DPF主动再生温度控制试验研究

由于柴油机运行工况条件复杂，中、低负荷工况下排气温度较低，无法满足柴油机颗粒捕捉器（DPF）主动再生的温度要求，因此需要对再生温度控制进行系统研究。研究了稳态工况下通过调节柴油机后喷油量、节气门开度对DPF内部温度控制的影响，以实现DPF入口温度满足主动再生的要求；同时研究分析降怠速（DTI）工况下不同炭载量载体再生时，DPF内部温度变化情况，以提高DPF主动再生过程中的安全性。结果表明：调节柴油机后喷油量、节气门开度，能够有效控制DPF内部温度，DTI工况下炭载量是影响DPF内部最高温度的主要因素。     

柴油机颗粒捕集器特性测试评价

为了满足柴油机颗粒物(particulate matter,PM)排放标准的要求,应用微粒捕集器(diesel particulate filter,DPF)对柴油机排放的PM进行捕集并再生。对涂覆前后DPF的压差、不同工况下的被动和主动再生速率、压降特性及极限情况下的累碳量等进行测试评价。研究结果表明:相对于白载体,涂覆后的DPF压差略为增加;在氧化催化器(diesel oxidation catalyst,DOC)作用下,DPF捕集的碳颗粒较易发生被动再生,连续再生速率随着温度升高而提高;温度为400℃时,累碳速率和被动再生速率达到动态平衡,超过600℃时发生主动再生;在降怠速情况下测试累碳量,并通过轻型车排放测试规程(world harmonized light vehicles test cycle,WLTC)进行排放试验验证,结果表明,DPF对PM和粒子数量(particle number,PN)的捕集效率满足工程目标要求。     

柴油机微粒捕集器降怠速再生过程载体温度的控制

针对柴油机微粒捕集器降怠速再生过程载体峰值温度偏高问题进行了基于排气中氧气体积分数控制策略的降怠速再生试验.结果表明:在高怠速工况通过耦合调整再循环废气和进气流量可有效控制排气中氧气体积分数低至8%以下,而氧控所引起的燃烧恶化也导致了HC、CO排放量增大;碳载量和排气流量相同条件下,进行的氧控降怠速再生试验过程其载体内部峰值温度显著低于原机非氧控降怠速再生数值;提高载体碳载量并进行氧控降怠速再生,微粒加载背压和载体峰值温度仍在发动机正常运转以及载体材料温度安全范围内,满足安全以及可靠再生的同时达到了拓展安全再生碳载量限值以及延长微粒捕集器再生周期的目的.     

基于气流引导的碳化硅CDPF主动再生温度特性

基于后处理系统的导流装置,采用模拟和试验对不同封装结构下的载体温度特性进行研究．结果表明：碳载量为6 g/L时,原机方案下喷油点火主动再生过程中的峰值温度和最大温度梯度分别为1 239℃和124.9℃/cm,造成柴油机颗粒捕集器(DPF)载体热熔失效和热应力失效．加装导流装置后,载体内部的速度、温度分布较均匀,其中,高开孔率方案的速度均匀性系数达到了0.967．碳载量为6 g/L时,高开孔率方案下采用喷油点火和喷油助燃两种主动再生方式,载体内部的再生峰值温度均出现在载体后段位置,且中心温度高于外缘温度,分别为845.5℃和597.8℃,最大温度升高速率和温度梯度分别为14.9℃/s、31.78℃/cm和8.7℃/s、4.37℃/cm,温度升高速率及温度梯度较原机均大幅降低,能够保证载体在主动再生过程中高效安全．     

DPF碳载量模型的建立及试验

为弥补微粒捕集器(DPF)压差传感器在低排气流量条件下测量结果偏差较大的不足,提高DPF主动再生触发时刻判断的准确性,建立了DPF碳载量理论计算模型,并在世界统一瞬态循环(WHTC)测试循环下进行了试验验证.结果表明:WHTC测试循环下DPF碳烟累积过程中,计算结果与测量结果间的偏差均值在3.4%左右,当DPF碳载量达到再生设定值为3.2,g/L时,计算结果偏差约为5.9%;DPF初始碳载量为3.94,g/L,在WHTC测试循环下触发主动再生,循环结束后DPF碳载量计算结果和测量结果分别为0.32,g/L和0.39,g/L,二者之间的偏差在0.07,g/L左右.     

DPF热再生过程温度控制与试验

柴油机颗粒物捕集器(DPF)热再生发生时,其内部温度受DPF碳载量、排气温度和排气流量等影响,在特殊运行工况下具有较强非受控特性.为避免非受控再生引起的DPF失效风险,确保安全和可靠再生,通过降怠速(DTI)再生方式探讨了一种确定DPF安全再生温度的试验方法,得到安全再生温度曲线.针对DPF热再生过程中温度控制的大滞后特性,研究了一种采用发动机排气温度和排气流量作为增益补偿的优化热再生温度控制结构,并进行了控制算法的仿真分析和整车道路试验验证.结果表明:再生过程中对实际排气温度控制的超调量小于3%,稳态控制误差小于20℃,为促进DPF的安全和高效率再生提供了参考.     

载体结构对柴油机微粒捕集器再生的影响研究

以氧气为气源,利用自行设计的低温等离子体(non-thermal plasma,NTP)喷射系统,采用三种不同结构的柴油机颗粒捕集器(diesel particulate filter,DPF)装载装置对已捕集PM的DPF进行再生试验。通过研究DPF再生过程中内部温度及温度梯度的变化,对三种装载装置的再生效果进行了对比。研究结果表明:DPF内部各位置的温度均在180℃以下,远低于DPF的最高使用温度;PM的氧化界面随来流方向从上游向下游移动;DPF轴向和径向温度梯度均小于30℃/cm,低于DPF温度梯度限值;再生时间来看载体B和载体C的再生效果优于载体A;载体C中DPF内部流速分布最为均匀,有利于DPF的再生;载体C中DPF的最大温度梯度小于载体A和载体B,所承受的热应力最小,故载体C的结构更有利于DPF的使用寿命。     

车用柴油机颗粒过滤器载体温度分布研究

在标定柴油机颗粒过滤器(DPF)再生温度的过程中,需要掌握DPF载体内的温度分布情况,然后根据温度分布及温度梯度,确定合适的再生目标温度及颗粒物的质量。通过试验的方法研究了回归怠速工况下的DPF载体温度场分布。结果表明:在怠速跌落工况(DTI)下,DPF载体内的最高温度基本出现在DPF载体径向中心线,且靠近DPF出口端面的位置处。在保持再生目标温度不变的条件下,DPF载体内的最高温度随着颗粒物质量的增加而升高,且到达最高温度点所需时间随着颗粒物的增加而缩短,然后当颗粒物增加到一定程度后,所需时间延长。     

不同海拔下柴油机颗粒过滤器碳烟加载及再生特性研究

为研究不同海拔下柴油机颗粒过滤器(diesel particulate filter,DPF)碳烟加载规律及再生特性,在一台高压共轨柴油机上分别在两种大气压力(80kPa和100kPa)下进行了试验研究。研究内容包括全球统一瞬态循环(world harmonized transient cycle,WHTC)排放测试、DPF碳烟加载及压降特性、DPF再生过程温度场及压降特性。结果表明:高原环境下DPF的排气温度和各项排放数据指标均高于平原环境。高原环境下压降损失随碳烟的累积呈现出先快速增加后缓慢增加的趋势。再生温度和海拔高度对DPF再生压降、载体再生峰值温度、载体再生径向和轴向温度梯度、再生时机均有影响;再生温度越高及海拔越低,DPF再生压降越高;再生温度及海拔越高,再生时载体的峰值温度越高且载体径向和轴向温度梯度越大。     

颗粒捕集器主动再生温度特性试验研究

通过发动机台架试验研究氧化型催化转化器(diesel oxidation catalyst,DOC)起燃温度及颗粒捕集器(diesel particulate filter,DPF)主动再生时内部温度场分布规律。结果表明,当DOC入口温度高于240℃时,DOC可以起燃达到DPF设定的主动再生目标温度600℃;当DOC入口排气温度为240～280℃时,为减少HC二次污染,需选用较高的喷油速率,使DPF尽快达到设定目标温度。DPF主动再生过程分为3个阶段,起燃阶段DPF入口至出口温度依次快速升高;再生阶段DPF内部和出口温度高于入口温度约50℃;再生结束阶段,DPF入口至出口温度迅速降低,研究可为DPF主动再生温度的安全控制提供依据。     

灰分分布系数对柴油机性能的影响研究

通过构建柴油机耦合柴油机颗粒捕集器(diesel particulate filter,DPF)的一维热力学仿真模型,研究了灰分分布系数对柴油机性能的影响,并重点分析了灰分分布系数对柴油机系统热效率的影响。结果表明:炭载量为6 g/L,灰分量为33 g/L时,DPF压降和捕集效率随灰分分布系数增加而上升;随着灰分分布系数增大,柴油机转矩、缸内最最高燃烧压力及氮氧化物排放量均下降,碳烟排放量升高;灰分分布系数增加,柴油机有效燃油消耗率增加,DPF再生频率增加,包含柴油机热效率和DPF再生效率的柴油机系统热效率降低。单一地依靠DPF压降对主动再生时刻进行判定误差较大,且误差会随灰分量的增加呈现类指数增大。     

Soot deposition effects and microwave regeneration modelling of diesel particulate filtration system

Regeneration of accumulated soot particles in the substrate walls of the diesel particulate filtration system is one of the major challenges faced by the automotive industry. This study investigated the conversion efficiency and filtration behaviour of the after treatment system comprising of diesel oxidation catalysis (DOC) and diesel particulate filtration (DPF) system. The average conversion efficiency of hydrocarbons was close to 54% and filtration efficiency of the particle number emissions was around 92%. Characterization of the DOC and DPF substrate were conducted using microscopic imaging, Fourier transform infrared spectroscopy (FTIR) and particle size analysis (PSA). The results of FTIR study indicated the presence of carcinogenic agents trapped in the porous walls of the filter substrate. A model for microwave based regeneration system is proposed in this article and CFD analysis were conducted to determine the temperature and electric field distribution in the DPF substrate for a regeneration time of 180 s. Results of simulation showed that the microwave radiations raise the temperature close to soot oxidation temperature (873 K), ensuring effective regeneration.     

一种柴油机颗粒过滤器碳烟负载量的在线预估方法与试验研究

通过建立柴油机氮氧化物(NOx)排放、碳烟排放预估模型和柴油机颗粒物过滤器(DPF)内碳烟颗粒的催化氧化反应模型,探讨了一种基于质量平衡的DPF碳烟负载量在线预估方法。欧盟驾驶循环(NEDC)测试工况的排放试验结果表明,柴油机NOx和碳烟排放预估模型计算结果与试验结果的误差分别为5.1%和3.9%。在车辆实际道路行驶工况进行了DPF碳烟颗粒加载试验,结果表明,试验过程中对DPF碳烟负载量的在线预估值与试验结果的最大偏差为0.48g/L,平均偏差为0.17g/L,模型的平均预测误差为2.1%。本研究为热再生时机的准确判断提供了有效参考。     

Effect of fuel on the soot nanostructure and consequences on loading and regeneration of diesel particulate filters

An automotive diesel engine was tested in three representative modes of soot accumulation, active regeneration and spontaneous regeneration of its catalyzed diesel particulate filter (DPF), among the typical driving operation modes. During the engine tests, pressure and temperature along the DPF were measured, and soot samples were taken from the exhaust manifold upstream of the DPF for their thermal, structural and morphological characterization. The collected soot samples were subjected to: Transmission Electron Microscopy (TEM) for morphological analysis, thermal heating under oxidant atmosphere for studying the oxidation kinetics, Raman spectroscopy for describing their nanostructure and X-ray diffraction spectroscopy (XRD) for studying their internal lattice parameters. When the engine was operated in a typical accumulation mode, the pressure drop across the DPF increased up to 80 hPa with diesel fuel, while pressure drop stopped increasing after 4000 s of engine testing with biodiesel. In the regeneration mode, the DPF regenerated more slowly in the biodiesel case as a consequence of lower post-injected fuel energy and thus lower exhaust temperature. In the self-regenerating mode, the DPF was charged more slowly with biodiesel than with diesel fuel and its break even temperature was 40 °C lower with biodiesel fuel. These results provide further evidence that biodiesel soot is more reactive to oxidation. Although thermogravimetric results confirmed this tendency based on the differences on the pre-exponential factor, Raman spectra showed that biodiesel soot reached more ordered graphite-like structures and lower amorphous carbon concentration and XRD analysis showed that biodiesel soot displayed a higher degree of graphitization. The TEM analysis of the agglomerates showed that soot primary particles obtained with biodiesel fuel were significantly smaller and had higher specific active surface than those of diesel soot. From these results, an interpretation of the differences in soot oxidation between both soot samples was made based on the different length scales, from the carbon fringes to the particulate filter.     

再生温度和来流参数对柴油机颗粒过滤器再生和 过滤特性影响的试验研究

基于外加热源再生性能测试台架,研究了不同再生温度和不同来流流量对柴油机颗粒过滤器(diesel particulate filter,DPF)出口颗粒排放的影响。试验结果表明:加载量为2.5g/L时,DPF出口颗粒物出现一个颗粒数浓度波峰;加载量为5.0g/L时,DPF出口颗粒物出现两个数量浓度波峰。相同来流流量下,再生效率和总质量浓度随着再生温度的增加而增加;升温阶段出口颗粒物以核模态为主;再生阶段时,内部出现温度波峰且出口颗粒物以50nm以上聚集态颗粒为主。相同再生温度下,加载量为2.5g/L时再生效率和总质量浓度随着来流流量的增加而增加,升温和再生阶段出口颗粒物均以核模态为主;加载量为5.0g/L时再生效率和总质量浓度随来流流量的增加呈现先增加后减少的趋势,升温阶段出口颗粒物以核模态为主,再生阶段在大流量时有部分聚集态颗粒物排出。     

NTP技术降低柴油机PM排放及低温再生DPF的研究

针对柴油机颗粒捕集器(diesel particulate filter,DPF)传统再生方法的缺陷,根据低温等离子体(non-thermal plasma,NTP)放电理论,探索了NTP低温再生DPF技术。从化学反应动力学角度探讨了基于NTP技术的DPF再生反应机理,并利用现代测试分析技术研究了NTP对颗粒物(particulate matter,PM)质量粒径分布、微观形貌、碳结构及表面官能团演变的作用规律。建立NTP技术再生DPF的试验系统,对已捕集PM的DPF进行再生试验研究。通过监测PM的氧化分解产物CO、CO2的体积分数和DPF的内部温度,结合DPF的背压变化,研究不同再生初始温度下的PM氧化分解特性和DPF再生特性,并考察NTP技术对DPF再生的安全性。研究结果表明,NTP技术可有效分解柴油机排气中的PM,显著降低DPF的再生温度,且无需催化剂。这为DPF再生提供了新的研究途径。     

DPF主动再生过程颗粒排放特性试验

通过柴油发动机台架,采用后喷助燃的再生方式研究了主动再生过程中柴油机颗粒捕集器(DPF)出口的颗粒排放特性.结果表明:在主动再生期间,DPF出口颗粒浓度可增加2~3个数量级;在升温过程和再生过程,出口颗粒物数量浓度和粒径分布会因为碳载量和再生温度的共同作用而表现出差异;升温过程中,10 nm左右核模态颗粒物的排放主要由来流中颗粒物的穿透引起;再生过程中,10 nm左右核模态颗粒物的排放主要由碳烟颗粒层氧化反应生成的二次颗粒逃逸引起;整个再生期间,100 nm左右的积聚态颗粒物的排放主要由DPF载体内碳烟颗粒的逃逸引起.     

Analysis of reformed EGR on the performance of a diesel particulate filter

The use of a diesel particulate filter (DPF) in combination with an upstream diesel oxidation catalyst (DOC) has been successfully implemented and shown to reduce carbon monoxide (CO), hydrocarbon (HC) and Particulate Matter (PM) diesel exhaust gas emissions. However issues including cost, size and uncontrolled active regeneration under a low temperature window still require attention. This study therefore primarily focuses on the potential benefits of using a single catalytic coated DPF (cDPF) and a combined DOC-cDPF instead of the DOC-DPF aftertreatment system utilising a passive, low temperature regeneration method. Comparisons were made through monitoring exhaust gas compositions from an experimental single cylinder diesel engine as well as measuring the pressure drop across the filters to analyse the accumulation of soot particles. The influence of reformed EGR (REGR), enriched simulated hydrogen (H₂) and CO, on DPF and cDPF soot loading was of interest as H₂ promotes the NO to NO₂ oxidation. Similarly the addition of simulated reformate (added either directly into the engine intake or exhaust manifold) for optimal performance of the aftertreatment systems was examined.The effects of adding REGR resulted in a significant decrease in total engine-out NO_x emissions, as well as an increase in both NO₂ concentration and NO₂/NO_x ratio. This resulted in improved filter efficiency and overall loading, especially under a DOC-cDPF aftertreatment configuration system. As a whole, a simultaneous NO_x and PM reduction was achieved.