Huelskamp B.C.,Innovative Scientific Solutions, Inc. |
Gokulakrishnan P.,Combustion Engineering Inc |
Kiel B.V.,Air Force Research Lab
Proceedings of the ASME Turbo Expo | Year: 2015
This study employed experimental data collected at the Air Force Research Laboratory (AFRL) as well as data from a review of past literature to develop a correlation for predicting lean blowout through the use of a least-squares curve-fit method. Combining data from the literature with data from AFRL allowed significant variations within the dataset with regard to velocity, flameholder diameter and shape, pressure, temperature, and fuel. Gaseous, single-component fuels as well as multi-component jet fuels were included in the study. The study reports new jet fuel blowout data. The laminar flame speed and ignition delay time calculated using detailed chemical kinetics mechanisms were used in the correlations to determine the chemical timescales relevant to lean blowout. The correlation presented here indicates that the lean blowout of bluff-body stabilized flames is dependent on the Damköhler number, with fuel variation being a significant factor. The ratio of the flameholder diameter to the lip velocity was found to influence the lean blowout. This ratio represents the fluid-mechanic timescale in the Damköhler number. Pressure, temperature, and the hydrogen-to-carbon ratio of the fuel affect the reactivity of the mixture, contributing to the chemical timescale in the Damköhler number. For a limited dataset, the ignition delay time is an adequate representation of the chemical timescale. Copyright © 2015 by ASME.
Foli K.,Combustion Engineering Inc
10AIChE - 2010 AIChE Annual Meeting, Conference Proceedings | Year: 2010
A procedure aimed at optimizing the design of catalyst layers for high temperature polymer electrolyte membrane (PEM) fuel cells is presented. In developing the methodology the concept of catalyst effectiveness expressed as a function of the Thiele modulus is applied in determining the optimum thickness of a catalyst layer. Three variables that control the catalyst layer performance are the catalyst loading, specific surface area of catalyst particles and the layer thickness. Given any two of the above variables it is possible to determine the third for optimum catalyst performance. The approach is very simple and only accurate for small size fuel cells systems because of the underlying assumptions in the analysis. For large size systems the method offers, at best, qualitative results that are good enough to guide the design of such systems and serve as a good first-step approach to more complex threedimensional analyses.
Gonzalez-Juez E.D.,Combustion Engineering Inc |
Jemcov A.,University of Notre Dame
Journal of Propulsion and Power | Year: 2014
Modeling tools used to estimate thermoacoustic combustion instabilities include classic network models, threedimensional frequency-domain acoustic solvers, and computational fluid dynamics. Motivated by the large gap in both computational cost and predictive capability between the first two tools and computational fluid dynamics, the present work discusses and tests an approach that bridges this gap: A three-dimensional finite volume, acoustic solver in the time domain. Distinguishing features of the newly developed solver include the ability to capture both linear and nonlinear acoustics, the use of a solution algorithm based on an approximate Riemann solver, and the ability to handle complex geometries with unstructured meshes. This new solver produces results that agree well with analytical solutions for a two-dimensional isothermal cavity and a one-dimensional Rijke tube, as well as with the experimental data of a reheat buzz. For this last problem, a limit cycle is produced with a physical model that bounds heat-release fluctuations. In addition, results from the new acoustic solver for an annular combustor compare well with those of a three-dimensional frequency-domain acoustic solver, demonstrating the capabilities of the new solver to capture multidimensional acoustics. Copyright © 2014 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved.
Akram M.,Indian Institute of Technology Bombay |
Kumar S.,Indian Institute of Technology Bombay |
Saxena P.,Combustion Engineering Inc
Journal of Engineering for Gas Turbines and Power | Year: 2013
The laminar burning velocity of liquefied petroleum gas (LPG) air mixtures at high temperatures is extracted from the planar flames stabilized in the preheated mesoscale diverging channel. The experiments were carried out for a range of equivalence ratios and mixture temperatures. Computational predictions of the burning velocity and detailed flame structure were performed using the PREMIX code with USC mech 2.0. The present data are in very good agreement with both the recent experimental and computational results available. A peak burning velocity was observed for slightly rich mixtures, even at higher mixture temperatures. The minimum value of th temperature exponent is observed for slightly rich mixtures. Copyright © 2013 by ASME.
Gonzalez-Juez E.D.,Combustion Engineering Inc
51st AIAA/SAE/ASEE Joint Propulsion Conference | Year: 2015
Screech is a thermoacoustic combustion instability related to the transverse acoustic modes of a combustor. Under certain conditions, the pressure oscillations associated with screech can reach high-enough amplitudes to pose a serious danger to combustion systems. Unfortunately, estimating such conditions still remains a formidable challenge. With this motivation in mind, the present work uses Computational-Fluid-Dynamic (CFD) simula- tions to analyze a classic problem in the study of screech, the bluff-body-stabilized combus- tor of Rogers and Marble, with the goal of providing a qualitative description and further insight into the mechanisms driving the combustion instability and the stable-to-unstable transition process. CFD results show that heat-release fluctuations induced by vortices occur during screech, in agreement with the experiments, but also show a flame/wall- interaction mechanism. The CFD model also agrees with the experiments on reproducing a stable-to-unstable transition produced by increasing the reactivity of the mixture. This transition is attributed to flame flashback and the concomitant establishment of conditions that increase the likelihood of screech. © 2015, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.