On the Conformation of a Sterically Congested Amide Group in the Crystalline State and in Solution

The conformation in the crystalline state and in solution of the sterically congested tetramethylpiperidinederived amide group of the symmetric diamide I formed from 2,2,6,6-tetramethylpiperidine ( b ) and 1,2,5-thiadiazole-3,4-dicarbonyl dichloride ( c ), and of the mixed diamide II derived from b , c , and piperidine ( a ) has been investigated. In crystals, as observed with II , this group is strongly bent out-of-plane at both the N-atom and the carbonyl C-atom, and there is also a sizable twisting around the amide bond. Furthermore, the amide bond is abnormally long (1.37 Å). In CD₂Cl₂ (or CDCl₃) solution, the group is apparently planar in its ground-state conformation, but the energy barrier to rotation around the amide bond is low. This conclusion is based on low-temperature ¹H-NMR measurements on I , II , and on the symmetric diamide III derived from a and c .     

On Efficient Computation of the Optimization Problem Arising in the Inverse Modeling of Non-Stationary Multiphase Multicomponent Flow Through Porous Media

In this paper we discuss a method of solving inverse problems in non-isothermal multiphase multicomponent flow through porous media. The conceptual model is described by a system of non-linear partial differential equations which involve unknown parameters. These parameters are to be determined using a set of observations at discrete points in space and time by an optimization method. It is based on a reduced Gauss-Newton iteration in combination with an efficient gradient computation which takes advantage of a recently developed efficient numerical simulation technique. A sensitivity analysis is carried out for the optimum parameter set. Numerical experiments are performed for a one dimensional column experiment carried out at the VEGAS, University of Stuttgart, Germany.     

Evaluation of toluene LIF thermometry detection strategies applied in an internal combustion engine

In the context of toluene laser-induced fluorescence (LIF) thermometry, the two common LIF detection strategies, namely one-color and two-color detection, have been simultaneously applied to compare each strategy’s ability to accurately resolve thermal gradients during an engine cycle within an optically accessible internal combustion (IC) engine. Temperature images are obtained from high-speed toluene LIF measurements and are combined with high-speed particle image velocimetry. The combination with flow data and Mie scattering images facilitates the interpretation of differences between the toluene LIF detection strategies. Two-color temperature images are limited in their ability to detect thermal gradients near the end of compression due to larger precision uncertainties. Local regions of cold gases in the two-color images are better identified with the guidance of the one-color images when homogeneous toluene mixtures preside. During expansion, large differences exist between one- and two-color temperature images and likely caused by local mixture fraction heterogeneities that bias the one-color detection strategy. Toluene condensation occurs during the expansion and exhaust stroke and causes local mixture fraction heterogeneities in the combustion chamber. Liquid toluene is in contact with solid surfaces and crevices of the combustion chamber and can evaporate during compression or expansion causing both local temperature and mixture stratification. This work demonstrates the advantage of high-speed imaging and use of multiple image diagnostics to reveal the development of natural temperature and mixture stratification in a motored IC engine. This work also suggests that natural temperature stratification typically regarded from gas-wall heat transfer may also be caused by liquid droplet evaporation on solid surfaces. Such phenomenon, however, is expected to be pertinent for all modern-day engine operating systems.