介质阻挡放电技术去除柴油机NOx、HC和PM排放物

本文主要研究将介质阻挡放电技术应用于柴油机尾气的净化过程,以达到同时去除NOx、HC和PM的目的。实验分别引入峰值电压、放电频率和发动机负载等工况参数,深入探讨它们对相关污染物去除效率的影响。研究结果表明,在同等频率条件下,NOx、HC和PM的去除效率随着放电峰值电压的升高而上升,并且在较高电压下PM和HC的去除效率出现饱和,而NOx的去除效率呈现下降的趋势;在同等放电电压下,能流密度和去除效率的最高值出现在放电频率的谐振点处。实验同时考察了不同的发动机工况条件下放电电压对能量效率的影响,研究表明,电压升高导致了能流密度的显著下降。     

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.     

Injection Strategy in Natural Gas–Diesel Dual-Fuel Premixed Charge Compression Ignition Combustion under Low Load Conditions

Dual-fuel premixed charge compression ignition (DF-PCCI) combustion has been proven to be a viable alternative to conventional diesel combustion in heavy-duty compression ignition engines due to its low nitrogen oxides (NO_x) and particulate matter (PM) emissions. When natural gas (NG) is applied to a DF-PCCI engine, its low reactivity reduces the maximum pressure rise rate under high loads. However, the NG–diesel DF-PCCI engine suffers from low combustion efficiency under low loads. In this study, an injection strategy of fuel supply (NG and diesel) in a DF-PCCI engine was investigated in order to reduce both the fuel consumption and hydrocarbon (HC) and carbon monoxide (CO) emissions under low load conditions. A variation in the NG substitution and diesel start of energizing (SOE) was found to effectively control the formation of the fuel–air mixture. A double injection strategy of diesel was implemented to adjust the local reactivity of the mixture. Retardation of the diesel pilot SOE and a low fraction of the diesel pilot injection quantity were favorable for reducing the combustion loss. The introduction of exhaust gas recirculation (EGR) improved the fuel economy and reduced the NO_x and PM emissions below Euro VI regulations by retarding the combustion phasing. The combination of an NG substitution of 40%, the double injection strategy of diesel, and a moderate EGR rate effectively improved the combustion efficiency and indicated efficiency, and reduced the HC and CO emissions under low load conditions.     

SO2 and NOx removal by electron beam and electrical discharge induced non-thermal plasmas

An installation containing a DC negative corona discharge reactor, a pulse corona discharge reactor and a combined electron beam and microwave induced plasma reactor is presented. SO₂ is removed up to 42% through spontaneous reaction with ammonia without electron beam or microwave irradiation at the temperature below 70 °C. For the same removal efficiency of 98% for SO₂ and 80% for NO_x at separate EB irradiation of 40 kGy, the required absorbed dose is about two times smaller for simultaneous electron beam and microwave irradiation. The SO₂ removal efficiency of simultaneous DC or positive discharge and microwave discharge is higher than separate DC, pulse and MW discharge. Also, the applied voltage level at which the removal efficiency reaches the maximum value is less than for the separate application of DC or pulse discharge. The NO_x removal efficiency of DC or pulse discharge suffers little change by additional use of the microwave energy.     

Diesel emission control system using combined process of nonthermal plasma and exhaust gas components' recirculation

A NO_x aftertreatment system, using nonthermal plasma (NTP) reduction and exhaust gas components' recirculation, is investigated. A pilot-scale system is applied to a stationary diesel engine. In this system, NO_x is first removed by adsorption, and subsequently, the adsorbent is regenerated by thermal desorption. NO_x desorbed is reduced by using nitrogen NTP. Moreover, NO_x, CO₂, and water vapor recirculated into the engine intake reduce NO_x. In this study, approximately 57% of the NO_x of the exhaust (NO_x: 240-325 ppm, flow rate = 300 NL/min) can be continuously treated for 58 h. A system energy efficiency of 120 g (NO₂)/kWh is obtained.     

A scheme for solving strongly coupled chemical reaction equations appearing in the removal of SO2 and NOx from flue gases

The removal of NO_x from mixtures of NO-NO₂-N₂ and NO-NO₂-O₂-H₂O is discussed theoretically in this study, and the removal of ₂SO and xNO is further discussed when a gas system of NO_x-N₂-O₂-H₂O contains CO₂ and SO₂. The involved chemical reaction rate equations in the process of SO₂/NO_x removal are solved numerically using Treanor's method, in which a scheme separating chemical reactions into fast and slow groups has been proposed for improving the numerical stability. Numerical results show that the contribution of ion reactions to xNO removal is negligible, and that high temperature is not beneficial for the NO oxidation. However, high concentration of O₂ is conducive to the NO oxidation. Addition of water facilitates the NO_x removal, and increasing water vapor concentration enhances the NO_x removal efficiency; inclusion of CO₂ and SO₂ into the system favors the NO removal.     

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.     

Photocatalytic NOx degradation of concrete surface layers intermixed and spray-coated with nano-TiO2: Influence of experimental factors

TiO₂ incorporated Eco-blocks have been successfully developed and widely used worldwide. However, under real-life service, various environmental factors will significantly influence their photocatalytic performance. In this study, the photocatalytic NO_x conversion of two sets of concrete surface layers (intermixed and spray-coated with nano-TiO₂) was investigated and compared under different NO flow rates, initial NO concentrations, ultraviolet (UV) light intensities, light sources and relative humidity (RH) conditions. In addition, the abrasion resistance of all the samples was examined. The results showed that the TiO₂ spray-coated samples (SP) outperformed the 5% TiO₂-intermixed samples with respect to NO_x removal efficiency under all the investigated conditions. Both the NO flow rate and initial NO concentration had a positive impact on the NO_x removal rate but a negative influence on the NO_x removal ratio. An increase in photocatalytic NO_x removal rate and NO_x removal ratio was attained by an increase in UV light intensity. Whereas, the NO_x removal efficiency first increased, reached a peak, and then decreased with increasing RH. It was found that the most effective light source for photocatalytic NO_x removal was UV-A, but Solar light (SL) irradiation resulted in a comparable NO_x removal. Moreover, the SP samples harboured robust resistance to abrading. The findings from this study would provide the basis for effectively evaluating the NO_x removal performance of concrete surface layers under atmospheric conditions.     

Chemiluminescence analyzer of NOx as a high-throughput screening tool in selective catalytic reduction of NO

A chemiluminescence-based analyzer of NO_x gas species has been applied for high-throughput screening of a library of catalytic materials. The applicability of the commercial NO_x analyzer as a rapid screening tool was evaluated using selective catalytic reduction of NO gas. A library of 60 binary alloys composed of Pt and Co, Zr, La, Ce, Fe or W on Al₂O₃ substrate was tested for the efficiency of NO_x removal using a home-built 64-channel parallel and sequential tubular reactor. The NO_x concentrations measured by the NO_x analyzer agreed well with the results obtained using micro gas chromatography for a reference catalyst consisting of 1 wt% Pt on γ-Al₂O₃. Most alloys showed high efficiency at 275 °C, which is typical of Pt-based catalysts for selective catalytic reduction of NO. The screening with NO_x analyzer allowed to select Pt-Ce_(X) (X=1–3) and Pt–Fe₍₂₎ as the optimal catalysts for NO_x removal: 73% NO_x conversion was achieved with the Pt–Fe₍₂₎ alloy, which was much better than the results for the reference catalyst and the other library alloys. This study demonstrates a sequential high-throughput method of practical evaluation of catalysts for the selective reduction of NO.     

Simultaneous absorption of NOx and SO2 from flue gas with pyrolusite slurry combined with gas-phase oxidation of NO using ozone

NO was oxidized into NO₂ first by injecting ozone into flue gas stream, and then NO₂ was absorbed from flue gas simultaneously with SO₂ by pyrolusite slurry. Reaction mechanism and products during the absorption process were discussed in the followings. Effects of concentrations of injected ozone, inlet NO, pyrolusite and reaction temperature on NO_x/SO₂ removal efficiency and Mn extraction rate were also investigated. The results showed that ozone could oxidize NO to NO₂ with selectivity and high efficiency, furthermore, MnO₂ in pyrolusite slurry could oxidize SO₂ and NO₂ into MnSO₄ and Mn(NO₃)₂ in liquid phase, respectively. Temperature and concentrations of injected ozone and inlet NO had little impact on both SO₂ removal efficiency and Mn extraction rate. Specifically, Mn extraction rate remained steady at around 85% when SO₂ removal efficiency dropped to 90%. NO_x removal efficiency increased with the increasing of ozone concentration, inlet NO concentration and pyrolusite concentration, however, it remained stable when reaction temperature increased from 20 °C to 40 °C and decreased when the flue gas temperature exceeded 40 °C. NO_x removal efficiency reached 82% when inlet NO at 750 ppm, injected ozone at 900 ppm, concentration of pyrolusite at 500 g/L and temperature at 25 °C.     

An experimental investigation on the performance,combustion and emission characteristics of a variable compression ratio diesel engine using diesel and palm stearin methyl ester

An attempt has been made to use biodiesel prepared from non-edible portion of palm oil as fuel of a conventional mono-cylinder compression ignition engine. The present experimental investigation takes into account the combined effect of using blends of diesel–palm stearin biodiesel as fuels and the compression ratio on different performance, combustion and emission characteristics of the said engine. The experiments have been carried out on a single-cylinder, direct injection diesel engine at varying compression ratio of 16:1–18:1 in four steps. It is observed that the brake thermal efficiency reduces by 7.9% when neat biodiesel is used instead of diesel. But, it increases with the increase in compression ratio for all the blends. Brake specific fuel consumption and exhaust gas temperature increase with the addition of biodiesel to diesel and also with the increase in compression ratio. Heat release rate decreases with biodiesel, and it is minimum at the rated compression ratio of 17.5:1 for all the fuels considered here. On the other hand, ignition delay is found to be more with neat diesel, and it increases with the decrease in compression ratio. Significant reductions in emissions of carbon monoxide (CO), hydrocarbon (HC) and smoke are observed with biodiesel, while the emissions of oxides of nitrogen (NO_x) and carbon dioxide (CO₂) increase. The decrease in compression ratio increases the emissions of CO, HC and smoke, but the emissions of NO_x and CO₂ decrease with the decrease in compression ratio.     

Removal of ammonia from gas streams with dielectric barrier discharge plasmas

We reported on the experimental study of gas-phase removal of ammonia (NH3) via dielectric barrier discharge (DBD) at atmospheric pressure, in which we mainly concentrated on three aspects--influence of initial NH3 concentration, peak voltage, and gas residence time on NH3 removal efficiency. Effectiveness, e.g. the removal efficiency, specific energy density, absolute removal amount and energy yield, of the self-made DBD reactor had also been studied. Basic analysis on DBD physical parameters and its performance was made in comparison with previous investigation. Moreover, products were detected via ion exchange chromatography (IEC). Experimental results demonstrated the application potential of DBD as an alternative technology for odor-causing gases elimination from gas streams.     

Effect of O2 on NO removal by ammonia radical injection using one-cycle sinusoidal power source

NO reduction experiment was performed by injecting ammonia radicals, which were externally generated by flowing the NH₃ gas diluted with Ar gas through a dielectric barrier discharge with a one-cycle sinusoidal-wave power source. The discharge was intermittently formed between coaxial cylindrical electrodes with a space of 1.5 mm at an applied peak-to-peak voltage of 3-25 kV. The generated radicals were injected into simulation gas (NO/O₂/N₂). The simulation gas contained 0-5.6% O₂, and the effect of O₂ on NO_x removal was discussed. The minimum reaction temperature for NO reduction was low when simulation gas contained O₂. High O₂ concentration (O₂=5.6%) in simulation gas, high repetition rate to NH₃, and high applied power to NH₃ decreased NO removal efficiency.     

Composite hydroxyapatite/TiO2 materials for photocatalytic oxidation of NOx

Hydroxyapatite/TiO₂ composite photocatalysts were obtained from sol–gel prepared TiO₂ and commercial hydroxyapatite (HA) powders. Composites with different HA/TiO₂ ratio were studied to assess the influence of HA on the morphology and the photocatalytic behavior of the materials. Morphological SEM analysis revealed that the presence of HA diminishes the aggregation of TiO₂ particles and leads to their higher dispersion in the composites that was confirmed by the N₂ adsorption–desorption isotherms and Barret–Joyner–Halenda analysis. The photocatalytic activity of the prepared catalysts was examined by monitoring photocatalytic oxidation of NO_x model gases over catalysts under UV illumination. The NO_x oxidation over the composite catalysts was improved in comparison with pure TiO₂ powder. Moreover, the decrease of the TiO₂ content, which is the photocatalytically active component in the composites, resulted in enhanced NO_x removal. Maximum activity was recorded for composites with HA/TiO₂ ratios 1 and 2 that was related to improved TiO₂ dispersion and NO₂ trapping by the composite materials.     

Development and test of a new catalytic converter for natural gas fuelled engine

This paper presents characteristics of a new catalytic converter (catco) to be used for natural gas fuelled engine. The catco were developed based on catalyst materials consisting of metal oxides such as titanium dioxide (TiO₂) and cobalt oxide (CoO) with wire mesh substrate. Both of the catalyst materials (such as TiO₂ and CoO) are inexpensive in comparison with conventional catalysts (noble metals) such as palladium or platinum. In addition, the noble metals such as platinum group metals are now identified as human health risk due to their rapid emissions in the environment from various resources like conventional catalytic converter, jewelers and other medical usages. It can be mentioned that the TiO₂/CoO based catalytic converter and a new natural gas engine such as compressed natural gas (CNG) direct injection (DI) engine were developed under a research collaboration program. The original engine manufacture catalytic conveter (OEM catco) was tested for comparison purposes. The OEM catco was based on noble metal catalyst with honeycomb ceramic substrate. It is experimentally found that the conversion efficiencies of TiO₂/CoO based catalytic converter are 93%, 89% and 82% for NO_x, CO and HC emissions respectively. It is calculated that the TiO₂/CoO based catalytic converter reduces 24%, 41% and 40% higher NO_x, CO and HC emissions in comparison to OEM catco respectively. The objective of this paper is to develop a low-cost three way catalytic converter to be used with the newly developed CNG-DI engine. Detailed review on catalytic converter, low-cost catalytic converter development characteristics and CNGDI engine test results have been presented with discussions.     

Synthesis and electrochemical behavior of layered Li(Ni0.5−xCo2xMn0.5−x)O2 (x = 0 and 0.025) materials prepared by solid-state reaction method

Layered Li(Ni_0.5−xCo_2xMn_0.5−x)O₂ (x=0 and 0.025) materials were prepared by conventional solid state reaction method combined with high energy ball milling (HEBM). The Li(Ni_0.5−xCo_2xMn_0.5−x)O₂ electrodes delivered discharge capacity of 142-185 mAh/g depending on upper cut-off voltage limit with excellent cycleability. The charge/discharge and differential capacity versus voltage studies show that only one phase reaction occurs and no phase transition takes place during the electrochemical cycling.     

Electron paramagnetic resonance (EPR) of antiferromagnetic nanoparticles of La1−xSrxCrO3 (0.000 ≤ x ≤ 0.020) synthesized by combustion reaction

Nanocrystalline particles of La_1−xSr_xCrO₃ (0.000 ≤ x ≤ 0.020) compounds were synthesized in order to investigate the antiferromagnetic (AFM) to paramagnetic (PM) phase transition temperature, g-factor, line width and intensity by electron paramagnetic resonance (EPR). All samples were synthesized by combustion reaction method using strontium nitrate, lanthanum nitrate, chromium nitrate and urea as fuel without subsequent heat treatment. X-ray diffraction patterns of all systems showed broad peaks consistent with orthorhombic structure of LaCrO₃. The absence of extra reflections in the diffraction patterns of as-prepared materials ensures the phase purity. The average crystallite sizes determined from the prominent (1 1 2) peak of the diffraction using Scherrer's equation was independent of the addition of Sr²⁺ ions; being ca. 31–29 nm for x = 0.000 and 0.020, respectively. The EPR line width and intensity were found to be dependent on Sr²⁺ addition and temperature. However, the AFM–PM transition temperature was found to be independent of strontium concentration, being ca. 296 K. In the PM phase, g-factor was nearly temperature independent with increasing of x. The EPR results indicated that the addition of Sr²⁺ ions may induce creation of Cr³⁺–Cr⁴⁺ clusters.     

Larger Ba(NO3)2/Sr(NO3)2 crystal growth and solubility determination

The solubility of Ba(NO₃)₂ and Sr(NO₃)₂ crystals in aqueous solution from 25 to 65 °C has been determined by both an optical interferometer and a weight technique. A Mach-Zehnder interferometer was used for measuring the concentration distribution of Ba(NO₃)₂ and Sr(NO₃)₂ near the solid/liquid interface during crystal growth and dissolution. A fringe carrier technique was introduced to visualize more clearly the boundary layer and to solve the concentration distribution. Crystals were successfully grown with sizes larger than  mm by a temperature cooling method. The Ba_xSr_1−x(NO₃)₂ crystal was also nucleated and grown. The Raman spectra of Ba_xSr_1−x(NO₃)₂ indicate that the barium ions probably degrade the properties of Sr(NO₃)₂.     

Characterisation of ultrasonically sprayed InxSy buffer layers for Cu(In,Ga)Se2 solar cells

In order to replace chemical bath deposited (CBD) CdS buffer layers in Cu(In,Ga)Se₂ (CIGS) solar cells by an alternative material, In_xS_y thin-film buffer layers were prepared by ultrasonic spray pyrolysis at various substrate temperatures. X-ray Diffraction measurements confirmed that the films contained primarily the tetragonal In₂S₃ phase. X-ray Photoelectron Spectroscopy measurements revealed a small concentration of chlorine impurity throughout the In_xS_y layer. By depositing the indium sulphide layer as buffer layer in the CIGS solar cell configuration, a maximum solar cell efficiency of 8.9% was achieved, whilst the reference cell with CdS/CIGS on a similar absorber exhibited 12.7% efficiency. Additionally, light soaking enhanced the efficiency of In_xS_y/CIGS cells primarily by improvements in fill factor and open circuit voltage.     

Chemiluminescence analyzer of NOx as a high-throughput screening tool in selective catalytic reduction of NO

Abstract

A chemiluminescence-based analyzer of NO_x gas species has been applied for high-throughput screening of a library of catalytic materials. The applicability of the commercial NO_x analyzer as a rapid screening tool was evaluated using selective catalytic reduction of NO gas. A library of 60 binary alloys composed of Pt and Co, Zr, La, Ce, Fe or W on Al₂O₃ substrate was tested for the efficiency of NO_x removal using a home-built 64-channel parallel and sequential tubular reactor. The NO_x concentrations measured by the NO_x analyzer agreed well with the results obtained using micro gas chromatography for a reference catalyst consisting of 1 wt% Pt on γ-Al₂O₃. Most alloys showed high efficiency at 275 °C, which is typical of Pt-based catalysts for selective catalytic reduction of NO. The screening with NO_x analyzer allowed to select Pt-Ce_(X) (X=1–3) and Pt–Fe₍₂₎ as the optimal catalysts for NO_x removal: 73% NO_x conversion was achieved with the Pt–Fe₍₂₎ alloy, which was much better than the results for the reference catalyst and the other library alloys. This study demonstrates a sequential high-throughput method of practical evaluation of catalysts for the selective reduction of NO.