Ignition delay measurements of four component model gasolines exploring the impacts of biofuels and aromatics

This study explores the impacts of combinations of biofuel (ethanol, isobutanol and 2-methyl furan) and aromatic (toluene) compounds in a four component fuel blend, at fixed research octane number (RON) on ignition delay measured in an advanced fuel ignition delay analyzer (AFIDA 2805). Ignition delay measurements were performed over a range of temperatures from 400 to 725 °C (673 to 998 K) and two chamber pressures of 10 and 20 bar. The four component mixtures are compared to primary reference fuels at RON values of 90 and 100. The ignition delay measurements show that as the aromatic and biofuel concentrations increased, two stage ignition behavior was suppressed, at both initial chamber pressures. But both RON 100 (isooctane) and RON 90 reference fuels showed two stage ignition behavior, as did fuel mixtures with low biofuel and aromatic content. RON 90 fuels showed stronger two stage ignition behavior than RON 100 fuels, as expected. Depending on the type of biofuel in the mixture, the ignition delay at low chamber temperatures could be far greater than for the reference fuels. In particular, for the RON 100 mixtures at either 10 or 20 bar initial chamber pressure, the ignition delay at 400 °C (673 K) for the high level blend of 2-methyl furan and toluene (30 vol% of each) exhibited an ignition delay that was 10 times longer than for neat isooctane. The results show the strong non-linear octane blending response of these three biofuel compounds, especially in concert with the kinetic antagonism that toluene is known to display in mixtures with isooctane. These results have implications for the formulation of biofuel mixtures for spark ignition and advanced compression ignition engines, where this non-linear octane blending response could be exploited to improve knock resistance, or modulate the autoignition process.     

Stimuli‐responsive ampholytic terpolymers of N‐acryloyl‐valine,acrylamide, and (3‐acrylamidopropyl)trimethylammonium chloride: Synthesis,characterization, and solution properties

Low‐charge density ampholytic terpolymers composed of acrylamide (AM), (3‐acrylamidopropyl)trimethyl ammonium chloride (APTAC), and N‐acryloyl‐valine were prepared via free‐radical polymerization in 0.5 M NaCl to yield terpolymers with random charge distributions. Sodium formate (NaOOCH) was employed as a chain transfer agent during the polymerization to suppress gel effects and broadening of the molecular weight distribution (MWD). Terpolymer compositions were determined by ¹³C NMR spectroscopy. Terpolymer molecular weights (MWs) and polydispersity indices (PDIs) were obtained via size exclusion chromatography/multi‐angle laser light scattering (SEC‐MALLS). Intrinsic viscosity values determined from SEC‐MALLS data using the Flory–Fox relationship were compared with those determined by low‐shear dilute solution viscometry and found to be in good agreement. SEC‐MALLS experiments allowed examination of radius of gyration‐MW (R_g‐M) relationships and the Mark‐Houwink‐Sakurada intrinsic viscosity‐MW ([η]‐M) relationships for terpolymers. The R_g‐M and [η]‐M relationships indicated little or no excluded volume effects under SEC conditions indicating that the terpolymers were in near theta conditions in an aqueous buffer solution. Potentiometric titration experiments were performed in deionized (DI) water. These studies revealed that the apparent pK_a of the AMVALTAC terpolymers increases with increasing VAL content. The solution properties of low‐charge density ampholytic terpolymers have been studied as functions of solution pH, ionic strength, and polymer concentration. The charge‐balanced terpolymers exhibit polyampholyte behavior at pH values ≥ 6.5. As solution pH is decreased, these charge‐balanced terpolymers become increasingly cationic due to the protonation of the VAL repeat units. Charge‐imbalanced terpolymers generally exhibit polyelectrolyte behavior, although the effects of intramolecular electrostatic interactions (e.g., polyampholyte effects) on the hydrodynamic volume are evident at certain values of solution pH and salt concentration. The solution behavior of the terpolymers in the dilute regime correlates well with that predicted by various polyampholyte solution theories. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 3125–3139, 2006     

Aerosols dispersion modelling using probabilistic particle tracking

A method is proposed which can facilitate parallel computations of particle transport in complex environments, such as urban landscapes. A two stage‐approach is used, where in the first stage, physical simulations of various aerosol release scenarios are conducted on a high‐performance distributed computing facility, such as a Beowulf cluster or a computing grid, and stored in a database as a set of transfer probabilities. In this stage, the method provides a partially decoupled parallel implementation of a tightly coupled physical system. In the second stage, various aerosol release scenarios can be analysed in a timely manner, using obtained probability distributions and a simpler stochastic simulator, which can be executed on a commodity computer, such as a workstation or a laptop. The method presents a possibility of solving the inverse problem of determining the release source from the available deposition data. Using the proposed approach and developed graphical tools, a case of aerosol dispersion in a typical urban landscape has been studied. A considerable speedup of analysis time for different aerosol dispersion scenarios has been demonstrated. The method is appropriate for the development of express risk analysis systems. Copyright © 2006 John Wiley & Sons, Ltd.     

Two-edge connected subgraphs with bounded rings: Polyhedral results and Branch-and-Cut

We consider the network design problem which consists in determining at minimum cost a 2-edge connected network such that the shortest cycle (a “ring”) to which each edge belongs, does not exceed a given length K. We identify a class of inequalities, called cycle inequalities, valid for the problem and show that these inequalities together with the so-called cut inequalities yield an integer programming formulation of the problem in the space of the natural design variables. We then study the polytope associated with that problem and describe further classes of valid inequalities. We give necessary and sufficient conditions for these inequalities to be facet defining. We study the separation problem associated with these inequalities. In particular, we show that the cycle inequalities can be separated in polynomial time when K≤4. We develop a Branch-and-Cut algorithm based on these results and present extensive computational results.     

Controlled/living polymerization of methacrylamide in aqueous media via the RAFT process

The polymerization of methacrylamide (MAM) was performed in aqueous media via reversible addition fragmentation chain transfer (RAFT) polymerization with the dithiobenzoate chain‐transfer agent (CTA) 4‐cyanopentanoic acid dithiobenzoate (CTP) and 4,4′‐azobis(4‐cyanopentanoic acid) (V‐501) as initiator. The polymerization in unbuffered water at 70 °C with a CTP/V‐501 ratio of 1.5 was controlled for the first 3 h, after which the molecular weight distribution broadened and a substantial deviation of the experimental from the theoretical molecular weight occurred, presumably because of a loss of CTA functionality at longer polymerization times. Conducting the polymerization in an acidic buffer afforded a well‐defined homopolymer (M_n = 23,800 g/mol, M_w/M_n = 1.08). To demonstrate the controlled/living nature of the system, a block copolymer of MAM and acrylamide was successfully prepared (M_n = 33,800 g/mol, M_w/M_n = 1.25) from a polymethacrylamide macro‐CTA. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3141–3152, 2005     

Veraverbeke’s theorem at large: on the maximum of some processes with negative drift and heavy tail innovations

Veraverbeke’s (Stoch Proc Appl 5:27–37, 1977) theorem relates the tail of the distribution of the supremum of a random walk with negative drift to the tail of the distribution of its increments, or equivalently, the probability that a centered random walk with heavy-tail increments hits a moving linear boundary. We study similar problems for more general processes. In particular, we derive an analogue of Veraverbeke’s theorem for fractional integrated ARMA models without prehistoric influence, when the innovations have regularly varying tails. Furthermore, we prove some limit theorems for the trajectory of the process, conditionally on a large maximum. Those results are obtained by using a general scheme of proof which we present in some detail and should be of value in other related problems.     

Optimization with unary functions

Most nonlinear programming problems consist of functions which are sums of unary functions of linear functions. Advantage can be taken of this form to calculate second and higher order derivatives easily and at little cost. Using these, high order optimization techniques such as Halley's method can be utilized to accelerate the rate of convergence to the solution. These higher order derivatives can also be used to compute second order sensitivity information. These techniques are applied to the solution of the classical chemical equilibrium problem.Supported by National Science Foundation grant ECS-8709795, co-funded by the U.S. Air Force Office of Scientific Research and by the Office of Naval Research grant N00014-86-K0052.Supported by National Science Foundation grant ECS-8709795, co-funded by the U.S. Air Force Office of Scientific Research.     

RIR-MAPLE deposition of conjugated polymers for application to optoelectronic devices

Resonant-infrared matrix-assisted pulsed laser evaporation (RIR-MAPLE) is a promising deposition technology for the fabrication of conjugated polymer-based optoelectronic devices for two primary reasons: (i) the ability to control film morphology, and (ii) the ability to deposit multi-layered heterostructures. This article reviews a variation of RIR-MAPLE that uses emulsified targets of organic solvents and water such that the incident laser wavelength (Er:YAG at 2.9 μm) is resonant with hydroxyl (O–H) bonds in the host matrix, which are absent from the guest material. The novelty of the approach lies in the fact that while most polymers of interest and many compatible solvents do not resonantly absorb the laser energy at 2.9 μm, the emulsion with water enables high-quality, thin-film deposition with minimal photochemical and structural degradation for almost any polymer of interest. In addition, the advantages of emulsion-based RIR-MAPLE for conjugated polymer-based optoelectronic devices are demonstrated by two important studies. First, conjugated polymer films deposited by RIR-MAPLE are shown to have higher hole drift mobilities than films deposited using traditional drop-casting and spin-casting techniques. Second, the unique capability of RIR-MAPLE to enable conjugated polymer-based optical heterostructures is demonstrated by the fabrication and characterization of a multi-layer, polymer distributed Bragg reflector.     

Optimal approximation of sparse hessians and its equivalence to a graph coloring problem

We consider the problem of approximating the Hessian matrix of a smooth non-linear function using a minimum number of gradient evaluations, particularly in the case that the Hessian has a known, fixed sparsity pattern. We study the class of Direct Methods for this problem, and propose two new ways of classifying Direct Methods. Examples are given that show the relationships among optimal methods from each class. The problem of finding a non-overlapping direct cover is shown to be equivalent to a generalized graph coloring problem—the distance-2 graph coloring problem. A theorem is proved showing that the general distance-k graph coloring problem is NP-Complete for all fixedk≥2, and hence that the optimal non-overlapping direct cover problem is also NP-Complete. Some worst-case bounds on the performance of a simple coloring heuristic are given. An appendix proves a well-known folklore result, which gives lower bounds on the number of gradient evaluations needed in any possible approximation method. This research was partially supported by the Department of Energy Contract AM03-76SF00326. PA#DE-AT03-76ER72018; Army Research Office Contract DAA29-79-C-0110; Office of Naval Research Contract N00014-74-C-0267; National Science Foundation Grants MCS76-81259, MCS-79260099 and ECS-8012974.