Experimental and kinetic modeling study of combustion of JP-8, its surrogates and components in laminar premixed flows

Experimental and kinetic modeling studies are carried out to characterize premixed combustion of jet fuels, their surrogates, and reference components in laminar nonuniform flows. In previous studies, it was established that the Aachen surrogate made up of 80 % n-decane and 20 % trimethylbenzene by weight, and surrogate C made up of 57 % n-dodecane, 21 % methylcyclohexane and 22 % o-xylene by weight, reproduce key aspects of combustion of jet fuels in laminar nonpremixed flows. Here, these surrogates and a jet fuel are tested in premixed, nonuniform flows. The counterflow configuration is employed, and critical conditions of extinction are measured. In addition, the reference components tested are n-heptane, n-decane, n-dodecane, methylcyclohexane, trimethylbenzene, and o-xylene. Measured critical conditions of extinction of the Aachen surrogate and surrogate C are compared with those for the jet fuel. In general the alkanes n-heptane, n-decane, and n-dodecane, and methylcyclohexane are found to be more reactive than the aromatics o-xylene and trimethylbenzene. Flame structure and critical conditions of extinction are predicted for the reference components and the surrogates using a semi-detailed kinetic model. The predicted values are compared with experimental data. Sensitivity analysis shows that the lower reactivity of the aromatic species arises from the formation of resonantly stabilized radicals. These radicals are found to have a scavenging effect. The present study on premixed flows together with previous studies on nonpremixed flows show that the Aachen surrogate and surrogate C reproduce many aspects of premixed and nonpremixed combustion of jet fuels.     

A lumped approach to the kinetic modeling of pyrolysis and combustion of biodiesel fuels

The aim of this work is to discuss a lumped approach to the kinetic modeling of the pyrolysis and oxidation of biodiesel fuels, i.e. rapeseed and soybean methyl esters. The lumped model is the natural extension of the kinetic scheme of methyl butanoate and methyl decanoate and takes also a great advantage from the detailed kinetic scheme of biodiesel fuels [Westbrook et al. Combustion and Flame 158 (2011) 742–755]. The combustion of methyl palmitate and methyl stearate is very similar to the one of methyl decanoate, while large unsaturated methyl esters are significantly less reactive at low and intermediate temperatures. The formation of resonantly stabilized allylic radicals from unsaturated methyl esters constitutes a critical element very useful to characterize the reactivity of the different fuels. The extension of the previous kinetic model of hydrocarbon and oxygenated fuel combustion to the methyl esters required the introduction of ～60 lumped species and ～2000 reactions. The dimension of the overall kinetic scheme (～420 species involved in ～13,000 reactions) allows a more flexible and direct application of the model without the need of kinetic reductions. The comparison of model predictions and different sets of experimental data from one side allows to verify the reliability of the proposed model, from the other side calls for further experimental and theoretical work on this subject.     

An easy access to α,β-unsaturated thioacylsilanes: a useful route to silylated 1,2-dithiins

Treatment of different silylated allenes with hexamethyldisilathiane (HMDST) in the presence of CoCl₂·6H₂O affords an easy and high yielding access to α,β-unsaturated thioacylsilanes, which undergo a self-dimerization reaction to afford polyfunctionalized 1,2-dithiins as the major products.     

The forward search interactive outlier detection in cointegrated VAR analysis

Cointegration analysis is particularly sensitive to outlying observations. Traditional robust approaches rely on parameter estimates based on weighting schemes to penalize aberrant units. This, in particular, is the idea underlying pseudo maximum likelihood robust estimators. Atypical observations, however, can reveal useful information about the investigated phenomenon. Aiming to detect these observations, we extend the forward search procedure to the cointegrated vector autoregressive model. The analysis is carried out by building up subsets of increasing dimension and monitoring suitable statistics at each subset size. Simulation experiments and real data analysis highlight that our forward search is more effective than the pseudo maximum likelihood in detecting atypical units and data structures.     

Integral equations for Rost’s reversed barriers: Existence and uniqueness results

We establish that the boundaries of the so-called Rost’s reversed barrier are the unique couple of left-continuous monotonic functions solving a suitable system of nonlinear integral equations of Volterra type. Our result holds for atom-less target distributions $\mu$ of the related Skorokhod embedding problem.The integral equations we obtain here generalise the ones often arising in optimal stopping literature and our proof of the uniqueness of the solution goes beyond the existing results in the field.     

A Convenient Procedure for the Synthesis of Ursodeoxycholic Acid Sulfated Derivatives

The mono- and bis(sulfooxy) derivatives of ursodeoxy-cholic acid are, contrary to a previous report, easily prepared by a very simple direct sulfation procedure.     

Butadiene–isoprene copolymerization with V(acac)3‐MAO. Crystalline and amorphous trans‐1,4 copolymers

Butadiene‐isoprene copolymerization with the system V(acac)₃‐MAO was examined. Crystalline or amorphous copolymers were obtained depending on isoprene content. Both butadiene and isoprene units exhibit a trans‐1,4 structure and are statistically distributed along the polymer chain. Polymer microstructure, comonomer composition, and distribution along the polymer chain were determined by ¹³C and ¹H NMR analysis. The thermal and X‐ray behaviors of the copolymers were also investigated and compared with results from solid‐state ¹³C NMR experiments. © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4635–4646, 2007