SynopsisT h e selt-association of N-acetylglycine N,N-dimethylamide, N-acetyl-L-valine N,Ndimethylamide, and N-acetyl-1.-phenylalanine N,N-dimethylamide in carbon tetrachloride was investigated hy using ir and 'H-nmr methods. It was concluded from ir measurements that the associat.ed species is the dimer formed as a result of the simultaneous formation of two intermolecular hydrogen bonds. This is supported by the results of 'H-nmr measurements. Thermodynamic quantities for the association were determined from the temperature and concentration dependence of the NH proton chemical shifts of the sample solutions. Compared with the Gly derivative, [.-Val and L-Phe derivatives have larger values of -AH I'or association, which shows good correlation with AUNH values, the difference between the maxima of the monomer and dimer hands, obtained from ir spectra. This is due to the less stahle monomer conformation and to the stronger intermolecular hydrogen bonding of the dimers in 1.-Val and I,-Phe derivatives. The line shapes of both methyl proton resonances of' I.-Val residue and methylene proton resonances of L-Phe residue were found to vary with concentration and temperature of the sample solutions. These data indicate that the rotation about the C1r-Cd bond is restricted by the steric hindrance present in the associated dimers. All these experimental results can he related to the fact that L-Val and L-Phe derivatives have a warped framework because of the bulky side chains, whereas the Gly derivative has a planar lramework.

The flow field characteristics of confined flames have been investigated for propane nonpremixed flames in cylindrical furnaces. The effects of furnace inner diameter D 1 , air inlet velocity difference ∆U a , and global equivalence ratio φ on the flow field are related to NOx emission. The emission index of NOx, EINOx, decreases roughly with the increases of the above parameters. This decrease is observed as a consequence of flame stretch and dilution by the burned gas. The flame stretch is related to the velocity difference introduced by multiple inlets, and the dilution is attributable to the recirculation structure formed at the bottom of the furnace. The present investigation shows the mechanism of burner/chamber configuration inciting the flow field and indirectly controlling NOx emission.

No abstract

No abstract