Adiabatic Combustion Temperature Research Articles

A New Approach to Performing Thermally Coupled Processes by the Example of a (Ni + Al)–(Ti + C) Granular Mixture

For the first time, for performing thermally coupled SHS processes, granular mixtures were used instead of powder ones. In this case, the rate of the heat transfer between the donor and the acceptor is virtually independent of the sample size and is determined only by the granule size. Therefore, an advantage of using a granular mixture is that the process optimized under laboratory conditions can be scaled without changing its characteristics and the properties of the desired synthesis product. The studied granular mixture comprised a mixture of (Ni + Al) granules (acceptor) and a mixture of (Ti + C) granules (donor), which differed in rate and temperature of combustion. It was determined that the ignition of the (Ni + Al) acceptor granules occurred in the combustion front. It was shown that using granular mixtures for performing coupled thermal reactions makes it possible to obtain the combustion products as a readily destructible sample, from which the desired product can be separated even if the melting point of the product of the interaction of the acceptor mixture is lower than the adiabatic combustion temperature.

Synthesis of Ni-based catalysts by hexamethylenetetramine-nitrates solution combustion method for co-production of hydrogen and nanofibrous carbon from methane

It was shown that hexamethylenetetramine (HMT) is a new effective fuel for single-step solutions combustion synthesis (SCS) of supported Ni catalysts for methane decomposition into hydrogen and nanofibrous carbon. Several generalized chemical equations reflecting different ideas about combustion of the HMT−Ni(NO3)2−Cu(NO3)2−Al(NO3)3−H2O system have been derived. On the basis of those equations the adiabatic combustion temperature (Tad) and the amount of gaseous products (ng) have been calculated depending on the ignition temperature (T1), water content (m), excess fuel coefficient (φ), and the composition of the obtained solid product. The calculations have shown that Tad, depending on m and φ, changes from hundreds to thousands of degrees Kelvin. Increase of Al2O3 content in the catalyst up to 0.6 increases Tad by hundreds of degrees, and that increase of the Ni:NiO ratio up to 0.5 lowers Tad by tens of degrees. Three samples of the supported unreduced 0.97NiO/0.03Al2O3 catalyst were successfully prepared with the help of the SCS method using HMT as the fuel at φ=0.7. Those samples, obtained at reaction mixture preliminary heating rates V = 1, 10, 15 K/min were characterised using XRD, TEM, and SEM, and further tested in a pure methane decomposition reaction (100 LCH4/h/gcat, 823К, 1 bar). Nanoparticles of metal Ni were found in the SCS products, in contrast to cases when other types of fuel were used with φ<1. The experimental results showed that the higher is V, the higher is the maximum SCS temperature, the larger is the average size of Ni nanoparticles in unreduced catalyst, the higher is the stability of unreduced catalyst (up to 14 h) and the higher is the specific yield of hydrogen (up to 818 mol/molcat) during the deactivation period. The activity value of our unreduced catalyst (0.7 mol/h/gcat) in the methane decomposition reaction is close to maximum activity values of pre-reduced Ni catalysts of different nature reported in published articles.

Image-Based Flame Detection and Combustion Analysis for Blast Furnace Raceway

Blast furnace tuyere is an important “window” between the inside and outside of blast furnace. Stable and accurate detection of the combustion condition of tuyere raceway plays a significant role in maintaining longevity, safety, and smooth of blast furnace. The adiabatic combustion temperature as a traditional measurable indicator of the raceway combustion condition considers the raceway temperature as a constant. It cannot explain the productivity and quality fluctuations of iron in practical production while the operation parameters are fixed and unchanged. Thus, this paper presents the image-based flame detection system specific to the blast furnace raceway to research the actual combustion condition in the raceway. The system mainly consists of an optical detector to capture raceway images and a digital image processing unit to extract flame features. In this paper, the nonlinear partial least-squares colorimetry and Monte Carlo method with iterative optimization are developed to obtain the temperature distribution of the raceway. Power spectral analysis is used to extract the flame flicker frequency. Massive raceway images captured from 15 raceways of a 2500-m3 blast furnace were used to analyze raceway flames. The results demonstrate that temperature distribution of the raceway can fluctuate in a wide range and considerable temperature nonuniformity exists among the 15 raceways. This case can explain why productivity and quality of iron are unstable under the same operation parameters. And, the detection system performs well in revealing the nature of the raceway combustion condition.

Synthesis and Properties of Composites Based on Zirconium and Chromium Borides

Experimental data on the fabrication of composites based on the ZrB2–CrB system by SHS compaction are presented. Adiabatic combustion temperatures of the Zr–Cr–B system and compositions of equilibrium synthesis products are calculated using the thermodynamic data, and optimal fabrication conditions for SHS composite production are determined. It is shown that the equilibrium synthesis products are ZrB2 and CrB refractory compounds. They provide the high thermodynamic stability of SHS composites, which are applied as a dispersed phase (ZrB2) and ceramic binder (CrB). The adiabatic combustion temperature decreases from 3320 to 2350 K with an increase in the binder content from 25 to 64 wt %. A hard dispersed phase (ZrB2) and molten binder (CrB) are formed under these conditions. It is revealed that the formation of a molten binder provides the formation of SHS composites with residual porosity lower than 1%. The influence of the composition of the reaction mixture on the phase composition, microstructure, and physicomechanical characteristics of SHS composites are investigated. It is established that the residual porosity at the CrB content in the limits of 30–50 wt % is <1%. Herewith, the Vickers hardness varies in a range of 31.3–42.6 GPa, while the ultimate bending strength varies in a range of 480–610 MPa. It is shown that physicomechanical characteristics depend on the residual porosity of SHS composites. Cutting plates are fabricated from the ZrB2–30CrB SHS composite and testing is performed with the treatment of high-hardness chilled steels. The results evidence that ceramic cutters made of the ZrB2–30CrB composite possess high wear resistance when treating ShKh15 bearing steel with hardness of 61–65 HRC.

SHS Metallurgy of Binary Silicides (MoW)Si2 for Sintering Composite Materials

The regularities of synthesis by the SHS metallurgy method of cast materials in the Mo-W-Si system are studied. The experiments were carried out in SHS reactors with a volume of 3, 20 and 30 L under the pressure of an inert gas (argon) P = 5 MPa. In the experiments, high-calorie mixtures of molybdenum (6) and tungsten (6) oxides with aluminum and silicon were used. Thermodynamic calculation of combustion parameters of the initial systems according to the Thermo program showed that they have high adiabatic combustion temperatures exceeding the melting points of the initial reagents and final products of synthesis. Studies have shown a strong effect of the ratio of the initial reagents on the regularities of synthesis. Cast (ingots) single-phase disilicides of molybdenum (MoSi2) and tungsten (WSi2), as well as their solid solutions MoSi2–WSi2, are obtained with any given ratio between them. Their microstructure and elemental and phase composition were investigated. Optimal modes of mechanical conversion of the obtained ingots of the target products into the powders of the required fractions are developed. The influence of the composition of composites on the strength and oxidation of sintered samples in air at different temperatures was studied. It was shown that sintered composites from MoSi2–WSi2 solutions have higher strength and are less susceptible to oxidation compared to ceramics obtained by solid-phase sintering from powders of individual MoSi2 and WSi2.

Equivalent analysis of the explosion overpressure of gasoline vapor–air mixture by using isooctane equivalence ratio

Isooctane is often used as a substitute to investigate the heat release, chemical kinetic models and flame behaviors of the gasoline vapor explosion process. Such substitution always leads to some inevitable errors between the overpressures of theoretical calculation value and the experimental data of the gasoline vapor explosion. Based on the deduction of the relationship between the equivalence ratio (\(\emptyset\)) and volume concentration of isooctane–air mixture, the constant volume adiabatic combustion temperature and overpressure of the isooctane explosion at different \(\emptyset\) were calculated by using the first law of thermodynamics. Then, through the experiments of gasoline vapor explosion in a standard 20-L spherical explosive device, explosion overpressures at different gasoline vapor volume concentrations were obtained. By analyzing the overpressure error between the theoretical value of the isooctane explosion and the experimental data of the gasoline vapor explosion, an equivalent relationship in terms of isooctane equivalence ratio for gasoline vapor constant volume explosion overpressure is proposed. This relationship not only can be used to accurately predict gasoline vapor constant volume explosion overpressure by means of isooctane, but also can be used to modify the gasoline explosion overpressure calculation model and enable the errors between the model’s calculation value and the actual experimental value to be significantly reduced.

Hydroxide‐Based Nanoenergetic Materials

AbstractHydroxide‐aluminum based nano‐energetic materials are new class of thermites which demonstrated high theoretical energy capacity of up to 50 kJ cm−3. Most of the hydroxide‐aluminum based systems exhibit a large gas generation (greater than two liters per gram) and high adiabatic combustion temperature (up to 3000 K), which ensures performance that attributes significantly for applications such as solid fuel propulsion, explosives, airbag deployment, etc. Thermodynamic calculations performed for a collection of 16 novel hydroxide‐based nano‐thermite systems show that most of the systems are stable. Four systems, based on bismuth, copper, nickel and cerium hydroxides, were mixed with aluminum to prepare nano‐thermites compositions. These formulations were tested to estimate the heat generation and pressure discharge values during the ignition. These systems were stable below ignition temperature, between 570–600 °C. The strongest performance was recorded for Al−Bi(OH)3 formulation with 5.6 kPa*m3 g−1 peak pressure, which is comparable to highest values reported in literature.

Experimental and modeling analysis of Air and CO2 biomass gasification in a reverse lab scale downdraft gasifier

Abstract This research work aims at investigating the effect of carbon dioxide feed in biomass gasification as a possible way to directly exploit the exhaust gas from the engine of combined heat and power systems to convert carbon dioxide to carbon monoxide via Boudouard reaction and consequently increase the carbon conversion and reduce char yield. The effects on biomass gasification using air, and air diluted with carbon dioxide were assessed in a reverse downdraft lab-scale gasifier utilizing 2 kg of pelletized biomass. This reactor is mounted on a digital weighing balance which enables the recording of mass loss during the gasification process. Furthermore, the mixture of air and CO2 is obtained from two mass flow controllers which enable constant and desired flux of gasifying agents across the gasifier. At the same time, an in-house developed thermodynamic equilibrium model was applied to predict the gas composition and char output. Unlike the classical equilibrium strategy that calculates the gasification products using the Gibbs energy minimization method at fixed temperature and pressure, the current approach is based on the enthalpy of the reactants, analogous to the adiabatic combustion temperature. Also, a correction factor accounting for the heat losses, was implemented. The model outcome shows a good agreement with the experimental results, especially in terms of predicted char yields and trends of the dominant producer gas species. The same strategy was used to describe the behavior of the gasification system and estimate the quality of producer gas and the cold gas efficiency of the system.

Shock-wave synthesis in powder mixtures

The work is aimed at studying the features and conditions of initiation, reaction, gas generation and final phase formation in the energy condensed “metal-teflon” systems with two types of initiation: local heat pulse and shock-wave loading. Approximate thermodynamic calculations were carried out using THERMO program, which took into account three mixtures and samples of them: (Ni + Al + Teflon), (Ti + B + Teflon), (Hf + B + Teflon). The adiabatic combustion temperatures of mixtures, the composition and the amount of condensed products, and the volume of gaseous products are calculated. Gas formation during combustion of mixtures was measured in a spherical ampoule equipped with temperature and pressure sensors. Shock-wave loading of the samples was carried out in a multi-cell matrix by throwing a flat impactor. The acceleration of the impactor was carried out by the detonation products of the explosive. The design of the recovery fixture provided the same loading conditions in all cells. The investigated compositions are capable of an intense exothermic reaction, both at traditional ignition of a heated spiral, and at shock-wave action.

SHS Metallurgy of Cr2AlC MAX Phase-Based Cast Materials

A review of publications on the structure, properties, fabrication methods, and application fields of materials based on the Cr2AlC MAX phase is given. It is noted that the most promising method of formation of such materials is self-propagating high-temperature synthesis (SHS), one of the directions of which is SHS metallurgy. A powder mixture of chromium III and chromium VI oxides of the analytical grade, aluminum of ASD-1 grade, and carbon is used as the base charge in investigations. The adiabatic combustion temperature and composition of final products is calculated using the THERMO special program. Experiments were performed in an SHS reactor with volume V = 3 dm3 under the initial pressure of inert gas (Ar) P0 = 5 MPa. The influence of the ratio of initial reagents on SHS parameters (the combustion rate, pressure increment, and yield of the target product), composition, and microstructure of target products is investigated experimentally. A scientific approach of the formation of cast materials in the Cr–Al–C system consisting of the Cr2AlC MAX phase and phases Cr3C2 and Cr5Al8 by the SHS metallurgy method is developed. The structural-phase states of target products are studied. It is established experimentally that, varying the content of initial reagents (aluminum and carbon) in the charge, it is possible to substantially affect the synthesis regularities, composition, and microstructure of final products. An increase in the content of the Cr2AlC MAX phase in the final product and a decrease in the Cr5Al8 content occur with an increase in the carbon content (above stoichiometric) in the initial mixture. An increase in the aluminum content (above stoichiometric) in the initial mixture leads to an increase in the content of the Cr2AlC MAX phase in the final product and a decrease in the content of the Cr3C2 phase.

Research into the Possibility of Producing Single-Phase Tantalum–Hafnium Carbide by SHS

The influence of mechanical-activation (MA) conditions on the microstructure and phase composition of Ta–Hf–C reaction mixtures and products fabricated from them by self-propagating high-temperature synthesis (SHS) is investigated. The Ta–Hf–C reaction mixtures are mechanically activated in centrifugal planetary mills with various drum revolution rates. It is revealed that an increase in the drum revolution rate from 250 to 900 rpm lowers the heterogeneity scale of the reaction charge, decreases the size of coherent scattering regions of tantalum and hafnium by an order of magnitude, and leads to a rise in the degree of microdeformation of their crystal lattices by a factor of 1.5–2.0. It is established experimentally that it seems impossible to initiate an SHS reaction in the Ta–Hf–C activated mixture at initial temperature T0 < 550 K. The combustion process is implemented only at T0 = 800 K, when the adiabatic combustion temperature reaches 3274 K in mixtures treated with a revolution rate higher than 678 rpm. Single-phase carbide (Ta,Hf)C with lattice parameter a = 0.4487 nm, which corresponds to 18.0 at % dissolved HfC in TaC, is formed from reaction mixtures activated according to optimal regimes. The hafnium oxide content in products does not exceed 1%. The sample structure has high porosity (larger than 30%) and small carbide grain size (smaller than 10 μm), which makes it possible to produce the (Ta,Hf)C powder by milling the SHS product in a ball rotary mill.

Considerations on the key precursor for the growth of carbon nanotubes using a diesel engine as a reactor

Carbon nanotube (CNT) was synthesized during combustion in a diesel engine by adding catalyst sources into fuel. Fuel used in this study was a mixture of normal dodecane/ethanol, methyl laurate/ethanol, and 1-decanol/ethanol. The analysis of an exhaust gas using a gas chromatograph revealed that the amount of carbon monoxide was most influential on the CNT formation than other factors such as adiabatic combustion temperatures and/or the amount of low molecular weight hydrocarbons like acetylene and ethylene. The significance of carbon monoxide in our system was also suggested by simulated and modeling works. Simulations of combustion reactions inside a cylinder were performed through CHEMKIN-PRO software for a qualitative evaluation. Modeling works of CNT growth rates were carried out by means of not only CO related reactions but also ethylene and acetylene related reactions as a source of carbon deposition. It was suggested that carbon monoxide had stronger connection with CNT synthesis in a diesel engine compared with other potential CNT precursors such as ethylene and acetylene. Furthermore, we proposed CNT growth route in our system by considering characteristics of combustion in a diesel engine.

SYNTHESIS AND PROPERTIES OF COMPOSITES BASED ON ZIRCONIUM AND CHROMIUM BORIDES

This paper provides experimental data on ZrB2–CrB composite production by SHS compaction. Thermodynamic data were used to calculate adiabatic flame temperatures of the Zr–Cr–B system and compositions of equilibrium synthesis products and to determine optimum conditions for SHS composite production. It was shown that equilibrium products of combustion synthesis are ZrB2 and CrB refractory compounds that ensure high thermodynamic stability of SHS composites. They are used as a dispersed phase (ZrB2) and a ceramic binder (CrB). As the binder content increases from 25 to 64 wt.%, the adiabatic combustion temperature decreases from 3320 to 2350 K. A solid dispersed phase (ZrB2) and a molten binder (CrB) are formed at these conditions. It was identified that SHS composites with a residual porosity less than 1% can be produced due to molten binder formation. The effect of reaction mixture composition on the phase composition, microstructure, physical and mechanical properties of SHS composites was studied. It was found that the residual porosity of SHS composites is ~1 % at the 30–50 wt.% CrB content. Vickers hardness is 31,3 to 42,6 GPa, and flexural strength is 480 to 610 MPa. It was shown that physical and mechanical properties depend on the residual porosity of SHS composites. The obtained ZrB2– 30CrB SHS composite was used to make cutting inserts and conduct tests for high-strength hardened steel machining. The test results proved that ZrB2–30CrB ceramic inserts feature high wear resistance when machining ShKh15 chromium bearing steel with a hardness of 61–65 HRC.

Submicron LaB6 powders with high purity prepared in large scale by salt-assisted combustion synthesis

LaB6 powders were synthesized in large scale by salt-assisted combustion synthesis (CS) with different NaCl diluent contents. The variety of phases, particle size and purity of the powders were investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), energy dispersive spectrometer (EDS), and transmission electron microscope (TEM). With increase of NaCl content, the adiabatic combustion temperature of the reaction system linearly declines, the average particle size of leached products decreases, the impurity phases are easier to remove, and the products purity enhances obviously. When NaCl content is 40 wt%, the purity of the superfine powders of LaB6 is more than 98 wt%, and the average particle size is 380 nm.

The Experiment Study of Performance, Combustion Process and NOX Emission of Diesel Engine with EGR System Using Angle Globe Valve

Exhaust Gas Recirculation (EGR) is technology to reduce NO X emission of diesel engine. This technology could circulate some exhaust gas into the combustion chamber. The adiabatic combustion temperature could decrease and reduce the reaction of oxygen in nitrogen. This method could inhibit the formation of NO X during the combustion process because NO X formation reactions occur at high temperatures. EGR has some effects such as decreased engine performance, SFOC increases and changes in the combustion process. In order to suppress the negative impact, the research carried out by replacing the EGR valve using a type angle globe valve. Experiments conducted using a single cylinder diesel engine YANMAR type TF85-MHDI. The result obtained in this study is the emission of NO X can be reduced up to 15.6 g/kWh or 44.2% of the engine condition without EGR. The experimental results indicate that the use of angle globe EGR valve can reduce the SFOC up to 35.29 gr/kWh. Results of power, torque and BMEP also better compared EGR standard. While in the combustion process showed that the use of EGR valve angle globe causing peak of combustion pressure becomes lower and the Rate of Heat Release (ROHR) is lowered.

Fire and Explosion Risks of Glycol-Based Vapor–Air Mixtures

@Abstraction limits of flame propagation are determined for 13 glycols, as well as their enthalpy of formation and enthalpy of combustion. These characteristics depend on the number of carbon atoms in the glycol molecule. The combustion parameters are calculated for vapor–air mixtures of glycols and monoatomic alcohols, in the case where P = 1 atm and V = const. The adiabatic combustion temperature of mixtures of limiting and stoichiometric composition does not depend on the number of hydroxyl groups in the alcohol molecule. The explosive pressure of glycol is slightly higher than for monoatomic alcohols.

Preparation of Fine-grained Silicon from Serpentine Mineral by Magnesiothermic Reduction of Silica in the Presence of Reaction Products as Diluents

In the work, the preparation of fine-grained silicon was performed in combustion mode by magnesiothermic reduction of silica, obtained from serpentine mineral, which is characterized by a high specific surface area (about 560 m2/g) and high reaction activity. It is manifested by the fact that the measured combustion temperature exceeded the adiabatic combustion temperature calculated with the ISMAN THERMO software, by about 200 °C. In order to mitigate the synthesis conditions, combustion products (Si+2MgO) were used as diluting agents allowing a significant decrease of combustion temperature and a finer silicon powder without contaminating the target product with incidental reagents and without decreasing the yield of the target product. Based on the measured values of combustion parameters (combustion temperature and combustion wave propagation velocity) vs diluent amount, it was estimated that the effective activation energy for SiO2+2Mg reaction by the solid+liquid mechanism in the temperature interval 1400–2100 °C was about 65±3 kJ/mol.

Highly efficient combustion with low excess air in a modern energy-from-waste (EfW) plant

The effect of low excess air and high adiabatic combustion temperatures on CO and NOx formation has been investigated on a commercially operated energy-from-waste plant. With optimal combination of low O2 levels and stable combustion control, uncontrolled NOx levels could be lowered to 100–150mg/Nm3 (dry, at 11% O2) while keeping CO emissions at low levels. Even at adiabatic temperatures above 1400°C thermal NOx hardly contributed to the total NOx emissions in a grate-fired EfW plant. An advanced combustion control system allowed continuous operation with very little excess air (λ<1.2) while keeping CO and NOx at levels well below the legal emission limits.

Energy and exergy analyses of natural gas-fired boilers in a district heating system

In this study, energy and exergy analyses of natural gas fired boilers in a district heating system are performed. Mass, energy and exergy balance equations are formed for the boilers and its components. In the boilers, energy or heat losses are examinated, and the biggest of these is identified as the heat loss of flue gases. Energy and exergy efficiencies of the heating system are researched, and the energy, exergy flow diagrams are illustrated by specifying locations of irreversibilities. According to the results of the analyses, the ratio of flue gas energy and exergy losses in the boilers are 16.81% and 6.14%, respectively. The energy and exergy efficiencies of the boilers are found to be 82% and 32.78%. The location, where the maximum of the irreversibility in the boilers is noticed as combustion chamber, and adiabatic combustion temperature is calculated as 1846°C.

Study of ethanol dehydrogenation reaction mechanism for hydrogen production on combustion synthesized cobalt catalyst

Cobalt nanoparticles synthesized via solution combustion synthesis were used to study the decomposition mechanism of ethanol for hydrogen production. Thermodynamic studies were conducted on the synthesis of cobalt nanoparticles using cobalt nitrate as a metal precursor in presence of different reducing agents; hydrazine, glycine, urea and citric acid. Thermodynamic results along with experimental characterizations show that the type and amount of fuel influence the adiabatic combustion temperature and the gases released during synthesis process affecting nanoparticle size, porosity and microstructure. The synthesized nanoparticles were activated by passing H2 at 300 °C inside the reaction chamber before being used for studying the reaction pathway of catalytic dehydrogenation of ethanol. These studies indicate that cobalt catalyst is selective for aldehyde and acetate species along with the formation of H2, H2O and CO2. Production of methane was also observed on cobalt surface at 400 °C. The spent catalyst nanoparticles were characterized after the reaction using XRD, SEM and TEM to analyze the particle size and its morphology. Results indicate a growth in particle size due to sintering, and carbon formation on the catalyst surface due to coking during ethanol dehydrogenation reaction.