Homogenous gas-phase reactions in exhaust-gas tail pipes of internal combustion engines

对控制内燃机NOx等污染物排放的要求越来越高，使用对气候影响较小的燃料，以及开发更高效的发动机，都要求有替代的后处理策略，如将催化转化器放置在离发动机更近的地方。由此产生的更高的温度和压力可能会在排气管内发生重大的气相反应，从而影响减排。例如，在选择性催化还原(SCR)系统中，通过气相反应可以改变NOx和NH3的摩尔比，从而增加NOx的排放。尾气组分HC/HCO/CO/NOx/O2/NH3/H2O/CO2/N2之间的均相反应几乎没有被研究过，而且在尾管条件下也远未被理解。目前的中德联合项目将在贫化操作条件下，在NH3-SCR系统存在的情况下，研究这些条件下的气相反应。通过对均相气相和催化蜂窝结构的开放通道的研究，将对发动机尾气和排放控制装置中原气中的气相反应进行表征、理解和建模。科学目的是提供对将在这些原料气体中发生的气相反应的基本了解。只有这样的基本了解才能准确地描述那些真正到达催化剂的活性混合物，从而开发出现实的化学模型，并优化与燃料发动机相关的后处理系统，以减少排放，降低毒性和化学危险性。为了实现这些目标，该项目将利用合作伙伴在燃烧化学诊断、动力学分析、与氧化和燃烧相关的模型开发以及后处理战略方面的综合、互补且往往是独特的专业知识。该项目将考虑(I)从传统汽油和柴油到目前的生物燃料和未来的电子衍生燃料的燃料多样性，(Ii)可变的发动机运行条件，以及(Iii)更接近发动机的催化转化器的运行。这种条件的巨大组合是目前对近发动机原料气中的气相反应缺乏基本了解的一个原因。因此，确定共同的、原型的成分和变量至关重要，包括混合物成分和温度以及潜在的压力敏感性。这一合作解决了也将对中国和德国的空气质量问题产生影响的严峻挑战。该项目将在德国和中国集团之间业已建立的合作伙伴关系的基础上发展和扩大。

Increasing demands on the control of pollutant emissions such as NOx from internal combustion engines, the use of fuels with decreased climate impact, and the development of more efficient engines call for alternate after-treatment strategies such as positioning of catalytic converters closer to the engine. The resulting higher temperature and pressure bear the potential for significant gas-phase reactions in the tailpipe effecting the emission reduction. For instance, in a selective catalytic reduction (SCR) system, the molar ratio of NOx and NH3 could be changed by gas-phase reactions leading to increased NOx emission. Homogeneous reactions among the exhaust gas components, HC/HCO/CO/NOx/O2/NH3/H2O/CO2/N2, have barely been investigated and are far from being understood at tail-pipe conditions. The present joint Sino-German project will study gas-phase reactions for those conditions in the presence of a NH3-SCR system at lean operating conditions. Gas-phase reactions in the raw gases in the engine-near tailpipe and in emission control devices will be characterized, understood, and modelled through studies in the homogeneous gas-phase and in the open channels of catalytic honeycomb structures. The scientific aim is to provide a fundamental understanding of gas-phase reactions that will occur in these raw gases. Only such a fundamental understanding will allow the characterization of exactly those reactive mixtures that indeed reach the catalyst and thus to develop realistic chemical models, and to optimize fuel-engine-associated aftertreatment systems towards reduced emissions with decreased toxicity and chemically less hazardous signature. To achieve these goals, the project will make use of the combined, complementary, and often unique expertise of the partners regarding combustion chemistry diagnostics, kinetic analyses, and model development relevant to oxidation and combustion, and aftertreatment strategies. The project will consider (i) fuel diversity reaching from conventional gasoline and Diesel to current biofuels and to future electrically-derived fuels, (ii) variable engine operation conditions, and (iii) operation of the catalytic converter closer to the engine. This vast combination of conditions is a reason for the current lack of fundamental understanding of gas-phase reactions in the near-engine raw gases. It is thus of utmost importance to identify common, prototypical compositions and variables, including mixture components and temperature as well as potentially pressure sensitivity.This collaboration addresses acute challenges that will also have an impact on air quality issues in China and Germany. The project will build upon and expand an already well-established partnership between German and Chinese groups.