Numerical Studies of H2 and H2/CO Autoignition in Turbulent Jets PDF Download

Author: Kamlesh Govindram Gupta
Publisher:
ISBN:
Category :
Languages : en
Pages : 134

View

Book Description
Keywords: hydrogen, turbulent jets, one-dimensional turbulence model, carbon-monoxide, autoignition.

Author:
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description
The present study is carried out in two parts. In the first part, the autoignition of hydrogen in a turbulent jet with preheated air is studied computationally using the stand-alone one-dimensional turbulence (ODT) model. The simulations are based on varying the jet Reynolds number and the mixture pressure. Also, computations are carried out for homogeneous autoignition at different mixture fractions and the same two pressure conditions considered for the jet simulations. The simulations show that autoignition is delayed in the jet configuration relative to the earliest autoignition events in homogeneous mixtures. This delay is primarily due to the presence of scalar dissipation associated with the scalar mixing layer in the jet configuration as well as with the presence of turbulent stirring. Turbulence plays additional roles in the subsequent stages of the autoignition process. Pressure effects also are present during the autoignition process and the subsequent high-temperature combustion stages. These effects may be attributed primarily to the autoignition delay time sensitivity to the mixture conditions and the role of pressure and air preheating on molecular transport properties. The overall trends are such that turbulence increases autoignition delay times and accordingly the ignition length and pressure further contributes to this delay. In the second part of this study, similar autoignition study of mixture of hydrogen and carbon monoxide is conducted. Two different mixture compositions are considered. They correspond to H2:CO:N2 ratios by volume of 15:35:50 and 20:30:50. Each composition is simulated for two oxidizer preheat temperatures and two fuel jet Reynolds numbers at atmospheric pressure. Homogeneous autoignition is carried out for same preheat mixture conditions for comparison with the turbulent jet results. The autoignition delay time recorded for jet cases is lower than the homogeneous autoignition delay time. This is attributed to the differentia.

Author: Donald Jerome Frederick
Publisher:
ISBN:
Category :
Languages : en
Pages : 63

View

Book Description
An ever increasing demand for energy coupled with a need to mitigate climate change necessitates technology (and lifestyle) changes globally. An aspect of the needed change is a decrease in the amount of anthropogenically generated CO2 emitted to the atmosphere. The decrease needed cannot be expected to be achieved through only one source of change or technology, but rather a portfolio of solutions are needed. One possible technology is Carbon Capture and Storage (CCS), which is likely to play some role due to its combination of mature and promising emerging technologies, such as the burning of hydrogen in gas turbines created by pre-combustion CCS separation processes. Thus research on effective methods of burning turbulent hydrogen jet flames (mimicking gas turbine environments) are needed, both in terms of experimental investigation and model development. The challenge in burning (and modeling the burning of) hydrogen lies in its wide range of flammable conditions, its high diffusivity (often requiring a diluent such as nitrogen to produce a lifted turbulent jet flame), and its behavior under a wide range of pressures. In this work, numerical models are used to simulate the environment of a gas turbine combustion chamber. Concurrent experimental investigations are separately conducted using a vitiated coflow burner (which mimics the gas turbine environment) to guide the numerical work in this dissertation. A variety of models are used to simulate, and occasionally guide, the experiment. On the fundamental side, mixing and chemistry interactions motivated by a H2/N2 jet flame in a vitiated coflow are investigated using a 1-D numerical model for laminar flows and the Linear Eddy Model for turbulent flows. A radial profile of the jet in coflow can be modeled as fuel and oxidizer separated by an initial mixing width. The effects of species diffusion model, pressure, coflow composition, and turbulent mixing on the predicted autoignition delay times and mixture composition at ignition are considered. We find that in laminar simulations the differential diffusion model allows the mixture to autoignite sooner and at a fuel-richer mixture than the equal diffusion model. The effect of turbulence on autoignition is classified in two regimes, which are dependent on a reference laminar autoignition delay and turbulence time scale. For a turbulence timescale larger than the reference laminar autoignition time, turbulence has little influence on autoignition or the mixture at ignition. However, for a turbulence timescale smaller than the reference laminar timescale, the influence of turbulence on autoignition depends on the diffusion model. Differential diffusion simulations show an increase in autoignition delay time and a subsequent change in mixture composition at ignition with increasing turbulence. Equal diffusion simulations suggest the effect of increasing turbulence on autoignition delay time and the mixture fraction at ignition is minimal. More practically, the stabilizing mechanism of a lifted jet flame is thought to be controlled by either autoignition, flame propagation, or a combination of the two. Experimental data for a turbulent hydrogen diluted with nitrogen jet flame in a vitiated coflow at atmospheric pressure, demonstrates distinct stability regimes where the jet flame is either attached, lifted, lifted-unsteady, or blown out. A 1-D parabolic RANS model is used, where turbulence-chemistry interactions are modeled with the joint scalar-PDF approach, and mixing is modeled with the Linear Eddy Model. The model only accounts for autoignition as a flame stabilization mechanism. However, by comparing the local turbulent flame speed to the local turbulent mean velocity, maps of regions where the flame speed is greater than the flow speed are created, which allow an estimate of lift-off heights based on flame propagation. Model results for the attached, lifted, and lifted-unsteady regimes show that the correct trend is captured. Additionally, at lower coflow equivalence ratios flame propagation appears dominant, while at higher coflow equivalence ratios autoignition appears dominant.

Author: Sayan Biswas
Publisher: Springer
ISBN: 3319762435
Category : Technology & Engineering
Languages : en
Pages : 230

View

Book Description
This book focuses on developing strategies for ultra-lean combustion of natural gas and hydrogen, and contributes to the research on extending the lean flammability limit of hydrogen and air using a hot supersonic jet. The author addresses experimental methods, data analysis techniques, and results throughout each chapter and: Explains the fundamental mechanisms behind turbulent hot jet ignition using non-dimensional analysis Explores ignition characteristics by impinging hot jet and multiple jets in relation to better controllability and lean combustion Explores how different instability modes interact with the acoustic modes of the combustion chamber. This book provides a potential answer to some of the issues that arise from lean engine operation, such as poor ignition, engine misfire, cycle-to-cycle variability, combustion instability, reduction in efficiency, and an increase in unburned hydrocarbon emissions. This thesis was submitted to and approved by Purdue University.

Author: Heinz Pitsch
Publisher: Springer Nature
ISBN: 3030447189
Category : Mathematics
Languages : en
Pages : 294

View

Book Description
This book presents methodologies for analysing large data sets produced by the direct numerical simulation (DNS) of turbulence and combustion. It describes the development of models that can be used to analyse large eddy simulations, and highlights both the most common techniques and newly emerging ones. The chapters, written by internationally respected experts, invite readers to consider DNS of turbulence and combustion from a formal, data-driven standpoint, rather than one led by experience and intuition. This perspective allows readers to recognise the shortcomings of existing models, with the ultimate goal of quantifying and reducing model-based uncertainty. In addition, recent advances in machine learning and statistical inferences offer new insights on the interpretation of DNS data. The book will especially benefit graduate-level students and researchers in mechanical and aerospace engineering, e.g. those with an interest in general fluid mechanics, applied mathematics, and the environmental and atmospheric sciences.

Author: Eric S. Bish
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description

Author: V. R. Katta
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description

Author: Nedunchezhian Swaminathan
Publisher: Cambridge University Press
ISBN: 1139498584
Category : Technology & Engineering
Languages : en
Pages : 447

View

Book Description
A work on turbulent premixed combustion is important because of increased concern about the environmental impact of combustion and the search for new combustion concepts and technologies. An improved understanding of lean fuel turbulent premixed flames must play a central role in the fundamental science of these new concepts. Lean premixed flames have the potential to offer ultra-low emission levels, but they are notoriously susceptible to combustion oscillations. Thus, sophisticated control measures are inevitably required. The editors' intent is to set out the modeling aspects in the field of turbulent premixed combustion. Good progress has been made on this topic, and this cohesive volume contains contributions from international experts on various subtopics of the lean premixed flame problem.

Author: C. J. Montgomery
Publisher:
ISBN:
Category :
Languages : en
Pages :

View

Book Description

Author: Seyed Ehsan Hosseini
Publisher: Academic Press
ISBN: 0323903460
Category : Technology & Engineering
Languages : en
Pages : 668

View

Book Description
Fundamentals of Low Emission Flameless Combustion and Its Applications is a comprehensive reference on the flameless combustion mode and its industrial applications, considering various types of fossil and alternative fuel. Several experimental and numerical accomplishments on the fundamentals of state-of-the-art flameless combustion is presented, working to clarify the environmentally friendly aspects of this combustion mode. Author Dr. Hosseini presents the latest progresses in the field and highlights the most important achievements since invention, including the fundamentals of thermodynamics, heat transfer and chemical kinetics. Also analyzed is fuel consumption reduction and the efficiency of the system, emissions formation and the effect of the flameless mode on emission reduction.This book provides a solid foundation for those in industry employing flameless combustion for energy conservation and the mitigation of pollutant emissions. It will provide engineers and researchers in energy system engineering, chemical engineering, industrial engineers and environmental engineering with a reliable resource on flameless combustion and may also serve as a textbook for senior graduate students. - Presents the fundamentals of flameless combustion and covers advances since its invention - Includes experimental and numerical investigations of flameless combustion - Analyzes emission formation and highlights the effects of the flameless mode on emission reduction