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 diesel engine with particulate filter using Fe-based fuel borne catalyst

The alteration and formation of toxic compounds and potential changes in the toxicity of emissions when using after-treatment technologies have gained wide attention. Volatile organic compound（VOC）, carbonyl compound and particle-phase polycyclic aromatic hydrocarbon（PAH） emissions were tested at European Steady State Cycle（ESC） to study unregulated emissions from a diesel engine with a fuel-borne catalyst and diesel particulate filter（FBC–DPF）. An Fe-based fuel-borne catalyst was used for this study. According to the results, brake specific emissions of total VOCs without and with DPF were 4.7 and4.9 mg/kWh, respectively, showing a 4.3% increase. Benzene and n-undecane emissions increased and toluene emission decreased, while other individual VOC emissions basically had no change. When retrofitted with the FBC–DPF, total carbonyl compound emission decreased 15.7%, from 25.8 to 21.8 mg/kWh. The two highest carbonyls, formaldehyde and acetaldehyde, were reduced from 20.0 and 3.7 to 16.5 and 3.3 mg/kWh respectively. The specific reactivity（SR） with DPF was reduced from 6.68 to 6.64 mg/kWh. Total particle-phase PAH emissions decreased 66.4% with DPF compared to that without DPF. However, the Benzo[a]pyrene equivalent（BaPeq） with DPF had increased from 0.016 to 0.030 mg/kWh.Fluoranthene and Pyrene had the greatest decrease, 91.1% and 88.4% respectively. The increase of two- and three-ring PAHs with DPF indicates that the fuel-borne catalyst caused some gas-phase PAHs to adsorb on particles. The results of this study expand the knowledge of the effects of using a particulate filter and a Fe-based fuel-borne catalyst on diesel engine unregulated emissions.     

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 di erent 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.     

柴油/甲醇二元燃料发动机的非常规排放特性研究

在一台电控单体泵增压中冷柴油机上,利用FTIR研究柴油/甲醇二元燃料发动机不同甲醇替代率下的非常规排放特性.结果表明,柴油/甲醇二元燃料燃烧模式下的非常规排放物甲醛、未燃甲醇、1,3-丁二烯及N_2O的比排放与纯柴油模式相比均有不同程度的增加,且均随着甲醇替代率的增加而增加;甲醛、未燃甲醇及N_2O的比排放随着负荷的增加逐渐降低;随着转速的增加,未燃甲醇的比排放趋势相差不大,排放量也无明显差别;CO_2的比排放随着甲醇替代率的增加而下降.     

DOC+CDPF对生物柴油燃烧颗粒排放特性的影响

以一台满足国五排放法规的车用柴油机为样机,研究加装氧化催化转化器DOC与催化型颗粒捕集器CDPF(DOC+CDPF后处理装置)前后,柴油机燃用B20燃料(燃料含20%体积掺混比的生物柴油)的颗粒排放特性.结果表明,在未加装该后处理装置时,该机排气颗粒数量浓度的粒径分布呈双峰形态,B20燃料的排气颗粒数量浓度的峰值粒径在10nm和50nm附近,纯柴油的排气颗粒数量浓度的峰值粒径在50nm和200nm附近.在颗粒粒径小于120nm的区域,该机燃用B20燃料的排气颗粒数量浓度大于纯柴油.加装该后处理装置后,该机排气颗粒数量浓度的粒径分布呈多峰形态,峰值粒径在10nm、20nm和60nm附近.加装DOC+CDPF后,不论是柴油还是B20燃料,与原机相比,柴油机排气颗粒总数量下降明显,其中60~200nm粒径范围的颗粒数量浓度降幅更为显著.在相同工况下,DOC+CDPF对柴油机燃用B20燃料的颗粒总数量净化效率高于纯柴油.     

Characterization of polycyclic aromatic hydrocarbon emissions from diesel engine retrofitted with selective catalytic reduction and continuously regenerating trap

Two after treatment units, selective catalytic reduction (SCR) and continuously regenerating trap (CRT), were independently retrofitted to a diesel engine, with the objective to investigate their impact on the conversion/reduction (CR) of polycyclic aromatic hydrocarbons (PAHs). The experiments were conducted under the European steady state cycle (ESC) first without any retrofits to get baseline emissions, and then with SCR and CRT respectively, on the same engine. The particulate matter (PM)-phase PAHs were trapped in fiberglass filters, whereas gas-phase PAHs were collected in cartridges, and then analyzed using a gas chromatograph-mass spectrometer (GC-MS). Both PM-phase and gas-phase PAHs were greatly reduced with CRT showing respective CR of 90.7% and above 80%, whereas only gas-phase PAHs were abated in the case of SCR, with CR of above 75%. Lower molecular weight (LMW) PAHs were in abundance, while naphthalene exhibited a maximum relative contribution (RC) to LMW-PAHs for all three cases. Further, the CR of naphthalene and anthracene were increased with increasing catalyst temperature of SCR, most likely due to their conversion to solid particles. Moreover, the Benzo[a]Pyrene equivalent (BaP_eq) of PAHs was greatly reduced with CRT, owing to substantial reduction of total PAHs.     

Impacts of continuously regenerating trap and particle oxidation catalyst on the NO2 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/NO_x 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/NO_x. 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.     

柴油/甲醇组合燃烧(DMCC)减少重载柴油机烟度排放的试验研究

在一台满足国三排放法规要求的重载车用增压中冷电控单体泵柴油机上,将其改造成柴油/甲醇组合燃烧(DMCC)发动机并进行台架试验.利用电控单元控制向进气歧管喷射的甲醇量及其喷射时刻,原柴油机供油系统保持不变.试验主要研究在稳定工况时,不同的负荷以及不同的甲醇对柴油的比例情况下,经催化转化后发动机干炭烟烟度(415烟度)和不透光烟度(439烟度)排放的情况.试验结果表明,在燃用现有市售的燃油条件下,与原机相比,相同工况下采用DMCC的干炭烟烟度和不透光烟度都有大幅度的减少.干炭烟的最大降幅达95%,平均降幅达到50%以上.在柴油喷射量不变的情况下,增加甲醇喷射量,干炭烟烟度会持续减小,而不透光烟度呈先减少后增加的趋势.同负荷时的甲醇对柴油替代率为44.88%到56.73%时,不透光烟度存在最低点,并且发动机的烟度排放存在最优值.在同一工况下,随着柴油对甲醇的比例增加,发动机的干炭烟烟度和不透光烟度排放都逐渐增加.     

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, CO2, O2, 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 Al and Cr in moss, was significantly increased. Glass-fibre filters were significantly enriched in Al, 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.     

FBC-DPF在柴油机颗粒物控制中的应用研究

目前针对加装FBC-DPF(燃油添加剂-柴油机颗粒捕集器)后的柴油机放特性研究较少,并且缺乏FBC-DPF对颗粒物中PAHs排放量的影响效果研究. 为全面评估加装FBC-DPF后柴油机颗粒物排放特性和FBC-DPF对柴油机尾气中的颗粒物排放污染控制效果,在发动机台架上对装有FBC-DPF的重型柴油机进行了颗粒物排放特性试验. 利用电子低压撞击仪(ELPI)测量加装FBC-DPF前、后柴油机颗粒物的数浓度与粒径分布,用玻璃纤维滤膜采集加装FBC-DPF前、后尾气中的固相PAHs,利用色谱质谱联用仪对加装FBC-DPF前、后尾气中的固相PAHs进行定量分析. 结果表明:①加装FBC-DPF后柴油机排放的颗粒物数浓度大幅降低,FBC-DPF对尾气中颗粒物的捕集效率平均值在95%左右;②加装FBC-DPF后柴油机固相PAHs总比排放量有所降低,在大负荷区域降幅在25.0%~88.0%之间;③加装FBC-DPF前的颗粒物中位直径为30~89nm,而加装FBC-DPF后的颗粒物中位直径为41~98nm,平均增幅为38.2%. 对于国Ⅳ及未来国Ⅴ柴油机排放法规,FBC-DPF是解决柴油机颗粒物排放的有效手段;此外,FBC-DPF可以大幅降低柴油机尾气中的有毒成分,并且能够适应高含硫量的燃油环境.      

柴油烃族组分对柴油机排放的影响

柴油烃族组分可影响柴油的理化特性,从而影响柴油机的燃烧过程,进而对排放产生重要影响.本研究针对烃族组分含量不同的14种柴油,开展了排放特性的试验研究,基于试验结果采用主成分分析法及回归分析法揭示影响柴油机排放性能的关键组分及作用规律,并得到了柴油机排放与关键组分的经验公式,可在一定程度上预测排放特性.分析结果表明,总芳烃是影响柴油机排放的关键组分,当其含量介于5%～17%时,可使NO_x、soot(碳烟)、CO、HC排放均处于较低水平.此外,多环芳烃对柴油机排放有重要影响,其中的苊类、苊烯类对NO_x、碳烟、CO排放的影响作用更为显著,而其他烃族组分与柴油机排放的规律性相对较差.不同工况下,柴油机排放规律有所不同,在低负荷下柴油机排放对总芳烃含量更加敏感.     

满足国五排放标准的柴油甲醇双燃料发动机非常规排放研究

在一台装备有电控单体泵增压中冷系统柴油机的进气管上,加装甲醇喷射装置并向进气道喷入定量的纯甲醇,结合废气再循环(EGR)技术并使用氧化催化转化器(DOC)组合微粒氧化催化器(POC)后处理系统,使其常规排放能满足国五排放法规基础上,全面研究了柴油甲醇双燃料(Diesel Methanol Dual Fuel,DMDF)发动机的非常规排放特性.在采用国五排放法规标准规定的ESC(稳态13点工况)测试方法条件下,利用FTIR(傅里叶变换红外检测法)对DMDF发动机的检测结果表明:该机非常规排放物主要为甲醇、甲醛、1,3-丁二烯、苯、甲苯和SO2,非常规排放物的全工况加权比排放为19.532 g·kW~(-1)·h~(-1),其中,甲醇的全工况加权比排放为11.395 g·kW~(-1)·h~(-1),甲醛的全工况加权比排放为5.927g·kW~(-1)·h~(-1),SO2的全工况加权比排放为0.053 g·kW~(-1)·h~(-1),其余排放物为痕量水平.在催化氧化装置处理后非常规排放物全工况加权比排放为0.115 g·kW~(-1)·h~(-1),降幅为99.41%.催化氧化装置对甲醇、1,3-丁二烯、苯和甲苯的消除率为100%,对甲醛的消除率为99.04%.     

采用SCR技术降低车用柴油机的NOx排放

NOx是车用柴油机排气中的主要有害排放物，机外措施是控制柴油机排放的有效措施，是柴油机排放控制的关键技术。文中重点介绍了降低车用柴油机NOx排放的机外措施之一选择催化还原(SCR)技术。     

车用柴油机燃用棕榈生物柴油的颗粒物排放特性研究

在满足国Ⅳ排放法规的车用柴油机上研究了燃用不同掺混体积比例的棕榈油生物柴油的颗粒物排放特性.试验中棕榈油生物柴油的掺混比例分别为0%、10%、20%、50%和100%,采用DMS500型快速颗粒光谱仪测试分析了发动机在外特性和负荷特性时的颗粒物数量浓度、质量浓度及粒径分布.研究结果表明:随生物柴油掺混比例的增加,颗粒物质量浓度降低.燃用生物柴油后颗粒物的数量浓度在大负荷明显降低,中小负荷呈升高趋势.生物柴油的排气颗粒物呈核态和凝聚态的双峰分布特征,核态数量浓度所占比例高于柴油,凝聚态的质量浓度所占比例略低于柴油.生物柴油颗粒物的几何平均直径小于柴油.     

DOC对柴油机燃用生物柴油颗粒物微观形貌及SOF组分的影响

为研究氧化催化转化器（DOC）对柴油机燃用调合生物柴油（B0,B20）后排放颗粒物微观形貌及可溶性有机组分（SOF）的影响规律,对DOC作用前后的排气颗粒物进行采样,利用透射电镜（TEM）和气相色谱-质谱仪（GC-MS）开展颗粒物理化特性研究.结果表明：未加装DOC时,与B0相比,B20排放颗粒物基本碳粒子粒径减小,分形维数增加,团聚堆积现象加剧;SOF组分中的脂类和酸类物质质量分数增加,烷烃类、芳香烃和酚类物质质量分数减少,C26~C35的质量分数降低.加装DOC后,B0和B20排气颗粒物团簇程度降低,分形维数降幅分别为10.1%和15.5%;SOF组分中芳香烃类和酚类物质质量分数增加,烷烃类、脂类、酸类质量分数减小,C15~C25质量分数下降;B0排放颗粒物SOF中C26~C35质量分数降低41.4%,而B20增加865.8%.     

不同喷射方式对柴油/甲醇组合燃烧尾气中甲醛排放的影响

在一台经过改装的压燃式柴油机上进行了柴油/甲醇组合燃烧试验,对比了甲醇的不同喷射方式(顺序喷射与连续喷射)对组合燃烧尾气中甲醛排放的影响.试验结果表明,顺序喷射方式下尾气中的甲醛浓度要低于连续喷射尾气中的结果,在低负荷工况时,顺序喷射最大降低量达32%,在中高负荷工况下,两种喷射方式的甲醛排放相差不大.对比甲醇对柴油相同替代率时,两种喷射方式均表现在低负荷时的甲醛排放最多,而且甲醛排放差值也较大.此外,试验结果还表明,顺序喷射的燃料经济性要优于连续喷射.     

正丁醇/柴油复合燃烧对轻型柴油机排放的影响

通过在一台轻型柴油机上加装低压共轨实现在进气歧管上的正丁醇喷射,喷射压力恒定为0.35 MPa;柴油采用缸内直喷,喷射压力恒定为120 MPa;采用自主开发的电控单元(ECU)分别控制柴油与正丁醇的喷射,实现正丁醇/柴油复合燃烧.试验研究了在2800 r·min~(-1)不同负荷下正丁醇喷射量对排放量及颗粒物粒径分布的影响.结果表明:随正丁醇喷射量增加,NO_x和碳烟排放减少,高负荷时降低幅度较大;HC和CO排放增加,低负荷时增加幅度较大;颗粒物生成总量降低且粒径分布重心左移;低负荷时相比于大粒径颗粒物,正丁醇对小粒径颗粒物数浓度的减少更明显;大粒径颗粒物减少比例与小粒径颗粒物减少比例的差距随正丁醇喷射量的增加而减小.     

Effect of catalyzed diesel particulate filter and its catalyst loading on emission characteristics of a non-road diesel engine

In this study, the effects of a diesel oxidation catalyst (DOC) coupled with a catalyzed diesel particulate filter (CDPF) with different catalyst loadings on the power, fuel consumption, gaseous and particulate emissions from a non-road diesel engine were investigated. Results showed that the after-treatment had a negligible effect on the power and fuel consumption. The reduction effect of the DOC on the CO and hydrocarbon (HC) increased with the engine load. Further reductions occurred coupling with the CDPF. Increasing the catalyst loading resulted in a more significant reduction in the HC emissions than CO emissions. The DOC could increase the NO₂ proportion to 37.9%, and more NO₂ was produced when coupled with the CDPF below 250°C; above 250°C, more NO₂ was consumed. The after-treatment could reduce more than 99% of the particle number (PN) and 98% of the particle mass (PM). Further reductions in the PN and PM occurred with a higher CDPF catalyst loading. The DOC had a better reduction effect on the nucleation particles than the accumulation ones, but the trend reversed with the CDPF. The DOC shifted the particle size distribution (PSD) to larger particles with an accumulation particle proportion increasing from 13% to 20%, and the geometric mean diameter (GMD) increased from 18.2 to 26.0 nm. The trend reversed with the CDPF and the accumulation particle proportion declined to less than 10%. A lower catalyst loading on the CDPF led to a higher proportion of nucleation particles and a smaller GMD.     

电动增压补气消除柴油机瞬态加速冒烟的试验

将自行开发的、适用车载24V电源的电动增压补气系统在一台490QDI柴油机上进行了实验研究.实验工况包括起始负荷分别为0和40N.m的加载加速的瞬态工况以及1400r·min-1、60N·m,1600 r·min-1、90N-m和1800 r.min-1、120N·m 3种低转速、大扭矩稳态工况,针对以上工况分别进行了有无电动增压补气的实验.试验结果表明,有电动增压补气的柴油机同原机相比,零负荷加载加速时的微粒排放降低达70%以上,瞬间输出功率最大可提高54.5%;在稳态工况时,HC、CO排放都随着电机转速的升高而降低,最大减少量分别达到66.7%和75.O%;波许烟度平均减小50%以上.此外,加速补气对提高燃油经济性也有一定效果,比油耗最大能降低7.46%.     

喷射时刻对柴油甲醇组合燃烧发动机颗粒物排放的影响

为了进一步减少甲醇掺烧后的柴油机颗粒物排放,在一台由增压中冷的高压共轨柴油机改造成的柴油甲醇组合燃烧(DMCC—diesel/methanol compound combustion)发动机上详细研究了柴油喷射时刻对两种燃料共燃时的颗粒物生成及其排放的影响.试验工况选择重型柴油机常用的A50工况.试验结果表明,当柴油在上止点后喷射时,颗粒物排放的数量浓度随着甲醇替代率的增加而减少,当上止点前喷射时,颗粒物的数量浓度先减少后增加.随着喷射时刻的提前,颗粒中超细颗粒所占比例增大.随着喷射时刻的推迟,甲醇替代率降低颗粒物质量浓度的作用增强,同时甲醇替代率降低颗粒物几何平均直径的作用减弱.