Advances and challenges of ammonia delivery by urea-water sprays in SCR systems

Over the past decades, selective catalytic reduction (SCR) using aqueous urea sprays as ammonia precursor has become the prevalent technique for NO$_{X}$ emission control in mobile applications. Preparation of ammonia from urea water sprays still represents a challenge in aftertreatment engineering as complex interactions of multi-phase physics and chemical reactions have to be handled. Increasingly stringent emission legislations and the ongoing development of fuel-efficient engines and close-coupled aftertreatment systems raise high demands to SCR systems. Due to highly transient conditions and short mixing lengths, incomplete spray evaporation can result in liquid/wall contact and formation of solid urea deposits lowering ammonia selectivity and homogeneity. This article reviews the ongoing development of SCR systems with focus on the efficient evaporation and decomposition of the injected spray for a homogeneous ammonia distribution in front of the SCR catalyst. Critical aspects of spray evaporation and impingement, liquid film and deposit formation are pointed out and potentials for system optimization are discussed

Modeling Elementary Heterogeneous Chemistry and Electrochemistry in Solid-Oxide Fuel Cells

This paper presents a new computational framework for modeling chemically reacting flow in anode-supported solid-oxide fuel cells (SOFC). Depending on materials and operating conditions, SOFC anodes afford a possibility for internal reforming or catalytic partial oxidation of hydrocarbon fuels. An important new element of the model is the capability to represent elementary heterogeneous chemical kinetics in the form of multistep reaction mechanisms. Porous-media transport in the electrodes is represented with a dusty-gas model. Charge-transfer chemistry is represented in a modified Butler-Volmer setting that is derived from elementary reactions, but assuming a single rate-limiting step. The model is discussed in terms of systems with defined flow channels and planar membrane-electrode assemblies. However, the underlying theory is independent of the particular geometry. Examples are given to illustrate the model

Methodological progress and substantial insights in the field of internet research

We are pleased to present the first issue of the International Journal of Internet Science (IJIS). As the mission statement indicates the journal is intended to cover two kinds of related research. On the one hand it presents methodological research that shows how the Internet can be used as a tool for data collection. On the other hand, it presents substantial research on the social and psychological implications of the Internet and other new online media. It is our conviction that both streams of research can profit from each other so that the journal includes both. The current issue is giving a first impression on the variety of approaches to be dealt with in this journal while exemplifying the common ground that good empirical research is enhanced by a clear theory-guidance. Many of the articles stem from earlier presentations given at one of the international conferences of the conference series General Online Research (GOR). The selection of articles brings together empirical methodological studies on important determinants of response behaviour in online data collection and empirical research on the social implications of web- and computer use. To the first type of research belong the contribution of Smyth, Dillman, Christian, and Stern, the contribution of Krysan and Couper, the paper of Göritz and the article of Ollesch, Heineken, and Schulte. To the second type belong the articles of Mesch and Talmud as well as the paper of Korupp