Search Results (313)

Methane oxy-combustion is a promising carbon capture pathway due to the high CO₂ concentration in the exhaust; however, combustion in pure oxygen produces excessively high flame temperatures that impair ignition and operational stability. To mitigate these effects, steam dilution is commonly applied, but it significantly prolongs ignition delay time (IDT). To address these limitations, hydrogen enrichment is proposed as a reactivity-enhancement strategy. The objective of this study is to quantify the combined effects of steam dilution and hydrogen enrichment on ignition behaviour, carbon species formation, and flame temperature in methane oxy-combustion, considering both ignition onset and equilibrium combustion states. A detailed numerical investigation is conducted using zero-dimensional constant-pressure simulations with detailed chemical kinetics implemented in Cantera, formulated in mixture-fraction space. IDT, CO/CO₂ formation, and adiabatic flame temperature are analysed over steam dilution levels of 0–40%, hydrogen enrichment up to 5% by mass, and initial temperatures between 1050 and 1200 K. The model is validated against experimental data for adiabatic flame temperature and key radical species. Results demonstrate that steam dilution effectively reduces the peak adiabatic flame temperature (by more than 300 K at 40% steam) and enhances the CO₂ mass fraction in the equilibrium state near the stoichiometric mixture fraction, but increases IDT by approximately 100–200% across the mixture-fraction range. Hydrogen enrichment strongly counteracts this inhibition, reducing IDT by up to one order of magnitude under high steam dilution (30–40%) while simultaneously suppressing CO. At the stoichiometric mixture fraction, H₂ addition decreases equilibrium CO₂ formation, indicating a trade-off between enhanced ignition reactivity and ultimate carbon conversion under equilibrium conditions. The use of steam dilution as a temperature-control strategy and hydrogen enrichment as a reactivity enhancer identifies a favourable mixture-fraction window. Full article

This study explores the viability of condensate petroleum, an ultra-light hydrocarbon derived from natural gas production, as an alternative diesel engine fuel. The researchers tested six different fuel blends, increasing the condensate volume by 10% increments, in a compression ignition engine under three distinct load conditions (25%, 50%, and 75%) to evaluate both combustion characteristics and emission performance. The results demonstrate that condensate blends significantly enhance key combustion parameters. The heat release rate, in-cylinder pressure, and in-cylinder temperature all increased, with the highest heat release rate improvement of 35.6% observed at a 75% load using a 60% condensate petroleum blend. However, increasing the condensate ratio also extended ignition delay times and raised the ringing intensity, which peaked with a 34.7% increase at a 25% load. Brake thermal efficiency improved at lower and medium loads—achieving a maximum 11.2% increase with the 50% condensate petroleum blend at 50% load—but decreased when the engine reached 75% load. In terms of environmental impact, the condensate blends proved largely beneficial. Carbon monoxide emissions dropped by 57.9% (at 75% load, 60% condensate petroleum), smoke opacity decreased by 72.6% (at 25% load, 40% condensate petroleum), and hydrocarbons fell by 34.4% (at 50% load, 60% condensate petroleum). The primary drawback was that nitrogen oxide emissions worsened, increasing by 20.4% at 75% load with the 50% condensate petroleum blend. Overall, the study concludes that the effects of condensate petroleum are highly acceptable, making it a promising alternative fuel and additive for diesel engines. Full article

To address the limitations of existing NH₃/H₂ combustion mechanisms, laminar flame speeds of NH₃/H₂/air mixtures were measured using the heat flux method over a range of equivalence ratios from 0.7 to 1.6 at different blending ratios. The results indicate that current mechanisms exhibit large prediction errors under fuel-rich conditions. Subsequently, based on the original mechanism, the pre-exponential factors of 13 key reactions were optimized using a particle swarm optimization algorithm, leading to the development of a new NH₃/H₂ chemical kinetic mechanism. The optimized mechanism not only improves the prediction of laminar flame speeds for NH₃/H₂/air mixtures but also significantly enhances accuracy in the fuel-rich region. In addition, it accurately predicts the ignition delay times of NH₃/H₂ and reliably reproduces the concentrations of H₂O, NH₃, NO, and N₂O under low-equivalence-ratio conditions. Although the optimized mechanism was not specifically developed for pure NH₃ or pure H₂ fuels, it still performs well in describing their combustion characteristics. Overall, the optimized mechanism provides reliable predictions for both the laminar flame speeds and ignition delay times of NH₃/H₂ mixtures. Full article

Hydrogen combustion is known to be fast compared to traditional hydrocarbon fuels. The fast combustion leads to a higher thermal efficiency. In this research a 600 cc single cylinder hydrogen engine was tested at 1250 rpm, lambda = 2 and 3, and three load levels (load was represented by Manifold Absolute Pressure (MAP); MAPs tested were 75, 95 and 120 kPa) and compared to operation with gasoline and propane. The fast burn duration (Mass Fraction Burnt MFB10% to MFB90%) and the MFB 50% were determined and analyzed. The hydrogen MFB50% location for Minimum Timing for Best Torque (MBT) was found to occur at around the typical 8 Crank Angle Degrees (CADs) After Top Dead Center (ATDC). Measurements of ignition delay based on the fast data direct measurement of spark ignition coil current drop to the change in polarity of net heat release are presented. With shifts towards direct injection and higher injection pressures, consideration was given to the hydrogen pressurization penalty, where it was calculated that pressurizing hydrogen to 100 bar at the flow required for lambda = 2 operation is 2.3 bar, i.e., higher than the Friction Mean Effective Pressure (FMEP)! Furthermore, hydrogen is widely cited to have a higher heat loss than typical hydrocarbon fuels. In this paper, detailed analyses at lambda 2 and lambda 3 showed that hydrogen in fact has lower heat losses. Full article

This study experimentally investigated the ignition and combustion characteristics of marine gas oil as a pilot fuel in dual-fuel marine engines using a constant-volume combustion chamber. In-cylinder temperature, pressure, and injection duration were the primary experimental variables. Results showed that temperature is the dominant factor governing ignition delay: increasing temperature from 520 °C to 580 °C reduced ID by 46.7% and its standard deviation by 62.8%. Increasing pressure shortened ID by 24.5% and reduced variability by 28.8%. In contrast, injection duration minimally affected ignition timing but increased accumulated heat release and maximum heat release rate by 37% and 20%, respectively. The time interval between ID and main combustion delay remained constant at approximately 0.30 ms across all conditions, indicating simultaneous advancement of ignition and combustion development. These findings demonstrate that ignition timing control (via temperature management) and combustion intensity control (via injection quantity) can be independently optimized, providing fundamental experimental data for the development of robust combustion-control strategies in dual-fuel marine engines. Full article

This study investigates the influence of highly thermally conductive coatings on the combustion thresholds of a TC4 titanium alloy, aiming to address the flame-retardant protection requirements for titanium alloys. The findings reveal that, in terms of combustion thermodynamics, as the thickness of the copper coating increases from 100 μm to 300 μm, the critical ignition power rises by 125–170 W compared to the substrate (235 W). Additionally, the critical oxygen pressure increases by 0.21–0.51 MPa relative to the substrate (0.03 MPa), and the ignition temperature is elevated by 119–184 K above that of the substrate (848.80 K). This phenomenon is primarily due to the high thermal diffusivity of copper. Increased coating thickness further enhances heat dissipation, significantly suppressing the local heat accumulation rate and thereby improving the coating’s combustion resistance. In terms of combustion kinetics, under fixed experimental conditions, the copper coating extends the ignition delay time by 0.670 s and reduces the combustion propagation rate by approximately 21% compared to the substrate (26.772 mm/s). The post-combustion microstructural analysis indicates that during the reaction process, the copper coating forms a TiCu₂Al-type intermetallic compound (Ti_0.5Al_0.5)Cu. This structure exerts an “anchoring” effect on the substrate material, decreases the Ti/O reaction efficiency, and consequently achieves effective flame retardancy. These findings inform the subsequent design and optimization of copper-based abradable coatings with enhanced combustion resistance. Full article

With increasingly stringent greenhouse gas emission regulations, carbon emissions from marine engines have become a major concern, driving the shipping industry to actively explore efficient and clean alternative fuels. Among the various candidates, ammonia has attracted considerable attention in recent years due to its carbon-free nature and potential as a high-quality clean fuel. However, its practical application in marine engines is constrained by several inherent drawbacks, including a high auto-ignition temperature, low flame propagation speed, and low calorific value. Blending ammonia with natural gas has been demonstrated as an effective strategy to enhance its ignition performance. In this study, the ignition characteristics of NH₃/C1–C4 alkane mixed fuels were systematically investigated using numerical simulations. Rate of production (ROP) analysis, reaction pathway analysis, and other kinetic evaluation methods were employed to elucidate the underlying ignition mechanisms. The results reveal that blending NH₃ with C1–C4 alkanes significantly shortens the ignition delay time. When X_CH ≥ 30%, at high initial temperatures, the ignition-promoting effect is most pronounced for NH₃/C₂H₆ mixtures. In contrast, under low temperature conditions, ignition performance progressively improves with increasing carbon chain length of the blended alkane fuel. The ignition delay time across different operating conditions is primarily governed by highly reactive radicals, including O, H, and OH. Elevating the initial temperature, pressure, and blending ratio promotes the earlier formation of these key radicals and increases their production rates. ROP analysis of OH radicals indicates that reaction R10 (O₂ + H ⇌ OH + O) contributes most significantly to OH generation. Furthermore, reaction pathway analysis of NH₃ shows that at lower initial temperatures, NH₃ dehydrogenation is dominated by reactions with OH radicals. At higher temperatures, a greater fraction of NH₃ participates in NO reduction reactions, thereby decreasing the proportion of NH₃ involved in dehydrogenation pathways. Full article

The utilization of low- and zero-carbon fuels in internal combustion engines is gaining increasing interest. In marine engine applications, the co-combustion of methane and ammonia has emerged as a promising strategy for reducing carbon emissions. In this work, a chemical kinetic mechanism for n-heptane/methane/ammonia blended fuel was developed and validated. Using this mechanism, sensitivity and chemical kinetic analyses were performed to explore the ignition characteristics of the fuel mixture. The results indicate that at an initial temperature of 1000 K, reaction R152 (C₇H_15-2 = CH₃ + C₆H₁₂) exerts the strongest inhibiting effect on ignition. C₇H_15-2 is a major low-reactivity intermediate generated during n-heptane decomposition, and the accumulation of such intermediates contributes to the negative temperature coefficient (NTC) behavior. A cross-reaction between CH₄ and NH₃, R111 (CH₄ + NH₂ = CH₃ + NH₃), was identified, which impedes the smooth progression of oxidation. Elevated temperatures, oxygen-rich conditions, and higher ammonia blending ratios promote the formation of NO. The production of N₂O is primarily governed by reaction R105 (NH + NO = N₂O + H), whose rate increases with the NH₃ molar fraction. Consumption of N₂O occurs mainly via reactions R92 (N₂O + H = N₂ + OH) and R94 (N₂O (+M) = N₂ + O (+M)), both of which occur later than its formation through R105, indicating that N₂O consumption is more sensitive to temperature. Full article

During the diesel engine start-up phase, low rotational speed and coolant temperature result in poor fuel atomization and prolonged ignition delay. This impedes the in-cylinder combustion process and directly impacts the engine’s emission performance. As the first combustion cycle during the starting process, the initial starting cycle significantly influences subsequent combustion cycles and overall starting performance. This paper proposes a target-torque-based control strategy for fuel injection quantity during the starting process. It optimally determines the target acceleration curve for the starting process, thereby calculating the optimal fuel injection quantity for the initial starting cycle. Based on this, a combustion system simulation model of the diesel engine was established using the 3D CFD software AVL FIRE v2010. The simulation investigated the impact of first injection speed on the combustion process and performance of the first firing cycle under different ambient temperatures: normal temperature (20 °C), low temperature (5 °C), and cold start (−10 °C). The results indicate that the optimal first cycle injection quantities under normal, low, and cold start conditions are 17.3 mg, 18.5 mg, and 20.4 mg, respectively. The impact of first injection speed on the first firing cycle combustion process primarily manifests in the mixture formation rate and time, and higher speeds do not necessarily yield better results. The optimal first injection speeds at normal temperature (20 °C), low temperature (5 °C), and cold start (−10 °C) were 220 r/min, 240 r/min, and 220 r/min, respectively. Corresponding indicated thermal efficiencies were 30.74%, 28.67%, and 28.7%, with relatively low emissions of pollutants such as CO, NOx, and HC. Full article

Ammonia–coal co-firing is emerging as a promising technological pathway to reduce carbon production during coal-fired power generation. However, the coupling effects of the ammonia energy ratio (E_NH3) and equivalence ratio on the ignition mechanism and emission characteristics—particularly under staged injection conditions—remain insufficiently understood. This study investigates these characteristics in a laboratory-scale furnace. Spontaneous chemiluminescence imaging and flue gas analysis were employed to decouple the effects of aerodynamic interactions and chemical kinetics. The experimental results reveal that the ammonia injection strategy is the critical factor governing coal ignition performance. Compared to the premixed mode, staged injection—which establishes an independent, high-temperature ammonia flame zone—provides a superior thermal environment and circumvents oxygen competition between the fuels, thereby markedly promoting coal ignition. At an E_NH3 of 50%, the staged configuration reduces the ignition delay time of coal volatiles by a striking 60.93%. Within the staged configuration, increasing either the co-firing ratio or the overall equivalence ratio further enhances coal ignition. Analysis of pollutant emissions elucidates that the formation of NO, N₂O, and NH₃ is intimately linked to the local combustion conditions of ammonia. An excessively lean local equivalence ratio leads to incomplete ammonia combustion, thereby increasing N₂O and NH₃ slip. Full article

Ammonia can significantly reduce carbon emissions when used in internal combustion engines. However, pure ammonia is considered difficult to ignite and has a slow flame propagation speed, which makes its application challenging. Furthermore, previous research on pure ammonia engines has been based on bench tests, with no vehicle-level tests reported to date. In this study, an engine was tested using pure ammonia as a single fuel in a range-extended hybrid electric vehicle. First, a pure ammonia hybrid power system was implemented in a light-duty vehicle. By motoring the engine instantly to its optimal operating window, the hybrid mode ensures a rapid transition to stable combustion. The results show that, using pure ammonia, the engine can operate stably within a speed range of 1000–3175 rpm. The engine achieves an output power of 45 kW, with an indicated thermal efficiency exceeding 40% under 3175 rpm. Compared to gasoline, pure ammonia has a longer ignition delay but a similar combustion duration. Pure ammonia requires an earlier spark timing and higher intake temperature. The ammonia and NO remain high even after being treated by a three-way catalyst. This research verifies the feasibility of using pure ammonia as a single fuel in hybrid modes, offering broad application prospects in scenarios such as marine power and stationary power generation. Full article

This study investigates the thermal decomposition, ignition, combustion, and gasification processes of composite fuels derived from anthracite coal and pine sawdust. The research highlights the non-additive behavior of composite fuels, demonstrating enhanced reactivity and combustion efficiency compared to simple mixtures. Thermogravimetric analysis (TGA) revealed distinct stages of thermal decomposition, with composite fuels exhibiting combined processes of volatile release and coke residue decomposition, unlike mixtures. Ignition experiments in a vertical tubular furnace showed reduced flash delay times for composites, attributed to the formation of active surface centers during mechanical activation. Flare combustion studies confirmed more stable and complete combustion of composites, achieving higher temperatures and improved flame stability. Plasma gasification experiments indicated that composite fuels provide more uniform gas evolution, with higher yields of hydrogen (H₂) and carbon monoxide (CO), while reducing nitrogen oxide (NO) emissions. The findings underscore the potential of composite fuels for optimizing energy efficiency and reducing environmental impact in coal-fired power plants, supporting the transition to sustainable energy solutions. Full article

This work proposes a coating approach for obtaining flame-retardant ethylene–vinyl acetate (EVA) and ethylene–butyl acrylate (EBA) copolymer-based materials. Nanocomposite films of EVA and EBA were first produced by cast extrusion, with two types of layered double hydroxides (LDHs) differing in the aspect ratio used as nanofillers. Subsequently, the films were applied as a coating to the corresponding neat copolymer substrate, and the combustion behavior of the so-obtained samples was evaluated through cone calorimeter tests. Despite the small amount of nanofillers (0.5 wt.% considering the whole specimen), the application of the coatings significantly improved the time to ignition compared to the pristine copolymers, while the shape of the heat release rate curves and the relative peak values remained relatively unchanged. The effect of the embedded nanofillers in delaying the ignition was more effective for the EVA-based systems than for the EBA ones (showing an increment of 30% and 12%, respectively, compared to the uncoated samples), likely due to the more homogeneous dispersion of the LDHs obtained in the first case. The obtained results demonstrate the effectiveness of the coating approach, since it allows the flame-retardant action to be concentrated on the surface of a polymer system, where combustion specifically takes place, while minimizing the required amount of flame retardant. Full article

Forest sub-surface fires represent a challenging combustion phenomenon to control, and the process of smoldering is often overlooked in wildfire incidents. Traditional forest fire research has prioritized flaming combustion over smoldering dynamics, despite its critical risk factors including sustained high temperature and ground surface collapse that significantly endanger firefighter safety. This study focuses on The Daxing’an Mountains, a prime sub-surface fire-prone region in China, employing field investigations and controlled smoldering experiments to quantify the key risk factors for sub-surface fires suppression while elucidating moisture content’s regulatory effects. The results demonstrate that sub-surface smoldering fires maintain elevated temperatures with the surface peak temperature reaching 600.24 °C and sub-surface peak temperature up to 710.70 °C. The spread rate is relatively slow (maximum 27.00 cm/h), yet exhibits pronounced fluctuations along the vertical profile, creating a critical predisposition to overhanging collapse. The moisture content has extremely significant effects (p < 0.01) on key risk factors including surface temperature, sub-surface temperature, collapse time and ignition duration. Lower moisture content prompted earlier surface collapses, whereas higher moisture content displays delayed collapse but resulted in dangerously elevated temperatures at collapse points, presenting extreme suppression risks. Full article

The downsized Wankel rotary engine (WRE) fueled with methanol is a promising power source for small unmanned aerial vehicles, owing to its simple structure, high-speed capability, and clean emissions. In general, a well-designed ignition timing (IT) can drastically enhance engine combustion performance. To assess the impact of IT, a numerical simulation study was conducted on a methanol-fueled WRE, analyzing its combustion characteristics and emissions to guide performance optimization. The results indicated that advancing the IT boosted the flame propagation velocity. The peak pressure increased slightly when delaying the IT from −24 °CA to −15 °CA but dropped sharply for −12 °CA at 5000 RPM. This contrasts with the behavior at 11,000 RPM and 17,000 RPM, where peak pressure clearly rose with advanced IT. Indicated thermal efficiency (ITE) decreased with the delay of the IT at 11,000 RPM and 17,000 RPM; the maximum values reached 24.98% and 25.78%, respectively. This contrasted with the trend observed at 5000 RPM, where ITE first increased and then decreased with IT delay. The optimized IT significantly affects pollutant emissions primarily under low-speed conditions (5000 RPM), while exhibiting limited impact at high engine speeds. At 5000 RPM, strategic IT adjustment achieves maximum reductions of 2% in CO emissions and 33% in formaldehyde emissions. Full article