Influence of injection of concentrated NOx into diesel engine intake on exhaust gas components and fuel consumption

The effect of injecting NO (major content of NO_x in diesel exhaust gas) into a diesel engine intake, on the reduction of NO_x generation at the combustion chamber was investigated. The results demonstrate that 20 to 30% of the injected NO [0.225 to 0.72 slm (slm: standard liter per minute)] is reduced. A discussion of the NO_x reduction based on the extended Zeldovich mechanism suggests that the reduction is mainly attributable to the region where the equivalence ratio ranges from 1.1 to 1.5 and that the reaction between NO and hydrocarbon species contributes slightly to the NO reduction. Further experimental data show that the injection of NO slightly improves the specific fuel consumption; for example, a 0.4% reduction is achieved when NO is injected at 0.72 slm for an intake airflow of 285 slm. The experimentally determined change in fuel consumption is highly consistent with the calculations based on the reaction enthalpy of NO reduction and CO oxidation. © 2012 Wiley Periodicals, Inc. Electr Eng Jpn, 182(3): 39–47, 2013; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.22341     

介质阻挡放电产生低温等离子体除去NO_x的实验研究

低温等离子体技术对氮氧化物(NOx)及多种污染物实现同步净化已成为尾气净化方面的研究热点。为此,针对国内外大多数研究采用模拟气体放电的现状,以实际柴油机尾气中NOx为研究对象,采用介质阻挡放电技术,实验研究了电压幅值、电源频率、高压电极直径、反应器体积、放电间隙对NOx去除的影响。实验结果证明,采用该研究所建立的低温等离子体处理装置,柴油机尾气中的NOx的除去率随着电压幅值及其频率的增加先升高后降低,即出现一个最大值,随电压幅值的增加其能耗增加;NOx除去率随放电间隙的减小和高压电极直径的增加而升高,随着反应器体积增加而增加。该研究成果对低温等离子处理NOx装置的车载化应用有一定的指导意义。     

Change of characteristics of desulfurization and denitrification by combustion flue gas composition and electrode configuration under pulsed corona discharge

Laboratory-scale and parametric experiments of SO₂ and NO_x removal from the simulated combustion gas by pulsed corona discharge have been performed by changing the combustion gas composition and temperature, the electrode configuration of plasma reactor, and the polarity of high-voltage electrode. The following results are obtained: 1) the higher the concentration of H₂O and O₂, the higher the efficiency of desulfurization and denitrification at the same specific input; 2) the pulsed corona discharge with a voltage pulsewidth as short as 200 ns of negative polarity shows the possibility to attain almost 90 percent deSO_x and deNO_x efficiency at the specific discharge input of 20 J/g, which is almost the same as the specific input in the electron-beam process; 3) the deNO_x characteristics show a little temperature dependence in the range of 70 to 130°C, but the deSO_x efficiency increases rapidly in the temperature region below 100°C suggesting the thermochemical dependence of deSO_x reaction; 4) when desulfurization and denitrification proceed, the white dendritic powder deposits on the plasma reactor whose composition is identified to be 49 mol% (NH₄)₂SO₄ and 47 mol% of 2NH₄NO₃ · (NH₄)₂SO₄, and the ratio of SO₂, NO and NH₃ of the deposit is almost equal to that of supplied gas.     

Pulsed plasma promoted adsorption/catalysis for NOx removal from stationary diesel engine exhaust

A detailed laboratory study on the removal of oxides of nitrogen (NO_x) from the exhaust of a stationary diesel engine was carried out using pulsed electrical discharge promoted adsorbent/catalytic processes. In this study, the filtered exhaust from the diesel engine is made to pass through a combination of plasma reactor and adsorbent/catalytic reactor connected in series. This combination is referred to as cascaded process. In the cascaded plasma-adsorbent process, the plasma treating filtered exhaust was cascaded with adsorbents (MS-13X/Activated alumina/Activated charcoal). The cascaded plasma-adsorbent process exhibits a superior NO_x removal characteristic compared to the individual processes-plasma or adsorbent processes. In the cascaded plasma-catalyst process, the plasma treating filtered exhaust was cascaded with activated alumina catalyst. For the purpose of investigation, both two-stage and four-stage cascaded plasma-activated alumina catalyst processes were separately studied. The synergy effect and limitation of two-stage process and improved performance of four-stage process are explained. Further, experiments were conducted at room temperature as well as at higher temperatures     

E级燃气轮机进气系统加湿降氮效果

燃气轮机在运行中氮氧化物受环境影响排放并不稳定,环境湿度是影响燃气轮机氮氧化物排放的因素之一。在大气湿度较低的工况下,燃气轮机极易出现排放超标情况,考虑氮氧化物排放的环境湿度影响因子,通过改造燃气轮机进气系统增加进气加湿装置,以实现在环境工况干燥时通过增加相对湿度降低重型燃气轮机氮氧化物排放水平。通过实际运行,验证了本文所提改造方法可有效降低燃气轮机在部分负荷工况下的氮氧化物排放。     

Regeneration of diesel particulate filter using nonthermal plasma without catalyst

Regulations regarding automotive diesel engine emissions become more severe every year, and it is difficult to meet the requirements with only combustion improvement techniques. More effective post-processing technology is desired especially for particulate matter (PM), such as carbon soots. Although the use of a ceramic diesel particulate filter (DPF) is now a leading technology for PM removal, the problem exists for the soot removal or regeneration at low temperature, especially at cold start. In the present study, a regeneration of a DPF with collected PM was investigated using the low-temperature atmospheric pressure nonthermal plasma. The method is to use the NO/sub 2/ and radicals induced by the plasma reactor to burn carbon soots deposited on the DPF. First, three types of DPF plasma reactors were made and the performance of the conversion of NO to NO/sub 2/ was evaluated at various conditions. Next, a regeneration experiment was carried out using a barrier-type pulse corona plasma reactor. As a result, it was confirmed that the pressure difference decreased when the plasma was turned on and the regeneration of the DPF (approximately 75% of soot removal) was confirmed when the gas temperature was 250/spl deg/C.     

Diesel engine exhaust treatment with a pulsed streamer coronareactor equipped with reticulated vitreous carbon electrodes

Reticulated vitreous carbon (RVC) has been shown to be useful for high-voltage and ground electrodes in gas-phase pulsed streamer corona reactors. RVC disks with large macroscopic porosity are placed perpendicular to the gas flow and the main axis of a cylindrical corona reactor. This electrode geometry produces streamers that propagate in the direction of the gas flow and are uniformly distributed in the cross section of the reactor. This highly electrically conductive material has large macroscopic porosity, thus allowing for gas flow through the electrodes with low pressure drop. Previous work has considered the effects of RVC electrodes on NO/NO_x removal from various test gases containing air, water vapor, and ethylene. The present studies show removal of NO/NO_x from the exhaust of a 5 kW diesel engine. Under cold reactor operating conditions (12°C) 81% NO and 53% NO_x could be removed at an energy yield of 4.8 g/kWh (based on NO). Furthermore, experiments with the combination of TiO₂ or γ-Al₂O₃ catalyst particles placed in the region between the high-voltage and ground electrode disks gave NO removal at energy yields of 29 g/kWh and 9 g/kWh, respectively, at about 100°C, and significant fractions of the nitrogen were recovered as NO₃^- deposited on the catalyst surface. The RVC electrode system without catalysts was found to lead to efficient ozone production (55-70 g/kWh) in dry air at room temperature     

Performance evaluation of nonthermal plasma reactors for NO oxidation in diesel engine exhaust gas treatment

The discharge plasma-chemical hybrid process for NO/sub x/ removal from the flue gas emissions is an extremely effective and economical approach in comparison with the conventional selective catalytic reduction system. In this paper we bring out a relative comparison of several discharge plasma reactors from the point of NO removal efficiency. The reactors were either energized by AC or by repetitive pulses. Ferroelectric pellets were used to study the effect of pellet assisted discharges on gas cleaning. Diesel engine exhaust, at different loads, is used to approximately simulate the flue gas composition. Investigations were carried out at room temperature with respect to the variation of reaction products against the discharge power. Main emphasis is laid on the oxidation of NO to NO/sub 2/, without reducing NO/sub x/ concentration (i.e., minimum reaction byproducts), with least power consumption. The produced NO/sub 2/ will be totally converted to N/sub 2/ and Na/sub 2/SO/sub 4/ using Na/sub 2/SO/sub 3/. The AC packed-bed reactor and pelletless pulsed corona reactor showed better performance, with minimum reaction products for a given power, when the NO concentration was low (/spl sim/100 ppm). When the engine load exceeds 50% (NO>300 ppm) there was not much decrease in NO reduction and more or less all the reactors performed equally. The total operating cost of the plasma-chemical hybrid system becomes $4010/ton of NO, which is 1/3-1/5 of the conventional selective catalytic process.     

$hbox{NO}_{rm x}$ Aftertreatment Using Thermal Desorption and Nitrogen Nonthermal Plasma Reduction

In this paper, the results of two experiments are reported. First, the performances of various types of nonthermal plasma reactors for $hbox{NO}_{rm x}$ reduction were compared. It was shown that the surface-discharge reactors have as high $ hbox{NO}_{rm x}$ reduction capabilities as pulse-powered wire–cylinder reactors. Second, $hbox{NO}_{rm x}$ treatment using the surface-discharge reactor with a NO-adsorbent zeolite 13X was performed. Thermal desorption was employed for the regeneration of the zeolite. The $hbox{NO}_{rm x}$ of 350 ppm was kept lower than 18 ppm for at least 11 h, whereas it degraded to 75 ppm in the absence of the regeneration. The result suggested the possibility of an aftertreatment system that employed thermal desorption by utilizing the waste heat of diesel engine exhaust and $hbox{NO}_{rm x}$ reduction by using a surface-discharge reactor.      

NO/sub x/ reduction after treatment system using nitrogen nonthermal plasma desorption

In the flue emission from an internal combustion system using diffusing combustion such as coal or oil fuel boiler, incinerator, or diesel engine, around 10% oxygen is usually included. It is difficult to reduce the NO/sub x/ in the emission completely using catalysts or plasma alone because part of the NO/sub x/ is oxidized under an O/sub 2/-rich environment. In order to overcome these difficulties, we proposed a new after treatment system of NO/sub x/ included in the exhaust gas of the combustion system using nonthermal plasma (NTP) desorption and reduction. In this system, exchangeable adsorbent columns are equipped. First, the exhaust gas including NO/sub x/ is adsorbed to an NO/sub x/ adsorbent for a period of /spl Delta/t/sub a/. After the period of /spl Delta/t/sub a/, the path of the exhaust gas is changed with a pair of rotary valves and NO/sub x/ adsorbent is changed. The adsorbed NO/sub x/ is desorbed from the adsorbent and reduced by applying NTP for a period of /spl Delta/t/sub d/ using N/sub 2/ or low-oxygen-concentration gas. The exhaust gas is always kept clean by the exchange of adsorbent. Further, total electric energy can be reduced because NTP is not applied for /spl Delta/t/sub a/. This system can be operated at atmospheric temperature because no catalyst is used. As an initial step to realize such kind of after treatment system, the basic characteristics of the N/sub 2/ NTP desorption and NO/sub x/ reduction were examined experimentally using a pulse corona NTP reactor. After several adsorption/desorption processes, the amount of NO/sub x/ adsorbed becomes equal to that of the NO/sub x/ desorbed, that is, all the NO/sub x/ was desorbed in a single desorption process. It is confirmed that the NO/sub x/ complete reduction using N/sub 2/ NTP desorption is possible not only for a simulated exhaust gas but for a real diesel engine gas. The effective specific energy density can be decreased down to 22 Wh/m/sup 3/.     

Pollution control of actual flue gas using pulsed power at a thermal power plant

There are several important environmental problems in the world. One of them is acid rain caused by combustion flue gases from thermal power plants, factories, and automobiles. Different kinds of gas discharges, such as surface discharge, dc and ac corona discharge, silent discharge, and electron beam controlled discharge, have been studied for the removal of NO_x and SO₂ from flue gases. The recent development of repetitive pulsed power generators gives the pulsed steamer corona discharges a chance of success in the removal of NO_x and SO₂. In this paper, the experimental results of NO_x and SO₂ removal by a repetitive pulse power generator are described. The actual flue gas at a thermal power plant was used. It is shown that about 90% of the NO was removed at a flow rate of 0.8 liters/min and a repetition rate of 7 pps. © 2001 Scripta Technica, Electr Eng Jpn, 134(4): 28–35, 2001     

Pulsed discharge purification of water containing nondegradable hazardous substances

We investigate the decomposition characteristics of phenol in an aqueous solution under exposure to pulsed discharge plasma. The investigation is carried out with different electrode configurations, applied voltages, and humidity levels and compositions of the background gas. It is possible that in the case of all gases, OH radicals are responsible for the decomposition of phenol in the solution. In pure O₂, the decomposition rate of phenol increases due to the generation of O and O₃. In pure N₂, OH radicals produced by N₂, which is excited in the metastable state, contribute to phenol decomposition. In N₂‐O₂, the decomposition rate of phenol remains low, and the NO_x produced by the pulsed plasma in a N₂‐O₂ mixture destroys O₃, and the production of the NO_x inhibits O₃ production. In Ar‐O₂, the decomposition rate of phenol increases with an increase in the concentration of Ar in the mixture. It is possible that excited Ar atoms are responsible for the decomposition of phenol in the solution at higher concentrations of Ar in Ar‐O₂. Further, it is found that the decomposition rate of phenol in aqueous solution exposed to a pulsed discharge is almost the same as that of phenol in aqueous solution exposed to a DC corona discharge. © 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 174(2): 1–8, 2011; Published online in Wiley Online Library ( wileyonlinelibrary.com ). DOI 10.1002/eej.20937     

Pulsed electrical discharges assisted by dielectric pellets/catalysts for diesel engine exhaust treatment

This paper reports the study on gaseous pollutants (NOx, CO and HCs) using a combination of electric discharge plasma and catalysts. In this study, catalysts being used in conventional catalytic converters of gasoline engine were tried, for the first time, in diesel engine exhaust treatment assisted by electric discharge plasma. Initial studies investigate the effect of packed dielectric materials and catalysts on NOx removal. Both conventional and non-conventional catalysts were used in the studies. With plasma alone, the removal efficiency of oxides of nitrogen was around 75% and with a suitable combination of catalytic reactor the removal efficiency was as high as 90%. Among the catalysts studied, a new catalyst (CuMnAlO/sub 4/) was found to be as effective as the conventional expensive catalyst. The formation of byproducts like N/sub 2/O and HNO/sub 3/ have been studied and the results are discussed.     

Ethanol used as an environmentally sustainable energy resource for thermal power plants

Justification of using renewable energy sources and a brief analysis of their application prospects is given. The most common renewable energy sources for mobile thermal power plants are presented. The possibilities and ways of using ethanol as an energy source for such plants with diesel engines are analyzed. It is shown that it is feasible to add small amounts of ethanol to oil diesel fuel (DF) for obtaining an environmentally sustainable energy source for diesel engines. Therewith, a stable mixture of components can be obtained by adding anhydrous (absolute) ethanol to the oil fuel. The authors studied a mixture containing 4% (by volume) of absolute ethanol and 96% of oil DF. The physicochemical properties of the mixture and each of its components are presented. Diesel engine of the type D-245.12S has been experimentally studied using the mixture of DF and ethanol. The possibility of reducing the toxicity level of the exhaust emissions when using this mixture as an energy source for diesel engines of mobile power plants is shown. Transition of the studied diesel engine from oil DF to its mixture with ethanol made it possible to reduce the smoke capacity of the exhaust gases by 15–25% and to decrease the specific mass emissions of nitrogen oxides by 17.4%. In this case, we observed a slight increase in the exhaust gas emissions of carbon monoxide and light unburned hydrocarbons, which, however, can easily be eliminated by providing the exhaust system of a diesel engine with a catalytic converter. It is noted that the studied mixture composition should be optimized. The conclusion is made that absolute ethanol is a promising ecofriendly additive to oil diesel fuel and should be used in domestic diesel engines.     

Removal of volatile organic compounds from air streams andindustrial flue gases by non-thermal plasma technology

Gaseous pollution control technologies for acid gases (NO_x , SO_x, etc.), volatile organic compounds (VOC), greenhouse gases, ozone layer depleting substance (ODS), etc., have been commercialized based on catalysis, incineration and adsorption methods. However, non-thermal plasma techniques based on electron beams and corona discharges become significant due to advantages such as lower cost, higher removal efficiency, smaller space volume, etc. In order to commercialize this new technology, the following needs faster investigation: pollution gas removal rates, energy efficiency of removal, pressure drop of reactors, usable byproduct production rates, identification of major fundamental processes, and optimization of reactor and power supply for an integrated system. In this work, recent development of gaseous pollution control technology based on discharge plasmas is reviewed critically and the principle of processes and reactor technologies are outlined     

电晕放电自由基簇射反应器中臭氧的生成

从电极气条件变化着手,对放电过程以及NO脱除过程中自由基簇射反应器内臭氧的生成进行了较为深入的分析。研究结果表明:(1)在相同的放电功率下,当电极气为氧气时产生的臭氧最多,通入空气时其次,而不通电极气时最少;(2)随着电极气湿度的增加,臭氧的产生量逐渐减少;(3)电极气流量的增加提高了臭氧的产生量,但考虑经济性,电极气流量有一最佳值;(4)在NOx脱除过程中,自由基簇射反应器内臭氧浓度大大减少,且随着烟气中NO浓度的增加,臭氧浓度逐渐减少,认为其主要原因是臭氧和氧自由基参与了NO的氧化过程。     

等离子体协助InZSM-5选择性催化还原贫燃NOx

为了解等离子体协助选择性催化还原(SCR)贫燃NOx的效果及相关因素,以NO模拟尾气中NOx,C2H4为还原剂,InZSM-5为催化剂,空速为32000h-1,试验研究了NO/O2/N2/C2H4系统中,单独等离子体、单独SCR及等离子体协助SCR 3种技术路线下NOx的去除率,并考察了等离子体电压、电源频率及空速对NOx去除的影响。试验发现:单独等离子体作用时NOx无法被有效的还原成N2,但等离子体在一定电压下可显著提高CH-SCR活性;较低空速下,等离子体协助InZSM-5效果明显提高;在2.5-4 kHz内,电源频率对等离子体协助SCR影响不大。     

Energy Efficiency of Corona Discharge Reactor Driven by Inductive Energy Storage System Pulsed Power Generator

Characteristics of a pulse corona reactor driven by an inductive energy storage (IES) pulsed power generator are described in this paper with focusing on the influence of streamer-to-glow transition on NO removal efficiency. A pulsed high voltage with a short rise time of under 30 ns is employed to generate streamer discharges homogeneously in whole the discharge region. Fast recovery diodes are used as semiconductor opening switch (SOS) to shorten the rise time. The various resistors are employed as dummy load to clarify a suitable circuit parameter such as the capacitance of a primary energy storage capacitor and/or the inductance of a secondary energy storage inductor. The energy transfer efficiency of the pulsed power generator has a maximum value of 50% at 714 Omega dummy load resistance. A co-axial cylinder type discharge chamber was used as the corona discharge plasma reactor driven by the IES pulsed power generator. The pulsed power generator supplies 30 kV pulse with 300 pps repetition rate. The co-axial cylinder plasma reactor consists of 1 mm diameter tungsten wire and 19 mm i.d. copper tube with 30 cm length. NO removal from the simulated diesel engine exhaust gas (N₂:O₂=9:1, Initial NO concentration=200 ppm) increased with input energy into the reactor. The energy efficiency for NO removal was obtained to be 25 g/kWh at 30 % removal in gas flow rate of 2 L/min. However, the energy efficiency decreased to 5 g/kWh with increasing capacitance of the primary capacitor from several hundreds pF to several nF. This decrease was caused by a streamer-to-glow transition. The efficiency was affected by oxygen concentration in the gas mixture.     

低温等离子体放电管发光光谱的检测分析

为解析放电等离子体形成过程,对过程参数进行优化,以低温等离子放电管作为研究对象,在常温常压下用组合式多功能光栅光谱仪对放电光进行测量,经计算机处理,可得到空气体系中放电光的近紫外段的发射光谱.通过对放电光谱的检测分析,可以察知放电等离子体形成的途径,了解各种粒子乃至电子的能量,从而可对放电管作出相应的评价.     

介质阻挡放电电气参数与反应器参数的测量

介质阻挡放电(DBD)是产生大气压低温等离子体的主要途径之一,准确地测量其电气参数与反应器参数对优化DBD等离子体反应器设计和提高放电效率具有重要意义。通过所建立的实验装置测量了DBD的电压-电流波形图、放电发光图像及电压-电荷Lissajous图形,利用所得到的测量结果进一步计算得到DBD的介质电容、气隙电容、起始放电电压和放电功率等电气参数和反应器参数,并将这些值与根据反应器结构计算得到的值进行比较。结果表明,测量结果得到的DBD电气参数和反应器参数与反应器结构计算得到的值是基本一致的。