Poly(ionic liquid)-based membranes have been the subject of intensive research in the last 15 years due to their potential for the separation of COsub.2 from other gases. In this short review, ...different types of PIL-based membranes for COsub.2 separation are described (neat PIL membranes; PIL-IL composite membranes; PIL-polymer blend membranes; PIL-based block copolymer membranes, and PIL-based mixed matrix membranes), and their state-of-the-art separation results for different gas pairs (COsub.2/Nsub.2, COsub.2/Hsub.2, and COsub.2/CHsub.4) are presented and discussed. This review article is focused on the most relevant research works performed over the last 5 years, that is, since the year 2017 onwards, in the field of poly(ionic liquid)-based membranes for COsub.2 separation. The micro- and nano-morphological characterization of the membranes is highlighted as a research topic that requires deeper study and understanding. Nowadays there is an array of advanced structural characterization techniques, such as neutron scattering techniques with contrast variation (using selective deuteration), that can be used to probe the micro- and nanostructure of membranes, in length scales ranging from ~1 nm to ~15 μm. Although some of these techniques have been used to study the morphology of PIL-based membranes for electrochemical applications, their use in the study of PIL-based membranes for COsub.2 separation is still unknown.
LaMnOsub.3-based perovskites are widely recognized as promising catalysts for several oxidation reactions, but the final physicochemical and catalytic properties can be greatly influenced by the ...adopted synthesis procedure. In this work, a series of A-site-deficient perovskites of composition Lasub.0.8MnOsub.3 and Lasub.0.8Mnsub.0.9Bsub.0.1Osub.3 (B = Ni, Cu) were prepared through the citrate combustion route with variations in two synthesis parameters: a citric acid/metal cations molar ratio (CA/M) of either 1.1 or 1.5 and either acidic (given by HNOsub.3 + citric acid) or neutral (after NHsub.3 addition) pH of the precursor solution. The obtained samples were characterized by XRD, Hsub.2-TPR, Osub.2-TPD, Nsub.2 physisorption, SEM-EDX and XPS. Acidic pH coupled with a CA/M ratio of 1.1 clearly emerged superior among all the other combinations of the two parameters, resulting in smaller crystallite size, higher surface area and porosity, enhanced Mnsup.4+ reducibility and the ability to release oxygen species; these features were even further improved by B-site substitution with 10 mol% Ni and Cu cations. The synthesized catalysts were tested in CHsub.4 oxidation to COsub.2 under stoichiometric Osub.2, confirming the great superiority of samples prepared in acidic pH with a CA/M ratio of 1.1. Ni and Cu doping had a beneficial effect on catalytic activity, which, however, was more evident for less optimized perovskites (acidic pH and CA/M ratio of 1.5), without significance differences among the two dopants.
Due to the extreme temperatures inside the combustion chambers of liquid propellant rocket engines, the walls of the combustion chamber and the nozzle are cooled by either the fuel or the oxidizer in ...what is known as regenerative cooling. This study presents an indigenous computational tool developed for the analysis of heat transfer in regenerative cooling of such rocket engines. The developed tool incorporates a one-dimensional (1-D) combustion analysis to calculate the thermophysical properties of the combustion gas. Basic engine properties were calculated and used to generate a thrust chamber profile based on a bell-shaped nozzle. The hot gas side was analyzed using 1-D isentropic flow assumptions, along with heat transfer correlations. The coolant side was evaluated using the hydraulic analysis in the axial direction and the heat transfer analysis in the radial direction. Thermophysical properties and the phase of the coolant were determined using the given property tables and the instantaneous state of the coolant. This flexible and computationally less demanding tool was used to analyze two small-scale engines utilizing liquid hydrocarbon fuels, which are used in modern rocket propulsion. The wall cooling analyses of a liquid oxygen (LOX)/liquid methane (LCHsub.4) engine and a liquid oxygen (LOX)/liquid propane (LCsub.3Hsub.8) engine are presented. Fuel and oxidizer were used separately as coolants for both engines, and both of them experienced phase change. Results reveal the advantage of the high mass flow rate of the oxidizer in cooling performance. In addition, the results of this study show that the cooling of the LOX/LCsub.3Hsub.8 engine is somewhat more challenging compared to the LOX/LCHsub.4 engine.
Colorless distributed combustion (CDC) has been demonstrated to provide ultra-low emission of NO
x and CO, improved pattern factor and reduced combustion noise in high intensity gas turbine ...combustors. The key feature to achieve CDC is the controlled flow distribution, reduce ignition delay, and high speed injection of air and fuel jets and their controlled mixing to promote distributed reaction zone in the entire combustion volume without any flame stabilizer. Large gas recirculation and high turbulent mixing rates are desirable to achieve distributed reactions thus avoiding hot spot zones in the flame. The high temperature air combustion (HiTAC) technology has been successfully demonstrated in industrial furnaces which inherently possess low heat release intensity. However, gas turbine combustors operate at high heat release intensity and this result in many challenges for combustor design, which include lower residence time, high flow velocity and difficulty to contain the flame within a given volume. The focus here is on colorless distributed combustion for stationary gas turbine applications. In the first part of investigation effect of fuel injection diameter and air injection diameter is investigated in detail to elucidate the effect fuel/air mixing and gas recirculation on characteristics of CDC at relatively lower heat release intensity of 5
MW/m
3
atm. Based on favorable conditions at lower heat release intensity the effect of confinement size (reduction in combustor volume at same heat load) is investigated to examine heat release intensity up to 40
MW/m
3
atm. Three confinement sizes with same length and different diameters resulting in heat release intensity of 20
MW/m
3
atm, 30
MW/m
3
atm and 40
MW/m
3
atm have been investigated. Both non-premixed and premixed modes were examined for the range of heat release intensities. The heat load for the combustor was 25
kW with methane fuel. The air and fuel injection temperature was at normal 300
K. The combustor was operated at 1
atm pressure. The results were evaluated for flow field, fuel/air mixing and gas recirculation from numerical simulations and global flame images, and emissions of NO, CO from experiments. It was observed that the larger air injection diameter resulted in significantly higher levels of NO and CO whereas increase in fuel injection diameter had minimal effect on the NO and resulted in small increase of CO emissions. Increase in heat release intensity had minimal effect on NO emissions, however it resulted in significantly higher CO emissions. The premixed combustion mode resulted in ultra-low NO levels (<1
ppm) and NO emission as low as 5
ppm was obtained with the non-premixed flame mode.
•Why hydrogen/ammonia combustion?•Challenges of hydrogen/ammonia combustion.•Chances and limitations of hydrogen internal combustion engine (H2-ICEs).•Chances and limitations of ammonia internal ...combustion engine (NH3-ICEs), and•Future perspectives and limitations of H2-ICEs and NH3-ICEs.
This review explores the required hardware changes and effects of incorporating hydrogen and ammonia on performance, combustion, and emissions of internal combustion engines (ICEs). Though hydrogen combustion is environmental-friendly, it burns much faster than conventional fuels, like gasoline or diesel, leading to challenges in controlling combustion and ignition timing, potentially causing engine knocking or misfiring. Ammonia is less combustible compared to hydrogen and traditional fuels, requiring specialized engine adjustments or dedicated combustion systems for effective use in ICEs. Like hydrogen, ammonia combustion results in minimal carbon emissions but might generate nitrogen oxides (NOx) emissions, necessitating additional after treatment for emission control. Adapting an ICE to utilize hydrogen or ammonia as a fuel necessitates significant modifications to enhance efficiency, manage combustion characteristics, and control emissions. By innovating safety techniques for handling hydrogen and ammonia with more reliable infrastructure, these fuels could potentially become viable energy sources soon.
•3 biomass fuels were tested in a BFB under air and oxy-fuel combustion conditions.•Similar temperature profiles found for combustion in air and in 30% O2/70% CO2.•Lower CO emission found for oxy ...combustion when O2 in O2/CO2 mixture is over 25%.•Similar NOx emissions found for biomass combustion in air and in 30% O2/70% CO2.•Freeboard temperature plays a major role influencing both CO and NOx emissions.
Oxy-fuel combustion is one of the promising carbon capture technologies considered to be suitable for future commercial applications with stationary combustion plants. Although more and more biomass and waste are now being burned in stationary combustion plants, research on oxy-fuel combustion of biomass has received much less attention in comparison to oxy-fuel combustion of coal. In this work, a series of tests was carried out in a 20 kWth fluidized bed combustor under oxy-fuel conditions firing two non-woody fuels (miscanthus and straw pellets) and one woody fuel (domestic wood pellet). The effects of the combustion atmosphere (air and oxy-fuel) and oxygen concentration in the oxidant of the oxy-fuel combustion on gas emissions and temperature profiles were systematically studied with the overall excess oxygen coefficient in the combustor being maintained roughly constant throughout the tests. The experimental results showed that replacing the air with an oxy-fuel oxidant of 21 vol% O2 and 79 vol% CO2 resulted in a significant decrease in combustion temperature and ultimately led to the extinction of the biomass flame due to the larger specific heat of CO2 compared to N2. To keep a similar temperature profile to that achieved under the air combustion conditions, the oxygen concentration in the oxidant of O2/CO2 mixture had to be increased to 30 vol%. A drastic decrease in CO emissions was observed for all three biomass fuels (up to 80% reduction when firing straw) under oxy-fuel combustion conditions providing that the oxygen concentration in the oxidant of O2/CO2 mixture was above 25 vol%. NOx emissions were found to decrease with the oxygen concentration in the oxy-fuel oxidant, due to i) the increase of bed temperature, which implies more volatile-N released and converted in the dense bed zone and ii) the less dilution of the gases inside the dense bed zone, which leads to a higher CO concentration in this region enhancing the reduction of NOx. Similar NOx emissions to those obtained with air combustion were found when the oxygen concentration in the oxy-fuel oxidant was kept at 30 vol%. Further analysis of the experimental results showed that the gas emissions when firing the non-woody fuels were controlled mainly by the freeboard temperature instead of the dense bed region temperature due to the characteristically high volatile matter content and fines of this kind of biomass fuels.
Combustion involves chemical reactions that are often highly exothermic. Combustion systems utilize the energy of chemical compounds released during this reactive process for transportation, to ...generate electric power, or to provide heat for various applications. Chemistry and combustion are interlinked in several ways. The outcome of a combustion process in terms of its energy and material balance, regarding the delivery of useful work as well as the generation of harmful emissions, depends sensitively on the molecular nature of the respective fuel. The design of efficient, low-emission combustion processes in compliance with air quality and climate goals suggests a closer inspection of the molecular properties and reactions of conventional, bio-derived, and synthetic fuels. Information about flammability, reaction intensity, and potentially hazardous combustion by-products is important also for safety considerations. Moreover, some of the compounds that serve as fuels can assume important roles in chemical energy storage and conversion. Combustion processes can furthermore be used to synthesize materials with attractive properties.
A systematic understanding of the combustion behavior thus demands chemical knowledge. Desirable information includes properties of the thermodynamic states before and after the combustion reactions and relevant details about the dynamic processes that occur during the reactive transformations from the fuel and oxidizer to the products under the given boundary conditions. Combustion systems can be described, tailored, and improved by taking chemical knowledge into account. Combining theory, experiment, model development, simulation, and a systematic analysis of uncertainties enables qualitative or even quantitative predictions for many combustion situations of practical relevance.
This article can highlight only a few of the numerous investigations on chemical processes for combustion and combustion-related science and applications, with a main focus on gas-phase reaction systems. It attempts to provide a snapshot of recent progress and a guide to exciting opportunities that drive such research beyond fossil combustion.
The combustion behavior of single fuel particles was assessed in O
2/N
2 and O
2/CO
2 background gases, with oxygen mole fractions in the range of 20–100%. Fuels included four pulverized coals from ...different ranks (a high-volatile bituminous, a sub-bituminous and two lignites) as well as pulverized sugarcane-bagasse, a biomass residue. Particles of 75–90
μm were injected under laminar flow in a bench-scale, transparent drop-tube furnace (DTF), electrically-heated to 1400
K where, upon experiencing high heating rates, they ignited and burned. The combustion of individual particles was observed with three-color optical pyrometry and high-speed high-resolution cinematography to obtain temperature and burnout time histories. Based on combined observations from these techniques, a comprehensive understanding of the behaviors of these fuels was developed under a variety of conditions, including simulated oxy-fuel combustion. The fuels exhibited distinct combustion behaviors. In air, the bituminous coal particles burned in two distinctive modes; the volatiles burned in bright envelope flames surrounding the devolatilizing char particles followed by heterogeneous char combustion. The volatile matter of sub-bituminous coal particles burned either in subdued envelope flames, surrounding devolatilizing and occasionally fragmenting chars, or heterogeneously at the char surface. Lignite particles typically burned with extensive fragmentation, and their volatiles burned simultaneously with the char fragments. The volatiles of bagasse particles burned in spherical and transparent envelope flames. Increasing the oxygen mole fraction in N
2, increased flame and char surface temperatures, and decreased burnout times; particles of all fuels burned more intensely with an increasing tendency of the volatiles to burn closer to the char surface. When the background gas N
2 was substituted with CO
2, the combustion of all fuels was distinctly less intense; at moderate O
2 mole fractions (<30%) most particles did not ignite under active flow conditions in the furnace (they did ignite under quiescent gas flow conditions in the DTF). Increasing the oxygen mole fraction in CO
2 increased the likelihood of combustion and its intensity. Combustion of volatiles in envelope flames was suppressed in the presence of CO
2, particularly under active gas flow in the DTF.
Combustion under sufficiently fuel-lean conditions can have the desirable attributes of high efficiency and low emissions, this being particularly important in light of recent and rapid increases in ...the cost of fossil fuels and concerns over the links between combustion and global climate change. Lean Combustion is an eminently authoritative, reference work on the latest advances in lean combustion technology and systems. It will offer engineers working on combustion equipment and systems both the fundamentals and the latest developments in more efficient fuel usage and in much-sought-after reductions of undesirable emissions, while still achieving desired power output and performance. This volume brings together research and design of lean combustion systems across the technology spectrum in order to explore the state-of-the-art in lean combustion and its role in meeting current and future demands on combustion systems. Readers will learn about advances in the understanding of ultra lean fuel mixtures and how new types of burners and approaches to managing heat flow can reduce problems often found with lean combustion such as slow, difficult ignition and frequent flame extinction. The book will also offer abundant references and examples of recent real-world applications. * Covers all major recent developments in lean combustion science and technology, with new applications in both traditional combustion schemes as well as such novel uses as highly preheated and hydrogen-fueled systems * Offers techniques for overcoming difficult ignition problems and flame extinction with lean fuel mixtures * Covers new developments in lean combustion using high levels of pre-heat and heat re-circulating burners, as well as the active control of lean combustion instabilities
New innovative advanced combustion design methodology for gas turbine applications is presented that is focused on the quest towards zero emissions. The new design methodology is called colorless ...distributed combustion (CDC) and is significantly different from the currently used methodology. In this paper forward flow modes of CDC have been investigated for application to gas turbine combustors. The CDC provides significant improvement in pattern factor, reduced NO
x
emission and uniform thermal field in the entire combustion zone for it to be called as an isothermal reactor. Basic requirement for CDC is carefully tailored mixture preparation through good mixing between the combustion air and product gases prior to rapid mixing with fuel so that the reactants are at much higher temperature to result in hot and diluted oxidant stream at temperatures that are high enough to autoignite the fuel and oxidant mixture. With desirable conditions one can achieve spontaneous ignition of the fuel with distributed combustion reactions. Distributed reactions can also be achieved in premixed mode of operation with sufficient entrainment of burned gases and faster turbulent mixing between the reactants. In the present investigation forward flow modes consisting of two non-premixed combustion modes and one premixed combustion mode have been examined that provide potential for CDC. In all the configurations the air injection port is positioned at the opposite side of the combustor exit, whereas the location of fuel injection ports is changed to give different configurations. Two combustion geometries resulting in thermal intensity of 5
MW/m
3-atm and 28
MW/m
3-atm are investigated. Increase in thermal intensity (lower combustion volume) presents many challenges, such as, lower residence time, lower recirculation of gases and effect of confinement on jet characteristics. The results are presented on the global flame signatures, exhaust emissions, and radical emissions using experiments and flowfield using numerical simulations. Ultra-low NO
x
emissions are found for both the premixed and non-premixed combustion modes at the two thermal intensities investigated here. Almost colorless flames (no visible flame signatures) have been observed for the premixed combustion mode. The reaction zone is observed to be significantly different in the two non-premixed modes. Higher thermal intensity case resulted in lower recirculation of gases within the combustion chamber and higher CO levels, possibly due to lower associated residence time. The characteristics at the two thermal intensity combustors investigated here were found to be similar.
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