Transformation of coal mineral matter during pulverized coal combustion

The theoretical development of a sequence of mathematical sub-models capable of calculating the fouling tendency of a coal based on microscopic analysis of the coal mineral matter is described. The sub-models interpret computer controlled-scanning electron microscope analysis data in terms of mineral size and chemical composition distributions; follow the transformation of these mineral property distributions during the combustion of the coal; determine the probability of the resultant fly ash particles impacting on boiler-tube surfaces and of their sticking upon impaction. The sub-models are probabilistic, and take account of the particle-to-particle variation of coal mineral matter and fly ash properties by providing mean values and variances for particle size, chemical composition and viscosity. The various sub- models are combined into a Coal Fouling Tendency (CFT) computer code. Comparison of CFT modeling results obtained for any coal or coal blend with those obtained for a coal whose behavior in a given boiler plant is known, can give useful information on their relative fouling tendencies. The report also includes data on the deposition characteristics of five coals or coal blends, obtained from combustion experiments in the 1-2 MW flame tunnel at MIT. The measurement data were used for validation of the CFT calculations, and for ranking the five fuels with respect to their fouling behavior. Similar ranking of other coals, without combustion testing, can be based solely on results from the CFT model, and examples are given in the report.New England Power Service Co., ABB-Combustion Engineering, Public Service Electric & Gas Co., Empire State Electric Energy Research Corp., ENEL S.p.A., and Electric Power Research Institut

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

Simulation of soot formation using particle dynamics with one dimensional nucleation mode

Journal ArticleTwo soot formation models using particle dynamics with one-dimensional nucleation mode directly coupled with gas phase chemistry are tested on three ethylene and three methane laminar premixed flames. These models demonstrate strength in the prediction of concentration profiles of major combustion products and critical intermediates, and the characteristics of soot particles. These models extend the practicability of simulation beyond the prediction of soot volume fraction and estimate the mean particle diameter quite well especially for methane flames. In particular, our second model expands the range of fuels that can be simulated, and also correctly predicts the effects of C/O ratio on the soot formation process. The strength and weakness of these models are investigated and new features are identified for the development of next generation of soot models

Relating prepotentials and quantum vacua of N=1 gauge theories with different tree-level superpotentials

We consider N=1 supersymmetric U(N) gauge theories with Z_k symmetric tree-level superpotentials W for an adjoint chiral multiplet. We show that (for integer 2N/k) this Z_k symmetry survives in the quantum effective theory as a corresponding symmetry of the effective superpotential W_eff(S_i) under permutations of the S_i. For W(x)=^W(h(x)) with h(x)=x^k, this allows us to express the prepotential F_0 and effective superpotential W_eff on certain submanifolds of the moduli space in terms of an ^F_0 and ^W_eff of a different theory with tree-level superpotential ^W. In particular, if the Z_k symmetric polynomial W(x) is of degree 2k, then ^W is gaussian and we obtain very explicit formulae for F_0 and W_eff. Moreover, in this case, every vacuum of the effective Veneziano-Yankielowicz superpotential ^W_eff is shown to give rise to a vacuum of W_eff. Somewhat surprisingly, at the level of the prepotential F_0(S_i) the permutation symmetry only holds for k=2, while it is anomalous for k>2 due to subtleties related to the non-compact period integrals. Some of these results are also extended to general polynomial relations h(x) between the tree-level superpotentials.Comment: 27 pages, 10 figures, modified version to appear in JHEP, discussion of the physical meaning of the Z_k symmetry adde

Muiltifunctional fuel additives for reduced jet particlate emissions

ReportUsing Government drawings, specifications, or other data included in this document for any purpose other than Government procurement does not in any way obligate the U.S. Government. The fact that the Government formulated or supplied the drawings, specifications, or other data does not license the holder or any other person or corporation; or convey any rights or permission to manufacture, use, or sell any patented invention that may relate to them

Using optimal control to adjust the production rate of a deteriorating inventory system

AbstractThis work represents is another contribution to the application of optimal control theory to production inventory systems. We consider a firm that produces some product at a certain rate and aims at improving this rate. We successfully formulated the model as an optimal control problem and obtained an explicit solution using the maximum principle. An illustrative example is provided and the sensitivity of the model to some of the system parameters was addressed