Increase In Flame Temperature Research Articles

Experimental study on combustion and thermoacoustic instability characteristics of ethanol/methane Co-firing flames

This paper investigates the combustion and thermoacoustic instability characteristics of ethanol/methane co-firing flames. Methane was introduced into the combustion chamber in three different mixing methods: the premixing method, single-tube injection, and dual-tube injection. The effects of mixing ratio, equivalence ratio, jet pipe diameter and position on combustion performance are also considered. The results show that under the premixed combustion mode, as the methane ratio increases, combustion instability shows a trend of first enhancement and then weakening, reaching a maximum pressure pulsation of 228.8 Pa at a 30 % mixing ratio. When methane is injected transversely into the combustion chamber using a single-tube or dual-tube, the inner diameter of the injection tube, injection height, and injection distance are essential factors affecting combustion instability, all of which will change the inhibitory effect of the transverse jet on instability. In addition, when the methane mixing ratio reaches 50 %, the co-firing flames will be in a relatively stable combustion state under all conditions. But at this time, the increase in flame temperature and the oxygen-deficient environment in the combustion chamber will cause simultaneous increases in CO and NOx emissions, which are not conducive to clean and efficient fuel combustion.

Effect of Hydrogen Addition on Soot Reduction in Diffusion Flames

This study explores the effects of hydrogen addition on soot reduction in methane-air diffusion flames, employing computational analysis coupled with chemical equilibrium and k-epsilon combustion turbulence models. By varying the fuel mixture with hydrogen mass percentages ranging from 0% to 11%, alterations in flame behaviour were observed. Results revealed a notable increase in maximum flame temperature at 1.3% hydrogen addition, attributed to enhance combustion efficiency, while subsequent additions led to temperature decrements due to dilution effects. Concurrently, soot production exhibited a general decrease, with reductions quantified up to 96.7% compared to baseline conditions, primarily due to improved oxidation and decreased carbon content. Additionally, the position of maximum flame temperature and soot mass fraction shifted along the axial direction owing to hydrogen's higher flammability compared to methane-air diffusion. These findings offer insights into optimizing flame characteristics for reduced particulate matter emissions, emphasizing the potential of hydrogen addition in mitigating soot formation in diffusion flames.

Enhancing ammonia combustion performance using hydrogen peroxide-enriched air: A computational fluid dynamics analysis

The effect of H2O2 addition to the air on ammonia combustion was investigated in the current research using a computational fluid dynamics approach. The numerical simulation was conducted in a 10-kW laboratory-scale furnace. The oxidizer and fuel were injected into the furnace in a non-premixed mode. Furthermore, a kinetic study was carried out to analyze the sensitivity of NO production during combustion and to determine reaction pathways under various conditions. The findings indicate that the addition of H2O2 to the mixture increases flame temperature and NO levels, while decreasing N2O levels. Moreover, the study demonstrates that, with a maximum concentration of only 10 ppm, the amount of NO2 is very low under various percentages of H2O2 and different operating conditions. Furthermore, it is concluded that during ammonia/air combustion, lowering the oxidizer inlet temperature and increasing wall heat extraction may cause the combustion to become unstable. Under pure air oxidizer conditions, where Tin = 973 K and Twall = 1273 K, the combustion is stable. However, instability occurs when Twall falls to 1173 K. In this instance, adding merely 5 % H2O2 to the oxidizer is sufficient to provide self-sustaining and stable burning. More H2O2 must be introduced into the furnace to maintain stable combustion as Tin and Twall continue to decline. Interestingly, while adding H2O2 raises NO levels, decreasing the inlet and wall temperatures at higher H2O2 concentrations can help regulate NO emissions. These findings clearly indicate that introducing H2O2 into the fuel mixture could be a promising strategy for reducing the inlet temperature and enhancing heat extraction, which will both reduce energy consumption and increase system efficiency.

Perforation performance and mechanism of a torch utilizing Al/PTFE/Fe2O3/CuO thermite composites

Aluminum-based thermite containing fluorine oxidizers exhibits excellent performance characteristics such as substantial heat release and tunable gas production. In this study, a torch loaded with Al/PTFE/Fe2O3/CuO thermite composites was recently designed to eject high-temperature jets and penetrate 10 mm-thick Q235 steel plates. The reactivity of the loading composites was systematically studied to analyze the perforation mechanism. The microstructure, the flame temperature, and pressure properties of the thermites were tested. The device’s perforation capacity was quantified. The research confirmed the application potential of fluoropolymer-based thermites in the field of metal perforation. The results of the pressure tests suggest that the composites have a synergistic effect on pressure properties, resulting in better peak pressure than single thermite. The fuel-rich thermite exhibited a higher flame temperature and heat of combustion. It is observed that the perforation velocity increased with the increase in flame temperature and peak pressure. By adjusting the Al and PTFE content of the near fuel-rich thermites, the torch with different equivalence ratios exhibited a tunable perforation time ranging from 0.4 s to 5.21 s. It is hypothesized that the formation of the alloy layer on the surface of the metal targets plays a significant role in the perforation process by weakening the strength of the plates and improving the mobility of the molten area. The results provide a new and practical path to designing efficient perforation agents.

Experimental and numerical study on flow/flame interactions and pollutant emissions of premixed methane-air flames with enhanced lean blowout hydrogen injection

This study investigates experimentally and numerically the stability, combustion, and emissions characteristics of premixed swirl-stabilized methane/air flames with enhanced lean blowout (ELBO) injection of hydrogen in the non-premixed mode for higher turndown ratio gas turbines. The study analyzed the effects of hydrogen fraction (HF: volumetric percentage of H2 in the total fuel) ranging from 0 to 25% and equivalence ratio (φ) ranging from 0.5 to 0.893 on flow/flame interactions and flame stability, structure, and emissions. The introduction of non-premixed H2 yields two conflicting outcomes, with enhancements in reaction kinetics and flame speed yet counteracted by increased hydrogen jet momentum dispersing the flame. The combustor lean blowout (LBO) limit remains relatively unaffected (φoverall≈ 0.5) by H2 injection. Flame temperature is primarily influenced by φ and minorly by HF. Increasing HF resulted in localized temperature rises around H2 jets without an overall increase in flame temperature, offering a promising strategy for reduction of NOx emissions. Nevertheless, using H2 as a pilot fuel leads to an increase in intermediate species like OH, H, and O, contributing to flame stabilization. However, this practice also results in higher CO and unburned hydrocarbons emissions due to the inherent characteristics and heightened reactivity of H2.

The Influence of Ozone on the Flame Propagation Behavior of n-Heptane/air and i-Octane/air Premixed Flame in an Engine-Relevant Environment

ABSTRACT The promotional effect of ozone on lean premixed spherical flame propagation in an engine-relevant, high-temperature, high-pressure environment was investigated using an optically accessible rapid compression and expansion machine (RCEM). The laminar burning velocity, burned gas Markstein length, and initial flame development time based on mass fraction burned (MFB), were examined for n-heptane/air and i-octane/air premixture (φ = 0.55) with 15 [ppm] ozone, through self-emission observation of a propagating flame with a high-speed camera and combustion pressure analysis. The results showed that ozone reduced the initial flame development time and increased the laminar burning velocity for n-heptane/air premixture under temperature conditions in which the low-temperature oxidation (LTO) reaction was more clearly pronounced; but ozone did not enhance either the initial flame development or the laminar burning velocity in the case of i-octane/air premixture, where the LTO reaction was weak owing to the fuel molecular structure, even under the same temperature conditions. These results suggest that the enhancement of the LTO reaction by ozone, and the subsequent generation of thermal energy and CO radicals through an H2O2 loop reaction in the pre-flame region, were responsible for the increase in the laminar burning velocity. Furthermore, ozone increased the burned gas Markstein length, flame thickness, and Zeldovich number of the n-heptane/air mixture under the temperature conditions in which the laminar burning velocity was enhanced by ozone. This suggests that the chemical reaction in the reaction zone was more active in response to the increase in flame temperature.

A simplified mechanism of hydrogen addition to methane combustion for the pollutant emission characteristics of a gas-fired boiler

The reaction mechanism of hydrogen-enriched methane (HEM) combustion is significant in the combustion process. In this study, four widely used reaction mechanisms for methane combustion are simplified to investigate the pollutant emission characteristics of a gas-fired boiler used for HEM combustion. The laminar burn velocity (LBV) and ignition delay time (IDT) of the four detailed and four simplified mechanisms are compared, and the simplified San Diego mechanism is identified as the optimal mechanism using relative error and population standard deviation analysis. The temperatures and key components of the simplified San Diego mechanism are also compared with those of the detailed San Diego mechanism under various XH2. Based on the simplified San Diego mechanism, a chemical reactor network model for gas-fired boilers is further established to investigate the pollutant emissions of HEM combustion, in which the hydrogen doping ratio XH2 ranged from 0 to 80% and the inlet air and fuel temperature Tin ranged from 300 K to 600 K. Results showed that at Tin = 300 K with XH2 ranging from 0 to 80%, the mole fraction of NO increase by 1.94 times because of the increase in peak flame temperature; moreover, the mole fractions of N2O, CO, and CO2 decrease by approximately 25%, 50%, and 52%, respectively. With XH2 ranging from 0 to 40% and Tin ≥ 500 K, the mole fraction of NO decreases because the reduction reaction of NO + H = N + OH is promoted, whereas when XH2 is further increased to 80%, the increased H promotes the increase in NO again. CO emissions decreased as XH2 increased from 0 to 80%, whereas they increased by approximately 1.3 times as Tin increased from 300 K to 600 K because of the CO2 decomposition. N2O emissions decreased by more than 25% as XH2 increased from 0 to 80%. Additionally, CO2 emissions decrease by 52% with an increase in XH2 and by only 5% with an increase in Tin, indicating that XH2 has a larger impact on CO2 emissions. The proposed optimal HEM combustion mechanism is conducive to improving the efficiency of numerical calculations.

Acoustic kinetic energy and soot suppression efficiency of acetylene diffusion flame under acoustic excitation at varying resonant frequencies in Rijke tube

The acoustic kinetic energy and soot suppression efficiency of acetylene diffusion flame under acoustic excitation at varying resonant frequencies in Rijke tube is investigated experimentally. The acoustic kinetic energy is introduced for the first time to explain the mechanism of soot suppression by acoustic oscillation. The soot suppression efficiency and acoustic kinetic energy is investigated by changing the acoustic parameters and the length of the Rijke tube. The results show that the efficiency of the soot suppression and the acoustic pressure increase significantly at the resonant fundamental frequency (167 Hz and 185 Hz) and resonant frequency (346 Hz and 373 Hz). The standing wave at the resonant fundamental frequency is a half wave, while the standing wave at the resonant frequency is a full wave. Soot suppression efficiency and acoustic kinetic energy reach the maximum at the wave nodes. When the efficiency of soot suppression is the same, the acoustic kinetic energy at the resonant frequency is twice that at the resonant fundamental frequency at the wave nodes. The flame brush, flame fluctuation velocity and the flame temperature are studied in detail by changing the acoustic parameters. The results show that the efficiency of soot suppression increase with the increase of flame fluctuation velocity and flame temperature. This is considered that the acoustic kinetic energy accelerates the flame fluctuation velocity which enhances the heat and mass transfer in the combustion field, resulting in an increase in the flame temperature, thereby soot is re-oxidized. This study can provide some reference for the practical application of acoustic oscillate combustion in soot suppression.

A 3D simulation model of thermal runaway in Li-ion batteries coupled particles ejection and jet flow

A coupled simulation model of the 18650 lithium-ion batteries (LIB) thermal runaway (TR) is presented in this study, which includes TR decomposition reaction, gas generation and combustion processes, solid particles ejection and particles heat transfer process. The model considers a combination of solid heat conduction, gas convection, flame and particles radiation, which is validated to accurately capture the temperature evolution and two typical jet processes during TR. Model validation conducts with experimental measurements for the temperature of the battery surface. The simulation results show that the “ignition” time of the flammable gas mixture is delayed and the rate of flame temperature increase is slowed down when the effect of solid particles is considered. The radiation heat transfer rate and convection heat transfer rate on the adjacent battery surfaces are 80.3W and 12.76W, and are approximately 4.29 times and 1.76 times larger than the results calculated by the model without solid particles, respectively. The difference between these two can be further magnified in confined space. The model developed in this study combines the effect of the solid particles’ radiation into the TR simulation innovatively. It can provide a more accurate calculation method for the prediction of TR propagation.

An experimental study of the characteristics of blended hydrogen-methane non-premixed jet flames

The addition of hydrogen to natural gas promotes the reactivity of fuel and thus increases the jet fire risk from pipeline leakage during the transport process of blended hydrogen-natural gas. Aiming to evaluating the potential jet fire risk, this paper experimentally studied the characteristics of H2/CH4 jet flames at varied heat release rates (HRRs) with H2 volume fraction (fv) ranging from 0% to 90% by two circular nozzles (diameters: 3 and 5 mm). The results show that with the increase of H2 volume fraction, two competing effects on flame height were observed, that is, the increase in mixture molecular diffusivity, radicals pool, and air entrainment decreases the flame height, while the increase in flame temperature and jet velocity of fuel flow with a small flow Reynold number increases the flame height. Comparisons of different previous correlations of flame height with current experiments were conducted to obtain the applicable flame height model for H2/CH4 flames. The ratio of flame width to flame height for two nozzle diameters increases with dimensionless HRR when HRR is small, and then becomes nearly constant (∼ 0.145). The flame width normalized by nozzle diameter has a power dependence on dimensionless HRR, i.e., 0.48 and 0.59 power for the 3 and 5 mm nozzle, respectively. Further theoretical analysis suggested the dimensionless correlations of lift-off height of H2/CH4 flames with fv ≤ 50%.

Experimental and numerical study on laminar premixed NH3/H2/O2/air flames

Adding the product of water electrolysis (i.e. 2:1 volume of H2 and O2) is an effective strategy to enhance the combustion intensity of NH3/air mixtures. In this work, the laminar burning velocity (LBV) of the obtained NH3/H2/O2/air mixtures was measured at 303 K, 0.1 MPa and compared with the values predicted by seven mechanisms. To improve the prediction performance, a new mechanism is developed based on the existing mechanism and adopted for numerical simulation. The results of this study show that the LBV of NH3 is significantly increased by additional H2 and O2. By comparison, it is found that H2 shows a more significant promoting effect on LBV when the volume ratio of additional H2 and O2 is 2. The concentration of key radicals and the flame temperature increase remarkably due to the addition of H2 and O2, which promote the flame propagation. Furthermore, the experimental results also indicated that the additional H2 and O2 make the burned gas Markstein length decrease on the lean side and increase on the rich side.

Eksperimental karakteristik api dari suplai udara pada pembakaran uap partalite-partamax

Partamax and partalate fuel are used as vehicle fuel in parts of the world, especially in Indonesia. Partamax and partalate have their own characteristics and if they are mixed, they will change the physicochemical properties of the pure fuel and affect the combustion behavior. In this study, an experiment was conducted on the combustion of partamax vapor, partalate and a mixture of partamax and partalate by varying the air supply by 1 liter/minute, 2 liters/minute and 3 liters/minute. The results of the combustion of fuel vapors were observed in the form of temperature by measuring using a thermocouple placed in two places with a height of 20 mm and 40 mm from the nozzle mouth and observing the flame using a camera. The results obtained from the observations are the flow of fire produced in the form of a laminar flame of all fuels, The highest flame temperature is owned by partamax fuel with an air supply of 3 liters/minute of 1047 o C on a thermocouple at an altitude of 20 mm and 1027 o C at an altitude of 40 mm, while the lowest temperature is owned by partalate fuel. This is because the octane value of partamax is higher. As the octane value increases, the flame temperature increases, but the flame height decreases. In addition, when the air supply is 3 liters/minute, a lift off phenomenon occurs in the partamax fuel and partamax-partalate mixture. This is because the octane value of partamax is higher. As the octane value increases, the flame temperature increases, but the flame height decreases. In addition, when the air supply is 3 liters/minute, a lift off phenomenon occurs in the partamax fuel and partamax-partalate mixture. This is because the octane value of partamax is higher. As the octane value increases, the flame temperature increases, but the flame height decreases. In addition, when the air supply is 3 liters/minute, a lift off phenomenon occurs in the partamax fuel and partamax-partalate mixture.

The effects of hydrogen addition on soot formation in counterflow diffusion n-heptane flames

The effects of H2 addition on soot formation are investigated in counterflow diffusion n-heptane flames. Three effects including chemical, thermal, and dilution are fully isolated and characterized by additions of H2, He, and Ar. Soot volume fractions are measured using LE-calibrated LII technique, and flame temperatures are measured using OH-TLAF method along with a thermocouple. Numerical simulations are conducted with a detailed mechanism with soot model. The simulated soot volume fractions and flame temperatures are in good agreement with experimental data. The experimental results show that H2 addition can greatly reduce the soot formation. It is also found that the chemical and dilution effects suppress soot formation, while the thermal effect with increasing flame temperature promotes soot formation. Kinetic analysis suggests that HACA growth rate could be the dominant factor that controls the final soot formation through the three effects due to H2 addition.

Demonstration of Natural Gas and Hydrogen Cocombustion in an Industrial Gas Turbine

Abstract Hydrogen cofiring in a gas turbine is believed to cover an energy transition pathway with green hydrogen as a driver to lower the carbon footprint of existing thermal power generation or cogeneration plants through the gradual increase of hydrogen injection in the existing natural gas grid. Today there is limited operational experience on cocombustion of hydrogen and natural gas in an existing gas turbine in an industrial environment. The ENGIE owned Siemens SGT-600 (Alstom legacy GT10B) 24 MW industrial gas turbine in the port of Antwerp (Belgium) was selected as a demonstrator for cofiring natural gas with hydrogen as it enables ENGIE to perform tests at higher H2 contents (up to 25 vol. %) on a representative turbine with limited hydrogen volume flow (one truck load at a time). Several challenges like increasing risk of flame flashback due to the enhanced turbulent flame speed, avoiding higher NOx emissions due to an increase of local flame temperature, supply and homogeneous mixing of hydrogen with natural gas as well as safety aspects have to be addressed when dealing with hydrogen fuel blends. In order to limit the risks of the industrial gas turbine testing a dual step approach was taken. ENGIE teamed up with the German Aerospace Center (DLR), Institute of Combustion Technology in Stuttgart to perform in a first step scaled-burner tests at gas turbine relevant operating conditions in their high-pressure combustor rig. In these tests the onset of flashback as well as the combustor characteristics with respect to burner wall temperatures, emissions and combustion dynamics were investigated for base load and part load conditions, both for pure natural gas and various natural gas and hydrogen blends. For H2 < 30 vol. % only minor effects on flame position and flame shape (analyzed based on OH* chemiluminescence images) and NOx emission were found. For higher hydrogen contents the flame position moved upstream and a more compact shape was observed. For the investigated H2 contents no flashback event was observed. However, thermo acoustics are strongly affected by hydrogen addition. In general, the scaled-burner tests were encouraging and enabled the second step, the exploration of hydrogen limits of the second generation dry low emissions burner installed in the engine in Antwerp. To inject the hydrogen into the industrial gas turbine, a hydrogen supply line was developed and installed next to the gas turbine. All tests were performed on the existing gas turbine hardware without any modification. A test campaign of several operational tests at base and part load with hydrogen variation up to 25 vol. % has been successfully performed where the gas composition, emissions, combustion dynamics and operational parameters are actively monitored in order to assess the impact of hydrogen on performance. Moreover, the impact of the hydrogen addition on the flame stability has been further assessed through the combustion tuning. The whole test campaign has been executed while the gas turbine stayed online, with no impact to the industrial steam customer. It has been proved that cofiring of up to 10% could be achieved with no adverse effects on the performance of the machine. Stable operation has been observed up to 25 vol. % hydrogen cocombustion, but with trespassing the local emission limits.

Experimental and numerical study of the effect of initial temperature on the combustion characteristics of premixed syngas/air flame

The effects of different initial temperatures (T = 300–500 K) and different hydrogen volume fractions (5%–20%) on the combustion characteristics of premixed syngas/air flames in rectangular tubes were investigated experimentally. A high-speed camera and pressure sensor were used to obtain flame propagation images and overpressure dynamics. The CHEMKIN-PRO model and GRI Mech 3.0 mechanism were used for simulation. The results show that the flame propagation speed increases with the initial temperature before the flame touches the wall, while the opposite is true after the flame touches the wall. The increase in initial temperature leads to the increase in overpressure rise rate in the early flame propagation process, but the peak overpressure is reduced. The laminar burning velocity (LBV) and adiabatic flame temperature (AFT) increase with increasing initial temperature. The increase in initial temperature makes the peaks of H, O, and OH radicals increase.

Effect of NO2 addition on flame dynamics and chemical kinetics of near-limit n-dodecane cool and warm diffusion flames

The present study is a continuation of the previous study by Zhou et al. (2021), in which kinetic effects of NO addition on n-dodecane cool and warm diffusion flames are investigated via counterflow flames and a skeletal n-dodecane/NOx model is developed by performing jet-stirred reactor experiments. Here, effects of NO2 addition on the flame dynamics and kinetics of n-dodecane diffusion flames are studied. The focus is on understanding the kinetic effects of NO2 on cool flame extinction limits and the transitions between cool, warm, and hot flames and elucidating the differentiated effects of NO and NO2 on low- and intermediate-temperature chemistry of n-dodecane. NO2 also plays different roles in cool and warm flames. Specifically, NO2 addition reduces the cool flame temperature and strain rates at cool flame extinction, indicating that NO2 inhibits the low-temperature chemistry of n-dodecane. NO2 addition increases the warm flame temperature, delays the warm flames extinction to cool flames, and promotes the warm flames re-ignition to hot flames, demonstrating NO2 enhances the intermediate-temperature oxidation of n-dodecane. However, reaction pathways and sensitivity analyses reveal that reactions responsible for NO2 and NO affecting the low- and intermediate-temperature oxidation of n-dodecane diffusion flames are differentiated. For cool flames, reaction R + NO2 <=> RO + NO for NO2 addition and reaction RO2 + NO <=> RO + NO2 for NO addition are the major corresponding reactions, respectively, which compete with the low-temperature chain-branching reaction pathway. For warm flames, the kinetic effects of NO on the intermediate-temperature oxidation are due to NO converting the relative inactive HO2 to reactive OH radicals via the reaction NO + HO2 <=> OH + NO2, which simultaneously accelerates radical production of QOOH => QO + OH to the increase of warm flame temperature, while the effect of NO2 is mainly induced by the conservation of NO2 to NO. Moreover, comparisons of the effects of NO and NO2 addition on cool flame extinction limits are performed, and results show that the kinetic effects of NO2 addition are weaker than those of NO addition since the effects of NO2 are partially contributed by NO from the conservation of NO2.

Soot formation from n-heptane counterflow diffusion flames: Two-dimensional and oxygen effects

Soot formation of n-heptane is experimentally and numerically studied in low-strain rate (K = 50 s−1) counterflow soot formation (SF) flames. Flame temperatures and soot volume fractions at different oxygen mole fractions on the oxidizer stream (xO2=0.3–0.45) are measured by using thermocouple-calibrated OH two colors laser-induced fluorescence (2C-PLIF) and laser-induced incandescence (LII) calibrated by light extinction methods, respectively. Mono (MAHs) and polycyclic aromatic hydrocarbons (PAHs) are also qualitatively measured by using the PAHs-LIF technique. Good agreement between measured and predicted maximum flame temperature (Tmax) and peak soot volume fraction (fv,peak) is obtained. However, discrepancies in the shape of the entire soot volume fraction profiles along the axial centerline are observed between 1D and 2D simulations. This result is found to be primarily related to the thermophoretic and radial effects in the low strain rate flames investigated, which hamper neglecting the underlying 2D effects. MAH/PAH peak mole fractions and fv,peak increase from xO2=0.3 to xO2=0.45 due to the related increase of flame temperature, which fosters n-heptane pyrolysis near the fuel nozzle leading to higher concentrations of C1C4 hydrocarbons. The latter are found to grow to MAHs/PAHs and finally to soot particles through analogous pathways independently of xO2. However, the higher flame temperature in the sooting region at xO2=0.45 leads to soot particles and aggregates characterized by larger sizes and more dehydrogenated than those produced at xO2=0.3.

Co-firing hydrogen and dimethyl ether in a gas turbine model combustor: Influence of hydrogen content and comparison with methane

To promote the utilization of hydrogen (H2) in existing gas turbines, dimethyl ether (DME) was used to co-fire with H2 in a model combustor. The swirl combustion characteristics of DME/H2 mixtures were measured under the varying H2 content up to 0.7. The results show that the flow velocity elevates as the H2 content increases, which is associated with the increased flame temperature. The OH level firstly increases and subsequently keeps nearly unchanged as the H2 content increases. Meanwhile, the OH area nonlinearly increases with the increasing H2 content. Moreover, the increasing H2 content induces almost linearly decreased lean blowout limit (LBO), increased NO emission, and intensified combustion acoustics. Furthermore, the combustion characteristics of the 0.46DME/0.54H2 mixture and CH4 with the same volumetric heat value were compared. The 0.46DME/0.54H2 flame displays lower LBO and higher NO emission than the CH4 flame, which mainly results from the higher reactivity of 0.46DME/0.54H2 mixture.

Laminar flame speed and autoignition characteristics of surrogate jet fuel blended with hydrogen

Hydrogen combustion has emerged as one promising option toward the achievement of carbon-neutral in aviation. In this study, the effects of hydrogen addition on laminar flame speeds, autoignition, and the coupling of autoignition and flame propagation for surrogate jet fuel n-dodecane are numerically investigated at representative engine conditions to elucidate the potential challenges for flame stabilization and the autoignition risks in combustor design. Results show that the normalized flame speed increases almost linearly with hydrogen addition for fuel-lean conditions, while for fuel-rich conditions it increases nonlinearly and can be up to 20. This poses great challenges for avoiding flameholding and flashback, particularly for fuel-rich mixtures. Results further show that flame speed enhancement due to the increased flame temperature can be neglected under fuel-lean conditions, but not for fuel-rich mixtures. For the dependence of ignition delay time on temperature, there exists a unique intersection between pure n-dodecane/air and H2/air mixtures. Near the intersection temperature, there exists subtle kinetic coupling of the two fuels, leading to different H2 roles, e.g., accelerator or inhibitor, for the autoignition process of n-dodecane/H2/air mixtures. With this intersection temperature, the diagram for autoignition risks is constructed, which demonstrates that H2 acts as an inhibitor under subsonic cruise conditions while either an inhibitor or an accelerator under supersonic cruise conditions depending on the combustor inlet temperature and the amount of hydrogen addition. With the potential coupling of autoignition and flame propagation, the 1-D autoignition-assisted flame calculations show that hydrogen addition can alleviate or even eliminate the two-stage ignition characteristics for pure n-dodecane/air flames. For n-dodecane blended with hydrogen, the autoignition-assisted flame propagation speed, as well as the global transition from flame propagation to autoignition, can still be described by an analytic scaling parameterized by the ignition Damkӧhler number.

Modeling the dual-fuel combustion of porous lycopodium particles and diesel using an analytical simulation framework

In this paper, a comprehensive analytical study is performed to assess the lycopodium-diesel dual-fuel combustion system in counter-flow premixed configuration. The system is modeled as multiple zones that are coupled together via proper boundary and jump conditions on interfaces. According to the respective reaction and transport phenomena in these zones, conservation equations of mass and energy are derived, non-dimensionalized, and solved by Matlab and Mathematica in an analytical way. The porosity of lycopodium particles and the thermal radiation from the reaction zone and the post-flame zones into the preheating zone are considered, in order to improve the realism and accuracy of the modeling. Experimental validation of the derived framework is first carried out with good agreement between our results and the data from the literature. Afterwards, the impacts of parameters such as reactants Lewis numbers, equivalence ratio, and critical strain rate on the flame structure, as well as lycopodium particles' combustion behavior in dual-fuel and single-fuel modes are evaluated and compared. It is found that dual-fuel combustion system enhances the vaporization and ignition of lycopodium particles resulting in a 13% increase in flame temperature. In addition, effects of thermal radiation and porosity of particles on both the flame temperature and position are quantified. The presence of biomass particle porosity and thermal radiation reduces the flame temperature and drive the flame front towards the fuel nozzle.