Bio: Manikanda Rajagopal is an academic researcher from Indiana University – Purdue University Indianapolis. The author has contributed to research in topics: Combustion & Computer science. The author has an hindex of 5, co-authored 9 publications receiving 47 citations.
TL;DR: In this article, the authors used a traversing jet of chemically active gas at one end of a long constant volume combustor (CVC) with aspect ratio similar to a wave rotor channel.
Abstract: Hot-jet ignition of a combustible mixture has application in IC engines, detonation initiation, and wave rotor combustion. Numerical predictions are made for ignition of combustible mixtures using a traversing jet of chemically active gas at one end of a long constant-volume combustor (CVC) with aspect ratio similar to a wave rotor channel. The CVC initially contains a stoichiometric mixture of ethylene or methane at atmospheric conditions. The traversing jet issues from a rotating pre-chamber that generates gaseous combustion products, assumed at chemical equilibrium for estimating major species. Turbulent combustion uses a hybrid eddy-break-up model with detailed finite-rate kinetics and a two-equation k-ω model. The confined jet is observed to behave initially as a wall jet and later as a wall-impinging jet. The jet evolution, vortex structure and mixing behavior are significantly different for traversing jets, stationary centered jets, and near-wall jets. Pressure waves in the CVC chamber affect ignition through flame vorticity generation and compression. The jet and ignition behavior are compared with high-speed video images from a prior experiment. Production of unstable intermediate species like C2H4 and CH3 appears to depend significantly on the initial jet location while relatively stable species like OH are less sensitive.Copyright © 2013 by ASME
••01 Dec 2012
TL;DR: In this article, a wave-rotor pressure gain combustor (WRPGC) is proposed to provide constant volume combustion and enable a gas turbine engine to operate on the Humphrey-Atkinson cycle.
Abstract: A wave-rotor pressure-gain combustor (WRPGC) ideally provides constant-volume combustion and enables a gas turbine engine to operate on the Humphrey-Atkinson cycle. It exploits pressure (both compression and expansion) waves and confined propagating combustion to achieve pressure rise inside the combustor. This study first presents thermodynamic cycle analysis to illustrate the improvements of a gas turbine engine possible with a wave rotor combustor. Thereafter, non-steady reacting simulations are used to examine features and characteristics of a combustor rig that reproduces key features of a WRPGC.In the thermodynamic analysis, performance parameters such as thermal efficiency and specific power are estimated for different operating conditions (compressor pressure ratio and turbine inlet temperature). The performance of the WRPGC is compared with the conventional unrecuperated and recuperated engines that operates on the Brayton cycle. Fuel consumption may be reduced substantially with WRPGC introduction, while concomitantly boosting power. Simulations have been performed of the ignition of propane by a hot gas jet and subsequent turbulent flame propagation and shock-flame interaction.Copyright © 2012 by ASME
••14 Jul 2013
TL;DR: In this article, the relative role of chemical kinetics and turbulent mixing in a transient hot jet on ignition in a constant-volume combustor was investigated in the presence of chemically active species in the hot jet.
Abstract: A jet of hot reactive gas can reliably ignite premixed gases in combustion engines. The presence of chemically active species in the hot jet may influence the time delay and ignitability limits for ignition of a combustible mixture. Rapid ignition and combustion may also involve complex interactions of pressure waves with flames in the transient jet, especially in a wave-rotor constant-volume combustor for gas turbine performance enhancement. In the present work, detailed numerical simulations are carried out to understand the relative role of chemical kinetics and turbulent mixing in a transient hot jet on ignition in a constant-volume combustor. A transient hot jet is modeled in two ways: as a relatively inert hot jet and as a radical-rich chemically active hot jet for slightly rich ethylene-air mixture. Combustion is modeled in the main constantvolume chamber for methane, hydrogen and blended methane-hydrogen mixtures. A hybrid eddy-break-up combustion model is applied, with detailed or reduced reaction mechanisms and the two-equation k-ω model. For stoichiometric methane mixture in the main chamber, the predicted ignition of the blended fuel mixture was surprisingly not any faster than that of pure methane. The ignition delay time of the more chemically active jet is slightly shorter than a jet of similar composition with only stable species. These observations generally point to a complex interaction of physical and chemical process in hot-jet ignition in a confined volume with shock dynamics and jet mixing processes playing a role that may be as important as chemical kinetics.
14 Nov 2013
TL;DR: In this paper, a relatively coarse initial mesh was refined selectively and automatically, based on predicted velocity and temperature gradients, tracking propagating pressure waves and flames, to avoid expensive kinetic calculations in every computational cell, with considerable speedup.
Abstract: More efficient and powerful gas turbine engines can be designed using constant-volume combustors that may involve ignition of a combustible mixture using a hot gas jet, subsequent flame and pressure-wave propagation, and their interactions. Accurate prediction of three-dimensional transient turbulent combustion is computationally challenging. To resolve propagating turbulent combustion, predict ignition, and track pressure waves accurately requires techniques to minimize the numerical cell count and kinetics calculation times. This study of shock-flame interaction (SFI) used detailed chemistry that includes low-temperature ignition reactions. Computational cells with similar temperatures and composition were grouped as ‘zones’ where kinetics are solved only once per zone per time step, using average values of species concentrations and thermodynamic properties for that zone. This avoids expensive kinetic calculations in every computational cell, with considerable speedup. A relatively coarser initial mesh was refined selectively and automatically, based on predicted velocity and temperature gradients, tracking propagating pressure waves and flames. The time step is variable, limited by the local speed of sound, to ensure accurate wave propagation. These techniques, previously validated for non-premixed, premixed and multiple-fuel turbulent combustion in industrial IC engines, are applied to study SFI during premixed combustion in a long constant-volume combustor.© 2013 ASME
31 Oct 2017
TL;DR: The modern evolution of America's Flagship Universities by Eugene M. Tobin this article has been studied extensively in the field of educational attainment: overall trends, disparities, and the public universities we study.
Abstract: Acknowledgments vii Preface xiii Chapter 1. Educational Attainment: Overall Trends, Disparities, and the Public Universities We Study 1 Chapter 2. Bachelor's Degree Attainment on a National Level 20 Chapter 3. Finishing College at Public Universities 32 Chapter 4. Fields of Study, Time-to-Degree, and College Grades 57 Chapter 5. High Schools and "Undermatching" 87 Chapter 6. Test Scores and High School Grades as Predictors 112 Chapter 7. Transfer Students and the Path from Two-Year to Four-Year Colleges 134 Chapter 8. Financial Aid and Pricing on a National Level 149 Chapter 9. Financial Aid at Public Universities 166 Chapter 10. Institutional Selectivity and Institutional Effects 192 Chapter 11. Target Populations 207 Chapter 12. Looking Ahead 223 Appendix A. The Modern Evolution of America's Flagship Universities by Eugene M. Tobin 239 Notes 265 List of Figures 337 List of Tables 347 List of Appendix Tables 349 References 357 Index 377
01 Jan 1989
TL;DR: Chickering is a Distinguished Professor of Higher Education at Memphis State University and a Visiting Professor at George Mason University as mentioned in this paper, and Gamson is a sociologist who holds appointments at the John W. McCormack Institute of Public Affairs at the University of Massachusetts-Boston, and in the Center for the Study of Higher and Postsecondary Education at University of Michigan.
Abstract: Arthur Chickering is Distinguished Professor of Higher Education at Memphis State University. On leave from the Directorship of the Center for the Study of Higher Education at Memphis State, he is Visiting Professor at George Mason University. Zelda Gamson is a sociologist who holds appointments at the John W. McCormack Institute of Public Affairs at the University of Massachusetts-Boston and in the Center for the Study of Higher and Postsecondary Education at the University of Michigan.
TL;DR: In this article, a parametric study was performed to understand the effects of pressure, temperature, equivalence ratio along with geometric factors such as orifice diameter and spark position on the ignition mechanisms and probability.
TL;DR: In this article, the characteristics of supersonic hot jets generated by combustion of stoichiometric H2/air in a pre-chamber to understand the ignition mechanism of ultra-lean mixtures by super-lean hot jets were investigated.
Abstract: Gas engines often utilize a small-volume pre-chamber in which fuel is injected at near stoichiometric condition to produce a hot turbulent jet which then ignites the lean mixture in the main chamber. Hot jet ignition has several advantages over traditional spark ignition, e.g., more reliable ignition of extra-lean mixtures and more surface area for ignition resulting in faster burning and improved combustion burn time. Our previous experimental results show that supersonic jets could extend the lean flammability limit of fuel/air mixtures in the main chamber in comparison to subsonic jets. The present paper investigated the characteristics of supersonic hot jets generated by combustion of stoichiometric H2/air in a pre-chamber to understand the ignition mechanism of ultra-lean mixtures by supersonic hot jets. Numerical simulations were carried out to examine the transient hot jets issued from six different nozzles (two straight nozzles, one converging nozzle, and three converging-diverging (C-D) nozzles) using a detailed H2/air chemistry. The detailed flame propagation process inside the pre-chamber was investigated. Then the characteristics of the hot jets from six nozzles were compared, including the spatial and temporal distribution of velocity, vorticity, pressure, turbulence quantities, temperature, shock structures, and species concentrations. The results show that supersonic jets exhibit shock diamond structures. The static temperature rises after each shock and a significant temperature rise occur after the final shock. The location of this high-temperature zone is consistent with the experimental observations where ignition was initiated. The profile of Damköhler numbers based on the local flow properties was determined. A critical Damköhler number was found to be 11, below which the main chamber ignition would unlikely to occur. Additionally, the Damköhler number profiles help to explain why the two C-D nozzles with an area ratio of 4 and 9 could extend the flammability limit, whereas the C-D nozzle with an area ratio of 16 failed to do so.
TL;DR: In this article, the regenerative cooling channels designed in a variety of non-uniform patterns are proposed and the conjugated flow and heat transfer behaviors of coolant and solid combustion chamber are numerically investigated.