HC-PM COUPLING MODEL FOR PARTICULATE MATTER EMISSION OF DIESEL ENGINES

A rapid, phenomenological model that predicts paniculate matter (PM) emissionof diesel engines is developed and formulated. The model is a chemical equilibrium compositionmodel, and is based on the formation mechanisms of PM and unburned hydrocarbon (HC) emissions ofdiesel engines. It can evaluate the emission concentration of PM via the emission concentration ofHC. To validate the model, experiments are carried out in two research diesel engines. Comparisonsof the model results with the experimental data show good agreement. The model can be used toevaluate the concentration of PM emission of diesel engines under lack of PM measuring instruments.In addition, the model is useful for computer simulations of diesel engines, as well as electroniccontrol unit (ECU) designs for electronically controlled diesel engines.

Soot Distribution and Thermal Regeneration of Marine Diesel Particulate Filter

Diesel particulate filter(DPF)is a leading technology reducing particle emissions from marine diesel engines.The removal or regeneration of soot in DPF is an important issue.The purpose of this study is to provide some reference strategies to design the DPF for marine diesel engines.In this paper,a mathematical model of a marine DPF was built up and the particle trap process and the regeneration dynamics were simulated.The results show that the cake soot mass concentrations from 0 to 4.2 g/L during the trap process increase linearly with the increase of the exhaust gas flows while the depth soot mass concentrations from 0 to 2.2 g/L firstly increase linearly and then keep constant.Soot is mainly concentrated in the front and rear portion of the filter and less soot is in the middle.The soot distribution in the cake and depth layers shows the unevenness during the trap and regeneration process.The initial soot loadings have great effects on pressure drops and soot mass concentrations before regeneration,but the little effect after regeneration.The exhaust gas temperature heated to 850 K can achieve 94%efficiency for the DPF regeneration.The heating rate has no effects on the pressure drops and soot mass concentrations,but the heating duration time of exhaust gas has an important impact on them.

Effects of continuously regenerating diesel particulate filters on regulated emissions and number-size distribution of particles emitted from a diesel engine

The effects of continuously regenerating diesel particulate filter （CRDPF） systems on regulated gaseous emissions, and number-size distribution and mass of particles emanated from a diesel engine have been investigated in this study. Two CRDPF units （CRDPF-1 and CRDPF-2） with different specifications were separately retrofitted to the engine running with European steady-state cycle （ESC）. An electrical low pressure impactor （ELPI） was used for particle number-size distribution measurement and mass estimation. The conversion/reduction rate （RcR） of hydrocarbons （HC） and carbon monoxide （CO） across CRDPF-1 was 83% and 96.3%, respectively. Similarly, the RCR of HC and CO and across CRDPF-2 was 91.8% and 99.1%, respectively. The number concentration of particles and their concentration peaks; nuclei mode, accumulation mode and total particles; and particle mass were highly reduced with the CRDPF units. The nuclei mode particles at downstream of CRDPF-1 and CRDPF-2 decreased by 99.9% to 100% and 97.8% to 99.8% respectively; and the particle mass reduced by 73% to 92.2% and 35.3% to 72.4%, respectively, depending on the engine conditions. In addition, nuclei mode particles increased with the increasing of engine speed due to the heterogeneous nucleation initiated by the higher exhaust temperature, while accumulation mode particles were higher at higher loads due to the decrease in the air-to-fuel ratio （A/F） at higher loads.

Emissions of particulate matter and associated polycyclic aromatic hydrocarbons from agricultural diesel engine fueled with degummed,deacidified mixed crude palm oil blends

Mixed crude palm oil （MCPO）, the mixture of palm fiber oil and palm kernel oil, has become of great interest as a renewable energy source. It can be easily extracted from whole dried palm fruits. In the present work, the degummed, deacidified MCPO was blended in petroleum diesel at portions of 30% and 40% by volume and then tested in agricultural diesel engines for long term usage. The particulates from the exhaust of the engines were collected every 500 hr using a four-stage cascade air sampler. The 50% cut-off aerodynamic diameters for the first three stages were 10, 2.5 and 1μm, while the last stage collected all particles smaller than 1 μm. Sixteen particle bounded polycyclic aromatic hydrocarbons （PAHs） were analyzed using a high performance liquid chromatography. The results indicated that the size distribution of particulate matter was in the accmnulation mode and the pattern of total PAHs associated with fine-particles （〈 1 μm） showed a dominance of larger molecular weight PAHs （4--6 aromatic rings）, especially pyrene. The mass median diameter, PM and total PAH concentrations decreased when increasing the palm oil content, but increased when the running hours of the engine were increased. In addition, Commercial petroleum diesel （PB0） gave the highest value of carcinogenic potency equivalent （BaPeq） for all particle size ranges. As the palm oil was increased, the; BaPeq decreased gradually. Therefore the degununed-deacidified MCPO blends are recommended for diesel substitute.

Combination of biodiesel-ethanol-diesel fuel blend and SCR catalyst assembly to reduce emissions from a heavy-duty diesel engine

In this study, the efforts to reduce NOx and particulate matter （PM） emissions from a diesel engine using both ethanol-selective catalytic reduction （SCR） of NOx over an Ag/Al2O3 catalyst and a biodiesel-ethanol-diesel fuel blend （BE-diesel） on an engine bench test are discussed. Compared with diesel fuel, use of BE-diesel increased PM emissions by 14% due to the increase in the soluble organic fraction （SOF） of PM, but it greatly reduced the Bosch smoke number by 60%-80% according to the results from 13-mode test of European Stationary Cycle （ESC） test. The SCR catalyst was effective in NOx reduction by ethanol, and the NOx conversion was approximately 73%. Total hydrocarbons （THC） and CO emissions increased significantly during the SCR of NOx process. Two diesel oxidation catalyst （DOC） assemblies were used after Ag/Al2O3 converter to remove CO and HC. Different oxidation catalyst showed opposite effect on PM emission. The PM composition analysis revealed that the net effect of oxidation catalyst on total PM was an integrative effect on SOF reduction and sulfate formation of PM. The engine bench test results indicated that the combination of BE-diesel and a SCR catalyst assembly could provide benefits for NOx and PM emissions control even without using diesel particle filters （DPFs）.

Unregulated emissions from a diesel engine equipped with vanadium-based urea-SCR catalyst

The present work is aimed at the study of number-size distribution of particles, volatile organic compounds （VOCs）, and carbonyl compounds （CC） or carbonyls emitted from a 4-cylinder turbocharged diesel engine equipped with a vanadium-based urea selective catalytic reduction catalyst. The engine was run on an electric dynamometer in accordance with the European steady-state cycle. Pollutants were analyzed using an electric low pressure impactor, a gas chromatograph/mass spectrometer, and a high performance liquid chromatography system for the number-size distribution of particles, VOCs, and CC emissions, respectively. Experimental results revealed that total number of particles were decreased, and their number-size distributions were moved from smaller sizes to larger sizes in the presence of the catalyst. The VOCs were greatly reduced downstream of the catalyst. There was a strong correlation between the conversion of styrene and ethyl benzene. The conversion rate of benzene increased with increase of catalyst temperature. Formaldehyde, acetaldehyde, acrolein and acetone were significantly reduced, resulting in a remarkable abatement in carbonyls with the use of the vanadium-based urea-SCR system.

Effect of indirect non-thermal plasma on particle size distribution and composition of diesel engine particles

To explore the effect of the gas source flow rate on the actual diesel exhaust particulate matter（PM）, a test bench for diesel engine exhaust purification was constructed, using indirect nonthermal plasma technology. The effects of different gas source flow rates on the quantity concentration, composition, and apparent activation energy of PM were investigated, using an engine exhaust particle sizer and a thermo-gravimetric analyzer. The results show that when the gas source flow rate was large, not only the maximum peak quantity concentrations of particles had a large drop, but also the peak quantity concentrations shifted to smaller particle sizes from 100 nm to 80 nm. When the gas source flow rate was 10L min^-1, the total quantity concentration greatly decreased where the removal rate of particles was 79.2%, and the variation of the different mode particle proportion was obvious. Non-thermal plasma（NTP） improved the oxidation ability of volatile matter as well as that of solid carbon. However, the NTP gas source rate had little effects on oxidation activity of volatile matter, while it strongly influenced the oxidation activity of solid carbon. Considering the quantity concentration and oxidation activity of particles, a gas source flow rate of 10L min^-1 was more appropriate for the purification of particles.

Impacts of continuously regenerating trap and particle oxidation catalyst on the NO_2 and particulate matter emissions emitted from diesel engine

Two continuously regenerating diesel particulate filter （CRDPF） with different configurations and one particles oxidation catalyst （POC） were employed to perform experiments in a controlled laboratory setting to evaluate their effects on NO2, smoke and particle number emissions. The results showed that the application of the after-treatments increased the emission ratios of NO2/NOx significantly. The results of smoke emissions and particle number （PN） emissions indicated that both CRDPFs had sufficient capacity to remove more than 90% of total particulate matter （PM） and more than 97% of solid particles. However, the POC was able to remove the organic components of total PM, and only partially to remove the carbonaceous particles with size less than 30 nm. The negligible effects of POC on larger particles were observed due to its honeycomb structure leads to an inadequate residence time to oxidize the solid particles or trap them. The particles removal efficiencies of CRDPFs had high degree of correlations with the emission ratio of NO2/NOx. The PN emission results from two CRDPFs indicated that more NO2 generating in diesel oxidation catalyst section could obtain the higher removal efficiency of solid particles. However this also increased the risk of NO2 exposure in atmosphere.

Experimental study on the effect of gaseous and particulate emission from an ethanol fumigated diesel engine

Experiments were conducted on a four-cylinder direct-injection diesel engine with 10% and 20% of the engine load taken up by fumigation ethanol injected into the air intake of each cylinder, to investigate the gaseous, particulate mass (PM) emissions, and number concentration and size distribution of the engine under five engine loads at the maximum torque engine speed of 1800 r/min. The experimental results show that at low engine loads, the brake thermal efficiency (BTE) decreases with increase in fumigation ethanol; but at high engine loads, the BTE is not significantly changed by fumigation ethanol. Fumigation ethanol can effectively decrease in brake specific nitrogen oxides (BSNOx), particulate mass and number emissions but significantly increase in brake specific hydrocarbon (BSHC), brake specific carbon monoxide (BSCO) and proportion of BSNO/BSNO2. Also, the geometrical mean diameter of the particles (GMD) increases with increase in engine load but the diameter is not changed by fumigation ethanol in all cases.

Instrumental and bio-monitoring of heavy metal and nanoparticle emissions from diesel engine exhaust in controlled environment

In the present article we characterized the emissions at the exhaust of a Common Rail （CR） diesel engine, representative of lightduty class, equipped with a catalyzed diesel particulate filter （CDPF） in controlled environment. The downstream exhausts were directly analyzed （for PM, CO, CO/, Oz, HCs, NOx） by infrared and electrochemical sensors, and SEM-EDS microscope; heavy metals were chemically analyzed using mosses and lichens in bags, and glass-fibre filters all exposed at the engine exhausts. The highest particle emission value was in the 7-54 nm size range; the peak concentration rose until one order of magnitude for the highest load and speed. Particle composition was mainly carbonaceous, associated to noticeable amounts of Fe and silica fibres. Moreover, the content of Cu, Fe, Na, Ni and Zn in both moss and lichen, and of A1 and Cr in moss, was significantly increased. Glass-fibre filters were significantly enriched in A1, B, Ba, Cu, Fe, Na, and Zn. The role of diesel engines as source of carbonaceous nanoparticles has been confirmed, while further investigations in controlled environment are needed to test the catalytic muffler as a possible source of silica fibres considered very hazardous for human health.

High NO_2/NO_X emissions downstream of the catalytic diesel particulate filter:An influencing factor study

Diesel vehicles are responsible for most of the traffic-related nitrogen oxide（NO x） emissions,including nitric oxide（NO） and nitrogen dioxide（NO2）. The use of after-treatment devices increases the risk of high NO2/NO x emissions from diesel engines. In order to investigate the factors influencing NO2/NO x emissions, an emission experiment was carried out on a high pressure common-rail, turbocharged diesel engine with a catalytic diesel particulate filter（CDPF）. NO2 was measured by a non-dispersive ultraviolet analyzer with raw exhaust sampling. The experimental results show that the NO2/NO x ratios downstream of the CDPF range around 20%–83%, which are significantly higher than those upstream of the CDPF. The exhaust temperature is a decisive factor influencing the NO2/NO x emissions. The maximum NO2/NO x emission appears at the exhaust temperature of 350°C. The space velocity,engine-out PM/NO x ratio（mass based） and CO conversion ratio are secondary factors. At a constant exhaust temperature, the NO2/NO x emissions decreased with increasing space velocity and engine-out PM/NO x ratio. When the CO conversion ratios range from 80% to 90%,the NO2/NO x emissions remain at a high level.

DOC+DPF系统对柴油机污染物排放特性的影响

对装有氧化催化器(diesel oxidation catalyst,DOC)和颗粒捕集器(diesel particulate filter,DPF)后处理系统的柴油机进行台架试验,利用烟气分析仪(Testo 350XL)和发动机废气排放颗粒物粒径谱仪(TSI EEPS 3090)研究不同负荷下柴油机原机、DOC后和DPF后排气中氮氧化物(NO_(x))和颗粒物(particulate matter,PM)的变化规律.结果表明:负荷大于50.0%时,DOC后的NO_(2)体积分数φ(NO_(2))显著增加,柴油机原机氮氧化物中NO_(2)体积分数φ(NO_(2)/NO_(x))随负荷增加而减小,DOC后和DPF后的φ(NO_(2))、φ(NO_(2)/NO_(x))随负荷增加先减小、后增大;柴油机原机PM排放取决于柴油机的运行工况,不同负荷下DOC的PM去除率为15%~30%,50.0%负荷下DOC的PM去除率最高,为26%;DPF的PM去除率超过90%,经过DPF后核态颗粒体积分数明显增加,聚集态颗粒体积分数明显减小.

煤基燃料燃烧颗粒物对颗粒捕集器沉积过程的影响

探讨了柴油机燃用代用燃料后,排气颗粒物结构特征的变化规律。依据柴油机台架试验,使用0%、5%、15%甲醇掺混比的F-T(Fischer–Tropsch)合成柴油,在标定工况下采集颗粒。用同步辐射小角散射分析方法测量颗粒物摩擦力、粒径等参数。基于实验数据,在EDEM软件中建立颗粒模型,模拟了颗粒碰撞沉积过程。结果表明:随甲醇掺混比的增加,甲醇、F-T柴油燃烧颗粒间摩擦力增加0.6 N,平均粒径增加2.44 nm。沉积过程中,颗粒捕集器(DPF)单元体非迎风面的沉积量急剧增加;颗粒沉积效率随沉积时间的增加而增加;随摩擦力增大、粒径增大,颗粒层厚度及颗粒链长度也随之增加。甲醇掺混比的改变使得颗粒整体向更多、更细的方向变化,燃料类型及掺混比的改变显著影响了颗粒在DPF载体上的沉积状态。

重型柴油机LLC循环与其他瞬态循环排放特性的对比分析

目前,城市车辆低负荷运行工况占比较多,但较容易被忽视。为深入探究低负荷循环(Low Load Cycle, LLC)排放特性与其他循环的差异,基于重型柴油发动机开展台架排放试验。通过运行LLC、全球统一的瞬态循环(World Harmonized Transient Cycle, WHTC)、中国发动机瞬态循环(China Heavy-duty Transient Cycle, CHTC)试验循环,测取NOx、碳氢化合物(Hydrocarbon, HC)和CO排放体积分数及颗粒数(Particulate Number, PN)排放因子数据,并对比上述3种循环的工况特征、负荷分布、比排放量结果,分析上述循环的高排放工况分布特征,进而对比LLC循环冷热态工况排放特性差异。结果发现:该发动机运行LLC循环时,怠速以及当转矩在400 N·m以下、转速为1 600~2 200 r/min时的工况点比其他循环分布更多,0~5%负荷区间分布占比更高;LLC循环热态NOx比排放量为1 572.13 mg/(kW·h),LLC循环和CHTC循环工况对于NOx排放的要求更为严格,LLC循环的排气温度总体相对偏低;冷态条件使得低负荷、低转速工况的NOx排放增加量尤为明显;LLC与CHTC循环的PN高排放现象主要出现在0~10%负荷区间,CHTC循环在50%~60%负荷区间也存在高排放峰值,WHTC循环PN高排放总体分布相对较为平均;LLC循环的低排气温度会对选择性催化还原(Selective Catalytic Reduction, SCR)转化效率产生负面影响,且冷启动条件下会进一步加剧,使得NOx排放水平远超WHTC和CHTC循环。

柴油机废气再循环冷却器翅片断裂分析及优化

针对某柴油机废气再循环冷却器进气口直齿翅片出现断裂问题,进行分析与优化。基于热流固耦合仿真方法,对废气再循环冷却器进行温度场与应变分析,结合翅片断裂处扫描电镜图像,确定断裂原因为热疲劳。为了解决热疲劳问题,设计三种方案,进行温度和应变仿真分析。三种方案分别为采用SUS444不锈钢材料,翅片厚度增大,将翅片向内缩进。将三种方案结合,采用综合方案完成优化,有效降低了翅片温度,减小了应变,并且通过冷热循环试验验证。

柴油车尾气颗粒物净化研究进展

柴油车尾气颗粒物是大气污染物来源之一,尾气颗粒物的净化是后处理的重要组成部分,且技术发展较快。综述了柴油机尾气颗粒物的组成以及柴油机尾气颗粒物的净化方法,包括微粒过滤捕集技术、折叠滤筒、尾气洗涤净化技术、低温等离子体协同催化净化技术、微型旋转超重力机净化技术等。各种技术都有其优势和不足,需要根据柴油车功率和应用环境选择适宜的净化技术和设备,把尾气预处理与深度净化相结合,把颗粒物净化技术与脱除CO、NO_(x)、碳氢技术协同应用,不影响发动机性能且无安全隐患。

柴油机DPF孔道内积碳层的运动及分布特性

为研究积碳层对柴油机颗粒捕集器(DPF)堵塞失效的影响,采用连续流体介质与固体颗粒层离散元耦合的方法,结合DPF可视化试验加以验证,研究DPF孔道内不同形状、尺寸和厚度的积碳层运动以及分布.结果表明:积碳层表面积越大,发生拥塞的位置越靠近孔道后段;圆形轮廓的积碳层易于相互堆叠,三角形轮廓的积碳层拥塞段会集中于孔道中段,正方形轮廓的积碳层拥塞段的结构较为稳定.积碳层长度与DPF进口孔径比例为0.5时,拥塞段的密度与长度会明显增加,但是拥塞段的稳定性会降低.随着积碳层厚度增加,拥塞段的位置会靠近孔道前段.

极限碳载量下催化型柴油机颗粒捕集器再生特性研究

基于某高压共轨柴油机搭建了三维催化型柴油机颗粒捕集器(catalytic diesel particulate filter,CDPF)模型,研究了极限碳载量下不同结构CDPF的再生特性,分析了不同极限碳载量条件下灰分量及灰分分布系数对不同结构CDPF再生特性的影响。结果表明:极限碳载量下对称孔道结构(symmetrical cell technology,SCT)和非对称孔道结构(asymmetric cell technology,ACT)CDPF最高温度峰值随着极限碳载量增加而上升,不同结构CDPF压降随着极限碳载量的增加而上升且差距明显。随着极限碳载量的升高,CDPF载体温度及碳烟再生速率上升迅速且峰值明显增高。极限碳载量下,CDPF压降及载体最高温度随着灰分量的增加而上升,不同结构CDPF压降特性差异较大,SCT结构载体最高温度高于ACT结构,CDPF碳烟再生速率随灰分量的增加先上升后下降,在灰分量高时碳烟再生速率上升快且峰值高。极限碳载量下,相同灰分分布系数的不同结构CDPF压降差距明显,SCT结构压降整体高于ACT结构,不同结构CDPF碳烟再生速率和载体温度均随灰分分布系数的增加先上升后下降。

基于响应曲面法的DPF捕集性能多目标优化

以提高整体捕集性能为目的开展柴油机颗粒捕集器(DPF)结构参数多目标优化设计,利用GT-Power建立DPF捕集模型,通过发动机台架试验验证了仿真模型的可靠性。以最大压降和初始过滤效率为优化目标,以孔隙率、孔直径、壁厚、过滤体长度和直径5个结构参数为优化变量,基于Box-Behnken试验设计方法构建了DPF捕集性能二阶响应面模型,通过三维响应面图对结构参数显著性与交互作用进行仿真分析,采用满意度函数法进行多目标参数优化。结果表明,孔直径对最大压降的影响较小,较小的孔隙率与壁厚、较大的过滤体直径有利于降低DPF最大压降,而适当增大过滤体直径与壁厚可提升DPF初始捕集效率。协同优化后的DPF压降较优化前下降51.34%,优化后的DPF初始过滤效率趋近于100%。