Combustion Instability Research Articles

α-Al2O3 Functionalized with Lithium Ions Especially Useful as Inert Catalyst Bed Supports

The alumina, in the form of α-Al2O3 tabular balls, considered in this study is a high-purity form of aluminum oxide that has been fired at high temperatures (well above 1900 °C), virtually removing porosity. However, the purity and inertness of the surface of the Al2O3 tabular balls minimize the catalytic activity, which is why lithium doping was tried. Thus, the target of this study was the effect of doping with lithium ions in some tabular balls of Al2O3 (the crystalline structure is corundum) on the improvement of the catalytic properties of alumina. This study examined the impact of a lithium catalyst on the combustion of various fuels within a porous inert medium (PIM) burner. This study specifically compared low calorific gaseous fuel (e.g., biogas) combustion in a PIM burner with and without the lithium catalyst. The experimental setup comprised a gas preparation unit for mixing CNG and CO2 to simulate biogas and a PIM burner. The PIM burner comprised Al2O3 spheres (13 mm diameter, 45% porosity) in a random packing configuration. Three fuels, varying in composition and lower heating value (LHV ranging from 20.771 to 27.695 MJ/m3), were combusted at air ratios ranging from 1.67 to 1.79. The results indicated that the catalyst increased peak combustion temperatures by 23.2 °C to 51.4 °C, depending on the fuel type and air ratio. Significantly higher carbon monoxide (CO) concentrations were observed without the catalyst, particularly with fuel type F1, while nitrous oxide (NOx) levels remained consistently low. Upstream flame propagation was observed in the presence of the catalyst. These findings demonstrate the potential of lithium catalysts to enhance combustion stability and reduce emissions in porous media combustion burners. Following these studies, it can be stated that Li(I) has the role of promoter of the catalytic process.

Thermoacoustic Instability in Combustors

Thermoacoustic instability is a flow instability that arises due to a two-way coupling between acoustic waves and unsteady heat release rate. It can cause damaging, large-amplitude oscillations in the combustors of gas turbines, aeroengines, rocket engines, etc., and the transition to decarbonized fuels is likely to introduce new thermoacoustic instability problems. With a focus on practical thermoacoustic instability problems, especially in gas turbine combustors, this review presents the common types of combustor and burner geometry used. It discusses the relevant flow physics underpinning their acoustic and unsteady flame behaviors, including how these differ across combustor and burner types. Computational tools for predicting thermoacoustic instability can be categorized into direct computational approaches, in which a single flow simulation resolves all of the most important length scales and timescales, and coupled/hybrid approaches, which couple separate computational treatments for the acoustic waves and flame, exploiting the large disparity in length scales associated with these. Examples of successful computational prediction of thermoacoustic instability in realistic combustors are given, along with outlooks for future research in this area.

Preparation and Properties of Solid Propellant Adhesive System Based on Ethylene Vinyl Acetate/Wax Thermoplastic Elastomer

ABSTRACTIn this study, an ethylene vinyl acetate (EVA)/wax‐based thermoplastic propellant was prepared using a planetary mixer. High‐viscosity EVA was used as the thermoplastic elastomer, and either solid wax based on EVA oligomers or alternative liquid tributyl 2‐acetylcitrate (TBAC) were used as plasticizers to adjust its viscosity. This enhances the flow characteristics and reduces torque during the mixing process. Results: The addition of 30 wt.% wax significantly reduced the viscosity from 218.8 to 12.67 Pa s, whereas the addition of liquid TBAC did not lead to a significant reduction in the viscosity of EVA. Designed with different ratios of EVA/wax binder with a superior stress–strain relationship over polyurethane (PU). The EVA/wax‐based propellant has stable combustion characteristics at different combustion chamber pressures. St. Robert's Law provides an equation for the rate of combustion, and the performance parameters of the propellant derived from the internal ballistics simulation analysis are very valuable.

Advances and Challenges in Thermoacoustic Network Modeling for Hydrogen and Ammonia Combustors

The transition to low-carbon energy systems has heightened interest in hydrogen and ammonia as sustainable alternatives to traditional hydrocarbon fuels. However, the development and operation of combustors utilizing these fuels, like other combustion systems, are challenged by thermoacoustic instabilities arising from the interaction between unsteady heat release and acoustic wave oscillations. Among many different methods for studying thermoacoustic instabilities, thermoacoustic network models have played an important role in analyzing the essential dynamics of these instabilities in combustors operating with low-carbon fuels. This paper provides a comprehensive review of thermoacoustic network modeling techniques, focusing specifically on their application to hydrogen- and ammonia-based combustion systems. We outline the key mathematical frameworks derived from fundamental equations of motion, along with experimental validations and practical applications documented in existing studies. Furthermore, current research gaps are identified, and future directions are proposed to improve the reliability and effectiveness of thermoacoustic network models, contributing to the advancement of efficient and stable low-carbon combustors.

The Effect of Intake Temperature on the Idle Combustion Cycle Variation of Two-Stroke Aviation Kerosene Piston Engines

In order to solve the problem of combustion cycle variation in two-stroke aviation kerosene piston engines under idle conditions, experiments were conducted to investigate the influence of intake air temperature on combustion cycle variation and output work. The coefficient of variation of the indicated mean effective pressure was used to characterize combustion cycle variation. The results showed that there is a negative correlation between the engine combustion work and the combustion cycle variation. In the lower range, increasing the intake air temperature has a greater effect on reducing the combustion cycle variation, while in the higher range, the combustion cycle variation has a greater impact on the output work. At the same time, the influence of intake air temperature on the fuel evaporation rate is related to engine speed, and this relationship weakens as the engine speed increases. In the range of 0~40 °C, the higher the intake air temperature, the larger the stable combustion range.

CFD study case of ammonia-hydrogen mixture powered methane gas microturbine combustor in the context of the temperature repartition modifications

Actually many research are conducted on the ability of hydrogen-ammonia mixture fuel to replace classical fuel such as methane for gas (micro)turbine use. These studies concern the combustion stability and NOx formation. Temperature repartition in gas (micro)turbine combustor is very important from a thermomechanical point of view. This issue is often omitted in research. If modifications occur in temperature repartition, an overheating zone can appear and lead to mechanical damage of the combustor liner. Numerical studies, CFD method based with the use of Ansys Fluent tools, were conducted on a self-designed gas microturbine combustor, for methane application, using various ammonia-hydrogen mixtures and methane fuelling. Then, the obtained temperature maps were compared between methane and ammonia-hydrogen mixtures with various compositions to find an ammonia-hydrogen mixture composition that permits to reproduce a similar temperature repartition as for methane fuelling; this mixture contains maximally 10%mass hydrogen (or 48%vol). This ammonia-hydrogen mixture composition was compared to others research where the ammonia-hydrogen composition was optimised for combustion stability and NOx reduction (hydrogen content of 30%vol). According to performed studies, the proposed ammonia-hydrogen composition in others research is confirmed to be safe for gas microturbine applications from a thermomechanical point of view.

Injection height impact on combustion instability in a centrally staged combustor

Injection height impact on combustion instability in a centrally staged combustor

Synergistic Effects of Graphene Quantum Dot Additives in Waste Plastic Oil Blends: Combustion Stability and Emission Reductions Analysis

Synergistic Effects of Graphene Quantum Dot Additives in Waste Plastic Oil Blends: Combustion Stability and Emission Reductions Analysis

Preparation of chitosan/HMX energy-containing microspheres with stable combustion performance by an environmentally friendly process based on ionic cross-linking mechanism

Preparation of chitosan/HMX energy-containing microspheres with stable combustion performance by an environmentally friendly process based on ionic cross-linking mechanism

Study on gas–particle flow and combustion stability of an improved burner for different boiler loads

Study on gas–particle flow and combustion stability of an improved burner for different boiler loads

Enhanced combustion stability of low-concentration methane though a flame buffer zone in a variable pore-density porous media burner

Enhanced combustion stability of low-concentration methane though a flame buffer zone in a variable pore-density porous media burner

Numerical Study on Pressure Oscillations in a Solid Rocket Motor with Backward Step Configuration Under Two-Phase Flow Interactions

The pressure oscillation caused by vortex–acoustic coupling is one of the main gain factors that results in the combustion instability of motors. Focusing on a solid rocket motor with a backward step configuration that can generate a corner vortex, this study aims to investigate the pressure oscillation characteristics in a combustion chamber under two-phase flow interactions through numerical simulations. The two-phase flow discrete phase model (DPM) was chosen to study particle motion and two-phase interactions. The numerical methodology was hence established by coupling the DPM with the large eddy simulation (LES) method. Taking the Clx motor as a reference and introducing aluminum oxide particles, two important particle parameters (diameter and concentration) and the key geometric parameters of the backward step were numerically studied. The numerical results show that both increased particle diameter and concentration can decrease the frequency and amplitude of pressure oscillations; additionally, the effects of geometric parameters on the pressure oscillations of the backward step, such as the downstream aspect ratio, the expansion ratio, and the step position, are basically consistent under both pure gas and two-phase flows. The influences of those geometric parameters are mainly reflected in defining the space for the development of upstream flow instability and the motion of downstream vortices. Compared with the pure-gas flow, the presence of aluminum oxide particles in two-phase flow globally decreases the vortex shedding frequency, the primary frequency, and the amplitude of pressure oscillations. It can also weaken the effects of vortex–acoustic coupling due to increased turbulent viscosity, which hinders the orderly development of vortices.

Thermodynamic model of coal direct chemical looping combustion

ABSTRACT Chemical looping combustion (CLC) technology offers cost-effective CO2 emission reduction. Coal direct chemical looping (CDCL) emerges as a promising solid fuel CLC technology owing to its ability to directly utilize coal without prior gasification, enhancing system integration and efficiency. Despite significant progress in CDCL, challenges persist, including carbon deposition and insufficient oxidation and reduction of oxygen carriers (OCs). This study conducted a thermodynamic equilibrium analysis of a CDCL combustion reactor using Cantera 3.0, a chemical calculation module developed at the California Institute of Technology. The analysis explored the impact of different temperatures, OC-to-coal molar ratios (θ), and OCs types on combustion products. By employing the minimum Gibbs function method and analyzing intrinsic reaction mechanisms, the study provides insights for predicting and optimizing system performance. Thermodynamic equilibrium analysis revealed that with CuO as the OC, insufficient OC (θ < 0.6) led to Cu as the reduction product, while sufficient OC (0.6 < θ < 1.3) yielded Cu and CuO, and excess OC (θ > 1.3) resulted in Cu2O. To optimize CO2 capture, a molar ratio of θ of at least 1.4 and a temperature of at least 800°C are recommended. When Fe2O3 served as the OC, insufficient OC (θ < 0.45) produced Fe and FeO, while excess OC generated FeO and Fe3O4. Optimal operational performance and CO2 capture efficiency required an OC-to-coal molar ratio exceeding 1.4 and a temperature higher than 700°C. This study demonstrates that in CDCL combustion systems, selecting appropriate OCs, temperatures, and OC-to-coal molar ratios ensures stable and efficient combustion and CO2 capture. These findings offer crucial guidance for optimizing system operation.

ENERGY-EFFICIENT HEATING SYSTEM OF TRANSITIONAL METALLURGICAL LADLES

In practice it was confirmed the effective use of the burner device of the diffusion method of natural gas burning in a high-speed direct-flow torch when heating the lining of transitional metallurgical ladles with the closed lid. Three designs of stabilizers for basal stabilization of the torch were developed and studied: 1) with stabilization flares formed when air flows onto 3 corner poorly streamlined stabilizers, in the shadow of which a part of the gas is supplied; 2) with a ring stabilization torch when burning a pre-mixed mixture of natural gas and air; 3) with a sudden expansion of the gas channel, in which a zone of intensive gas recirculation is formed. The GGPK-1.0 burner was developed for transitional ladles that operate within a wide range of changes in thermal power 1–5.29 and stabilizer with constant burning of the ignition ring, which contributes to the stability of combustion and allows the heating of ladles with tightly closed heat-saving lids. After the introduction of the developed burners at all stands for heating the ladles of the “Azovstal” metallurgical plant in 2019–2020 were obtained a significant improvement in the operation of the stands and a reduction in natural gas consumption. The fuel economy during heating the ladles is at least 20 %. The heating temperature of the inner surface of the lining of the transitional ladles is even over the entire surface. The temperature difference on the surface of the lining does not exceed 50 °C. Bibl. 16, Fig. 6.

Numerical Simulation and Analysis of Semi-Industrial Retrofit for Tangentially Fired Boilers with Slag-Tap Technology

High-alkali Zhundong coal presents significant challenges for power generation, due to its propensity for fouling and slagging. This study investigates a retrofit of a 300 MW tangentially fired boiler with the integration of a slag-tap chamber to improve combustion performance. Computational fluid dynamics (CFD) simulations are employed to examine the influence of this modification on combustion dynamics and the effects of Zhundong coal blending ratios on heat and mass transfer. The results demonstrate that the retrofit facilitates stable airflow recirculation, optimizing combustion efficiency with a peak temperature of 2080 K in the combustion chamber. The flue gas temperature decreases to approximately 1650 K upon exit, which can be attributed to the slag catcher cooling. The integration of the liquid slagging chamber significantly mitigates slag formation, while enhancing oxygen and CO2 distribution throughout the furnace. As the blending ratio of Zhundong coal increases, oxygen concentrations rise in the bottom burner region, indicating improved air–fuel mixing. With a 30% Zhundong coal ratio, the combustion chamber temperature increases by 3%, and flow velocity in the upper and middle furnace sections decreases by 15%, leading to enhanced combustion intensity. This retrofit demonstrates substantial improvements in combustion stability, slagging control, and the efficient utilization of high-alkali coal.

PENGARUH VARIASI BENTUK FLAME HOLDER TERHADAP KARAKTERISTIK NYALA API PADA PEMBAKARAN MESO SCALE COMBUSTOR

This study used an experimental method by directly observing the object under study. The independent variables in this study include the geometry of the flame holder on the meso-scale combustor, airflow, and fuel discharge. The research data were analyzed and displayed in graphical form as well as flame visualization. This research concludes that combustion using a flame holder circle has a more stable and even flame compared to a flame holder concentric ring and backward facing step. The shape of the Flame holder circle also produces a higher flame temperature. The results of this study contribute to the development of MPG based on micro combustion with a better understanding of the interaction between flame holders, reactant velocities and equivalent ratios in achieving stable and efficient combustion in meso-scale combustors. This research can provide important input for the development of high-efficiency micro-combustion-based power generation technology in the future.

Resonator-based broadband noise absorber to control combustion instability

Resonator-based broadband noise absorber to control combustion instability

The Development and Future Trends in HCCI and DF-PCCI Engines for Sustainable Transportation

Internal combustion (IC) engines have long been the dominant technology in transportation, but their environmental impact, particularly in terms of air pollution, has become a growing concern. To address these challenges, advanced combustion technologies like homogeneous-charge compression ignition (HCCI) and dual-fuel premixed-charge compression ignition (DF-PCCI) engines have been developed. This paper explores the potential of HCCI and DF-PCCI engines to serve as more sustainable alternatives to conventional IC engines by analysing their combustion mechanisms, thermal efficiency, and emissions performance. While both engines offer significant environmental benefits, such as lower NOx, particulate matter, and CO2 emissions, they each face unique challenges in terms of fuel injection control, biofuel integration, and combustion stability. DF-PCCI demonstrates advantages in combustion phasing and high-load performance, while HCCI requires further development in fuel injection and exhaust gas recirculation (EGR) systems. Hybridization emerges as a promising solution to improve the flexibility and real-time control of both engines. Ultimately, this paper highlights the potential of HCCI and DF-PCCI engines to significantly reduce transportation-related emissions and contribute to global sustainability goals.

The Application of HCCI Technology in the Automotive Industry: Technical Analysis and Future Prospects with Mazda as an Example

Homogeneous Compression Combustion Ignition (HCCI) engine is a new type of combustion engine technology that realizes fuel combustion through compression ignition. It combines the benefits of gasoline and diesel engines to improve fuel efficiency and reduce emissions significantly. Its huge advantage of improving efficiency is widely used in the automotive field. This paper summarizes the achievements and challenges of HCCI engines and their application in automotive industries especially in Mazda. Mazda uses its SkyActiv-X engine to produce the car model to achieve high efficiency and low emissions. Another company, General Motors, has its own Ecotec engine to ensure the stability of combustion conditions, thus applying the HCCI technology. HCCI technology faces challenges such as ignition control and stable combustion conditions, but through continuous technological innovation and optimization, HCCI is expected to become one of the mainstream internal combustion engine technologies in the future. It solved the problem of high efficiency and being environmentally friendly, which could help the global warming caused by too much fossil fuel use.

Miraculous Al/PDF Composites Using NF2 to Enhance the Energy Release of Al, Prepared Through an Efficient Method.

To enhance the energy release of Al powder in solid propellant, ploy (difluoroaminomethyl-3-methylethoxybutane) (PDF), which has difluoroamino (NF2), was utilized to improve energy and promote combustion efficiency. In this study, Al with three distinct powder sizes (29 μm, 13 μm, and 1~3 μm) was coated with PDF using the solvent/non-solvent method, leading to the formation of Al/PDF composites. The morphology and characteristics of Al/PDF were then characterized. The results demonstrated that all powder sizes of Al/PDF had core-shell structures, and NF2 of the PDF layer on the Al surface maintained the original structure. The TG curves indicated the amount of the PDF layer related to the powder sizes. Furthermore, Al/PDF exhibited greater hydrophobicity. NF2 prompted Al/PDF, with better catalysis on ammonium perchlorate (AP) decomposition. Compared to Al powder, the ignition delay of Al/PDF was significantly shortened. For mixed samples of Al/PDF and AP, NF2 shorted the ignition delay, improving combustion stability, extending the combustion duration, and forming volatile fluorine compounds. These findings underscore the effects of NF2 in Al/PDF composites, which enhances the energy release of Al and holds promising potential applications.