Ammonia storage and slip under steady and transient state in close-coupled SCR

The close-coupled selective catalytic reduction(cc-SCR)catalyst is an effective technology to reduce tailpipe NOx emission during cold start.This paper investigated the optimal ammonia storage under steady and transient state in the cc-SCR.The study showed that a trade-off between NOx conversion efficiency and ammonia slip is observed on the pareto solutions under steady state,and the optimal ammonia storage is calculated with ammonia slip less than 10μL/L based on the ChinaⅥemission legislation.The rapid temperature increase will lead to severe ammonia slip in the transient test cycle.A simplified 0-D calculation method on ammonia slip under transient state is proposed based on kinetic model of ammonia adsorption and desorption.In addition,the effect of ammonia storage,catalyst temperature and temperature increasing rate on ammonia slip are analyzed.The optimal ammonia storage is calculated with maximum ammonia slip less than 100μL/L according to the oxidation efficiency of ammonia slip catalyst(ASC)downstream cc-SCR.It was found that the optimal ammonia storage under transient state is much lower than that under steady state in cc-SCR at lower temperature,and a phase diagram is established to analyze the influence of temperature and temperature increasing rate on optimal ammonia storage.

High-Efficiency and Clean Combustion Natural Gas Engines for Vehicles

Natural gas engines have become increasingly important in transportation applications,especially in the commercial vehicle sector.With increasing demand for high efficiency and low emissions,new technologies must be explored to overcome the performance limitations of natural gas engines such as limits on lean or dilute combustion,unstable combustion,low burning velocity,and high emissions of CH_(4) and NO_(x).This paper reviews the progress of research on natural gas engines over recent decades,concentrating on ignition and combustion systems,mixture preparation,the development of different combustion modes,and after-treatment strategies.First,the features,advantages,and disadvantages of natural gas engines are introduced,following which the development of advanced ignition systems,organization of highly turbulent flows,and the preparation of high-reactivity mixtures in spark ignition engines are discussed with a focus on pre-chamber jet ignition,combustion chamber design,and H_(2)-enriched natural gas combustion.Third,the progress in natural gas dual-fuel engines is highlighted,including the exploration of new combustion modes,the development of novel pilot fuels,and the optimization of combustion control strategies.The fourth section discusses after-treatment systems for natural gas engines operating in different combustion modes.Finally,conclusions and future trends in the development of high-efficiency and clean combus-tion in natural gas engines are summarized.

新冠疫情期间保障急诊医疗服务质量的探究--基于Python网络爬虫可视化分析公众对疫情期间急诊延误事故的反应

目的基于公众对疫情期间急诊延误事故的反应,分析疫情期间如何保障急诊医疗服务质量。方法采用Python网络爬虫抓取知乎平台下公众对某一疫情期间急诊延误事故相关问题的回答,采用词云图可视化展现回答内容,并统计公众关注的导致疫情期间急诊服务质量下降的原因、公众对法规改进和社区医疗的建议。结果公众普遍认为,此次急诊事故的发生与疫情防控密切相关。公众关注的因素主要包括私立医院的营业性质、法规不合理、行政管理者、医院基层和社区的过失。通过进一步分析讨论可知,疫情对急诊就诊的影响主要在于急诊就诊资源减少、急诊流程延长和交叉感染风险增加等。私立医院存在大量监管漏洞,监管机构可以从检查方式和准入标准等方面强化监督。卫生行政管理部门应当合理统筹医疗资源,建设实时应急管理信息发布通道并严惩急诊拒诊。医院应当优化医院结构,设置不同等级的院感风险区,并设立专门值班室。社区卫生服务中心应当做好预检分流工作,落实双向转诊并优化医疗配置。结论从政府、医院、社区多角度协同保障疫情期间的急诊医疗质量,可改善现有卫生管理的不足。

Impact Resistance of Spark Plug’s Ceramic Insulator During Ultra-high-Pressure Combustion Under Deto-Knock Conditions

The ceramic insulators of spark plugs in gasoline engines are especially prone to damage when deto-knock occurs.To under-stand the damage process and mechanism,the present work investigated the impact resistance of ceramic insulators using detonation waves as impact sources.A test device that generates detonation waves was developed,representing a novel means of evaluating the knock resistance of ceramic insulators.Various impact types and detonation intensities were employed,and detonation initiation and propagation at peak pressures greater than 100 MPa were assessed using synchronous high-speed direct photography and pressure measurements.The test results demonstrate that ceramic insulators tend to break at the base of the breathing chamber when damaged by a single high peak pressure detonation wave impact.In contrast,multiple low pressure impacts eventually break the insulator into multiple fragments.The data also show that the positioning of a ground electrode upstream of the ceramic insulator greatly increases the resistance of the ceramic to the detonation impact.A two-dimensional computational fluid dynamics simulation coupled with a chemical kinetics analysis demonstrated that this improved resistance can be ascribed to a reduced peak pressure that appears after the detonation wave diffracts from the electrode prior to contacting the ceramic insulator.