汽车催化剂快速起燃技术

百气中大部分的ＣＯ和ＨＣ是汽车冷起动期间１－２ｍｉｎ内排放的,但是由于冷起动时催化剂未达到工作温度而不能起转化作用,使冷起动排放超标。本文介绍了车用催化剂的快速起燃技术,它们包括电加热催化剂、燃烧器、前置主催化剂、碳氢收集器,排气点火器、前级催化器及二次空气技术等。快速起燃技术以使催化剂在冷起动时加快起燃,达到其工作温度,从而有效转化污染物。     

小型 LPG 发动机匹配三效催化器的起燃特性研究

对小型点燃式电控LPG发动机匹配三效催化器的冷起动过程进行了试验研究，测量了冷起动过程排气管不同位置的排温变化，对比了催化器不同安装位置、不同点火提前角下的起燃特性。通过优化催化器安装位置，调整发动机起动后的怠速转速和点火提前角来改变排气温度，从而使催化器快速起燃，降低了冷起动过程HC和CO的排放。     

汽油机冷起动排放研究进展

简要分析了汽油机冷起动过程的特征;介绍了汽油机冷起动排放的研究进展,包括基于循环控制技术、缸内油膜和蒸发研究、环境温度对冷起动排放影响、冷起动空燃比模型、HC捕集技术以及快速起燃技术等.可以看出,后处理技术将获得更多的应用,密耦催化器则是欧Ⅲ排放的首选技术,HC捕集器是降低冷起动排放的最佳技术之一,多种技术的结合与系统优化可以满足更高的排放法规.     

催化剂的低温活性及催化器的预热措施

未来的排放标准对汽车工业是一个很大的挑战，要达到这些要求，在排气系统中安装废气催化器是一个有效的措施。由于汽油车排放大部分是在发动机冷态和暖机运转过程中生成的，所以要尽可能地改善催化剂的低温活性以降低催化剂的起燃温度，提高其反应速率；另外还要对催化器进行预热处理，优化催化剂的激化环境，使其尽快投入反应。本文描述了近年来为满足未来排放要求而在汽油机废气催化剂上所采取的激化措施和在催化器上所采取的预热措施。     

三效催化器起燃特性影响因素的仿真研究

三效催化器在冷起动期间主要靠排气来加热升温,而发动机控制策略对排温影响很大。利用FIRE仿真软件建立了催化器模型,采用仿真和试验相结合的手段对催化器的起燃特性影响因素进行了研究。结果表明：所建模型能够比较准确地模拟冷起动过程中催化器内的温度场和浓度场变化;延迟发动机的点火提前角可以明显提高进入排气管的温度,从而使催化器快速起燃。     

采用两次喷油策略降低直喷增压汽油机爆震和碳烟排放及改善冷起动特性的研究

在某款增压直喷汽油机上,分别在爆震工况及冷起动工况采用燃油两次喷油策略和单次喷油策略,通过对比两种喷油策略的结果发现:在爆震工况,采用合适的两次喷油策略可使CA50提前3.3°CA,抑制发动机爆震倾向,并使碳烟排放从0.59FSN降低到0.45FSN;在冷起动工况,采用合适的两次喷油策略有利于改善着火性能和提高燃烧稳定性,使得最迟点火提前角比单次喷油推迟47°CA,可以提高排气温度,使三元催化器快速起燃,降低HC排放。     

PFI汽油机快速拖动起动控制策略与碳氢排放

搭建了汽油机起动过程模拟试验平台,对比分析了采用普通起动马达和ISG(起动/发电一体化)电机高转速拖动起动时,汽油机的瞬时转速、气缸压力、燃油补偿系数、进气压力、点火时刻、HC转化效率、排气温度及瞬态HC排放浓度的变化规律。试验结果表明:随着拖动转速升高,进气压力降低,进气量减少,燃油蒸发时间缩短,雾化不充分,缸内发生失火的可能性增加,瞬态排放急剧升高,并与冷却液温度有着对应关系。通过瞬态燃油补偿可以改善汽油机起动后若干工作循环混合气偏稀的情况,降低HC排放。推迟点火,可提高排气温度,但冷机和热机状况下三效催化器转化效率存在较大差异。暖机后,当点火提前角为-10°CA时,三效催化器能在40s内起燃,HC转化率在60s内达到90%左右。     

排气门正时对柴油机冷起动性能的影响

通过在一台单缸直喷柴油机上进行实验,分析了不同排气门正时条件对柴油机冷起动过程燃烧及排放性能的影响.结果表明,通过调节排气门关闭正时,适当增大缸内残余废气量,可显著改善起动过程初始着火循环的着火燃烧性能和提高起动过程缸内燃烧的稳定性.不同排气门关闭条件对起动过程的排放有着非常重要的影响.适当提前排气门关闭时刻,可以显著降低冷起动过程的烟度排放,特别是降低冷起动过程初始阶段的烟度排放.而对于NO2排放,由于残余废气具有很强的热效应,随着排气门关闭时刻提前,Nox排放呈上升趋势.     

电喷汽油机冷起动过程研究

本文根据实测的催化器入,出口温度及HC排放浓度，结合示功图对电喷汽油机冷起动时HC排放量在台架上进行了模拟分析，认为起动过程以节气门突开为界，可划分为2个阶段，其中HC排放主要集中在开始起动到节气门开这一段时间内，而这段时间的HC排放又以起动后最初几秒钟为主，适当减稀空燃比，促使缸内发生不完全燃烧，则未燃HC在排气管内可继续氧化，使得最终排出的HC量降低，并有利于催化剂的起燃。     

降低混合动力乘用车冷起动排放的策略探讨

为了降低混合动力乘用车冷起动排放,从混合动力汽车的排放特性出发,阐述了控制和降低冷起动原始排放和尾气排放的技术及其手段,结合市场上量产发动机及整车的实例解析,提出了有效降低混合动力汽车冷起动排放的策略及其技术路线.     

小排量增压汽油机国Ⅴ排放系统研究

全面阐述了三元催化器特性,指出了小排量增压汽油机的排放特点。综合成本及法规要求,明确了国Ⅴ的技术路线,比较了不同催化器涂层和贵金属设计对排放结果的影响。着重结合整车标定就如何提高催化器转化效率降低排放进行了多方面的试验研究,通过不同冷气动策略,催化器起燃,后氧窗口等标定参数更改,提高了排放水平。所研究的结果表明,在合理的三元催化转化器成本内通过发动机电子控制和标定可以满足国Ⅴ排放法规要求。     

ISG混合动力汽车起动及加速策略

混合动力车的怠速停机功能既增加了起动次数又会减缓催化器起燃,对排放产生不利的影响,因此必须对混合动力起动过程进行专门的优化.为了满足驾驶性和加速性能,传统车辆加速时发动机提供的瞬态燃油必然会恶化排放性能,因此加速过程的瞬态排放成为排放控制的另一难点.基于ISG电机的快速响应特性以及性能参数,对ISG混合动力车的起动及加速策略进行了优化.对冷机及热机的起动空燃比进行控制;提出了ISG快慢转矩的概念,以ISG转矩代替传统车的瞬态燃油,确定了理想的混合动力起动及加速的ECU和VCU参数.对混合动力车以不同模式进行NEDC循环测试,试验结果表明,混合动力起动避免了传统车起动时的过浓喷油,ISG转矩有效地取代了传统车加速时的瞬态燃油,使混合动力车在节油的同时较大地改善了排放性能.     

Cold-start performance of an ammonia-fueled spark ignition engine with an on-board fuel reformer

This work demonstrated the first-ever cold-start operation of an ammonia (NH₃)-fueled four-cylinder spark ignition engine with an on-board fuel reformer, applying autothermal reforming. In this system, an electrically heated NH₃-air mixture was provided to a reforming catalyst and approximately 3 s was found to elapse between the start of engine rotation and the onset of combustion. Stable fast idle operation in conjunction with a cold start was realized with a H₂-to-NH₃ molar ratio of 2:1. Nearly zero NH₃ emissions were achieved during cold start and fast idle until the engine warmed up, by adsorbing unburned NH₃ passing through a three-way catalyst before the catalyst was sufficiently warmed up. The NH₃ adsorption capacity of this system could be regenerated during the engine warm-up when the engine was running under lean conditions.     

Life-cycle analysis of energy use and greenhouse gas emissions of gas-to-liquid fuel pathway from steel mill off-gas in China by the LanzaTech process

The LanzaTech process can convert carbon monoxide-containing gases produced by industries, such as steel manufacturing, into valuable fuel products. The life-cycle analysis (LCA) of energy use and greenhouse gas emissions from the LanzaTech process has been developed for a Chinese setting using the original Tsinghua China Automotive LCA model along with a customized module developed principally for the process. The LCA results demonstrate that LanzaTech gas-to-liquid (GTL) processing in China’s steel manufacturing is favorable in terms of life-cycle fossil energy and can reduce greenhouse gas emissions by approximately 50% compared with the conventional petroleum gasoline. The LanzaTech process, therefore, shows advantages in both energy-savings and a reduction in greenhouse gas emissions when compared with most bio-ethanol production pathways in China.     

A review on various after treatment techniques to reduce NOx emissions in a CI engine

NOx emissions have always been a main concern in the development of diesel engines. This paper summarizes the studies about NOx emission reduction in diesel engines. The need for meeting the stringent requirements with regard to NOx emissions in a diesel engine has led to the development of a range of after treatment techniques. After treatment methods are required to reduce NOx emissions that cannot be controlled by fuel composition and combustion phenomena. Current after treatment techniques that are being employed are Selective Catalytic Reduction (SCR), Lean NOx Trap (LNT) and SCR Filter (SCRF). The benefits and constraints of different types of SCR are discussed. Urea SCR is a prominent well proven technology. Urea SCR produces 96–99% conversion efficiency with the help of a reductant NH₃. The operating parameters such as nature of catalyst, temperature range of catalyst, flow of DEF (Diesel Exhaust fluid) to injector and mixing of NH₃ and NOx are discussed. Hybrid SCR such as Cu-SCR + Fe-SCR, SCR + LNT moderates fuel consumption and augments the catalytic activity at low temperature. SCRF has low cell density (200–300 csi vs 400–600 csi for SCR), and also has lower deNOx efficiency for a number of reasons. Pre-stored NH₃ and Preheating helps in low temperature reaction of SCRF. Technical problems in aqueous urea systems have led to the evolution of solid SCR system (SSCR). This review incorporates the study of solid ammonium salts decomposition, temperature range of the salts and infrastructure required for SSCR.     

Biodiesel production from waste chicken fat based sources and evaluation with Mg based additive in a diesel engine

In this study, chicken fat biodiesel with synthetic Mg additive was studied in a single-cylinder, direct injection (DI) diesel engine and its effects on engine performance and exhaust emissions were studied. A two-step catalytic process was chosen for the synthesis of the biodiesel. Methanol, sulphuric acid and sodium hydroxide catalyst were used in the reaction. To determine their effects on viscosity and flash point of the biodiesel, reaction temperature, methanol ratio, type and amount of catalyst were varied as independent parameters. Organic based synthetic magnesium additive was doped into the biodiesel blend by 12 μmol Mg. Engine tests were run with diesel fuel (EN 590) and a blend of 10% chicken fat biodiesel and diesel fuel (B10) at full load operating conditions and different engine speeds from 1800 to 3000 rpm. The results showed that, the engine torque was not changed significantly with the addition of 10% chicken fat biodiesel, while the specific fuel consumption increased by 5.2% due to the lower heating value of biodiesel. In-cylinder peak pressure slightly rose and the start of combustion was earlier. CO and smoke emissions decreased by 13% and 9% respectively, but NO_x emission increased by 5%.     

基于轻型柴油车的柴油机氧化催化器入口温度升温特性及策略研究

选取了高、中、低负荷的3个典型工况,研究了进气节流及喷油策略对柴油机缸内燃烧过程、排放性、经济性及柴油机催化氧化器(diesel oxidation catalyst,DOC)入口温度的影响,得到全工况区域的DOC入口温度的升温策略。试验结果表明:随进气节流阀开度减小,进气流量降低,压缩压力下降,燃烧始点滞后,最高燃烧压力下降,循环指示功降低;HC排放得到抑制,其他排放恶化;DOC入口温度得到有效提升,负荷越小,温升效果越显著。喷油规律耦合进气节流发现,主喷提前角的推迟使得滞燃期缩短、后燃加重,DOC入口温度小幅度提升;近后喷油量增加可提高DOC入口温度,推迟近后喷,DOC入口温度先增大后降低,存在最佳的近后喷时刻。依据样机全工况排温分布特征,提出了不同工况区域DOC入口温度升温控制策略。     

Semi-analytical proton exchange membrane fuel cell modeling

Mathematical techniques are presented which allow for analytical solutions of the catalyst layer transport and electrochemical problem in PEM fuel cells. These techniques transform the volumetric reaction terms to boundary flux terms, thereby eliminating the need for computational solving of the catalyst layer problem. The result is a semi-analytical fuel cell model—a computational model that entails analytical rather than computational catalyst layer solutions. This helps to alleviate the meshing difficulties inherent in the catalyst layers caused by large geometric aspect ratios, and hence reduce the computational requirements for fuel cell models.     

The comparison of engine performance and exhaust emission characteristics of sesame oil–diesel fuel mixture with diesel fuel in a direct injection diesel engine

The use of vegetable oils as a fuel in diesel engines causes some problems due to their high viscosity compared with conventional diesel fuel. Various techniques and methods are used to solve the problems resulting from high viscosity. One of these techniques is fuel blending. In this study, a blend of 50% sesame oil and 50% diesel fuel was used as an alternative fuel in a direct injection diesel engine. Engine performance and exhaust emissions were investigated and compared with the ordinary diesel fuel in a diesel engine. The experimental results show that the engine power and torque of the mixture of sesame oil–diesel fuel are close to the values obtained from diesel fuel and the amounts of exhaust emissions are lower than those of diesel fuel. Hence, it is seen that blend of sesame oil and diesel fuel can be used as an alternative fuel successfully in a diesel engine without any modification and also it is an environmental friendly fuel in terms of emission parameters.     

Water management characteristics of electrospun micro-porous layer in PEMFC under normal temperature and cold start conditions

Micro-porous layer (MPL) is the key component in proton exchange membrane fuel cell for water management. Electrospinning technique, providing a novel nanofiber structure, is recently used to fabricate MPL which gave improved fuel cell performance at normal temperature operation. However, underlying causes are not well understood, and no attempt has been made to study its effects on the cold start performance. In this work, electrospun MPL using non-toxic solvent was fabricated, and water management characteristics under both normal temperature and cold start conditions were compared with commercial MPL using the same catalyst coated membrane (CCM). Electrospun MPL outperformed the commercial MPL at 70 °C under high relative humilities due to marked reduction in mass transport losses. Under cold start conditions, fuel cell with electrospun MPL generated electricity for a longer time, possibly due to better interfacial connection, which facilitated water removal from catalyst layer.