Current Issue : October-December Volume : 2026 Issue Number : 4 Articles : 5 Articles
This paper presents a numerical comparative study on the ignition characteristics of straightchannel and U-bend micro catalytic combustors, with particular focus on the role of inlet velocity. A two-dimensional computational fluid dynamics model with coupled gas-phase and surface catalytic reaction kinetics for propane combustion is developed using a fluid simulation program ANSYS Fluent. The catalyst coating (Pt/Al2O3) is modeled as a zero-thickness reaction surface, and the U-bend design features an uncoated recirculating channel to ensure identical catalyst loading between the two configurations. Simulations are conducted over an inlet velocity range of 0.25–8 m/s. Key ignition and combustion metrics including ignition temperature, ignition time, maximum combustion temperature, heterogeneous reaction contribution, and thermal/species field distributions are systematically compared. Results reveal a crossover in relative performance depending on flow regime. At low velocities (≤2 m/s), the straight-channel combustor exhibits lower ignition temperatures; at high velocities (≥4 m/s), the U-bend design achieves superior ignition performance with lower ignition temperatures (e.g., 526 K vs. 555 K at 8 m/s) and higher combustion temperatures (1726 K vs. 1474 K at 8 m/s). However, the straight-channel combustor consistently yields shorter ignition times across all velocities (25.9–108.6 s) compared to the U-bend (52.6–145.2 s). The heterogeneous reaction contribution decreases with increasing inlet velocity for both designs, with the straight-channel maintaining higher values than the U-bend. The U-bend achieves higher maximum temperatures due to enhanced heat recirculation, particularly at high flow rates. The findings suggest that the U-bend configuration is advantageous for high-flow-rate applications requiring low ignition temperatures and high combustion temperatures, whereas the straight-channel design is preferable for rapid cold-start scenarios....
The primary factor in the formation of polycyclic aromatic hydrocarbons (PAHs) in diesel engines, which pose environmental and health risks, is the chemical composition of the diesel fuel. Higher-carbon alcohols have emerged as promising oxygenated blending components for compression ignition engines due to their potential to improve combustion and reduce harmful emissions. However, limited data exist regarding their impact on PAH formation and toxicity characteristics. This study investigates the effects of 15% (v/v) n-propanol, n-butanol, and n-pentanol blends with petroleum diesel (D) and waste cooking oil biodiesel (B) on total PAH emissions, PAH dispersion, and toxicity in a diesel engine under steady-state conditions. Total PAH concentrations and individual species distributions were quantified, and toxicity was evaluated using toxicity equivalency factor (TEF) methodology. Results indicate that the addition of higher alcohols significantly reduces total PAH emissions compared to the respective base fuels. A marked decrease in high-molecular-weight (4–6 ring) PAH compounds was observed, suggesting suppression of heavy PAH formation pathways. Toxicity-weighted PAH emissions also decreased with alcohol blending. Furthermore, total PAH concentrations for all tested blends remained below the Occupational Safety and Health Administration (OSHA) permissible exposure limit (PEL = 0.2 mg/m3) under the examined operating conditions. These findings demonstrate that 15% higher alcohol blends are effective in mitigating PAH emissions without adverse environmental health implications....
To improve the proactive prevention and control of coal spontaneous-combustion disasters in the goafs of deep coal mines, this study identifies the factors associated with hazard-source recognition for coal spontaneous combustion in the goaf of a coal mine in Hebi, China. The mine is characterized by coal-seam explosibility and spontaneous-combustion proneness, large quantities of residual coal under fully mechanized top-coal caving, a complex air-leakage field, and concealed fire sources that are difficult to detect in a timely manner. On the basis of systems engineering theory and accident-causation theory, literature analysis, field investigation, and expert evaluation were integrated to conduct hierarchical identification of hazard sources related to goaf coal spontaneous combustion. A risk-evaluation indicator system was then established from four dimensions: human factors, equipment factors, environmental factors, and management factors. The results indicate that goaf coal spontaneous combustion is not governed by a single factor; rather, it is a dynamic disaster process driven by the coupled effects of residual-coal oxidation and heat accumulation, air leakage and oxygen supply, production organization, equipment reliability, and management execution. Among the identified indicators, the accuracy of early hazard recognition, reliability of standby power supply and emergency equipment, matching degree between longwall face advance rate and the spontaneous-combustion period, and closed-loop rate of hazard investigation and rectification exert critical influences on risk evolution. The findings provide theoretical support for precise prevention and control of goaf coal spontaneous-combustion risk in the studied mine and offer a reference for fire-prevention and fire-extinguishing management in similar deep, fully mechanized top-coal-caving mines....
Replacing traditional hydrocarbon fuel in aircraft turbine engines with hydrogen fuel contributes, in line with current trends, to reducing harmful carbon dioxide emissions and enabling increased flight altitude. Given the high research costs of full-scale turbine engines, research on miniature turbojet engines, due to their availability and relatively low modification costs, can play a significant role in better understanding and developing concepts for adapting existing hydrocarbon-based fuel systems to hydrogen fuel. This article presents the results of a comprehensive numerical analysis of the hydrogen combustion process—illustrating changes in its location and structure—for multiple variants of design changes to the combustion chamber of the miniature GTM-140 turbojet engine, primarily involving appropriate shaping of airflows through the holes in the glow tube and the location of the hydrogen injection point. Based on this analysis, a modernized combustion chamber geometry was proposed, which should ensure a stable hydrogen combustion process that is safe for the thermal resistance of the structural material—and structurally comparable to the baseline Jet-A1 hydrocarbon fuel combustion process. The obtained results can give ground for the construction and experimental testing of a hydrogen-powered turbine engine....
Based on a three-dimensional simulation platform, this study investigated the effects of N2, CO2, and O2 as dilution gases on the combustion and emission performance of methanol engines under constant total fuel quantity, dilution ratio of 10%/20%, and blending ratio of 0%/10%/20% conditions. In terms of combustion performance, diluting the syngas can shorten the ignition delay period and combustion duration, advance the combustion center, increase the peak cylinder pressure and temperature, and the effect is most significant when CO2 is diluted (for example, in the 20% dilution ratio CO2 condition, the 20% blending ratio is 3.5 °CA shorter than 0%); the ignition delay period and combustion duration become longer, the cylinder pressure decreases under CO2 conditions, and slightly increases under N2 and O2 conditions. In terms of emission performance, NOX emissions are CO2 < N2 < O2 (at a 10% dilution ratio and 10% blending ratio, CO2 relative to O2 reduces NOX by 98.5%); under O2 conditions, syngas blending reduces CO emissions, while under N2 and CO2 conditions, it increases, and under CO2 with a 20% dilution ratio, CO sharply increases; syngas blending reduces the emissions of HC, CH3OH, and CH2O, and under O2 dilution, the CO emissions are the lowest, and they increase as the dilution ratio increases. In summary, N2 dilution is beneficial for the coordinated optimization of combustion and NOX emissions....
Loading....