Rich Flames Research Articles

Carbon quantum dots in breast cancer modulate cellular migration via cytoskeletal and nuclear structure

Carbon nanomaterials have been widely applied for cutting edge therapeutic applications as they offer tunable physio-chemical properties with economic scale-up options. Nuclear delivery of cancer drugs has been of prime focus since it controls important cellular signaling functions leading to greater anti-cancer drug efficacies. Better cellular drug uptake per unit drug injection drastically reduces severe side-effects of cancer therapies. Similarly, carbon dots (CDs) uptaken by the nucleus can also be used to set-up cutting edge nano delivery systems. In an earlier paper, we showed the cellular uptake and plasma membrane impact of combustion generated yellow luminescing CDs produced by our group from fuel rich combustion reactors in a one-step tunable production. In this paper, we aim to specifically study the nucleus by establishing the uptake kinetics of these combustion-generated yellow luminescing CDs. At sub-lethal doses, after crossing the plasma membrane, they impact the actin and microtubule mesh, affecting cell adhesion and migration; enter nucleus by diffusion processes; modify the overall appearance of the nucleus in terms of morphology; and alter chromatin condensation. We thus establish how this one-step produced, cost and bulk production friendly carbon dots from fuel rich combustion flames can be innovatively repurposed as potential nano delivery agents in cancer cells.

Numerical investigation of NOx emission characteristics in air-staged combustion system fueled by premixed ammonia/methane

For the purpose of achieving global CO2 reduction, decarbonization at the source of fuels is a practical approach. The transition phase of blending fossil fuels with carbon-free fuels for combustion is a hot topic in the current carbon emission reduction process. In order to achieve efficient and low-pollution combustion of NH3/CH4, the combustion and emission characteristics of NH3/CH4 under single-stage and air-staged combustion methods were numerically investigated in this work. The emissions were compared for different equivalence ratios and different ammonia content conditions. rate of production (ROP) and sensitivity analysis were performed for NOx, and the reaction path of NH3/CH4 was analyzed. The results indicate that the C-N interaction of the NH3/CH4 mixed combustion process is not significant and turns weaker in the lean flames. HNO intermediate is an important specie for NO generation, and HCN together with HNO intermediate, are essential species for NO generation. NH2 and NH almost dominate the promotion and inhibition of NO generation. Given that the contrasting NOx and CO emission behavior of NH3/CH4 in rich and lean flames, the single-stage combustion approach is not suitable. Air-staged combustion achieves both ensuring complete burning of NH3 and CH4 while reducing NOx and CO emissions. Moreover, the results suggest that Φpri=1.2/Φtotal=0.6 is the optimal NH3/CH4 combustion staging method for controlling NOx emissions.

Calibration techniques for quantitative NO measurement using Laser-Induced Fluorescence

Laser-Induced Fluorescence (LIF) is an essential optical diagnostic technique for the high-resolution and low-uncertainty measurement of combustion species concentration in a variety of applications and conditions. Two different calibration techniques are explored in this study to obtain quantitative Nitric Oxide (NO) concentration measurements in flames. The first technique, the most employed in the literature, uses the extrapolation of the fluorescence signal from seeded to nascent NO and is only valid under negligible NO reburn conditions. The second technique uses the optical calibration of the experimental setup to relate it to a modelled LIF signal and can be applied regardless of NO reburn. Both of these techniques are explored under two different assumptions: constant and non-constant interfering LIF signal on the NO absorption spectrum. While the former is most often used in the literature, the latter is necessary when the LIF signal from interfering species cannot be distinguished from the NO-LIF signal, especially in high pressure conditions. Hence, a total of four techniques are presented in this work and are found to be in excellent agreement when performed in different flame conditions. The calibration techniques are applied to three lean, atmospheric, laminar, premixed, methane-air flames to explore their field of applicability. Specifically, the study explores the relevance of the techniques in reburn conditions, which occur mostly in high pressure, rich, highly-seeded, or NH3-containing flames. This study aims to offer the reader a portfolio of calibration techniques to use according to the conditions in which they need to be applied. While this study was carried out measuring NO concentration in a stagnation flame burner, the concepts and equations presented can be transposed to the measurement of other species and to other experimental configurations.

Effect of stratification on the combustion behavior and dynamic response of a bluff-body stabilized ammonia–hydrogen flames with radial staging

The present study deals with the flames of ammonia–hydrogen blends that form a prospective fuel for power generation in practical devices. In particular, the spatial flame dynamics of the bluff body stabilized laminar and stratified ammonia–air/hydrogen–air mixtures with acoustic excitation are considered. For this, we consider a radially staged burner consisting of two concentric tubes namely, the inner and outer tubes with the bluff body housed by the former. Two annulus passages are formed between (i) the inner and outer tube, and (ii) the inner tube and bluff body in which premixed hydrogen–air and ammonia–air mixtures are supplied, respectively. The stratification is controlled by varying the upstream location of the inner tube about the burner exit, termed mixing length taking the values namely, 20 mm (stratified), 60 mm, and 100 mm (unstratified). Time-resolved images of the flames are obtained using OH* (320 ± 10 nm) and NH2* (632 nm ± 10 nm) filters. For the unforced stratified flames, the flames are narrower and the spatial separation between OH* and NH2* region increases towards rich NH3/air mixtures ( ϕNH3–air) compared to the unstratified flames. In addition, the mean spatial OH* is relatively localized for the unforced stratified flames. For any operating condition of the flames, the forced flame response is significant for frequencies < 120 Hz. The rich stratified flame exhibits a higher response at a frequency of ∼ 40 Hz compared to the unstratified flame having a flatter response. The forced flames accompany lobed spatial patterns in OH* and NH2* for richer ϕNH3–air. The flame oscillation registers a non-sinusoidal oscillation for the rich stratified flame compared to flames of any other condition. The main effect of stratification is the alteration of flame shape resulting in a low-frequency response for which regions of significant flame flapping coincide with regions of peak flame OH*.

Combustion characteristics of premixed ammonia-hydrogen/air swirl flames at elevated pressure

Ammonia (NH3)-hydrogen (H2) blends which are obtainable by NH3 cracking can be an eminent carbon-free fuel. To provide a valuable database for the practical application of cracking-based NH3-H2 fuel, the effects of pressure on the combustion characteristics of premixed NH3-H2(-nitrogen (N2))/air swirl flames are investigated in terms of H2 mole fraction in the NH3-H2 blend and fuel-equivalence ratio. Extinction mechanisms at fuel-lean and rich flames are the same for both normal and elevated pressures, though only the blowoff is observed for elevated pressure. With increasing pressure, fuel-rich limits are generally extended but fuel-lean limits are reduced, NOx emissions decrease and the condition of the maximum NOx emissions moves towards fuel-richer condition. Flame visualization exhibits the shifted main reaction zone upstream, the increased flame wrinkling and the reduced OH and NO intensities with increasing pressure. Dilution effects of N2 at elevated pressure become remarkable compared with those at normal pressure.

On the difficulty of interpreting NO-LIF measurements around 226 nm in confined ammonia flames

This paper addresses how NH3 and NO absorption along the laser axis disrupts NO-LIF measurements made around 225 nm in NH3/O2/N2 premixed flames confined at low pressure (10 kPa). Measurements were performed in 3 flames (equivalence ratio ϕ = 0.87, 1.1 and 1.3) with 24 % N2 dilution. Together with the LIF measurements, single-pass absorption measurements were obtained in all flames as a function of the height above the burner (HAB) and of the wavelength. A significant NH3 absorption of the laser beam is found in the pre-heat zone and flame front of each flame, as well as in the burned gas in the rich flame. In the lean flame, whatever the HAB, an additional significant absorption is due to the NO present in the gas surrounding the flame. Whereas NH3 absorbance only occurs inside the flame under all conditions, NO absorbance is mainly due to the high concentration of NO produced in the lean flame and spread in the entire confined vessel around the flame. From this analysis, relative NO rotational population profiles were recorded by measuring the temporal peak of the LIF signals (prompt-LIF) which were corrected for absorption to account for the available energy at burner's center. NO-LIF thermometry was conducted to determine the temperature in the flames through collecting excitation LIF spectra and performing spectral fitting using a dedicated software (thermo NO-LIF, https://pc2a.univ-lille.fr/thermo-no-lif/). The procedure developed to collect the NO profiles could not be transposed to determine the temperature in the lean flame. Indeed, the attenuation of the laser beam depends on whether the laser is tuned on a “cold” transition (strongly impacted by absorption outside the flame) or on a “hot” transition of NO, little affected. Thus, two tubes (with N2 flushing) were installed inside the vessel along the laser axis and surrounding the flame to suppress the NO absorbance.

Numerical Study of Premixed PODE3-4/CH4 Flames at Engine-Relevant Conditions

Polyoxymethylene dimethyl ether (PODEn, n ≥ 1) is a promising alternative fuel to diesel with higher reactivity and low soot formation tendency. In this study, PODE3-4 is used as a pilot ignition fuel for methane (CH4) and the combustion characteristics of PODE3-4/CH4 mixtures are investigated numerically using an updated PODE3-4 mechanism. The ignition delay time (IDT) and laminar burning velocity (LBV) of PODE3-4/CH4 blends were calculated at high temperature and high pressure relevant to engine conditions. It is discovered that addition of a small amount of PODE3-4 has a dramatic promotive effect on IDT and LBV of CH4, whereas such a promoting effect decays at higher PODE3-4 addition. Kinetic analysis was performed to gain more insight into the reaction process of PODE3-4/CH4 mixtures at different conditions. In general, the promoting effect originates from the high reactivity of PODE3-4 at low temperatures and it is further confirmed in simulations using a perfectly stirred reactor (PSR) model. The addition of PODE3-4 significantly extends the extinction limit of CH4 from a residence time of ~0.5 ms to that of ~0.08 ms, indicating that the flame stability is enhanced as well by PODE3-4 addition. It is also found that NO formation is reduced in lean or rich flames; moreover, NO formation is inhibited by too short a residence time.

Role of the Equivalence Ratio on Soot Formation in a Perfectly Premixed Turbulent Swirled Flame: A Combined Experimental and Large Eddy Simulations Study

Abstract The understanding of processes that govern soot production in aero-engines is fundamental for the design of new combustion systems with low environmental impact. Many combustors, more specifically those used in aero-engines, feature rich flame regions typically exploited in the so-called rich-quench-lean (RQL) technology. Thus, it is important to consider rich turbulent flames operating in the premixed mode. To this purpose, a model scale swirled combustor, called EM2Soot, was designed at the EM2C laboratory to analyze soot production under perfectly premixed rich conditions. In this work, the effect of the equivalence ratio on soot production in this burner is experimentally characterized and numerically simulated. Measurements of Planar Laser Induced Fluorescence of polycyclic aromatic hydrocarbons (PLIF-PAH) were performed to examine soot precursors presence, whereas soot volume fraction is measured with planar laser-induced incandescence (LII). Large Eddy Simulations (LES) are carried out using models already established in literature. By considering a range of equivalence ratios, the soot volume fraction from the experiments was found to reach a maximum near 1.8, whereas a lower level of soot volume fraction was measured for lower and for higher equivalence ratios. The large eddy simulations are found to be in qualitative agreement with experimental data in terms of polycyclic aromatic hydrocarbons (PAHs) and soot location. The soot volume fractions fv are notably overestimated with respect to the LII measurements. However, the numerical results correctly retrieve a reduction of soot production for the highest considered equivalence ratio value and can be used to explain the experimental behavior.

Heat release surrogates for NH3/H2/N2–air premixed flames

The present study investigates the performance of NH, NH2, O-atom, and H-atom as heat release rate (HRR) surrogates for NH3/H2/N2–air premixed flame through simulations. The simulations are conducted across different pressures, reactant inlet temperatures, fuel blend compositions, and equivalence ratios. Cantera is used to simulate one-dimensional (1D) freely propagating flames to investigate the spatial correlations of the species with the HRR. PeleLMeX, a low-Mach direct numerical simulation (DNS) code with Adaptive Mesh Refinement (AMR), is used to simulate two-dimensional (2D) flame-vortex interactions to investigate the temporal correlations including stretch effects. Three different mechanisms (Jiang et al. 2020; Glarborg et al. 2018; Okafor et al. 2018) were considered in the 1D flame simulations, whereas only the Jiang mechanism was considered in the flame-vortex simulations. The HRR surrogate performance for the 2D flames is evaluated at two different locations: (1) the centerline and (2) the flame cusp. The cusp is defined as the region in the flame front with the greatest curvature and the centerline encounters the highest tangential strain rate. The 1D flame results suggest that, although there is not uniformly good spatial correlation for HRR across all flame conditions, NH is the best overall as a HRR surrogate for laminar flames. The 2D flame results, however, suggest that O-atom and H-atom have satisfactory temporal correlations at different conditions—the former for rich flames, the latter for high-pressure flames. These simulations provide guidance to experimental measurements of surrogate HRR markers in unsteady multi-dimensional flames using laser diagnostics to detect species such as NH, O-atom, and H-atom.

A Comparative Study between FGM and SLF Approach for Turbulent Piloted Flame of Methane

This study validates the RANS simulation results by comparing them with experimental data. Numerical simulations were performed for a piloted methane-air jet flame in an axisymmetric burner. It is noteworthy that RANS simulations have been performed using a Non-premixed model with Steady Laminar Flamelet (SLF) and a partially premixed model with Flamelet Generated Manifold (FGM) of the Ansys-Fluent solver are used to express the chemistry-turbulence interaction, to provide an initial solution to the simulation performed by the Pdf transported, joint two kinetic mechanisms for oxidation of methane, detailed GRI-Mech 3.0 mechanism (53 species, 325 reactions), and CH4-Skeletal mechanism (16 species, 41-step). The case test consists of a rich premixed flame (Sandia Flame D). A comparison between the results of the obtained simulations and experimental data shows good agreement, in particular in the context of RANS/FGM with both mechanisms (GRI 3.0 and CH4-Skel).

Study on the mechanism of nitrogen conversion in NH3-doped methane premixed flame based on multi-spectral analysis methods

It is essential to obtain the in-situ key radicals and components in the combustion process of NH3 oxidation to reveal the volatile nitrogen conversion mechanism. In this work, multi-spectral analysis methods, including image spectroscopy, Tunable diode laser absorption spectroscopy (TDLAS), and plane laser-induced fluorescence (PLIF) were used to obtain the spatial distribution characteristics of the main excited radicals (C2*/CH*/CN*/OH*), H2O, and NO in NH3-doped methane flames, respectively. Furthermore, the kinetic simulation was combined to obtain the key reactions and main pathways of nitrogen conversion. The experimental results showed that when the concentration of NH3 was low, the NO generated in lean flame was less than that in rich flame, which was more than that in rich flame when the concentration of NH3 was high. NH3 also promoted the formation of H2O in flames. The image spectral intensity of CN* had a significant linear relationship with the CN concentration obtained by simulation, indicating that CN* was mainly generated by CN thermal excitation. The results of sensitivity and path analysis indicated that rich flame contributed to the reaction of N-species with H and that high NH3 concentration promoted the conversion of NH2 to HNO. With increasing NH3 concentration and equivalence ratio, the proportion of CH3 conversion to C2H6 was enhanced, while the proportion of CH3 oxidized decreased. This work reveals the mechanism of volatile nitrogen (NH3) conversion and the influence of equivalence ratio and NH3 concentration on it, which provides theoretical guidance for NOx emission reduction.

Acoustic and Optical Investigations of the Flame Dynamics of Rich and Lean Kerosene Flames in the Primary Zone of an Air-Staged Combustion Test-Rig

Abstract In this study, the thermoacoustic behavior of nonpremixed kerosene flames from rich to lean combustion conditions is investigated. Flame-transfer-functions (FTF) measured purely acoustically are compared with results based on flame chemiluminescence. OH*, CH*, C2*, and CO2* were selected as potential measures for representing steady and fluctuating heat release when burning nonpremixed kerosene. In addition, their ability for the quantification of equivalence ratio fluctuations will be highlighted. The measurements were performed in the primary zone of an atmospheric rich-quench-lean (RQL) combustion test-rig. The new experimental approach allows a characterization of the primary zone independent of the secondary zone. Rich and lean operating points were analyzed by fueling an aero-engine prototype injector with and without acoustic excitation. To improve the quality of the acoustic wavefield reconstruction a thermocouple correction method was implemented. The flame dynamics determined with the multimicrophone method (MMM) exhibit a frequency and equivalence ratio depending effect of rich combustion conditions. The results for the steady behavior of the chosen radicals by altering equivalence ratio and thermal power indicate proportionality of the chemiluminescence to thermal power. Furthermore, the CH*/C2* ratio is found to be a promising indicator for the global equivalence ratio in the combustion chamber. The flame-transfer-functions based on chemiluminescence show a good qualitative agreement with the multimicrophone method. Based on the experimental findings a calibration curve for the different radicals to obtain quantitatively correct flame-transfer-functions from chemiluminescence is presented.

Laminar premixed hydrogen/air flame dynamics with/without sidewall interactions

This paper investigates laminar premixed hydrogen/air flame-wall interactions (FWI) subject to flame stretch (curvature and strain rate). Direct numerical simulations of finite-rate chemical reactions and in-depth molecular diffusion are used to numerically study two-dimensional (2D) V-shaped flames, with one side functioning as an isothermal cold wall that interacts with the flame and the other as a symmetrical center for free-propagating flame. An isometric grid with a grid resolution of 10 μm is used to resolve the FWI zone. It is discovered that the wall at the flame tip experiences increased negative stretching and enhanced local preferential diffusion which reduces the intensity of local combustion. This effect is especially noticeable at low equivalent ratios. Additionally, there is a close relationship between quenching behavior and flame dynamics. The present results show that the Markstein numbers for both the sidewall quenching flame and the freely propagating flame (MaSWQ and MaFF) are negative in lean hydrogen flames and positive in rich hydrogen flames. Cold wall has less impact on Ma. Furthermore, an intersection in the equivalence ratio is observed in the lean-fuel hydrogen/air flame, located at Φ = 0.8–1.0, with a change in the sign of Ma.

Ultraviolet electronic spectroscopy of heavily substituted naphthalene derivatives

Context. The so-called bump spectral signature observable on interstellar extinction curves, peaking at 217.5 nm, is commonly assigned to π* ← π transitions from carbonaceous carriers, but the exact nature of the carbonaceous carriers remains debated. Aims. To constrain the chemical structures associated with the bump carriers, we record and compare the UV spectra of a large variety of carbonaceous molecules to this interstellar feature. Methods. Large carbonaceous molecules, such as polycyclic aromatic hydrocarbons (PAHs), were produced by a combustion process stabilized at low pressure under rich flame conditions. Species were extracted and probed through resonance enhanced multiphoton ionization spectroscopy coupled to a time-of-flight mass spectrometer. Masses and absorption profiles of the carbonaceous molecules were measured, and their spectra were compared to the bump feature. Results. Species showing a specific mass progression starting at mass 128 u visible up to mass 394 u with a characteristic progression of +14 u present a common electronic absorption band profile peaking asymptotically around 220 nm. The first masses were assigned to a naphthalene C10H8 molecule and two of its derivatives: C10H7CH3 and C10H7C2H5. The mass progression of +14 u is explained by successive H atom substitutions by CH3 functional groups. This mass distribution was thus assigned to naphthalene derivatives with large aliphatic carbon substitution. This derivative family shows an electronic band assigned to S3 ← S0 transitions involving electron promotion within the π aromatic orbitals of the naphathlene chromophore. More importantly, after a few substitutions, the position of the band converges asymptotically to a value close to the interstellar bump signature, independent of the molecule size. Conclusions. Based on the asymptotic behavior of the larger members in the species distribution, a similar band position is expected from double aromatic ring substructures within hydrogenated amorphous carbons (HACs). Similar to the conclusions of previous works, we find substituted naphthalene units as substructures of interstellar HACs to be good candidates as carriers of the bump feature.

Study on the laminar combustion characteristics and kinetic of IC8H18/NH3 premixed flames

To promote the transition to a carbon neutral society, it is necessary to conduct a comprehensive research on the utilization of ammonia contained in gasoline engine. In the present study, the laminar burning velocity (SL), Markstein length (Lb) and flame instability of isooctane/ammonia (IC8H18/NH3)-air mixtures were analyzed at the initial temperatures (T) of 400 K and 470 K, initial pressure (P) of 1–4 atm, ammonia mole fraction (XNH3) of 0%-70% and an equivalence ratio (ϕ) ranging from 0.8 to 1.3. Also, the kinetic mechanism of IC8H18/NH3 as proposed by Cai et al. [Combust. Flame, 162, 2015] was further optimized and compared with the mechanism of CRECK and Cai. The results show that the difference between the Cai and present mechanisms is largely attributable to the variation in sensitivity of NH3 oxidation-related reaction to SL. In addition, it is widely known that SL is dependent on the initial temperature and pressure. In order to improve the applicability of IC8H18/NH3 fuel mixtures, their temperature (α) and pressure (β) coefficients were determined given varying ϕ and XNH3. Meanwhile, a mathematical correlation for SL was also conducted. The analysis of Lb was also conducted to obtain the results showing that Lb decreases with ϕ increasing, except for NH3-air flame. Moreover, as XNH3 increases, Lb varies between lean and rich flames. For lean-flames, NH3 addition leads to a significant decrease in Lb, while for rich-flames, NH3 addition causes a marginal increase in Lb. All these are attributed to the variation in Zel’dovich number (Ze), effective Lewis number (Leeff) and flame thickness (δ). Furthermore, the instability of flame suggests that the addition of ammonia enhances the stability of the flame due to the reduced molecular diffusion effect. Moreover, an increase in XNH3 contributes only to a slight decrease of critical Peclect number (Pecr), and a sharp rise in the critical flame radius (Rcr) results from the increase of flame thickness (δ).

Spherically expanding flame simulations using Cantera coupled to an unsteady Lagrangian formulation

A Lagrangian-based one-dimensional approach has been applied, using Cantera libraries, to study the dynamics of spherically expanding flames. Detailed reaction models have been employed to examine spherical flame propagation in hydrogen-air mixtures. In the first part, our approach was validated against laminar flame speed and Markstein number data from the literature. It was shown that the laminar flame speed was predicted within 5% on average but that significant discrepancies were observed for the Markstein number, especially for rich mixtures. This suggests that even application of detailed reaction models can lead to inaccurate prediction of the stability of rich flames, which can be detrimental to the prediction of flame acceleration and the deflagration to detonation transition process. In the second part, a detailed analysis of the thermo-chemical dynamics along the path of Lagrangian particles propagating in stretched flames was performed. For mixtures with negative Markstein lengths, it was found that at high stretch rates, the mixture entering the reaction-dominated period is less lean with respect to the initial mixture than at low stretch rates. This induces faster rates of chemical heat release and active radical production which results in higher flame propagation speed. Opposite effects were observed for mixtures with positive Markstein lengths, for which slower flame propagation was observed at high stretch rates compared to low stretch rates.

Investigation of cellularization characteristics of hydrogen-methane-ethanol expanding spherical flame at elevated pressures

The incorporation of ethanol into hydrocarbon fuels for use is attracting increasing interest and it is necessary to investigate its inherent flame instability for better application in combustion units. The instability of hydrogen-methane-ethanol spherically expanding flame has been investigated at an initial temperature of 400 K, initial pressures of (2–4 bar), ethanol fraction of (20%, 50%, 80%), and equivalence ratios (Ф) of (0.7–1.4) using the constant volume combustion chamber (CVCC). High-speed schlieren technology was used to record flame propagation images. The effects of hydrodynamic and thermal-diffusion effect on the inherent instability of the flame were investigated. As the ethanol ratio increased, the hydrodynamic effect was enhanced. The thermal-diffusion effect was discovered to stabilize the flame surface under all conditions, as judged jointly by the effective Lewis number and the critical Lewis number. The critical conditions (critical radius and Peclet number) at the onset of unstability were evaluated, and it was found that the flames were more prone to flame instability at higher pressures. The critical Peclet number increased with the increase in the equivalence ratio when the ethanol ratio was 20%, and showed the opposite trend when the ethanol ratio was 50% and 80%. In addition, as the ethanol ratio increases, the stability of the lean mixtures flame increases, while the rich mixtures flame suffers from early onset of instability. The theoretical and experimental results were consistent, with some differences at Ф = 1.4. An empirical correlation formula for the critical Peclet number (Pec) and Markstein number (Mb) was further proposed (Pec= 18.03Mb+214.78). Finally, the Karlovitz number was used to study the instability behavior of the flame. The critical Karlovitz number (Kac) decreased with increasing Mb and the tendency of the flame to suffer from instability diminished, and the following correlation was obtained Kac=0.05635×e−0.13852Mb. Furthermore, the flame was more unstable in rich mixtures, this was consistent with the conclusion of instability derived from the critical radius.

Study on the inhibitory effect and mechanism of perfluoro(2-methyl-3-pentanone) on the combustion of gasoline blended with biomass additives

Perfluoro(2-methyl-3-pentanone) (C6F12O, Novec 1230) has been considered as an emerging alternative to halon fire extinguishing agents, but its inhibiting characteristics for different concentrations of gasoline blended with biomass ethanol is still unclear. A new kinetic mechanism containing 241 substances and 1346 radical reactions was developed to investigate the combustion characteristics of ethanol gasoline and the inhibition characteristics of C6F12O. Experiments and previous data was used to confirme the mechanism's reliability. The results show that increasing the volume fraction of ethanol increases the laminar burning velocity and decreases the flame temperature of the mixture. A similar inhibitory effect of C6F12O is observed for gasoline at different ethanol blending concentrations. For rich flames, the fluorinated substances produced by C6F12O reduce the intensity of the reaction by trapping free radicals (OH, H, etc.), thereby reducing flame temperature and laminar burning velocity. For lean flames, adding sub-inerting concentrations of C6F12O produces large amounts of CO, which is an essential intermediate in promoting R24: CO + OH <=> CO2 + H, resulting in increased reaction strength. Combustion intensity is significantly reduced as more C6F12O is added, as the trapping of free radicals by the inhibitor becomes dominant.

Spray Flamelet Modeling of Turbulent Two-Phase Reacting Flows with Multi-Component Fuel in a Lean Direct Injection Combustor

ABSTRACT Towards the numerical evaluation of the performance in aero-engine combustors, implementing detailed reaction kinetics into the large eddy simulation (LES) cost-effectively is highly desirable. In this work, a newly-developed spray flamelet model is combined with a four-component jet fuel surrogate model to allow integration of the detailed kinetics in the open-source CFD code. The spray flamelet approach (SFGM) can take into account the non-adiabatic effect caused by the evaporating spray and can directly reflect the preferential evaporation, as well as multiple combustion regimes present in complex spray combustion systems. The coupling of the SFGM-LES approach is assessed by comparison with the experimental data from a Lean Direct Injection (LDI) combustor, where the real aviation kerosene, Jet-A, was utilized. The SFGM-LES approach well predicts the experimental statistics in both gas and liquid phases. It is capable of capturing the rich physics and complex flame structures, including the preferential evaporation effect and the multi-regime combustion phenomenon. The present work demonstrates that the complex nature of multi-components and the multiple-combustion regimes in the two-phase combustion can be directly included in the spray flamelet approach, and thus this model can provide new insights into the turbulent spray combustion phenomena.

Experimental and theoretical research on the inhibition performance of ethanol gasoline/air explosion by C6F12O

The safety issue of ethanol gasoline and the methods to control or weaken its explosion have attracted attention. To clarify the effect of C6F12O (perfluoro(2-methyl-3-pentanone)) on the explosion of ethanol gasoline-air mixtures and intrinsic mechanism, the explosion overpressure and flame propagation behavior under different equivalence ratios (φ = 0.6–0.8) and C6F12O concentrations (χinh = 0–4.0%) were experimentally obtained. The detailed inhibitor reaction process was also obtained by CHEMKIN based on a new assembly kinetic mechanism. The results show that the effects of C6F12O on the explosion characteristics of ethanol gasoline varied with χinh and φ. For rich flames, C6F12O is more effective than and heptafluoropropane (C₃HF₇) and nitrogen (N2) in suppressing explosions; for lean and equivalence ratio flames, the addition of C6F12O may result in more severe explosions. The decrease in chemical reactivity is mainly because the mole fractions of OH and H radicals and the proportion of paths H radicals involved decrease after adding C6F12O, and R1500: CF3COF + H = CF3CO + HF, R965: CF2:O + H = CF:O + HF, R863: CF3 + H = CF2 + HF are main suppressing reactions.