Solid Fuels Research Articles

The sensitivity of health impact assessments of PM2.5 from South African coal-fired power stations

Unabated emissions of precursor gases from coal-fired power stations in South Africa greatly contribute to ambient PM2.5 concentration in the region, but estimates of the number of associated premature mortalities vary vastly. The application of the exposure-response function is one of the reasons for the differences in estimates of premature mortalities; since the relationship between mortality and PM2.5 exposure flattens out at higher PM2.5 concentrations, a smaller number of premature mortalities is calculated if a reduction in PM2.5 concentration occurs at the actual ambient concentration (“avoidable deaths”), while a greater number of mortalities is calculated if other sources are not considered (at low ambient concentrations) (“single-source deaths”). It is more appropriate to attribute deaths to a source in proportion to the contribution made by the source to ambient PM2.5 levels (“attributable deaths”). Total ambient PM2.5 concentrations are extrapolated from 38 ambient monitoring stations in the north-eastern region of South Africa using a regression model based on household socio-economic factors, and PM2.5 concentrations derived from power station emissions are estimated using a reduced-form intake fraction model. It is estimated that there are around 800 attributable premature mortalities per year due to PM2.5 from coal-fired power station emissions in South Africa. The number of premature mortalities is 44% higher when calculating single-source deaths and 53% lower when calculating avoidable deaths. Using the attributable death approach is particularly important in highly polluted areas such as low-income residential areas where households use solid and liquid fuels.

Investigation of Swelling Properties and Liquefaction of Solid Fuels

In this study, the effect of various parameters on the swelling of Edirne Uzunköprü, Edirne Keşan Çanakkale Yeniçirpılar and Bursa Mustafa Kemal Paşa lignites was investigated. In the first part of the study, swelling processes were applied to the lignites. Swelling measurements were made in closed glass tubes using 10 different solvents. Swelling ratios of lignite samples treated with solvents were determined and the dependence of these ratios on the properties of the solvent was examined. In the second part, the original lignite samples, swollen with various solvents, were subjected to soxhlet extraction with THF and the liquid product yields obtained from each sample were determined. Then, the same samples were extracted with toluene under supercritical conditions, and the effects of temperature, pressure, and pre-expansion on the extract yield were investigated. Extract yields of lignite samples swollen with solvents such as THF, TBAH, DMSO, DMF, and EDA were found to be higher than those of other solvents. The common features of these solvents are that they have atoms containing unpaired electrons such as N, O, etc. In addition, it was thought that the high extract yields of solvents with a large and positive difference in the number of donors and acceptors may be related to the breaking of the cross-links in the lignites by the solvent.

Estimation of the coal higher heating value for energy systems relied on ultimate analysis with machine learning techniques

The calorific value of solid fuels, also referred to as the gross calorific value (GCV) or the higher heating value (HHV), is a crucial property for its use as a fuel in energy systems. The HHV of coal as a resource can be predicted by more effective algorithms that use schedule information in engineering, like ultimate analysis, enabling fast decisions about its use as fuel in energy systems. The goal of this research was to acquire a global artificial prediction model relied on an interesting algorithm, a nonlinear model termed multivariate adaptive regression splines (MARS), in addition to the grid search (GS) optimizer, for characterization of coal HHV (output variable) using constituents of coal ultimate analysis: carbon (C), nitrogen (N), oxygen (O), hydrogen (H) and sulphur (S) (5 specific input variables). Moreover, a multivariate linear regression (MLR) and a multilayer perceptron-type (MLP) artificial neural network (ANN) were adjusted to the observed data as well as known empirical correlations for comparison purposes. The current investigation has produced two results. The MARS model is used to first demonstrate the significance (or strength) of each input variable on the coal HHV (output variable). Second, the most accurate predictor of the coal HHV was the MARS–relied approximation. In fact, using this method on coal testing samples resulted in a MARS regression with coefficients of determination and correlation coefficients for the coal HHV estimation of 0.9921 and 0.9960, respectively. The agreement between the data that were observed and those that were predicted using the GS/MARS–relied approximation proved that the latter had performed satisfactorily.

Autoignition of methane/coal particle/air mixture under constant-volume conditions

Autoigniton of methane/air mixture loaded with uniform coal particles is simulated using the Eulerian-Lagrangian method. A zero-dimensional constant-volume approach is employed to investigate the impacts of particle diameter, particle concentration, and initial gas pressure on the two-phase mixture ignition process. Different stages are found from the ignition transient: particle heating, particle/gas thermal runaway, two-phase heat exchanges, and thermal quasi-equilibrium of two phases. Moreover, the ignition delay time of the two-phase mixture changes nonmonotonically with the particle size. Also, as the particle concentration increases, the magnitude of the differences in two-phase mixture ignition delays gradually decreases. At low particle concentrations, the particle temperature rises and then rapidly drops due to burnout of the fixed carbon, while the two-stage gas temperature increase is found. In addition, the two-phase mixture is more easily ignited under high pressure conditions. The particle ignition is more sensitive to pressure change than the gas ignition. An ignition diagram of methane/coal two-phase mixture with various particle concentrations, initial pressure and diameters is determined based on parametric studies. It is shown that particle addition promotes the gas ignition when the particles are small. Moreover, the particles can have inhibitory effects on gas ignition at high particle concentrations, and lower pressure. The results from this study are significant for explosion hazard mitigation implementations and detonation propulsion systems with pulverized solid fuels.

Effect of demineralization on waste tire pyrolysis char physical, chemical characteristics and combustion characteristics

Waste tire carbon black particles (CBp) are the main pyrolysis products of waste tires (WT), and CBp is difficult to use directly. This work mainly focuses on the physicochemical and combustion characteristics of demineralized CBp (DCBp) to explore the resourceful utilization of CBp resources in large quantities. This work also provides a comprehensive comparison with CBp and other carbon-based solid fuels. The results show that most of the minerals in CBp can be removed by chemical demineralization treatment (Ash content of DCBp <0.11 %). DCBp has a more developed pore structure than CBp. The deashing process affects the degree of loosening and stacking of the graphitic carbon microcrystalline structure, and the relative content of oxygen-containing functional groups in CBp to a minor extent. The deashing process leads to a decrease in the relative strength of the cross-linked stable structure and an increase in the disordered structure of carbon in CBp. The volatile fraction to fixed carbon ratio of DCBp is only 0.0467, and a large number of catalytic alkali metal elements and alkaline earth metal elements are removed in the demineralization process, which makes the early combustion of DCBp more difficult. As the combustion reaction proceeds, the internal pores of the particles are opened, and the micropores and mesopores in DCBp provide a larger surface area for the reaction. In addition, the decrease in the relative strength of the cross-linked stable structure and increases in the disordered structure of carbon can increase the intermolecular collision frequency during the combustion process, thus improving the burnout characteristics of DCBp. The above results indicate that DCBp has the potential to be used as fuel for large-scale resource utilization.

Decarbonising of the Indian Cement Industry Through Alternative Fuels – Challenge of Transfer Chute Jamming

The Indian cement industry in COP27 highlighted its commitment to achieving net zero CO2 emission by 2070 made during COP26. The industry is moving towards decarbonisation and has identified various levers to achieve the goal. Fossil fuel replacement by Alternative Fuels (AFs) has been identified as one of the levers. Refused Derived Fuel (RDF), surplus biomass, industrial waste, and other societal wastes, etc., have emerged as potential AFs; however, their use comes with technical challenges like transfer chute jamming due to the wide range of variations in their properties. Jammed transfer chute leads to the breakdown of the entire transportation system and further fluctuation in AFs feeding to the kiln/calciner. Fluctuation in the feed rate of the AFs disturbs the fuel mix ratio (mix ratio of fossil fuel and AFs) and ultimately negatively impacts the process, operation, and quality of the produced cement. Transfer chute design is often overlooked, leading to build-up, blockage, and wear in chutes. Designing of transfer chute is more challenging when handling solid alternative fuels in cement plants, as the properties of these fuels have a wide range of variation where moisture may be as high up to 40%, bulk density may vary from 0.1 to 0.75 tonnes/m3, and particle size ranges from 1 to 100 mm, etc. This study covers a survey to establish which types of AFs, and their characteristics contribute to the chute jamming problem. The outcome of this study shall help the Indian cement industry to consider the appropriate inputs for transfer chute design and selection of the correct alternative fuels and their mix to avoid chute jamming.

Influence of the Composition and Particle Sizes of the Fuel Mixture of Coal and Biomass on the Ignition and Combustion Characteristics

The work determines the characteristics of the processes of thermal decomposition and combustion when heating coal, cedar needles, and their mixtures with different fuel particle sizes. Based on the results of thermal analysis, the following characteristics were determined: the temperature at which the coke residue ignition occurs, the temperature at which the combustion process is completed, and the combustion index. An analysis was carried out of the interaction between the fuel mixture components on the characteristics of their combustion for compositions (50% coal and 50% biomass) with a particle size of 100–200 μm and 300–400 μm. The combustion kinetic parameters of individual solid fuels and their mixtures containing 50% coal and 50% biomass are compared. The activation energy for coal combustion was 60.3 kJ mol−1, for biomass 24.6 kJ mol−1, and for mixture 42.5 kJ mol−1. The co-combustion of coal and biomass has a positive effect on the main combustion characteristics of solid fuels. Fuels with particle sizes of 100–200, 200–300, and 300–400 μm were studied at temperatures of 500–800 °C under heating conditions in a heated airflow. Using a hardware-software complex for high-speed video recording of fast processes, the ignition delay times were determined, the values of which for the considered fuels vary in the range from 0.01 to 0.20 s. Adding 50 wt% biomass with particle sizes of 100–200, 200–300, and 300–400 μm to coal reduces the ignition delay times of mixtures by 55, 41, and 27%, respectively. The results obtained can become the basis for the conversion and design of modern power plants operating on solid fuel mixtures to co-combust coal with biomass.

Sugar Extraction from Secondary Agricultural Waste Biomass Using Hydrothermal Carbonization and Direct Contact Membrane Distillation

Sustainable and renewable sources of liquid and solid fuels are essential to prevent fossil fuel use from damaging the environment. Secondary agricultural residues, which are already transported to food processing centers, have great potential to be converted into biofuels. The wastes from coffee roasting, sugar production, and rice milling have been investigated using hydrothermal carbonization (HTC) to produce aqueous products containing monosaccharides alongside solid biofuels. These sugar-laden liquid products were characterized after pretreating coffee silverskins, sugarcane bagasse, and rice husks with HTC. They were then concentrated using direct contact membrane distillation (DCMD), a low-energy process that can use waste heat from other biorefinery processes. The higher heating value of the solid products was also characterized by bomb calorimetry. The liquid products from HTC of these wastes from food production were found to contain varying concentrations of glucose, xylose, galactose, and arabinose. DCMD was capable of concentrating the liquid products up to three times their original concentrations. Little difference was found among the higher heating values of the solid products after 180 °C HTC pretreatment compared to 200 °C pretreatment. HTC of waste from food processing can provide solid biofuels and liquid products containing sugars that can be concentrated using DCMD.

Disease Burden and Prediction Analysis of Tracheal, Bronchus, and Lung Cancer Attributable to Residential Radon, Solid Fuels, and Particulate Matter Pollution Under Different Sociodemographic Transitions From 1990 to 2030

This study investigated the impact of epidemiologic and sociodemographic changes in tracheal, bronchus, and lung cancer associated with residential radon, solid fuels, and particulate matter. What are the influencing factors of tracheal, bronchus, and lung cancer disease burden attributable to the three pollutants? Data were obtained from the Global Burden of Disease 2019. Age-standardized mortality rate (ASMR) and sociodemographic index (SDI) values were collected from 21 regions, and restricted cubic splines and quantile regression were used to investigate the relationship between ASMR or age-standardized disability-adjusted life years rate (ASDR), and SDI. Additionally, five countries with different SDIs were selected, and the Bayesian age-period-cohort model was used to predict the ASMR trends from 2020 to2030. High SDI quintiles were associated with increased residential radon pollution. The disease burden attributed to these three pollutants was particularly severe in the middle SDI quintiles. Older adults aged 80 to 89 years had the highest age-specific mortality, and the disease burden was greater in male patients than in female patients with these cancers attributed to the pollutants. The highest ASMR attributable to particulate matter when the SDI was 0.7. As the SDI increased, the disease burden caused by radon increased, whereas the burden caused by solid fuels decreased. Projections have indicated a rise in the death burden in patients with this cancer from particulate pollution in China, India, and Uganda over the next decade. The disease burden of tracheal, bronchus, and lung cancer attributed to the three pollutants was influenced by SDI, sex, and age. Older men are more susceptible to be affected. More preventive interventions may be required for men at younger ages to reduce the high death burden of older men. However, it is necessary to give due attention to women in specific countries in the future.

Geospatial determinants of maternal and child exposure to fine particulate matter in Kintampo, Ghana: Levels within the household and community, by surrounding building density and near roadways.

Personal exposure to fine particulate matter (PM2.5) from household air pollution is well-documented in sub-Saharan Africa, but spatiotemporal patterns of exposure are poorly characterized. We used paired GPS and personal PM2.5 data to evaluate changes in exposure across location-time environments (e.g., household and community, during cooking and non-cooking hours), building density and proximity to roadways. Our study included 259 sessions of geolocated, gravimetrically-calibrated one-minute personal PM2.5 measurements from participants in the GRAPHS Child Lung Function Study. The household vicinity was defined using a 50-meter buffer around participants' homes. Community boundaries were developed using a spatial clustering algorithm applied to an open-source dataset of building footprints in Africa. For each GPS location, we estimated building density (500 m buffer) and proximity to roadways (100 m buffer). We estimated changes in PM2.5 exposure by location (household, community), time of day (morning/evening cooking hours, night), building density, and proximity to roadways using linear mixed effect models. Relative to nighttime household exposure, PM2.5 exposure during evening cooking hours was 2.84 (95%CI = 2.70-2.98) and 1.80 (95%CI = 1.54-2.10) times higher in the household and community, respectively. Exposures were elevated in areas with the highest versus lowest quartile of building density (FactorQ1vsQ4 = 1.60, 95%CI = 1.42-1.80). The effect of building density was strongest during evening cooking hours, and influenced levels in both the household and community (31% and 65% relative increase from Q1 to Q4, respectively). Being proximal to a trunk, tertiary or track roadway increased exposure by a factor of 1.16 (95%CI = 1.07-1.25), 1.68 (95%CI = 1.45-1.95) and 1.27 (95%CI = 1.06-1.53), respectively. Household air pollution from cooking with solid fuels in sub-Saharan Africa is a major environmental concern for maternal and child health. Our study advances previous knowledge by quantifying the impact of household cooking activities on air pollution levels in the community, and identifying two geographic features, building density and roadways, that contribute to maternal and child daily exposure. Household cooking contributes to higher air pollution levels in the community especially in areas with greater building density. Findings underscore the need for equitable clean household energy transitions that reach entire communities to reduce health risks from household and outdoor air pollution.

Age-Period-Cohort Analysis of Cardiovascular Mortality Attributable to Environmental Risks in China

This study aimed to analyze changes in cardiovascular disease (CVD) mortality attributable to major environmental risks in China during 1990-2019, and their associations with age, period, and birth cohort. Mortality data were obtained from the Global Burden of Disease Study 2019. Major environmental risks included ambient particulate matter pollution (APMP), household air pollution from solid fuels (HAP), low temperature, high temperature, and lead exposure. Age-period-cohort modeling was used to estimate the overall annual percentage change in CVD mortality (net drift), annual percentage change for each age group (local drift), expected longitudinal age-specific rate (longitudinal age curve), period and cohort relative risks (RRs, period/cohort effects) between 1990 and 2019. Analyses were conducted in 2021-2022. In China, five major environmental risks led to 1.62 million CVD deaths in 2019. Among these risks, the primary contributor to CVD mortality transited from HAP in 1990 to APMP in 2019. There was also an improvement in attributable CVD mortality rates for low temperature and lead exposure during 1990-2019, while an unfavorable trend was noted for high temperature. The longitudinal age curve demonstrated increased attributable CVD mortality rates with age groups for all environmental risks, with similar patterns for both sexes. Period and cohort RRs suggested generally improved risks of attributable CVD mortality for HAP, low temperature, and lead exposure, but worsening risks for APMP and high temperature in both genders, except for period risks after 2010-2014 for APMP in both sexes, period risks after 2000-2004 for high temperature in females, and cohort risks in cohorts born after 1955 for APMP and high temperature in females. Over the study period, there was a significant improvement in attributable CVD mortality rates in China for HAP, low temperature and lead exposure, but an unfavorable trend was noted for APMP and high temperature.

Primary Energy Consumption Patterns in Selected European Countries from 1990 to 2021: A Cluster Analysis Approach

This study delves into the structure of primary energy consumption in European countries, utilizing data from the Eurostat database, and focuses on the years 1990 and 2021. Through cluster analysis, countries were categorized based on their consumption patterns, revealing significant insights into energy security. The findings indicate a discernible shift away from solid fossil fuels, with renewable energy sources witnessing the most substantial growth. Natural gas, serving as a transitional fuel, has seen a rise in consumption, while nuclear energy’s development remained relatively stagnant. Oil, despite its declining share, remains a crucial component in the European energy mix. The study also highlights the challenges and implications of over-reliance on a single energy source, emphasizing the need for a diversified energy strategy. The analysis underscores the importance of diversifying primary energy sources to ensure energy security. While renewable sources are environmentally favorable, their inherent instability necessitates backup from other energy sources. Solid fossil fuels, despite their availability, face challenges due to environmental concerns. Natural gas, while flexible, requires extensive infrastructure and is highly politicized. Nuclear energy, despite its potential as an ideal complement to renewables, faces barriers in terms of investment and public perception. Oil, though convenient, is a fossil source with associated CO2 emissions and largely needs to be imported. In conclusion, the study advocates for a well-diversified set of energy sources tailored to individual country-specific situations, emphasizing the importance of strategic planning in energy consumption to ensure long-term energy security.

Insight into personal exposure characteristics and health effects of PM2.5 and PM0.25-bound PAHs and their derivatives with different heating ways in the Fenwei Plain, China

Personal exposure (PE) to polycyclic aromatic hydrocarbons (PAHs) and their derivatives in particulate matter with two aerodynamic sizes of 2.5 and 0.25 μm (PM2.5 and PM0.25) from rural housewives was studied in the Fenwei Plain, China. A total of 15 households were divided into five different groups based on the type of solid fuel and heating device used, including biomass briquette-furnace (BBF), biomass-elevated Kang (BEK), outdoor lump coal-boiler (OLC), indoor briquette coal-stove (IBC), and electricity (ELE). The PE concentrations of the PAHs and biomarkers in urine collected from the participants were determined. The results showed that the PE concentrations of total quantified PAHs in the biomass group (i.e., BBF and BEK) were 2.2 and 2.0 times higher than those in the coal groups (i.e., OLC and IBC) in PM2.5 and PM0.25, respectively. The housewives who used biomass as fuel suffered from higher potential health impacts than the coal fuel users. The incremental lifetime cancer risk for the PAHs in PM2.5 in the BBF and BEK groups exceeded the international safety threshold. Furthermore, the PE concentrations of oxygenated PAH (o-PAHs) in PM2.5 and PM0.25 in the biomass groups and the nitrated PAHs (n-PAHs) in PM0.25 in the coal groups showed strong correlations with the biomarkers. The results of this study proved the associations between exposure to the different classes of PAHs and health hazards. The findings could also serve as a guideline in establishing efficient measures for using solid fuels for cooking and household warming in northern China.

Cooking with Modern Energy in Rural Households of India

Between 2016 and 2019, there has been an improvement in the percentage of rural households using clean cooking energy, partly owing to government interventions. However, unclean solid fuels are still the primary source of energy for cooking purposes for about 60% of rural households. One of the foremost reasons for this is the cost of acquiring and using clean energy sources. This paper estimates the cost incurred by a household when switching from solid fuels to liquefied petroleum gas (LPG) or electricity for cooking, followed by a social cost–benefit analysis of two interventions: universal provision of LPG to all rural households and universal provision of electricity to all rural households. The findings suggest that electricity is a cheaper alternative to LPG at the household level; however, investing in the universal provision of LPG is socially beneficial for the government. Universal provision of electricity for cooking can only become socially beneficial if the proportion of renewable electricity increases, reducing the environmental costs of carbon emissions from coal-based power plants. Keywords: LPG, electricity, cost, benefit, social, energy

Pairing combustion experiments and thermogravimetric analysis to uncover timescales controlling cellulose ignition and burnout in a Hencken burner

Solid biomass fuels are potential components of several industrial and power-generation decarbonization pathways. Despite considerable literature that documents the fuel properties of lignocellulosic biomass, the fundamental combustion characteristics of biomass constituents are not well understood. We tackle this knowledge gap by analyzing the combustion properties of cellulose (a key biomass component) in a Hencken burner across various temperature and oxygen mole fractions of the oxidizer gases. Combustion data are compared with results from thermogravimetric analysis (TGA) and scaling analyses to reveal two rate-controlling timescales in the ignition of cellulose: devolatilization time and volatile ignition delay time. TGA shows that the devolatilization time is only a function of temperature and occurs on a considerably shorter timescale than oxidation. Hencken burner experiments show that ignition delay time is highly sensitive to temperature; at very low levels of oxygen in the oxidizer gas (mole fractions of 0.01–0.04), the ignition delay time is sensitive to oxygen mole fraction, but this sensitivity disappears at higher oxygen levels. Burnout time is the least sensitive parameter investigated. The combination of experiments and chemical kinetic simulations begins to explain the ignition behavior of the volatiles from cellulose decomposition and lays groundwork for future research to address uncertainties in quantifying the kinetics of cellulose ignition. Finally, this combined combustion-fuel science study raises serious doubts about the use of combustion indices and TGA-calculated properties to predict the true combustion behavior of biomass.

AUTONOMOUS POWER SUPPLY ON SOLID FUEL AND BIOGAS

"The article considers two options for autonomous power supply using both traditional and non-traditional fuels. The efficiency of using renewable energy sources is described depending on the climate, geographical location and method of energy production. The relevance of this topic is caused by increasingly high environmental requirements for production. Moreover, decentralization with the use of unconventional sources allows the energy system to be more flexible in an autonomous mode, taking into account the time of day, the intensity of solar, wind and hydropower. The use of renewable energy sources is also possible in combination with solid, liquid and gaseous fuels. Combined systems are very convenient for power supply of small objects. These can be settlements remote from centralized power supply, autonomous industrial facilities, peasant farms, livestock farms. One of the energy supply options is more suitable for the northern region of the country with a long cold period and the presence of large coal reserves, there is an opportunity for the consumer to receive gas, as well as heat and electric energy when using coal as a feedstock, a kind of local gas network. The second method will ensure the disposal of animal waste and organic waste. Keywords: alternative energy sources, biogas, gaseous fuel, coal processing, autonomous power supply."

The effects of pulsating wind on the transition from smouldering to flaming combustion

Smouldering and flaming of solid fuels both originate after the pyrolysis reaction, and fires often transition between the two types of combustion. Smouldering-to-flaming (StF) transition introduces a sudden increase of the fire hazard in terms of temperature, spread rate, and power. The literature has studied the effect of wind on StF but only with continuous wind. Here, we show for the first time the influence of pulsating wind by studying the StF transition on wood samples that have been ignited and where smouldering is spreading. The time to StF transition with pulsating wind takes place, on average, ∼39% earlier than continuous wind, and it is highly repeatable, which is unusual for the previous literature. Pulsating wind enhances the transition by temporarily eliminating the cooling and dilution effects of the wind. This study contributes to the fundamental understanding of StF transition for pulsating wind that often occurs in real conditions but had not been studied before.

Indoor exposure to polycyclic aromatic hydrocarbons associated with solid fuel use in rural China.

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants associated with various health risks including lung cancer. Indoor exposure to PAHs, particularly from the indoor burning of fuels, is significant; however, long-term large-scale assessments of indoor PAHs are hampered by high costs and time-consuming in field sampling and laboratory experiments. A simple fuel-based approach and statistical regression models were developed as a trial to predict indoor BaP, as a typical PAH, in China, and consequently spatiotemporal variations in indoor BaP and indoor exposure contributions were discussed. The results show that the national population-weighted indoor BaP concentration has decreased substantially from 46.1ng/m3 in 1992 to 6.60ng/m3 in 2017, primarily due to the increased use of clean energies for cooking and heating. Indoor BaP exposure contributed to > 70% of the total inhalation exposure in most cities, particularly in regions where solid fuels are widely utilized. With limited experimental observation data in building statistical models, quantitative results of the study are associated with high uncertainties; however, the study undoubtedly supports effective countermeasures on indoor PAHs from solid fuel use and the importance of promoting clean household energy usage to improve household air quality.

Enhancement of the energetic performance of solid fuels with metal-fluoropolymer additives

Aluminum (Al) holds a pivotal role in augmenting the energetic potential of solid fuel formulations. Its incorporation can notably amplify the energy yield upon combustion. Nevertheless, challenges such as ignition delay and incomplete combustion have hindered its optimal utilization. In the context of hybrid rocket propulsion, where reignition and high regression rates are sought, a promising solution lies in harnessing the potential of metal-fluoropolymer combinations. This paper explores the influence of polytetrafluoroethylene (PTFE) and Viton fluoropolymer additives on the combustion and regression rates of hydroxyl‑terminated polybutadiene (HTPB)-based solid fuels loaded with nano-aluminum (nAl). To comprehensively address these objectives, binary composites of nAl-PTFE and nAl-Viton were prepared using high-energy ball-milling, and the resulting mixtures were incorporated into hydroxyl‑terminated polybutadiene (HTPB)-based fuel through a vacuum-casting technique. The ignition and combustion characteristics of the solid fuels, as well as the post-combustion products, were examined using an opposed flow burner setup to gain insights into their oxidation and combustion mechanisms. The findings demonstrate that the inclusion of PTFE and Viton in nAl has a positive impact on the ignition delay time, combustion behavior, and regression rates of the solid fuels. The HTPB-nAl-PTFE(S3) sample exhibited the shortest ignition delay time of 108 ms, outperforming the other tested samples (S1: 227 ms, S2: 182 ms, S4: 122 ms). Furthermore, the addition of nAl to pure HTPB resulted in an average regression rate of 0.3–0.6 mm/s for HTPB-nAl (S2), representing a two fold improvement compared to pure HTPB-based samples. Compared to the baseline HTPB fuel, HTPB-nAl-PTFE(S3) demonstrated a significant increase in regression rate by approximately 178%, while HTPB-nAl-Viton(S4) exhibited an increased regression rate of 122%. These results highlight the positive influence of fluoropolymers on combustion behavior, ultimately enhancing the overall performance of the fuel. Additionally, the study observed gas-phase reactions during the combustion process, including the reaction between nano-aluminum (nAl) and fluoride, the intermediate product of Al oxidation, and the decomposition products of fluoride. These reactions resulted in the faster fracture of the alumina (Al2O3) shell, leading to improved heat release and regression rate performance.

Nepalese indoor cookstove smoke extracts alter human airway epithelial gene expression, DNA methylation and hydroxymethylation

Household air pollution caused by inefficient cooking practices causes 4 million deaths a year worldwide. In Nepal, 86% of the rural population use solid fuels for cooking. Over 25% of premature deaths associated with air pollution are respiratory in nature. Here we aimed to identify molecular signatures of different cookstove and fuel type exposures in human airway epithelial cells, to understand the mechanisms mediating cook stove smoke induced lung disease. Primary human airway epithelial cells in submerged culture were exposed to traditional cook stove (TCS), improved cook stove (ICS) and liquefied petroleum gas (LPG) stove smoke extracts. Changes to gene expression, DNA methylation and hydroxymethylation were measured by bulk RNA sequencing and HumanMethylationEPIC BeadChip following oxidative bisulphite conversion, respectively. TCS smoke extract alone reproducibly caused changes in the expression of 52 genes enriched for oxidative stress pathways. TCS, ICS and LPG smoke extract exposures were associated with distinct changes to DNA methylation and hydroxymethylation. A subset of TCS induced genes were associated with differentially methylated and/or hydroxymethylated CpGs sites, and enriched for the ferroptosis pathway and the upstream regulator NFE2L2. DNA methylation and hydroxymethylation changes not associated with a concurrent change in gene expression, were linked to biological processes and molecular pathways important to airway health, including neutrophil function, transforming growth factor beta signalling, GTPase activity, and cell junction organisation. Our data identified differential impacts of TCS, ICS and LPG cook stove smoke on the human airway epithelium transcriptome, DNA methylome and hydroxymethylome and provide further insight into the association between indoor air pollution exposure and chronic lung disease mechanisms.