Combustion Behavior Research Articles

The integration of civilian nitrocellulose in propellant with highly improved mechanical property and thermal stability, and study on its combustion behavior

Developing binders for propellants with balanced mechanical and energy properties is important and challenging. Herein, high-viscosity civilian nitrocotton (CNC) was used as reinforcing binder to prepare CNC-based propellant by solvent method. The influence of viscosity and content of CNC on mechanical properties, thermal stability, and combustion performance of propellants was investigated. The plasticizing process of nitrocellulose fibers can be well described by swelling mass changes and has a strong correlation with mechanical properties. The impact test combined with morphology observation by scanning electron microscope (SEM) and evaluation about matrix, fiber, and structure systems revealed that the subsidiary plasticizing mechanism of CNC and the homogeneous system of CNC-based propellant play the dominant role in enhancement of macroscopic mechanical properties. Besides, the structure of propellant was investigated using FTIR, XRD, and Raman, which indicated that propellant containing CNC exerting similar structure with NC-based propellant. Moreover, the analysis of thermal decomposition kinetics demonstrated that the introduction of CNC could further enhance the thermal stability of propellant, like the increased activation energy. Finally, the study of combustion performance demonstrated that CNC-based propellant can burn steadily, and energy out-put was further enhanced as compared with NC propellant. Therefore, this design and adjustment for the introduction of CNC in propellant could provide fundamental theory and data support for the development of CNC in propellants.

Use of Artificial Neural Network to Develop Surrogates for Hydrotreated Vegetable Oil with Experimental Validation in Ignition Quality Tester

<div>This article presents surrogate mixtures that simulate the physical and chemical properties in the auto-ignition of hydrotreated vegetable oil (HVO). Experimental investigation was conducted in the Ignition Quality Tester (IQT) to validate the auto-ignition properties with respect to those of the target fuel. The surrogate development approach is assisted by artificial neural network (ANN) embedded in MATLAB optimization function. Aspen HYSYS is used to calculate the key physical and chemical properties of hundreds of mixtures of representative components, mainly alkanes—the dominant components of HVO, to train the learning algorithm. Binary and ternary mixtures are developed and validated in the IQT. The target properties include the derived cetane number (DCN), density, viscosity, surface tension, molecular weight, and volatility represented by the distillation curve. The developed surrogates match the target fuel in terms of ignition delay and DCN within 6% error range. This investigation will be of value to developing high-fidelity models to investigate HVO combustion and spray behavior. This will be beneficial to researchers advancing the design and development of compression ignition engines to efficiently operate on renewable fuels such as HVO.</div>

Enhancing energy release of aluminized propellants and explosives through fluorinated binder

AbstractThe use of fluorinated binders can enhance the combustion properties of Al in energetic materials. The underlying mechanism is under investigation and a rational strategy in terms of application has yet to be fully developed. In this study, we have investigated the effect of using a fluorine‐modified hydroxy‐terminated polyether (HTPE) binder to cast aluminized propellants and explosives. We have focused on the combustion behavior and energy release characteristics of Al particles with and without the fluorinated binder during propellant combustion and explosive detonation. The propellants combustion process was recorded using a high‐speed camera and an infrared thermometer. The heat of detonation, detonation velocity and thermal stability of the explosives were investigated using a constant temperature calorimeter, an electrometric method and a small‐scale thermal cook‐off test, respectively. The fluorine‐modified HTPE propellant has exhibited a higher flame temperature and greater energy release efficiency than the HTPE propellant. Moreover, the fluorine‐modified HTPE propellant is characterized by smaller particle agglomerates, leading to a reduction in the mass percentage of agglomerates from 73 wt% to 42 wt%. The detonation heat of fluorine‐modified HTPE explosive increases from 75.2 % to 81 %, but the detonation velocity decreased from 7745 m/s to 7622 m/s. In addition, the fluorine‐modified HTPE binder maintained the thermal stability of explosives due to a milder decomposition before thermal runaway.

Chemical Kinetic Analysis of High-Pressure Hydrogen Ignition and Combustion toward Green Aviation

In the framework of the “Multidisciplinary Optimization and Regulations for Low-boom and Environmentally Sustainable Supersonic aviation” project, pursued by a consortium of European government and academic institutions, coordinated by Politecnico di Torino under the European Commission Horizon 2020 financial support, the Italian Aerospace Research Centre is computationally investigating the high-pressure hydrogen/air kinetic combustion in the operative conditions typically encountered in supersonic aeronautic ramjet engines. This task is being carried out starting from the zero-dimensional and one-dimensional chemical kinetic assessment of the complex and strongly pressure-sensitive ignition behavior and flame propagation characteristics of hydrogen combustion through the validation against experimental shock tube and laminar flame speed measurements. The 0D results indicate that the kinetic mechanism by Politecnico di Milano and the scheme formulated by Kéromnès et al. provide the best matching with the experimental ignition delay time measurements carried out in high-pressure shock tube strongly argon-diluted reaction conditions. Otherwise, the best behavior in terms of laminar flame propagation is achieved by the Mueller scheme, while the other investigated kinetic mechanisms fail to predict the flame speeds at elevated pressures. This confirms the non-linear and intensive pressure-sensitive behavior of hydrogen combustion especially in the critical high-pressure and low-temperature region which is hard to be described by a single all-encompassing chemical model.

Repeat Fire Tests of Upholstered Furniture: Variability and Experimental Observations

A series of trials were conducted to investigate the repeatability of furniture-scale calorimetry experiments. Twenty-five identical upholstered chairs were ignited under the same experimental conditions. Experimental results of heat release rate (HRR), mass loss rate (MLR), and emission yields (CO, CO2, N2O, NO, CH4, HCN) are presented. Discrepancies were observed between the time resolved evolution of the various recorded data. However the development of each fire was observed to be tied to common events. By accounting for these events, a more consistent representation of the burning behaviour can be expressed. Each experiment displayed distinct burning regimes (i.e., pyrolysis, flaming, and smouldering) which were identified through visual observation and through analysing the emission data. Some species yields were found to be approximately constant over some burning regimes (e.g., CO2 yield over the flaming regime) while others displayed highly transient behaviour (e.g., CO yield was found to be burning regime dependent). Results from upholstered furniture scale experiments, including HRR and emission yields, are commonly used in various engineering applications; this study lends insight into the variability that can be observed for such data and the implications in applying this data in further analysis.

Burning characteristics of power cables with cone calorimeter

Power cables consist of insulation, padding and sheathing, which are highly susceptible to ignition. Power cables are an important factor affecting fire risk in urban utility tunnels (UUTs). In this paper, the combustion characteristics of four types of power cables (YJV, ZR-YJV, ZR-VV, and ZR-PE) in UUTs were investigated using a cone calorimeter. In this paper, laboratory experiments were conducted to investigate the combustion characteristics of power cables with two different parameters including two heat fluxes (35 kW/m2 and 75 kW/m2) and two sheath thicknesses (3 mm and 5 mm). The effects of heat release rate (HRR), effective heat combustion (EHC), optical density index (ODI) and smoke production rate (SPR) on ignition and combustion were investigated. The results showed that ZR-VV power cables have lower TTI, lower average HRR, lower EHC, higher MLR, and lower SEA than YJV and ZR-YJV power cables.With a conical calorimeter and heat flux of 35 kW/m2, the HRR of the power cables increased within 200 s, while for ODI, the total smoke output of ZR-YJV cables was minimized. Heat flux has a significant effect on HRR, SPR and EHC of ZR-PE cable. Sheath thickness has little effect on HRR, SPR and EHC of ZR-PE cables. In addition, one of the most important parameters, the ignition time, which depends on the composition and structure of the cable, was identified. Finally, the effect of external heat flux is complex and depends on the combustion characteristics of the power cable. Laboratory tests provide useful information for understanding the combustion behavior of power cables, including heat release rate, effective thermal burn, optical density index, and smoke production.

Spontaneous Combustion in Coal Stockpiles with Different Particle Sizes

In this study, the spontaneous combustion behavior of stocks created with coals of 3 different particle sizes (0-18/18-28/25-100 mm) was examined for 2 months and the results were analyzed. For this purpose, daily temperaturechanges in the stockpiles were recorded by means of temperature measurement probes placed in the stocks designed in2x3x10 m size. According to the results obtained; Coal stocks with grain sizes of 18-25 and 25-100 mm started to catchfire before the end of the first month of storage. While no open flame ignition was observed in the stock with the finestgrain size (0-18 mm), at the end of the 2nd month, a temperature increase was observed only at a single point accordingto the wind direction.

Dry and Hydrothermal Co-Carbonization of Mixed Refuse-Derived Fuel (RDF) for Solid Fuel Production

The present study aims to test several conditions of the thermochemical pretreatment of torrefaction and carbonization to improve the physical and combustible properties of the Portuguese RDF. Therefore, two different types of RDF were submitted alone or mixed in 25%, 50%, and 75% proportions to dry carbonization processes in a range of temperatures between 250 to 350 °C and residence time between 15 and 60 min. Hydrothermal carbonization was also carried out with RDF samples and their 50% mixture at temperatures of 250 and 300 °C for 30 min. The properties of the 51 chars and hydrochars produced were analyzed. Mass yield, apparent density, proximate and elemental analysis, ash mineral composition, and higher heating value (HHV), among others, were determined to evaluate the combustion behavior improvement of the chars. The results show that after carbonization, the homogeneity and apparent density of the chars were increased compared to the raw RDF wastes. The chars and hydrochars produced present higher HHV and lower moisture and chlorine content. In the case of chars, a washing step seems to be essential to reduce the chlorine content to allow them to be used as an alternative fuel. In conclusion, both dry and wet carbonization demonstrated to be important pretreatments of the RDF to produce chars with improved physical and combustion properties.

Numerical Evaluation of Sodium Droplet Swarm Combustion and Its Modeling Optimization

Because of its superior thermal-hydraulic qualities, liquid sodium has been applied to a variety of industries, including energy storage, solar energy, sodium-cooled fast reactors, and aerospace. However, fires brought on by sodium leaks at high pressure can have major thermodynamic repercussions and put employees and equipment in use at risk directly or indirectly. As a result, a realistic and accurate forecast of the combustion behavior of sodium droplet swarm can offer technical backing for the use of liquid sodium in engineering as well as a way of sodium fire prevention and control. Spray dynamics (droplet settling, droplet particle size distribution, etc.), combustion kinetics (premixed combustion, gas phase combustion, etc.), sodium aerosol diffusion, and other specialized phenomena all contribute to the complex process of sodium droplet swarm combustion. The NACOM code created by Brookhaven National Laboratory for sodium droplet swarm combustion is utilized in this paper as a framework. The code is first validated using the benchmark of the sodium droplet swarm combustion tests carried out by prestigious institutions. The validation results demonstrate that the code’s drag model, droplet combustion model, and heat transfer model are to blame for the significantly overestimated thermodynamic effects of sodium droplet swarm combustion. NACOM is subsequently developed twice for the authors’ previously developed vapor-liquid two-layer-structure drag model, chemical kinetic combustion model, and suitable heat transfer coefficient. It is then thoroughly assessed for the separate-effects tests and integral-effects test. The evaluation results demonstrate that the optimized drag model accelerates the settling of sodium droplets due to the consideration of the sodium-vapor drag reduction effect, reducing the thermodynamic effects of liquid sodium combustion; the optimized premixed combustion model can accurately predict the low-temperature sodium droplet swarm combustion conditions, resolving the issue of serious misvaluation of the original version of NACOM. The associated research findings can serve as valuable resources and tools for deeper comprehension of the combustion effects and mechanisms of sodium droplet swarm under various operating settings (such as leakage rate and oxygen concentration).

Block it and rock it: Smoke suppressants that form a protective layer in PA 6.6

To ensure fire safety, polymers are filled with flame retardants and smoke suppressants. To meet the highest requirements, it is essential to understand the decomposition of those polymeric materials. This study reveals interactions between polymer, smoke suppressants, and flame retardants, and discusses their impact on the materials’ flame retardancy, smoke emission, smoke toxicity, and particle emission in conventional loadings to provide deeper general understanding. Low melting oxide glass, melem, spherical silica, sepiolite, melamine polyphosphate, and boehmite in an aluminum diethylphosphinate flame-retarded polyamide 6.6 were investigated. All smoke suppressants improve the protective layer and act as an adjuvant. Silica and melem performed best under forced flaming conditions. Spherical silica reduces the peak of heat release rate by 39% and the total heat evolved by 14%, whereas 10 wt% melem lowers the total smoke production by 41%. Melem alters the mode of action of aluminum diethylphosphinate from gas to more condensed phase activity. This change reduces flame inhibition and hence smoke toxicity, but further improves the protective layer due to charring reactions in the decomposition mechanism. In addition, the sizes of the smoke particles decrease because of the prolonged time in the pyrolytic zone. This study highlights that interactions between polymer, flame retardants, and smoke suppressants can significantly determine the smoking and burning behavior.

Split injection strategies for a high-pressure hydrogen direct injection in a small-bore dual-fuel diesel engine

Hydrogen-diesel dual direct-injection (H2DDI) engines present a promising pathway towards cleaner and more efficient transportation. In this study, hydrogen split injection strategies were explored in an automotive-size single-cylinder compression ignition (CI) engine, with a focus on varying the injection timings and energy fractions. The engine was operated at an intermediate load with fixed combustion phasing through adjustments of pilot diesel injection timing. An energy substitution principle guided the variation in energy fraction between the two hydrogen injections and then diesel injection while keeping the total energy input constant. The findings demonstrate that early first hydrogen injection timings lead to characteristics indicative of premixed combustion, reflecting a high homogeneity of the hydrogen-air mixture. In contrast, hydrogen stratification levels were predominantly influenced by later second injection timings, with mixing-controlled combustion behaviour apparent for very late injections near top dead centre or when the second hydrogen injection held high energy fractions, which led to decreased nitrogen oxides (NOx: NO and NO2) emissions. The carbon dioxide (CO2) emissions did not show high sensitivity to the hydrogen split injection strategies, exhibiting about 77 % reduction compared to the diesel baseline due primarily to increased hydrogen energy fraction of up to 90 %.

In-situ torrefaction-densification approach for pelletizing of rice hull/rice stalk and the combustion behavior analysis

The utilization of biomass resources could optimize the energy consumption structure and achieve the goal of carbon neutrality. Torrefaction and densification pretreatment could improve the defects of high oxygen content, low energy density, and low bulk density of biomass. In this work, high-density and hardness pellets were prepared by torrefaction coupling densification (in-situ torrefaction-densification without binders). In-situ torrefaction-densification significantly reduced the pressure required for the densification process. In-situ torrefaction-densification lowered the pressure required to prepare RH pellets with a bulk density of 1000 kg/m3 from 88.23 MPa to 30.95 MPa. The effects of the in-situ torrefaction-densification method and pelletizing pressure on the pellet combustion process were investigated by non-isothermal and isothermal combustion. The volatile and carbon of TCDP could be burned intensively during combustion, and the emissions of CO and CxHy were reduced during combustion. The original structural strength of TCDP was still maintained in the combustion process. The alkali metal K in TCDP was difficult to escape, effectively reducing the emission of K in the flue gas. In-situ torrefaction-densification could not only improve the quality of biomass solid fuel but also facilitate the storage and transportation of biomass solid fuel.

Optimization of convection cooling by pressed brick structure and coke conversion rate in coke dry quenching furnace

Segregation of coke temperature and gas flow in Coke Dry Quenching furnace is a crucial issue in coke production, and the pressed brick structure of Coke Dry Quenching furnace plays a significant role in the problem of segregation. In this work, computational fluid dynamics simulation software Ansys Fluent and self-programmed equations were utilized to investigate the fluid flow and heat transfer processes, as well as coke particle combustion behavior, based on the No. 2 Coke Dry Quenching furnace at the Bayuquan coking plant of Ansteel. The focus was on analyzing the impact of gas flow rate and pressed brick structure on the furnace’s flow and temperature fields, as well as assessing the extent of coke particle combustion under different gas flow rates. The simulation involved the use of porous media models, pseudo-fluid models, and non-local thermal equilibrium to simulate the heat transfer processes within the CDQ furnace. The simulation results show that when the coke discharge rate was set at 160 t/h, selecting a circulating gas flow rate of 180,000 m3/h could ensure that the outlet temperature of coke meet the production requirement and reducing energy consumption. Optimizing the pressed brick structure appropriately can clearly improve the segregation in gas flow and temperature within the furnace. This led to a reduction of approximately 0.3 m in the height of coke isotherm line segregation at 500 K, while also lowered the average temperature at the coke outlet. Furthermore, we established the improved random pore model with two new equations to describe the evolution of coke porosity and the molar composition of the ambient gas, and real-time tracking of changes in coke porosity and considered the impact of variable gas concentration on coke conversion rate were provided. These findings offer valuable insights and reference for optimizing operational conditions and coke quality prediction in actual production scenarios.

Investigation of marginally explosible dusts

“Marginally explosible dusts (MEDs)” are a group of combustible dusts that are distinguished by relatively low volume-normalized maximum rate of pressure rise (KSt) and maximum explosion pressure (Pmax) values. Earlier studies have suggested that dusts with KSt values less than 45 bar m/s in the laboratory-scale 20-L chamber would not explode in the 1-m3 chamber and therefore not on an industrial scale. Conversely, for some metallic dusts, significantly higher KSt values are generated in the 1-m3 chamber. Industries that handle MEDs continue to search for answers to the questions “are they explosible or not?” and “should we protect or not protect against potential explosions of these dusts?“. To answer these questions, four well-characterized materials namely, carbon black, oat grain flour, urea, and zinc were tested in the current study. These materials were selected because they exhibit different combustion behaviors and also cover a range of industries. Five ignition energies (i.e., 0.5, 1, 2.5, 5, and 10 kJ) were used in the 20-L chamber tests. The results show a clear case of overdriving (as a result of the high ignition energy density in the 20-L chamber) with respect to urea and carbon black dusts. Nevertheless, the urea dust is non-explosible. The data also suggests that the choice of test chamber to generate suitable explosion data is strongly dictated by the combustion path of MEDs. However, there are exceptions. The study also establishes the importance of both chemico-physical and thermal analyses to understanding the explosion behavior of MEDs. With reference to urea dust, a new definition for MEDs has been suggested as dusts having Pmax < 3.0 bar(g), KSt < 20 bar m/s (in the 20-L chamber), MEC >1000 g/m3, MIE >1000 mJ, and MIT >600 °C. This work provides guidelines to industries that handle MEDs on the explosibility classification of these dusts, thus addressing the existing difficulty, and informing industry on the safety strategies required when handling this group of dusts.

Optimizing CI Engine Ethanol Fuel Induction Techniques Using the AHP-PROMETHEE II Hybrid Decision Model

Ethanol along with nanoparticles stands out as a promising alternative in the pursuit of environmentally sustainable fuel options, offering a potential solution to the dual challenge of curbing NOx and PM/soot emissions while optimizing engine performance in compliance with stringent pollution regulations for compression ignition (CI) engines. The research study aims to optimize ethanol fuel induction techniques for CI engines. It utilizes a hybrid decision-making approach that integrates the analytic hierarchy process- AHP- for problem structuring and the derivation of preference weights. Subsequently, the preference ranking organization method for enrichment evaluations-PROMETHEE II is applied to assess and rank the existing alternatives. The study entails a methodical assessment of diverse ethanol induction methods across varying engine load ranges, considering multiple criteria including engine performance, emissions, combustion behavior, and exhaust after-treatment efficiency. Hybrid AHP-PROMETHEE II model provides criteria weights and ranks ethanol induction techniques and fuel blends across low, medium, and high engine loads for decision-making. It ensures that the method chosen aligns with goals, such as reducing NOx and soot emissions, optimizing engine performance, enhancing combustion, and minimizing exhaust after-treatment costs for CI engines. According to the research findings, the hybrid AHP-PROMETHEE II model identifies the CI engine operating at medium load with ethanol blending (DE10) and without the use of nanoparticles as the preferred choice. Additionally, AHP-PROMETHEE II (AHP derived criteria weights) and PROMETHEE II (direct rating derived criteria weights) models, suggested DE10 with nanoparticle (DE10_NP) using blending technique at low load and combined blending-fumigation technique with nanoparticles at high load. However, at medium load, PROMETHEE II recommends DE10_NP, while AHP-PROMETHEE II recommends DE10 blending technique. To assess the performance and reliability of this model, the consistency ratio and Spearman's rank correlation coefficient indices were computed, yielding values of 0.05 and 0.59, respectively. Both indices fall below the predetermined threshold limits, indicating a high level of consistency of the model.

Preparation and application of durable and efficient flame retardants: phosphorus–nitrogen–boron synergistic effect, flame retardant properties, combustion behavior and mechanical properties

Preparation and application of durable and efficient flame retardants: phosphorus–nitrogen–boron synergistic effect, flame retardant properties, combustion behavior and mechanical properties

Eco-friendly flame-retardant coatings based on γ-ureidopropyltriethoxysilane for cotton fabrics with improved flame retardancy and mechanical properties

In this study, a bio-based coating was constructed by sol-gel technique deposition based on γ-ureidopropyltriethoxysilane (TESPR) and ammonia phytate (AP) to acquire fire-safety cotton fabrics. The flame retardancy, thermal stability, burning behavior, flame retardant mechanism, and mechanical properties of the coated cotton fabrics were evaluated. With about 9.91% weight gain of TESPR/AP coatings, the coated cotton fabrics self-extinguished in the vertical flame test, and the limiting oxygen index arrived at 31%. The thermogravimetric analysis revealed that although the initial thermal degradation temperature of Cotton/TESPR/AP was lower than that of uncoated cotton fabrics, the char residues in the high-temperature range increased. Meanwhile, the results of the cone calorimetry test revealed that both the heat and smoke production released of cotton/TESPR/AP was greatly reduced during burning. The flame-retardant mechanism of this system was eventually suggested depending on the assessment of gaseous products and char residues. Furthermore, TESPR/AP coatings did improve the breaking force of cotton fabrics compared with that of AP coatings, while retained better air permeability compared with that of uncoated cotton fabrics. These bio-based coatings not only ensure safety, but also provide a practical flame-retardant solution for inflammable natural fabrics.

Burning and plume flow behaviors of annular pool fires: with and without air entrainment through the pool center.

Annular pool fires, frequently happened in chemical industries, have a significant influence on environmental pollution. Air pollution, greenhouse gas emissions, water pollution, and soil contamination are general ways of environmental hazards caused by the annular pool fires. This study built upon our previous study (Environ. Sci. Pollut. Res., 2023, 30(21): 59781-59792.), and extended to investigate the combustion and fire plume flow behaviors of annular pool fires, both with and without air entrainment through the hollow center of the annular pool. Results show that when there is no air entrainment through the hollow center, the low combustion intensity area at the plume's central axis gradually extends while the high combustion intensity area concentrates at higher places and the flame height increased by nearly 40% from a solid pool (Din/Dout = 0) to the annular pool (Din/Dout = 0.80). Additionally, the area with high combustion intensity is more concentrated at a higher position. The combustion of annular pool fires was found to be dominated by non-premixed diffusion combustion. The center of the annular pool fires is dominated by air prior to flame merging and by fuel vapor after the merging occurs. For annular pool fires with air entrainment through the center of the pool, the combustion intensity increases as Din/Dout at the plume base increases. And, the flame height decreased by nearly 25% as Din/Dout increases. Flame burning occurs both on the outside and inside of the plume, exhibiting a "double layer" combustion characteristic. It reveals that the combustion of the fire plume transitions to premixed diffusion combustion. The center of the annular pool fire is predominantly composed of air. Understanding and controlling annular pool fires can lead to new methods for remediating fuel spills, reducing pollution from combustion, and advancing research in fluid mechanics.

Combustion behavior of co-injecting flux, pulverized coal, and natural gas in blast furnace and its influence on blast furnace smelting

The integration of advanced high-ratio pellet ore smelting technology with flux injection at the blast furnace tuyere offers significant carbon emission and air pollution reductions for iron and steel manufacturers. This study presents a comprehensive thermogravimetric analysis and burnout rate assessment of Russian Bituminous Coal (RB) and flux mixtures across varying mass ratios, alongside a detailed exploration of the catalytic mechanisms of three distinct fluxes on RB combustion. The findings reveal that lime, when added to the coal-flux blend, markedly enhances the overall combustion characteristic index and catalytic impact, more so than limestone or dolomite. The optimal lime admixture of 5 % resulted in a peak S value of 6.30 and a burnout rate of 70.63 %, constituting an increase of 7.64 % over the base case without flux. Lime's superior catalytic performance is attributed to its higher content of calcium-containing compounds, which amplify catalytic activity through increased Ca2+ ion exchange with carboxyl groups. Mathematical model calculations considering the combustion rate of the pulverized coal show that: after the addition of 5 % lime, there is a 133.43 t/d increase in iron production, compared to the 11,323.98 t/d without the addition of flux. When the lime addition amount is 7 %, the proportion of sintered ore in the blast furnace decreases by 6.53 %, and the coke saving is 2.8 kg/t. This research is expected to enhance the understanding of pulverized coal combustion when amalgamated with basic fluxes and serve as a theoretical foundation for optimizing industrial applications.

Experimental and numerical investigation of methane combustion in a HCCI engine under enriched oxygen conditions

The challenge in the energy transition lies in the intermittent nature of renewable energy, requiring the development of effective storage methods. E-fuels are considered a promising solution, with potential applications to Homogeneous Charge Compression Ignition (HCCI) engines known for their high thermal efficiency and low nitrogen oxide emissions. However, HCCI engines face limitations such as low power density and a narrow operating range. To overcome these issues, oxygen-enriched combustion is proposed, aiming at enhancing the mixture reactivity and expanding the operating range by decreasing the intake temperature. As the potential of the expansion of the operating range has never been investigated, we performed an experimental campaign using a methane-fuelled HCCI engine at variable oxygen fractions in the oxidizer. To further elucidate the effects of oxy-fuel combustion, we also performed a kinetic analysis of the reactions driving the combustion behaviour. It has been experimentally found that increasing the oxygen content in the mixture, up to 90%, has a significant potential to decrease the needed intake temperature (up to 70 °C) of the charge to keep the Maximum Pressure Rise Rate (MPRR) below the safety threshold of 8 bar/CAD. Despite the notable IMEP increase achieved, operating the engine at high oxygen content presents significant technical challenges. Therefore, to make HCCI engines competitive with other combustion modes, it is essential to combine oxygen enrichment with additional power density enhancement techniques. The kinetic analysis has highlighted that the mixture is less sensitive to intake temperature changes at higher oxygen percentages (above 50%) and that the rates of the main reactions involved in methane and OH consumption are highly enhanced by oxygen addition.