Jet Burner Research Articles

Investigation of mixing model performance in transported PDF calculations of turbulent lean premixed jet flames through Lagrangian statistics and sensitivity analysis

The piloted premixed jet burner (PPJB) methane–air flame series have been developed to study turbulence–chemistry interactions in lean and highly turbulent premixed flames. The two flames with the largest jet velocities, denoted as PM1-150 and PM1-200, remain challenging for combustion models up to the present. In this work, the flames with the lowest and highest jet velocities, PM1-50 and PM1-200 respectively, are simulated using a hybrid RANS-PDF method to examine the composition evolution and the mixing model performance through Lagrangian particle tracking, and to reveal the controlling physio-chemical processes through particle-level sensitivity analysis. The mixing-reaction budget analysis reveals that for the PM1-50 flame, the implied combustion modes by IEM and EMST mixing models are different: the simulation with EMST is consistent with a flame propagation process, whereas the one with IEM is consistent with an autoignition process. In this regard, for the PM1-50 in the flamelet regime, EMST predicts the correct combustion process whereas IEM does not, despite the fact that the radial profiles of species concentration predicted by these two models are almost identical and are both in good agreement with the experimentally measured values. For the PM1-200 flame closest to global blow-off, EMST and IEM yield similar characteristics: both predict a balance between mixing and reaction in the reaction zone, and both are consistent with flame propagation processes. Due to strong turbulent mixing, the mixing in the preheat zone is greatly enhanced. The change of combustion modes predicted by IEM, i.e. from an autoignition process in PM1-50 to a flame propagation process in PM1-200, is further explored by examining some representative particle trajectories in progress variable space. The PDFs and the mixing-reaction budgets of the progress variable predicted by IEM and EMST demonstrate that the localness of mixing in composition space is essential for a flame in the flamelet regime (PM1-50), while it is less important for a flame in the broken reaction zone regime (PM1-200). The particle-level sensitivity approach has been augmented to further investigate the sensitivities of combustion process to mixing and reaction with an attenuation factor R for the overall reaction rate being introduced to quantify the sensitivities to chemical reaction. It is observed that the sensitivities in PM1-50 and PM1-200 are very different. For PM1-50, the sensitivities of the progress variable to the mixing model constant Cϕ and to the attenuation factor R are both positive, indicating that the reaction progress can be promoted by enhancing either mixing or reaction. In contrast, for PM1-200, the progress variable at the upstream location shows negative sensitivities to Cϕ, which indicates that enhancing mixing suppresses combustion progress due to the fact that the flame is already near the blow-off limit. At downstream locations, the sensitivities of progress variable to reaction is significantly larger than its sensitivity to mixing, indicating that the controlling process during the reignition stage is chemical reaction. These sensitivities are insightful in explaining the observed trends in previous parametric studies of Cϕ for high speed PPJB flames, in which it is found that increasing Cϕ alleviates the overpredition of reaction progress at the upstream location but does not help improve the prediction at the downstream location where the controlling process is chemical reaction.

Flow Field and Scalar Measurements in a Series of Turbulent Partially-Premixed Dimethyl Ether/Air Jet Flames

We present a series of benchmark flames consisting of six partially-premixed piloted dimethyl ether (DME)/air jet flames. These flames provide an opportunity to understand turbulence-flame interactions for oxygenated fuels and to develop predictive models for these interactions using a canonical burner geometry. The development of accurate models for DME/air flames would establish a foundation for studies of more complex oxygenated fuels. The flames are stabilized on a piloted jet burner similar to that of the partially-premixed methane/air jet flames that have been studied extensively within the context of the TNF Workshop. This series of six jet flames spans jet exit Reynolds numbers, ReD, from 29,300 to 73,300 and stoichiometric mixture fractions, ξst, from 0.35 to 0.60. Flame conditions range from very low probability of localized extinction to a high probability of localized extinction and subsequent re-ignition. Measurements in the flames are compared at downstream locations from 5 to 25 diameters above the nozzle exit. Mean and fluctuating velocity components are measured using stereo particle image velocimetry (SPIV). Simultaneous laser-induced fluorescence (LIF) imaging of OH and CH2O provides insights into the distribution of these intermediate species in partially-premixed DME/air flames. OH LIF imaging is also combined with SPIV to investigate the strain rate field across the reaction zone.

Features Of The Diffusion Combustion Of Hydrogen Microjet At Various Spatial Orientation Of The Nozzle Exit With Top – Hat Mean Velocity Profile At The Nozzle Exit

The purpose of the given work will consist in the experimental studies of features diffusion combustion of a hydrogen round microjet, effusing from micronozzle with top – hat mean velocity profile at the nozzle exit, depending on spatial orientation of the nozzle exit. It is revealed, that in conditions of a jet velocity vector orientation towards terrestrial gravitation vector «g» (opposite or perpendicular) the basic characteristics of the flame evolution depending on gas consumption (Q) (or jet velocity U) are rather close to each other. To these characteristics concern such as ranges of the «bottleneck flame area» presence, flame separation at presence of the «bottleneck flame area», presence of the «bottleneck flame area» but absence of a turbulent jet combustion and finally ending of the microjet combustion. On the contrary, in situation of the hydrogen round microjet diffusion combustion in conditions of a jet velocity vector orientation towards terrestrial gravitation vector «g» (orientability – like) the basic characteristics of the flame evolution depending on a jet velocity are sharply differed from two previous cases. The range of existence of the «bottleneck flame area» is reduced, flame separation occurs in absence of the «bottleneck flame area», there is no situation of the «bottleneck flame area» combustion at turbulent flame separation and there is no situation of the «bottleneck flame area» combustion at burn termination of the turbulent part of a microjet and finally ending of the microjet combustion occurs at the much greater jet velocity.

Computational fluid dynamics analysis of a synthesis gas turbulent combustion in a round jet burner

In this study, the RNG-Large Eddy Simulation (RNG-LES) methodology of a synthesis gas turbulent combustion in a round jet burner is investigated, using OpenFoam package. In this regard, the extended EDC extinction model of Aminian et al. for coupling the reaction and turbulent flow along with various reaction kinetics mechanisms such as Skeletal and GRI-MECH 3.0 have been utilized. To estimate precision and error accumulation, we used the Smirinov's method and the results are compared with the available experimental data under the same conditions. As a result, it was found that the GRI-3.0 reaction mechanism has the least computational error and therefore, was considered as a reference reaction mechanism. Afterwards, we investigated the influence of various working parameters including the inlet flow temperature and inlet velocity on the behavior of combustion. The results show that the maximum burner temperature and pollutant emission are affected by changing the inlet flow temperature and velocity.

The combined finishing of geometrically-complex parts

The paper describes the combined hydroabrasive dimensional processing, which involves the application of an electric field of metal parts with complex volumetric profiles, requiring jet control with reference to 5-6 coordinates. One should also consider the reciprocal impact of technological parameters upon formation of parts machined. The mechanism of dimensional material removal has been developed, which is the basis for working out the informational technology of a combined process. The objects of study are adjoining parts of spatially complex surfaces, like gas-turbine engine blades, or axial and radial wheels of turbopump units, as well as the processes of unsoldering in cooled parts of combustion chambers, jet nozzles and complex-shaped part sections with limited tool access into the processing zone, including those made from materials of low machinability. The combined process of hydroabrasive finishing has been developed, which involves the induction of electric current for geometrically-complex surfaces of any geometry, including in areas, inaccessible or hardly accessible for a metal-cutting tool when manufacturing parts from alloys of low machinability.

Computational study of flame characteristics of a turbulent piloted jet burner with inhomogeneous inlets

Recent experimental studies of a piloted turbulent jet burner at Sydney and Sandia with inhomogeneous mixture composition at the inlet have revealed that the flame stability of a partially premixed flame can be significantly increased with a tailored mixture fraction profile at the burner exit. In the present work, large-eddy simulations of this burner are performed with three different levels of mixture inhomogeneity. A multi-regime flamelet model is employed, which accounts for the range of combustion modes found in these flames. The results of the simulations are validated against experimental data for the case with the highest blowoff velocity. Good agreement is observed for velocity, mixture fraction, and temperature fields. The simulations with the multi-regime model provide detailed data of the prevalent combustion regime as well as the heat release. The location of heat release and differences in the combustion modes are analyzed for three cases with different mixture inhomogeneities. The progress variable source term is split up into the individual contributions of the combustion regimes. Substantial differences are found for the contributions of premixed and non-premixed combustion in the different flames as well as the location of the heat release. These results are used to explain the respective flame stabilities. For the inhomogeneous case, which features substantially increased flame stability, hot pilot gases are in contact with reactive mixture directly at the nozzle. Therefore a predominantly premixed zone of strong heat release develops at the jet exit and stabilizes the flame. For both other cases, the heat release at the nozzle is lower leading to smaller blowoff velocities. For the non-premixed case, this is due to air shielding the pilot from the reactive mixture. For the premixed case, the homogeneous mixture issuing from the jet is above the flammability limit and consequently the heat release is diffusion dominated.

Quantitative and qualitative relationship between swirl burner operatingconditions and pulverized coal flame length

Currently, there are used in power plants two types of burners to combustion the pulverized coal: jet burners and swirl burners. Most of the published works in the field of analysis of burners operating conditions are related to jet burners and are limited to initial region of the flame at the outlet of the burner. For jet burners an offset between the burner outlet and the flame beginning point could be analyzed. In the case of swirl burners with the pre-mixing diffuser chamber an offset between flame ignition point and burner outlet is usually not visible. Because already in the pre-mixing diffuser chamber of swirl burner occurs the ignition of coal-dust together with oxidant-gas cloud and thereby the formation of the flame. Therefore, the analysis of operating conditions for this types of burners requires a different approach. There is a lack of researches, in which will be analyzed changes of the flame length, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. Therefore the aim of this study was to implement and verify the methodology for estimating the flame length, which will allow monitoring changes of operating conditions, that are caused by changes of design and operating parameters of swirl burner with the pre-mixing diffuser chamber. To carry out the analysis of the image of the coal flame, the two algorithms have been presented. This two algorithms, being based on the video images of the coal flame allows to specify and detect the end point of the flame and on that basis the length of the flame, as well as the fluctuation changes of flame length can be later determined. Both, the change thermal loads of coal burner, streams of secondary air, as well as the constructional change of the angle of swirler assemblies, resulted in distinct changes in the length of the pulverized coal flame.

Flame Enhancement by Microwave-Induced Plasma: The Role of Major Bath Gas N2 Versus Ar

ABSTRACTA novel centralized microwave jet burner system is proposed here that can be used as a test platform to enable studies of plasma-assisted combustion (PAC) under various operation conditions and combustible mixtures. Spectroscopic characterizations of this burner are conducted using optical emission spectrum with methane/O2/N2 and methane/O2/Ar mixtures for comparison to distinguish the effects of the bath gas on flame enhancement and to delineate the flame enhancement mechanism of microwave induced plasma. The results show that the flame enhancement, by applying a nonequilibrium plasma, is more efficient when the dilution inert N2 in the air is replaced by Ar. The bath gas in the oxidizer stream plays an important role in the flame enhancement mechanism for the PAC system through more efficient direct impact of excited electrons on oxygen in the plasma and resulting in earlier initiation of the chain reactions through branched OH formation reactions in the flame.

Exploring the performance limits of a stratified torch ignition engine using numerical simulation and detailed experimental approaches

In a torch ignition engine system, the combustion starts in a pre-combustion chamber, where the pressure increase pushes the combustion jet flames through calibrated nozzles to be precisely targeted into the main combustion chamber. This paper presents the layout of the prototype engine and the developed fuel injection system. It continues with a detailed description of the performance of the torch ignition engine running on a gasoline/ethanol blend for different mixture stratification levels as well as engine speeds and loads. Also detailed analyses of specific fuel consumption, thermal and combustion efficiency, specific emissions of CO2 and the main combustion parameters are carried out. A numerical model based on thermodynamic and kinetic analyses has been established in order to explore the performance limit of a stratified torch ignition engine. The paper concludes presenting the main numerical results obtained in this work, which show a significant increase in the torch ignition engine performance as compared with the commercial baseline engine.

Stabilization of diffusion flames of impacting and opposing fuel jets

Stability of diffusion combustion of fuel jets impacting on targets and interaction of two jets (pure propane–butane and the same fuel with addition of carbon dioxide) are experimentally studied. Data on combustion failure are obtained for various variants of jet interaction, as well as information about the composition of combustion products, air-to-fuel ratio, and completeness of combustion before combustion failure. It is shown that the domain of stable combustion of impacting and opposing jets is expanded by more than an order of magnitude as compared to combustion of individual free jets.

Modelling of soot formation in laminar diffusion flames using a comprehensive CFD-PBE model with detailed gas-phase chemistry

A discretised population balance equation (PBE) is coupled with an in-house computational fluid dynamics (CFD) code in order to model soot formation in laminar diffusion flames. The unsteady Navier–Stokes, species and enthalpy transport equations and the spatially-distributed discretised PBE for the soot particles are solved in a coupled manner, together with comprehensive gas-phase chemistry and an optically thin radiation model, thus yielding the complete particle size distribution of the soot particles. Nucleation, surface growth and oxidation are incorporated into the PBE using an acetylene-based soot model. The potential of the proposed methodology is investigated by comparing with experimental results from the Santoro jet burner [Santoro, Semerjian and Dobbins, Soot particle measurements in diffusion flames, Combustion and Flame, Vol. 51 (1983), pp. 203–218; Santoro, Yeh, Horvath and Semerjian, The transport and growth of soot particles in laminar diffusion flames, Combustion Science and Technology, Vol. 53 (1987), pp. 89–115] for three laminar axisymmetric non-premixed ethylene flames: a non-smoking, an incipient smoking and a smoking flame. Overall, good agreement is observed between the numerical and the experimental results.

Numerical study of characteristics on NO formation in methane MILD combustion with simultaneously hot and diluted oxidant and fuel (HDO/HDF)

Recently, MILD combustion without preheated air was achieved using a parallel jet burner, in which the fuel and air streams can entrain the hot exhaust gas simultaneously before their mixing. In this manuscript, the mechanisms of the effect of the entrainment ratio on NO formation in the MILD combustion without preheated air were critically focused on using OPPDIF with simultaneously diluted and preheated oxidant and fuel (HDO/HDF), in addition the effects of the inlet temperature and equivalence ratio are discussed. The variations of the NO production index at (1) Tin = 1300 K with the range of Kv from 1 to 8 (2) φ = 1 with the range of Tin from 1000 K to 1300 K (3) Tin = 1300 K with the range of φ from 0.4 to 1.6 were numerically investigated. The results indicate that the NO emission decreases sharply when Kv increases from 1 to 3. This is attributed to the decrease in the NO production rate of N + OH <=> NO + H, the reduction of HNO to NO and the conversion of NO to NO2. When the entrainment ratio increases from 1 to 8, the pyrolysis zone is depressed and the reaction zone is broadened, resulting in an increase in OH consumption. Therefore, N + OH <=> NO + H and HNO + OH <=> NO + H2O sharply decrease in the production of NO. The mutual conversion between NO2 and NO is significantly enhanced in the MILD combustion mode without the preheated air. Consequently, NO2 + H <=> NO + OH makes the largest contribution to NO formation in the reaction region of the MILD combustion. The contribution of N + O2 <=> NO + O in NO formation increases because CH + N2 <=> HCN + N plays an increasingly important role in NO formation. Moreover, both of the inlet temperature and equivalence ratio enhance the NO formation, CH + N2 <=> HCN + N are responsible for this effects.

Modeling the kinetics of the Shockless Explosion Combustion

The Shockless Explosion Combustion (SEC) is a novel approach to approximating constant volume combustion in gas turbines. It promises an efficiency gain comparable to that of pulse detonation combustion without the drawbacks associated with detonations. It utilizes quasi-homogeneous combustion of a volume of fuel & air mixture to avoid strong shock waves, similar to the Homogeneous Charge Compression Ignition (HCCI) process in internal combustion engines. Recharging is handled in analogy to a pulse jet combustor through resonant pressure waves in the combustion chamber. To achieve nearly homogeneous auto-ignition, a stratified layer of fuel/air is set up such that almost constant time to ignition remains across the charge once the recharging process is completed. Here we introduce simplified chemical kinetics models that enable efficient computational modeling of the entire process. Based on numerical simulations we assess essential influences of chemical kinetics on the subtle gasdynamics involved in the SEC process and discuss results on its feasibility.

A two mixture fraction flamelet model for large eddy simulation of turbulent flames with inhomogeneous inlets

A revised flamelet/progress variable (FPV) model in which two mixture fractions are defined has been developed to address the limitations of single mixture fraction FPV models that presume a single, compositionally uniform fuel stream. The revised model is applied in Large Eddy Simulation of the modified University of Sydney turbulent jet burner with compositionally inhomogeneous inlet conditions. The first mixture fraction (Z) characterizes the mixing between the methane/air mixture issuing from the burner and the surrounding coflow air. The second mixture fraction (Z*) tracks mixing of methane and air without regard to the point of origin of the air. Additionally, a fuel premixing fraction (F) has been defined that corresponds to the fuel side boundary condition for the solution of the 1D flamelet equations in terms of the first mixture fraction. Two methods of characterizing the thermochemical state are considered, one using Z and Z* and the other using Z and F. Comparison of temperature and species predictions with experimental data shows that the structure of the flame with inhomogeneous inlets cannot be predicted by a single mixture fraction model while this is successfully achieved with the two mixture fraction models. Even for a near-homogeneous inlet with only minor variations in composition, the two mixture fraction model predictions provide significant improvements over a single mixture fraction model.

Human and Environmental Dangers Posed by Ongoing Global Tropospheric Aerosolized Particulates for Weather Modification.

U.S. military perception of nuclear warfare led to countless unethical nuclear experiments performed on unsuspecting individuals without their informed consent. As evidenced here, subsequent perception of weather warfare has led to exposing millions of unsuspecting individuals to toxic coal fly ash with no public disclosure, no informed consent, and no health warnings. Three methods were used: (1) comparison of eight elements analyzed in rainwater samples, thought to have leached from aerosolized coal fly ash, with corresponding coal fly ash laboratory leachate; (2) comparison of 14 elements analyzed in air filter dust with corresponding elements in coal fly ash; and (3) comparison of 23 elements analyzed in fibrous mesh found after snow melted with corresponding elements in coal fly ash. The rainwater element ratios show that the aerial particulate matter has essentially the same water-leach characteristics as coal fly ash. The air filter dust element ratios occur in the same range of compositions as coal fly ash, as do element ratios in fibrous mesh found on grass after snow melted. The fibrous mesh provides an inferred direct connection with the aerosolizing jet aircraft via coal fly ash association with the jet combustion environment. Strong evidence for the correctness of the hypothesis: coal fly ash is likely the aerosolized particulate emplaced in the troposphere for geoengineering, weather modification, and/or climate alteration purposes. The documented public health associations for ≤2.5 μm particulate pollution are also applicable to aerosolized coal fly ash. The ability of coal fly ash to release aluminum in a chemically mobile form upon exposure to water or body moisture has potentially grave human and environmental consequences over a broad spectrum, including implications for neurological diseases and biota debilitation. The ability of coal fly ash to release heavy metals and radioactive elements upon exposure to body moisture has potentially grave human health implications including cancer, cardiovascular disease, diabetes, respiratory diseases, reduced male fertility, and stroke. The fibrous mesh data admit the possibility of environmentally disastrous formation of methylmercury and ozone-depleting chlorinated-fluorinated hydrocarbons in jet exhaust. Geophysical implications include atmospheric warming and rainfall retardation.

Multiple-scale thermo-acoustic stability analysis of a coaxial jet combustor

In this paper, asymptotic multiple-scale methods are used to formulate a mathematically consistent set of thermo-acoustic equations in the low-Mach number limit for linear stability analysis. The resulting sets of nonlinear equations for hydrodynamics and acoustics are two-way coupled. The coupling strength depends on which multiple scales are used. The double-time-double-space (2T-2S), double-time-single-space (2T-1S) and single-time-double-space (1T-2S) limits are revisited, derived and linearized. It is shown that only the 1T-2S limit produces a two-way coupled linearized system. Therefore this limit is adopted and implemented in a finite-element solver. The methodology is applied to a coaxial jet combustor. By using an adjoint method and introducing the intrinsic sensitivity, (i) the interaction between the acoustic and hydrodynamic subsystems is calculated and (ii) the role of the global acceleration term, which is the coupling term from the acoustics to the hydrodynamics, is analyzed. For the confined coaxial jet diffusion flame studied here, (i) the growth rate of the thermo-acoustic oscillations is found to be more sensitive to small changes in the hydrodynamic field around the flame and (ii) increasing the global acceleration term is found to be stabilizing in agreement with the Rayleigh Criterion.

High temperature O2 vibrational CARS thermometry applied to a turbulent oxy‐fuel combustion process

An O2 vibrational coherent anti‐Stokes Raman scattering system for the temperature analysis of industrially relevant staged oxy‐fuel jet burners with a thermal load of 400 kW is presented. The equivalence ratio for both investigated burners was set to ϕ = 0.9 using a mixture of pure oxygen and natural gas H (high calorific value). Temperature profiles were achieved in the mixing region of the turbulent diffusion type burners at a selected downstream position. Temperature distributions and scatter plots show local temperature variations between 447 and 3085 K and demonstrate the turbulent behavior of the combustion process. Copyright © 2016 John Wiley &amp; Sons, Ltd.

E25 stratified torch ignition engine emissions and combustion analysis

Vehicular emissions significantly increase atmospheric air pollution and greenhouse gases (GHG). This fact associated with fast global vehicle fleet growth calls for prompt scientific community technological solutions in order to promote a significant reduction in vehicle fuel consumption and emissions, especially of fossil fuels to comply with future legislation. To meet this goal, a prototype stratified torch ignition (STI) engine was built from a commercial existing baseline engine. In this system, combustion starts in a pre-combustion chamber, where the pressure increase pushes the combustion jet flames through calibrated nozzles to be precisely targeted into the main chamber. These combustion jet flames are endowed with high thermal and kinetic energy, being able to generate a stable lean combustion process. The high kinetic and thermal energy of the combustion jet flame results from the load stratification. This is carried out through direct fuel injection in the pre-combustion chamber by means of a prototype gasoline direct injector (GDI) developed for a very low fuel flow rate. In this work the engine out-emissions of CO, NOx, HC and CO2 of the STI engine are presented and a detailed analysis supported by the combustion parameters is conducted. The results obtained in this work show a significant decrease in the specific emissions of CO, NOx and CO2 of the STI engine in comparison with the baseline engine. On the other hand, HC specific emission increased due to wall wetting from the fuel hitting in the pre-combustion chamber wall.

Numerical and experimental investigation of turbulent three separated jets

In this work three-dimensional turbulent and separated jets are numerically studied and compared with experimental data. The basic idea of the separated jet burner consists in separating fuel and oxidizer injection to dilute reactants with combustion products before the reactants mix. The computation is achieved using the finite-volume numerical method. The turbulence is modeled using a second order Reynolds Stress Model (RSM) by Launder–Reece–Rodi. A non uniform grid is applied and particularly tightened close to the exit jets in order to capture the near field mechanisms. The validation of the numerical tools is done by comparison with experimental data of the non ventilated jets. Ventilated jets are investigated only numerically. The obtained results show that mixing is improved using three jets compared to the single jet. A comparison between computed ventilated and non ventilated jets is presented. It yields a larger velocity mean value, but a decreasing of the corresponding root mean square of the turbulent velocity fluctuations (rms).

Ignition and combustion characteristics of jet fuel liquid film containing graphene powders at meso-scale

At meso-scale, ignition and combustion characteristics of jet fuel liquid film containing graphene powders were investigated. Jet fuel/graphene suspensions were prepared, and sprayed to produce the liquid film. Liquid film was ignited by optical tweezers, five distinctive stages including graphene trap, ignition and combustion of graphene, bubble formation, jet fuel vaporization and bubble growth, bubble rupture and combustion of liquid film were identified. Ignition of graphene is prior to jet fuel. The combustion heat of graphene serves a heat source to accelerate the vaporization of jet fuel. The graphene serves as a nucleation point to form a bubble. Expansion of both combustion products and jet fuel vapor result in the bubble growth. The thickness of bubble boundary layer depends on graphene concentration. As the bubble escaped, liquid film ruptured and micro-explosion occurred. Jet fuel was then ignited, and combusted sustainably till burnt out. During combustion, the flame front fluctuated slightly, indicating good flame stability. Finally, a schematic physical model was presented to analyze the inductive mechanism of graphene for ignition and combustion of jet fuel liquid film by optical tweezers.