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This paper presents a method for evaluating the risk of autoignition for the canonical problem of an enclosed hydrogen jet in crossflow (JICF), which is highly relevant to the design of mixing ducts. The proposed method is based on the separation of the underlying mixing pattern from the evolution of the chemical reactions, whereas the effect of mixing is maintained on the latter with the purpose of creating a reliable yet computationally efficient design tool for hydrogen gas turbines. Two variants of the incompletely stirred reactor network (ISRN) approach are proposed that provide the evolution of preignition radicals and autoignition kernel location, leveraging a nonreacting computational fluid dynamics solution or an analytical mixing pattern. The ISRN governing equations include all the salient features of hydrogen transport and lead to a conservative estimate of autoignition risk. Application to a few model problems with varied operating conditions suggests that radical buildup in the JICF can lead to autoignition in the vicinity of a most reactive mixture fraction, which is consistent with other laminar or turbulent hydrogen flows. However, the radical formation and autoignition kernel location strongly depend on the prediction of the underlying mixing field and the amount of differential diffusion within the JICF, which here primarily favors lower values of the composite mixture fraction and the transport of hydrogen and radicals away from the jet trajectory.

In this study, the impact of butanol-diesel blends and exhaust gas recirculation (EGR) on engine performance, NOX emissions, smoke, and particulate matter (PM) characteristics were experimentally investigated under fuel post-injection condition. The maximum peak of cylinder pressure is achieved under without EGR compared with applied different rates of EGR. Furthermore, the brake thermal efficiency (BTE) increased during the combustion of B20 and B10 by 4.25% and 2.61%, respectively, compared with diesel fuel combustion. Considerable reductions in carbonaceous gas emissions (CO and THC) and nitrogen oxides (NOX) were achieved from combustion of B20 and B10 compared to the diesel fuel for with and without EGR. The NOX emissions decreased with 30% of EGR compared with 15% of EGR for all fuels studied. The results indicated that the addition butanol to the diesel fuel significantly reduced smoke opacity and soot emissions by 31.3% and 35.26%, respectively, compared with diesel. It is observed that an effective reduction of the NOX emissions to be higher during the combustion of B20 compared to the combustion of B10 and diesel for different EGR rates. The results of PM emission showed increase by 16% under 15% of EGR and 28% under 30% of EGR compared to the without EGR for all fuels tested. The number, concentration and size of PM decreased from combustion of B20 and B10 compared with diesel fuel combustion for with and without EGR.

The properties of the combustion and deflagration to detonation transition (DDT) of Al/Fe2O3/RDX hybrid nanocomposites, a type of potentially novel lead-free primary explosives, were tested in weakly confined conditions, and the interaction of Al/Fe2O3 nanothermite and RDX in the DDT process was studied in detail. Results show that the amount of the Al/Fe2O3 nanothermite has a great effect on the DDT properties of Al/Fe2O3/RDX nanocomposites. The addition of Al/Fe2O3 nanothermite to RDX apparently improves the firing properties of RDX. A small amount of Al/Fe2O3 nanothermite greatly increases the initial combustion velocity of Al/Fe2O3/RDX nanocomposites, accelerating their DDT process. When the contents of Al/Fe2O3 nanothermite are less than 20 wt%, the DDT mechanisms of Al/Fe2O3/RDX nanocomposites follow the distinct abrupt mode, and are consistent with that of RDX, though their DDT processes are different. The RDX added into the Al/Fe2O3 nanothermite increases the latter's peak combustion velocity and makes it generate the DDT when the RDX content is at least 10 wt%. RDX plays a key role in the shock compressive combustion, the formation and the properties of the DDT in the flame propagation of nanocomposites. Compared with RDX, the fast DDT of Al/Fe2O3/RDX nanocomposites could be obtained by adjusting the chemical constituents of nanocomposites.

As an innovative propulsion technique, laser augmented chemical propulsion (LACP) seems superior to the traditional ones. However, the corresponding combustion theories have still to be ascertained for LACP. Burning rate of 5-aminotetrazole (5-ATZ) propellant has been studied by testing pressed samples under different combustor pressures and laser powers. Based on micro computed tomography (MicroCT), an advanced thickness-over-time (TOT) method to characterize the regression of the produced non-planar burning surface is established. Because of a shell structure covering the combustion surface, the burning rate of the implemented 5-ATZ propellant is not constant during laser ablation. Resorting to functional fitting, a new law of non-constant burning including the effect of the observed unique burning surface structures is proposed. Accordingly, applicable combustion conditions of 5-ATZ based propellants have been preliminarily speculated for future research activities.

International audience; Flame spread over an insulated electrical wire is a major source of fire scenario in a space vehicle. In this work, an engineering model that predicts the creeping flame spread over cylindrical wires in microgravity is developed. The model is applied to interpret experimental data obtained in parabolic flights for wires composed by a 0.25 mm radius nickel-chromium (NiCr) metallic core coated by low-density polyethylene (LDPE) of different thicknesses ranging from 0.15 mm to 0.4 mm. The model relies on the assumption that, in the pyrolysis region, the NiCr and the LDPE are in thermal equilibrium. This assumption is supported by more detailed numerical simulations and the model reduces then to solving the heat transfer equations for both NiCr and LDPE in the pyrolysis region and in the region ahead of the flame front along with a simple degradation model for LDPE, an Oseen approximation of opposed oxidizer flow and an infinitely fast gas-phase chemistry. The flame spread rate (FSR) is controlled by two model parameters, which are measurable from intrinsic material and ambient gas properties: the convective flame heat flux transferred to the solid ahead from the flame front and the gaseous thermal heat length near the flame front. These parameters are then calibrated from experimental data for a given wire geometry and the calibrated model is validated against experimental data for other wire geometries and ambient conditions. The heat transfer mechanisms ahead of the pyrolysis front are investigated with a special emphasis on the LDPE thickness and the conductivity of the metallic core. In addition to NiCr, metallic cores of lower and higher conductivities are considered. The polymer is shown to be thermally thick for all tested wire geometries and core conductivities. The flame heat flux is found to dominate the heat transfer in the preheat zone where it applies. The core has nevertheless a significant impact in the heating of the LDPE with its contribution increasing with the core conductivity and when decreasing the LDPE thickness.

The cold filter plugging point (CFPP) value of biodiesel fuel blends need to be improved because of it has been reported that utilizing high concentrations of biodiesel blends in cold climates can cause major issues. Therefore, the main objective of the study is to improve CFPP value of biodiesel blends using ethyl proxitol additive. It is also to examine combustion and emission of the blends behavior. Biodiesel blends were prepared as; 5% ethyl proxitol-10% biodiesel-85% ultra-low sulfur diesel (ULSD) named as E5B10 and 5% ethyl proxitol-20% biodiesel-75% ULSD named as E5B20 fuel. These fuel blends were compared with ULSD fuel in a compression ignition engine at a constant engine speed of 1500 rev/min and four different loads (idle, 1, 2, and 3 bar BMEP) of eddy current dynamometer. The addition of ethyl proxitol led to a decrease in in-cylinder pressure and temperature due to an about 1˚ later SOC and 2˚ earlier EOC compared to ULSD. The pressure rise rate was slightly higher compared to ULSD at both low and high loads, with a difference of about 1 bar per degree. As a result, these blends with improved CFPP value can be used in cold climates.

Fluid catalytic cracking (FCC) is a method of cracking vegetable oils into simpler fractions and green fuel oils. One component of the FCC system is the FCC furnace. The FCC furnace is where the combustion process occurs and provides high heat transfer throughout the FCC system, especially for heating the reactor. The reactor temperature is the catalyst cracking temperature. The cracking temperature of the catalyst depends on the feed oil used in the cracking process, such as crude palm oil at 450‒550 °C or crude bio-oil at 300 °C. The fuel for heating an FCC furnace is usually coal. To reduce coal, we use a mixture of Azolla microphylla biomass with biochar and bio-oil from goat manure. The aim of this study was to analyze the mixture of Azolla microphylla biomass with biochar and bio-oil from goat manure to obtain sufficient furnace temperature to heat the FCC reactor, perform analytical calculations to obtain the volume of flue gas formed from the combustion reaction. We conducted two experiments; the first experiment used a mixture of 1 kg of Goat Manure Biochar (GMBC) with 0.5 kg of Azolla microphylla and the second experiment used a mixture of one kg of GMBC with 0.5 kg of Azolla microphylla plus 300 ml of Goat Manure Bio-oil (GMBO). A fuel mixture of one kilogram GMBC with 0.5 kg Azolla is not effective in combustion because the maximum temperature in the furnace is 177 °C but the fuel mixture of one kg GMBC, 0.5 kg Azolla and 300 ml GMBO has a furnace temperature of 472.75 °C, which can heat the stripper up to 313.25 °C so that cracking can occur in the raw bio-oil. Analysis of combustion results showed an increase in total CO2 volume from experiment one and experiment two of 0.966, Флюїд-каталітичний крекінг (ФКК) являє собою метод крекінгу рослинних масел на більш прості фракції та екологічно чисті мазути. Одним із компонентів системи ФКК є піч ФКК. Піч ФКК є місцем, де відбувається процес горіння, і забезпечує високу теплопередачу по всій системі ФКК, особливо для нагріву реактора. Температурою реактора є температура крекінгу каталізатора. Температура крекінгу каталізатора залежить від вихідної олії, що використовується в процесі крекінгу, наприклад, сирої пальмової олії при 450–550 °C або сирого біомасла при 300 °C. Паливом для нагрівання печі ФКК зазвичай є вугілля. Для зменшення використання вугілля ми використовуємо суміш біомаси азоли дрібнолистої з біовугіллям та біомаслом з козячого гною. Метою даного дослідження був аналіз суміші біомаси азоли дрібнолистої з біовугіллям та біомаслом з козячого гною для отримання температури печі, достатньої для нагрівання реактора ФКК, виконання аналітичних розрахунків для одержання об'єму димових газів, що утворюються в результаті реакції горіння. Нами проведено два експерименти; у першому експерименті використовувалася суміш 1 кг біовугілля з козячого гною (GMBC) з 0,5 кг азоли дрібнолистої, в другому використовувалася суміш 1 кг GMBC з 0,5 кг азоли дрібнолистої та 300 мл біомасла з козячого гною (GMBO). Паливна суміш з 1 кг GMBC з 0,5 кг азолла неефективна при згорянні, оскільки максимальна температура в печі становить 177 °C, в той час як паливна суміш з 1 кг GMBC, 0,5 кг азолла та 300 мл GMBO забезпечує температуру печі 472,75 °C, що дозволяє нагрівати відпарну колону до 313,25 °C для проведення крекінгу в сирому біомаслі. Аналіз результатів спалювання показав збільшення загального обсягу CO2 в порівнянні з першим та другим експериментами на 0,966 м3СО2/кг палива

The photoluminescent behavior of Eu-doped Sr3Al2O6 obtained by highly efficient solution combustion synthesis is reported. In order to understand the influence of the fuel on the synthesis, the stoichiometric quantity and an excess of fuel were evaluated. By adjusting the amount of fuel, different luminescence responses were obtained, allowing europium cations incorporation into the Sr3Al2O6 lattice to serve as effective luminescence activators in such a short time during the rapid combustion synthesis process. The higher amount of fuel in the presence of the oxidizing agent produced Sr3Al2O6:Eu particles with higher phosphorescence brightness, owing to the increase of the reduction process from Eu3+ to Eu2+. The synthesized phosphor showed an intense band emission centered at 515 nm and could be excited over a broad spectral range in the UV-visible region. Particles having nanostructured flake-type morphology were obtained, which was considered a micro-nanofunctional candidate for practical applications.

Tunable diode laser absorption spectroscopy tomography (TDLAST) has been widely applied for imaging two-dimensional distributions of industrial flow-field parameters, e.g., temperature and species concentration. Two main interested imaging objectives in TDLAST are the local combustion and its radiation in the entire sensing region. State-of-the-art algorithms were developed to retrieve either of the two objectives. In this paper, we address the both by developing a novel multi-output imaging neural network, named as Spatially Progressive Neural Network (SpaProNet). This network consists of locally and globally prioritized reconstruction stages. The former enables hierarchical imaging of the finely resolved and highly accurate local combustion, but coarsely resolved background. The later retrieves a fine-resolved image for the entire sensing region, at the cost of slightly trading off the reconstruction accuracy in the combustion zone. Furthermore, the proposed network is driven by the hydrodynamics of the real reactive flows, in which the training dataset is obtained from large eddy simulation. The proposed SpaProNet is validated by both simulation and lab-scale experiment. In all test cases, the visual and quantitative metric comparisons show that the proposed SpaProNet outperforms the existing methods from the following two perspectives: a) the locally prioritized stage provides ever-better accuracy in the combustion zone; b) the globally prioritized stage shows turbulence-indicative accuracy in the entire sensing region for diagnosis of heat radiation from the flame and flame-air interactions.

openaire: EC/H2020/101006744/EU//EHLCATHOL Small aromatic molecules with oxygen-containing functional groups (monoaromatic oxygenates) are common products of the catalytic depolymerization of lignin, which can be considered as a promising class of fuel additives. This mini-review article starts with an introduction of second generation (2G) of biofuel production from lignocellulose and the further conversion of lignin into fuel performance boosting blends. The discussion is divided into four parts. The first part gives a brief overview of the production of aromatic oxygenates from the catalytic conversion of lignin of different origin. The three following parts are focused on the aromatic oxygenates, for which combustion data can be found. The second part describes their chemical structure and physical properties. The third part is dominated by their global combustion performance, i.e., the commercial fuel parameters as lower heating value, octane and cetane numbers. A few studies on ignition delay times and laminar flame velocities are also described. The fourth part shortly reviews the kinetic studies presenting product quantifications, the proposed detailed kinetic models and the influence of the structure of the aromatic reactant on soot formation. To finish, a perspective on future research directions is given.

Due to rapid movement of rural population to new regions and countries in order to find work and for better living conditions, population growth and economic development, there is gradual increase in production of waste and demand of electricity worldwide. According to World Bank statistics, the global Municipal Solid Waste generated was 1.3 billion tons in year 2012 and this is expected to increase above 2.2 billion tons per year by 2025. Due to lack of sites for waste disposal, it has become a serious environmental as well as health issue. Now various methods have been adopted for waste disposal. Among this, energy accessed from municipal solid waste is the most common practice adopted by developing countries. In addition, Waste to Energy and Energy from Waste technologies are used which include thermal and biological technologies. Gasification, pyrolysis and incineration are thermal technologies used in conversion of waste to energy. During these processes, syngas is produced which is used in combustion engine or turbines to generate electricity. Apart from this, biomethanation is also used in which biogas is produced. In this review article, we have discussed all the environmental and green methods used for the generation of energy from Municipal Solid Waste their advantages and drawbacks.

In this study, it was investigated some properties of gypsum particleboards which is produced with olivine mineral. Wood particles were added as reinforcement in different proportions (70% and 30%) to two types of plasterboard. The effects of inorganic olivine mineral added to these two types of boards were evaluated in terms of their physical and mechanical properties, thermal conductivity, and combustion behaviour. Subsequently, tests were carried to determine their water absorption, thickness swelling, internal bonding, bending strength, modulus of elasticity, thermal conductivity, and combustion performance. The properties of the boards were then examined using Fourier-transform infrared spectroscopy and thermogravimetric analysis. The Fourier-transform infrared analysis revealed the typical traces of cellulose, hemicellulose, and lignin in the wood material, traces of gypsum as the binder, and varying traces of olivine, according to the additive ratio, were also observed. Thermal analysis determined the positive contribution of olivine to the basic stability of both types of boards. It can be concluded that olivine, when added in different proportions, is a suitable reinforcement material for improving the technical properties of gypsum particleboard., Bu çalışmada, olivin minerali ile üretilen alçılı yonga levhaların bazı özellikleri araştırılmıştır. İki farklı oranda alçı (%70 ve %30) eklenerek oluşturulan levhalara farklı oranlarda odun yongaları eklenmiştir. Bu iki tip levhaya ilave edilen inorganik olivin mineralinin, levhanın fiziksel özellikleri, mekanik özellikleri, ısıl iletkenlik ve yanma davranışlarına olan etkileri değerlendirilmiştir. Üretilen levhaların su alma, kalınlığına şişme, çekme direnci, eğilme direnci, elastikiyet modülü, termal iletkenlik ve yanma performansını belirlemek için testler yapılmıştır. FTIR analizi, ahşap malzemede selüloz, hemiselüloz ve lignin varlığını, bağlayıcı olarak alçının ve katkı oranına göre değişen olivinin varlığını ortaya koymaktadır. Termal analiz ile olivin'in her iki tip levhanın stabilitesine olumlu etkisi olduğu belirlenmiştir. Olivin, farklı oranlarda eklendiğinde, alçılı yonga levhanın bazı özelliklerini geliştirmek için uygun bir takviye malzemesi olduğu sonucuna varılabilir

The broad properties of nanostructured materials based on transition metal oxides have received great attention from researchers. Copper (II) Oxide (CuO) due to its excellent physical and chemical properties, has numerous potential applications. Among the different methods previously reported to prepare CuO nanoparticles (CuO NPs) such as sonochemical, sol-gel, and electrochemical techniques, this study proposes an easeful, simple, and cost-effective method to synthesize CuO NPs by thermal decomposition of a coordination complex i.e., a binuclear copper (II) carboxylate complex.

Refereed/Peer-reviewed This work investigates the effects of ambient and injection parameters on the ignition and combustion characteristics of hydrogen (H₂)–methane (CH₄) jet (50% H₂ by volume, with the remaining CH₄) in simulated direct-injection, compression-ignition conditions. Parameter variations include ambient gas temperature (1060–1200 K), ambient oxygen (O₂) concentration (10–21 vol %), and injection pressure (10–20 MPa reservoir pressure). The results show that the ignition delay of the H₂–CH₄ jet decreases with increasing ambient temperature. In most cases, the ignition initiates from a localized kernel before spreading across the jet volume downstream. The lower ambient O₂ cases display a more voluminous ignition sequence. The results also show that the jet flame recesses upstream to attach or stabilize close to the nozzle but becomes increasingly lifted with lower ambient temperature and O₂ conditions. The flame autoignition process displays increased variation at the lowest tested ambient temperature condition in this work, which affects the ensuing flame evolution and heat release profile.

The existing results show that the combustion heat, energy level and some other performance indices of system could be improved effectively, while opportune percentages of metal hydrides (MHs) are added in solid propellants or explosives. Despite huge potentials exist for the addition of MHs in energetic materials (EMs), some practical difficulties hinder the widespread application of them. For example, the compatibility between metal hydrides materials and other components in EMs is one of the key concerns. The synergy of energy release between MHs and EMs will be limited if the interaction mechanism between them are not clear. Combustion, thermal and microscopic interaction between MHs and EMs were summarized in this paper. From our point of view, laser ignition is the most effective and convenient method to study the combustion interaction between metal hydrides and energetic compounds, the research on such mechanism should start with quantum chemical computation (QCC) and molecular dynamics simulation (MDS), in which the interaction energy (binding energy, adsorption energy) and radial distribution function (RDF) are identified as key characteristic parameters to estimate the nature of the interaction.

We have developed a comprehensive 3D heating test simulation model of a Li-ion battery cylindrical cell and module, taking gas flow and combustion into account. The model is based on the equivalent circuit model and includes not only the heating of a cell (joule heating and thermal decomposition) but also gas ejection flow from the cell and combustion. First, the validation of the cell model for surface temperature and voltage profiles was conducted for a commercial 18650-type cell with an actual heating experiment. Subsequently, a simulation model of the battery module, composed of total 98 cells heated by a burner, was developed, and the behavior of thermal runaway was evaluated. This model makes it possible to evaluate the events that occur from the start of heating the battery module to gas ejection, including housing melting, separator shutdown, and the propagation of thermal decomposition reactions between the cells, and might be a helpful tool for designing battery cells and modules.

Plasma ignition in the volume of liquid solution/water initiates the chemical activation of the liquid phase (formation of chemically active particles) and the sputtering of electrode materials, which leads to the formation of nanostructured materials. In this work, the synthesis of structures was carried out by means of underwater plasma excited in water between electrodes composed of different materials. The polarity of the Fe and Cu electrodes was varied at two plasma currents of 0.25 and 0.8 A. The kinetics of the sorption and photocatalysis of three dyes (Rhodamine B, Reactive Red 6C, and Methylene Blue) were studied. According to the results obtained, the polarity of the electrode material has a greater effect on the phase composition than the plasma current. The sorption process can be limiting depending on the type of dye and phase composition. The sorption kinetics can be described by various models at different stages of the process. Photocatalytic studies have shown that the complete decomposition of the three dyes can be achieved in 15–30 min of irradiation.

The development of low-temperature combustion models combined with the use of biofuels has been considered as an efficient strategy to reduce pollutant emissions like CO, HC. NOx, and smoke. Indeed, Homogeneous Charge Compression Ignition (HCCI) is the new approach to drastically minimize NOx emissions and smoke owing to the lower cylinder temperature and a higher rate of homogeneous A/F mixture as compared to compression ignition (CI) engines. The present research deal with the behavior analysis of a CI engine powered by diesel, Euglena Sanguinea (ES), and their blends (ES20D80, ES40D60, ES60D40, ES80D20). The experimental results revealed the highest brake thermal efficiency for ES20D80 although it decreased by 4.1% compared to diesel at normal mode. The average drop in HC, CO, and smoke was 2.1, 2.3, and 5.7% for ES20D80 as opposed to diesel fuel. Therefore, in the next stage, ES20D80 with various concentrations of graphite oxide (GO) nanoparticle (20, 40, 60, and 80 ppm) was chosen to carry out experiments in the HCCI mode, in which hydrogen gas was induced along with air through the intake pipe at a fixed flow rate of 3 lpm for the enrichment of the air-fuel mixture. As a result, the combination of hydrogen-enriched gas and GO-added ES20D80 in the HCCI mode showed similar performance to the CI engine but registered a major reduction of NOx and smoke emissions, corresponding to 75.24% and 53.07% respectively, as compared to diesel fuel at normal mode.

The monolithic foamed propellants with high densities were prepared by casting and two-step foaming processes. Glycidyl azide polymer (GAP) and isocyanate were used as the binder system and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (HNIW, CL-20) was employed as the energetic component. The newly designed formulation containing 60 % CL-20 produced a force constant of 1077 J/g and low flame temperature of 2817 K. Two foamed propellants with densities of 1.32 g/cm3 and 1.53 g/cm3 were fabricated by a confined foaming process and examined by closed bomb tests. The results revealed that porosity significantly affects burning performance. A size effect on combustion behaviors was observed for the foamed propellant with 5.56 % porosity, and a double-hump progressive dynamic vivacity curve was obtained. At last, the 30 mm gun test was carried out to demonstrate the interior ballistic performance, and the muzzle velocity increased by 120 m/s at the same maximum chamber pressure when monolithic propellant was added in the charge.

Improving the thermal decomposition performance of hexanitrohexaazaisowurtzitane (CL-20) by appropriate methods is helpful to promote the combustion performance of CL-20-based solid propellants. In this study, we synthesized a sandwich structure of CL-20 and nanoporous carbon scaffolds film (NCS) and emphatically studied the thermal decomposition performance of the composite structure. Thermogravimetric analysis and differential scanning calorimetry were used to measure the thermal decomposition process of the composite structure. The kinetic parameters of thermal decomposition were calculated by the thermal dynamic analysis software AKTS. These results showed that the thermal decomposition performance of the sandwich structure of CL-20 and NCS was better than CL-20. Among the tested samples, NCS with a pore size of 15 nm had the best catalytic activity for the thermal decomposition of CL-20. Moreover, the thermal decomposition curve of the composite structure at the heating rate of 1 K/min was deconvoluted by mathematical method to study the thermal decomposition process. And a possible catalytic mechanism was proposed. The excellent thermal decomposition performance is due to the sandwich structure enhances the interface reaction of CL-20 and NCS. This work may promote the extensive use of CL-20 in the field of solid rocket propellant.

Hydrogen is a renewable gas, efficient to produce energy that makes it a suitable alternative and effective solution for a carbon-free environment. Unlike other fossil fuels, combustion of hydrogen does not produce toxic compounds, such as greenhouse gases, carbon monoxide, hydrocarbons, etc., resulting in less environmental pollution. Agro-industrial residues contain several lignocelluloses that favor the growth of microorganisms to produce valuable products such as hydrogen. Of the diverse techniques in hydrogen production, bioconversion proves to be an efficient method in permuting agro-industrial residues into hydrogen. This review provides detailed information on the bioconversion processes and factors involved in hydrogen production from agro-industrial residues including different fermentation processes such as dark fermentation and photo-fermentation, and fuel cell systems such as microbial electrolysis cell and microbial fuel cell. Different pretreatment techniques to enhance the availability of lignocellulose for hydrogen production have been elaborated in this review. Various factors including pH, temperature and nutrient composition of feed, affecting the production efficiency and purity of the products during fermentation have been discussed.

The main purpose of this study is to analyse the effects of oxy hydrogen (HHO) along with the Moringa oleifera biodiesel blend on engine performance, combustion and emission characteristics. HHO gases were generated using the typical electrolysis process using the potassium hydroxide solution. The experiments were performed under various engine loads of 25%, 50%, 75%, and 100% in a constant speed engine. Biodiesel from the M. oleifera was prepared by the transesterification process. Further, the procured biodiesel blends mixed with neat diesel at the concentration of 20% (B20) and 40% (B40). In addition to above, the HHO gas flow rate to the engine chamber maintained at the flow rate of 0.5 L-1. The use of the 20% and 40% blends with HHO reported less BTE compared to the neat diesel. However, B20 reported marginal rise in the BTE due to the addition of the HHO gas. On the other hand, addition of HHO gas to the blends significantly dropped the brake specific fuel consumption. With regard to the emissions, addition of the biodiesel blends reduced the concentration of the CO, HC, and CO2. Nevertheless, no reduction reported in the formation of the NO. However, adding the HHO to the biodiesel reduced the average NOx by 6%, which is a substantial effect. Overall, HHO enriching biodiesel blends are the potential replacement for the existing fossil fuels for its superior fuel properties compared to the conventional diesel.

Replacing fossil fuels by oxymethylene ethers (OMEs) produced from renewable resources could help to reduce the rising CO2 levels. In this work, the thermal decomposition chemistry of methoxymethyl formate (CH3O-CH2OCHO) and formic anhydride (OCHOCHO) is investigated by means of a combination of quantum chemical calculations and kinetic modeling. The latter compounds are two important intermediates formed during the thermal decomposition chemistry of synthetic fuel OMEs. Two detailed kinetic models are developed based on first principles to describe the radical decomposition chemistry of methoxymethyl formate and formic anhydride, which are ultimately incorporated into the OME-2 model from De Ras et al. (Combustion and Flame, 2022). This newly obtained kinetic model describes experimental measurements for pyrolysis from literature significantly better than the model from the original study, without any fitting of thermodynamic or kinetic parameters. More particularly, some minor compounds are now satisfactorily reproduced within the experimental uncertainty margin of 10 mol% relative. Methoxymethyl formate and formic anhydride are found to be more reactive compared to OMEs. Both a reaction pathway analysis and sensitivity analysis reveal the important decomposition pathways under pyrolysis conditions.

An investigation into the exhaust emissions of carcinogenic polycyclic aromatic hydrocarbons (PAHs) from a diesel engine was reported. The study is reinforced by the experimental results obtained from a tube reactor aimed at examining the PAH formation processes from these fuels. The paper cantered on the 16 priority PAHs suggested by the United States Environmental Protection Agency (US-EPA). These PAHs were produced by burning conventional diesel fuel and a few binary fuels prepared by blending various proportions of toluene into heptane. Special consideration was given to the B2 subgroup of PAHs which are known human-carcinogens. Both the gas born (smaller) PAHs, as well as the larger PAHs, adsorbed onto the particulate were investigated. The engine used was a single-cylinder, light duty, high speed, diesel automotive research engine run at an Indicated Mean effective pressure (IMEP) of 7 bar. Particulate matter was also produced in a tube reactor at temperatures ranging from 1050 to 1350 °C under pyrolysis (oxygen-free) conditions to study PAH and soot formation in conditions which resemble, to an extent, those found in the core of diesel engine fuel sprays. In the diesel engine, it was found that exhaust PAHs were influenced by combustion characteristics like heat release rates and ignition delay. However, in the quiescent oxygen-free conditions of the reactor, chemical composition of the fuels and temperature dominated PAH formation.

Black carbon (BC) is considered the second largest anthropogenic climate forcer, but the radiative effects of BC are highly correlated with its combustion sources. On-road vehicles are an important source of anthropogenic BC. However, there are major uncertainties in the estimates of the BC emissions from on-road light-duty passenger vehicles (LDPVs), and results obtained with the portable emissions measurement system (PEMS) method are particularly lacking. We developed a PEMS platform and evaluated the on-road BC emissions from ten in-use LDPVs. We demonstrated that the BC emission factors (EFs) of gasoline direction injection (GDI) engine vehicles range from 1.10 to 1.56 mg·km−1, which are higher than the EFs of port fuel injection (PFI) engine vehicles (0.10–0.17 mg·km−1) by a factor of 11. The BC emissions during the cold-start phase contributed 2%–33% to the total emissions. A strong correlation (R2 = 0.70) was observed between the relative BC EFs and average vehicle speed, indicating that traffic congestion alleviation could effectively mitigate BC emissions. Moreover, BC and particle number (PN) emissions were linearly correlated (R2 = 0.90), and compared to PFI engine vehicles, the instantaneous PN-to-BC emission rates of GDI engine vehicles were less sensitive to vehicle-specific power-to-velocity (VSPV) increase in all speed ranges.

Calcium phosphates are biomaterials widely used in bone tissue engineering. In recent years, the alternative of obtaining these materials with antimicrobial properties, has been explored due to the multiple advantages that this would imply in the design of devices or implants that prevent the failure of these associated with bacterial colonization. The goal of the present work was obtaining gold nanoparticles supported on biphasic calcium phosphates (BCPs) with high crystallinity by one-step solution combustion technique, and with antimicrobial response, a fact that can significantly reduce the production cost of these materials. X-ray diffractograms (XRD) showed that prepared powders have high crystallinity owing to high temperatures during the combustion reaction, also Rietveld refinement showed that the inclusion of gold nanoparticles (AuNPs) influenced the phases’ ratio obtained. Furthermore, scanning electron microscopy (SEM) showed agglomeration of particles with morphologies with shape tending to be equigranular, while the presence of AuNPs was corroborated by transmission electron microscopy (TEM). All samples that were obtained in a single step, by solution combustion, showed antimicrobial behavior validated through the inhibition halos, whereas particles subjected to thermal treatment lost their antimicrobial response.

Boron is a very promising and highly attractive fuel because of high calorific value. However, the practical applications in explosives and propellants of boron have been limited by long ignition delay time and low combustion efficiency. Herein, nano-Al and graphene fluoride (GF) as surface activated materials are employed to coat boron (B) particles to improve ignition and combustion performance. The reaction heat of nano-Al coated B/KNO3 and GF coated B/KNO3 are 1116.83 J/g and 862.69 J/g, respectively, which are higher than that of pure B/KNO3 (823.39 J/g). The ignition delay time of B/KNO3 could be reduced through nano-Al coating. The shortest ignition delay time is only 75 ms for B coated with nano-Al of 8 wt%, which is much shorter than that of pure B/KNO3 (109 ms). However, the ignition delay time of B/KNO3 coated with GF has been increased from 109 to 187 ms. B coated with GF and nano-Al shown significantly influence on the pressure output and flame structure of B/KNO3. Furthermore, the effects of B/O ratios on the pressure output and ignition delay time have been further fully studied. For B/KNO3 coated with nano-Al and GF, the highest pressures are 88 KPa and 59 KPa for B/O ratio of 4:6, and the minimum ignition delay time are 94 ms and 148 ms for B/O ratio of 7:3. Based on the above results, the reaction process of boron coated with GF and nano-Al has been proposed to understand combustion mechanism.

The motivation of this work is to produce an integrated mathematical formulation for the numerical modelling of material response due to detonation wave loading. In particular, we are interested to capture miscible and immiscible behaviour within condensed-phase explosives arising from the co-existence of a reactive carrier mixture of miscible materials, and several material interfaces due to the presence of immiscible impurities such as particles or cavities. The dynamic and thermodynamic evolution of the explosive is communicated to one or more inert confiners through their shared interfaces, which may undergo severe topological change. We also wish to consider elastic and plastic structural response of the confiners, rather than make a hydrodynamic assumption for their behaviour. Recently developed methodologies meet these requirements by means of the simultaneous solution of appropriate systems of equations for the behaviour of the condensed-phase explosive and the elastoplastic response of the confiners. In the present work, we employ a mathematical model proposed by Peshkov and Romenski, which unifies fluid and solid mechanics by means of generalising the concept of distortion tensors beyond solids. We amalgamate this model with a single system of partial differential equations (PDEs) which meets the requirement of co- existing miscible and immiscible explosive mixtures. We present the mathematical derivation of our unified model and construct appropriate algorithms for its solution. The model is extensively verified and validated against exact numerical or analytical solutions and available experimental results. To enable the application of the model to a wider range of problems, we consider two further extensions. The first addresses the extension to multiple inert or reactive materials and its assessment on realistic scenarios like the mechanical sensitisation of liquid explosives. The second is concerned with the use of hyperbolic thermal impulse equations to model the conduction of heat across material interfaces. This is assessed in the scenario of thermal-induced ignition and transition to detonation in explosives. Results of this work indicate that the developed formulation provides a powerful alternative to existing combustion models, able to seamlessly account for the complex and highly non-linear multi-material interactions present in combustion applications.

The increasing demands in modern combustion engines for low emissions and low fuel consumption improved methods for the cycle of combustion. The Beare Heads is a recent 6-hour version of the Beare Heads, recognized also as Malcolm Beare model. Beare Heads uses pistons and harbours such as a 2-hour motor and replacements for the overlap valve system of 4-hour motors. The four-stroke engine, block as well as shaft remain intact. The six-time engine was a mix of two-hit and four-hit technologies. Six Stroke is a six-stroke engine that uses two energy strokes. The six-time engine including external combustion as well as internal dual stream is the same as the real interior combustion engine, according to its mechanical design. Air heating system as well as a combustion chambers, each separate of the cylinder, are two extra chambers throughout the thermodynamic cycles. The six-stroke is heat efficient, since the power pulse pressure changes are larger than for the injection process as well as compression strokes. The major benefits of six-stroke engines included lowering fuel consumption by 40 percent, reducing emissions, versatility for multi-fuel service by 2 power strokes over the six-stroke cycles.

In this paper, we revisit a turbulent mixing of gas and air in a gas burner with computational fluid dynamics (CFD) models. The quality of such a turbulent mixture is based on temperature, pressure, and velocity distributions as well as the distributions of different molecules, turbulent kinetic energy, and turbulent dissipation rate. In order to identify a precise combination of a gas and air mixture in a gas burner, which directly influences the quality of the combustion flame and reduces the amount of carbon monoxide (CO) emission in flue gases, thermodynamic principles are utilized based on the balancing ratio of molecular weights and the balancing ratio of mass flows between gas and air. Moreover, input parameters, such as volume flow rates, pressure, mass ratio, temperature, turbulent kinetic energy, and turbulent dissipation rate, are judiciously chosen with proper boundary conditions for both axisymmetric two-dimensional and three-dimensional models. It is confirmed that the effectiveness of gas and air mixture and combustion depends on the gas burner model, more specifically, on the sizes and locations of gas and air inlets and outlets as well as operation conditions.

Constructing cerium and manganese bimetallic catalysts with excellent catalytic performance for soot combustion is the research frontier at present. In order to find out the key factors for catalytic soot combustion of Ce-Mn-O catalysts, a series of Ce-Mn-O catalysts with different Ce/Mn proportions were prepared by co-precipitation method. The activity test results show that it increases first and then decreases with the increase of Mn content. The best catalytic activity is obtained for Ce0.64Mn0.36 catalyst, which shows a maximum rate temperature (Tm) at 306 °C for CO2 production in TPO curve. Compared with non-catalytic soot combustion, the Tm decreases by more than 270 °C. Systematical characterization results suggest that when the adsorbed surface oxygen, lattice oxygen, specific surface area and total reduction amount of the catalysts reach a certain value, the key factors leading to the difference of catalytic activity become the readily reducible and highly dispersed surface manganese oxide species and contact performance of the external surface. The surface manganese oxide species is beneficial to improving the low-temperature reducibility of catalysts and the porous surface is conducive to the contact between catalyst and soot. Furthermore, for the soot combustion reaction containing only O2, the promoting effect of Mn4+ is not obvious.

The anthropogenic carbon emissions in the power system would continue to increase with growing energy consumption. In this regard, researchers have focused on managing the demand side with carbon tracing tools (e.g., carbon emission flow model) to achieve low-carbon transition, as it is the need of customers that drives the combustion of fossil fuels and creates substantial carbon emissions. However, such a low-carbon transition cannot be achieved effectively without the right incentive scheme. It is desired to improve the computation quality of carbon tracing tools and extend their applications by state-of-art techniques. To fulfil these existing research gaps, in this paper, a low-carbon optimal scheduling model with carbon intensity control by demand response (DR) mechanism is proposed. It aims to reduce the dependence of customers on energy sources with high carbon intensities while decreasing reasonable energy consumption. Herein, energy consumption is linked to carbon emission via carbon emission flow (CEF) model. Also, a data-driven approach conducted with the Bayesian interfere regression is proposed to carry out the CEF analysis to cope with the drawbacks of the conventional emission calculation. Moreover, the storage emission and relevant dynamic impacts to the system are fully considered.

In this study, based on a closed bomb test combined with computational fluid dynamics, a structural finite element method, and an acoustic boundary element method, a fluid-solid acoustic one-way coupling calculation model is established for the combustion process of energetic materials in a closed bomb, and the effectiveness of the model is verified by experiments. It is found that the maximum peak sound pressure increases exponentially with an increase in loading doses or gas pressure. However, a change in the combustion coefficient of the energetic materials has little effect on the noise generated during the combustion process in the closed bomb. When the combustion coefficient is reduced by a multiple of 16, the maximum transient sound pressure is reduced by 1.79 dB, and the sound pressure level in the frequency band is reduced by 1.75 dB. With an increase in shell thickness, the combustion noise of the energetic materials in the closed bomb decreases, and the reduction range of the combustion noise increases with the increase in shell thickness.

In this paper, the combustion characteristics of kerosene-fueled supersonic combustor under the conditions of Mach number 2.0, the total temperature at 700 K and the total pressure at 520 kPa (simulated flight Mach number at 3.5) were studied by using the flame stabilizing method of cavity and strut from three aspects such as blockage ratios, kerosene equivalence ratios, location and quantity of injection holes. The results showed that: (A) The combustor with the strut realized the independent and stable combustion of kerosene. The combustion-induced back pressure in the block test with blockage ratio of 20% and 10% destroyed the inlet flow conditions; while the blockage ratio was 7.3% and 5%, the incoming flow conditions when kerosene was burned stably were not destroyed. (B) The kerosene Equivalence Ratio (ER) was more likely to be disturbed upstream than the induced back pressure when it rose, and an excessively high-ER would reduce the combustion efficiency; when the equivalence ratio was constant, the combustion efficiency of the blockage ratio of 7.3% was higher than the blockage ratio of 5%. The combustion efficiencies were 0.86 (ER = 0.13) and 0.78 (ER = 0.19) when the blockage ratio was 5%, respectively; the combustion efficiencies were 0.89 (ER = 0.16) and 0.82 (ER = 0.19) when the blockage ratio was 7.3%, respectively; the combustion efficiencies were 0.51 (ER = 0.25), 0.81 (ER = 0.3), 0.65 (ER = 0.34) and 0.62 (ER = 0.42) when the blockage ratio was 20%, respectively. (C) The porous injection provided behind the strut was beneficial to the atomization of kerosene and improved the combustion efficiency of kerosene; the second injection after the cavity would reduce the combustion efficiency due to insufficient oxygen and combustion space. This study expanded the working range of ramjet and provided a reference fuel injection scheme for Turbine-Based Combined Cycle (TBCC) engine.

This paper develops a size-adaptive hybrid meshing scheme for Chemical Species Tomography (CST) that is driven by the customized spatial resolution of the sensing region. Traditionally, the entire sensing region in CST is uniformly discretized with the empirically determined density of the meshes. Such a discretization results in a) waste of computational efforts on the less spatially resolved location; and b) much severer rank deficiency. To solve the above-mentioned issues, we introduce, for the first time, a size-adaptive hybrid meshing scheme for CST. Driven by the spatial resolution, dense meshes are deployed in the region of interest (RoI) to detail the target flow field while sparse ones are deployed out of the RoI to fully consider the physically existing laser absorption. The proposed scheme is numerically validated using a CST sensor with 128 laser beams. The visual and quantitative metric comparisons show that the proposed hybrid-size meshing scheme outperforms the traditionally uniform-size meshing scheme, giving 35% lower image error and 38% less significant dislocation at a typical 35 dB signal-to-noise ratio in the RoI. The proposed hybrid-size meshing scheme significantly facilitates the reconstruction of the industrial combustion processes where the combustion zone is bypassed by cooling flows. In these scenarios, the proposed scheme can adapt a finer resolution to detail the combustion zone, while maintaining the integrity of the physical model by less resolved reconstruction of the bypass flows.

Ethanol and palm oil biodiesel blended with diesel fuel have the potential to reduce greenhouse gas emissions, such as carbon dioxide (CO2), and can gradually decrease dependence on fossil fuels. However, the combustion products from these fuels, such as oxides of nitrogen (NOx), total hydrocarbons (THC) and particulate matter (PM), require to be examined and any beneficial or detrimental effect to the environment needs to be assessed. This study investigates the hydrocarbon selective catalyst reduction (HC-SCR) activities by the effect of combustion using renewable fuels (biodiesel-ethanol-diesel) blends and the effect of hydrogen addition to the catalyst, with the various diesel engine operating conditions. Lower values rate of heat released were recorded as the ethanol fraction increases, resulting in trade-off where, lower NOx was produced while greater concentration of carbon monoxide (CO) and THC was measured in the exhaust. Consequently, increasing the THC/NOx promoting the NOx reduction activity (up to 43%). Additionally, the HC-SCR performance was greatly heightened when hydrogen was added into the catalyst and able to improve the NOx reduction activity up to 73%. The experiment demonstrated plausible alternatives to improve the HC-SCR performance through the aids from fuel blends and hydrogen addition.

Injecting hydrogen into the natural gas network to reduce CO2 emissions in the EU residential sector is considered a critical element of the zero CO2 emissions target for 2050. Burning natural gas and hydrogen mixtures has potential risks, the main one being the flame flashback phenomenon that could occur in home appliances using premixed laminar burners. In the present study, two-dimensional transient computations of laminar CH4- + air and CH4 + H-2 + air flames are performed with the open-source CFD code OpenFOAM. A finite rate chemistry based solver is used to compute reaction rates and the laminar reacting flow. Starting from a flame stabilized at the rim of a cylindrical tube burner, the inlet bulk velocity of the premixture is gradually reduced to observe flashback. The results of the present work concern the effects of wall temperature and hydrogen addition on the flashback propensity of laminar premixed methane-hydrogen-air flames. Complete sequences of flame dynamics with gradual increases of premixture velocity are investigated. At the flame flashback velocities, strong oscillations at the flame leading edge emerge, causing broken flame symmetry and finally flame flashback. The numerical results reveal that flashback tendency increase with increasing wall temperature and hydrogen addition rate. (C) 2022 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.

Bayesian optimization (BO) is a global optimization algorithm well-suited for multimodal functions that are costly to evaluate, e.g. quantities derived from computationally expensive simulations. Recent advances have made it possible to scale BO to high-dimensional functions and accelerate its convergence by incorporating derivative information. These developments have laid the groundwork for a productive interplay between BO and adjoint solvers, a tool to cheaply obtain gradients of objective functions w.r.t. tunable parameters in a simulated physical system. In thermoacoustics, adjoint-based optimization has previously been applied to Helmholtz solvers and low-order network models to find optimally stable combustor configurations. These studies have used conjugate gradient or quasi-Newton optimizers which can get stuck in local optima and may require many evaluations of the underlying model to find a good optimum. In this paper, we propose using gradient-augmented BO to optimize adjoint models. We consider two test cases from the thermoacoustics literature: optimizing design parameters in a 1D adjoint Helmholtz model of a Rijke tube and geometry optimization in a low-order network model of a longitudinal combustor. We show that compared to BFGS, a standard quasi-Newton method, our gradient-enhanced BO arrives at multiple, more optimal configurations using considerably fewer evaluations of the solver. This approach holds great promise for efficient thermoacoustic stabilization when designing using expensive 3D adjoint Helmholtz solvers.

This study presents an algebraic combustion closure for Large eddy simulation (LES) exhibiting attributes of simplicity and simultaneous accuracy under realistic combustion conditions. The model makes use of the interlink between the reaction and dissipation rates in premixed turbulent combustion but relaxes the thin flame assumption by considering finite-rate chemistry effects in the small-scale turbulence structure. The core idea of the approach is to approximate the reaction progress in the unresolved spectrum of wave lengths and to use it within a filtered reaction rate expression. The model is implemented in OpenFOAM 4.0 and is tested on a turbulent, premixed flame behind a bluff-body, applying an LES approach for turbulence modelling. The cross comparison of velocity, temperature and composition data with experiments and a wellinvestigated combustion model in literature reveals competitive performance of the new model. Especially in the near-field of the bluff body flame, corresponding to thin and moderately thickened flame regions, its ability to capture the flame structure is highly promising. The chosen, partly explicit approach to recover the temperature from the transported sensible enthalpy, involving a strong coupling between filtered reaction and heat release rate, also shows advantages over obtaining the temperature from presumed probability density functions. Development of a turbulence dissipation based reaction rate model for progress variable in turbulent premixed flames

Electromagnetic launchers are somewhat preferred to combustion and mechanical ones due to their superior advantages. Acceleration improvement in a limited motor length is the major problem of these machines. Optimal shape of secondary sheet has the great importance on launching procedure, which is investigated in this paper. The common methods of acceleration improvement have been explored on a 4kW, 600mm case-studied launcher. Multi-layer secondary is then proposed and investigated on case-studied machine. The efficacy of proposed topology is verified by finite elements method (FEM) as well as experimental tests.

Relight of jet engines at high altitude is difficult due to the relatively low pressure and temperature of inlet air. The penetration of initial flame kernel affects the ignition probability in the turbine engine combustor greatly. In order to achieve successful ignition at high altitude, a deeper penetration of initial flame kernel should be generated. In this study, a Gliding Arc Plasma Jet Igniter (GAPJI) is designed to induce initial flame kernel with deeper penetration to achieve successful ignition at high altitude. The ignition performance of the GAPJI was demonstrated in a model combustor. It was found that GAPJI can generate plasma with deeper penetration up to 30.5 mm than spark igniter with 22.1 mm. The discharge power of GAPJI was positively correlated with flow rate of the carrier gas, approaching 200 W in average. Ignition experiments show that GAPJI has the advantage of extending the lean ignition limit. With GAPJI, the lean ignition limit of the combustor is 0.02 at 0 km, which is 55.6% less than that with spark igniter (0.045). The evolution of flame morphology was observed to explore the development of the flame kernel. It is shown that the advantage of a high penetration and continuous releasing energy can accelerate the ignition process and enhance combustion.

Rice hulls, a harmful biowaste, were used to produce nanosized activated carbon (RHAC) by combustion and phosphoric acid treatment. The developed RHAC was characterised using various structural and morphological techniques (scanning electron microscopy, X-ray diffraction, Fourier transform infrared spectroscopy and nitrogen (N2) adsorption). The prepared RHAC was used to remove heavy metal ions (iron (III) (Fe3+) and chromium (VI) (Cr6+)) by using the adsorption mechanism. Adsorption parameters, such as contact time, dose and initial concentration of the heavy metal ions, were investigated. Five adsorption models (two and three parameters) were studied. Also, the adsorption kinetics through the intraparticle diffusion model was applied. RHAC showed adsorption capacities of 47.00 and 45.00 mg/g for iron (III) and chromium (VI), respectively. The findings recommend using RHAC as a low-cost and eco-friendly adsorbent for metal ion removal and water-treatment applications.

Keeping combustion stable and detecting unstable states in time is crucial for coal-fired furnaces such as rotary kilns, boilers, and oxygen furnaces. Because of the interference and complex conditions in the industrial field, recognition of combustion conditions by vision analysis is difficult. In this paper, we propose a robust nonlinear dynamic system analysis-based approach for combustion condition recognition by extracting chaotic characteristics from a flame video. We first discover chaotic characteristics in the intensity sequence extracted from a flame video of coal-fired kilns, and then we further find that the underlying chaos rules differ between combustion conditions. Based on this finding, we design a set of trajectory evolution features (TEFs) and morphology distribution features (MDFs) of chaotic attractors for combustion condition recognition. After reconstructing the chaotic attractors from the intensity sequence of a flame video by phase space reconstruction (PSR), the quantified features are extracted from the recurrence plot (RP) and morphology distribution (MD) and put into a decision tree to recognize the combustion condition. The experimental results on real-world data show that the proposed method can recognize the combustion condition in coal-fired kilns effectively and promptly. Compared with other methods, the recognition accuracy is improved more than 5%.

Producción Científica, In the present work an analysis of the origin and nature of intrinsic instabilities in combustion processes with different hydrogen/methane mixtures is developed. These expanding spherical flame front experiments have been developed in a cylindrical constant volume combustion bomb, which allows recording the process through Schlieren photography method. The stability study in combustion processes has a great importance to assure their security and control, since the understanding of flame instabilities is necessary for improving the internal combustion engines performance. To carry out this mentioned study, a review of the concepts and parameters used in spherical flame front instabilities research is first proposed, as well as a physical explanation of each concept and the relations among them. Additionally, a methodology that aims to determine the influence of the fuel mixtures in the origin and development of the flame front instabilities is suggested. Moreover, the intrinsic effects of the combustion process, such as the thermal-diffusive and the hydrodynamic effect, are separately studied, including their individual contributions to the growth rate of instabilities which allows to determine combustion nature and to obtain the instability peninsula of each fuel mixture. Finally, this methodology includes a qualitative study of the cellularity phenomenon (when the instabilities develop all over the flame front), considering the parameters which influence on this phenomenon., Ministerio de Ciencia, Innovación y Universidades - Agencia Estatal de Investigación (grant PID2019-106957RB-C2)

This work presents a computational investigation of hydrodynamics, coal combustion and NOx emissions in a tangentially fired pulverized coal boiler at different loads (630, 440 and 300 MW; relative loads of 100%, 70% and 48%) to clarify the effect of load change on the furnace processes. A computational fluids dynamics model was established; the flow field, temperature profile, species concentration and NOx emissions were predicted numerically; and the influence of burner tilt angles was evaluated. Simulation results indicate that a decrease in boiler load decreases the gas velocity, attenuates the airflow rotations, and increases the tangent circle size. The high-temperature zone and flame moved toward the side walls. Such behaviors impair air–fuel mixing, heat transfer and steady combustion in the furnace. In terms of species concentrations, a decrease in boiler load increased the O2 content, decreased the CO content, and decreased the char burnout rates only slightly. A change in boiler load from 630 to 440 and 300 MW increased the NOx emissions from 202 to 234 and 247 mg/m3, respectively. Burner tilt angles are important in coal combustion and NOx emissions. A burner angle of –15° favors heat transfer and low NOx emissions (

[ES] Desde la irrupción de los vehículos eléctricos en el mercado automotriz como una opción de transporte limpia y asequible, los fabricantes de motores han estado buscando nuevas formas de reducir la huella ambiental de los actuales motores de combustión interna alternativos (MCIA). Hoy en día, la mayoría de las investigaciones en aplicaciones de vehículos de pasajeros se centran en desarrollar aún más los motores de encendido provocado (MEP) para promover una nueva generación de sistemas de propulsión sostenibles y de alto rendimiento. En este contexto, el concepto de encendido de precámara se está convirtiendo en una solución atractiva para aumentar la eficiencia térmica de los futuros MEP para vehículos de pasajeros, debido a su capacidad de acelerar el proceso de combustión. Además, la combinación de esta estrategia de encendido con mezclas diluidas (ya sea con aire o gases de escape) tiene el potencial de mejorar aún más el rendimiento del motor. En particular, en comparación con los sistemas de precámara activa con suministro de combustible auxiliar, la versión pasiva ofrece ventajas evidentes en términos de simplicidad mecánica, ensamblaje y coste. Sin embargo, todavía existen importantes obstáculos relacionados con la comprensión de los aspectos fisicoquímicos fundamentales del concepto (turbulencia, aerodinámica, conversión de energía, dinámica de los chorros, geometría de precámara...), que en última instancia han limitado la integración de esta tecnología en producción. Por lo tanto, esta tesis doctoral pretende extender el nivel de conocimiento de este concepto de encendido mediante el uso de un modelo CFD de última generación, validado con un extenso conjunto de medidas experimentales y siguiendo una metodología especialmente desarrollada para este trabajo de investigación. Los resultados obtenidos se dividieron en tres partes: La primera parte evaluó un MEP monocilíndrico de investigación, representativo de vehículos automóviles, que integraba el concepto de precámara pasiva en condiciones estequiométricas sin dilución. Aquí se evaluó el impacto del punto de operación del motor, el avance del encendido y la geometría de la precámara sobre los procesos físicos y termoquímicos que intervienen en este concepto de combustión. La segunda parte del estudio se centró en caracterizar el concepto en condiciones diluidas con aire y recirculación de gases de escape (EGR). Se analizó en profundidad la evolución del proceso de combustión y la distribución de energía en la precámara y cámara principal para los límites de dilución experimentales. Además, también se evaluó el uso de hidrógeno para ampliar el límite de dilución con aire. La última etapa de la investigación consistió en evaluar una posible aplicación tecnológica de este concepto de encendido a partir de los conocimientos adquiridos. Por ello, se desarrolló una metodología de diseño de precámara que combina herramientas numéricas 0D/1D y CFD. Posteriormente, la metodología fue validada en el banco de ensayos del motor, y la precámara resultante ofreció buenos niveles de rendimiento térmico y fue capaz de extender el límite de dilución con EGR. Con ello, la presente tesis doctoral supone un avance significativo en el campo del análisis del impacto de la integración de sistemas avanzados en MCIA en general, y en MEP en particular, con el objetivo de mejorar sus prestaciones, emisiones o rendimiento, contribuyendo al esfuerzo que está realizando la comunidad científica para mitigar el impacto ambiental del sector del transporte., [CAT] Des de la irrupció dels vehicles elèctrics en el mercat automotriu com una opció de transport neta i assequible, els fabricants de motors han estat buscant noves maneres de reduir la petjada ambiental dels actuals motors de combustió interna alternatius (MCIA). Hui dia, la majoria de les investigacions en aplicacions de vehicles de passatgers se centren a desenvolupar encara més els motors d'encesa provocada (MEP) per a promoure una nova generació de sistemes de propulsió sostenibles i d'alt rendiment. En aquest context, el concepte d'encesa de precàmera s'està convertint en una solució atractiva per a augmentar l'eficiència tèrmica dels futurs MEP per a vehicles de passatgers, a causa de la seua capacitat d'accelerar el procés de combustió. A més, la combinació d'aquesta estratègia d'encesa amb mescles diluïdes (siga amb aire o productes de la combustió) té el potencial de millorar encara més el rendiment del motor. En particular, en comparació amb els sistemes de precàmera activa amb subministrament de combustible auxiliar, la versió passiva ofereix avantatges evidents en termes de simplicitat mecànica, assemblatge i cost. No obstant això, encara existeixen importants obstacles relacionats amb la comprensió dels aspectes fisicoquímics fonamentals del concepte (turbulència, aerodinàmica, conversió d'energia, dinàmica d'ejecció, geometria de precàmera...), que en última instància han limitat la integració d'aquesta tecnologia a la producció en sèrie. Per tant, aquesta tesi doctoral pretén estendre el nivell de coneixement d'aquest concepte d'encesa mitjançant l'ús d'un model CFD d'última generació, validat amb un extens conjunt de mesures experimentals i seguint una metodologia especialment desenvolupada per a aquest treball de recerca. Els resultats obtinguts es divideixen en tres parts. La primera part estudia un MEP monocilíndric d'investigació, representatiu dels vehicles actuals d'automoció, que integra el concepte de precàmera passiva en condicions estequiomètriques sense dilució. Ací s'avalua l'impacte del punt d'operació del motor, l'avanç de l'encesa i la geometria de la precàmera sobre els processos físics i termoquímics que intervenen en aquest concepte de combustió. La segona part de l'estudi se centra a caracteritzar el concepte en condicions diluïdes amb aire i recirculació de gasos produïts per la combustió (EGR). S'analitza en profunditat l'evolució del procés de combustió i la distribució d'energia en la precàmera i en cambra principal per als límits de dilució experimentals. A més, també s'avalua l'ús d'hidrogen per a ampliar el límit de dilució amb aire. L'última etapa de la investigació consisteix a avaluar una possible aplicació tecnològica d'aquest concepte d'encesa a partir dels coneixements adquirits. Per això, es desenvolupa una metodologia de disseny de precàmera que combina eines numèriques 0D/1D i CFD. Posteriorment, la metodologia és validada al banc d'assajos del motor, on la precàmera resultant ofereix bons nivells de rendiment tèrmic i és capaç d'estendre el límit de dilució amb EGR. Amb això, la present tesi doctoral suposa un avanç significatiu en el camp de l'anàlisi de l'impacte de la integració de sistemes avançats en MCIA en general, i en MEP en particular, amb l'objectiu de millorar les seues prestacions, emissions o rendiment, contribuint a l'esforç que està realitzant la comunitat científica per a mitigar l'impacte ambiental del sector del transport., [EN] Since the irruption of electric vehicles in the automotive market as a clean and affordable transportation option, engine manufacturers have been looking for new ways to reduce the environmental footprint of current internal combustion engines (ICE's). Nowadays, most of the research efforts in passenger car applications focus on further developing spark-ignition (SI) engines to promote a new generation of high-performance and sustainable powertrains. In this context, the pre-chamber ignition concept is becoming an attractive solution to increase the thermal efficiency of future light-duty SI engines, due to its inherent capability of enhancing the combustion process. Moreover, combining this ignition strategy with diluted mixtures (either with air or exhaust gases) has the potential to further improve the engine performance and reduce pollutant emissions. In particular, compared to active pre-chamber systems with an auxiliary fuel supply, the passive version provides advantages in terms of mechanical simplicity, packaging and cost-effectiveness. However, there are still major hurdles related to the understanding of the fundamental physicochemical aspects of the concept (turbulence, scavenging, energy conversion, jet dynamics, pre-chamber geometry...), that ultimately have limited the integration of this technology into production vehicles. Therefore, this doctoral thesis intends to fill these knowledge gaps by using a state-of-the-art CFD model, validated with an extensive set of engine tests and following a simulation methodology specially developed for this research work. The obtained results were divided into three parts: The first part evaluated a research single-cylinder SI engine, representative of light-duty applications, operating with the passive pre-chamber system in un-diluted stoichiome\-tric conditions. Here, the impact of the engine operating point, spark timing and pre-chamber geometry over the physical and thermochemical processes that are involved in this combustion concept were evaluated. The second part of the study focused on characterizing the concept in diluted conditions with air and exhaust gas re-circulation (EGR). The combustion evolution and energy distribution in the pre-chamber and main chamber for the experimental dilution limits were deeply analyzed. In addition, the use of hydrogen to extend the air-dilution limit was also assessed. The final part of the investigation consisted in developing a potential technological application of this ignition concept from the acquired knowledge. Therefore, a pre-chamber design methodology combining 0D/1D and CFD numerical tools was developed and validated in the engine test bench. The resulting pre-chamber offered good levels of thermal efficiency and was able to extend the EGR dilution limit. This doctoral thesis represents a significant advancement in the frame of analyzing the impact of advanced ignition systems and their integration in ICE's in general, and in SI engines in particular, with the aim of improving the global features of these powerplants (efficiency and emissions), contributing to the effort that the scientific community is carrying out to mitigate the environmental impact of the transportation sector.