Initial Stage Of Combustion Research Articles

Flame propagation analyses of aluminium coated with various concentrations of stearic acid based upon elementary reaction simulation

Coated aluminium, a novel material, has been employed in a multitude of applications. However, the thermal physicochemical properties of certain coated materials can elevate the ignition sensitivity and exacerbate explosion hazard of coated aluminium powder, posing serious thermal risks throughout the production, processing and storage. To render a theoretical basis for the prevention and mitigation of stearic acid-aluminium (SA-Al) dust explosion accidents, the flame propagation and elementary reaction sensitivity characteristics of SA-Al dust with various stearic acid concentrations were analysed by experiment and numerical simulation. Results showed that as the SA coating concentration increased from 0 % to 20 %, the flame propagation behaviour changed from dust-driven to gas-driven combustion, the flame luminous intensity and temperature abated gradually, and the average flame propagation velocities and free radical accumulation tended to first increase and then decrease, reaching maximum value in the 10 % SA-Al explosion. There may be synergistic combustion effect during Al cores and SA coating, which reflected in that a series of branch chain reactions of H and OH of SA in the initial combustion stage resulted in the accelerating melting and the forward explosion reaction kinetics of Al cores. Concurrently, the accelerated combustion of Al intensified the pyrolysis and oxidation of unburned SA-Al particles.

Characterization of pressure oscillations and combustion noise of hydrogen reactivity-controlled compression ignition (RCCI)

Knock and combustion noise are the main reasons limiting the increase in hydrogen (H2) replacement rate in H2 reactivity-controlled compression ignition (RCCI). This study aims to identify the knock-dominated mechanism and elucidate the characteristics of knock and combustion noise of H2 RCCI operated at a broad range of parameters through the combined analysis of the heat release profile and pressure oscillations. The results indicated that under inhomogeneous heat release conditions, the onset of pressure oscillations is mainly attributed to the local fast heat release at the initial combustion stage, but for the conditions with relatively homogeneous and high-reactivity mixture, the pressure oscillations are primarily excited by the end-gas autoignition. Compared with the single injection strategy, the double injection strategy with the first and second start of injection of −60 and −15°CA ATDC (SOI1/2 = −60/-15°CA ATDC) can effectively mitigate the pressure oscillations and shorten the propagation period of pressure waves. However, as the SOI2 is advanced to −30°CA ATDC, the pressure oscillations dramatically increase, because the enhanced fuel reactivity of premixed H2 exacerbates the end-gas autoignition. The results of frequency analysis of in-cylinder pressures show that with the increase in inhomogeneous combustion, the first resonance frequency reduces. As the intake pressure (Pin) is raised from 1.2 to 1.6 bar, the first resonance energy increases, since the elevated in-cylinder temperature associated with the piston compression during the compression stroke enhances the propagation and development of pressure waves. The high-order resonance is closely related to the autoignition of end gas with higher fuel reactivity. Overall, the combustion noise shows a good linear correlation with peak heat release rate for all the points investigated in this work, but the linearity of H2/polyoxymethylene dimethyl ethers RCCI is better than that of H2/diesel RCCI. Moreover, with the increase in Pin, the engine noise associated with the piston compression increases.

Oxidation progress and inner structure during single micron-sized iron particles combustion in a hot oxidizing atmosphere

The present experimental study focuses on the determination of the oxidation progress and internal structures during the combustion of single iron particles using combined in-situ optical measurements and ex-situ material examination of rapidly quenched particles. Narrowly sieved iron particles with a mean diameter of 49µm are ignited and burn in the hot exhaust of a premixed CH4/O2/N2 flat flame with remaining 20vol% O2, provided by a laminar flow reactor with well-defined thermal and flow boundary conditions. During particle combustion, key parameters of oxidation progress are determined optically in a time-resolved manner, such as the time-resolved particle surface temperature and the reaction time relative to the instant of the particle peak temperature. Furthermore, individually burning particles are rapidly quenched at different combustion stages and then extracted from the exhaust gas using an isokinetic extraction probe. The bulk composition of the quenched particles with respect to α-Fe and its three oxides FeO, Fe3O4, and Fe2O3 is determined using Wide-angle X-ray Scattering and 57Fe Mössbauer Spectroscopy. Combining the information obtained from in-situ and ex-situ measurements, it is shown that iron particles oxidize rapidly to FeO during the initial stage of combustion, followed by a much slower oxidation to Fe3O4 as the particles cool down. The peak particle temperatures are measured during the fast initial oxidation. Finally, particles sampled from representative positions of the oxidation process are analyzed by Energy-Dispersive X-ray Spectroscopy and Focused Ion Beam Scanning Electron Microscopy, revealing different particle morphology and internal structures. For the first time, the clear presence of an oxide shell and iron-core structure in quenched particles suggests that liquid iron and liquid iron oxide are layered during liquid phase combustion, if the particle remains within the miscible gap.

Experimental study and chemical equilibrium calculation on the mineral transformation of high-alkali coal under oxy-fuel condition

The study aimed to study the mineral transformation of high-alkali coal to address the ash-related issues in oxy-fuel combustion. However, the traditional ashing method alone is inappropriate to study the mineral transformation at the initial stage of coal combustion due to the high ashing temperature. Hence, both the plasma ashing method (<200 °C) and traditional ashing method (600–1200 °C) were employed in this research to prepare the ash samples for characterization. The plasma ashing method is an efficient way to determine the original minerals in coal because it can consume the organic matter at low temperature. The recirculation of flue gas in oxy-fuel combustion can lead to high SO2 and H2O concentrations, while their influences on mineral transformation need to be clarified. In this work, SO2 and H2O were injected into CO2 to simulate the recycled flue gas (RFG). Furthermore, the chemical equilibrium calculation was conducted besides multiple experimental tests to acquire more comprehensive information of mineral transformation. The results show that high sodium and calcium contents are determined in these high-alkali coals, and two of them are rich in iron. In O2/CO2 atmosphere, some sodium (e.g. NaCl) volatilizes into the gas phase and the others converts into aluminosilicates (e.g. NaAlSi3O8) during the heating process. The calcium salts (mainly CaCO3 and CaSO4) decompose and produce silicates, aluminosilicates, and magnesium silicates. The major iron-containing minerals are identified as FeS, FeS2, and Fe2O3. Both FeS and FeS2 are oxidized into Fe2O3 below 600 °C. Moreover, the kaolinite (Al2Si2O5(OH)4) in raw coals decomposes at low temperature (<600 °C). In O2/RFG atmosphere, the additions of SO2 and H2O enhance the sulfation of AAEMs (alkali and alkaline earth metals) and delay the decomposition of sulfates. The productions of some silicates, aluminosilicates, and magnesium silicates of AAEMs are inhibited to varying degrees, and there could be complicated salts containing sulfur (e.g. hauyne). The transformations of iron-containing minerals are little related to the presences of SO2 and H2O. This work obtained the transformations of main minerals in high-alkali coal under O2/CO2 and O2/RFG conditions, which helps to address the ash-related issues.

Minimizing Redundancy and Data Requirements of Machine Learning Potential: A Case Study in Interface Combustion.

The machine learning potential has emerged as a promising approach for addressing the accuracy-versus-efficiency dilemma in molecular modeling. Efficiently exploring chemical spaces with high accuracy presents a significant challenge, particularly for the interface reaction system. This study introduces a workflow aimed at achieving this goal by incorporating the classical SOAP descriptor and practical PCA strategy to minimize redundancy and data requirements, while successfully capturing the features of complex potential energy surfaces. Specifically, the study focuses on interface combustion behaviors within promising alloy-based solid propellants. A neural network potential model tailored for modeling AlLi-AP interface reactions under varying conditions is constructed, showcasing excellent predictive capabilities in energy prediction, force estimation, and bond energies. A series of large-scale MD simulations reveal that Li doping significantly influences the initial combustion stage, enhancing reactivity and reducing thermal conductivity. Mass transfer analysis also highlights the considerably higher diffusion coefficient of Li compared to Al, with the former being three times greater. Consequently, the overall combustion process is accelerated by approximately 10%. These breakthroughs pave the way for virtual screening and the rational design of advanced propellant formulations and microstructures incorporating alloy-formula propellants.

Evaluation Indicator for the Spontaneous Combustion of Biomass Fuel Pellets and Its Self-Ignition Control

ABSTRACT To investigate the spontaneous combustion characteristics of biomass fuel particles, spontaneous combustion processes of 10 biomass samples were simulated by programmed-heating and continuous oxidation experiments. Analysis results indicated that during the very initial stage of spontaneous combustion (<90 °C), each biomass fuel particles merely yielded CO at 0–20 ppm, while the subsequent exponential growth of gas emissions tended to exhibit a significant variation on spontaneous liability. Due to the diversity of biomass material sources, its spontaneous combustion tendency is not only determined by internal properties, but also influenced by external factors such as particle size, ventilation rate, moisture, etc. There are many factors affecting the spontaneous combustion tendency, which cannot be analyzed accurately and quantitatively. Therefore, it is necessary to propose a stable indicator based on thermal analysis to objectively evaluate the tendency of biomass spontaneous combustion. A scientific index was proposed to precisely assess the spontaneous combustion tendency of biomass materials. Specifically, the activation energy (E) at the O2 gain stage was adopted as the priority criterion: If E < 70 kJ/mol, the biomass was defined to be highly flammable; if 70 ≤ E ≤ 80 kJ/mol, the biomass was considered to be prone to self-ignition; and if E > 80 kJ/mol, the biomass was regard as non-spontaneous combustion. Besides, data from cross-point temperature tests fundamentally support the reliability of mentioned evaluation methodology. In fire-extinguishment experiments, a conventional approach, such as suffocate by self-extinguishing, only reduced the temperature to 99.9–238.7°C. The comparison of extinguishing materials such as gaseous N2/liquid nitrogen, CO2, and C3HF7 revealed that extinguishing fire with C3HF7 exhibited a dramatic advantage at burning temperature > 500°C. However, fire extinguishing with CO2 was more suitable for the spontaneous combustion ignition of biomass at temperature ≤ 300°C.

Experimental study of flame extension lengths and fire pattern lengths induced by the turbulent jet fire impinging on inclined wooden boards

The safety of producing and transporting flammable gas may be compromised by the occurrence of jet fires resulting from pipeline leakage. During such incidents, combustible obstacles can impede the development of vertical jet fires, leading to impingement. Wood, a typical building material, was chosen as a combustible solid for the experiment due to its ability to produce regular fire patterns on its surface when heated, making it useful for fire investigation. A series of experiments were conducted to examine the flame extension length and fire pattern length resulting from a jet fire impinging on inclined wooden boards with different nozzle diameters, inclination angles, and heat release rates. This work showed that, unlike non-combustible boards, the rate of increase in flame extension length beneath a wooden board continues to rise as the heat release rate increases. Additionally, the boards' ability to absorb heat during the initial stages of combustion affects the flame extension length at low heat release rates. This work introduces a new correlation that can predict the length of flame extension under wooden boards, addressing a gap in research on jet fire impingement on combustible ceilings. For the regular fire patterns left by jet fires impinging on wooden boards, a new correlation of fire pattern length with flame extension length for different inclination angles of wooden boards is proposed. Considering the characteristics of turbulence, a novel model for fire pattern length is introduced, incorporating the Karlovitz flame stretch factor, nozzle inner diameter, and fire source-wooden board spacing.

NOx formation mechanism of plasma assisted ammonia combustion: A reactive molecular dynamics study

The effects of ionization ratio (α) on the reaction rate of NH3 combustion and the formation characteristics of NOx are studied by ReaxFF MD, and the formation mechanism of NOX in plasma assisted NH3 combustion are analyzed from the molecular level. It is found that the maximum growth rate of NOX gradually slows down with increasing reaction system temperature. The plasma promotes NOX formation at the initial stage of NH3 combustion, and when the nitrogen-containing radicals are consumed, the non-nitrogen-containing components will inhibit NO formation. When the α is 25%, the NH3 reaction rate reduces slightly. This is attributed that the proportion of NH2/H is the larger at this lower α. The plasma effect at lower α = 25% enhances the N2 formation path from NH3 by the primary reaction pathway of NH3→NH2→NH→NNH→N2, and the intermediate NH consumes some of the NO to form N2 by NH + NO↔HN2O and HN2O↔N2+OH. As α increases to 50%, the plasma leads to the direct generation of NO from NH by NH + OH↔H2NO and H2NO + O↔H2O + NO, which makes the maximum of NO increase.

Study on the synergistic flame-retardancy of phenyl/vinyl siliconesquioxane and aluminum diethyl phosphinate on polyethylene terephthalate

Polyethylene terephthalate (PET), a widely used engineering thermoplastics, is inherently flammable, presenting significant fire risks. Aluminum diethyl phosphinate (ADP) is widely used in PET, while they tend to increase smoke hazards in its flames retardancy. A novel flame-retardant ladder phenyl/vinyl polysilsesquioxane (VPPSQ) acting as both a charring flame retardant and smoke suppressant was introduced into the PET/ADP composites. For PET/ADP6/VPPSQ4, the limiting oxygen index increased to 32.8 % from 23.3 %, and the amount of heat and smoke released was significantly reduced, compared with neat PET. Additionally, the hazard of dripping was eliminated and the UL 94 rating reaches to V-0 level. This work provides a new strategy for eliminating multiple fire hazards of smoke, heat and dripping of PET. The gas phase flame retardancy effect of ADP is primarily present during the initial stages of combustion, with the carbonization action of ADP becoming more crucial during the middle and later stages of burning. However, the char layer formed by PET/ADP is unstable and undergoes further degradation. When VPPSQ is introduced into PET/ADP, the pyrolysis products of VPPSQ, including silicon fragments, SiO2, and graphitized structures, significantly enhance the thermal stability and barrier effect of the char layer.

An Emergency Decision-Making Method for Coal Spontaneous Combustion Based on Improved Prospect Theory

In response to the limited available information during the initial stages of coal spontaneous combustion and the influence of decision makers’ risk preferences on decision-making, this paper proposes an emergency decision-making method for coal spontaneous combustion that integrates grey correlation degree and TOPSIS with an enhanced prospect theory. Firstly, a normalized weighted evaluation matrix is established for the emergency response plan of coal spontaneous combustion, and the entropy method is utilized to determine the weights of various indexes. Then, considering the imperfect rationality of decision makers and their diverse individual risk preferences, they are categorized into three types: risk-seeking type, risk-neutral type, and risk-averse type. The corresponding risk coefficients are determined based on these different types. Positive and negative ideal solutions are taken as reference points, and matrices representing gains and losses are constructed. The grey correlation degree is introduced to calculate both positive and negative prospect values based on these matrices. Moreover, the prospect value for each emergency response plan is calculated, respectively, based on different types of decision makers, and the entropy method is used to assign weights to decision makers according to their respective risk preferences. Consequently, based on these prospect values and the weights, comprehensive prospect values for each emergency response plan are obtained and ranked to identify the optimal one. Finally, in order to validate the effectiveness of our proposed approach, a case study is conducted, and the results obtained from this case study are discussed and compared with those from other methods.

Thermogravimetric experimental study on the co-combustion of coal gangue and polypropylene

To address the challenges posed by the challenging ignition, low volatile content, and high ash content of coal gangue (CG) during separate combustions, a proposed treatment involves mixing CG with polypropylene (PP), offering the potential for centralized treatment. Co-combustion experiments were carried out at varying ratios, and a corresponding model for co-combustion was established. The thermal impact of temperature variations during co-combustion is analyzed, and the kinetic characteristics of the co-combustion process are explored. The findings indicate that the volatile matter released by PP notably decreases the activation energy of the mixed fuel in the initial combustion stage. Co-combustion at different ratios enhances overall combustion, particularly when the PP content is 20 %. At this specific ratio, the temperature-averaged thermal relative coupling coefficients are 1.64 and 2.30 times greater than those at PP contents of 50 % and 80 %, respectively. These results hold significance for the comprehensive utilization of CG.

Quantitative investigation of explosion behavior and spectral radiant characteristics of free radicals for syngas/air mixtures

The combustion characteristics and explosive hazard of syngas (H2/CO)/air mixtures are affected by its exact composition and equivalence ratios. In this paper, the explosion pressure and spectral radiant intensity of free radicals were quantitatively examined for syngas with different H2 proportions ([H2 in syngas] = 0, 30, 50, 70, 100 vol%) and equivalence ratios (φ = 0.8, 1.0, 1.2, 1.4, 1.6, 2.0, 2.5). The results show that the explosion process of syngas/air mixtures can be separated into the initial slow combustion stage, the violent deflagration stage and the deflagration ending stage. The peaks of explosion pressure, pressure rise rate, OH*spectral intensity and rise rate of spectral intensity first increase and then decrease with increasing the equivalence ratio, and they reduce gradually with the decrease of H2 proportion in syngas. The H2 content in syngas greatly affects the heat release and the concentration of excited state OH*, especially for the syngas/air mixtures with smaller proportion of H2. Additionally, the presence of H2 greatly increases the deflagration index and spectral radiant index of OH* for syngas/air mixtures. The average rise rates of explosion pressure and spectral intensity of free radicals are introduced and the coupling model between them is established based on the first law of thermodynamics and the principle of chain reaction. The established model is furthermore verified by the experimental results. It is indicated that there is a linear relationship between average rise rates of explosion pressure and spectral intensity (OH*). The results can be used to improve the combustion efficiency of syngas and to guide theoretically the prevention, mitigation and control of syngas explosions.

Study on combustion stability and flame development of ammonia/n-heptane dual fuel using multiple optical diagnostics and chemical kinetic analyses

Ammonia is considered as one of the most potential clean energy due to its carbon-free structure, which ensures the extensive decrease in global CO2 emissions. However, it has difficulty in using ammonia as a single fuel in actual apparatus due to the low reactivity and slow laminar flame speed. The dual fuel combustion of ammonia and high reactivity fuel is a potential solution, which is expected to address the issues raised by ammonia. Nevertheless, the investigations on the influence of boundary conditions on combustion stability and related mechanisms in dual fuel approach of ammonia and high reactivity fuel are still scarce at present. Therefore, in current study, n-heptane was used as the direct-injected fuel, and the investigations on combustion stability and relevant mechanisms of ammonia/n-heptane dual fuel approach were conducted by using optical diagnostics and chemical kinetic analyses. Results indicate that in n-heptane-only combustion, the premixed blue flames are found in the initial combustion stage. The auto-ignition sites dominated by orange chemiluminescence are generated near the combustion chamber wall in ammonia/n-heptane dual fuel combustion and then the flames develop towards the combustion chamber center. The addition of ammonia inhibits the combustion of n-heptane. The ammonia/n-heptane dual fuel combustion is more sensitive to the change of intake temperature compared with n-heptane-only combustion. The increase of directed-injection pressure from 300 bar to 600 bar and compression ratio from 11 to 14.5 favors the flame development speed. The increase of compression ratio is an effective mode to improve the ammonia/n-heptane dual fuel combustion stability compared with increasing intake temperature and modulating directed-injection strategies. The chemical kinetic analyses indicate that the ignition delay of dual fuel combustion of ammonia and n-heptane is more sensitive to the variations of ambient temperature compared with ambient pressure. Consequently, the changes of ambient temperature on the dual fuel combustion stability of ammonia and n-heptane play a dominant role. In a word, the dual fuel combustion stability of ammonia and n-heptane can be achieved through the collaborative optimization of multiple boundary conditions to reduce the dependence on single factor.

Effect of oxygen-supply on the reburning reactivity of pyrolyzed residual from sub-bituminous coal: A reactive force field molecular dynamics simulation

The lean-oxygen combustion of incompletely pyrolyzed char dominated at the combustion front of coalfield fires. Functional group distributions and carbon micro-crystal dimensions were characterized for developing the molecular model (C184H124N2O16S) of pyrolyzed coal char at 400 °C (TLG P400). The overall combustion process of TLG P400 under various oxygen/fuel ratios (Ω) were simulated in an intuitive approach with ReaxFF. The findings indicated that the primary carbon-containing intermediates transformed from large pieces of aromatic fragments C40+ with self-similarity to heavy components of C15–C40 in initial combustion stage, then to light components of C5–C14 in late stage. With Ω increasing from 1.0 to 5.0, the final carbon conversion was found to rise from 78.50% to 96.32%, while the CO/CO2 ratio in the products sharply decreased from 2.575 to 0.213. The apparent activation energy was calculated as 194.49 kJ/mol for TLG P400 combustion at Ω = 1.0. Higher oxygen concentration enhanced the adsorption proportion of edge carbon, resulting in the generation of unstable intermediates featuring meta- or para-semiquinone. These transformations promoted the detachment of edge carbon and weakened the bottle-neck effect of the single-benzene ring on rapid oxidation. This study provides valuable insights into combustion mechanism and monitoring approaches for controlling coalfield fires.

The effect of coke and soot formation on the bio-oil combustion at high temperatures

Bio-oil shows promising potential as an alternative fuel source. However, the formation of coke and soot during the combustion process hinders its use. This study investigates the formation mechanisms of primary coke, secondary coke, and soot during the initial stage of bio-oil combustion. The relationship between the physicochemical properties and the combustion characteristics of coke and soot is further analyzed to mitigate their adverse effect. It indicates that heavy aromatic compound polymerization plays a dominant role in primary coke formation, while graphitization and aromatic ring growth initially increase and then decrease with increasing temperature. Primary coke obtained at 1000 °C exhibits the highest degree of graphitization but small microscopic size, resulting in poor combustibility. Secondary coke is generated by the recombination reaction and its yield increases with temperature. The intensified reaction results in increased graphitization and decreased microscopic size, further leading to reduced combustibility due to its condensed structure. Soot generated above 1100 °C has low graphitization and combustibility due to short residence time. Based on the analysis, the temperature range around the feeding port is recommended to be controlled in 800–900 °C as it produces less coke and soot with better combustibility.

Combustion behavior and mechanism of TC25 alloy

The combustion behavior and mechanism of TC25 alloy were investigated by titanium fire melt liquid droplet tests. Moreover, the microstructure and element distribution after combustion were analyzed. Results showed that the combustion reaction zone was composed of the oxide zone, melting zone and heat affected zone. The enrichment of alloying elements, such as Si, Zr, Mo, Sn and W at the melting zone/heat affected zone interface played a pivotal role in regulating the interface propagation rate. The diffusion of Al element was the rate-determining step in the initial stable combustion stage, whereas the diffusion of O element became the rate-determining step in the subsequent combustion stage.

Numerical study of the firing, radicals and intermediates in the combustion process of a H2-assisted combustion DISI methanol engine

The firing, radicals and intermediates in the combustion process of a port-injection hydrogen (H2)-assisted combustion direct-injection spark-ignition (DISI) methanol engine were numerically simulated. The engine with port-injection H2 plus direct-injection methanol was tested at 1800 rpm with intake manifold absolute pressure of 68 kPa. AVL-Fire coupling the detailed methanol chemical kinetics modeling with 21 components and 84 elementary reactions was used to simulate in this study. The model calculation results agreed well with the experiments, and the average error is less than 3% and can guarantee other outcomes. The simulation results show that high added H2 ratio (RH2) has higher turbulent kinetic energy in the region closer to the combustion chamber wall. When RH2 is greater than 6%, the formation time of fire core is obviously shortened and the average flame propagation velocity is significantly increased. Increasing RH2, the generation speed and the peak value of H, O and OH radicals increase, and higher concentration of radicals accelerates the diffusion of combustion from the hot flame zone. OH radical is a key reactant, which always plays a decisive role in the process of methanol oxidation. Effect of added H2 on methanol oxidation reaction is reflected in accelerating the initial stage of combustion and ameliorating the intensity of reaction. The mass fractions of HCHO, HCO and CO, as the main intermediate products, all show a trend of increasing first and then decreasing with the crank angle (CA), and their peak values indicate the phase of the most violent reaction. The peak values of HCHO and HCO are all near the top dead center (TDC), which is consistent with the trend of H and OH radicals generation rate. The relationship between consumption rate of methanol and CA shows that the consumption rate of methanol at RH2 = 9% is the earliest and steepest, and most of methanol has been consumed by reaction before TDC. Added H2 accelerates the fire propagation, H2 dominates the process of radical formation and methanol chain reaction, the flame spread period is shortened rapidly, and the effect of added H2 to promote combustion is obvious.

Effects of carbonization on the physical properties and combustion behavior of fiberboard sanding dust pellets

In this study, sanding dust pellets were prepared using a flat-die extrusion molding machine and then carbonized at temperatures ranging from 300 to 600 °C. The density and mechanical compression resistance of pellets carbonized at 400 °C decreased by about 30% and 80%, respectively. Carbonization led to a homogeneous structure in the pellets, with a slight change in the surface area. When the carbonization temperature was increased to 600 °C, the composition and higher heating value (27,732 kJ/kg) of pellets approached the anthracite level. Additionally, 40%–80% of nitrogen in pellets could be removed through carbonization. Thermogravimetric studies indicated that the combustion end temperatures of pelletized samples were delayed at about 500 °C, compared with those of powdered samples. The only main peak of the derivative thermogravimetric analysis for carbonized pellets combustion indicated that the combustion was relatively slow and stable. Kinetic analyses revealed that the apparent activation energy (E) increased during the later combustion stages of the carbonized pellets with increasing carbonization temperature. However, pellets carbonized at 300 °C had the highest E (186,358 J mol−1) in the initial combustion stage, compared with those of other pellets (50,000 to 114,507 J mol−1).

On Initial Stage of Combustion of Acetylene–Oxygen Mixtures in a Tube

On Initial Stage of Combustion of Acetylene–Oxygen Mixtures in a Tube

Blending n-octanol with biodiesel for more efficient and cleaner combustion in diesel engines: A modeling study

Biodiesel has become a popular alternative fuel to fossil diesel. However, compared to conventional diesel engines, the adoption of pure biodiesel often leads to higher NOx though soot emissions can be reduced. In this study, the alcoholic fuel n-octanol was chosen as the blending fuel in biodiesel. The modeling study was carried out to investigate the effects of blending n-octanol on the combustion characteristics and emissions formation process in a diesel engine. At first, a multi-component reaction mechanism involving 115 species and 489 reactions was constructed to better predict the combustion process of biodiesel and n-octanol. This mechanism was then coupled with KIVA-CHEMKIN to implement a three-dimensional simulation of the engine. The developed mechanisms and adopted models were validated under a variety of conditions. At last, to examine the effects of n-octanol, simulations were carried out by gradually increasing the percentage of n-octanol from 0% to 100% with an interval of 10%. Analysis of the simulation results revealed that blending more n-octanol with biodiesel could lead to a prolonged ignition delay. Due to the high latent heat of vaporization of n-octanol, the temperature at the initial stage of combustion can be reduced which subsequently mitigated the formation of NOx. The higher oxygen content of n-octanol was beneficial for the improvement in power output and the decrease of soot emissions. Overall, B20/O80 blends were found to be capable of achieving more efficient and cleaner combustion in the diesel engine at both speeds.