Combustion Conditions Research Articles

Phosphorus Release Dynamics from Ashes during a Soil Incubation Study: Effect of Feedstock Characteristics and Combustion Conditions

Recovering phosphorus (P) through combustion from waste streams, like wastewater sludge and animal manure, offers a promising solution. This research explores the P release patterns in different ashes derived from secondary raw materials, using a long-term soil incubation lasting 160 days. The study evaluated the P release dynamics in five types of ashes from enhanced biological phosphorus removal (EBPR) systems and pig slurry burned at different temperatures. According to the results, a primary effect was observed on P bioavailability during the initial incubation period. All tested ashes release more than 50% of the total P applied between days 5 and 10. Ashes from EBPR exhibited higher P release than those from pig manure, indicating ash origin as a key factor in P release. Additionally, combustion temperature was crucial, with higher temperatures resulting in increased P release rates. Furthermore, the Pearson correlation revealed a strong relationship between the characteristics of the ashes and the amount of P release. Overall, these findings suggest that ashes could be a valuable P-source for agriculture avoiding the process of wet chemical P extraction, thus reducing both economic and environmental costs.

Experimental and simulation research on the lean combustion characteristics of direct-injection hydrogen engine

At a constant engine speed of 2000 r/min and 5 bar gross indicated mean effective pressure, experiments were carried out on a 1.5 L engine with a variable geometry turbocharger to examine the combustion and emission characteristics of a direct injection hydrogen engine under lean combustion conditions. Additionally, a CFD simulation model was established to investigate the formation process of the air-fuel mixture and the generation of nitrogen oxides (NOx). The findings demonstrated that the uniformity of the hydrogen-air mixture in the cylinder descended with a delay in SOI (start of injection), and that the thermal efficiency often rose initially before declining. When SOI was set at −80°CA ATDC, the engine achieved maximum indicated thermal efficiency, brake thermal efficiency, and output torque values of 40.8%, 36.22%, and 61.2 Nm, respectively. However, as the SOI was delayed, the combustion variability ascended, and when the SOI was delayed to −20°CA ATDC, there was a significant chance that abnormal phenomena like pre-ignition would occur. BTE achieves a maximum of 36.38% when λ is 2.2 and SOI is −40°CA ATDC. Under lean combustion conditions, temperature was a major factor in the generation of NOx, and homogenous combustion can substantially reduce NOx emissions. NOx emissions are always less than 100 ppm when SOI is before −80°CA ATDC.

Performance Evaluation of Low-Concentration Methane Combustion in a Four-Layer Gradually-Varied Porous Burner

ABSTRACT Porous media combustion (PMC) has made a comeback as a practical technology for the utilization of low-concentration methane (LCM) from coal mining. However, the conventional direct-fired PM burner still suffers from the rampart of flame stability and combustion efficiency not addressing industrial demands. Herein, a four-layer gradually-varied porous burner was innovatively developed for LCM combustion to investigate combustion performance under lean combustion conditions (CH4 volume fraction below 5%). The methane conversion, pollutant emissions, and flue gas temperature were also evaluated in detail. The results indicated that the burner offered a favorable combustion resistance due to the gradually-varied PM arrangement to heighten combustion stability with subtle temperature fluctuation and flame migration. The flammability limit of LCM was extended to the lowest equivalence ratio of 0.43 with stationary combustion at 240°C for 120 min. The energy efficiencies of the LCM combustion under lean combustion conditions were greatly boosted with the highest combustion and thermal efficiencies attained at 99.52% and 70.05%, respectively. The maximum 99.93% CH4 conversion was acquired at an equivalence ratio of 0.45 and a flow rate of 80 L/min. LCM combustion in the burner achieved extremely low pollutant emission levels and the overall CO and NOx emissions were 58.04 ppm and below 23 ppm respectively under the experimental conditions. In addition, the high-quality flue gas with an average temperature of more than 516°C was detected in the operating process, which allowed the available heat utilization at the coal mine scenes or in other industries.

Velocity match between plasma and flame in microwave-assisted spark ignition

As a prospective ignition technique, microwave-assisted spark ignition (MAI) can accelerate flame and thus satisfy the demand for effective ignition. However, its acceleration mechanism on flame velocity is still unclear, which hinders its application and optimizations. Therefore, this research focuses on understanding the flame acceleration mechanism behind MAI. In this paper, MAI is achieved through radiating a microwave pulse after spark ignition. The flame velocity and the precise absorbed energy under different combustion conditions are investigated with flame kernel's Schlieren images and microwave energy diagnostics, respectively. The results show that MAI accelerates flame primarily by the interaction between microwave plasma and flame front, rather than the free electrons within the flame. Specifically, microwave accelerating flame takes two processes: energy absorption, and velocity match. Energy absorption refers to the microwave energy absorbed by residual electrons after ignition to generate and sustain microwave plasma, while velocity match involves the outward plasma with faster velocity propelling the slower flame front. Moreover, the plasma velocity shows a positive relationship with absorbed microwave energy. The velocity match between microwave plasma and flame is important to successful flame acceleration. Besides, the efficiency of energy absorption and flame acceleration varies with plasma type (glow or incandescent). Glow plasma is characterized by effective flame acceleration but relatively low absorption efficiency, and incandescent plasma is in reverse. The maximum absorption efficiency can be elevated to 70 % with incandescent plasma occurring. Ultimately, the plasma velocity declines with its traveled distance, which might impair the flame acceleration.

Effects of ignition methods and control parameters on the lean combustion performance and flame geometry of jet ignition based on constant-volume combustion chamber

Pre-chamber jet ignition provides one of the most reliable thermal efficiency improvement technologies for future gasoline engines, especially hybrid gasoline engines. The effects of jet ignition control parameters on the jet flame morphology and combustion characteristics are still unclear, for example, the fuel injection mass in the pre-chamber and the time interval between low-flow injection and ignition. The paper explored the effects of jet ignition stoichiometric and lean combustion performance on the flame propagation process of high-energy spark ignition, passive and active pre-chamber, using direct flame imaging in a constant-volume combustion chamber. The jet ignition performance under lean combustion conditions is further enhanced by optimizing the jet ignition control parameters. Based on the luminance characterization of the image, the active pre-chamber with additional low-flow injection can provide 281% of the ignition intensity equivalent to high-energy spark plug ignition. Increasing the fuel injection mass in the pre-chamber can improve heat release and enhance ignition performance. However, the jet ignition performance will drop sharply due to the too-rich pre-chamber gas mixture. Extending the mixing time interval after ignition will enrich the lean ambient mixture outside the pre-chamber and increase the ignition performance. Over-mixing will occur if the mixing time interval is too long, especially under a few injected fuel mass situations. The radial stretch coefficient of the jet flame is defined to characterize the flame geometry during the jet flame propagation process. The jet ignition performance reaches its best when the jet flame propagates at high speed in both radial and circumferential directions, namely a wide jet flame.

Nano triumphs bulk in red light emission from Eu3+ doped Y2Zr2O7: Gel combustion versus solid state synthesis

Red phosphors are integral element of a phosphor converted white light emitting diodes (pc-WLEDs) which significantly impacts the color rendering index (CRI) and correlated color temperature (CCT) and thus provides a white light suitable for indoor applications. Red Light emitting Eu doped Y2Zr2O7 (YZOE) has been synthesized by two different synthesis methods viz. gel combustion (GC) and solid-state route (SS) wherein the former yielded nanocrystalline and latter leads to bulk YZOE. By virtue of lower light scattering, better electron-hole overlap integral and lower symmetric surrounding, nano YZOE displayed better photoluminescence properties in terms of emission intensity, photoluminescence quantum yield (PLQY) and excited state lifetime compared to its bulkier counterpart.

Experimental Observation of the Turbulent Jet Ignition for Extending the Lean Combustion Tolerance with Carbon Dioxide Diluted Mixture

ABSTRACT Exhaust Gas Recirculation (EGR) technology is widely employed to reduce NOx emissions from engine combustion, and a major challenge of this technology is to achieve stable ignition and high burning rate at higher EGR dilution ratios. Turbulent jet ignition (TJI) is a reliable ignition resource for improving ignition stability and burning rate. Therefore, in the present work, the ability of pre-chamber turbulent jet ignition for extending the lean combustion tolerance at different EGR dilution ratios was investigated in a constant volume combustion chamber. The experimental results indicate that the methane-fueled pre-chamber and the hydrogen-fueled pre-chamber cannot improve the combustion conditions as expected. On the other hand, when an appropriate quantity of air or oxygen is injected, the EGR tolerance limit can be extended due to a decrease in the EGR concentration and an increase in the mixture reactivity in the pre-chamber. However, at higher EGR dilution ratios, more air or oxygen is required to be injected to increase the mixture reactivity in the pre-chamber, which decreases the equivalence ratio of the mixture in the pre-chamber and limits further extension of the EGR tolerance. For the mixture in the active pre-chamber under EGR dilution, the competition mechanism between EGR concentration and equivalence ratio is the key that affects turbulence intensity and chemical reactivity, thereby determining the ignition and combustion results. During the extension of the EGR tolerance limit, the variations in turbulence and chemistry are accompanied by a series of ignition modes, involving jet re-ignition, re-ignition failure, and misfire. Compared to the passive pre-chamber with an EGR tolerance limit of 18%, the air-assisted pre-chamber extended the limit to 23% and the oxygen-assisted pre-chamber to 30%.

Spatial modeling of micro‐scale carbon dioxide sources and sinks in urban environments: A novel approach to quantify urban impacts on global warming

AbstractUrban environments play a significant role in global carbon emissions and sequestration, necessitating a comprehensive understanding of their spatial distribution. This study presents a micro‐scale spatial modeling framework to elucidate the complex interplay between CO2 sources and sinks within urban settings. Utilizing advanced geospatial analysis, remote sensing data, and geographically weighted regression (GWR) modeling techniques, we provide a detailed characterization of emission patterns and identify the spatial distribution of carbon dioxide sequestration. Employing the bottom‐up method and geographic information system techniques, we quantified carbon dioxide emissions in Isfahan City, Iran, attributing 81.68% to stationary combustion sources (residential, commercial, industrial, and power plant sectors) and 18.32% to mobile combustion sources (road‐rail transportation, and non‐road transportation [agricultural machinery]). To model carbon sequestration, we calculated tree biomass using allometric equations and estimated carbon sequestration per tree unit. Subsequently, we employed GWR to map the spatial distribution of carbon deposition across the city. The results revealed an annual carbon sequestration capacity of 7,704 tons, equivalent to storing 28,275 tons of CO2. Our findings highlight the substantial contribution of urban areas to greenhouse gas emissions and the potential of urban green spaces to mitigate these emissions. The spatial modeling framework developed in this study provides a valuable tool for urban planners to optimize carbon management strategies and promote sustainable urban development. © 2024 Society of Chemical Industry and John Wiley & Sons, Ltd.

An image-processing method based on regional separation-parameter coupling for the stability analysis of biodiesel flame

Flame stability is vital to obtain good combustion performance. Therefore, the development of flame stabilization technologies and stability evaluation methods has always received considerable research attention. However, the existing evaluation methods have low precision, which makes it difficult to accurately assess the flame stability. To address this issue, we proposed an effective flame state evaluation method in this study. We conducted relevant combustion experiments, and applied the proposed method to evaluate the flame stability of biodiesel. Furthermore, we established a numerical evaluator of the flame state based on a regional separation-parameter coupling image-processing method. This numerical evaluator combines the statistical characteristics of six flame parameters, which we derived from the flame images. The experimental results suggested that the proposed method can be used to determine some characteristic parameters that cannot be obtained by traditional methods, such as oscillation frequency and propagation velocity. Notably, these characteristic parameters are important for the evaluation of flame stability. At an oxygen concentration of 24 % and fuel pressure of 0.5 MPa, we subdivided the combustion state of biodiesel into stable, relatively stable, unstable, and extinguished states. We observed that by decreasing the airflow rate from 0 to 12.50 m3/h, the flame color changed from orange to green, then blue, and finally to yellow-green. We also observed, contraction and spreading in the flame highlight region. The color space analysis revealed that the larger the blue-to-red ratio, the more complete the combustion, which led to a blue flame. Overall, the proposed evaluation method provides a useful guide for regulating the combustion of biodiesel. Furthermore, these result can be generalized to assess the combustion states of other fuels.

Modeling the drivers of fine PM pollution over Central Europe: impacts and contributions of emissions from different sources

Abstract. Fine particulate matter (PM2.5) is among the air pollutants representing the most critical threat to human health in Europe. For designing strategies to mitigate this kind of air pollution, it is essential to identify and quantify the sources of its components. Here, we utilized the regional chemistry transport model CAMx (Comprehensive Air Quality Model with Extensions) to investigate the relationships between emissions from different categories and the concentrations of PM2.5 and its secondary components over Central Europe during the period 2018–2019, both in terms of the contributions of emission categories calculated by the particle source apportionment technology (PSAT) and the impacts of the complete removal of emissions from individual categories (i.e., the zero-out method). During the winter seasons, emissions from other stationary combustion (including residential combustion) were the main contributor to the domain-wide average PM2.5 concentration (3.2 µg m−3), and their removal also had the most considerable impact on it (3.4 µg m−3). During the summer seasons, the domain-wide average PM2.5 concentration was contributed the most by biogenic emissions (0.57 µg m−3), while removing emissions from agriculture–livestock had the most substantial impact on it (0.46 µg m−3). The most notable differences between the contributions and impacts for PM2.5 were associated with emissions from agriculture–livestock, mainly due to the differences in nitrate concentrations, which reached up to 4.5 and 1.25 µg m−3 in the winter and summer seasons, respectively. We also performed a sensitivity test of the mentioned impacts on PM2.5 on two different modules for secondary organic aerosol formation (SOAP and VBS), which showed the most considerable differences for emissions from other stationary combustion (in winter) and road transport (in summer).

Kinetical driving force analysis of unstable combustion behavior in ammonia/hydrogen blending system

Unstable combustion states are frequently observed in ammonia/hydrogen blended combustion systems. This study aims to explore the underlying thermokinetic feedback driving forces responsible for the occurrence of unstable combustion states based on the identified dominant reactions. To achieve this, the newly developed functional weight analysis method is employed and compared with the combination of heat-release/temperature sensitivity anaylsis. Analysis conducted within several popular mechanisms over a wide temperature and pressure range reveals that the important reactions identified in different mechanisms consistently exhibit loop-formed kinetics with similar mechanism functions.These loops include a hydrogen chain-branching loop, a NH2 dehydrogenation-oxidation loop, and a NOx-DeNOx loop. All of these loops encompass a combination of exothermic and endothermic reactions, and they mutually promote each other due to their loop-formed kinetic. Consequently, when the heat release/heat absorption ratios within the loop kinetics meet specific quantitative criteria, they establish effective thermokinetic feedback. This feedback mechanism initiates and sustains non-constant heat release, serving as a monopole sound source that produces acoustic waves. It is worth noting that the discovery of NOx-DeNOx loop provides a compelling explaination for the frequently observed association between oscillatory combustion states and elevated NOx emissions.

Agglomeration behaviour of various biomass fuels under different air staging conditions in fluidised bed technology for renewable energy applications

The most common technology for thermochemical conversion of solid fuel through the process of gasification, such as coal, varieties of residues from biomass and agriculture are the bubbling fluidised bed or fluidised bed systems. However, there are some disadvantages within these systems including the formation of eutectic mixtures, increased process of melting and bed agglomeration. Hence, the current study aimed to evaluate the agglomeration behaviour of various biomass fuels. Characteristics of five biomass fuels (miscanthus, peanut, straw, domestic wood and industrial wood) in a bubbling fluidised bed (BFB) combustor were studied by SEM-EDX, XRD and XRF analysis of bed materials and ash samples. The influence of bed temperatures on the fuel ash composition and bed particles was evaluated, as well as fuel ash components, their interaction with the particles from the bed sand and morphology of the bed material. The combustion efficiency ranged from 95.5 to 99.5% with the highest value obtained for miscanthus under SA conditions. The peanut and straw had the highest K content, whereas the industrial wood ash contained the highest Ca content compared to other biomasses. The XRF results showed that most of the potassium (K) from the wheat straw biomass was converted to K2O with 19%. No bed agglomeration was noticed without staging-air (WSA) and with staging-air (SA) combustion conditions, even with temperatures up to 850 °C during the testing period. Overall obtained results demonstrated that agglomeration is unlikely expected to be a major problem during fluidised bed combustion of tested biomass fuels.

Experimental investigation of the effect of the electromagnetic field on the stability of the hydrogen enriched methane flame under acoustic enforcement

ABSTRACT The current research has investigated the effects of magnetic fields on molecular structures, especially on flame formation, flame behavior and emission gases. This study particularly examines the phenomenon of combustion instability and emission characteristics of CH4 and CH4/H2 fuels under lean combustion conditions and under external acoustic forcing. Conducted within a combustor utilizing premixing and swirl techniques, experiments strategically generated magnetic fields in specific regions: the burner input, pre-mixer, and fuel supply lines. Trials maintained a constant magnetic field intensity of 3500 gauss, with a thermal output of 3 kW, swirl number of 1, and equivalency ratio of 0.7. Evaluation of acoustic resonance was performed at 95 Hz and 175 Hz frequencies within the combustion chamber. Findings suggest that applying a magnetic field positively impacts the combustion process, reducing instabilities in fuels like CH4 and CH4/H2, especially at a 95 Hz frequency. During pure methane combustion, CO emissions initially measured 4785 ppm but decreased to 4143 ppm under the magnetic field’s influence. Introducing the magnetic field to the pre-mixer increased CO emissions to 4233 ppm, while its application to the fuel line reduced emissions to 4104 ppm. For the CH4/H2 fuel mix, CO emissions decreased from 2638 ppm to 1961 ppm with the magnetic field, indicating improved combustion and reduced pollutant gases, including CO and NOx. This study highlights the potential of magnetic fields to improve combustion efficiency and address environmental concerns.

Application of MOFs-membrane in post-combustion carbon capture for electricity and thermal energy plants

Greenhouse gas emission typically carbon dioxide which result to global warming is becoming a very acute issue to human society. In order to achieve a sustainable development and society, various approaches to reduce carbon emission have been investigated and applied to industry where the majority of carbon emission happens in recent decays. Carbon capture is one of the key ways to address the emission and widely applied to coal-fired power plants. However, typically carbon capture process requires high energy input during the absorption and desorption process with lead to a low net carbon captured rate and high cost of operation. Materials with low energy penalty and high carbon affinity is desired to address this problem. In this research, a more advanced material, metal-organic frameworks (MOFs), for carbon capture under post combustion condition is introduced and evaluated from single material and cooperating with mixed-matrix-membranes to achieve membrane separation. Furthermore, MOFs are usually lack of stability and CO2/H2O selectivity. CALF-20 as the solution to these problems will be introduced later.

An Innovative Retrofit Design for Energy Efficiency and Emission Reduction: MAN B&W Marine Engine Slide Fuel Injector

Background:: The fuel injector is one of the most essential parts in marine diesel engines. For MAN B&W two-stroke engines, the conventional fuel injector, due to the existence of sac volume, can result in problems such as increased emission and fuel consumption and shortened service life of combustion chamber components. Objective:: The MAN B&W marine engine slide-type fuel injector is a structural retrofit of conventional injectors, improving diesel engine combustion conditions, fuel efficiency, and emission reduction in hydrocarbon, NOx, smoke, and particulate matter by eliminating sac volume with patented technology. Methods:: This study employed a comparative analysis approach to evaluate the performance of conventional fuel injectors versus slide-type fuel injectors in MAN B&W two-stroke engines. Data collection involved practical experiences, onboard operations, and analysis of fuel efficiency, emission reduction, and combustion improvement. The structural differences and operational advantages of both injector types were examined to assess the environmental benefits and economic implications of adopting slide fuel injectors. Recommendations for the gradual replacement of conventional injectors with slide-type injectors were based on empirical data and industry best practices. Results:: Slide fuel injectors obtain a reduction of about 75% of the HC emissions at all loads. The slide fuel injector significantly decreases the smoke emission level at low engine load, at 25% load. A reduction in PM of up to 50% has been confirmed, and slide fuel injectors can reduce NOx emission by approximately 15% on average. result: The smoke emission level at low engine load, at 25% load in particular, is greatly decreased by slide fuel injector. Conclusion:: Slide fuel injectors, with a granted patent, are commonly used in marine low-speed engines due to their advantages.

A Hybrid Soft Sensor Model for Measuring the Oxygen Content in Boiler Flue Gas.

As an indispensable component of coal-fired power plants, boilers play a crucial role in converting water into high-pressure steam. The oxygen content in the flue gas is a crucial indicator, which indicates the state of combustion within the boiler. The oxygen content not only affects the thermal efficiency of the boiler and the energy utilization of the generator unit, but also has adverse impacts on the environment. Therefore, accurate measurement of the flue gas's oxygen content is of paramount importance in enhancing the energy utilization efficiency of coal-fired power plants and reducing the emissions of waste gas and pollutants. This study proposes a prediction model for the oxygen content in the flue gas that combines the whale optimization algorithm (WOA) and long short-term memory (LSTM) networks. Among them, the whale optimization algorithm (WOA) was used to optimize the learning rate, the number of hidden layers, and the regularization coefficients of the long short-term memory (LSTM). The data used in this study were obtained from a 350 MW power generation unit in a coal-fired power plant to validate the practicality and effectiveness of the proposed hybrid model. The simulation results demonstrated that the whale optimization algorithm-long short-term memory (WOA-LSTM) model achieved an MAE of 0.16493, an RMSE of 0.12712, an MAPE of 2.2254%, and an R2 value of 0.98664. The whale optimization algorithm-long short-term memory (WOA-LSTM) model demonstrated enhancements in accuracy compared with the least squares support vector machine (LSSVM), long short-term memory (LSTM), particle swarm optimization-least squares support vector machine (PSO-LSSVM), and particle swarm optimization-long short-term memory (PSO-LSTM), with improvements of 4.93%, 4.03%, 1.35%, and 0.49%, respectively. These results indicated that the proposed soft sensor model exhibited more accurate performance, which can meet practical requirements of coal-fired power plants.

Comparative Experimental Assessment of Pollutant Emission Behavior in Combustion of Untreated and Thermally Treated Solid Biofuels from Spruce Chips and Rapeseed Straw

Biomass energy for heating is going to be part of the spectrum of renewable energy sources. However, biomass combustion produces emissions of various pollutants with negative effects at both local and global scales. To reduce some of the locally important pollutant load, thermally treated biomass fuels may offer a partial solution. In this study, two biomass feedstocks, i.e., spruce chips and rapeseed straw, were thermally treated at 300 °C to produce biochars. Subsequently, both original materials and biochars were burned in a 25 kW retort combustion device. In both cases, the biochar showed lower emissions of carbon monoxide and nitrogen oxides, usually almost across the whole range of tested combustion conditions. In total, for the emission production per unit of net calorific value, the spruce biochar showed reductions in CO and NOx productions of 10.8% and 14.5%, respectively. More importantly, in rapeseed straw biochar, the difference was more pronounced. The total production was reduced by 28% and 42%, again in CO and NOx emissions, respectively.

Structural Performance of Outdoor Mechanical Garages under Combustion Conditions

In this paper, the firing process and structural failure behavior of outdoor mechanical car parks are innovatively investigated under diverse conditions, leveraging fire experiments, FDS fire simulation, and finite element simulation. The fire experiments reveal the intricate interplay between flame spread and airflow, highlighting the enhanced risk of fire propagation among adjacent spaces. The temperature profile, mirroring the fire’s lifecycle, is delineated into three distinct stages: initial growth, full development, and eventual decay. Notably, full-scale fire simulation in FDS validates the experimental outcomes, underscoring the scalability and reliability of our scaled-down experiments. Furthermore, finite element simulations offer a profound understanding of structural safety in various parking spaces during a fire. Critically, the susceptibility of columns to failure underscores the imperative need for enhanced fire prevention measures in column design, representing a significant advancement in fire protection engineering.

Stable lean co-combustion of ammonia/methane with air in a porous burner

Ammonia is being considered as a promising zero carbon fuel due to its unique properties, while its combustion still poses challenges in term of instability and higher nitrogen oxides (NOx) emissions. In this study, the co-combustion stability of ammonia/methane with air under lean burn condition is experimentally investigated using a silicon carbide (SiC) ceramic foam burner with a two-layer structure stabilizing the flame. The influences of different operating parameters (methane fraction ω, equivalence ratio φ, and flow velocity V) on the co-combustion flame temperature and emissions are analyzed. The results indicate that the lean stable co-combustion of ammonia/methane with air can be achieved in two-layer ceramic foam burner, with its lower limit extending to φ = 0.5, even for the pure ammonia at specific operating conditions. Notably, the nitric oxide (NO) emissions decrease significantly as the equivalence ratio increases, particularly with a rise in methane fraction. The reduction can reach as low as 843 ppm with φ increasing to 0.9, further reducing to an ultra-low level of less than 150 ppm at φ = 1.3, significantly lower than those of traditional free flame burners. Carbon monoxide (CO) emissions remain at ultra-low levels, indicating the excellent co-combustion efficiency of ammonia/methane-air in the porous burner. An optimal co-combustion region with lower NO and CO emissions were conclusively identified. These findings demonstrate the effectiveness of porous media combustion in improving the co-combustion stability of ammonia/methane and reducing NO emissions, thereby helping to develop the porous burners of ammonia-based fuel and promoting its clean utilization for realizing carbon neutrality.

Experimental investigation on dynamic characteristics of methane/air combustion in double‐layer pellets porous media

AbstractThe double‐layer porous media burner is considered as an effective way to realize stable lean‐burn. In order to quickly achieve a stable combustion state in a double‐layer porous media burner, this work investigated the dynamic characteristics of methane/air premixed combustion in a bench‐scale double‐layer porous media burnspanning from ignition to stable combustion and ultimately flameout. The experimental results indicate that regulating the equivalence ratio and the inlet velocity enables the establishment of a stable flame front and the φ = 0.75 and the Vin = 0.20 m/s are the appropriate start‐up conditions. The average propagation velocity of the combustion wave variation along the axial direction and ranged approximately from −0.022 to −0.078 mm/s. Moreover, the transition time to a stable combustion state is reduced by nearly 47.14% as the equivalence ratio increases from 0.60 to 0.70. During start‐up stage, there are significant fluctuations in CO and NOx concentrations, but both emissions remain low during steady combustion state, with the maximum concentrations of 37.5 and 40.2 mg/m3, respectively. Furthermore, the porous media combustion exhibits a pronounced re‐ignition capacity. At higher equivalence ratios, longer interruptions of premixed gas are allowed.