RDF pyrolysis by TG-FTIR and Py-GC/MS and combustion in a double furnaces reactor

With the increasing depletion of fossil energy, the refuse-derived fuel (RDF) as an unavoidable by-product of human activities has been used as an alternative fuel in the precalciner cement kilns. Since the RDF combustion also brings the problems of NOx pollution, it is quite important to find ways to lower the NOx emission during RDF combustion in the precalciner. The pyrolysis characteristics and products of RDF were studied by TG-FTIR and Py-GC/MS. From TG-FITR and Py-GC/MS tests, various carboxylic acids and alkenes formed with NOx released at the RDF pyrolysis process at 200–550 °C. By simulating the temperature (700 °C, 800 °C and 900 °C) and O₂ (12%, 14%, 16%, 18% and 21%) environment of the precalciner using a double furnaces reactor, the combustion processes and NOx formation characteristics of RDF combustion were studied. The results showed that the volatile-N was the dominant reactant source of fuel NOx during RDF combustion. The fuel-N conversion and NOx emission yield showed a continuous decreasing trend with temperature increasing from 700 to 900 °C. The fuel-N conversion and NOx emission yield showed a slight increasing trend with the oxygen concentration increase, and the optimum oxygen concentration for RDF combustion was 14%. In this study, the optimum temperature was 900 °C and oxygen concentration was 14% for de-NOx in the precalciner.

     

Investigation on the performance,emissions and combustion characteristics of CRDI engine fueled with tallow methyl ester biodiesel blends with exhaust gas recirculation

This paper demonstrates the study of performance, combustion and emission characteristics of a common rail diesel injection (CRDI) engine with the influence of exhaust gas recirculation (EGR) (5, 15 and 25%) at various fuel injection pressures (400, 500 and 600 bar) under the effective load conditions (0, 25, 50, 75 and 100%). The experiments were carried out in a controlled manner using the CRDI engine fuelled with 80% (D80) diesel (98% purity) blended with 20% (B20) tallow biodiesel. The engine has been operated at a rated speed of 1500 rpm on all load conditions, fuel injection timings of 10°, 15° and 20° bTDC, fuel injection pressures of 400, 500 and 600 bar, respectively. Combustion-influenced performance characteristics such as variation of in-cylinder pressure and net heat release rate in J deg^?1 are also studied with the above operating conditions. It was observed that the usage of 20% biofuel blend shows considerable improvement in combustion, and it further enhances with an increase in the injection pressures. Besides, EGR (up to 25%) reduced significant pollutants at higher operating pressures (600 bar) at higher load conditions. It was also observed that CO₂ emission increased with increase in the % EGR with an increase in the load conditions. However, for CO emission increased up to 50% load condition and subsequently tends to decrease due to improved combustion at higher load; hence higher temperature. NO_x, smoke opacity continue to increase with the increase in pressure and the percentage increase in EGR due to its attainment of adiabatic temperature, which leads to the pathway for the Zeldovich mechanism. The present work shows light on the usage of tallow methyl ester produced from the wastes in the tannery industry as alternate biofuel operating the CRDI engines without compromising its combustion and emission characteristics to deliver the same power as petro-diesel.

     

Combustion synthesized crystalline La-Mn perovskite catalysts: Role of fuel molecule on thermal and chemical events

Solution combustion synthesis (SCS) technique was applied to produce LaMnO_3+δ with the aim to investigate the effect of the chemical nature of a series of six fuel molecules (glycine, maleic acid, succinic acid, citric acid, acetic acid, urea) on the combustion reaction mechanism and physicochemical properties of the as-prepared powders. The whole SCS process was found to involve two types of combustion reactions depending on the used sacrificial molecules. Type I (with glycine, maleic acid and succinic acid) was characterized by a one-step exothermic reaction implying a semi-decomposed mixed nitrate-fuel complex and NO₂ arising from manganese nitrate decomposition. The heat emission allows reaching the temperature suitable for well crystallized as-prepared perovskite powders. Type II (with citric acid, acetic acid and urea) was typified by a multi stage process in which intermediate decomposition reactions occurred before the formation of a mixed nitrate-fuel complex. In this case, the heat emission became lower than that expected from stoichiometric reaction, thus limiting the completion of the direct reaction for perovskite production. Consequently, part (with citric acid and acetic acid) or totally (with urea) of lanthanum and manganese remained distinctly combined in two amorphous phases (La(OH)₂NO₃, MnO_x) that were intimately mixed. With respect to other fuels, combustion synthesis, using glycine, produced better crystallized, more defective and performant catalytic perovskite phase toward deep ethanol oxidation.