Spelling suggestions: "subject:"nonpremixed"" "subject:"unpremixed""
11 |
Conversion of a Gas Turbine Engine to Operate on Lean-Premixed Hydrogen-Air: Design and CharacterizationFarina, Jordan Thomas 10 February 2010 (has links)
The continued use of fossil fuels along with a rise in energy demand has led to increasing levels of carbon emissions over the past years. The purpose of this research was to design a lean premixed hydrogen fuel system that could be readily retrofit into an existing gas turbine engine to provide a clean renewable energy solution to this growing problem. There were major hurdles that had to be overcome to develop a hydrogen fuel system that would be practical, stable, and would fit into the existing space.
High flame temperatures coupled with high flame speeds are major concerns when switching from jet fuel or natural gas to hydrogen. High temperatures lead to formations of pollutants such as oxides of nitrogen (NOx) and can potentially cause damage to critical engine components. High flame speeds can lead to dangerous flashbacks in the fuel premixers. Past researches have developed various hydrogen premixers to combat these problems. This research designed and developed new hydrogen premixers using information gathered from these designs and utilized new ideas to address their shortcomings.
A gas turbine engine was modified using 14 premixers and a matching combustor liner to provide lean operation with the existing turbomachinery. The engine was successfully operated using hydrogen while maintaining normal internal temperatures and practically eliminating the NOx emissions when compared to normal Jet-A operation. Even though full power operation was never achieved due to flashbacks in two premixers, this research demonstrated the feasibility of using lean-premixed hydrogen in gas turbine engines. / Master of Science
|
12 |
Attachment point characteristics and modeling of shear layer stabilized flames in an annular, swirling flowfieldFoley, Christopher William 07 January 2016 (has links)
The focus of this work was to develop a deeper understanding of the mechanisms of flame stabilization and extinction for shear layer stabilized, premixed flames. Planar experimental studies were performed in the attachment point region of an inner shear layer stabilized flame in an annular, swirl combustor. Through high resolution, simultaneous PIV & CH-PLIF measurements, the instantaneous flow field and flame position was captured enabling the characterization of 2D flame stretch and velocity conditions in the attachment point region. In addition, measurements performed at various equivalence ratios and premixer velocities provided insight into the physics governing blowoff. Most notably, these studies showed that as lean blowoff conditions are approached by decreasing equivalence ratio, the mean stretch rates near the attachment point decrease but remain positive throughout the measurement domain. In fact, compared to numerically calculated extinction stretch rates, the flame becomes less critically stretched as equivalence ratio is decreased. Also, investigation of the flame structure at the leading edge of the flame showed strong evidence that the flame is edge flame stabilized. This was supported by inspection of the CH-PLIF images, which showed the CH-layer oriented tangent to the flow field and terminating abruptly at the leading edge. Lastly, the flame anchoring location was observed to be highly robust as the mean flame edge flow conditions and mean location of leading edge of the flame were insensitive to changes in equivalence ratio, remaining nearly constant for values ranging from 0.9 to 1.1. However, at the leanest equivalence ratio of 0.8, the flame leading edge was located farther downstream and subject to much higher flow velocities. These results thus suggest that blowoff is the result of a kinematic balance and not directly from stretch induced flame extinction.
|
13 |
Study of Interaction of Entrained Coal Dust Particles in Lean Methane-Air Premixed FlamesXie, Yanxuan 18 October 2011 (has links)
"This study investigates the interaction of micron- sized coal particles entrained into lean methane €“ air premixed flames. In a typical axisymmetric burner, coal particles are made to naturally entrain into a stream of the premixed reactants using an orifice plate setup. Pittsburgh seam coal dust, with three particle sizes in the range of 0 to 25 µm, 53 to 63 µm, and 75 to 90 µm is used. The effects of different coal dust concentrations (10 €“ 300 g/m3) at three lean equivalence ratios, ϕ (methane-air) of 0.75, 0.80 and 0.85 on the laminar burning velocity are determined experimentally. The laminar burning velocity of the coal dust-methane-air mixture is determined by taking a shadowgraph of the resulting flame and using the cone-angle method. The results show that the addition of coal dust in methane-air premixed flame reduces the laminar burning velocity at particle size of 53 to 63 µm and 75 to 90 µm. However, burning velocity promotion is observed for 0 to 25 µm particles at ϕ = 0.80. Two competing effects are assumed involved in the process. The first is burning velocity promotion effect that the released volatile increases the gaseous mixture equivalence ratio and thus the burning velocity. The second is the heat sink effect of the coal particles to reduce the flame temperature and accordingly the burning velocity. A mathematical model is developed based on such assumption and it can successfully predict the change of laminar burning velocity at various dust concentration. Furthermore, the implication of this study to coal mine safety is discussed."
|
14 |
Influence of the Reactant Temperature on Particle Entrained Laminar Methane-Air Premixed FlamesLee, Minkyu 01 May 2014 (has links)
This study investigates the laminar burning velocity of premixed methane-air mixtures, having controlled supply of micron-sized (75-90 ¥ìm) coal dust and sand particles over a range of gas phase equivalence ratios (0.9-1.2), dust concentrations (0-250 g/m3) and reactant temperatures (297, 350, 400 K) using a novel Bunsen-burner type experimental design. The experimental results show that, the laminar burning velocity is enhanced by the increase in the reactant temperature, irrespective of the equivalence ratio of the mixture due to enhanced reaction rates. Addition of coal particles in fuel lean (ϕ < 1) mixtures increases the laminar burning velocity initially up to a certain coal dust concentration, but after that, the trend is altered; either it remains constant or shows a decreasing trend. The dust concentration value, which produces the initial or local maximum, increases with increase in reactant temperature. In other words, the reactant temperature plays a significant role in the trend of increase in laminar burning velocity with dust addition. For ϕ > 1, at a given reactant temperature, a linear decay of burning velocity with dust addition is observed. When a combustible dust particle interacts with the flame zone, it extracts energy from the flame (heat sink effect) and releases volatiles, thereby changing the local equivalence ratio around the flame zone. Both, increase in the equivalence ratio and the heat sink effect, are influenced by the reactant temperature. A mathematical model including these effects is developed and the model predictions are compared with the experimental results. The results are in a good agreement for fuel lean and stoichiometric mixtures; whereas the model is found to under predict results for fuel rich cases, and needs further improvements.
|
15 |
Physical insights of non-premixed MILD combustion using DNSDoan, Nguyen Anh Khoa January 2019 (has links)
Moderate or Intense Low-oxygen Dilution (MILD) combustion is a combustion technology that can simultaneously improve the energy efficiency and reduce the pollutant emissions of combustion devices. It is characterised by highly preheated reactants and a small temperature rise during combustion due to the large dilution of the reactant mixture with products of combustion. These conditions are generally achieved using exhaust gas recirculation. However, the physical understanding of MILD combustion remains limited which prevents its more widely spread use. In this thesis, Direct Numerical Simulation (DNS) is used to study turbulence, premixed flames and MILD combustion to obtain these additional physical insights. In a first stage, the scale-locality of the energy cascade is analysed by applying a multiscale analysis methodology, called the bandpass filter method, on DNS of homogeneous isotropic turbulence. Evidence supporting this scale-locality were obtained and the results were found to be similar for Reynolds numbers ranging from 37 to 1131. Using the same method in turbulent premixed flames, the scale-locality of the energy cascade was still observed despite the presence of intense reactions. In addition, it was found that eddies of scales larger than the laminar flame thickness were imparting the most strain on the flame. In a second part, a methodology was developed to conduct the DNS of MILD combustion with mixture fraction variations. This methodology included the effect of mixing of exhaust gases with fuel and oxidiser in unburnt, burnt and reacting states. In addition, a specific chemical mechanism that includes the chemistry of ${\rm OH^*}$ was developed. From these DNS, the role of radicals on the inception of MILD combustion was studied. In particular, due to the reactions initiated by these radicals, the initial temperature rise in MILD combustion was occurring concurrently with an increase in the scalar dissipation rate of mixture fraction which is contrasting to conventional combustion. The reaction zones in MILD combustion were also analysed and extremely convoluted reaction zones were observed with frequent interactions among them. These interactions yielded the appearance of volumetrically distributed reactions. Furthermore, the adequacy of some species to identify these reaction zones was assessed and ${\rm OH}$ showed a poor correlation with regions of heat release. On the other hand, ${\rm OH^*}$, ${\rm HCO}$ or ${\rm OH} \times {\rm CH_2O}$ were found to be well correlated. Through the study of the flame index, the existence of non-premixed and premixed modes of combustion were also highlighted. The premixed mode was observed to be dominant but the contribution of the non-premixed mode to the total heat release was non negligible. Because of the presence of radicals and high reactant temperatures, auto-igniting regions and propagating reaction zones are both observed locally. The balance between these phenomena was investigated and it was found that this was strongly influenced by the typical lengthscale of the mixture fraction field, with a smaller lengthscale favouring sequential autoignition. Finally, using the bandpass filtering method, the effect of heat release rate in MILD combustion on the energy cascade was studied and this showed that the energy cascade was not unduly affected.
|
16 |
Structure of Partially Premixed Flames Using Detailed Chemistry SimulationsKluzek, Celine D. 2009 August 1900 (has links)
State-of-the-art reacting-flow computations have to compromise either on the detail of chemical reactions or on the dimensionality of the solution, while experiments
in flames are limited by the flow accessibility and provide at best a limited number of observables. In the present work, the partially premixed laminar flame structure is examined using a detailed-chemistry, one-dimensional simulation. The computational results are compared to unpublished single-point multiscalar measurements obtained at Sandia National Labs in 2001. The study is focused on axisymmetric laminar partially-premixed methane/air flames with varying premixture strength values of 1.8, 2.2, and 3.17. The combination of computational and experimental results is
used to analyze the spatial and scalar flame structure under the overarching concept of flamelets. The computations are based on the Cantera open-source software package developed at CalTech by D. Goodwin, and incorporating the GRI 3.0 chemical kinetic mechanism utilizing 325 chemical reactions and 53 species for methane combustion. Cross-transport effects as well as an optically-thin radiation model are included in the calculations. Radiation changes the flame profiles due to its effect on temperature, and the attendant effects on a number of species. Using the detailed analysis of different reaction rates, the adiabatic and radiative nitric oxide concentrations are compared. The cross-transport effects, i.e. Soret and Dufour, were studied in detail. The Soret term has a small but important effect on the flame structure through a reduction of the hydrogen mass fraction, which changes the conserved scalar values.
Based on the flamelet approach and a unique formulation of the conserved scalar, the flame thermochemistry can be analyzed and understood. A number of interesting effects on the flame thermochemistry can be discerned in both experiments and computations when the premixture strength is varied. An increase in premixing results in a counterintuitive decrease in intermediate species such as carbon monoxide and hydrogen, as well as an expected increase in nitric oxide concentrations. Good agreement is found between experiments and calculations in scalar space, while the difference in dimensionality between axisymmetric measurements and opposed jet computations makes comparison in physical space tentative.
|
17 |
強乱流予混合火炎の流れ場と構造山本, 和弘, YAMAMOTO, Kazuhiro, 西澤, 泰樹, NISHIZAWA, Yasuki 25 January 2002 (has links)
No description available.
|
18 |
OH-HCHO同時PLIF法による乱流予混合火炎の可視化と火炎構造山本, 和弘, YAMAMOTO, Kazuhiro, 大西, 將博, OHNISHI, Masahiro, 林, 直樹, HAYASHI, Naoki, 尾関, 賢宏, OZEKI, Masahiro, 山下, 博史, YAMASHITA, Hiroshi 25 September 2007 (has links)
No description available.
|
19 |
Flow Field of Turbulent Premixed Combustion in a Cyclone-Jet CombustorYAMAMOTO, Kazuhiro, INOUE, Satoshi, YAMASHITA, Hiroshi, SHIMOKURI, Daisuke, ISHIZUKA, Satoru 2 May 2007 (has links)
No description available.
|
20 |
Numerical study of helicopter combustor and exhaust emissions using large eddy simulationDumrongsak, Janthanee 02 1900 (has links)
Although Large Eddy Simulation (LES) has demonstrated its potential for
modelling the reaction in simple academic combustors, it is more
computationally expensive than Reynolds Averaged Navier-Stokes (RANS)
which has been used widely for industrial cases. The aim of this research is to
employ LES at minimal grid resolution and computational resource
requirements to capture the main characteristics of the reacting flows in a
helicopter combustor and exhaust plume with the focus on NOx emissions.
Test cases have been carried out to validate the current LES code for non-
reacting jet, non-premixed combustion and unstructured grids. Despite the
moderate grid refinement and simple chemistry models employed, the findings
from these test cases have demonstrated good capabilities of the current LES
to capture the mixing, flame and flow characteristics. In a farther test case, a
key gas-phase chemical reaction selected for the helicopter exhaust plume
modelling has also been tested.
The validated LES code is then employed in the numerical study of the reaction
in the helicopter combustor. The LES predictions in terms of the temperature
and EINOx agree generally well with the combustor design, analytical solutions,
previous LES and test measurements. Subsequently, the potential application
of LES for the calibration of simpler models has been assessed for the generic
and helicopter combustors. The results obtained from LES are compared with
those from a one-dimensional combustor performance and emissions code,
HEPHAESTUS, developed within the Cranfield University Power and
Propulsion Department. The discrepancies between the results are found to be
primarily due to specific simplification and assumptions established in the
HEPHAESTUS model which can be addressed.
Finally, LES has been employed to model the transformation of NO to NO2 in
the helicopter exhaust plume. The findings from this research have
demonstrated that, even without the implementation of highly dense mesh or
advanced reaction model, LES is able to provide results with an acceptable
level of fidelity at relatively low computational costs. These advantages make it
a powerful predictive tool for future design and emissions optimisation
investigations, and calibration of other simpler modelling approaches.
|
Page generated in 0.0604 seconds