Low-temperature Ignition Research Articles

An experimental and kinetic modeling study of the ignition of methane/n-decane blends

An experimental and kinetic modeling study of the combustion of methane/n-decane blends is performed. Ignition delay times (IDTs) of the pure fuels in addition to their blends are measured using both a shock tube and a rapid compression machine at three different methane/n-decane (mol%) compositions of 99/1 (M99D1), 95/5 (M95D5), and 80/20 (M80D20) in ‘air’, over the temperature range of 610–1495 K, at a pressure of 30 bar. A new chemical kinetic mechanism, GalwayMech1.0, is proposed to describe the combustion of these blends and is validated against the new IDT data including 1st-stage and total IDTs as well as existing experimental n-decane data available in the literature. Sensitivity analyses reveal that H-atom abstraction from n-decane by methyl peroxy radicals (CH3Ȯ2) play an important role in promoting blend reactivity at intermediate temperatures, which is not observed for pure n-decane. By investigating the effect of the n-decane concentration on the ignition characteristics, we found that the low ignition temperature limit is extended with increasing n-decane content with a non-linear reactivity-promoting effect. Flux analyses reveal that CH4 oxidation in the blends is initiated via CH4 + ȮH = ĊH3 + H2O, driven by the ȮH radicals produced from the early oxidation of n-decane and the CH3Ȯ2 radicals formed from CH4 oxidation which subsequently accelerates nC10H22 consumption via H-atom abstraction. Comparisons of CH4/nC10H22 and H2/nC10H22 blends from a previous study demonstrate consistently higher reactivity for hydrogen blending compared to methane and that the magnitude of this increase diminishes with increasing n-decane content. Finally, we also compare our current model predictions of our new data with other n-decane models available in the literature.

Research on the impact of nitromethane on the combustion mechanism of ammonia/methanol blends

Ammonia/methanol co-combustion is considered an effective liquid-liquid blending strategy to enhance the combustion performance of ammonia. However, both methanol and ammonia have high latent heats of vaporization, which necessitate significant heat absorption during the vaporization process. This often results in excessively low ambient temperatures before the ignition of the mixture, negatively affecting low-temperature ignition and combustion. To improve the combustion characteristics of ammonia/methanol blends, this study proposes the addition of nitromethane, forming a ternary blend of ammonia/methanol/nitromethane to enhance fuel performance. To evaluate the impact of nitromethane on the combustion mechanism of ammonia/methanol blends, this study utilizes synchronous vacuum ultraviolet photoionization mass spectrometry to analyze the oxidation reactions of the ammonia/methanol/nitromethane blends. Based on the Brequigny model, cross-reactions involving C-N bonds and reactions related to nitromethane were incorporated for model modification, resulting in the newly modified model, termed A-M. Pathway and sensitivity analyses, as well as ignition delay time simulations, were conducted to further understand the combustion process. The results indicate that the addition of nitromethane to the ammonia/methanol blend lowers the initial reaction temperature from 860 K to 740 K and increases nitrogen oxide (NOx) concentrations at 1050 K. At 800 K, nitromethane reduces the conversion of NH2 to NH3, thereby enhancing ammonia consumption and altering the NOx consumption pathway. Furthermore, at 1020 K, 98.6 % of H2NO reacts with H to form NH2, which is a crucial species in ammonia regeneration. Additionally, at 1020 K, 90.8 % of nitromethane decomposes through the reaction CH3NO2(+M) = CH3 + NO2(+M), contributing to increased NOx emissions. Moreover, the incorporation of nitromethane significantly reduces the ignition delay time of ammonia/methanol blends, demonstrating its potential to improve the overall combustion performance of these mixtures.

Optimization of the full-load combustion schemes of n-butanol/biodiesel reactivity-controlled compression ignition (RCCI) toward high-efficiency and low-emission engines

Biodiesel and n-butanol, as popular alternative fuels, can be used in advanced reactivity-controlled compression ignition (RCCI) engines for efficient and clean combustion. However, the complex interactions between n-butanol and biodiesel, as well as the best combustion schemes at different loads, remain poorly understood. Given this, the objective of this paper is to identify optimal fuel organizations for n-butanol/biodiesel RCCI engines across different load scenarios by combining engine simulation with a global optimization algorithm, explore the potential synergies of control parameters, and analyze microscopic dual-fuel interactions based on the integrated average reaction path analysis. Results show that the optimal scheme at low load employs almost homogeneous fuel-air mixtures at elevated temperature atmosphere above 390 K, with n-butanol energy share exceeding 96% and optimal biodiesel injection timing between −70 and −50 °CA. Higher n-butanol ratio coupled with increased intake temperature improves engine performance. For mid load, biodiesel injection timing is retarded to −55 to −30 °CA, and biodiesel proportion is increased to introduce reactivity stratification, while maintaining its energy share below 20% to mitigate NOx emissions. Notably, biodiesel density is identified as the primary physical property influencing NOx formation. At high load, a split combustion scheme involving premixing and subsequent diffusion combustion is optimal. The physical effects of n-butanol addition minimally impact the low-temperature ignition of biodiesel, while its chemical effects significantly defer the low-temperature reactivity. The reaction path analysis reveals that n-butanol competes with biodiesel for OH radical consumption, with a large proportion of OH and HO2 consumed in the cyclic reactions of nC4H9OH and nC4H8OH. Adjusting the reactivity stratification affects the reaction state of n-butanol entrained by the biodiesel jets. Higher reactivity gradient intensifies biodiesel reactions to induce the pyrolysis of the involved n-butanol through nC4H8OH => 2C2H4 + OH, therefore resulting in more staged heat release.

Research on mechanical properties of HTPB propellants

Abstract Slat propellants with different sizes and shapes are designed to investigate the strength criteria of HTPB propellants. According to the calculation and simulation results, with the increase of multiple, the designed size slat specimens can achieve equivalent biaxial tensile stress ratios of 1:2, 1:2.5, 1:3, 1:3.5, and 1:4 under uniaxial tensile conditions. The biaxial mechanical properties of the slab with a stress ratio of 1:2 were tested at low temperatures (25°C, −30°C, −50°C, and 0.4 s−1, 4.0 s−1, 14.29 s−1, 42.86 s−1). It was found that as the temperature and the strain rate rise, an increase is observed in the maximum tensile strength and the initial modulus, a decrease is observed in the maximum elongation of the propellant, and the strength envelope is constructed according to the typical mechanical parameters: the strength envelope of HTPB propellant increases as the temperature decreases. The research findings are expected to provide statistical support for the analysis of the structural integrity of HTPB propellants under low-temperature ignition.

High spatiotemporal resolution optical measurements of two-stage ignition and combustion in Engine Combustion Network Spray D flames

This study explores flame structures and combustion dynamics in high-pressure n-dodecane fuel sprays, focusing on the formation and consumption of formaldehyde (CH2O) during autoignition and the development of poly-aromatic hydrocarbons (PAH) as soot precursors. These processes are crucial for optimizing combustion efficiency and reducing emissions. However, traditional approaches, which rely on single-shot measurements or ensemble-averaged visualizations, often overlook critical early-stage processes during low-temperature ignition. To overcome these challenges, we employed an innovative high-speed planar laser-induced fluorescence (PLIF) technique at 50 kHz using a pulse-burst Nd:YAG laser system with an excitation wavelength of 355 nm. This approach, applied for the first time to Engine Combustion Network (ECN) Spray D flames, provides unprecedented insights into the combustion processes at varying ambient temperatures and oxygen concentrations. Additionally, simultaneous high-speed schlieren imaging at 100 kHz was used to visualize spray penetration, first-stage ignition, and thermal expansion zones. Our findings reveal that, similar to Spray A flames, CH2O forms in cold, fuel-rich zones well upstream of the combustion zone. However, in Spray D flames, the schlieren signal softening observed in the jet's head does not lead to complete disappearance, and the CH2O signal is absent from the full head of the spray. During the second-stage ignition, CH2O consumption accelerates due to high-temperature reactions, leading to a significant reduction in its signal. Unlike the mushroom-shaped structure seen in Spray A flames, Spray D flames exhibit a quasi-steady PAH phase structure, with lean peripheral mixtures insufficient for soot precursor formation. Notably, reducing ambient oxygen concentration to 13 % while maintaining or increasing temperature prolongs the presence of CH2O, highlighting its influence on ignition dynamics and oxidation processes in dodecane spray flames. This study provides new insights into the combustion mechanisms of high-pressure sprays and offers valuable data for developing next-generation combustion technologies, including models, aimed at improving efficiency and reducing emissions.

Hypergolic fuel impacting a gelled oxidizer wall: Droplet dynamics, heat release, ignition, and flame analysis

The combination of high-concentration solutions of hydrogen peroxide, known as High Test Peroxide (HTP), with the green fuel composed of tetramethylethylenediamine, dimethylaminoethanol, and methanol (TMEDA/DMEA/MeOH, 1:1:1 vol%), catalyzed by 1 wt% of copper chloride dihydrate, has significant potential for space hypergolic propulsion applications in terms of performance and safe operation. Besides the well-known and mature propulsion systems adopting liquid and solid propellants, gel propellants also present interesting characteristics that can be better explored to enable the creation of alternative propulsive systems. The present work employed HTP at 98 wt% with 6 wt% of fumed silica as a gelling agent to create gelled HTP (GHTP). Droplets of the green fuel impinged on a layer of GHTP placed over a glass slide, acting as a solid oxidizer, mimicked an element of a new hybrid gel/liquid hypergolic propulsion system. Data from infrared and visible light cameras enabled a detailed analysis of the dynamics of a reactive droplet impinging on a gelled oxidizer wall, as well as the heat release, ignition, and flame spread of the hypergolic GHTP/green fuel pair under open-air conditions. The heat release was observed to be distributed across concentric annular areas for both the fuel surrogate and the fuel with catalyst, before and after ignition, demonstrating a strong correlation with non-reactive droplet fluid dynamics, which was corroborated by spread diameter analysis processed from visible image data. Vapor and Ignition Delay Times (VDT and IDT) were found to be as low as 4 and 17 ms, respectively, for the highest droplet impact velocity and catalyst concentration. The reaction rate in the gas phase, considering the flame spread area, showed a dependency of both impact velocity and catalyst concentration, with the latter exhibiting a more pronounced and clear effect. The surface temperature ranges where first vaporization and ignition occurred were 60 °C ∼ 70 °C and 120 ∼ 170 °C, respectively, which is close to the boiling point of methanol and the auto-ignition temperature of TMEDA. This finding, along with the chemical mechanisms in the gas phase related to the presence of a catalyst in the fuel, may be important for hypergolic ignition. The relatively low ignition temperatures and the short ignition times represent additional advantages of the present hypergolic combination for propulsion applications.

Performance of a Methanol-Fueled Direct-Injection Compression-Ignition Heavy-Duty Engine under Low-Temperature Combustion Conditions

Low-temperature combustion (LTC) concepts, such as homogeneous charge compression ignition (HCCI) and partially premixed combustion (PPC), aim to reduce in-cylinder temperatures in internal combustion engines, thereby lowering emissions of nitrogen oxides (NOx) and soot. These LTC concepts are particularly attractive for decarbonizing conventional diesel engines using renewable fuels such as methanol. This paper uses numerical simulations and a finite-rate chemistry model to investigate the combustion and emission processes in LTC engines operating with pure methanol. The aim is to gain a deeper understanding of the physical and chemical processes in the engine and to identify optimal engine operation in terms of efficiency and emissions. The simulations replicated the experimentally observed trends for CO, unburned hydrocarbons (UHCs), and NOx emissions, the required intake temperature to achieve consistent combustion phasing at different injection timings, and the distinctively different combustion heat release processes at various injection timings. It was found that the HCCI mode of engine operation required a higher intake temperature than PPC operation due to methanol’s low ignition temperature in fuel-richer mixtures. In the HCCI mode, the engine exhibited ultra-low NOx emissions but higher emissions of UHC and CO, along with lower combustion efficiency compared to the PPC mode. This was attributed to poor combustion efficiency in the near-wall regions and engine crevices. Low emissions and high combustion efficiency are achievable in PPC modes with a start of injection around a crank angle of 30° before the top dead center. The fundamental mechanism behind the engine performance is analyzed.

Biochar as a Sustainable Alternative to Pulverized Coal: Comprehensive Analysis of Physicochemical Properties, Combustion Performance, and Environmental Impact

This study comprehensively evaluates the potential of biochar as a substitute for high‐rank pulverized coal in various aspects including physicochemical properties, combustion performance, environmental emissions, and application costs. Biochar, characterized by its small particle size, reduced emissions, high volatility, elevated calorific value, and facile combustion, emerges as a promising alternative fuel to pulverized coal. Despite a lower ignition temperature, biochar demonstrates superior burnout efficiency and combustion kinetics, as indicated by its lower activation energy compared to pulverized coal. Moreover, considering China's substantial energy consumption, the substitution of coal with biochar could significantly reduce CO2 and SO2 emissions, making it a viable strategy for mitigating environmental pollution. In addition, the application cost of biochar is not higher than that of pulverized coal. This study underscores the feasibility and effectiveness of utilizing biochar as a sustainable alternative to high‐rank pulverized coal, offering valuable insights into cleaner and more efficient energy utilization.

Preparation of high-energy Al-Li alloy powders with enhanced compatibility and combustion performance by dense fluorosilane polymer composite coating

The superior combustion heat, lower ignition temperature, and enhanced combustion efficiency of aluminum–lithium (Al-Li) alloy powders have garnered significant research attention in relation to Al powders. However, the inadequate compatibility between Al-Li alloy powders (especially when Li > 3 wt%) and propellant components limits its application in the development of composite solid propellants. This study focuses on the surface-coating active Al-4.3Li (wt.%) alloy powder using a composite fluorosilane coupling agent to improve compatibility and combustion performance. A coating layer with a thickness of 30–40 nm was successfully formed on the surface of Al-4.3Li alloy powder through interactions involving Al-F, Al-O-Si, and Li-O-Si bonds, thereby achieving remarkable hydrophobicity. The heat release increased by 7.5 %, while the ignition delay time of the alloy powder decreased by nearly 200 ms, resulting in a significantly enhanced combustion performance in relation to that of the original Al-4.3Li alloy powder. Moreover, the modified Al-4.3Li alloy powder exhibited better compatibility, and no cracks or bubbles were observed in the cross-section of the propellant containing modified Al-4.3Li metal fuel. This study provides an effective approach for utilizing Al-Li alloy powders in solid propellants, which is of great significance for the development of high-energy propulsion systems.

Reaction characteristics of Al–Mg alloy fuels with heterogeneous oxidation shell structures

Al–Mg alloy fuels are the most widely used Al-based alloy fuel in energetic material systems owing to their low ignition temperature and fast reaction. However, their surface oxide layer structure and oxidation, ignition, and combustion mechanisms differ from those of single-metal fuels. Furthermore, insufficient information has been reported on Al–Mg alloy fuels. In this study, Al–Mg alloy fuels were formed by introducing Mg into Al via centrifugal atomization. The microstructure and thermal reaction characteristics of the Al–Mg alloy fuel were evaluated. The ignition and combustion characteristics of the Al–Mg alloy fuels were monitored via single-particle ignition. When the Mg content was increased from 5 % to 40 %, a typical core–shell structure formed, the oxide shell thickness increased from 4.50 to 6.41 nm, and the content of the internal alloy compounds gradually increased. The surfaces of the Al–Mg alloy fuel particles with different Mg contents exhibited heterogeneous oxidation shells. Compared to Al powder, the Al–Mg alloy fuel exhibited better melting and oxidation peak temperatures and higher oxidation weight gain. As the Mg content was increased, the combustion of the Al–Mg alloy fuel intensified with more severe microexplosions and a shorter combustion time. The microexplosion of the Al–Mg alloy fuel was elucidated by theoretical calculations, and its combustion mechanism was proposed. The detailed description of the oxide layer structure, oxidation, and combustion of the Al–Mg alloy fuel provides a reliable explanation of its energy release mechanism in energetic material systems.

Effects of wall confinement on flame topologies and lean blowout characteristics of partially premixed DME/air flames in a gas turbine model combustor

Dimethyl ether (DME) is a promising alternative fuel for gas turbines, considering its renewable nature and potential for large-scale synthesis from CO2 feedstock. However, there are limited studies on the swirl combustion characteristics of DME, particularly regarding the stability performance. This work investigates the effects of wall confinement on flow, mixing, and lean blowout (LBO) characteristics of partially premixed DME/air swirl flames in a gas turbine model combustor. Flow and flame macrostructures are captured using particle image velocimetry and planar laser-induced fluorescence (PLIF) measurements, respectively. The results show remarkable differences in flame topologies between unconfined and confined flames, especially the formation of inner recirculation zone and outer recirculation zone. The LBO limits are measured over various Reynolds numbers and flame dynamics approaching LBO are captured using 10 kHz OH* chemiluminescence imaging. Unconfined flames have unexpectively lower LBO limits (∼0.4) than the LBO limits of confined flames (over 0.5). Approaching LBO, unconfined flames display a quiet blowout mode featuring swirling spiral blow-off behaviors. In contrast, confined flames exhibit a violent blowout mode featuring large-scale quasi-instability behaviors, including periodic events of local extinction, flame lift-off, and re-ignition. Based on the numerical simulations and simultaneous OH- and CH2O-PLIF measurements, the large discrepancy in the measured LBO limits between the two configurations is found to result from different re-ignition processes related to the low-temperature ignition before the final blowout. These findings highlight the crucial roles of wall confinement in determining the stable flame topologies, LBO characteristics, and mechanisms driving the LBO physics for partially premixed DME/air swirl flames.

Co-pyrolysis of plastic waste and eucalyptus waste wood for fuel pellets production: A study of fuel, mechanical, and combustion characteristics under varying binder proportion

The study explores the effect of varying molasses proportions as a binder on the characteristics of densified char obtained through the slow co-pyrolysis of plastic waste and Eucalyptus wood waste (Waste low-density polyethylene – Eucalyptus wood (WLDPE–EW) and Waste Polystyrene – Eucalyptus wood (WPS–EW)). Pyrolysis was conducted at 500 °C with a residence time of 120 min, employing plastic to wood waste ratios of 1:2 and 1:3 (w/w). The focus was on how varying the proportion of molasses (10–30 %), influences the physical and combustion properties of the resulting biofuel pellets. Our findings reveal that the calorific value of the pellets decreased from 28.94 to 27.44 MJ/Kg as the molasses content increased. However, this decrease in calorific value was compensated by an increase in pellet mass density, which led to a higher energy density overall. This phenomenon was attributed to the formation of solid bridges between particles, facilitated by molasses, effectively decreasing particle spacing. The structural integrity of the pellets, as measured by the impact resistance index, improved significantly (43–47 %) with the addition of molasses. However, a significant change in the combustion characteristics depicted by lower ignition and burnout temperatures were observed due to decrease in fixed carbon value and increase in volatile matter content, as the proportion of molasses increased. Despite these changes, the pellets demonstrated a stable combustion profile, suggesting that molasses are an effective binder for producing biofuel pellets through the densification of char derived from the co-pyrolysis of plastic and Eucalyptus wood waste. The optimized molasses concentration analyzed through multifactor regression analysis was 16.96 % with 28 % WLDPE proportion to produce WLDPE–EW char pellets. This study highlights the potential of using molasses as a sustainable binder to enhance the mechanical and combustion properties of biofuel pellets, offering a viable pathway for the valorization of waste materials.

A Low-Noble-Metal Ru@CoMn2O4 Spinel Catalyst for the Efficient Oxidation of Propane.

Noble metals have become a research hotspot for the oxidation of light alkanes due to their low ignition temperature and easy activation of C-H; however, sintering and a high price limit their industrial applications. The preparation of effective and low-noble-metal catalysts still presents profound challenges. Herein, we describe how a Ru@CoMn2O4 spinel catalyst was synthesized via Ru in situ doping to promote the activity of propane oxidation. Ru@CoMn2O4 exhibited much higher catalytic activity than CoMn2O4, achieving 90% propane conversion at 217 °C. H2-TPR, O2-TPD, and XPS were used to evaluate the catalyst adsorption/lattice oxygen activity and the adsorption and catalytic oxidation capacity of propane. It could be concluded that Ru promoted synergistic interactions between cobalt and manganese, leading to electron transfer from the highly electronegative Ru to Co2+ and Mn3+. Compared with CoMn2O4, 0.1% Ru@CoMn2O4, with a higher quantity of lattice oxygen and oxygen mobility, possessed a stronger capability of reducibility, which was the main reason for the significant increase in the activity of Ru@CoMn2O4. In addition, intermediates of the reaction between adsorbed propane and lattice oxygen on the catalyst were monitored by in situ DRIFTS. This work highlights a new strategy for the design of a low-noble-metal catalyst for the efficient oxidation of propane.

Four-channel catalytic micro-reactor based on alumina hollow fiber membrane for efficient catalytic oxidation of CO

The traditional automotive catalytic converter using commercial ceramic honeycomb carriers has many problems such as high back pressure, low engine efficiency, and high usage of precious metals. This study proposes a four-channel catalytic micro-reactor based on alumina hollow fiber membrane, which uses phase inversion method for structural molding and regulation. Due to the advantages of its carrier, it can achieve lower ignition temperature under low noble metal loading. With Pd/CeO2 at a loading rate of 2.3% (mass), the result showed that the reaction ignition temperature is even less than 160 °C, which is more than 90 °C lower than the data of commercial ceramic substrates under similar catalyst loading and airspeed conditions. The technology in turn significantly reduces the energy consumption of the reaction. And stability tests were conducted under constant conditions for 1000 hours, which proved that this catalytic converter has high catalytic efficiency and stability, providing prospects for the design of innovative catalytic converters in the future.

Thermogravimetric Analysis of Eucalyptus Leaves as An Alternative Fuel for Rural Areas

The utilization of biomass waste as a substitute for conventional energy sources has gained popularity, and one possible source is the litter generated by eucalyptus plantations. The present study used thermogravimetric analysis (TGA) gain insight into the thermochemical characteristics of eucalyptus leaves. It was identified by heating the sample in a nitrogen environment from ambient temperature to 850oC at a rate of 10 oC/minute. Eucalyptus leaves have a high volatile matter (VM) content and a calorific value (CV) of 17.26 MJ/kg, according to the ultimate and proximate analysis. Additionally, the TGA results showed that eucalyptus leaves had a lower ignition temperature than other biomasses. Eucalyptus leaves began to devolatilize at 119 oC, reaching a peak temperature of 326 oC, and losing 68% of their weight as a result.

Copper–Cobalt Oxide Nanoparticles with Tailored Cobalt Oxidation State and Lattice Oxygen Vacancy for Low-Temperature Ignition of Ammonium Dinitramide Monopropellants

Copper–Cobalt Oxide Nanoparticles with Tailored Cobalt Oxidation State and Lattice Oxygen Vacancy for Low-Temperature Ignition of Ammonium Dinitramide Monopropellants

Highly energetic formulations of boron and polytetrafluoroethylene for improved ignition and oxidative heat release

Boron (B) is desirable for energetic applications due to high gravimetric and volumetric energy densities. However, their use is limited because the native oxide shells on their surfaces limit oxidation and heat release by acting as a diffusion barrier and dead weight that does not contribute to heat release during oxidation. This paper reports a facile and efficient method of blending B with perfluoro additives to obtain materials with augmented heat release. We use polytetrafluoroethylene (PTFE) as a fluorine source that reacts with the oxide layer exothermally and use thermochemical analysis to identify the optimum composition of PTFE to extract high energy from B as a result of synergistic oxidation and fluorination reactions. The reduction in ignition temperatures of B is also observed due to its blending with PTFE. In this work, we determined B/PTFE blends with lower ignition temperature and higher oxidative heat release. These effects are due to the gasification of native surface oxide by fluorine via exothermic reactions that facilitate the enhanced reactions in the exposed metal core by eliminating the kinetic/thermodynamic barrier in the diffusion of the oxidizer to the B particle core. The study demonstrates the optimized formulation of highly energetic blends of B/PTFE for energetic applications.

Experimental and simulation study of diesel/methane/hydrogen triple-fuel combustion progression in a heavy-duty optical engine

Experiments were carried out in an optical engine, and the effects of hydrogen ratio on the combustion process of diesel/methane/hydrogen triple fuel combustion with 5% diesel fuel ratio were studied. The natural photometric images of the combustion process were recorded by a high-speed camera. Combined with the optical experimental results, the combustion process of methane and hydrogen mixture ignited by trace diesel oil was simulated. The development process of in-cylinder temperature, OH group and combustion components during combustion with different hydrogen ratios was studied. It is found that the increase of hydrogen ratio promoted the combustion, the ignition delay time and combustion duration were significantly reduced, and the heat release stage of combustion was also advanced. When the second derivative of the heat release rate is the largest, a low temperature ignition point is formed at the edge of the cylinder at first, and the flame expands with the increase of temperature in a short time. With the increase of intake pressure, the ignition delay period decreases at the same hydrogen ratio. High hydrogen ratio leads to more NOx emissions due to higher combustion temperature, and CO and CH4 emissions decrease with the increase of hydrogen ratio.

Smart Predictor for Spontaneous Combustion in Cotton Storages Using Wireless Sensor Network and Machine Learning

The splendid technological inventions supersede many traditional agricultural monitoring systems. In the last decade, a variety of new techniques and tools are proposed to monitor storage areas, which provide more safe and secure storage for different crops. The term storage area monitoring is supposed to check and avoid fire hazards, whereas numerous other hazards also need attention. One such hazard to cotton storage is spontaneous combustion, a process by which an element having comparatively low ignition temperature (hay, straw, peat, etc.) starts to relieve heat. In the presence of spontaneous combustion and lack of oxygen, if cotton catches any sparks from bales or physicochemical heat to ignite, the combustion can convert in to smoldering, and it can last up to several days without being discovered. Consequently, the actual fire occurs, cotton silently smoldering which not only affects cotton quality but also became the reason of big fire event. Many researchers propose valuable tools and techniques based on laboratory methods and modern techniques as well for detection and prevention of security hazards in storages. However, there is no standalone efficient tool/technique to monitor the storage area for spontaneous combustion. In current research, we propose an efficient wireless sensor network (WSN) and machine learning- (ML-) based storage area monitoring system for early prediction of spontaneous combustion in the cotton storage area. The WSN is used to collect real-time values from storage field by different combinations of sensors and send this over the network, where data is processed to identify spontaneous combustion and distribute the prediction results to the end user. The real-time data collection and ML-based analysis make the system efficient and reliable. The efficiency of the current system is verified by presenting two groups of cotton stored with different conditions. The results showed that the proposed system is able to detect spontaneous combustion well in time with a 95% accuracy rate.

Relationship between low-temperature oxidation activity and second-stage ignition delay: Experimental insights on n-pentanol / hydrogenated catalytic biodiesel blends

N-pentanol exhibits promising potential as a sustainable and eco-friendly biomass energy source. However, certain challenges such as ignition difficulty and unstable combustion exist. This study investigates the influence of low-temperature auto-ignition of n-pentanol/HCB (Hydrogenated Catalytic Biodiesel) blends on ignition and combustion characteristics and evaluates the correlation between low-temperature oxidation and second-stage ignition delay. Results show a linear positive correlation between the HCB content in n-pentanol and its low-temperature oxidation reactivity. The stronger the low-temperature oxidation activity of the blends, the shorter the second-stage ignition delay of blends. When the HCB content in blends is below 40 %, the low-temperature oxidation rate initially increases and then decreases. However, the low-temperature oxidation rate increases again when the HCB content exceeds 40 %. Moreover, the relationship between the initial CO2 generation rate and the HCB blending ratio follows an Exp exponential function under different critical compression ratios. Beyond 43.7 % HCB, an acceleration in the high-temperature combustion rate owing to an increase in the low-temperature oxidation rate again. In addition, the minimum ignition limit of n-pentanol/HCB blends was identified with 40 % HCB blends closely resembling diesel conditions and 50 % HCB blends showing a lower ignition limit, characterized by a critical temperature and pressure of 517.3 K and 8.66 bar, respectively. Furthermore, two distinct conditions for the minimum ignition boundary region of n-pentanol/HCB blends were defined, offering practical insights. In summary, a blend with a 50 % HCB ratio provides a promising solution for the low-temperature ignition and stable combustion of n-pentanol, addressing the challenges of simultaneous use in internal combustion engines.