Methane Fuels Research Articles

Effects of hydrogen and methane anti-knocking characteristics on the efficiency and power output in argon power cycle engines

Argon Power Cycle (APC) combustion engine has a high efficiency, zero carbon emissions, and zero pollutant emissions, rendering it a promising way for achieving zero or carbon neutrality within the realm of internal combustion engine (ICE) technology. Previous studies have shown that while APCs significantly improve the thermal efficiency of ICEs, they also face serious knock problems due to their high temperatures and pressures, especially when hydrogen is used as a fuel. In this study, the anti-knocking characteristics of hydrogen, methane, carbon monoxide, and ammonia were first investigated in APC through thermodynamic calculations by Ignition Delay Time. Then, based on testbench experiments, hydrogen and methane fuels were selected to further investigate the effect of different fuel anti-knocking characteristics on the indicated thermal efficiency and power of APC combustion engine. Test results showed that when using hydrogen, the APC ICE exhibited a pronounced knock tendency, and the test engine could not operate stably when the excess oxygen ratio <2.1 at compression ratio = 9.6. The CA50 of the maximum efficiency point was delayed in APC than in air for both hydrogen and methane, specially H2 has an obvious lag at about 5–15 ° CA. In comparison, when using methane, the combustion control of engine is easier, and the peak indicated thermal efficiency 59% and the peak indicated mean effective pressure 0.92 MPa are higher than 54.3% and 0.60 MPa of using hydrogen. The use of hydrogen still needs an anti-knocking strategy while an extra carbon capture device is necessary to ensure a closed argon cycle if methane is employed.

Unusual Promoting Effect of Ni–Cu Alloy Formation on Carbon Deposition in Carbonate-Superstructured Solid Fuel Cell with Methane Fuel

Unusual Promoting Effect of Ni–Cu Alloy Formation on Carbon Deposition in Carbonate-Superstructured Solid Fuel Cell with Methane Fuel

Experimental study of the influence of Lewis number, laminar flame thickness, temperature, and pressure on turbulent flame speed using hydrogen and methane fuels

To experimentally explore the influence of Lewis number Le, laminar flame thickness δL, pressure P, and unburned gas temperature Tu on turbulent flame speed ST, a set of conditions is designed by adjusting nitrogen mole fraction in lean H2/O2/N2 (Le=0.35) and stoichiometric CH4/O2/N2 (Le≈1) mixtures. The adjustment is performed by simulating complex-chemistry laminar flames to obtain the same laminar flame speeds SL not only for different fuels, but also for different pressures (1, 2, and 5 atm). The mixtures are characterized by significantly different SL at Tu=300 K and 400 K, whereas variations in δL with the temperature are sufficiently weak. Moreover, laminar flame thicknesses are approximately equal for H2-based and CH4-based mixtures at the same P, but are significantly decreased with increasing pressure. For this set of conditions, ST is measured by applying schlieren imaging techniques to film expansion of centrally ignited, statistically spherical flames in homogeneous isotropic turbulence generated by a dual-chamber, constant-pressure, fan-stirred explosion facility. Analyses of the measured data show the following trends. First, turbulent flame speed is increased by both P and Tu, whereas ST/SL is decreased with increasing Tu. Second, turbulent flame speed measured at different P and Tu can be predicted by allowing for SL(P,Tu) and δL(P,Tu). Thus, the present data do not call for explicitly substituting normalized pressure or temperature into a turbulent flame speed approximation. Third, ST is increased with decreasing laminar flame thickness. Fourth, speeds of the lean H2/O2/N2 flames are higher when compared to the stoichiometric CH4/O2/N2 flames, with this difference is increased (reduced) by P (Tu, respectively). Fifth, all measured data on ST can quantitatively be described by substituting SL and δL with the counterpart characteristics of highly strained twin laminar flames. The latter finding supports leading point concept of premixed turbulent combustion.

Energy-related carbon dioxide emission factors from combustion of gaseous methane fuels

Abstract The topic of this paper concerns energy-related carbon dioxide emission factors from the combustion of gaseous methane fuels. It is a very current subject, as methane fuels, mainly of fossil origin, are one of the primary energy carriers used in industrial and municipal applications for energy purposes. Consequently, the emitted carbon dioxide contributes to the intensification of the greenhouse effect in the atmosphere. The problem of the quantities characterising emissions from the combustion of methane fuels is complicated by the diversity of these fuels. This paper presents background information on the gaseous hydrocarbon fuels and the composition of the main types of natural gas. The structure of natural gas consumption in Poland, depending on the sectors of application for particular types of natural gas, is presented. On the basis of the existing data, aggregated energy-related carbon dioxide emission factors were estimated and analysed. The analysis was carried out for high-methane natural gas (HM), colliery gas (CG) and nitrified natural gas (N)—for the years 1988–2021. Trends in fuel consumption and energy-related carbon dioxide emission factors were determined for the years 1988–2021.

Pollutant Emissions Reporting and Performance Considerations for Ammonia-Blended Fuels in Gas Turbines

Abstract To limit climate change and promote energy security, there is widespread interest toward transitioning existing fossil fueled combustion systems to sustainable, alternative fuels such as hydrogen (H2) and ammonia (NH3) without negatively impacting air quality. However, quantifying the emission rate of air pollutants such as nitrogen oxides (NOx) is a nuanced process when comparing pollutant emissions across different fuels, as discussed in our paper GT2022-80971 presented last year. That study indicated that the standardized approach for measuring combustion emissions in terms of dry, oxygen-referenced volumetric concentrations (i.e., dry ppmv at the reference O2 concentration (ppmvdr)) inflates reported pollutant emissions by up to 40% for hydrogen combustion relative to natural gas. In this paper, we extend our prior analysis of these so-called “indirect effects” on emissions values to ammonia (NH3) and cracked ammonia (i.e., molecular hydrogen and nitrogen, 3H2 per N2) fuel blends. The results reveal that ppmvdr-based pollutant reporting approaches have a less prominent influence on emissions interpretations for molecular ammonia–methane blends than for hydrogen–methane blends. Nonetheless, we still find that ppmvdr reporting induces up to a 10% relative increase in apparent emissions when comparing 100% NH3 and 100% methane (CH4) fuels at an equal mass-per-work emission rate. Cracking the ammonia is shown to increase this relative bias up to 21% in comparison to a methane system. Further analysis shows how drying, dilution, thermodynamic, and performance effects each influence the relationship between ppmvdr and mass-per-work emissions across the spectrum of fuels and fuel blends. Following discussion of these findings, we conclude that quantifying combustion emissions using ppmvdr is generally inappropriate for emissions comparisons and advise the combustion community to shift toward robust mass-per-energy metrics when quantifying pollutant emissions.

Visible light promoted low temperature photothermal CO2 methanation over morphologically engineered Ni/TiO2 NWs catalyst

Mankind is currently faced with two ongoing major issues, namely the energy crisis and climate change. This is due to the growing human population, causing a steep increase in energy demand which is usually catered via the combustion of depleting fossil fuels. In accordance with the Sustainable Development Goals (SDGs), the utilization of carbon dioxide greenhouse gas to produce green methane fuels is deemed to be a promising approach to tackle both the aforementioned issues. Here, we successfully engineered the morphology of 3D TiO2 microparticles (TiO2 MPs) into wire-like 1D TiO2 nanowires (TiO2 NWs) via a facile solvothermal method. The nickel dispersed Ni/TiO2 NWs catalyst was then compared with its microparticle counterpart for visible light promoted low temperature photothermal CO2 methanation. Various characterization methods were conducted such as BET, BJH, FE-SEM, EDX, HR-TEM, XRD, UV–vis DRS and H2-TPR to investigate the physical and chemical properties of the catalyst samples. Initial temperature screening (150 to 300 °C) under dark and visible light irradiated conditions revealed that photothermal CO2 hydrogenation was not feasible below 250 °C. Nevertheless, the promotional effect of visible light was diminished at elevated temperatures. It was observed that the structurally modified 1D TiO2 NWs yielded a higher production rate (19.8 mmol gcat-1h−1) and selectivity (84 %) as compared to its 3D microparticle counterpart. This is mainly due to the 1D wire like structure which possesses a high surface area which increased the exposed area to visible light irradiations while promoting the dispersion of Ni active metals while limiting the growth of NiO particles. The porosity and wire like structure of 10Ni/TiO2 NWs also promoted an intimate contact between catalyst and reactants, in turn showing a prolonged durability up to 4 reaction cycles. Interestingly, the methanation performance over the 1D catalyst gradually improved over time, suggesting the visible light assisted photoreduction of NiO to metallic Ni. Thus, our findings elucidated the significance of catalyst support morphology on the photothermal driven CO2 methanation reaction.

Options for Methane Fuel Processing in PEMFC System with Potential Maritime Applications

Proton-exchange membrane fuel cells (PEMFCs) are low-temperature fuel cells that have excellent starting performance due to their low operating temperature, can respond quickly to frequent load fluctuations, and can be manufactured in small packages. Unlike existing studies that mainly used hydrogen as fuel for PEMFCs, in this study, methane is used as fuel for PEMFCs to investigate its performance and economy. Methane is a major component of natural gas, which is more economically competitive than hydrogen. In this study, methane gas is reformed by the steam reforming method and is applied to the following five gas post-treatment systems: (a) Case 1—water–gas shift only (WGS), (b) Case 2—partial oxidation reforming only (PROX), (c) Case 3—methanation only, (d) Case 4—WGS + methanation, (e) Case 5—WGS + PROX. In the evaluation, the carbon monoxide concentration in the gas did not exceed 10 ppm, and the methane component, which has a very large greenhouse effect, was not regenerated in the post-treated exhaust gas. As a result, Case 5 (WGS and PROX) is the only case that satisfied both criteria. Therefore, we propose Case 5 as an optimized post-treatment system for methane reforming gas in ship PEMFCs.

Rotating Detonation Combustion for Advanced Liquid Propellant Space Engines

Rotating (also termed continuous spin) detonation technology is gaining interest in the global research and development community due to the potential for increased performance. Potential performance benefits, thrust chamber design, and thrust chamber cooling loads are analyzed for propellant applications using liquid oxygen or high-concentration hydrogen peroxide oxidizers with kerosene, hydrogen, and methane fuels. Performance results based on a lumped parameter treatment show that theoretical specific impulse gains of 3–14% are achievable with the highest benefit coming from hydrogen-fueled systems. Assessment of thrust chamber designs for notional space missions shows that both thrust chamber length and diameter benefits are achievable given the tiny annular chamber volume associated with the rotating detonation combustion. While the passing detonation front drastically increases local heat fluxes, global energy balances can be achieved if operating pressures are limited to be comparable to existing or prior space engines.

Nanofiber Composites as Highly Active and Robust Anodes for Direct-Hydrocarbon Solid Oxide Fuel Cells.

Direct utilization of methane fuels in solid oxide fuel cells (SOFCs) is a key technology to realize the immediate inclusion of such high-efficiency fuel cells into the current electricity generation infrastructure. However, the broad commercialization of direct-methane fueled SOFCs is critically hindered by the inadequate electrode activity and their poor longevity, which primarily stems from the carbon build-up issues. To make the technology more competitive, a novel electrode structure that can dramatically improve the tolerance against coking is essential. Herein, we present highly active and robust core-shell nanofiber anodes, La0.75Sr0.25Cr0.5Mn0.5O3@Sm0.2Ce0.8O1.9 (LSCM@SDC), directly obtained with a single-nozzle electrospinning process through the use of two immiscible polymers. The intimate coverage of SDC on LSCM not only increases the active reaction sites but also promotes resistance toward carbon deposition and thermal aggregation. As such, the electrode polarization resistance obtained with LSCM@SDC NFs is among the lowest value ever reported with LSCM derivatives (∼0.11 Ω cm2 in wet H2 at 800 °C). The facile fabrication process of such complex heterostructures developed in this work is attractive for the design of not only SOFC electrodes but also other solid-state devices such as electrolysis cells, membrane reformers, and protonic cells.

Pilot impact on turbulent premixed methane/air and hydrogen-enriched methane/air flames in a laboratory-scale gas turbine model combustor

The impact of pilot flame operation on the combustion of pure methane and hydrogen-enriched methane (H2/CH4: 50/50 in vol%) fuels was investigated in a gas turbine model combustor under atmospheric conditions. The burner assembly was designed to mimic the geometry of an industrial burner, the Siemens DLE Burner, in which a concentric annular ring equipped with pilot flame burners is implemented in the dome of the combustor. Two pilot burner configurations have been investigated: a non-premixed and a partially premixed pilot arrangement. The performance of the pilot burners was evaluated for varying Reynolds number (Re) and H2 enrichment. High-speed OH∗ chemiluminescence imaging, as well as simultaneous planar laser-induced fluorescence measurements of the OH radicals and formaldehyde (CH2O) were used for evaluating the dynamics and structures of the flames for different conditions. Furthermore, emission measurements were carried out to determine the influence of hydrogen dilution on the NOx and CO emission levels. The main findings are (a) the effect of the pilot flame is sensitive to the Reynolds number of the main flame and the type of the pilot flame, (b) the stability range becomes narrower with increasing hydrogen ratio, due to the tendency to flashback, (c) non-premixed pilot flames lower the NOx and increase the CO emissions, albeit rather small differences in the emissions have been detected, and (d) the NOx and CO emissions become significantly lower with increasing hydrogen ratio.

Numerical comparative study on performance and emissions characteristics fueled with methanol, ethanol and methane in high compression spark ignition engine

Methane, methanol and ethanol are three common high-octane alternative fuels. As fuels for high compression ratio engines, they can improve thermal efficiency while preventing knocking. However, each of these three fuels has its own physicochemical properties and presents different engine performance. This study compares in detail the performance, combustion and emissions of a high-compression-ratio SI engine fueled by methanol, ethanol and methanol. A 4-cylinder high compression ratio SI engine simulation model was built based on 1-D simulation platform. The engine was converted from a CI diesel engine with a CR of 17.5, and the methanol, ethanol of methane injector was installed in the intake port. The results showed that for the methanol, ethanol and methane fuels, under the same engine speeds and equivalence ratios, the BP and BT of methanol were higher than ethanol and methane fuels, methane has the lowest BP and BT; methane has a lower BSFC and BTE than methanol and ethanol, with methanol having the highest BSFC and BTE; the CO and NOx emissions of methanol were lower than ethanol and methane fuels; the HC and CO2 emissions of methane were lower than methanol and ethanol fuels.

H2 – CH4 blending fuels combustion using a cyclonic burner on colorless distributed combustion

H 2 – CH 4 mixture fuels can be promising for reducing carbon-based emissions. However, because of higher pollutant emission (such as NO X ) problems during hydrogen combustion, a new combustion method can be favorable. Colorless distributed combustion (CDC) is emerging here. CDC enables ultra-low pollutant emissions along with reduced flame instabilities, combustion noise, improved combustion efficiency, etc. Considering those benefits, methane and the hydrogen-enriched methane (60% CH 4 – 40% H 2 , 50% CH 4 – 50% H 2 , 40% CH 4 – 60% H 2 ) fuels have been consumed using a cyclonic burner providing more residence time at an equivalence ratio of 0.83 under distributed regime. For the modelings, Reynolds Stress Model (RSM) turbulence model, the assumed-shape with β-function Probability Density Function combustion model, and P-1 radiation model have been selected. To seek CDC, the oxygen concentration in the oxidizer was reduced with N 2 or CO 2 diluent from 21% O 2 to 13% O 2 at an interval of 2%. The air and the fuel temperatures were kept constant at 300 K. Besides, for seeking high-temperature air combustion (HiTAC) conditions the oxidizer temperature was changed to 600 K to simulate flue gas recirculation. The results showed that the temperature distributions changed to be more uniform considerably with a decrease in oxygen concentration for all cases. CDC also provided a considerable decrease in NO X and a favorable reduction in CO at a certain oxygen concentration. It has been concluded that CO 2 as the diluent was more effective for reducing temperature levels and NO X levels due to its greater heat capacity. • H 2 – CH 4 blending fuels combustion have been examined in a cyclonic burner. • Colorless distributed combustion (CDC) was sought for H 2 – CH 4 blending fuels. • Reduced oxygen concentration affected considerably all combustion characteristics. • Combustion characteristics were changed with increase in hydrogen content. • Ultra-low pollutant emissions were achieved under CDC.

Assessment of the Environmental Impact of Using Methane Fuels to Supply Internal Combustion Engines

This research paper studied the environmental impact of using methane fuels for supplying internal combustion engines. Methane fuel types and the methods of their use in internal combustion engines were systematized. The knowledge regarding the environmental impact of using methane fuels for supplying internal combustion engines was analyzed. The authors studied the properties of various internal combustion engines used for different applications (specialized engines of power generators—Liebherr G9512 and MAN E3262 LE212, powered by biogas, engine for road and off-road vehicles—Cummins 6C8.3, in self-ignition, original version powered by diesel fuel, and its modified version—a spark-ignition engine powered by methane fuel) under various operating conditions in approval tests. The sensitivity of the engine properties, especially pollutant emissions, to its operating states were studied. In the case of a Cummins 6C8.3 modified engine, a significant reduction in the pollutant emission owing to the use of methane fuel, relative to the original self-ignition engine, was found. The emission of carbon oxide decreased by approximately 30%, hydrocarbons by approximately 70% and nitrogen oxide by approximately 50%, as well as a particulate matter emission was also eliminated. Specific brake emission of carbon oxide is the most sensitive to the operating states of the engine: 0.324 for a self-ignition engine and 0.264 for a spark-ignition engine, with the least sensitive being specific brake emission of nitrogen oxide: 0.121 for a self-ignition engine and 0.097 for a spark-ignition engine. The specific brake emission of carbon monoxide and hydrocarbons for stationary engines was higher in comparison with both versions of Cummins 6C8.3 engine. However, the emission of nitrogen oxide for stationary engines was lower than for Cummins engines.

Performance Investigation of a Nickel Cermet Anode Modified with Copper, Alkaline Earth Metal Oxide, Boron, and Perovskite for Direct Methane Fuel Cell

The metallic copper, alkaline earth metal oxide, boron, and perovskite were incorporated on the surface of a Ni-cermet anode, and the performance of the modified Solid Oxide Fuel Cell (SOFC) anode was evaluated. The cell performance was analyzed by voltage-current characteristics (V-I curve) and H2-CH4 step reactions (P-t curve) in a potentiostatic mode. Besides, we also determined if a metallic phase or high electronic conductivity of the anode is important for a cell to perform well when H2 is used as a fuel, whereas both conductivity and anti-coking capability are critical while using CH4 as a fuel. The results showed that the anodes containing magnesium oxide (MgO), lanthanum strontium titanate (La0.4Sr0.4TiO3−γ), and boron were relatively resistant to the degradation in the CH4 environment when compared with others. The underlying mechanism varied mainly with electronic and structural promotion by the dopants as well as their material compatibility with the Ni-cermet substrate. These findings were evidenced and supported by surface analysis as well as in-situ infrared and mass spectroscopic studies too.

The Effect of Biogas Origin on the Electricity Production by Solid Oxide Fuel Cells

This work simulates electricity production in a Solid Oxide Fuel Cell (SOFC)-based power plant, fed by biogas of various compositions. Steam reforming of the gas feed stream is used to produce the required supply for the SOFC. Given the constraints of the feed stream compositions, resulting from the origin of biogas, i.e., by the biomass from which the biogas has been produced as well as by the operating conditions selected for its production, the overall plant performance is modelled in terms of energy and exergy. The model provides results on the efficiency, power output and thermal behavior of the system, thus presenting the potential to offer great advantages in generating electricity from biogas and reducing the environmental impact. This research study presents the efficiency of such a system in terms of energy and exergy, by considering several values of the operational parameters (extensions of reactions that take place in the apparatus, temperatures, feed stream compositions, etc.). It is found that moving towards a methane richer fuel, the energy and exergy efficiency can remain almost constant at high levels (around 70%), while in absolute value the electric energy can increase up to 35% according to the system’s needs. Therefore, under this prospect, the present research study reveals the usefulness of low content methane fuels, which through the optimization process can succeed identical energy management compared to high content methane fuels.

A method to convert stand-alone OH fluorescence images into OH mole fraction

Due to the accessibility of the planar laser-induced fluorescence technique, images of OH fluorescence intensity are often used to study the structure of turbulent flames. However, there are differences between the measured OH fluorescence intensity and the actual OH mole fraction. These are often neglected because accurate conversion from fluorescence to mole fraction requires the combined knowledge of all major species mole fractions and temperature, which was rarely achieved in 2-D. Here, a new method to convert images of OH fluorescence intensity into OH mole fraction is proposed. This model relies only on inexpensive 1-D laminar flame calculations and does not require information on major species or temperature. The primary assumption behind the applicability of this model is the local approximation of multi-dimensional flames with 1-D counterflow flames. The method utilizes the fact that both OH mole fraction and OH fluorescence intensity profiles are self-similar with pressure and scalar dissipation rate. Only two empirical constants need to be calibrated using 1-D laminar flame calculations. The model was validated using computed 2-D axisymmetric laminar flames and 3-D turbulent flames computed with LES. The accuracy of the conversion model was estimated to about 8% (for Reynolds number up to Re =66,800), which includes errors due to the 3-D effects that are not included in this method relying on 2-D images. As a proof of concept, the conversion model was finally applied to one single-shot image of OH fluorescence intensity measured with OH-PLIF for syngas at P=4bar and Re =16,700, demonstrating potential applications of this new method. The method was tested for hydrogen, syngas and methane fuels but, for brevity, only syngas results are reported in detail.

Aid of a metallic functional layer on Ni/YSZ anode for Direct Methane Fuel Cell

Aid of a metallic overlayer to nickel/yttrium-stabilized-zirconia (Ni/YSZ) anode is investigated in Direct Methane Fuel Cell. Copper modified nickel metallic overlayer shows high activity for fuel cell performance and good stability to coking in methane atmosphere. The copper-nickel overlayer provides advantages of material compatibility with the substrate and catalytic function on copper-modified nickel sites. The results suggest that the overlayer is effective for decomposition of methane and tolerant to coking by removal of deposited carbon via oxidation and gasification reaction.

Improved Electrochemical Properties of an Ni-Based YSZ Cermet Anode for the Direct Supply of Methane by Co Alloying with an Impregnation Method

To avoid the proneness to degradation due to coking in the operation of solid oxide fuel cells (SOFCs) directly running on methane (CH4) fuels, a modified porous anode of the Ni1−XCoX/YSZ (yttria-stabilized zirconia) cermet prepared by an impregnation method is presented. The influence of the Co alloying content on the cermet microstructure, SOFC characteristics, and prolonged cell performance stability has been studied. Co was incorporated into Ni and formed a solid solution of Ni1−XCoX alloy connected with the YSZ as the cermet anode. The porous microstructure of the Ni1−XCoX/YSZ cermet anode formed by sintering exhibited a grain growth with an increase in the Co alloying content. The electrochemical performance of the cells consisting of the Ni1−XCoX/YSZ cermet anode, the YSZ electrolyte, and the LSM (La0.8Sr0.2MnO3) cathode showed an enhancement by the Ni1−XCoX impregnation treatment for the respective supply of H2 and CH4 to the anode. The cell using the Ni0.75Co0.25/YSZ cermet anode (the Ni0.75Co0.25 cell) showed the highest cell performance among the cells tested. In particular, the performance enhancement of this cell was found to be more significant for CH4 than that for H2; a 45% increase in the maximum power density for CH4 and a 17% increase for H2 at 750 °C compared with the performance of the cell using the Ni/YSZ cermet anode. Furthermore, the prolonged cell performance stability with a continuous CH4 supply was found for the Ni0.85Co0.15 and Ni0.75Co0.25 cells at least for 60 h at 750 °C. These enhancement effects were caused by the optimum porous microstructure of the cermet anode with the low anodic polarization resistance.

Performance of Ni/10Sc1CeSZ anode synthesized by glycine nitrate process assisted by microwave heating in a solid oxide fuel cell fueled with hydrogen or methane

Nickel/scandia-ceria-stabilized-zirconia (Ni/10Sc1CeSZ) cermet is a potential anode for solid oxide fuel cells. The anode powder is prepared through a microwave-assisted glycine nitrate combustion process, and its properties, including phase and chemical composition as well as morphology, are characterized by XRD, TEM, and EDS techniques. The electrical conductivity and electrochemical behavior under low concentration of dry hydrogen (H2:N2 volume ratio = 10:90) and dry methane (CH4:N2 volume ratio = 50:50) fuels are determined. XRD results show two phases, namely, cubic NiO phase and cubic 10Sc1CeSZ phase, with the crystallite sizes of 67 and 40 nm, respectively. The area specific resistances (ASRs) of the prepared anode measured using a symmetrical cell of Ni/10Sc1CeSZ|10Sc1CeSZ|Ni/10Sc1CeSZ are 0.96 and 24.3 Ω cm2 observed at 800 °C in dry low hydrogen concentration (10 vol% hydrogen–90 vol% nitrogen) and dry methane (50 vol% methane–50 vol% nitrogen) fuels, respectively. The ASR in methane fuel is higher than that in hydrogen fuel at all operating temperatures (600–800 °C) because of carbon deposition. The amount of deposited carbon and degree of graphitization (IG/ID) of this anode after exposure in methane at 800 °C for 3 h are 4.34% and 2.1, respectively. Overall, Ni/10Sc1CeSZ cermet synthesized by glycine nitrate process assisted with microwave-heating technique exhibits acceptable electrochemical behavior even at low hydrogen concentration and also in dry methane. This can be related to the improved powder morphology as a result of uniform heating assisted by microwave energy.

Flame structure and emission signature in distributed combustion

Colorless distributed combustion (CDC) combustion technology offers significant advantages of ultra-low pollutants emission, stable operation and improved pattern factor for high intensity stationary gas turbines applications. Detailed knowledge on distributed combustion behavior is required to further deploy this technology. This paper reports the evolution of swirl flame shape, flame expansion and pollutants emission characteristics using propane, methane, and 20% and 40% hydrogen enriched methane fuels. The entrainment of hot reactive gases was simulated by diluting the inlet air stream with inert nitrogen or carbon dioxide. OH* chemiluminescence signatures, captured at different dilution levels, manifested gradual reduction of flame luminosity when CDC was approached. Flame boundaries derived using image threshold technique helped to visualize the broadened reaction zone under CDC conditions, which had much reduced chemiluminescence signal intensity. The rms to mean OH* signal variation at different dilution levels were analyzed to detect the initiation of CDC. The higher flame lift-off observed with CO2 dilution was due to higher heat capacity of CO2, resulting in greater flame speed reduction. Flame expansion, evaluated from the area encompassed within the flame boundary at different dilution levels showed a power-law behavior with both the diluents. Expansion of 4 to 5 times of initial flame volumes was observed under CDC using CO2 and N2 dilution, respectively. Significant reduction of NO and CO emission achieved under CDC was due to reduction of overall flame temperature, hotspot mitigation, and widened reaction zone occupying large flame volume, which makes it favorable for many practical combustor applications.