Flame Characteristics Research Articles

Characterizing turbulent non-premixed flame structure and pollutant formation of cracked ammonia jet flames using simultaneous NH and NO PLIF

The combustion of cracked ammonia is crucial for enhancing flame stability and reducing pollutant emissions in ammonia-based combustion systems. This study investigated the flame structure and pollutant formation in cracked ammonia jet flames (CAJFs) to improve our understanding of the turbulence-chemistry interactions in ammonia combustion. A simultaneous NH and NO planar laser-induced fluorescence (PLIF) technique was employed to analyze the flame structure of turbulent non-premixed CAJFs, emulated using ammonia-hydrogen–nitrogen mixtures. Experimental measurements were conducted across a range of pressures (1–5 bar) and cracking ratios (7 %-28 %). The results revealed the significant influence of the cracking ratio on the chemical reactivity and NH-layer characteristics of ammonia-hydrogen flames. NH effectively marked the heat release layer of CAJFs. Reducing the cracking ratio from 28 % to 7 % resulted in increased local extinction-induced NH-layer fragmentation and reduced reaction area. The reaction layer thickness exhibited low sensitivity to the cracking ratio and pressure, while the broadening of the NH layer displayed a slowdown pattern with increasing height, differing from premixed flames. The pollutant NO rapidly formed within the reaction zone, persisting in the outer hot products until reduced by turbulent mixing. The fragmented flame structure promoted decreased NO formation and potentially lower NO concentration. A novel approach of multiplying NH and NO was proposed to reflect the formation characteristics of another important pollutant N2O. The effect of turbulent disturbances on N2O formation needs to be considered in turbulent CAJFs because N2O formation is strongly suppressed when turbulent transport reduces local NO concentration. This research enhances understanding of turbulence-chemistry interactions in cracked ammonia combustion, benefiting ammonia flame stability and pollutant emission control.

Experimental investigation on heat transfer characteristics of an annual jet flame in a pore-array spray gun

Oxyacetylene ablation is widely used to assess high-temperature thermal protection materials. This study investigated the heat transfer characteristics of an oxyacetylene spray gun structured with pore arrays for long-term ablation. The effects of oxyacetylene test parameters (Reynolds number (Re), equivalence ratio (φ), and ablation distance (H)) on the flame shape and heat flux distribution were studied to explore heat transfer behavior. Subsequently, ablation experiments were performed to verify the heat transfer characteristics under different operating conditions. The following conclusions were obtained: (1) The flame shape is characterized by the base flame, flame neck, and main flame, depending on the mixedness of the inner and outer jets. (2) The position of peak heat flux occurred in the radial direction, and the peak heat flux reached 4792 kW/m2 when the Reynolds number, impingement distance, and equivalence ratio were 77700, 20 mm, and 0.72, respectively. (3) The suggested ablation distance is Hs = (57.65–61.98) × [MR]−0.56 (MR: momentum ratio). This study provides useful data for high-enthalpy, long-duration ablation.

On ammonia/diesel dual-fuel combustion in optical engine

Ammonia-diesel dual-fuel combustion mode is one of the potential ways to achieve lower carbon emissions in compression ignition engines. In this work, the effects of ammonia addition on diesel combustion characteristics were experimentally investigated in an optical CI engine. The gaseous ammonia is introduced to the engine through a port injection while diesel is directly injection into the cylinder. A color high-speed camera was utilized to detect and differentiate between diffusion burning and lean-premixed ammonia combustion. Additionally, computational models were conducted and the findings were coupled with the experimental data. According to optical investigations, the lift-off distance is created during the diesel spray and progressively grows as the ammonia energy ratio (AER) rises. The findings indicate that, in comparison to pure diesel combustion mode, combustion in an ammonia environment exhibits prolonged ignition delay duration and lesser flame luminosity. Secondly, a multi-injection strategy for diesel fuel was used where the diesel pre-injection timing (SOPI) values adjusted from −30 °CA ATDC to −60 °CA ATDC). Advancing SOPI is an effective approach to suppress diesel diffusion flame and reduce soot production in the cylinder. For advanced SOPI, findings reveal that rich pockets have decreased drastically as the combustion progresses. With the advancement of SOPI, there is a notable a connection between the flame speed and the peak heat release rate, where a high flame speed correlates to a greater heat release rate peak. Finally, the ratio of pre-injection of diesel fuel (ROPI) varied from 0 to 100% as a mean to improve flame propagation. There is a crucial threshold of pre-injection (ROPI) mass ratio of 45%, at which the initial flame features alter considerably. As the ROPI exceeds 45%, the flame kernel appears as a visible flame near to the main injection timing (SOMI), indicating that the ignition delay duration is decreasing.

Precision-Boosted Forest Fire Target Detection via Enhanced YOLOv8 Model

Forest fires present a significant challenge to ecosystems, particularly due to factors like tree cover that complicate fire detection tasks. While fire detection technologies, like YOLO, are widely used in forest protection, capturing diverse and complex flame features remains challenging. Therefore, we propose an enhanced YOLOv8 multiscale forest fire detection method. This involves adjusting the network structure and integrating Deformable Convolution and SCConv modules to better adapt to forest fire complexities. Additionally, we introduce the Coordinate Attention mechanism in the Detection module to more effectively capture feature information and enhance model accuracy. We adopt the WIoU v3 loss function and implement a dynamically non-monotonic mechanism to optimize gradient allocation strategies. Our experimental results demonstrate that our model achieves a mAP of 90.02%, approximately 5.9% higher than the baseline YOLOv8 network. This method significantly improves forest fire detection accuracy, reduces False Positive rates, and demonstrates excellent applicability in real forest fire scenarios.

The effect of CH4 addition on high-H2 syngas combustion characteristics under N2/CO2 dilution

The composition of biomass gas is complex, in order to promote the more extensive and efficient utilization of low-calorific syngas, it is necessary to master the basic combustion characteristics of low-calorific syngas under different compositions. In this paper, the effects of addition of CH4 (0% – 20%) on the combustion characteristics of laminar flow flame of high-H2 syngas (H2:CO = 3:1) were studied by experiments and numerical simulations under the dilution of N2 and CO2 (40%). The laminar burning velocity (LBV) and Markstein length are obtained by experiments. CHEMKIN-PRO software package was used to compare the prediction results of the four mechanisms with the measured data. Finally, GRI3.0 mechanism was selected as the simulation mechanism in this paper. The experimental results indicate that the LBV of N2 dilution is higher than that of CO2 dilution, and the flame is more stable, with adding CH4, the LBV of syngas mixtures is decreased, and the LBV of rich-fuel mixtures is decreased faster, but the stability of premixed flames of syngas is improved. Numerical simulation shows that the dominant branch chain reaction changes from R99 to R38 after CH4 is added, and the mole fraction of H, O decreases while the mole fraction of OH, CH3 increases. The dilution of CO2 results in a lower concentration of active radicals than N2 because CO2 inhibits the important reaction R99. The GRI 3.0 mechanism was used to simulate the formation of NO: the addition of CH4 promoted the formation of hot NO. The NO production of NNH and N2O intermediate mechanism is decreased, and a new way of N2 and CH reaction to HCN is increased. The dilution of CO2 can reduce NO emission more than that of N2. The insights gained from this study have practical implications in a variety of production applications. For example, optimizing mixture equivalence ratios can improve combustion efficiency, thereby increasing energy efficiency and reducing environmental emissions.

The properties of sustainable aviation fuel II: Laminar flame speed

This work reports on the study of flame characteristics and laminar flame speeds (LFS) of sustainable aviation fuel (SAF) and conventional fuels (Jet-A1 and JP-5) premixed with air at elevated pressures. The experimental facilities included the constant volume combustion chamber (CVCC) and used a shadowgraph system to quantify the LFS. The effects of equivalence ratio and ambient pressure on the flame speeds were examined by varying the initial pressure 1, 2, and 3 bar (in addition to 0.1 and 0.5 bar for flame morphology) and the equivalence ratio from 0.8 to 1.8 at 423 K of temperature. The results indicated that JP-5 had the highest LFS value (90.1 cm/s) compared to the other two fuels. Jet-A1 and SAF have the same LFS result, which is less than a 15% difference, excluding the high equivalence ratio and initial pressure. The higher the initial pressure, the lower the LFS for all conditions. The equivalence ratio of 1.2 resulted in the highest LFSs. In addition, in order to understand the laminar flame speed of SAF and its combustion chemical kinetics. Therefore, the sensitivity analysis of SAF was performed. Results indicated that the chain branching reaction (O2 + HOH + O) positively enhanced flame speed as equivalence ratios (φ) increased, while chain propagation reactions, notably O2 + HHO2 (+M), had a negative effect on flame speed, particularly diminishing their influence at higher φ due to limited oxygen availability.

Research on explosion venting characteristics of CH4/H2/Air mixture in square explosion vessels

Hydrogenation of methane (CH4) is an important means of achieving energy savings and large-scale hydrogen (H2) transportation. Explosion venting is considered to be an effective method to reduce the risk of gas explosions. To investigate the parameters of the explosion characteristics of CH4/H2/Air premixed fuel under venting conditions, the explosion characteristics and the dynamic propagation law of venting flame in CH4/Air mixtures with 5% concentration were studied in 20 L and 40 L square explosion venting vessels. The development process of flames inside vessels, the evolution characteristics of explosive venting flames, and the changes in explosion pressure were tested using a high-speed camera and pressure sensors. The maximum explosion pressure, the maximum explosion pressure rise rate, and the maximum flame velocity increased first and then decreased with the addition of H2. However, the maximum flame length increased continuously with the increase of H2. With the increase of hydrogenation, the maximum flame area showed an exponential increase. At equivalence ratio less than 1, the effect of hydrogenation on the flame area was much attenuated than that at equivalence ratio was greater than 1.

Radiating biofuel-blended turbulent nonpremixed hydrogen flames on a coaxial spray burner

The low radiant intensity and luminosity of hydrogen flames can be enhanced by the addition of a small portion of sooting biofuels. To achieve higher effectiveness, the impact of blending turbulent nonpremixed hydrogen flames with liquid biofuels, by gas-assist atomisation, is investigated and compared with the introduction methods of prevapourisation and ultrasonic spray. The flame appearance, luminosity, radiant fraction, centreline temperature, and the near-field spray characteristics of four biofuel surrogates (eucalyptol, D-limonene, guaiacol, and anisole) blended into hydrogen flames are measured experimentally. Radiating biofuel/hydrogen flames are achieved on a coaxial needle spray burner by the addition of 0.1–0.3 mol% biofuel surrogates. Compared with the unblended hydrogen flame, the luminosity and radiant fraction are enhanced by 30%–500% and 2%–15%, respectively, with the addition of biofuel surrogates. The results show that adding the biofuel surrogates by gas-assist atomisation is more effective than prevapourisation and ultrasonic atomisation in luminosity and radiant fraction enhancement. It is found that the local fuel-rich conditions, which are beneficial for soot formation, are further facilitated by the larger droplets and spray objects generated by gas-assist atomisation. Of the additives tested, anisole is the most effective for luminosity and radiant fraction enhancement of a hydrogen flame while exhibiting the largest flame temperature drop due to the enthalpy of vapourisation and the radiative loss from the promoted soot formation. The viscosity and surface tension greatly influence the spray characteristics which in turn impacts the flame characteristics. Guaiacol, the representative of lignin, appears to have the lowest effectiveness in radiant fraction enhancement due to the presence of a hydroxy group, a higher bond dissociation enthalpy, and a coarser spray ascribed to higher viscosity and surface tension.

Flame characteristics and abnormal combustion of ammonia-diesel dual-fuel engine with considering ammonia energy fractions

Carbon neutrality is a significant challenge but also an essential opportunity for internal combustion engines (ICE), and fueled with low-carbon fuels is the key for ICE to reduce carbon emissions. Ammonia is a carbon-free fuel, whereas ammonia-diesel dual-fuel (ADDF) combustion can provide efficient and clean combustion of ammonia. In this study, the flame characteristics and abnormal combustion of ADDF engines are studied by considering ammonia energy fractions and diesel injection timings. The results show that a high ammonia energy fraction led to an extended period of combustion, while the CA05 first advances and then decreases with the decrease of ammonia energy fraction. This phenomenon indicates that an easily ignitable ammonia-air mixture is also important for ammonia-diesel dual-fuel ignition. Besides, an optimal SOI is needed to maximize the promoting effect of ignited fuel on ammonia combustion, and the optimal SOI changes with the ammonia energy fraction. Flame images confirm that the weightiness of the auto-ignition and flame propagation changes with the SOI, and the auto-ignition kernels gradually reduce and flame propagation plays a more and more important role as the SOI advances. At high loads, knocking combustion will also occur for ADDF engines, although the knock intensity is low. Besides, due to the enhancement effect of the knocking pressure wave, the flames show a strong white light at the knocking onset. The current results can help understand the combustion process and thus find the optimization method of ADDF engines.

Modeling of high-speed, methane–air, turbulent combustion, Part I: One-dimensional turbulence modeling with comparison to DNS

The ability of the one-dimensional turbulence (ODT) model to serve as a surrogate direct numerical simulation (DNS) is assessed for highly turbulent flames. The ODT model is applied to freely propagating premixed methane–air flames at Karlovitz numbers 10, 102, 103, and 104, and results are compared with DNS. The ODT model solves the conservation equations for momentum, energy, and species on a one-dimensional domain, which corresponds to a streamwise line of sight spanning the DNS domain. The effects of turbulent advection are modeled via a stochastic process, in which the Kolmogorov and reactive length and time scales are explicitly resolved. Molecular transport and chemical kinetics are concurrently advanced in time. Both the ODT and DNS simulations use a 21-species skeletal chemical model for methane combustion. The accuracy of the ODT model is assessed by comparing its predictions of several key characteristics of the flames for each Karlovitz number tested, including the turbulent flame speed and width and the joint probability density functions (jPDFs) of major and selected minor species as well as the heat release rate conditioned on temperature with the results of DNS under comparable conditions. The ODT model is shown to yield qualitative and quantitative agreement with the DNS data for most of the above flame characteristics. Discrepancies are observed primarily for the jPDFs of several minor species examined. Overall, the ODT approach is shown to be an effective surrogate of DNS, potentially useful for guiding chemical reaction model reduction and for assessing the sensitivities of the flame structure and the burning rate to chemistry under highly turbulent conditions.Novelty and Significance:The direct numerical simulations (DNS) of premixed turbulent methane–air flames presented in this work span a uniquely wide range of turbulent intensities, from relatively modest corresponding to Karlovitz number Ka=10 to ultra-high intensities at Ka=104. This represents virtually the entire range of turbulent intensities that could be encountered in any realistic situation. This is also the first time that such a wide range of conditions is probed for methane in high-fidelity, fully resolved simulations, which use a fully compressible set of flow equations. The one-dimensional turbulence (ODT) model utilizes the same forcing that is present in the DNS enabling a direct comparison between the ODT and DNS. The results show that ODT captures the key features of the DNS results. ODT is shown to be an effective surrogate for DNS and may be useful in guiding chemical reaction model reduction, where many simulations are required.

Effect of excitation Strouhal number on a backward-inclined jet flame in crossflow

Combustion is often accompanied by environmental pollution due to incomplete reaction. A non-excited flame usually exhibits poor combustion performance with features of diffusion flame such as dual-peak temperature distributions and large combustion product concentrations. Efficient fuel-air mixing has been identified as a key factor in mitigating this issue. The present study investigated the effects of the acoustic excitation Strouhal number on the combustion performance of a backward-inclined jet flame in crossflow. A loudspeaker was used to induce jet pulsations with excitation Strouhal numbers ranging from 0.47 to 1.54 at a pulsation intensity of 0.90. Time-averaged and instantaneous flame images were captured using digital cameras. A customized R-type thermocouple and a commercial gas analyzer were employed to analyze the thermochemical structures. A critical excitation Strouhal number of approximately 0.9, distinguishing two characteristic flame modes: strongly affected flame (SA flame) and weakly affected flame (WA flame), was found. At excitation Strouhal numbers lower than the critical value, the SA flame featured single-peak temperature profiles and low unburned hydrocarbon, carbon monoxide, and nitric oxide emissions. The combustion performance was significantly improved due to the strong mixing effect induced by the acoustic excitation. The WA flame appeared at excitation Strouhal numbers higher than the critical value. It exhibited dual-peak temperature distributions and slightly improved combustion performance. The dynamic behavior and emissions of acoustically excited jet flames offered a fascinating insight into the influence of excitation Strouhal numbers on combustion characteristics. More excitation conditions were expected for future research.

Implementation of an Electric Turbocharger on A Single-Cylinder Spark Ignition Engine in an Effort to Use Ethanol Gasoline E40

This study delves into the impact of electric turbochargers on fuel efficiency and emissions in ethanol-gasoline blends. Informed by relevant literature, the research zeroes in on the positive influence of electric turbochargers, emphasizing their role in reducing fuel consumption and emissions while also addressing the trade-off between flame characteristics and NOx emissions. The experimental focus is on the injection modification of a single cylinder, with samples including engines equipped with and without an electric turbocharger. Statistical analysis utilizing percentage-based methods reveals that this technology leads to a substantial 94% reduction in CO emissions at idle speed, a 49% decrease in HC emissions at idle speed, and a 10% increase in CO2 at idle speed. Additionally, it also results in a notable 16.04% reduction in fuel consumption at 40 km/h. These outcomes underscore the potential of electric turbochargers to enhance automotive efficiency and sustainability while acknowledging the trade-off that necessitates further exploration for optimal emission control. The research provides concrete insights for refining electric turbocharger technology and optimizing its practical application.

Visualization on spray and flame characteristics of wall-impinging spray under marine diesel engine conditions

Due to the longer nozzle-to-wall distance, spray-wall interaction with only vapor fuel impinging on the wall occurs generally in large-bore marine diesel engines. The interaction between the vaporized spray and wall not only impacts the combustion process, heat transfer, but also may condense and dilute the oil film on the cylinder wall. However, different from the scenario involving both liquid and vapor impinging on the wall in direct injection vehicle engines, the unique characteristics of vaporized diesel spray impingement have not been addressed in detail. To address the behavior of vapor diesel impinging spray and its influence on subsequent combustion in marine diesel engines, a 0.3 mm diameter single-hole injector, commonly used in marine diesel engines with a bore diameter around 170 mm, was utilized. The inclination angle of the injector is 30° and a flat wall was positioned 40 mm below the nozzle tip to approximate the relative positioning of the piston to the injector when the spray impinges on the wall in the engine. The interactions between spray and wall were studied under both inert and reactive conditions by altering the ambient gas to N2 and air, respectively. Back-illumination imaging, schlieren, and natural luminosity imaging were applied to study the impacts of ambient pressure, ambient temperature, and injection pressure on the evolution of impinging spray and diesel combustion within an optically-accessible constant volume chamber. Specifically, to evaluate the impact of spray-wall interaction with only vapor diesel impinges on the wall, the impinging sprays were compared to free sprays under the same experimental conditions. It shows that the impinging spray has a similar development mechanism with the free jet, while due to the varying air–fuel mixing rates at ambient pressures of 1 MPa and 3 MPa, the fuel film height on the wall exhibits different trends along the wall. At an ambient pressure of 5 MPa, the ignition delay of vaporized impinging spray is 17.62 % longer than that of free jet, while exhibiting a notable reduction in the soot emissions. The average time-integrated natural luminosity for jet impingement is found to be 71.28 % lower compared to the free jet with the same conditions.

Experimental investigations on in-cylinder flame and emission characteristics of butanol-gasoline blends in SI engine using combustion endoscopic system

The objective of this study is to characterize the in-cylinder flames of butanol-gasoline blends in a spark ignition (SI) engine. The experiments were performed using butanol-gasoline blends prepared in the ratio of 10:90, 20:80, and 30:70 by volume. The in-cylinder combustion was visualized and captured using a combustion endoscopic system. From the captured combustion images, spatial flame distribution was evaluated for butanol-gasoline fuel blends. Furthermore, combustion, emission, and performance characteristics were investigated in a SI engine for the same blends. The engine test results were rationalized from the flame characterization results of butanol–gasoline combustion to improve the fundamental understanding. The experimental outcome is that the flame spread region (%) was found to be higher for butanol blends when compared to sole gasoline fuel. The addition of butanol to gasoline increased the flame speed and consequently increased the combustion burn rate, as well as the pressure and heat release rate within the cylinder. The brake thermal efficiency of the engine increased with increasing butanol concentration in the blend. In addition, the butanol-gasoline blends showed decreased CO and HC emissions when compared to gasoline but reportedly increased NO emission for butanol-blended gasoline blend fuels. Overall, this study concludes that butanol has the potential to be used as a supplement to gasoline due to improved flame and engine characteristics and can be used in the conventional gasoline engine without any major engine modification.

Unraveling the impact of CO2 exhaust gas recirculation on flame characteristics and NOx emissions of premixed NH3/DME swirl flames

The low combustion intensity and high NOx emissions of ammonia (NH3) pose challenges to its applications in energy and power devices. Co-firing strategies with reactive fuels, such as hydrogen, methane, syngas, and dimethyl ether (DME), have been proposed to enhance the combustion stability of NH3 in gas turbine, while exhaust gas recirculation (EGR) has the potential to reduce NOx emissions of combustion systems. This work explores the impact of CO2 EGR on the flame characteristics and NOx emissions of premixed NH3/DME swirl flames. CO2 EGR is observed to have a profound impact on both flame morphology and chemiluminescence intensity. With increasing CO2 EGR rate, which is described by the CO2 content in the oxidizer (χCO2), the chemiluminescence intensity becomes much weaker, the flame height rises, and the lean blowout (LBO) limit grows, indicating a reduced flame stability. Moreover, CO2 EGR affects the distribution of OH radical and weakens the OH fluorescence intensity. These impacts on flame characteristics mean that practical energy and power devices should be better designed to stabilize the flame. To unravel the underlying mechanism, kinetic analysis on premixed NH3/DME/air flame under non-EGR and CO2 EGR conditions is performed. Simulation results show that CO2 EGR substantially reduces the laminar burning velocity, maximum OH mole fraction, and NO mole fraction. The reduction of NO mole fraction is mainly attributed to the thermal effect of CO2 EGR. The chemical effect plays a positive role in reducing NO formation under lean conditions but enhances NO formation under rich conditions.

Flame and Flow Analysis of LPG in Household Cookers with Rectangular Ports

The cold flow and flame characteristics of liquefied petroleum gas (LPG- mixing 70% butane and 30% propane) in a household stove are experimentally investigated. The household stove has three cookers with rectangular ports and different sizes. The flame temperature and gas flow velocity are measured at maximum and minimum flow rates under laboratory conditions. Temperatures in the horizontal, vertical, and diagonal directions are measured at a distance between the reference point and 3 cm. The temperatures between the maximum and minimum flow rates show significant differences for all cookers. Flame temperatures at the gas exit point are 620‒710 °C at the maximum gas flow rate. On the largest cooker, the gas emissions in the diagonal direction at the maximum flow rate are also measured. The maximum value of CO emissions 7000 ppm is measured at the reference point. CO2 emissions are 12% between the reference point and 1.5 cm and slightly decreasing to 11% at other points. NOx measurements (ppm) show a peak value of 180 ppm at the 0.5 cm point. Cooker 1 is in the turbulence regime at maximum flow rate, while the other cookers are in the laminar regime.

Influence of different transverse positions of two fires on flame characteristics in a tunnel

The flame-to-flame interaction in a dual-pool fire scenario is a crucial issue. However, current research on multiple fires in tunnels primarily focuses on scenarios where the fire sources are situated along the central axis of the tunnel. However, in real tunnel fires, the lateral positions of the fire sources are variable and unpredictable. Therefore, studying the flame behavior of two fire sources at different lateral positions within the tunnel is of significant importance in elucidating the interaction mechanisms between two fire sources inside the tunnel. In this investigation, a synergistic approach involving experimental inquiry and theoretical derivation was employed to systematically examine the phenomena of flame merging and tilting induced by two pool fires at diverse lateral positions within a naturally ventilated tunnel. The results indicate that flame entrainment is more likely to occur due to sidewall restrictions in tunnels, thereby increasing the probability of flame merging. A piecewise expression for determining the probability of flame merging from dual fire sources within tunnels was established. Furthermore, considering how sidewalls influence flame tilting angles, an air entrainment model for dual fire sources within tunnels was developed to derive flame tilting angles at different lateral positions and fire source spacing within tunnels.

Energy balance and global characteristics of metal dust flames

Recently demonstrated high values of radiative loss during metal combustion require a new approach to describing dust flames. In particular, given strong light emission, the adiabatic flame temperature (AFT) concept is not applicable due to high radiative losses. Accordingly, global flame characteristics such as an expansion factor become unrelated to the AFT. That expansion factor can be directly inferred from the flame geometry, and therefore, its analysis offers a simple path to justify the need for a detailed energy balance in metal dust combustion. The analysis can also provide insight into peculiarities of the temperature distribution within the flame. In the current paper, previously published data on flow velocities in a metal dust flame are used for the expansion factor analysis. A relatively low value of the obtained expansion factor is reconciled with the advanced comprehension of metal particle combustion.

Development of a Compact Skeletal Mechanism for Thermally Cracked Hydrocarbon Fuels

ABSTRACT The construction of a compact kinetic mechanism for thermally cracked hydrocarbon fuels holds great importance for developing advanced engine with regenerative cooling. In the present study, a skeletal oxidation mechanism consisting of 104 species and 373 reactions, which can be divided into two parts, i.e. a core mechanism for pyrolysis gas, and a skeletal sub-mechanism for pyrolysis liquid, was developed by a decoupling method. The combustion process of pyrolysis gas and its pure constituents was depicted by incorporating detailed reaction pathways of H2/CO/C1-C4 molecules, and variations of hydrocarbon classes, as well as carbon number distributions were also considered by introducing eight skeletal sub-mechanisms for heavy hydrocarbons which covered chain alkanes, cycloalkanes, and monocyclic aromatics in pyrolysis liquid, thus the newly developed mechanism was suitable for thermally cracked hydrocarbon fuels over a wide range of pyrolysis temperatures. The skeletal mechanism was extensively validated by experimental data of laminar burning velocities and ignition delay times, confirming its applicability for reproducing the flame characteristics of pyrolysis gases, pyrolysis liquids, and thermally cracked fuels. Sensitivity analyses showed that laminar burning velocities of thermally cracked fuels were only affected by reactions involving small radicals when the pyrolysis temperature was lower than 600°C, while reactions involving benzene rings started to dominate the flame propagation of thermally cracked fuel at 650°C under fuel-lean, stoichiometric, and fuel-rich conditions. Reactions of small radicals and heavy hydrocarbons both affected the ignition process of thermally cracked fuels.

Experimental and numerical study on a cavity-swirler-based combustion strategy for advanced gas turbine engine

A cavity-swirler-based combustor has been found to possess the capability of achieving robust stability, high combustion efficiency, low emissions, and a short flame length. However, the effect of cavity air-injection mode on the combustion and emission performances of the cavity-swirler-based combustor was not well understood to date. In this work, numerical and experimental investigations were conducted to analyze the flowfield, combustion efficiency, combustion stability, pollutant emissions, temperature distribution, and flame characteristics of the combustor under two different cavity air-injection modes, namely case-1 and case-2. The air-injection hole of case 1 was designed on the cavity inner-wall, while the air-injection hole of case 2 was designed on the cavity outer-wall. The results indicate that the combustion performance of the combustor is significantly influenced by the air-injection mode, leading to different flow fields within the combustor. Case 1 demonstrates notable advantages in terms of lean blowout limit compared to case 2. However, case 2 achieves a much more uniform distribution of outlet temperature. Higher combustion efficiency was achieved by case-1 under low fuel equivalence conditions, whereas case-2 exhibited greater combustion efficiency under high fuel equivalence conditions. Both case-1 and case-2 displayed distinct combustion zones that were separate from each other.