Modeling benzene and naphthalene formation in a premixed propylene flame

Journal ArticleThe Utah Surrogate Mechanism was used to model a fuel-rich, non-sooting premixed laminar flame of propylene at 5000 Pa with an equivalence ratio of 2.32. The simulation results were found to be satisfactory in comparison with the experimental data. For example, the measured concentration profiles of the fuel, oxidizer, inert and major products were successfully reproduced. The predictive ability of the model for soot precursors is one of the major foci of this paper; the maximum acetylene and benzene concentrations were predicted within 15% and 30% of the measured values, respectively. The formation of benzene and naphthalene has been critically examined to identify the major reaction pathways of these smallest aromatics, the chemistry of which initiates the growth of PAH species. Combination reactions involving resonant stabilized species such as propargyl, allyl and benzyl radicals were found to be the most important formation pathways for aromatics. Reactions involving benzene have profound impacts on those of naphthalene; however, other formation routes bypassing benzene via reactions of C3+C4 were identified to be the major formation pathways of the higher aromatic species

Numerical combustion of aviation fuel part I: a cross-model comparison of n-heptane premixed flame

Journal ArticleFour different n-heptane mechanisms were used to simulate a fuel rich n-heptane premixed flame and their results were compared with experimental measurements. In addition to discussion of the numerical performance of each mechanism, flux analysis coupled with the atomic distribution technique was used to find the major reaction pathways for fuel consumption, product formation, and the evolution of olefins and other intermediates. Hydrogen abstraction followed by B scission is the major fuel consumption route overtaken by unimolecular decomposition only at 1400-1500K. At that high temperature, however, not much fuel remains so that unimolecular decomposition reactions contribute insignificantly toward the overall fuel decomposition process. Low temperature chemistry of peroxy radicals forms a minor fuel consumption route in this premixed flame. Olefins are formed by B scission and consumed by direct decomposition, radical addition, and hydrogen abstraction reactions. The techniques and pitfalls of flux analysis were also discussed in order to map out a methodology that can be used to identify the true nature of the combustion chemistry. The results obtained from this study for n-heptane is critical to build practical combustion mechanisms for large paraffins, which are major components of liquid aviation transportation fuels. It should be recognized that the conclusions derived here arc for premixed flames, and may not apply to diffusion flames

Introduction: Dialogues about the local and the global in education

This issue of the journal is based on an OCIES-sponsored program for Early Career Researchers (ECRs). The program has established an academic alliance of ECRs to explore educational issues in Oceania and Asia through the lens of local knowledges, wisdoms and theories, helping us to de-centre ourselves from an obsession with the West and Western epistemologies. Philip Chan and Hongzhi Zhang are the conveners, and Bob Teasdale and Zane Ma Rhea have acted as mentors of the program

Improving Sparse Representation-Based Classification Using Local Principal Component Analysis

Sparse representation-based classification (SRC), proposed by Wright et al., seeks the sparsest decomposition of a test sample over the dictionary of training samples, with classification to the most-contributing class. Because it assumes test samples can be written as linear combinations of their same-class training samples, the success of SRC depends on the size and representativeness of the training set. Our proposed classification algorithm enlarges the training set by using local principal component analysis to approximate the basis vectors of the tangent hyperplane of the class manifold at each training sample. The dictionary in SRC is replaced by a local dictionary that adapts to the test sample and includes training samples and their corresponding tangent basis vectors. We use a synthetic data set and three face databases to demonstrate that this method can achieve higher classification accuracy than SRC in cases of sparse sampling, nonlinear class manifolds, and stringent dimension reduction.Comment: Published in "Computational Intelligence for Pattern Recognition," editors Shyi-Ming Chen and Witold Pedrycz. The original publication is available at http://www.springerlink.co

The DNA Methylome of Human Peripheral Blood Mononuclear Cells

Analysis across the genome of patterns of DNA methylation reveals a rich landscape of allele-specific epigenetic modification and consequent effects on allele-specific gene expression

The asparagus genome sheds light on the origin and evolution of a young Y chromosome

Several models have been proposed to explain the emergence of sex chromosomes. Here, through comparative genomics and mutant analysis, Harkess et al. show that linked but separate genes on the Y chromosome are responsible for sex determination in Asparagus, supporting a two-gene model for sex chromosome evolution

Carotenoids Play a Positive Role in the Degradation of Heterocycles by Sphingobium yanoikuyae

BACKGROUND: Microbial oxidative degradation is a potential way of removing pollutants such as heterocycles from the environment. During this process, reactive oxygen species or other oxidants are inevitably produced, and may cause damage to DNA, proteins, and membranes, thereby decreasing the degradation rate. Carotenoids can serve as membrane-integrated antioxidants, protecting cells from oxidative stress. FINDINGS: Several genes involved in the carotenoid biosynthetic pathway were cloned and characterized from a carbazole-degrading bacterium Sphingobium yanoikuyae XLDN2-5. In addition, a yellow-pigmented carotenoid synthesized by strain XLDN2-5 was identified as zeaxanthin that was synthesized from β-carotene through β-cryptoxanthin. The amounts of zeaxanthin and hydrogen peroxide produced were significantly and simultaneously enhanced during the biodegradation of heterocycles (carbazole < carbazole + benzothiophene < carbazole + dibenzothiophene). These higher production levels were consistent with the transcriptional increase of the gene encoding phytoene desaturase, one of the key enzymes for carotenoid biosynthesis. CONCLUSIONS/SIGNIFICANCE: Sphingobium yanoikuyae XLDN2-5 can enhance the synthesis of zeaxanthin, one of the carotenoids, which may modulate membrane fluidity and defense against intracellular oxidative stress. To our knowledge, this is the first report on the positive role of carotenoids in the biodegradation of heterocycles, while elucidating the carotenoid biosynthetic pathway in the Sphingobium genus

Coal devolatilization at very slow heating rates

The yield of volatiles of liquid and gaseous species is a function of operational conditions, including effects of reactor atmosphere gases, coal ranks, heating rates, ultimate devolatilization temperatures, pressure, soak time at ultimate temperatures, and catalysts. One important factor of coal devolatilization is the extent of secondary reactions. Various research groups obtained observations for the volatile yields, e.g., as a function of the heating rate. Of the most importance, higher volatile yields are obtained if the operational conditions allow secondary reactions to proceed so that coal can be degraded to tar, and tar to gaseous species. The other important factor is the reactor atmospheric gases. The two reacting gases are hydrogen and steam. Hydrogen atmosphere enhance the secondary reactions during the coal pyrolysis, and the effect of steam atmosphere is obtained because of physical processes that degrade and rupture fragments from coal and tar. Certain catalytic effects are found in various coal devolatilization experiments. Again, minerals in coal samples catalyze the devolatilization process by enhance the secondary reactions by weakening chemical interactions with forming interactions between the volatile matter and mineral particles. Keywords: Coal devolatilization, slow heating rate, secondary reaction, reactor atmosphere, catalyzed devolatilization

Mechanism reduction and generation using analysis of major fuel consumption pathways for n-heptane in premixed and diffusion flames

abstractReaction pathway analyses were conducted for three mechanisms (designated as the Pitsch, Utah, and Lawrence Livermore National Lab) for a normal heptane premixed flame (? = 1.9) and a normal heptane opposed diffusion flame, in order to identify the relative importance of the major fuel consumption pathways in the two flame classes. In premixed flames, hydrogen abstraction is found to be the major fuel consumption route although it is surpassed by thermal decomposition when the flame temperature exceeds 1400?1500 K. At the higher temperatures, however, little fuel remains in a premixed flame so that thermal decomposition provides a minor pathway for overall fuel decomposition. The principal abstractor is the hydrogen radical in all three mechanisms with the hydroxyl radical having a secondary role. In opposed diffusion flames, thermal decomposition competes with hydrogen abstraction in providing the major pathway for fuel consumption. Thermal decomposition becomes important when a large fraction of the fuel reaches the high-temperature zone in a flame. By understanding the relative importance of competing fuel consumption pathways, mechanisms can be tailored to each specific application by eliminating or lumping insignificant reactions. The results obtained in this study for n-heptane may be used to guide the reduction of existing mechanisms for a particular application or the generation of mechanisms for the combustion of larger paraffins that are major components of liquid aviation and transportation fuels