不同反应气氛下负载型Cu-Co/ZSM-5催化剂的柴油车NO_x净化性能

在模拟柴油车尾气气氛下,利用微反装置研究了浸渍法制备的Cu-Co/ZSM-5催化剂在不同反应气氛下的C3H8选择性催化净化NOx性能。结果表明,具有良好的净化NOx起燃性能和高温选择性的3%Cu-3%Co/ZSM-5催化剂在不同的反应气氛下催化性能各异。O2体积分数较低时(≤6%),O2的存在有利于C3H8催化还原NOx,催化剂的NOx转化率随O2体积分数的增加而增加;高温(300~400℃)反应时O2体积分数较高(≥6%)对C3H8催化还原NOx是不利的,O2的增加使催化剂的NOx转化选择性变差,NOx转化率下降。催化剂最适于的O2体积分数为2%~8%。C3H8体积分数越高,越有利于NOx的还原。反应气氛中的CO2和CO的体积分数变化对催化剂的C3H8催化还原NOx活性没有明显的影响,该催化剂仍具有较高的稳定NOx净化性能。催化剂在使用过程中应匹配好发动机的空燃比。     

Investigation on Spray Behavior and NOx Conversion Characteristic of a Secondary Injector for a Lean NOx Trap Catalyst

Lean NOx trap (LNT) catalyst has been used to reduce NOx emissions from diesel engines. The LNT absorbs NOx in lean condition and discharges N2 by reducing NOx in rich conditions. Thus, it is necessary to make exhaust gas lean or rich conditions for controlling LNT system. For making a rich condition, a secondary injector was adopted to inject a diesel fuel into the exhaust pipe. In the case of secondary injector, the behavior of spray is easily affected by high temperature (i.e., 250 ～ 350 °C) occurred in the exhaust manifold. Therefore, it is needed to investigate the spray behavior of diesel fuel injected into an exhaust manifold, as well as the conversion characteristics for a lean NOx trap of a diesel engine with LNT catalyst. The characteristics of exhaust emissions in NEDC (New European Driving Cycle) mode were analyzed and spray behaviors were visualized in various exhaust gas conditions. The results show that as the exhaust gas mass flow increases, the spray cone angle becomes broad and the fuel is directed to the flow field. Besides, the cone angle of spray is decreased by centrifugal force caused in exhaust gas flow field. In addition, the effects of nozzle installation degree, injection quantity, and exhaust gas flow on NOx conversion performance were clarified.     

采用低温等离子体同步净化柴油机PM和NO_x(一):物理仿真

为了实现对柴油机尾气中PM和NOx的同步去除,将静电旋风捕集技术与等离子体协同烃类选择性催化还原技术(Plasma/HC-SCR)相结合开发了一套柴油机后处理原理性试验装置。该装置集柴油机PM的静电捕集、PM的氧化燃烧、NOx的选择性催化还原于一体,对在富氧条件下利用烃类选择还原催化和静电旋风捕集同步去除柴油机PM和NOx进行了利用可控标准气体的模拟试验研究,得到了净化效率随相关参数之间的变化规律。在单纯的等离子体环境下,NO浓度降低,NO2浓度增加,但总的NOx基本保持不变;使用催化剂的同时辅助等离子体可以使NO的峰值转化率所对应的温度向低温区偏移50℃左右;催化剂、等离子体、还原HC对于降低炭烟的起燃温度都有影响,同时使用可以使炭烟的起燃温度最低降低到280℃。此装置实现了柴油机PM和NOx的同步去除。     

Combustion characteristics of hydrotreated vegetable oil – diesel blend under EGR and supercharged conditions

This paper investigates the effects of Hydrotreated vegetable oil-diesel blend to combustion characteristics under various ambient oxygen concentrations and ambient pressure. Combustion characteristics were investigated using heat release rate analysis, two color method, soot concentration measurement and NOx concentration measurement. The experiments were carried out on a rapid compression expansion machine to simulate the ambient condition of a CI engine at TDC. Synthetic gas with oxygen concentrations of 21 %, 15 % and 10 % were used to simulate EGR conditions. A single hole injector was used with five different fuels: commercial diesel, HVO-commercial diesel blends and HVO. The results showed that increasing HVO blending percentages decreased ignition delay, flame temperature, soot concentration and NOx concentration. Heat release at oxygen concentration of 10 % dramatically dropped due to a shortened ignition delay, which resulted in less combustion. A decreased oxygen concentration from applied EGR conditions not only increased ignition delay, heat release, flame temperature and NO_x concentration, but also increased soot concentration. A combination of EGR and supercharged conditions by increasing ambient pressure and decreasing oxygen concentrations resulted in increased heat release, decreased flame temperature, ignition delay and soot concentration, compared to EGR conditions.     

柴油机SCR后处理控制策略开发与研究

为选择性催化还原技术提出了还原剂喷射的控制策略。它根据原机NOx排放浓度脉谱、排气温度和空速脉谱等计算还原剂的喷射速率。分别通过试验研究了NH3/NOx比值、排气温度和空速对NOx转化率和氨泄漏浓度的影响以及SCR催化剂的氨吸附和脱附特性,并根据研究结果,分别确定稳态和瞬态工况下尿素溶液喷射的控制方案,因而实现了ESC稳态循环和ETC瞬态循环下的控制目标。此外,冷机起动试验表明,该阶段的排气温度低,NOx排放浓度较高,故应采取措施减少低温工况下NOx的排放。     

尿素-SCR技术对NOx转化率和NH3排放的影响

在AVL发动机台架上就尿素-SCR技术对NOx转化率和NH3排放的影响进行了试验,催化剂为钒氧化物,尿素质量分数从0变化到50%.研究发现,排气温度、空速、尿素浓度、尿素喷射量对NOx转化率和NH3排放有着重要影响:排气温度升高,NOx转化率先升高后下降,400～450℃是转折点;提高排气空速,NOx转化率线性下降,N...     

基于一维/三维模型耦合的富氧燃烧天然气发动机数值模拟

以某1.0L3缸汽油机为基础,利用GT-Power与Converge建立了天然气发动机耦合仿真模型,并利用原机试验数据对模型进行了验证,研究了进气富氧与EGR对天然气发动机性能的影响特性,对利用进气富氧与EGR改善天然气发动机的性能进行了探讨。结果表明,随进气氧气体积分数提高,天然气发动机平均有效压力显著提高,最大可提高22.8%(氧体积分数为28%时);同时缸内温度和NOx排放升高,排气与传热的能量损失增加,燃气消耗率略有升高。加入EGR可以降低富氧燃烧下天然气发动机燃气消耗率,随着EGR率增加,燃气消耗率主要呈先减小后增加趋势;且随进气氧浓度提高,各浓度下最低燃气消耗率对应的EGR率逐渐提高;NOx排放随EGR率增加而逐渐降低,在进气氧体积分数为23%,25%,27%,29%时,EGR率分别为10%,15%,20%,25%即可将NOx排放降到原机水平;利用进气富氧与EGR可以有效地改善天然气发动机动力不足与NOx排放高的状况。     

Simulation Study on Thermal Management Strategy to Achieve 99 % SCR Efficiency of a Heavy-Duty Diesel Engine over a Transient Cycle

In this study, NOx conversion characteristics of a urea selective catalytic reduction (SCR) system equipped on a heavy-duty diesel engine were evaluated through engine dynamometer bench tests over a scheduled world harmonized transient cycle (WHTC). Also, based on transient SCR simulations, the thermal management strategy to improve SCR NOx conversion efficiency was investigated. As a result, it was found that a selective increase in exhaust temperature at low temperature period would be a useful measure to increase SCR efficiency on WHTC mode. From the baseline SCR efficiency of around 98 % on WHTC mode, the current simulation results have shown that around 99 % level of SCR efficiency would be achievable by increasing exhaust temperatures with modifying diesel exhaust fluid (DEF) dosage. Another valuable contribution of this study is that the design guidelines for controlling exhaust temperature and DEF injection to obtain a target NOx conversion efficiency are presented for SCR systems of heavy-duty diesel engines on transient operating conditions.     

集成式SCR催化转化消声器性能研究

运用GT-Power软件对两种不同结构的集成式SCR催化转化消声器进行了声学性能模拟,通过试验研究对比分析了集成式SCR催化转化消声器的压力损失及其NOx转化效率。结果表明:在增加穿孔管后集成式SCR催化转化消声器的消声效果在400~750 Hz区间内受到了削弱,在750~1 000 Hz区间内增强,增加穿孔管后压力损失增加。在绝大部分工况下,增加穿孔管后SCR催化转化消声器的NOx转化效率要明显高于无穿孔管的结构。     

采用低温等离子体同步净化柴油机PM和NO_x(二):试验研究

采用静电旋风捕集技术与等离子体协同烃类选择性还原技术相结合的方法研制了柴油机后处理装置,在柴油机试验台架上进行了实际柴油机排气净化试验,考察了实际柴油机排气环境下低温等离子体净化柴油机NOx和PM的实际效果。研究结果表明,随着进口流速的增加静电旋风捕集效率略有下降;低温等离子体降低了炭烟的再生温度,炭烟在等离子体和催化的共同作用下280℃即可催化燃烧;等离子体催化系统在外加还原HC的条件下NOx转化率最高可达60%。     

基于液压驱动气门的柴油机性能优化研究

在某柴油机上将传统凸轮驱动气门机构改进设计为液压驱动气门机构,利用仿真软件GT-Power建立液压驱动气门柴油机模型,分析进气滞后角、排气提前角和气门重叠角对柴油机动力性的影响,然后以扭矩最大为目标对配气正时进行联合仿真优化,最后对比两种内部EGR实现方法在不同负荷下的EGR率和对NOx排放量的改善效果。研究结果表明,在外特性下,液压驱动气门柴油机在中低转速时的动力性和经济性有了明显改善,扭矩比原机提高了5.6%,燃油消耗率降低了5.1%;但由于液压气门响应滞后,随着转速的升高,改善效果逐渐降低。在转速2 000r/min时,排气门晚关比排气门早关可以获得更大的EGR率,NOx排放量降幅也比排气门早关的大,在50%负荷时,NOx排放量降幅最大为23.8%。     

Effect of Hydrothermal Aging over a Commercial DOC on NO<Subscript>2</Subscript> Production and Subsequent SCR Efficiency

In this study, the effect of hydrothermal aging over a commercial diesel oxidation catalyst (DOC) on deterioration in nitrogen dioxide (NO₂) production activity has been experimentally investigated based on a micro-reactor DOC experiment. Through this experimental result, the NO₂ to nitrogen oxides (NOx) ratio at DOC outlet has been mathematically expressed as a function of DOC temperature according to various aging conditions. The current study reveals that the catalyst aging temperature is a more dominant factor than the aging duration in terms of the decrease in NO₂ production performance through DOC. The DOC sample hydrothermally aged for 25 h at 750 °C has displayed the lowest NO₂ to NOx ratio compared to the samples aged for 25 ~ 100 h at 650 °C. Also, in this study, the impact of hydrothermal aging of a DOC on the selective catalytic reduction (SCR) efficiency in a ‘DOC + SCR’ aftertreatment system was predicted by using transient SCR simulations. To validate the SCR simulation, this study has conducted a dynamometer test of a non-road heavy-duty diesel engine with employing a commercial ‘DOC + SCR’ system on the exhaust line. The current study has quantitatively estimated the effect of the variation in NO₂ to NOx ratio due to the hydrothermal aging of DOC on the NOx removal efficiency of SCR.     

Study of n-C<Subscript>12</Subscript>H<Subscript>26</Subscript> reforming over DFC catalyst in a simulated diesel exhaust

In lean-DeNOX catalysis reactions, hydrogen is a good reducing agent in PGM catalysts as well as an effective promoter in selective catalytic reduction reactions over base metal oxide catalysts. However, such a lean-DeNOX system, which uses hydrogen, requires an on-board fuel reforming system applicable to internal combustion engines. In this study, catalytic partial oxidation (CPOx) performance was tested in a laboratory for various reactants and hydrocarbon conditions. Volume concentrations of 5–10% oxygen and 0-5% water vapor were used to simulate diesel exhaust, and n-C₁₂H₂₆ was used as the feedstock for the reforming reaction. In the CPOx of n-C₁₂H₂₆, the highest hydrogen selectivity was 64% and was achieved at 100,000 h-1 GHSV. Additionally, the C/O ratio was less than unity in the absence of water vapor. However, as the water concentration was increased to 2.5 and 5.0 vol. % in the n-C₁₂H₂₆ CPOx reactions, the maximum hydrogen selectivity was increased from 64% in the absence of water to 70% and 75%, respectively. This effect is a consequence of the water-gas shift reaction over the catalyst bed. Regarding oxygen concentration effects, hydrogen selectivity slightly increased with increasing oxygen concentration from 10% to 15%. It was also found that the CPOx reaction of n-C₁₂H₂₆ can be ignited at temperatures below 300 C. Accordingly, it can be concluded that CPOx is a useful and feasible device for promoting diesel DeNOx catalysis in terms of hydrogen productivity and reaction initiation.     

废气再循环对车用柴油机性能与排放的影响

为了降低车用柴油机的NOx排放，研究了不同工况下EGR率对柴油机性能的影响。试验结果表明，采用EGR可以有效地降低NOx排放。大负荷比小负荷效果显著，但微粒的排放有所增加。小负荷采用EGR时可以改善发动机的燃烧，微粒排放基本没有变化。空燃比是影响微粒排放的关键因素，小负荷宜采用大EGR率，大负荷时宜采用小EGR率，以求在控制NOx排放降低的同时，总的微粒排放不至增加过多。     

前置DOC对SCR系统柴油机NO_x排放的影响

对装配前置DOC和无DOC的SCR系统柴油机进行稳态和瞬态试验,研究了前置DOC在不同循环状态下对NOx排放的影响。结果表明:前置DOC能显著提高SCR入口处NO2与NOx的体积比V(NO2)∶V(NOx),加速SCR反应,提高NOx转化效率,改善NOx排放;在ESC非怠速工况下,DOC对V(NO2)∶V(NOx)的影响会随着排气中氧含量和排气温度、空速的提高逐渐降低;温度超过一定范围时,NH3对O2的选择性突然提高,V(NO2)∶V(NOx)对NOx转化效率的影响将减小;DOC内氧化反应产生的热量有限,不足以提高SCR入口处排气温度,而DOC陶瓷载体的储热特性在瞬态循环下会对SCR入口温度产生一定影响,但这并不是改善NOx排放的主要原因。     

汽油机富氧燃烧特性试验研究

在1台4G18汽油机上进行富氧燃烧试验,进气中O2体积分数分别为21%,23%和25%,研究了不同富氧燃烧条件下的缸内压力、瞬时放热率及THC,CO和NOx排放.研究结果表明:在汽油机中低负荷典型工况下,随着进气中O2体积分数的增加,燃烧与排放均有改善,燃烧相位提前,缸内压力峰值和瞬时放热率峰值均增大,THC,CO排放...     

Operating strategy for gasoline/diesel dual-fuel premixed compression ignition in a light-duty diesel engine

Environmental problems have become a major issue for diesel engine development. Although emission aftertreatment systems such as DPFs (diesel particulate filters), LNTs (lean NOx traps) and SCR (selective catalytic reduction) have been used in diesel vehicles, the manufacturing cost increase caused by this equipment can be hard to be control. Thus, it is better for engine emissions to be reduced by improving the combustion system. A dual-fuel combustion concept is a recommended method to improve a combustion system and effectively reduce emissions. Low reactivity fuel including gasoline and natural gas, which was supplied to the intake port by the FPI (port fuel injector), improved the premixed air-fuel mixture conditions before ignition. Additionally, a small amount of high reactivity fuel, in this case diesel, was injected into the cylinder directly as an ignition source. This dual-fuel combustion promises lower levels of NOx (nitrogen oxide) and PM (particulate matter) emissions due to the elimination of local rich regions in the cylinder. However, it is challenging to control the dual-fuel combustion because the combustion stability and efficiency deteriorate due to the lack of ignition source and reactivity. Thus, it is important to establish an appropriate dual-fuel operating strategy to achieve stable, high efficiency and low emission operation. As a result of this research, a detailed operating method of dual-fuel PCI (premixed compression ignition) was introduced in detail at a low speed and low load condition by using a single cylinder diesel engine. Engine operating parameters including the gasoline ratio, a diesel injection strategy consisting of multiple injectors and timing, the EGR (exhaust gas recirculation) rate and the intake pressure were controlled to satisfy the low ISNOx (indicated specific NOx) and PM emissions levels (0.21 g/kWh and 0.1 FSN, 0.040 g/kWh, respectively) as per the EURO-6 regulation without any after-treatment systems. The results emphasized that a well-constructed dual-fuel PCI operating strategy showed low NOx and PM emissions and high GIE (gross indicated fuel conversion efficiency) with excellent combustion stability.     

混合动力控制策略对催化转化率影响的研究

在NEDC循环工况下,研究了采用400目催化转化器的混合动力汽车的动力控制策略对其催化转化器的转化效率的影响。研究表明,怠速停机后,残余排放物附着在气缸及排气管内,在发动机重新启动后,会造成催化转化器过载,从而使转化率下降;在加速断油过程中,由于没有燃油喷射,新鲜空气被直接排入排气管,造成排气管内氧浓度的增加,从而影响NOx的转化。更换600目催化转化器后,催化转化率有明显改善,但仍不能根除控制策略对转化率的影响。     

提高柴油机尿素SCR系统氮氧化物转化效率的试验研究

针对柴油机Urea-SCR后处理系统,为了有效提高NOx转化效率,考虑了包裹保温材料减少排气管散热从而提高载体温度、调整喷嘴位置、安装混合器等3种方法,并进行了不同温度和空速下SCR的NOx转化效率试验。试验结果表明:包裹保温材料能够在ETC循环中提高SCR载体温度20℃左右,从而使发动机更多工况处于SCR催化剂反应高效区域;喷嘴安装在更靠近发动机涡轮出口处(沿排气流反方向移动20 cm后),各工况下NOx转化效率均有所提高;安装混合器后在各工况下NOx的转化效率均有5%左右的提高,尤其在低温220℃时NOx的转化效率提高7%。     

非平衡等离子体净化发动机尾气的研究

按照“严控两端”的创新思路,以气体放电理论为基础,研制出了一套去除汽车尾气有害排放物的非平衡等离子体反应装置,并进行了去除NOx的试验研究。结果表明,在一定范围内,NOx去除率随进气放电反应管通电数目、排气梯度钢筒通电数目和钢筒内钼丝缠绕数目的变化而变化。在发动机中低速工况下,该尾气处理装置对NOx的去除率可达到65%左右。与传统三元催化器相比,该装置结构简单、成本低、可靠性高。若能进一步提升去污效果,具有很好的应用前景。