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Special Issue "Cleaner Combustion"

A special issue of Energies (ISSN 1996-1073). This special issue belongs to the section "Energy and Environment".

Deadline for manuscript submissions: closed (31 March 2019)

Special Issue Editors

Guest Editor
Prof. Dr. Derek Dunn-Rankin

Mechanical and Aerospace Engineering Department, University of California, Irvine, CA 92697, USA
Website | E-Mail
Interests: combustion; sprays; particle transport; non-intrusive optical diagnostics
Guest Editor
Dr. Yu-Chien Chien

Mechanical and Aerospace Engineering Department, University of California, Irvine, CA 92697, USA
Website | E-Mail
Interests: combustion; flames; energy systems; emissions

Special Issue Information

Dear Colleagues,

The Special Issue in Energies on “Cleaner Combustion” focuses on how the combination of fuel treatment, effective energy extraction, and emission mitigation in combustion can be optimized to reduce the environmental impact that threatens living systems because humans rely heavily on energy for basic necessities and economic development. We refer to “cleaner combustion” as an explicit acknowledgment that any improvements in this critical technology can have a significant global impact because of the ubiquitous nature of combustion. A growing population and growing standards of living have produced explosive growth in energy demand, and the environmental upset has started feeding back. This Special Issue includes a spectrum of research on cleaner combustion that helps balance our needs for energy with cognizant respect for the environment.

The goal of this collection is to identify the challenges and improvements of existing energy generation strategies in combustion, as well as reaching various pathways that resolve combustion emissions. The topics range from combustion and flame research that directly or indirectly impact the optimization of combustion processes using conventional carbon-based or hydrocarbon fuels, to options leading to a cleaner combustion outcome by using alternative fuels, biofuels, or low carbon fuels, or including new methods to process exhausted gases.

Prof. Dr. Derek Dunn-Rankin
Dr. Yu-Chien Chien
Guest Editors

Manuscript Submission Information

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Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

  • cleaner combustion
  • low NOx
  • low carbon fuel
  • biofuel
  • alternative fuel
  • exhaust gas cleanup
  • emission control
  • MILD combustion
  • highly preheated combustion
  • oxy-fuel
  • chemical looping

Published Papers (12 papers)

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Research

Open AccessArticle
Combustion Characteristics of Methane Hydrate Flames
Energies 2019, 12(10), 1939; https://doi.org/10.3390/en12101939
Received: 15 April 2019 / Accepted: 8 May 2019 / Published: 21 May 2019
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Abstract
This research studies the structure of flames that use laboratory-produced methane hydrates as fuel, specifically for the purpose of identifying their key combustion characteristics. Combustion of a methane hydrate involves multiple phase changes, as large quantities of solid clathrate transform into fuel gas, [...] Read more.
This research studies the structure of flames that use laboratory-produced methane hydrates as fuel, specifically for the purpose of identifying their key combustion characteristics. Combustion of a methane hydrate involves multiple phase changes, as large quantities of solid clathrate transform into fuel gas, water vapor, and liquid water during burning. With its unique and stable fuel energy storage capability, studies in combustion are focused on the potential usage of hydrates as an alternative fuel source or on their fire safety. Considering methane hydrate as a conventional combustion energy resource and studying hydrate combustion using canonical experimental configurations or methodology are challenges. This paper presents methane hydrate flame geometries from the time they can be ignited through their extinguishment. Ignition and burning behavior depend on the hydrate initial temperature and whether the clathrates are chunks or monolithic shapes. These behaviors are the subject of this research. Physical properties that affect methane hydrate in burning can include packing density, clathrate fraction, and surface area. Each of these modifies the time or the temperature needed to ignite the hydrate flames as well as their subsequent burning rate, thus every effort is made to keep consistent samples. Visualization methods used in combustion help identify flame characteristics, including pure flame images that give reaction zone size and shape and hydrate flame spectra to identify important species. The results help describe links between hydrate fuel characteristics and their resulting flames. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
General Correlations of Iso-octane Turbulent Burning Velocities Relevant to Spark Ignition Engines
Energies 2019, 12(10), 1848; https://doi.org/10.3390/en12101848
Received: 10 April 2019 / Revised: 8 May 2019 / Accepted: 12 May 2019 / Published: 15 May 2019
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Abstract
A better understanding of turbulent premixed flame propagation is the key for improving the efficiency of fuel consumption and reducing the emissions of spark ignition gasoline engines. In this study, we measure turbulent burning velocities (ST) of pre-vaporized iso-octane/air mixtures [...] Read more.
A better understanding of turbulent premixed flame propagation is the key for improving the efficiency of fuel consumption and reducing the emissions of spark ignition gasoline engines. In this study, we measure turbulent burning velocities (ST) of pre-vaporized iso-octane/air mixtures over wide ranges of the equivalence ratio (φ = 0.9–1.25, Le ≈ 2.94–0.93), the root-mean-square (r.m.s.) turbulent fluctuating velocity (u′ = 0–4.2 m/s), pressure p = 1–5 atm at T = 358 K and p = 0.5–3 atm at T = 373 K, where Le is the effective Lewis number. Results show that at any fixed p, T and u′, Le < 1 flames propagate faster than Le > 1 flames, of which the normalized iso-octane ST/SL data versus u′/SL are very scattering, where SL is the laminar burning velocity. But when the effect of Le is properly considered in some scaling parameters used in previous correlations, these large scattering iso-octane ST/SL data can be collapsed onto single curves by several modified general correlations, regardless of different φ, Le, T, p, and u′, showing self-similar propagation of turbulent spherical flames. The uncertainty analysis of these modified general correlations is also discussed. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Performance Analysis of Air and Oxy-Fuel Laminar Combustion in a Porous Plate Reactor
Energies 2019, 12(9), 1706; https://doi.org/10.3390/en12091706
Received: 12 March 2019 / Revised: 28 April 2019 / Accepted: 30 April 2019 / Published: 6 May 2019
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Abstract
Greenhouse gas emissions from the combustion of fossil fuels pose a serious threat to global warming. Mitigation measures to counter the exponential growth and harmful impact of these gases on the environment require techniques for the reduction and capturing of carbon. Oxy-fuel combustion [...] Read more.
Greenhouse gas emissions from the combustion of fossil fuels pose a serious threat to global warming. Mitigation measures to counter the exponential growth and harmful impact of these gases on the environment require techniques for the reduction and capturing of carbon. Oxy-fuel combustion is one such effective method, which is used for the carbon capture. In the present work, a numerical study was carried out to analyze characteristics of oxy-fuel combustion inside a porous plate reactor. The advantage of incorporating porous plates is to control local oxy-fuel ratio and to avoid hot spots inside the reactor. A modified two-steps reaction kinetics model was incorporated in the simulation for modeling of methane air-combustion and oxy-fuel combustion. Simulations were performed for different oxidizer ratios, mass flow rates, and reactor heights. Results showed that that oxy-combustion with an oxidizer ratio (OR) of 0.243 could have the same adiabatic flame temperature as that of air-combustion. It was found that not only does OR need to be changed, but also flow field or reactor dimensions should be changed to achieve similar combustion characteristics as that of air-combustion. Fifty percent higher mass flow rates or 40% reduction in reactor height may achieve comparable outlet temperature to air-combustion. It was concluded that not only does the oxidizer ratio of oxy-combustion need to be changed, but the velocity field is also required to be matched with air-combustion to attain similar outlet temperature. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Numerical Study of the Structure and NO Emission Characteristics of N2- and CO2-Diluted Tubular Diffusion Flames
Energies 2019, 12(8), 1490; https://doi.org/10.3390/en12081490
Received: 28 February 2019 / Revised: 10 April 2019 / Accepted: 13 April 2019 / Published: 19 April 2019
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Abstract
The structure of methane/air tubular diffusion flames with 65% fuel dilution by either CO2 or N2 is numerically investigated as a function of pressure. As pressure is increased, the reaction zone thickness reduces due to decrease in diffusivities with pressure. [...] Read more.
The structure of methane/air tubular diffusion flames with 65 % fuel dilution by either CO2 or N2 is numerically investigated as a function of pressure. As pressure is increased, the reaction zone thickness reduces due to decrease in diffusivities with pressure. The flame with CO2-diluted fuel exhibits much lower nitrogen radicals (N, NH, HCN, NCO) and lower temperature than its N2-diluted counterpart. In addition to flame structure, NO emission characteristics are studied using analysis of reaction rates and quantitative reaction pathway diagrams (QRPDs). Four different routes, namely the thermal route, Fenimore prompt route, N2O route, and NNH route, are examined and it is observed that the Fenimore prompt route is the most dominant for both CO2- and N2-diuted cases at all values of pressure followed by NNH route, thermal route, and N2O route. This is due to low temperatures (below 1900 K) found in these highly diluted, stretched, and curved flames. Further, due to lower availability of N2 and nitrogen bearing radicals for the CO2-diluted cases, the reaction rates are orders of magnitude lower than their N2-diluted counterparts. This results in lower NO production for the CO2-diluted flame cases. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Study on Powder Coke Combustion and Pollution Emission Characteristics of Fluidized Bed Boilers
Energies 2019, 12(8), 1424; https://doi.org/10.3390/en12081424
Received: 22 February 2019 / Revised: 6 April 2019 / Accepted: 9 April 2019 / Published: 13 April 2019
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Abstract
The fluidized reactor is widely used in a number of chemical processes due to its high gas-particle contacting efficiency and excellent performance on solid mixing. An improved numerical framework based on the multiphase particle-in-cell (MP-PIC) method has been developed to simulate the processes [...] Read more.
The fluidized reactor is widely used in a number of chemical processes due to its high gas-particle contacting efficiency and excellent performance on solid mixing. An improved numerical framework based on the multiphase particle-in-cell (MP-PIC) method has been developed to simulate the processes of gas–solid flow and chemical reactions in a fluidized bed. Experiments have been carried out with a 3-MW circulating fluidized bed with a height of 24.5 m and a cross section of 1 m2. In order to obtain the relationship between pollutant discharge and operating conditions and to better guide the operation of the power plant, a series of tests and simulations were carried out. The distributions of temperature and gas concentration along the furnace from simulations achieved good accuracy compared with experimental data, indicating that this numerical framework is suitable for solving complex gas–solid flow and reactions in fluidized bed reactors. Through a series of experiments, the factors affecting the concentration of NOx and SOx emissions during the steady-state combustion of the normal temperature of powder coke were obtained, which provided some future guidance for the operation of a power plant burning the same kind of fuel. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
The Impact of Fuel Type on the Output Parameters of a New Biofuel Burner
Energies 2019, 12(7), 1383; https://doi.org/10.3390/en12071383
Received: 26 February 2019 / Revised: 8 April 2019 / Accepted: 8 April 2019 / Published: 10 April 2019
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Abstract
Intensified action aimed at reducing CO2 emissions and striving for energy self-sufficiency of both business entities and individual consumers are forcing the sustainable development of environmentally friendly and renewable energy sources. The development of an appropriate class of equipment and production technology [...] Read more.
Intensified action aimed at reducing CO2 emissions and striving for energy self-sufficiency of both business entities and individual consumers are forcing the sustainable development of environmentally friendly and renewable energy sources. The development of an appropriate class of equipment and production technology is not without significance in this process. On the basis of a proven design for a combustion burner for ecological fuels, a new biofuel burner, also dedicated to prosumers’ energetics, was built. The aim of the study was to determine the effect of the type of biofuel on a burner’s output parameters, especially gaseous emissions, during the combustion of four types of fuels, including three types of biomass. The combustion temperature was measured for lignite, wood pellets, straw pellets, and sunflower pellets. An analysis of exhaust gas composition was performed for lignite and wood pellets. The results of exhaust emissions and combustion temperatures were compared with the burners currently in use. The use of a new burner might contribute to cleaner combustion and reducing the emissions of some gaseous components. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Emissions from Solid Fuel Cook Stoves in the Himalayan Region
Energies 2019, 12(6), 1089; https://doi.org/10.3390/en12061089
Received: 12 January 2019 / Revised: 1 March 2019 / Accepted: 12 March 2019 / Published: 21 March 2019
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Abstract
Solid fuel cooking stoves have been used as primary energy sources for residential cooking and heating activities throughout human history. It has been estimated that domestic combustion of solid fuels makes a considerable contribution to global greenhouse gas (GHG) and pollutant emissions. The [...] Read more.
Solid fuel cooking stoves have been used as primary energy sources for residential cooking and heating activities throughout human history. It has been estimated that domestic combustion of solid fuels makes a considerable contribution to global greenhouse gas (GHG) and pollutant emissions. The majority of data collected from simulated tests in laboratories does not accurately reflect the performance of stoves in actual use. This study characterizes in-field emissions of fine particulate matter (PM2.5), carbon dioxide (CO2), carbon monoxide (CO), methane (CH4), and total non-methane hydrocarbons (TNMHC) from residential cooking events with various fuel and stove types from villages in two provinces in China (Tibet and Yunnan) in the Himalayan area. Emissions of PM2.5 and gas-phase pollutant concentrations were measured directly and corresponding emission factors calculated using the carbon balance approach. Real-time monitoring of indoor PM2.5, CO2, and CO concentrations was conducted simultaneously. Major factors responsible for emission variance among and between cooking stoves are discussed. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Characterization of Performance of Short Stroke Engines with Valve Timing for Blended Bioethanol Internal Combustion
Energies 2019, 12(4), 759; https://doi.org/10.3390/en12040759
Received: 19 January 2019 / Revised: 20 February 2019 / Accepted: 21 February 2019 / Published: 25 February 2019
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Abstract
The present study provides a feasible strategy for minimizing automotive CO2 emissions by coupling the principle of the Atkinson cycle with the use of bioethanol fuel. Motor cycles and scooters have a stroke to bore ratio of less than unity, which allows [...] Read more.
The present study provides a feasible strategy for minimizing automotive CO2 emissions by coupling the principle of the Atkinson cycle with the use of bioethanol fuel. Motor cycles and scooters have a stroke to bore ratio of less than unity, which allows higher speeds. The expansion to compression ratio (ECR) of these engines can be altered by tuning the opening time of the intake and exhaust valves. The effect of ECR on fuel consumption and the feasibility of ethanol fuels are still not clear, especially for short stroke engines. Hence, in this study, the valve timing of a short stroke engine was tuned in order to explore potential bioethanol applications. The effect of valve timing on engine performance was theoretically and experimentally investigated. In addition, the application of ethanol/gasoline blended fuels, E3, E20, E50, and E85, were examined. The results show that consumption, as well as engine performance of short stroke motorcycle engines, can be improved by correctly setting the valve controls. In addition, ethanol/gasoline blended fuel can be used up to a composition of 20% without engine modification. The ignition time needs to be adjusted in fuel with higher compositions of blended ethanol. The fuel economy of a short stroke engine cannot be sharply improved using an Atkinson cycle, but CO2 emissions can be reduced using ethanol/gasoline blended fuel. The present study demonstrates the effect of ECR on the performance of short stroke engines, and explores the feasibility of applying ethanol/gasoline blended fuel to it. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Efficiency of the Air-Pollution Control System of a Lead-Acid-Battery Recycling Industry
Energies 2018, 11(12), 3465; https://doi.org/10.3390/en11123465
Received: 31 October 2018 / Revised: 4 December 2018 / Accepted: 6 December 2018 / Published: 11 December 2018
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Abstract
The air-pollution control system of a lead-acid-battery recycling industry was studied. The system comprised two streams with gravity settlers followed by filter bags for the factory indoor air and the metal-recycling furnace, respectively. Efficiency in particle removal according to mass was found to [...] Read more.
The air-pollution control system of a lead-acid-battery recycling industry was studied. The system comprised two streams with gravity settlers followed by filter bags for the factory indoor air and the metal-recycling furnace, respectively. Efficiency in particle removal according to mass was found to be 99.91%. Moreover, filter bags and dust from the gravity settlers were analyzed for heavy metals by Wavelength Dispersive X-Ray Fluorescence. The results showed high concentrations of Pb and Na in all cases. In the filter bag samples from the indoor atmosphere stream, Ca, Cu, Fe, and Al were found in concentrations higher than that in the filter bag samples from the furnace stream. The opposite was found for Na. Tl and K were only found in furnace stream bag filters. The elemental concentration of the dust from the furnace fumes stream contained mainly Fe, Na, Cd, Pb, Sb, and Cl, while the indoor main stream contained mainly P, Fe, Na, Pb, and Sb. In all cases, impurities of Nd, Ni, Rb, Sr, Th, Hg, and Bi were found. The high efficiency of the air-pollution control system in particle removal shows that a considerable reduction in emissions was achieved. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Density Functional Theory Study on Mechanism of Mercury Removal by CeO2 Modified Activated Carbon
Energies 2018, 11(11), 2872; https://doi.org/10.3390/en11112872
Received: 28 September 2018 / Revised: 19 October 2018 / Accepted: 22 October 2018 / Published: 23 October 2018
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Abstract
Doping of CeO2 on activated carbon (AC) can promote its performance for mercury abatement in flue gas, while the Hg0 removal mechanism on the AC surface has been rarely reported. In this research, density functional theory (DFT) calculations were implemented to [...] Read more.
Doping of CeO2 on activated carbon (AC) can promote its performance for mercury abatement in flue gas, while the Hg0 removal mechanism on the AC surface has been rarely reported. In this research, density functional theory (DFT) calculations were implemented to unveil the mechanism of mercury removal on plain AC and CeO2 modified AC (CeO2-AC) sorbents. Calculation results indicate that Hg0, HCl, HgCl and HgCl2 are all chemisorbed on the adsorbent. Strong interaction and charge transfer are shown by partial density of states (PDOS) analysis of the Hg0 adsorption configuration. HCl, HgCl and HgCl2 can be dissociatively adsorbed on the AC model and subsequently generate HgCl or HgCl2 released to the gas phase. The adsorption energies of HgCl and HgCl2 on the CeO2-AC model are relatively high, indicating a great capacity for removing HgCl and HgCl2 in flue gas. DFT calculations suggest that AC sorbents exhibit a certain catalytic effect on mercury oxidation, the doping of CeO2 enhances the catalytic ability of Hg0 oxidation on the AC surface and the reactions follow the Langmuir–Hinshelwood mechanism. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Combustion Characteristics and NOx Emission through a Swirling Burner with Adjustable Flaring Angle
Energies 2018, 11(8), 2173; https://doi.org/10.3390/en11082173
Received: 1 July 2018 / Revised: 13 August 2018 / Accepted: 18 August 2018 / Published: 20 August 2018
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Abstract
A swirling burner with a variable inner secondary air (ISA) flaring angle β is proposed and a laboratory scale opposed-firing furnace is built. Temperature distribution and NOx emission are designedly measured. The combustion characteristics affected by variable β are experimentally evaluated from [...] Read more.
A swirling burner with a variable inner secondary air (ISA) flaring angle β is proposed and a laboratory scale opposed-firing furnace is built. Temperature distribution and NOx emission are designedly measured. The combustion characteristics affected by variable β are experimentally evaluated from ignition and burnout data. Meanwhile, NOx reduction by the variable β is analyzed through emissions measurements. Different inner/outer primary coal-air concentration ratios γ, thermal loads and coal types are considered in this study. Results indicate that β variation provides a new approach to promote ignition and burnout, as well as NOx emission reduction under conditions of fuel rich/lean combustion and load variation. The recommended β of a swirling burner under different conditions is not always constant. The optimal βopt of the swirling burner under all conditions for different burning performance are summarized in the form of curves, which could provide reference for exquisite combustion adjustment. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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Open AccessArticle
Numerical Investigation of the Effects of Steam Mole Fraction and the Inlet Velocity of Reforming Reactants on an Industrial-Scale Steam Methane Reformer
Energies 2018, 11(8), 2082; https://doi.org/10.3390/en11082082
Received: 1 July 2018 / Revised: 3 August 2018 / Accepted: 8 August 2018 / Published: 10 August 2018
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Abstract
Steam methane reforming (SMR) is the most common commercial method of industrial hydrogen production. Control of the catalyst tube temperature is a fundamental demand of the reformer design because the tube temperature must be maintained within a range that the catalysts have high [...] Read more.
Steam methane reforming (SMR) is the most common commercial method of industrial hydrogen production. Control of the catalyst tube temperature is a fundamental demand of the reformer design because the tube temperature must be maintained within a range that the catalysts have high activity and the tube has minor damage. In this paper, the transport and chemical reaction in an industrial-scale steam methane reformer are simulated using computational fluid dynamics (CFD). Two factors influencing the reformer temperature, hydrogen yield and stress distribution are discussed: (1) the mole fraction of steam (YH2O) and (2) the inlet velocity of the reforming reactants. The purpose of this paper is to get a better understanding of the flow and thermal development in a reformer and thus, to make it possible to improve the performance and lifetime of a steam reformer. It is found that the lowest temperature at the reforming tube surface occurs when YH2O is 0.5. Hydrogen yield has the highest value when YH2O is 0.5. The wall shear stress at the reforming tube surface is higher at a higher YH2O. The surface temperature of a reforming tube increases with the inlet velocity of the reforming reactants. Finally, the wall shear stress at the reforming tube surface increases with the inlet velocity of the reforming reactants. Full article
(This article belongs to the Special Issue Cleaner Combustion)
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