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While hydrogen is a promising clean fuel for gas turbines, reconciling its physical and chemical characteristics with the requirements of low NOx emissions is challenging. Consequently, hydrogen combustion often results in high NOx emissions and susceptibility to flashbacks, limiting its widespread application in the gas turbine industry. While moderate or intense low-oxygen dilution (MILD) combustion technology offers the potential to address these problems, its performance degrades significantly under partial-load conditions, making it unsuitable for the wide range of load requirements of gas turbines. This study explores a novel method for expanding the stable operating range of MILD combustion using catalytic combustion to promote the development of a carbon-free energy society and address the severe performance degradation of MILD combustion. Increasing the heat energy of the gas to compensate for the lack of kinetic energy in the air reduced the dependence of MILD combustion on the recirculation ratio, resulting in high combustion efficiency and low NOx emissions. The performance of a simplified combustor model was studied through numerical simulations using a decoupling catalytic and MILD combustion strategy. Under two typical operating conditions, the numerical results showed combustion efficiencies of 99.99% with NOx emissions of 23 ppm and 3 ppm, thus demonstrating that the proposed scheme can achieve MILD combustion with high efficiency and low NOx emissions under different load conditions, thereby realising stable operation. Moreover, this approach can provide a feasible combustion path for future decarbonisation of gas turbines. • A stage and catalytic combustion scheme is designed. • MILD combustion, thermal and emission characteristics are investigated. • Excellent combustion performance and low emissions under wide load conditions is achieved. [ABSTRACT FROM AUTHOR]

For sintering pot productive process with various fuel particle size distributions, a transient numerical simulation sintering model based on the computational fluid dynamics approach is developed using Fluent 2021R1. The model combines chemical reaction, mass and heat transfer, Euler–Euler model, and fluid flow in porous media. In this study, CO is employed as the combustion's intermediate product, which is further oxidized by secondary combustion in the high‐temperature zone. Through calculations, the solid fuel combustion behavior of the sintering is explained collectively with the changing bed temperature, CO emission, and solid fuel combustion efficiency of the process under various fuel particle size distribution. In the sintering process, the fuel particle size distribution is crucial for lowering CO emissions and increasing combustion efficiency. The combustion efficiency shows a tendency of increasing initially before decreasing with the reduction of solid fuel particle size, while CO emissions show a trend of reducing first and then increasing. It is advantageous to lower the CO emission in the sintering process, and the combustion efficiency of the sintering process is greatly boosted by 5.13% when the proportion of solid fuel with 5 mm particle size decreases and the proportion of solid fuel with 3 mm particle size increases. [ABSTRACT FROM AUTHOR]

Air quality in airport attracts a widespread attention due to the emission of GHGs and pollutants related with aircraft flight. Sustainable aviation fuel (SAF) has confirmed PM2.5 reduction due to free of aromatics and sulphur, and thus air quality improvement in airport is prospected by SAF blend. Two types of SAF were assessed the potential of energy saving and emission reduction by ZF850 jet engine. FT fuel is characterized with only paraffins without aromatics and cycloparaffins while HCHJ fuels is characterized with no aromatics. The descend of air quality and SAF blend were both investigated the effect on the engine performance and emission characteristic. The critical parameters were extracted from fuel compositions and air pollutants. Ambient air with a higher PM2.5 could lead to the rise of engine emission especially in UHC and PM2.5 despite at the low thrust setting and high thrust setting, and even couple with 3.2% rise in energy consumption and 1% reduction in combustion efficiency. CO, NO and NO2 in ambient air show less influence on engine performance and emission characteristic than PM2.5. Both types of SAF blend were observed significant reductions in PM2.5 and UHC. PM2.5 reduction obtained 37.9%—99.8% by FT blend and 0.64%-93.9% by HCHJ blend through the whole trust settings. There are almost 6.67% positive benefit in TSFC through the whole thrust setting by 7% FT blend. The effects of air quality and SAF blend on engine emission present significant changes on PM and UHC but the slight change on CO and NOx. By SAF blend, the energy saving and pollutant reduction obtained could be both benefit for air quality improvement in airport and further reduce engine emission as the feedback of less pollutants in ambient air. Highlights: Reduction of fuel consumption and engine emission by SAF blends; Higher PM in ambient air leads to the increase of fuel consumption and engine emission; Significantly reducing PM and UHC in airport by SAF blends; [ABSTRACT FROM AUTHOR]

The Mach 6-capable turbine based combined cycle engine is a potential first-stage propulsion for TSTO mission. In order to improve thrust-to-weight ratio, an innovative tandem combined ramjet engine-FABRE (Fan Augmented Air-Breathing Ramjet Engine) is designed utilizing a versatile multi-mode combustor working at both high-speed ramjet mode and low-speed turbocharged mode. Employing the strut as mixer and flame holder in multi-mode combustor presents theoretical advantages. Nonetheless, a thorough investigation into its practical feasibility and combustion characteristics is essential. This paper experimentally verifies the feasibility of strut approach in multi-mode combustor at various speeds and evaluates the effects of different strut schemes on flow field structure, thermodynamic characteristics, and combustion performance via simulation. The experimental results affirm that employing the strut scheme as a combustion organization method enables the multi-mode combustor to operate effectively under diverse inflow conditions at both high and low speeds. Simulation results further validate that these strut solutions consistently demonstrate superior combustion performance. Additionally, the influences of the strut geometry on heat release and high-temperature area are highly consistent with its effects on combustion efficiency. At low speed, wider struts lead to increased combustion efficiency, while at high speed, they initially rise before declining with further widening. Regardless of speed, increasing strut slant angle consistently reduces efficiency. At low speed, widening the strut lowers the total pressure recovery coefficient, peaking at 45° with varying strut slant angle. Conversely, at high speed, changes in strut width minimally impact, while increasing strut slant angle reduces the coefficient. These conclusions provide valuable insights for the optimization of combustion organization in the design of combined ramjet engine with a wide range of operating conditions. • An innovative Mach 6-capable combined ramjet engine is designed to enhance the thrust-to-weight ratio for TSTO. • Experimentally validating the strut scheme for combustion organization in multi-mode combustor. • Combustion characteristics are numerically investigated using different strut schemes. [ABSTRACT FROM AUTHOR]

Experiments and numerical simulations were conducted across a range of contraction ratio to investigate the detonation combustion characteristics of liquid aviation kerosene/air rotating detonation combustor. The research indicates that extremely low and high contraction ratio adversely affect the stable operation of the two-phase rotating detonation combustors. At a contraction ratio that is too low (19.03 % in the RDC discussed in this paper), the atomization and mixing properties of the two-phase fuel are poor, with a lower reaction pressure in the fresh mixture, hindering the initiation of detonation waves. On the other hand, a contraction ratio (85.7 % in the RDC discussed in this paper) that is too high enhances the energy of the detonation wave; it triggers oblique shockwave feedback, preventing the fresh mixture from entering the combustor and thus leading to the quenching of detonation waves. With an increase in the contraction ratio of outlet configurations, there is a noticeable rise in both the peak pressure and combustion efficiency of detonation waves. In contrast, the wave height gradually decreases, and the wave velocity shows a pattern of initially increasing and then decreasing. Along the axial position inside the two-phase rotating detonation combustor, the upstream detonation wave is caused by the reflected shockwaves increasing the pressure of the upstream fresh mixture. In contrast, the downstream detonation wave results from increased fresh mixture pressure and enhanced fuel atomization and mixing due to the increased contraction ratio of outlet configurations and wave feedback. So, the detonation wave exhibits a strong-weak-strong distribution characteristic. • Three-dimensional numerical simulation and experiment in a RDC with separate feeding of kerosene and air is achieved. • Two atomization and mixing structures ("Kerosene" and "Enhanced Kerosene" region) is found. • An optimal contraction ratio size enables the RDC to achieve the best operational characteristics. [ABSTRACT FROM AUTHOR]

A strategic pathway to decarbonizing internal combustion engines and advancing toward sustainable energy includes the transition from conventional fuels to methane combustion, followed by methane-hydrogen mixtures, and ultimately to hydrogen-only combustion. This progression leverages the miscibility of hydrogen and methane, enabling the use of Hythane, a fuel blend that combines the advantages of both gases. Methane's widespread availability and existing infrastructure facilitate a cost-effective transition, while its combustion produces lower emissions compared to gasoline and diesel. Hydrogen's high reactivity and clean combustion properties enhance engine efficiency and reduce emissions, making it a crucial component in this phased transition. Challenges in homogeneous charge compression ignition (HCCI) combustion of CH₄-H₂ mixtures, such as controlling ignition timing and managing stable combustion, are addressed by the direct injection jet ignition (DIJI) technique. DIJI creates stratified air-fuel mixtures that ensure rapid and complete combustion, minimizing quenching and reducing heat losses. This study presents a comprehensive analysis of the combustion properties of methane and hydrogen, the benefits of phasing the transition with the availability of green hydrogen, and the technical challenges and solutions in developing HCCI and DIJI combustion systems for Hythane. The research underscores the potential of DIJI to enhance engine performance, efficiency, and emissions control, paving the way for a sustainable energy future in transportation. • Hythane is part of a strategic transition from methane to hydrogen in internal combustion engines. • Hythane and DIJI permit enhanced efficiency and reduced emissions with Hythane. • DIJI provides improved ignition control, combustion stability, and NOx reduction. • DIJI provides superior control and efficiency compared to HCCI. • The work encourages investment in hydrogen technologies for a sustainable energy future. [ABSTRACT FROM AUTHOR]

This study focuses on numerically exploring the effect of coupling factors on enhanced combustion performance in a two-strut scramjet combustor. The impact of five geometric variables, namely d (the vertical distance between the two struts), ur (lr) (the radius of the upper(lower) strut' tip), and ul (ll) (the length of the upper(lower) strut), is investigated through univariate analysis. While increasing ur and lr intensifies shocks at the cost of great total pressure loss, decreasing ul (ll) strengthens the upper(lower)flame but compresses the other. Besides, changing d influences the interaction of shocks and shear layers. To investigate the coupling effect of these variables, the combustion efficiency of the two-strut combustor is optimized through the SEGA algorithm based on a Kriging model built by small sampling points in 5D design space, which increases combustion efficiency by 14% and thrust by 27%. The optimum design features small ur and zero lr , larger d and ll and smaller ul. Further analysis performed on it revealed that the mechanism for enhancing combustion performance involves coupling the five geometry variables to assist combustion of the fuel closer to the upper expanding wall via stronger shock waves. Simultaneously, it weakens the shocks induced by the other strut to balance the total pressure loss. • Study coupling factors for efficient combustion in a two-strut scramjet combustor. • Enhance combustion in an asymmetry two-strut configuration via optimization. • Alternate shocks to enhance ignition and decrease total pressure loss. [ABSTRACT FROM AUTHOR]

The combustion cycle‐to‐cycle variations (CCV) are the typical combustion phenomena in the internal combustion engine, which will not only affect the combustion efficiency, heat‐work conversion process, and emission formation in the cylinder, but also cause the output torque and power fluctuation, resulting in unstable and even misfire. These phenomena are particularly evident in the spark ignition (SI) engine, especially at idle, acceleration, and high exhaust gas recirculation conditions. Consequently, it is quite important to explore the internal relationship and correlation mechanism between the CCV and the affecting factors. This paper comprehensively reviewed the fundamental reasons and mechanisms of CCV of the SI engine. In addition, the characteristic parameters and characterization methods of the CCV, the laws and influencing factors of the CCV, and the numerical simulation methods of the CCV were introduced in detail to quantitatively analyze the performance, combustion, and emissions characteristics of the SI engine. Each research direction is discussed in detail in various sections. The research status of the CCV of the SI engine from the experimental and numerical simulation aspects was also presented and discussed. Lastly, effective methods and strategies were proposed to improve the combustion process and fuel economy, and reduce exhaust emissions of the SI engine for high efficiency and clean combustion. [ABSTRACT FROM AUTHOR]

The term "e-fuel" typically refers to synthetic fuels produced using renewable energy sources, primarily starting with green hydrogen. Hydrogen serves as the foundational e-fuel, but there are also proposed solutions involving combining hydrogen with carbon dioxide to produce e-fuels that resemble today's alkanes or alcohols. The production process integrates water electrolysis, CO₂ capture, and fuel synthesis, all powered by renewable sources like wind and solar energy. Key processes include hydrogen generation using various electrolyzers and CO₂ capture from either direct air capture or industrial sources. Subsequently, hydrogen and captured CO₂ are synthesized into hydrocarbons using methods such as Methanol Synthesis, Fischer-Tropsch Synthesis, and the Sabatier Process. Advances in catalyst technology, reactor design, and renewable energy integration are enhancing production efficiency and feasibility. Although currently more expensive than fossil fuels, e-fuels are expected to become cost-competitive with technological advancements and supportive policies. They offer significant environmental benefits, including carbon neutrality and reduced pollution. One crucial enabler of e-fuels is the development of novel combustion systems for internal combustion engines. Innovations such as direct injection and jet ignition improve combustion efficiency when using e-fuels. These systems enable optimized premixed or diffusion combustion, balancing efficiency and performance for both liquid and gaseous fuels resembling diesel or gasoline. E-fuels are poised to play a vital role in achieving a sustainable, low-carbon energy future, particularly in sectors where direct electrification is challenging. Continued research and policy support are essential for their further development, with direct injection and jet ignition systems playing an integral part in this transformative journey. [ABSTRACT FROM AUTHOR]

In modern society where fossil fuel prices are increasing and environmental issues are becoming more severe, biodiesel, as a new type of clean fuel, is receiving increasing attention. Biodiesel has the advantages of renewability, environmental friendliness, and good fuel properties, demonstrating broad application prospects. However, the use of biodiesel also faces some challenges, such as higher density and kinematic viscosity, lower calorific value, etc. The application of nanoparticles in biodiesel engines helps to achieve the goal of clean fuel. In terms of fuel characteristics, nanoparticles increase the calorific value, cetane value, and flash point of the fuel, improving combustion efficiency and safety, but increasing density may affect combustion. The use of nanoparticles can promote micro explosions and secondary atomization of fuel, improve combustion characteristics, and increase cylinder pressure, heat release rate, and brake thermal efficiency while reducing fuel consumption. Nanoparticles reduce HC and CO emissions, improve combustion through higher oxygen and reaction area, and reduce incomplete combustion products. On the contrary, nanoparticles also increase CO2 emissions because better combustion conditions promote oxidation reactions. For NOX emissions, some nanoparticles lower the combustion temperature to reduce emissions, while others increase emissions. Comparison shows that all nanoparticles offer varying degrees of improvement in engine performance and emissions, but the improvement provided by TiO2 nanoparticles is significantly better than that of other nanoparticles. In the future, the synergistic effect of multiple nanoparticles should be explored to further improve performance and reduce emissions, achieving effects that cannot be achieved by a single nanoparticle. [ABSTRACT FROM AUTHOR]

This study investigates the enhancement of combustion efficiency in a dual-fuel diesel engine powered with oxyhydrogen as the primary fuel and a Graphene oxide nanoparticle-dispersed biodiesel/diesel blend as the pilot fuel. A Box-Behnken design (BBD) is employed to develop an L 17 orthogonal array for three factors and three levels of input parameters: engine load, HHO flow rate, and EGR ratio. An RSM-based 3D surface plot is utilized to analyze the interaction between input parameters and responses. Multi-objective optimization through RSM-based desirability and genetic algorithms (MOGA) is conducted to obtain the optimal engine operating parameters. The MOGA approach demonstrates superior performance compared to the RSM-based desirability approach. The optimal engine operating parameters identified by the MOGA approach are an engine load of 9.89 kg (approximately 3.43 kW), an HHO flow rate of 5.78 L/min, and an exhaust gas recirculation (EGR) ratio of 10.18%. At this optimized operating condition, the performance and combustion output are 31.85% BTE, 0.3268 kg/kWh of BSFC, and 60.16 bar of peak cylinder pressure (PCP). In terms of emissions, carbon monoxide (CO) is 0.04152 vol %, hydrocarbon (HC) is 25.45 ppm, and nitrogen oxide (NO x) is 746.12 ppm. Experimental validation confirms that all results are within an acceptable limit with a maximum error of 6%. Oxyhydrogen significantly enhances fuel efficiency and consumption while simultaneously reducing carbon-based emission levels, except for nitrogen oxide emissions. The adverse effects of an increase in NO x are mitigated by the addition of EGR. [Display omitted] • Biodiesel synthesis using ultrasonic-assisted technology. • Study of dual-fuelled diesel engine behavior with nanoparticles, HHO and EGR. • Application of RSM-based predictive models for performance and emission analysis. • Multi-objective optimization through RSM and GA for engine response optimization. • The optimal engine operating conditions are: load 9.89 kg, HHO flow rate 5.78 L/min, and EGR 10%. [ABSTRACT FROM AUTHOR]

Turbojet engines play a crucial role in air transportation, providing superior thrust-to-weight ratios and lower NOx emissions compared to gas turbine engines, particularly at high speeds. Although they are efficient, environmental concerns and rising fuel costs have led to the exploration of alternative fuels. This study examines the use of green gaseous fuels, specifically hydrogen, in the SR-30 turbojet engine. Engine performance, combustion characteristics, and emissions were measured across a range of speeds from 40,000 to 75,000 rpm, without altering the combustion chamber. Hydrogen was injected into the engine air inlet manifold at a constant volume. The hydrogen used in the study was a mixture of 75% biogas and 25% hydrogen by volume. Due to hydrogen's high flammability, a flashback arrestor was employed to prevent backfire. The introduction of gaseous fuel increased maximum thrust by 4.5% and reduced fuel consumption by 2.2%. The addition of hydrogen improved thrust and combustion efficiency while lowering specific fuel consumption and unburned fuel. However, the presence of nitrogen and hydrogen may lead to increased NOx emissions. By optimizing fuel injection strategies, it is possible to mitigate NOx emissions, thereby improving engine efficiency and minimizing environmental impact. The study concludes that gaseous fuels like hydrogen provide a promising alternative for enhancing turbojet engine performance and reducing emissions. • Hydrogen was tested in the SR-30 turbojet engine without modifications with gaseous fuel. • Inclusion of gaseous fuel increases maximum thrust by 4.5% along with 2.2% reduction in fuel flow rate. • Hydrogen increases NOx emissions due to high combustion temperatures. • Injecting hydrogen via air intake is not effective. [ABSTRACT FROM AUTHOR]

Biodiesel, an eco-friendly fuel with lower greenhouse gas emissions, is a crucial alternative to traditional fossil fuels. Adding hydrogen and nanoparticles to biodiesel enhances diesel engine performance, reduces emissions, and improves fuel efficiency through better combustion and fuel atomization. In this study, various nanoparticles were experimented, and their performance, emission, and acoustic outcomes were systematically evaluated, resulting in a comprehensive ranking and clustering. The k-means clustering-Entropy-TOPSIS method is applied to weigh performance outcomes, rank the nanoparticles, and create clusters among them among best and worst, considering multiple criteria's in this study. This study further divides diverse nanoparticles into clusters, employing a hybrid machine learning k-means clustering method. The CO parameter carries the highest weight (57%), followed by UBHC (22%), owing to their significant variation induced by the addition of nanoparticles, surpassing the variability observed in other parameters. Manganese oxide nanoparticles exhibited superior performance across various critical parameters among all nanoparticles with a minimum centroidal distance of 25.97. Moreover, enrichment with hydrogen gas, combined with nanoparticles, significantly enhanced diesel engine performance, manifesting in an approximate 8 % increase in Brake Thermal Efficiency (BTE) and 23 % reduction in CO emissions. Identifying the optimal nanoparticles is crucial for enhancing biodiesel properties, and the paramount importance of hydrogen mixing lies in its potential to significantly improve combustion efficiency, emissions, and overall diesel engine performance. • This study experimented with various nanoparticles in biodiesel-hydrogen blends within a diesel engine. • The study employs K-means clustering-Entropy-TOPSIS method to cluster nanoparticles based on performance, emissions, and acoustic outcomes. • The CO parameter carries the highest weight (57%), followed by UBHC (22%). • Manganese oxide nanoparticles exhibited superior performance across other nanoparticles. [ABSTRACT FROM AUTHOR]

Hydrogen/ammonia has a good prospect as an alternative fuel to traditional fossil fuels, and is one of the best ways to realize the goal of energy saving and emission reduction. However, due to hydrogen fuel's high flame propagation velocity and low ignition energy, abnormal combustion, such as backfire in port hydrogen injection engines, while ammonia fuel, characterized by high ignition energy and low laminar burning rate, thus the mixing of ammonia fuel as one of the effective methods to realize the hydrogen engine. This study endeavors to investigate the constraints of H 2 /NH 3 by utilizing a combined experimental and simulation approach to investigate the effect of the hydrogen/ammonia mixture ratio on engine combustion and emission performance at different injection timings. The results show that reasonable selection of injection timing can improve the fuel trapping ratio and reduce the fuel residue in the intake tract, which has an important effect on reducing the probability of backfire. For engine performance, the indicated mean effective pressure (IMEP), indicated thermal efficiency (ITE), and indicated power (IP) of the hydrogen internal combustion engine were reduced to 5.7 bar, 30%, and 5.1 kW, respectively, when ammonia was doped at a mass ratio of 50%. For combustion characteristics, ammonia addition reduced the in-cylinder pressure and exothermic rate, and extended the combustion duration. At the same time, chemical kinetic analysis showed that with the addition of ammonia, the concentration of H and OH radicals decreased, which would have a negative effect on the in-cylinder reaction rate, slowing down the reaction rate of the primitives, thus reducing the overall combustion rate and combustion efficiency. In terms of emissions characterisation, an increase in the ammonia content leads to higher nitrogen oxide (NO x) emissions, but these start to decrease once the ammonia content exceeds 40%. The results of the research could advance the development of hydrogen/ammonia engines and contribute to the realization of a zero-carbon combustion model for internal combustion engines. • The optimal hydrogen injection starting point should be selected 330° CA BTDC. • Ammonia doping reduces the speed and rate of combustion. • Ammonia addition reduces the maximum heat release rate and cylinder pressure. • As The ammonia in the fuel increases, the NOx emissions increase and then decrease. [ABSTRACT FROM AUTHOR]

In this study, the combustion and emission characteristics of natural gas/diesel dual-fuel engines under low load in diesel pilot ignition (DPI) and reactivity controlled compression ignition (RCCI) combustion modes were compared and analyzed by parametric study. The results show that compared with DPI mode, RCCI mode has lower NOx, CO and HC emissions and relatively higher thermal efficiency. However, under low load conditions, the in-cylinder mean temperature and combustion efficiency were reduced, and HC and CO emissions were still high in the RCCI combustion mode. The combustion characteristics of the fuel in the cylinder are changed by adding argon, hydrogen and syngas into the cylinder. The ability of additives to expand the low load operation range of natural gas/diesel RCCI engine was discussed and compared from the aspects of macroscopic combustion process and microscopic chemical reaction kinetics. The results show that argon, hydrogen and syngas can change the combustion characteristics of fuel. When argon, hydrogen and syngas are added, the gross indicated efficiency (GIE) can be increased from 38.1% to more than 50% compared to the basic condition. Maximum GIE and low HC emissions can be achieved with the introduction of 10% argon mass fraction, while a 20% hydrogen or syngas mass fraction is required to maintain low HC emissions. Therefore, argon has the greatest potential to improve the performance of natural gas/diesel RCCI engines under low load conditions. [Display omitted] • The effect of using Ar, H 2 and syngas on natural gas/diesel RCCI engine at low load. • The RCCI mode has lower NOx, HC, and CO emissions than the DPI mode. • The use of Ar, H 2 and syngas can improve the combustion of RCCI engine at low load. • Ar has the greatest potential to improve the performance of RCCI engines at low load. [ABSTRACT FROM AUTHOR]

Ammonia, as a renewable energy with broad future application prospects, can alleviate its deficiencies in combustion stability as well as NOx emission by swirl premixed combustion technology. To investigate the impacts of swirler configuration parameters on ammonia premixed combustion, vanes numbers, vanes angles, and inner/outer diameter ratios of the swirler are varied. The combustion characteristics and NOx emissions in the combustion chamber are analyzed using the ammonia combustion mechanism model proposed by Stagni, which is done by large eddy simulation and Flamelet generated manifold combustion model. The results indicate that a stronger inner recirculation and lower NO 2 /N 2 O emissions were obtained when the number of vanes is 10. Increasing the vanes angles has several benefits, including expanding the flame's main combustion region, enhancing the heat release rate and improving turbulence in the flow field. The highest combustion efficiency and the lowest NO emissions are achieved at a vanes angle of 35°. Additionally, a moderate inner/outer diameter ratio of 0.447 can ensure appropriate inner and outer circulation intensity and NOx emissions. Based on the investigation results, the references for swirler parameters design in premixed ammonia combustion are provided. • NH 3 /air premixed flames were modeled by LES and FGM model. • Effects of vanes number, angle, and inner/outer diameter ratio were analyzed. • Linked thermal performance and pollutant emissions to flow field features. [ABSTRACT FROM AUTHOR]

Diesel generators are widely used to produce electricity and heat in remote communities. However, their use contributes to harmful pollutant and greenhouse gas (GHG) emissions, negatively impacting the environment and public health. Syngas, which is a sustainable fuel, can play an important role in the transition from petroleum to renewable fuels. When used in dual-fuel diesel engines, it can contribute to reducing GHG emissions and the cost of transporting diesel, especially for rural and remote communities. This study investigates the effects of optimizing the diesel direct injection (DI) and exhaust gas recirculation (EGR) strategies on the combustion and emission performance of a syngas-diesel dual-fuel generator at constant load. The experiments were conducted using a 30-kW generator with a four-stroke, four-cylinder, turbocharged, and electronically controlled direct-injection diesel engine. The intake manifold of the engine was modified to allow introducing syngas upstream of the turbocharger. The syngas was simulated using individually controlled flow rates of hydrogen (H 2), carbon monoxide (CO), carbon dioxide (CO 2), and nitrogen (N 2). The syngas flow rate was adjusted to replace 40% of the energy provided by diesel fuel while optimizing the diesel DI parameters such as the pilot injection timing, main injection timing and diesel direct injection rail pressure, as well as the EGR rate. The findings of this study reveal that optimizing diesel injection strategy and appropriately raising the EGR rate have a positive impact on the engine performance and emissions. • Optimizing diesel injection strategies and EGR rate of a syngas-diesel dual-fuel diesel engine. • Hydrogen-rich syngas enhances combustion efficiency and emissions control. • Fine-tuning of pilot injection timing and duration improved the engine efficiency and emissions. • Increasing EGR rate stabilized emissions, with notable reductions in NOx and CO levels. • Adjustment of the main injection timing positively impacted combustion characteristics. • Increasing the injection pressure resulted in notable reductions in CO and PM emissions. [ABSTRACT FROM AUTHOR]

As global demands for enhanced energy efficiency and environmental protection continue to grow, optimizing the combustion processes of industrial boilers has become a critical challenge. These processes involve complex thermodynamic and chemical reactions that directly impact energy utilization and pollutant emissions. However, existing methods for combustion prediction and optimization often fall short in terms of accuracy and efficiency, making it difficult to adapt to varying operational conditions. This study proposes a thermodynamics-based multi-objective optimization method for industrial boiler combustion. A high-precision combustion prediction model is established using deep learning, and an evolutionary algorithm is employed for multi-objective optimization, aiming to achieve an optimal balance between combustion efficiency and pollutant emissions. The findings of this research not only offer new insights into combustion optimization for industrial boilers but also contribute valuable theoretical and practical implications for enhancing energy utilization efficiency and reducing environmental pollution in industrial production. [ABSTRACT FROM AUTHOR]

Natural gas (NG) is favored for transportation due to its availability and lower CO2 emissions than fossil fuels, despite drawbacks like poor lean combustion ability and slow burning. According to a few recent studies, using hydrogen (H2) alongside NG and diesel in Tri-fuel mode addresses these drawbacks while enhancing efficiency and reducing emissions, making it a promising option for diesel engines. Due to the importance and novelty of this, the continuation of ongoing research, and insufficient literature studies on HNG–diesel engine emissions that are considered helpful to researchers, this research has been conducted. This review summarizes the recent research on the HNG–diesel Tri-fuel engines utilizing hydrogen-enriched natural gas (HNG). The research methodology involved summarizing the effect of engine design, operating conditions, fuel mixing ratios and supplying techniques on the CO, CO2, NOx and HC emissions separately. Previous studies show that using natural gas with diesel increases CO and HC emissions while decreasing NOx and CO2 compared to pure diesel. However, using hydrogen with diesel reduces CO, CO2, and HC emissions but increases NOx. On the other hand, HNG–diesel fuel mode effectively mitigates the disadvantages of using these fuels separately, resulting in decreased emissions of CO, CO2, HC, and NOx. The inclusion of hydrogen improves combustion efficiency, reduces ignition delay, and enhances heat release and in-cylinder pressure. Additionally, operational parameters such as engine power, speed, load, air–fuel ratio, compression ratio, and injection parameters directly affect emissions in HNG–diesel Tri-fuel engines. Overall, the Tri-fuel approach offers promising emissions benefits compared to using natural gas or hydrogen separately as dual-fuels. [ABSTRACT FROM AUTHOR]

This paper presents an experimental study of lean flames stabilization with nanosecond repetitively pulsed discharges. The two-stage, swirled-stabilized, multipoint injector BIMER operates at atmospheric pressure with methane-air mixtures in the present study. It is representative in its design of a realistic lean premixed prevaporized injector of gas turbine engines operated at a lab-scale level. The lean blow-off extension with plasma is characterized. The combustion efficiency and the pollutant emissions are quantified near blow-off with and without plasma for 50-kW flames. We show that it is possible to stabilize lean flames down to an equivalence ratio of 0.3, with less than 5 ppm of NOX emitted, thanks to nanosecond repetitively pulsed (NRP) discharges with an electric power that represents less than 0.25% of the flame thermal power. This study also clearly shows that it is necessary to account for the plasma system integration at the early stage of the combustor design to fully benefit from the plasma stabilizing effects on the flame. [ABSTRACT FROM AUTHOR]

The quest for clean, efficient engine technologies is imperative in reducing transportation's environmental impact. Hydrogen, as a zero-emission fuel, offers significant potential for internal combustion engines but faces challenges such as optimizing engine performance and longevity. Water injection is proposed as a solution, yet its effects on engine performance require thorough investigation. This study bridges the knowledge gap by examining various water injection ratios (WIRs) and their impact on engine performance, focusing on the balance between power output and engine longevity. We identified the existence of an optimum WIR (e.g., 10% in this study), which provides peak performance with minimal adverse effects on engine performance and health. Computational simulations of a single-cylinder engine revealed how WIRs influence in-cylinder temperature, pressure, and IMEP, emphasizing the nuanced benefits of water injection. Additionally, our analysis of turbulence, through TKE and dissipation rate, deepens the understanding of combustion and fuel efficiency in hydrogen engines. This research provides valuable guidance for optimizing engine operations and paves the way for advanced water injection systems in hydrogen engines, marking a significant step towards cleaner engine technology. [ABSTRACT FROM AUTHOR]

Although bamboo is widely distributed in Japan, its applications are very limited due to its poor combustion efficiency for fuel. In recent years, the expansion of abandoned bamboo forests has become a social issue. In this research, the possibility of a liquefaction process with fast and efficient liquefaction conditions using moso bamboo as raw material was examined. Adding 20 wt% ethylene carbonates to the conventional polyethylene glycol/glycerol mixed solvent system, the liquefaction time was successfully shortened from 120 to 60 min. At the same time, the amount of sulfuric acid used as a catalyst was reduced from 3 wt% to 2 wt%. Furthermore, polyurethane foam was prepared from the liquefied product under these conditions, and its physical properties were evaluated. In addition, the filler effects of rice husk biochar and moso bamboo fine meals for the polyurethane foams were characterized by using scanning electron microscopy (SEM) and thermogravimetry and differential thermal analysis (TG-DTA), and the water absorption and physical density were measured. As a result, the water absorption rate of bamboo fine meal-added foam and the thermal stability of rice husk biochar-added foam were improved. These results suggested that moso bamboo meals were made more hydrophilic, and the carbon content of rice husk biochar was increased. [ABSTRACT FROM AUTHOR]

The trapped vortex combustor (TVC) has shown promise for use in advanced aircraft engines due to its high combustion efficiency, excellent stability, compact geometry, and low pressure loss. However, the mainstream-forced entrainment phenomenon presents a significant challenge to implementing the TVC. This study conducted experimental and numerical investigations to examine the effect of different cavity-air-injection modes on mainstream-forced entrainment. The results indicate that the entrainment of mainstream air into the cavity is greatly affected by the cavity-air-injection mode, subsequently influencing the combustion performance of the TVC. Compared to the front/rear air-injection mode (case 1) or the front air-injection mode (case 3) of the cavity, the rear air-injection mode (case 2) can effectively reduce the entrainment of the main flow into the cavity, creating a stable large-scale single vortex flow structure. Additionally, the fuel distribution in the cavity is somewhat influenced by the cavity's air-injection design. The local equivalence ratio of the cavity in case 1 is higher than that of cases 2 and 3, which benefits lean ignition and blowout performance. Case 1 demonstrates superior ignition and blowout performance compared to case 2, which exhibits the poorest ignition–blowout performance. Cases 1 and 3 share similar ignition processes, although case 3 has a significantly longer ignition time than case 1. In contrast, case 2 experiences ignition with the flame primarily concentrated in the mainstream area due to its air-injection mode. The cavity's air-injection mode leads to a rapid influx of fuel into the mainstream area, resulting in the lowest combustion efficiency observed in case 2. [ABSTRACT FROM AUTHOR]

A scramjet engine offers a potential route to achieve supersonic speeds using airbreathing engines. Achieving proper mixing and combustion poses a challenge due to the supersonic inflow of air. Researchers have explored multi-strut configurations to tackle this issue. However, multiple struts supplying fuel inefficiently can lead to fuel loss and reduced efficiency. Alternatively, utilizing a multi-strut setup passively could enhance combustion and mixing efficiency. In this study, two types of jet splitting passive strut configurations were investigated computationally with the improved delayed detached-eddy simulation turbulence model. Implementation of passive strut altered vortical structures, influencing mixing and combustion performance. The splitting of the jet introduces large-scale vortices downstream. Strategically placing the passive strut in the wake of the combustion zone was found to improve both mixing and combustion efficiency. Acoustic loading was seen to increase with the introduction of passive strut. It was observed that the diamond-shaped passive strut has the highest combustion efficiency; however, it suffers from higher acoustic loading. The dynamic mode decomposition analysis revealed the coupling frequency of fluctuating pressure and heat release rate, which causes thermoacoustic loading. Overall, passive strut placement significantly influenced combustion, mixing, and thermoacoustic properties, highlighting the importance of considering passive strut configurations in design optimization for scramjet engines. [ABSTRACT FROM AUTHOR]

Owing to their unique non-Newtonian characteristics, gel propellants have become a new type of fuel with promising applications in the aerospace industry. However, the complex rheological properties and high viscosity of gels pose significant challenges for flow control in gel engines, particularly in terms of fuel atomization and combustion efficiency. Focusing primarily on kerosene gel, this study investigates the secondary atomization characteristics of shear-thinning droplets, where the volume of fluid method is employed to capture interface dynamics on adaptive grids, and the viscosity of the gel is described by a power-law model. The accuracy of the numerical model is validated by comparing it with the experimental observations of the breakup process of 1% silica kerosene gel droplets. Numerical simulations are conducted to analyze the droplet breakup processes and formation mechanisms under bag, multimode, and shear breakup. Compared to kerosene, the apparent viscosity distribution inside the kerosene gel droplets is non-uniform, and the inhibition of viscous force delays the breakup time and reduces the droplet deformation, thereby affecting the transition of the breakup mode. By varying the Weber number, We, the rheological parameters, and the density ratio, the quantitative effects of these factors on droplet deformation, centroid velocity, average viscosity, the breakup time, etc. are revealed. The results indicate that the breakup becomes more severe with increasing We number, resulting in larger deformation and a greater number of smaller droplets; the rheological parameters significantly affect the droplet breakup by altering the fluid viscosity; moreover, under the same flow condition, the higher the density ratio, the more difficult it is for the droplet to break up; however, on dimensionless scales, the effect of density ratio appears weak. Additionally, a breakup regime diagram is constructed in the We–Oh (Ohnesorge) number space for low Weber numbers. This study validates the numerical method for simulating the secondary atomization of kerosene gel propellants, providing a thorough analysis of three breakup mechanisms and the impact of key parameters on kerosene gel droplets. These insights offer a theoretical foundation for the optimization of gel propellants, aiding in the development of efficient and stable propulsion systems. [ABSTRACT FROM AUTHOR]

The computational studies carried out previously taking as an example the BKZ-210-140 boiler installed at Tomsk-2 state-owned district power plant (SDPP) have shown that, given the existing scatter in the characteristics of coals fired at the power plant, the temperature of gases at the boiler furnace outlet may vary in a wide range (more than 100°С). Such variability of the operational parameters entails a number of problems, including difficulties with keeping a stable superheated steam temperature, increased risk of heating surfaces becoming slagged, and less efficient fuel combustion. A conclusion has been drawn based on the obtained computation results that the possibility of adjusting the flame's initial section vector by ±15° will make it possible to solve the above-mentioned problems to a significant extent. A tiltable burner is the key component of the combustion system with adjusting the flame position. Based on an analysis of the current operation conditions of the Tomsk-2 SDPP BKZ-210-140 boiler, technical solutions were developed on the design of a tiltable vortex burner intended for combusting pulverized coal as well as natural gas and fuel oil. The burner's outlet part is made so that it is possible to tilt it by ±15° in the vertical plane and by ±5° in the horizontal plane, which will make it possible to adjust the combustion mode in an efficient manner. The furnace process is simulated in the ANSYS Fluent software package under different boiler operation conditions. The simulation results show that, in the case of using the new burners, it is possible to improve the furnace process efficiency. By tilting the burner by ±15° in the vertical plane, it becomes possible to obtain the temperature adjustment range at the furnace outlet equal to 120°С. Based on the adopted technical solutions, design documentation for the burner has been developed. An experimental sample of the low-toxic tiltable vortex burner installed in the Tomsk-2 SDPP BKZ-210-140 boiler has been manufactured. [ABSTRACT FROM AUTHOR]

The flow performance of a dual wall-mounted cavity in a strut-injector scramjet combustor in steady reacting flow conditions is computationally analyzed. A baseline configuration corresponding to DLR experiments and two proposed configurations with varying bottom wall cavity depth and fixed top wall ramp is considered. Steady-flow computations are performed using the 2-D Reynolds Averaged Navier–Stokes method with k-ω SST turbulence closure coupled and single-step reaction chemistry. The calculated flow patterns, density, pressure, and temperature fields are compared with shadowgraph and wall pressure measurements from DLR experiments. The cavity and strut are mounted downstream of the strut to analyze the shock patterns and their interference with the shear layer mixing features. The estimated flow patterns, density, pressure, and temperature fields are compared with shadowgraph and wall pressure measurements from DLR experiments. Incorporating cavity and ramp configuration provides earlier complete combustion compared to the baseline model, with a marginal rise in the total pressure caused by additional shock wave formation that emanates from the corners of the cavity and ramp. The combustion zone widens in the lateral direction as the cavity shifts the shock train downstream of the strut injector owing to intense shock shear layer interactions. [ABSTRACT FROM AUTHOR]

Incorporating silver wires into propellant has emerged as a highly effective strategy for enhancing propellant burning rates, a technique extensively deployed in the construction of numerous fielded sounding rockets and tactical missiles. Our research, employing a multi-faceted approach encompassing thermogravimetric-differential scanning calorimetry measurements (TG-DSC), combustion diagnoses, burning rate tests, and meticulous collection of condensed combustion products, sought to elucidate how variations in silver wire quantity and winding configuration impact the combustion properties of propellants. Our findings underscore the remarkable efficacy of double tightly twisted silver wire in significantly boosting propellant burning rates under ambient conditions. Moreover, at lower temperatures, the reduced gap between the propellant and silver wire further magnifies the influence of silver wire on burning rates. However, it is noteworthy that the relationship between burning speed and combustion efficiency is not deterministic. While a smaller cone angle of the burning surface contributes to heightened burning rates, it concurrently exacerbates the polymerization effect of vapor phase aluminum particles, consequently diminishing propellant combustion efficiency. Conversely, propellants configured with sparsely twinned silver wires exhibit notable enhancements in combustion efficiency, despite a less pronounced impact on the burning rate attributed to the larger cone angle of the burning surface. Remarkably, these trends persist at lower temperatures. Based on the principle of heat transfer balance, a theoretical model for the combustion of propellants with wire inserts is developed. The reliability of this theoretical model is validated through a comparison of calculated values with experimental data. Our research outcomes carry significant implications for guiding the application and advancement of the silver wire method in solid propellants for solid rocket motors, offering valuable insights to inform future research and development endeavors in this domain. [ABSTRACT FROM AUTHOR]

The forthcoming implementation of national policies towards hydrogen blending into the natural gas grid will affect the technical and economic parameters that must be taken into account in the design of building heating systems. This study evaluates the implications of using hydrogen-enriched natural gas (H2NG) blends in condensing boilers and Gas Adsorption Heat Pumps (GAHPs) in a residential building in Rome, Italy. The analysis considers several parameters, including non-renewable primary energy consumption, CO2 emissions, Levelized Cost of Heat (LCOH), and Carbon Abatement Cost (CAC). The results show that a 30% hydrogen blend achieves a primary energy consumption reduction of 12.05% and 11.19% in boilers and GAHPs, respectively. The presence of hydrogen in the mixture exerts a more pronounced influence on the reduction in fossil primary energy and CO2 emissions in condensing boilers, as it enhances combustion efficiency. The GAHP system turns out to be more cost-effective due to its higher efficiency. At current hydrogen costs, the LCOH of both technologies increases as the volume fraction of hydrogen increases. The forthcoming cost reduction in hydrogen will reduce the LCOH and the decarbonization cost for both technologies. At low hydrogen prices, the CAC for boilers is lower than for GAHPs; therefore, replacing boilers with other gas technologies rather than electric heat pumps increases the risk of creating stranded assets. In conclusion, blending hydrogen into the gas grid can be a useful policy to reduce emissions from the overall natural gas consumption during the process of end-use electrification, while stimulating the development of a hydrogen economy. [ABSTRACT FROM AUTHOR]

Indirect combustion with the chemical looping combustion (CLC) of solid oxygen carriers is one of the most promising technologies for capturing carbon dioxide (CO2) in energy production from fossil fuels since the separation of the generated CO2 is inherent to the process itself. Therefore, the cost associated with capturing this gas will be significantly reduced. This technology transfers oxygen from air to fuel through a metal oxide that acts as an oxygen carrier, avoiding direct contact between air and fuel. This oxygen carrier circulates in a fluidized bed reactor called a reduction reactor and an oxidation reactor. (1) This research work has focused on evaluating the behavior of oxygen carriers based on the original and improved manganese mineral (copper-impregnated mineral) named for this study, OXMN009 and OXMN009P, respectively. (2) Equilibrium experiments were carried out on a thermogravimetric balance (TGA) to evaluate the kinetic behavior of these oxygen transporters OXMN009 and OXMN009P, using the gases methane (CH4), carbon monoxide (CO), and hydrogen (H2). (3) The enhanced solid oxygen carrier OXMN009P exhibited good performance for the CLC process with gaseous fuels in terms of reactivity and combustion efficiency, having high reactivity and oxygen transfer properties due to copper impregnation. (4) The results show that OXMN009P has comparable reactivity to other manganese-based materials reported in the literature. It may be an effective option for carbon dioxide capture, as it uses metal oxides as the oxygen transporters (TO). (5) These oxygen transporters, OXMN009 and OXMN009P, are used in a cyclic process that prevents the formation of nitrogen oxides by keeping the air and fuel separate. (6) Thermogravimetric balance (TGA) experiments were conducted to evaluate the kinetic behavior of these copper-modified oxygen transporters. (7) It was found that OXMN009P improved the reactivity and oxygen transfer properties due to copper impregnation. The kinetic parameters obtained in the TGA indicate that the reaction is non-thermal and requires less energy to initiate. (8) The results show that OXMN009P has reactivity comparable to other manganese-based materials reported in the literature and can be an effective option for carbon dioxide capture. [ABSTRACT FROM AUTHOR]

To accelerate the transition toward zero net carbon emissions, developing the technologies which are already mature enough to be integrated technologically and economically in existing systems is essential. Most of the recent studies are focusing on large scale energy systems which require lot of assumptions such as linear approximations. This paper presents the economical optimization of combined thermal and electrical supply of multiple cities in Japan through utilization of combined heat and power boilers. A nonlinear approach is used to consider phenomena including combustion efficiencies variations or effect of scale. Different technologies of combined heat and power are modeled with different properties and fuels such as household wastes and multiple biomass woods. The cost is used as the objective function to minimize considering current energy costs. With each boiler modeled and sized, optimization results show an optimal operation of 100% renewable resources, especially biomass power with accurate indicators on the operating mode of those technologies. [ABSTRACT FROM AUTHOR]

This review examines the potential of hydrogen, ammonia, and biodiesel as alternative fuels, focusing on spray dynamics, droplet evaporation, combustion, andemissions. Hydrogen offers superior combustion characteristics but faces challenges in NOx emissions. Strategies like non premixed direct injection, increased intake boost pressure, and low-pressure EGR are suggested for robust hydrogen combustion in compression-ignition engines. Control of hydrogen start of injection (SOI) and water injection (WI) are identified as effective techniques for reducing NOx emissions. Ammonia shows inferior combustion and higher NOx and unburned NH3 emissions in the same conditions as conventional fuels with conventional engines. Understanding ammonia spray and evaporation conditions is significant for optimizing an ammonia-air mixture and minimizing wall impingement and ammonia trap in the crevice, thereby improving combustion and emission reduction. Increasing intake pressure, injection pressure, and EG Rrate, employinga turbulent jet, and preheating ammonia improve efficiency and reduce NOx emissions. Utilizing ammonia combustion requires the implementation of after-treatment systems such as NH3 adsorber and DeNOx catalysts to mitigate unburned NH3 and NOx emissions. Biodiesel affects the fuel supply system, combustion, and emission characteristics according to its viscosity and density. Increasing injection pressure and blending with volatile fuels enhance spray and combustion. Optimum biodiesel preheating temperatures for the injection pump and injector are crucial for achieving the best pump capacity and spray formation. By utilizing biodiesel-PODE blends and investigating low-temperature biodiesel combustions, there is potential to improve thermal efficiency and PM-NOx trade-off. Therefore, carbon-neutral fuel adoption should be accelerated to mitigate CO2 emissions, highlighting the importance of combustion techniques and emissions reduction strategies. [ABSTRACT FROM AUTHOR]

Decarbonizing maritime transport hinges on transitioning oil-fueled ships (98.4% of the fleet) to renewable and low-carbon fuel types. This shift is crucial for meeting the greenhouse gas (GHG) reduction targets set by the IMO and the EU, with the aim of achieving climate neutrality by 2050. Ammonia, which does not contain carbon atoms that generate CO2, is considered one of the effective solutions for decarbonization in the medium and long term. However, the concurrent increase in nitrogen oxide (NOx) emissions during the ammonia combustion cycle, subject to strict regulation by the MARPOL 73/78 convention, necessitates implementing solutions to reduce them through optimizing the combustion cycle. This publication presents a numerical study on the optimization of diesel and ammonia injection phases in a ship's medium-speed engine, Wartsila 6L46. The study investigates the exhaust gas emissions and combustion cycle parameters through a high-pressure injection strategy. At an identified 7° CAD injection phase distance between diesel and ammonia, along with an optimal dual-fuel start of injection 10° CAD before TDC, a reduction of 47% in greenhouse gas emissions (GHG = CO2 + CH4 + N2O) was achieved compared to the diesel combustion cycle. This result aligns with the GHG reduction target set by both the IMO and the EU for 2030. Additionally, during the investigation of the thermodynamic combustion characteristics of the cycle, a comparative reduction in NOx of 4.6% was realized. This reduction is linked to the DeNOx process, where the decrease in NOx is offset by an increase in N2O. However, the optimized ammonia combustion cycle results in significant emissions of unburnt NH3, reaching 1.5 g/kWh. In summary, optimizing the combustion cycle of dual ammonia and diesel fuel is essential for achieving efficient and reliable engine performance. Balancing combustion efficiency with emission levels of greenhouse gases, unburned NH3, and NOx is crucial. For the Wartsila 6L46 marine diesel engine, the recommended injection phasing is A710/D717, with a 7° CAD between injection phases. [ABSTRACT FROM AUTHOR]

Detecting temperature and concentration fields within engine combustors holds paramount significance in enhancing combustion efficiency and ensuring operational safety. Within the realm of engine combustors, the laminar absorption spectroscopy technique has garnered considerable attention. Particularly crucial is the optimization of the optical path configuration to enhance the efficacy of reconstruction. This study presents a flame parameter field reconstruction model founded on laminar absorption spectroscopy. Furthermore, an optimization approach for refining the optical path configuration is delineated. In addressing non-axisymmetric flames, the simulated annealing algorithm (SA) and Harris's Hawk algorithm (HHO) are employed to optimize the optical path layout across varying beam quantities. The findings underscore a marked reduction in imaging errors with the optimized optical path configuration compared to conventional setups, thereby elevating detection precision. Notably, the HHO algorithm demonstrates superior performance over the SA algorithm in terms of optimization outcomes and computational efficiency. Compared with the parallel optical path, the optimized optical path of the HHO algorithm reduces the temperature field error by 25.5% and the concentration field error by 26.5%. [ABSTRACT FROM AUTHOR]

The mixing and combustion processes are linked and challenging for a supersonic combustion engine. Supersonic air doesn't spend much time in the combustor, making it challenging to blend fuel with supersonic air. The expansion of shear-mixing layer with shock waves and their interactions are the primary characteristics of mixing augmentation. This paper investigates the same methodology for a model scramjet combustion chamber with wedge and wavy sides. The novel scramjet combustion models include wedge and way-wall sidewalls based on the basic scramjet model. By combining the finite volume approach with a second-order upwind discretization method, the Reynolds-averaged Navier-Stokes equations are numerically analyzed. The interplay between wedge and wavy-wall effects and free stream flows is taken into consideration by using the shear stress transport (SST) k−ω turbulence model. The effect of the wedge and wavy wall combustor has been evaluated by analysing the shock production and their interactions with the mixing layer and internal flow structure. The turbulence characteristics are also examined to analyse the degree of flow disturbance for wedge and wavy-wall combustion. The wavy wall combustor model results in a 14.5% increase in turbulence intensity, which raises air-fuel mixing and there by improves mixing and combustion efficiency by 12.59% and 11.23%, compared to the base wedge type combustor. [Display omitted] • Shock-induced mixing and combustion in the scramjet combustor with wavy and wedge walls. • The combustor's flow structure has been evaluated for shock wave production and interactions. • The wavy wall combustor promotes combustion in the radial direction. • The wavy wall combustor increases turbulent intensity by 14.5%, improving air-fuel mixing. • Wavy wall combustor improve mixing and combustion efficiency by 12.59% and 11.23%, respectively. [ABSTRACT FROM AUTHOR]

In this research study, fuel blends of pine oil and waste cooking oil biodiesel (P/WCO) were examined for combustion analysis, engine performance, and emission characteristics tests. Improved combustion and engine performance were achieved using a toroidal re-entrant combustion chamber (TCC) and hydrogen supply as a dual fuel. The combustion behavior of fuel blends and hydrogen fuel was examined by varying the engine load at a constant speed. The results revealed that significant reduction in the specific fuel consumption for rich pine oil. Thus, a slightly lesser energy share from the fuel blends and a higher energy share from the hydrogen fuel was required for the engine to maintain the same brake power. Lower viscosity, higher flash point, and presence of oxygen in the pine oil enhance the combustion rate and brake thermal efficiency. Furthermore, hydrogen induction in the engine improves the flame velocity. A lesser crevice volume in the TCC can trap the unburnt fuel which can further increase the combustion efficiency. Thus, rich pine oil with the support of hydrogen induction in TCC causes advanced ignition, improved combustion, and more heat release during the combustion. The investigation results revealed that hydrogen induction increases the heat release rate and peak pressure by 7.4% and 2.67%, respectively. Similarly, the maximum of 24.55% increase in BTE and 18.22% reduction in BSFC was observed due to a constant 10 lpm hydrogen induction. Furthermore, hydrogen fuel significantly reduces the emissions such as CO, HC, CO 2 , and smoke. However, more NO x was generated due to more heat release rate during combustion. Thus, pine oil and waste cooking oil biodiesel blends with the support of hydrogen induction in TCC improve the engine performance and mitigate the toxic pollutants and can be a suitable alternative to diesel fuel. • Combustion effects of pine oil and waste cooking oil biodiesel blends were examined. • The influence of hydrogen addition in dual fuel mode is highlighted. • Impact of the toroidal re-entrant combustion chamber concerning BTE, BSFC, and emissions was discussed. • The energy share between biodiesel and hydrogen is discussed. [ABSTRACT FROM AUTHOR]

Over the past years, several efforts have been made to reduce greenhouse gas emissions coming from the transport sector. Due to the highly efficient CO2-free combustion and low manufacturing costs, Hydrogen Internal Combustion engines (H2ICEs) are considered one of the most promising solutions for the future of medium and heavy duty vehicles. However, the combustion of an air-hydrogen mixture presents challenges related to the production of nitrogen oxides (NOx) and high knock tendency, mainly due to the chemical characteristics of the fuel. Although these problems can be mitigated by the use of a lean mixture, which is also useful to increase the combustion efficiency, the presence of excess air reduces exhaust temperatures and, consequently, the enthalpy content in the exhaust would be limited, leading to a reduced boosting capability. Therefore, a proper control of mixture preparation and combustion phasing is mandatory to limit NOx emissions, avoid abnormal combustions, and maximize efficiency without performance limitations. This paper focuses on the design of a dedicated control strategy for H2ICEs. Starting from a previously validated 1-D engine model operated with hydrogen, a 0-D Artificial Neural Network (ANN) - based engine model has been designed and calibrated. By using the obtained fast running ANN-based model, an innovative torque-based engine controller has been developed and both engine and controller models have been tested covering different torque profiles. The results show good accuracy within a range of ±5% on producing the requested torque by controlling the centre of combustion. [Display omitted] • Hydrogen represents an optimal solution for the abatement of CO2 emissions related to the transport sector. • Hydrogen combustion is prone to abnormal combustions and NOx emissions. • Dedicated control strategies are needed to achieve an efficient, clean and reliable H2 combustion. • Model in the Loop approach aimed at testing the proposed control strategy. • Artificial neural network – based fast running engine model enabled testing the control system in relevant running conditions. [ABSTRACT FROM AUTHOR]

The present study explores the characteristics of reacting flow in a scramjet combustor with struts, focusing particularly on implementing different injection strategies. A three-dimensional DLR scramjet combustor is utilised to assess the impact on the system, incorporating multiple injections and varying injection angles on the triangular wedge. The analysis considers three injectors with parallel, upward and downward injections at angles of 15° and 30°. The numerical investigation is conducted under a constant total pressure of 7.82 bar, a temperature of 340 K, and an airspeed of Mach 2 at the inlet. The results highlight the significance of injector location and shape in promoting flame stabilization. Furthermore, injection angles play a crucial role in mitigating shockwave intensity. The numerical analysis involves a steady-state Reynolds-averaged Navier- Stokes equation with the shear stress transport k--ω turbulence model. The obtained results were analyzed by examining the critical variables such as Mach number, static pressure and combustion efficiency across the combustor. Based on the computational results, injecting fuel upward not only increases the overall pressure loss but also enhances the subsonic regime downstream of the strut, which leads to better mixing and combustion efficiencies. This is primarily due to shockwave generation from the edges of the strut and the interactions with the fuel stream shear layers. [ABSTRACT FROM AUTHOR]

The backflow of high-temperature products in an engine's combustion chamber is a key issue which can significantly reduce combustion efficiency. This is particularly problematic for hypergolic propellants, as the high-temperature products may still contain fuel or an oxidizer. If either the fuel or the oxidizer backflows into the manifold of the other, it can easily lead to micro-explosions, thereby creating a threat. To address this problem, this paper proposes a new design of an anti-backflow injector, aimed at effectively preventing the backflow of combustion products to the propellant manifold. A steady-state, non-reactive Computational Fluid Dynamics (CFD) model is employed to evaluate the steady internal flow characteristics of the proposed anti-backflow injector. Additionally, a complementary transient, multiphase fluid dynamics simulation is carried out to assess the response characteristics of the anti-backflow injector. Our analysis focuses on the response characteristics of the concave valve core. The study also explores the impact of different expansion port angles on the injection effect, finding that the vortex diameter at the injector outlet is positively related to the expansion port angle. It is also shown that the injection angle becomes more stable as the expansion angle increases. When the expansion port angles are 10° and 20°, the injection angles show similar trends. In terms of anti-backflow effect, taking the injection stiffness of 150% and a time range of 300 µs as examples, the response time of the anti-backflow models with expansion ports of 10°, 15°, and 20° is increased by 67 µs, 99 µs, and 213 µs, respectively, compared to the base models with the same expansion angles. Meanwhile, when the injection stiffness is 50%, the response time of the anti-backflow models with expansion ports of 10°, 15°, and 20° is increased by 207 µs, 210 µs, and 207 µs, respectively. When the injection stiffness is 20%, the response recovery speed of the anti-backflow models with expansion ports of 10° and 15° is increased by 41 µs and 96 µs, respectively. However, the performance of the anti-backflow model with a 20° expansion port is 216 µs of the base model. The optimized design of the anti-backflow injector has potential applications in solving the propellant backflow problem and contributes to the advancement of combustors. [ABSTRACT FROM AUTHOR]

The combustion of briquettes made from organic and industrial residues in small boilers requires researchers to consider the characteristics of this type of fuel and methods of its combustion. For the efficient combustion of fuel briquettes, a layered combustion method with the ability to regulate the supply of combustion air is better suited. The purpose of this research is to study the thermal technical conditions of briquetted fuel combustion. In order to carry this out, a stand was created, which made it possible to determine the combustion efficiency of this type of fuel. Two types of briquettes were studied: one with 30% sunflower husks and 70% leaves, and one with and 70% sunflower husks and 30% coke breeze. The combustion results of the briquettes show that heat loss from chemical under-burning was no more than 6.25%. To determine the temperature distribution in the fuel layer, a model of unsteady heat transfer in a fixed layer was used. A calculation of the temperature fields in the layer of burned fuel briquettes was carried out, which showed that the most favorable conditions for burning briquettes were created with a layer about 15–20 cm thick for both burned briquette options. The temperature was in the range of 450–750 °C, which on the one hand corresponds to experimental data and on the other hand provides a combustion regime that occurs with a relatively low loss to the environment. This installation and mathematical model will help future studies based on the processes of other types of organic waste combustion with a grate system. [ABSTRACT FROM AUTHOR]

The hybrid rocket motor (HRM) emerges as a promising propulsion system offering thrust adjustment at a low cost. Prior research has indicated that the inclusion of micro Al additives enhances HRM performance, yet a comprehensive investigation remains absent. Thus, this study aims to explore the impact of Al particle additive content and size variation on the characteristics of hybrid rocket motors (HRMs) through experiments and simulations. Firing tests are conducted on HRMs employing unadulterated HTPB, 38 % additive Al (2 μm), and 58 % Al (2 μm). Experimental findings reveal enhancements of 12.6 % and 33.9 % in regression rate, and 2.5 % and 8.0 % in specific impulse for the 38 % Al and 58 % Al fuel configurations, respectively, compared to the base case. Subsequently, a numerical two-phase combustion model is built to analyze the inner flow field characteristics. The high consistency between experimental and simulation results validates the efficacy of the numerical approach employed. Following this, a series of simulations covering Al content ranging from 0 % to 58 % and Al particle sizes from 0.4 μm to 75 μm is conducted. Simulation outcomes indicate that specific impulse and combustion efficiency enhancements correlate with the increase in Al mass fraction for particles with diameters under 35 μm. However, high Al content proves detrimental to specific impulse and combustion efficiency when particle diameter exceeds 35 μm. Additionally, regression rate and thrust demonstrate an increase with Al content, albeit the rate of increment diminishes with larger Al particles. This study comprehensively examines the influence of Al particle addition on HRM performance and elucidates the underlying mechanisms, thereby offering insights into HRM design and manufacture. • Hybrid rocket firing tests are performed on HTPB, 38 %, and 58 % Al particle fuel. • Simulations with various Al particle contents and diameters are performed. • High Al content with diameter under 35 μm is beneficial for combustion efficiency. • High Al content with diameter over 35 μm is detrimental for combustion efficiency. • Large particle reduces the thrust enhancement brought by Al content rise. [ABSTRACT FROM AUTHOR]

Methane emissions from oil and gas production can occur throughout the value chain, but for many producers, one of the most significant sources is flaring. Understanding the influence of the operating conditions and the environmental factors the combustion efficiency and destruction and removal efficiency (CE/DRE) of flares is essential if their role in methane emissions, a potent but short-lived greenhouse gas, is to be better understood and mitigated. An industry-scale experimental study was focused on the emissions of un-assisted flares commonly encountered in upstream oil and gas production. This paper simulates two un-assisted flare tips combustions by using the commercial computational fluid dynamics (CFD) software package Fluent 21R2 to augment the physical experimental testing. Two three-dimensional (3D) flare tips models are built, and the k-omega SST turbulence model and flamelet generated manifold (FGM) combustion model are applied to simulate flaring combustion. The CFD model is first validated against full-scale industry flare tests that use extractive sampling of the combustion plume. CFD results are in good agreement with measured results when the vent gas net heating value (NHV) is greater than 300 BTU/SCF. Greater uncertainty exists for both CFD results and measured data if the NHV is less than 300 BTU/SCF. Then, the CFD model is extended to include high crosswind states up to 50 m/s that cannot be readily or safely examined empirically. The results emphasize the critical role of the vent gas net heating value (NHV) on flare combustion and crosswind in reducing the CE. The comparison helps pave the way for further use of CFD simulation to improve flare designs and modes of operation and supports the use of parametric models to track and report methane losses from flaring. [ABSTRACT FROM AUTHOR]

The purpose of this paper is to discuss a study aiming to optimize the performance of a DLR-type scramjet engine using computational fluid dynamics (CFD). For this purpose, the response surfaces technique is employed to carry out a multi-objective optimization of the strut geometry used in this engine. In the simulation, strut length and width are considered as design variables. Thrust and combustion efficiency are also constituted as objective parameters. Response surfaces are created using two methods: Kriging and nonparametric regression (NPR). The obtained results indicate a higher accuracy of the Kriging approach. The optimization results show that in the best case the amount of thrust can be increased up to 62.618 N, which is 5.6% more than the base value. Also, the combustion efficiency can be raised to a maximum value of 74.4%, which is 12.37% higher than the base value. In order to determine which design variables have a more significant effect on objective factors, sensitivity analysis has been performed. This analysis revealed that the strut width has more significant effect on the combustion efficiency, while the thrust was more dependent on the strut length. [ABSTRACT FROM AUTHOR]

This document discusses the importance of high-temperature low-emission combustion technology in reducing dependence on fossil fuels and mitigating environmental pollution. The use of catalysts is highlighted as an effective strategy for reducing pollutant emissions, particularly nitrogen oxide (NOx). The document also presents research on various aspects of catalytic combustion, including pyrolysis, synergistic reactions, and ash sintering. The findings emphasize the potential of catalytic combustion in enhancing energy production efficiency and reducing environmental impact. [Extracted from the article]

The accuracy of sampling of gas components has a significant impact on the measurement of various performance parameters in the combustion chamber of an aero-engine. In order to investigate the effect of the probe geometry of a six-point gas sampling probe on sampling accuracy in supersonic gas flow, a three-dimensional probe gas flow characteristic solution model is established through numerical simulation methods of components of transport and fluid–solid coupling. Probes with three angles of 28°, 30°, and 32° and an optimized conical probe are constructed. The sampling accuracy of the probes with different geometries is compared and evaluated by the deviation of the component volume fraction before and after sampling and the resulting combustion efficiency error. This paper presents a set of calculation methods for solving the relative deviation of volume fraction by an iterative method based on the ideal gas law and the Redlich–Kwong equation (R-K equation). The method is designed to solve the exact component volume fraction problem in the simulation calculation. The study results demonstrate that the 28° and optimized conical probes improve sampling accuracy more effectively than the original 30° structure. The deviation of the volume fractions of the two structures is less than 1.7%, and the combustion efficiency error is less than 0.09%. The developed iterative calculation method can significantly reduce the theoretical calculation error to less than 0.06%. The experimental data of the test bench are in good agreement with the simulation results, thereby demonstrating the reliability and accuracy of the sampling probe following structural optimization. [ABSTRACT FROM AUTHOR]

A micro-pulse detonation engine (μPDE) was designed and installed to a direct-connect scramjet combustor of Pusan National University (PNU-DCSC). The active excitation on the scramjet combustor was experimentally studied using the μPDE operating at frequencies of 10–20 Hz. A vitiation air heater (VAH) was used to supply high-enthalpy vitiated air to the isolator and the scramjet combustor at a Mach number of 2.0, with a total temperature of 1600 K and a total pressure of 1.68 MPa. The exit of μPDE was located at the center of the cavity of the scramjet combustor. Active excitation was performed at equivalence ratios of 0.111 and 0.163, and characteristics were analyzed through Schlieren recording and bottom wall pressure measurement. As a result, when the detonation emitted from the μPDE entered the scramjet combustor, it instantly formed a shock train and moved forward within the scramjet combustor. The flame instantaneously changed from the cavity shear layer flame to the cavity flame. Through bottom wall pressure measurement, it was also observed that active excitation resulted in a significant pressure increase near the cavity compared to when active excitation was not performed. This revealed combustion characteristics, indicating improved combustion efficiency from the pressure increase in the scramjet combustor. [ABSTRACT FROM AUTHOR]

Increasing aviation activities have heightened concerns about particulate emissions from aircraft engines. Current ICAO standards mainly focus on large civil turbofan engines, leaving a gap in the research on PN emissions from small aircraft engines. This study examined the PN emission characteristics of micro-turbojet engines, including the morphology, PN, and size distribution under different load conditions, compared with a micro-piston engine. The results showed that the nvPM from micro-turbojet engines was larger and more complex than typical aviation soot, likely due to reduced combustion efficiency and incomplete fuel combustion. Micro-turbojet engines exhibited fewer fluctuations in their emission index number (EIn) and emission index mass (EIm) at lower speeds. The geometric mean diameter (GMD) of particles was inversely correlated with thrust, while the geometric standard deviation (GSD) slightly increased with thrust. Quantitative comparisons indicated that PN emissions from micro-turbojet engines were higher, with EIn values ranging from 2.0 to 3.3 × 1016/kg fuel compared with 1.2 to 1.5 × 1016/kg fuel for micro-piston engines. EIm values for micro-turbojet engines ranged from 8 to 40 mg/kg fuel, while micro-piston engines had slightly higher values due to better carbonization. These findings validated the measurement methodology used to accurately assess PN emissions under low-thrust conditions in micro-turbojet engines. These results provide crucial insights and support for the future monitoring and regulation of PN emissions across all thrust conditions in small aircraft engines. [ABSTRACT FROM AUTHOR]

With increasing environmental pollution from ship exhaust emissions and increasingly stringent International Maritime Organization carbon regulations, there is a growing demand for cleaner and lower-carbon fuels and near-zero-emission marine engines worldwide. Liquefied natural gas is a low-carbon fuel, and when liquefied natural gas (LNG) is used on ships, dual-fuel methods are often used. The pre-chamber plays a key role in the working process of dual-fuel engines. In this paper, an effective three-dimensional simulation model based on the actual operating conditions and structural characteristics of a marine low-pressure dual-fuel engine is established. In addition, the effects of changing the Precombustion chamber (PCC) volume ratio and the PCC orifice diameter ratio on the mixture composition, engine combustion performance, and pollutant generation were thoroughly investigated. It was found that a small PPC volume ratio resulted in a higher flame jet velocity, a shorter stagnation period, and an acceleration of the combustion process in the main combustion chamber. When the PCC volume was large, the Nitrogen oxygen (NOx) ratio emission was elevated. Moreover, the angle of the PCC orifice affected the flame propagation direction of the pilot fuel. Optimizing the angle of the PCC orifice can improve combustion efficiency and reduce the generation of NOx. Furthermore, reasonable arrangement of the PCC structure can improve the stability of ignition performance and accelerate the flame jet velocity. [ABSTRACT FROM AUTHOR]