Ignition Temperature Research Articles

Experimental and computational (Chemical Kinetic + CFD) analyses of Self-Recuperative annular tubular porous burner for NH3/CH4 -air Non-Premixed combustion

Ammonia is now being explored as a potential gas turbine fuel because of its renewable and carbon-free nature. Ammonia combustion possesses various limitations, such as high NO emissions, low burning velocity, and high auto-ignition temperature. Moreover, dual-fuel combustion approaches can be used to mitigate these drawbacks. However, the limitations of available information about the resulting emissions are insufficient to encourage widespread adoption. In this work, an NH3/CH4-air fueled self-recuperative high aspect ratio annular tubular porous burner is developed for gas turbine power applications. In this burner, an annular zone surrounds the combustion chamber to preheat the incoming air, while two perforated discs are mounted between the combustor and annular zone for uniform distribution of air. Eight Zirconia foams (4 of 10 PPI and 4 of 20 PPI) are stacked at the upstream side of the combustor. Experimentally, air preheat temperature, combustor exit temperature, NO, and CO emissions are analyzed and measured for various ammonia addition (0–41 % by weight) percentages, equivalence ratio of 1.0, and heat inputs of 17 & 21 kW for 10 PPI and a combination of 10 and 20 PPI porous foams. A preheated air stream coming from the annular zone speeds up fuel dissociation and helps in stabilizing the flame on the upstream side of the combustor. Combustor exit temperatures are lower in sandwich cases of 10 + 20 PPI than the porous foams of 10 PPI. However, with porous foams of 10 PPI, the air preheat temperature is higher. The insertion of porous foams shows better recirculation of heat and stable combustion is observed for higher percentages of ammonia and higher thermal inputs. The OH radicals are distributed for larger areas inside the dumb combustor, while for porous combustion, it is distributed near the porous foams. The porous sandwich cases of 10 + 20 PPI shows higher combustion efficiency compared to 10 PPI and without porous cases. The chemical kinetic analysis shows that the HNO and HCO radicals act as the main intermediate channel for NO and CO production.

Advanced wrought Mg-4.5Al-2.5Ca-0.02Mn (at%) alloys with exceptional balance of high thermal conductivity, yield strength, ductility, nonflammability, and corrosion resistance

Advanced wrought Mg-Al-Ca-Mn alloys were developed, demonstrating an outstanding array of technical advantages due to the remarkably high negative mixing enthalpy of an Al and Ca pair. This was achieved through meticulous optimization of alloy composition, heat treatment procedures, and extrusion parameters. The primary alloy under consideration was designated as Mg-4.5Al-2.5Ca-0.02Mn (at%). While maintaining a low density of 1.76 g/cm3, this alloy exhibited an exceptional properties profile, comprising a high thermal conductivity up to 124 Wm−1K−1 (approximately 79% of pure magnesium), a high tensile yield strength of 397 MPa (surpassing the high-strength aluminum alloy 7075-T6, by 25% in specific tensile yield strength), a notable tensile elongation of 5.5%, and remarkable nonflammability with a high ignition temperature of 1355 K. Finally, its corrosion resistance was twice that of the AZ91D alloy. The microstructure of the developed alloy system comprised α-Mg, eutectic C36 and C14 compounds, and precipitated C15 compound. The enhanced thermal conductivity was attributed primarily to the purification of the α-Mg matrix, facilitated by C15 plate precipitation during the heat treatment process. The superior mechanical properties were associated with the refinement of the α-Mg phase grain structure and the uniform dispersion of fine compounds achieved through extrusion. Based on the findings derived from this experimental study, a novel approach to designing multifunctional magnesium-based alloys has been formulated; that is, high thermal conductivity and high strength are attainable in plastically deformed Mg alloys composed of element pairs with a negatively high mixing enthalpy.

Kestabilan Pencucuhan Hidrogen dalam Persekitaran Gas Adi dalam Enjin Pencucuhan Mampatan

Hydrogen fuel promises a high engine efficiency and the ability to eliminate harmful emissions in an internal combustion engine. However, the ignition stability of hydrogen in compression ignition engine is unstable due to the high-auto ignition temperature of hydrogen. Noble gases such as argon, krypton and xenon have a larger molecular weight compared to nitrogen. Therefore, replacing nitrogen with noble gases appears to be a promising option due to their high specific heat ratio. This paper aims to investigate the ignition stability in a heavy molecular noble gases atmosphere in a CI engine. In this study, Converge CFD software simulates a singlecylinder compression ignition engine model based on the Yanmar NF19SK engine parameters. Hydrogen combustion in a noble gas atmosphere resulted in low ignition stability when operated at low intake temperature. Based on this study, we found that increasing intake temperature improves the ignition stability. As a result, argon is the most preferable among other noble gases. Nevertheless, future research should investigate the other noble gases’ capability under different parameters to improve the engine's thermal efficiency.

Uniformly Dispersed Nano Pd-Ni Oxide Supported on Polyporous CeO2 and Its Application in Methane Conversion of Tail Gas from Dual-Fuel Engine

The development of catalysts for low-temperature methane combustion is crucial in addressing the greenhouse effect. An effective industrial catalyst strategy involves optimizing noble metal utilization and boosting metal–metal interaction. Here, the PdNi-H catalyst was synthesized using the self-assembly method, achieving the high dispersion and close proximity of Pd and Ni atoms compared to the counterparts prepared by the impregnation method, as confirmed by EDS mapping. The XRD and TEM results revealed Pd2+ and Ni2+ doping within the CeO2 lattice, causing distortions and forming Pd-O-Ce or Ni-O-Ce structures. These structures promoted oxygen vacancy formation in CeO2, and this was further confirmed by the Raman and XPS results. Consequently, the PdNi-H catalyst demonstrated an excellent redox ability and catalytic activity, achieving lower ignition and complete methane burning temperatures at 282 and 387 °C, respectively. The highly dispersed PdNi species played a pivotal role in activating methane for enhanced redox ability. Additionally, the narrow size distribution range contributed to more vacancies on the surface of CeO2, as confirmed by the XPS results, thereby facilitating the activation of gas phase oxygen to form oxygen species (O2−). This collaborative catalytic approach presents a promising strategy for developing efficient and stable methane combustion catalysts at low temperatures.

A numerical study of hetero-homogeneous ignition of hydrogen/air mixture over platinum

The study numerically investigates the hetero-homogeneous ignition of H2/air jet over Pt surface by using 2D stagnation flow model. The surface ignition temperature is predicted to increase with the incident equivalence ratio φ due to H2 self-inhibition, but the post-ignition surface temperature does not follow the monotonic trend. It peaks at φ = 0.43, where the differential diffusion between H2 and O2 maximizes surface consumption, thereby most effectively inhibiting the shift to homogeneous ignition. The homogeneous ignition is facilitated at φ = 2.5, where the gas composition and temperature are suitably combined for ignition. Flames are then established above the surface and their variation in term of shape and strength are evaluated in conjunction with jet φ and speed.

Experimental Tests on In Situ Combustion Using Dynamic Ignition Simulation System in High-Temperature and High-Pressure Conditions

The study of crude oil oxidation characteristics is fundamental to the design of ignition in situ combustion. Experimentation is the most crucial method for studying the oxidation characteristics of crude oil. Aiming to address the challenges posed by high temperature, high pressure, and rapid temperature changes during the combustion of crude oil, a dynamic simulation system for high-temperature and high-pressure ignition is designed. In order to study the oxidation characteristics of the crude oil ignition process, we conducted experiments using a high-temperature and high-pressure dynamic ignition simulation device. The experiments focused on determining the ignition point of crude oil under different pressure conditions, oil–water ratios, heating rates, gas injection rates, and other relevant characteristics. The kinetic model for the oxidation process of crude oil ignition was established. The kinetic parameters were calculated for different ignition conditions and the apparent activation energy for each oxidation stage was determined. Additionally, the stability of in situ combustion was evaluated under various ignition parameters. The results show that the Arrhenius curves for crude oil exhibit noticeable differences in the HTO (high-temperature oxidation) and LTO (low-temperature oxidation) regions. The curves demonstrate good linearity in the HTO region, with correlation coefficients exceeding 0.9. Moreover, the apparent activation energies in the HTO region range from 8.01 to 26.7 kJ/mol. The apparent activation energies and finger front factors were calculated for the HTO stage under different pressure conditions. The results showed that, as the pressure increased, the autoignition point, inflection point temperature, and apparent activation energy of the crude oil decreased. This suggests that increasing the pressure can enhance the HTO of the crude oil. The spontaneous ignition point of the crude oil exhibited an upward trend as the heating rate increased. Additionally, the maximum temperature during the combustion process generally increased with the heating rate, reaching a maximum temperature of 453.1 °C. The tests demonstrated that the simulation system is capable of real-time monitoring and recording of oxidation parameters during the combustion process of crude oil. This system can provide essential data for project implementation and numerical simulation.

Carbon neutrality with ammonia: An analysis of its feasibility as a fuel for diesel engines fuelled with spirulina microalgae and oxygenated additives

Ammonia has emerged as a promising gaseous fuel for replacing conventional fossil fuels and achieving carbon neutrality. This research explores the viability of using ammonia as a fuel in compression ignition diesel engines operating in dual-fuel mode. The study investigates the performance and emission characteristics of diesel engines fueled with ammonia, microalgae-based biodiesel, and their combinations, with the addition of Fe2O3 nanoparticles to enhance combustion efficiency. A series of experiments were conducted using various blends of ammonia, biodiesel, and nanoparticles in a single-cylinder engine. The objective was to assess the impact of ammonia and biodiesel on thermal efficiency and carbon-based emissions. Comparative analysis revealed that ammonia-based fuels exhibited higher brake thermal efficiency and lower carbon emissions compared to traditional diesel fuel. The combination of ammonia, biodiesel, and nanoparticles resulted in an 8.5% increase in thermal efficiency compared to diesel fuel. However, the fuel consumption increased by 18% due to the lower energy density and higher viscosity of the biodiesel blends. Furthermore, the study examined the emissions profile of the tested fuels. The use of ammonia and nanoparticles led to significant reductions in carbon monoxide, hydrocarbon, and smoke emissions. However, there was a slight increase in nitrogen oxides and carbon dioxide emissions, regardless of engine loading conditions. It was observed that the emission of NOx was influenced by combustion delay and autoignition temperature. To mitigate NOx emissions, optimizing the combustion delay and avoiding premixed combustion phases are crucial. Based on the findings, the study concludes that ammonia has the potential to serve as a viable substitute for diesel fuel in engines. Ammonia-based fuels exhibit higher brake thermal efficiency and lower carbon emissions. Future research should focus on optimizing combustion parameters to minimize NOx emissions, thereby facilitating the widespread adoption of ammonia in diesel engines and contributing to the decarbonization of the transportation sector.

Toward Zero Carbon Emissions: Investigating the Combustion Performance of Shaped Microcombustors Using H2/Air and NH3/Air Mixtures

The research effort in the microcombustor field has recently increased due to the demand for high-performance systems in microelectromechanical and micro power generation devices. To address rising concerns about pollutants from fossil sources, zero-carbon fuels such as hydrogen (H2) and ammonia (NH3) have been considered as an alternative in microcombustion processes. In a microcombustor, the surface area-to-volume ratio is much higher compared to conventional combustion systems, resulting in faster heat transfer rates and more intense combustion reactions. However, achieving efficient mixing of fuel and an oxidizer in a microcombustor can be challenging due to its small size, particularly for highly reactive fuels like H2. For NH3, challenges in microcombustion involve a low reactive, high ignition temperature (923 K vs. 793 K of H2) and high concentration of NOx combustion products. Therefore, studying the performance of these fuels in microcombustors is important for developing clean energy technologies. In this paper, to explore features of non-premixed NH3/air and H2/air combustion in micro-scale combustors, an Ansys Fluent numerical investigation was conducted on a Y-shaped microcombustor. Results show that for combustion with H2, stationary flames can be achieved even at lower equivalence ratios. Additionally, the pollutants generated from H2 in the flame are generally twice those of NH3. The overall efficiency of the microcombustor is two times greater for NH3 conditions than for H2 conditions.

Hot surface ignition of H2-air and CH4– H2-air mixtures for various equivalence ratios and heating Rates

Gaseous mixtures ignite when they come in contact with a surface with the ignition threshold temperature of the mixture. The hot surface ignition of fuels like hydrogen poses a safety threat due to its wide flammability range and high diffusivity. The present study numerically investigates hot surface ignition of H2-air and CH4/H2/air mixtures using detailed chemistry. The effects of the equivalence ratio (φ), composition and heating rate on the ignition threshold temperature of the mixture are studied. At rich mixture conditions, the ignition occurs at the side of the heated surface (glow plug). On the other hand, the lean mixtures ignite at the top of the heated surface. The variations in heating rates significantly affect the ignition temperature of rich mixtures. In contrast, the ignition temperature of the lean mixture does not show any considerable deviation concerning the variation in heating rates. The phenomenon of puffing flame is observed at lean extinction limits of H2-air mixtures. Lower ignition thresholds are observed in CH4/H2/air mixtures with high concentrations of H2. Mixtures having higher CH4 concentrations show higher ignition thresholds. The role of local equivalence ratio and heat release rate on the ignition characteristics has been studied to predict the behaviour of ignition kernel at various mixture conditions.

Experimental and modeling study of the N, N-dimethylformamide pyrolysis at atmospheric pressure

As a polar solvent, N, N-Dimethylformamide (DMF) is a potential source of volatile organic compounds during industrial processing. The potential energy surface and pressure-dependent rate coefficients of DMF primary and secondary thermal decomposition were theoretically investigated by automatic ab initio calculations. A singlet aminohydroxycarbene route generating CO is found to be the most energetically favored channel among the unimolecular initiation reactions with a tight transition state. A kinetic model was proposed for DMF pyrolysis prediction and validated against the speciation data newly obtained from synchrotron vacuum ultraviolet photoionization mass spectrometry in a flow reactor within 773 K–1048 K and literature data in a jet stirred reactor within 450 K–900 K at atmospheric pressure. Satisfactory agreements were obtained for the major intermediates and products, but the model failed to capture the formation of some oxygenated compounds, possibly due to the missing reaction pathway for bimolecular addition. During pyrolysis, DMF is mainly consumed by the hydrogen abstraction reaction as the relatively high CN bond energy hinders the barrierless homolytic cleavage. Unlike aldehydes where the carbonyl site is favored, H-abstraction from DMF methyl sites is prevalent, although the acylamino group readily undergoes decarbonylation and β-scission forming oxygenated and nitrogenous parts. Consequently, CO and HCN are the major pyrolysis products. Besides, by incorporating essential high temperature kinetics, extended validation was conducted against the available intermediate temperature autoignition delay times (1000–1350 K, 2 bar) and laminar burning velocity data, and the reason for the discrepancy between the model prediction and experiments was inferred according to the sensitivity analyses.

Enhancing Multiple Properties of a Multicomponent Mg-Based Alloy Using a Sinterless Turning-Induced Deformation Technique

A magnesium-based multi-component alloy (MCA), Mg70Al18Zn6Ca4Y2, was successfully synthesized using the Turning-Induced Deformation (TID) method, with promising improvements in multiple properties such as damping capabilities, hardness (11% to 34% increase), and strength (5% to 15% increase) over its conventional cast and extruded equivalent which has already been established as a high-performance MCA exhibiting superior mechanical properties over other Mg-based materials while retaining acceptable ductility. This new TID-based MCA comes only at a slight compromise in the aspects of ductility, ignition resistance, and corrosion resistance, which was previously observed in other TID-based materials. In addition, the general microstructure and secondary phases of this MCA were retained even when using the TID method, with only minimal porosity (<1%) incurred during the process. Furthermore, the ignition temperature of the TID Mg70Al18Zn6Ca4Y2 remained very high at 915 °C, positioning it as a potential Mg-based material suitable for aerospace applications with a high ignition resistance. This is tantamount to a successful application of TID to yet another class of Mg-based materials and opening the door to future explorations of such materials.

Effect on the oxidation characteristic at lignite of two types of endogenous microorganisms from coal

In recent years, coal biotechnology has gained considerable popularity due to its economic, eco-friendly, and sustainable advantages, which offer a novel perspective and pathway for the development of green technologies aimed at preventing and controlling coal spontaneous combustion (CSC). Two endogenous microorganisms from lignite were succeeded in extracting in this work, namely Aspergillus and Bacillus velezensis. Subsequently, the effect of these microorganisms on the microscopic structure and macroscopic oxidation characteristics of coal was investigated by X-ray diffraction, Fourier-transform infrared spectroscopy, and thermogravimetric analysis. The results revealed that both Aspergillus and Bacillus velezensis treatments altered the microcrystalline structure of the coal, disrupting the aliphatic hydrocarbon structure and oxygen-containing functional groups of the coal molecules. Particularly, the OH − O hydrogen bond of two kinds of microbial treatment coal samples content respectively decreased significantly by 17.29 % and 11.06 % compared to the raw coal sample. However, the effects of different microorganisms on coal varied. Thermodynamic behavior demonstrated that the critical temperature of the two treated coal samples was delayed by 29.44 °C and 26.62 °C, and the ignition temperature was delayed by 11.31 °C and 5.18 °C. Overall, all characteristic temperature points of the Aspergillus group were delayed, but the maximum weight loss rate temperature and the burn-out temperature of the Bacillus velezensis group exhibited slight advancement. The thermal mass loss characteristics also changed during the oxidation combustion stage. In addition, the average activation energies of oxidized combustion stage calculated by the Kissinger-Akahira-Sunose method were 74.26 kJ/mol and 78.61 kJ/mol, respectively, and 82.41 kJ/mol and 86.15 kJ/mol for the Friedman method, which were both increased compared to the raw coal. The results indicate that both Aspergillus and Bacillus velezensis have effects with varying degrees on the coal oxidation characteristics. It can be observed that the effect of treatment with Aspergillus is better than Bacillus velezensis from the overall changes in characteristic temperature points. This work lays the foundation for investigating the effect of microbial action on the oxidative properties of CSC.

Study on the catalysis of copper-based compounds on coal spontaneous combustion and its mechanism

ABSTRACTTo study the effect of the copper element in coal on the spontaneous combustion process of coal, corresponding copper-containing compounds were added to the coal-based on their occurrence state, and thermodynamic experiments and in-situ diffuse reflectance infrared spectroscopy experiments were conducted. Thermodynamic oxidation experiments have shown that the catalytic effects of Cu (NO3)2, CuCl2, CuCl, and Cu2O on three types of coal with different degrees of metamorphism are mainly reflected in the accelerated oxidation stage. After adding copper-containing compounds, the ignition temperature of coal decreased by 22.1°C to 134.4°C, the heat release increased by 1.33 to 3.19 times, and the CO emission and oxygen consumption rate also increased. CuCl has the greatest impact on the ignition point temperature of coal and increases the oxygen consumption rates of DNH and TS by 2.32 and 1.51 times that of raw coal. CuCl2 has the strongest catalytic effect on coal oxidation heat release. Through in-situ diffuse reflectance infrared spectroscopy experiments, it was found that the reaction rate of fatty hydrocarbons in the oxidation process of three types of coal with the addition of copper-containing compounds increased to 1.3–3 times that of raw coal, and the oxidation rate of oxygen-containing functional groups also significantly increased, while the cracking temperature of aromatic structures significantly decreased. This is because copper ions, as strong free radicals, induce free radical chain reactions in coal and exhibit a strong promoting effect on the coal oxygen reaction process.

A journey through space and time in the Godbert-Greenwald furnace: The evolution of a dust cloud particle size distribution

Minimum Ignition Temperature (MIT) characterizes the ignition sensibility of a dust cloud. This work assesses the role of a standard Godbert-Greenwald furnace in the agglomeration/deagglomeration and fragmentation phenomena. Several organic powders and different dispersion pressures were tested. The average residence time varied from 120 to 330 ms according to the amount of powder injected and the pulse pressure. Entanglement was observed for coarser cellulose particles, while surface cohesion forces characterised the agglomerates of finer cellulose, glucose and ascorbic acid. The latter was characterised by fragmentation, especially at 0.5 and 1 bar(g). Biot, Pyrolysis and Damköhler numbers were used to analyse the effects of cellulose agglomeration and deagglomeration. At 600 K, the pyrolysis is the rate-limiting step, but from 700 K, the external heat transfer becomes the rate-limiting step, which would not happen without agglomeration. Due to the particle size distribution evolution, but also to turbulence and residence time variation, MIT can vary by 50 °C.

Analyzing the gas temperature of a hydrogen jet fire in a compartment with the Fire Dynamics Simulator

This study presents a method to simulate hydrogen jet fire using the Fire Dynamics Simulator (FDS). To avoid modeling an actual nozzle, high-speed Lagrangian particles released from a virtual nozzle are introduced to simulate released hydrogen. The capability of this FDS model to predict gas temperature is validated by comparing simulation results with five existing experiments in a rectangular steel compartment with an open end. The effects of relevant parameters prescribed in the FDS model on the gas temperature are also analyzed, including numerical parameters (auto-ignition exclusion zone, offset, particle count, and grid) and physical parameters (particle velocity, spray angle, and auto-ignition temperature). The results show that gas temperatures near the nozzle are sensitive to these parameters. Based on the grey relational analysis, the auto-ignition temperature is the least important parameter to predict gas temperatures, while the grid is the most significant parameter for gas temperatures near the ceiling.

The thermal behavior during the co-combustion of bituminous coal and oil palm trunk hydrochars

ABSTRACT Utilizing oil palm trunk (OPT) residue as a co-fuel in coal-fired plants offers an environmentally favorable solution to agricultural waste disposal and fossil fuel combustion impacts. This study investigates the potential of hydrochar from OPT (HTC-OPT) as a coal-like solid fuel for co-combustion. The combustion characteristics of coal, HTC-OPT, and their blends (10–50% HTC-OPT) were analyzed via thermogravimetric analysis with heating rates ranging from 10 to 30°C/min. The Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS) models were employed to explore co-combustion interactions and kinetic parameters. Results reveal enhanced combustion efficiency with HTC-OPT addition to coal. Higher HTC-OPT ratios correlate with increased maximum combustion rates, ignition and comprehensive combustibility indices, and decreased ignition and burnout temperatures. Additionally, blended fuels exhibit a proportionally synergistic co-combustion interaction. Both KAS and FWO models indicate similar trends in activation energies, with the lowest values (49.94 kJ/mol for KAS and 60.90 kJ/mol for FWO) at a 10% HTC-OPT ratio.

Poultry manure combustion parameters to produce bioenergy: A thermogravimetric analysis by isoconventional models and machine learning

Poultry manure has immense potential to generate bioenergy to supply some of producers’ electrical consumption. However, if desired, the combustion of this biomass requires the investigation of important thermal parameters for its efficient and automated industrial-scale application. This study determined combustion parameters such as ignition and burnout temperatures, activation energy, and combustibility indices by thermogravimetric analysis under two approaches: isoconventional models with a set of differential and integral equations and previously trained and validated machine learning models. Poultry manure combustion ignition and burnout temperatures were 212.28 and 443.94, 214.30 and 452.70, and 223.31 and 464.09 °C for 10, 25 and, 20 °C min−1 heating rates, respectively. The combustion index calculated from these temperatures was of 4.78, 6.13, and 4.22 × 10−7. Activation energy was calculated based on isoconventional models, whose values were 99.11 (Friedman), 117.78 (FWO), and 107.50 kJ mol−1 (KAS). Isoconventional models adequately represented mass degradation as a function of temperature. Moreover, after training and testing, our machine learning models (neural networks, decision trees, and random forests) satisfactorily described the combustion of poultry manure, enabling the optimization of parameters such as ignition and burnout temperatures. Poultry manure combustion showed interesting thermal characteristics that can be optimized by machine learning.

Study on the thermal reaction characteristics and kinetics of coal and coal gangue coexisting spontaneous combustion

In the hope of exploring the effect of coal gangue left in goaf on coal spontaneous combustion, the variations of thermal effects and free radical parameters during coexisting spontaneous combustion of coal and coal gangue were tested, and kinetic at different heating stages were calculated. The following beneficial findings were obtained. For the mixed samples, the heat flow curve, ignition temperature, and free radical concentration all decline with the increase of coal gangue content, and the free radical parameters exhibit periodic changes with increasing temperature. Both the experimental value of thermal effect and free radical concentration with coal and coal gangue mixture during the spontaneous combustion process are higher than the calculated value. The calculation results of kinetic show that at the endothermic stage, the activation energies of the mixed samples decline with the increase of coal gangue, and the experimental value of activation energy is greater than the calculate value; at the exothermic stage, the case is exactly the opposite. Furthermore, due to the higher reactivity of coal gangue groups and stronger thermal conductivity, the coexistence of coal and coal gangue spontaneous combustion reaction is promoted. Resultantly, coal spontaneous combustion is normally more threatening in gangue-containing goafs.

Classification and characteristics of ammonia combustion in well stirred reactor

The present work investigates the regime classification and chemical characteristics of the premixed ammonia combustion in a well stirred reactor (WSR). Three combustion regimes can be classified based on the lowest autoignition and highest extinction temperatures and the reacting temperature increment, which are: (i) flameless combustion (FLC); (ii) high temperature combustion (HTC); (iii) traditional combustion (TC). When introducing the upper limit of NOx emission into the classification, MILD combustion can be defined as a sub-regime of FLC. Relative to the methane counterpart, the ammonia combustion is found to exhibit larger FLC and smaller HTC regimes delimited by the inlet temperature and oxygen fraction. It is also revealed that the MILD combustion of ammonia differs significantly from its burning under other regimes in heat production and NO formation mechanisms. In the MILD combustion, multiple reactions dominate the heat production while the DeNOx route greatly reduces the NO formation. Contrarily, in other combustion regimes, heat is controlled by one or two specific reactions while notably the Extended Zeldovich route dominates the NO destruction. Moreover, the working temperature controls the top reactions for both heat and NOx productions, regardless of different combustion regimes.

Clean solid fuel production through co-hydrothermal carbonization of polyvinyl chloride mat and wheat straw with acid assistance: Conversion mechanism and combustion performance

Hydrothermal carbonization (HTC) of polyvinyl chloride (PVC) to produce high-value-added hydrochars as a solid fuel alternative can play a pivotal role in carbon sequestration and energy supply. However, there is unclear for the interaction mechanism and combustion performance of co-hydrochars derived from PVC waste and biomass. In this study, waste PVC mats (PVCM) mixed with wheat straw (WS) were as feedstocks to prepare the co-hydrochars by the acid-catalyzed co-HTC at different hydrothermal temperatures and mass ratios. The presence of WS enhanced the PVCM substitution and prevented the condensation of the PVCM-derived hydrochar aggregation. In turn, PVCM played a stimulative role in the WS decomposition. Meanwhile, the interactions were improved sufficiently in the acidic mediums. The fuel properties and combustion behavior of co-hydrochars were elevated by valid interactions between PVCM and WS. The co-hydrochar obtained using co-HTC at a mass ratio of 1:1 under 240 °C (HC-240–1:1) exhibited the optimal higher heating value (32.72 MJ/kg), splendid dechlorination efficiency (97.41%) as well as worthy fuel ratio (0.89). The combustion process of HC-240–1:1 was more facile and consistent as a result of the elevated ignition and burnout temperatures along with reduced activation energies. Furthermore, the liquid phase products were recycled to assess the reusability. The process water expedited the process of co-HTC, which was confirmed by the improved HHV (32.72 MJ/kg to 39.71 MJ/kg) and mass yield (30.73% to 32.44%). The strategy of PVC waste mixed with biomass through the acid-catalyzed co-HTC was considered a promising way to produce environmentally friendly solid fuels, providing some theoretical basis for the commercialization of co-HTC.