Showing papers in "Combustion Science and Technology in 2009"
TL;DR: A simple algebraic model for the Favre averaged scalar dissipation rate, c, in high Damkohler number premixed flames is obtained from its transport equation by balancing the leading order terms as discussed by the authors.
Abstract: A simple algebraic model for the Favre averaged scalar dissipation rate, c, in high Damkohler number premixed flames is obtained from its transport equation by balancing the leading order terms Recently proposed models for the dominant terms in the transport equation are revisited and revised The algebraic model incorporates essential physics of turbulent premixed flames, namely, dilatation rate, its influence on turbulence-scalar interaction, chemical reactions, and dissipation processes A realizability analysis is carried out to show that the algebraic model is always unconditionally realizable The model predictions of dissipation rate are compared with the DNS results, and the agreement is good over a range of flame conditions Application of the Kolmogorov-Petrovski-Piskunov (KPP) theorem along with the above algebraic model gives an expression for the turbulent flame speed Its prediction compares well with a range of experimental data with no modifications to the model constants
194 citations
TL;DR: In this article, the impact of dilution on laminar burning speed of two different fuels (methane and isooctane) is studied, and three different diluents are used: nitrogen, carbon dioxide and a mixture representative of exhaust gases issued from a stoichiometric combustion of methane.
Abstract: The impact of dilution on laminar burning speed of two different fuels (methane and isooctane) is studied. In the present study, three different diluents are used—nitrogen, carbon dioxide, and a mixture representative of exhaust gases issued from a stoichiometric combustion of methane. Experimental results and PREMIX computations of the CHEMKIN package, using two different kinetic schemes, are presented and compared with literature results, when available. Initial pressure and temperature conditions are respectively 0.1 MPa and 300 K. For both fuels, a larger decrease of the laminar burning speed is obtained for carbon dioxide dilution than for nitrogen dilution. This observation is directly linked to the increase in heat capacity of the dilution gas but also to the carbon dioxide dissociation, even if the heat capacity effect seems to be predominant.
122 citations
TL;DR: In this paper, a low-temperature premixed compression ignition combustion (PCI) is achieved via late injection timing (close to top dead center) and heavy exhaust gas recirculation (EGR) using ultra low sulfur Swedish diesel fuel (sulfur content less than 15ppm).
Abstract: Low-temperature premixed compression ignition combustion (PCI) discussed in this study is achieved via late injection timing (close to top dead center) and heavy exhaust gas recirculation (EGR) using ultra low sulfur Swedish diesel fuel (sulfur content less than 15 ppm). PCI obtains a simultaneous decrease in particulate matter (PM) and oxides of nitrogen (NOx), as where injection timing is retarded, as opposed to conventional combustion, where a PM-NOx trade-off is observed. In PCI, hydrocarbon (HC) and carbon monoxide (CO) are increased, and must be removed using aftertreatment. In order to understand the sources of HC from the PCI regime, gas chromatography with a flame ionization detector is employed to perform exhaust HC speciation at three EGR rates and three injection timings. Volatile HC, semi-volatile HC, and CO increase as the injection timing is retarded or EGR is increased. Retarded injection timing or increased EGR reduces peak cylinder bulk temperature and thereby increases the yield of CO a...
62 citations
TL;DR: In this paper, an analytical model of endwall emission measurements is presented, and recent experimental results are studied to determine whether or not endwall measurements are useful for monitoring ignition delay times in shock-heated mixtures.
Abstract: Chemiluminescence emission from exited species such as OH* or CH* as well as pressure can be convenient and effective diagnostics for monitoring ignition delay times in shock-heated mixtures. Ideally, the ignition delay time obtained from the radical-species emission signal should agree with ignition delay time as obtained from the pressure trace. Under ideal shock-tube conditions, ignition behind the reflected shock wave occurs first at the endwall, so the measurement of endwall pressure is often considered the best way to determine ignition delay time when such an increase in pressure is available. However, the signal-to-noise ratio of data from a pressure transducer mounted in the endwall can be relatively low when compared to that of an emission signal, so the latter technique provides a useful alternative to pressure. In the present paper, an analytical model of endwall emission measurements is presented, and recent experimental results are studied to determine whether or not endwall measurements are...
60 citations
TL;DR: In this article, a multi-dimensional CFD code, KIVA-ERC-Chemkin, coupled with improved sub-models and the Chemkin library, was employed.
Abstract: Parametric studies of direct injection (DI) compression ignition (CI) engine combustion fueled with gasoline are presented. A multi-dimensional CFD code, KIVA-ERC-Chemkin, coupled with improved sub-models and the Chemkin library, was employed. The oxidation chemistry of the fuel was calculated using a reduced mechanism for primary reference fuel combustion. The results show that high pressure DI gasoline engine combustion and emissions are successfully predicted and are in good agreement with available experimental measurements under various operating conditions. It is seen that gasoline has a much longer ignition delay than diesel fuel for the same combustion phasing; thus, oxides of nitrogen (NOx) and particulate emissions are significantly reduced compared to corresponding diesel-fueled cases. The results also suggest possible methods for expanding the operating conditions of DI gasoline compression ignition (CI) combustion. This indicates that the application of gasoline fueling to compression ignitio...
59 citations
TL;DR: The benchmarking results show that the DMZ scheme accurately reproduces the pressure and key species profiles obtained from the fully resolved calculations using direct-injection compression-ignition engine cases in simulations that range from homogeneous to highly stratified.
Abstract: A dynamic multi-zone (DMZ) partitioning scheme is proposed for enhancing the computational efficiency associated with solving detailed chemistry in reactive flow calculations. The DMZ scheme employs a novel and highly flexible evolutionary data clustering algorithm to partition a group of computational cells into zones for solving the chemistry source terms at each hydrodynamic time step. The algorithm dynamically determines the optimal number of zones for each time step of the calculation based on the thermochemical conditions in the cells and user-specified dispersion thresholds. After solving the chemistry equations on zonal level, the DMZ scheme maps the updated solution back to the cells while preserving the initial parameter stratification. The DMZ scheme is implemented into a KIVA3V-CHEMKIN code and benchmarked against fully resolved (non-partitioned) calculations using direct-injection compression-ignition engine cases. The benchmarking results show that the DMZ scheme accurately reproduces the pr...
56 citations
TL;DR: In this paper, an experimental study was conducted on the emission of volatile organic compounds emitted by Rosmarinus officinalis plants when exposed to an external radiant flux, and the results of the experiments were used in a simplified analysis to determine if the emissions of VOCs in an actual forest fire situation could produce a flammable gas mixture and potentially lead to an accelerating forest fire.
Abstract: An experimental study is conducted on the emission of volatile organic compounds (VOCs) emitted by Rosmarinus officinalis plants when exposed to an external radiant flux. The thermal radiation heats the plant and causes the emission of VOCs. The thermal radiation simulates the radiant flux received by vegetation in a forest fire. The results of the experiments are used in a simplified analysis to determine if the emissions of VOCs in an actual forest fire situation could produce a flammable gas mixture and potentially lead to the onset of an accelerating forest fire. The experiments consist of placing a plant in a hermetic enclosure and heating it with a radiant panel. The VOCs produced are collected and analyzed with an automatic thermal desorber coupled with a gas chromatograph/mass spectrometer (ATD-GC/MS). The effects of the fire intensity (radiant panel heat flux) and the fire retardant on the VOCs emission are then investigated. Two thresholds of the VOCs emission are observed. The first is for plan...
56 citations
TL;DR: In this article, the effects of low oxygen levels of MILD combustion leads to both a reduction in reaction rates and an increase in transport of O2 across the reaction zone, which suggests partial premixing can occur under MILD.
Abstract: This paper reports computational results, to complement experimental observations, on the turbulence–chemistry interaction of nonpremixed jet flames issuing into a heated and highly diluted oxidant stream. It is found experimentally that large-scale vortices and flame stretch can lead to spatial thinning and a decrease in OH concentration. This reduction in OH is described as a weakening of the reaction zone. Accompanying reaction zone weakening is also an increase in H2CO levels. The reduction in reaction rates is most noticeable at low oxidant stream O2 levels. The heated and low oxygen oxidant conditions typify those of moderate or intense low oxygen dilution (MILD) combustion. The computational results indicate that the effects of the low oxygen levels of MILD combustion leads to both a reduction in reaction rates and an increase in transport of O2 across the reaction zone. The relationship between the reaction rate and level of O2 permeation suggests that a form of partial premixing can occur under M...
55 citations
TL;DR: In this paper, aluminum particles ranging from 2 to 100μm were subjected to the flow of detonation products of a stoichiometric mixture of hydrogen and oxygen at atmospheric pressure, and luminosity emitted from the reacting particles was used to determine the reaction delay and duration.
Abstract: Aluminum particles ranging from 2 to 100 μm were subjected to the flow of detonation products of a stoichiometric mixture of hydrogen and oxygen at atmospheric pressure. Luminosity emitted from the reacting particles was used to determine the reaction delay and duration. The reaction duration was found to increase as d n with n ≈ 0.5, which is more consistent with kinetically controlled reaction rather than the classical diffusion-controlled regime. Emission spectroscopy was used to estimate the combustion temperature, which was found to be well below the flow temperature. This fact also suggests combustion in the kinetic regime. Finally, the flow field was modeled with a CFD code, and the results were used to model analytically the behavior of the aluminum particles.
54 citations
TL;DR: In this article, a comprehensive hydrocarbon oxidation mechanism in the literature was integrated with a hydrogen-nitrous oxide sub-mechanism, and computational flame speed results using this mechanism were compared to experimental data.
Abstract: Mixtures of four fuels (hydrogen, methane, acetylene and propane) with nitrous oxide were studied to experimentally and numerically determine the laminar flame speeds at near atmospheric pressure (0.8 atm). Using the flat flame method, laminar flame speeds for these nitrous oxide flames were determined for different levels of dilution with nitrogen. A comprehensive hydrocarbon oxidation mechanism in the literature was integrated with a hydrogen-nitrous oxide sub-mechanism, and computational flame speed results using this mechanism were compared to experimental data. For all four fuel systems (hydrogen-, methane-, acetylene-, and propane-nitrous oxide), the compiled chemical mechanism under-predicted the measured laminar flame speeds over the whole range of equivalence ratio investigated. Flame speed sensitivity analyses for the hydrogen-, acetylene-, and propane-nitrous oxide systems have shown that the most sensitive reactions are within the hydrogen-nitrous oxide sub-mechanism. A revision to the reactio...
54 citations
TL;DR: In this paper, the particle size distribution functions (PSDF) and mean particle sizes have been determined in a laminar premixed ethylene/air flame with three different experimental approaches: photo-ionization mass spectrometry, scanning mobility particle sizing (SMPS), and laser-induced incandescence (LII).
Abstract: Particle size distribution functions (PSDF) and mean particle sizes have been determined in a laminar premixed ethylene/air flame with three different experimental approaches: photo-ionization mass spectrometry (PIMS), scanning mobility particle sizing (SMPS), and laser-induced incandescence (LII). The main goal of this investigation was the cross-validation of these three methods used at our institute for the determination of particle sizes in a great variety of flames or exhaust gases. We found good agreement between the three methods in the ranges where they are comparable as well as a complementary behavior for the different size ranges. PIMS and SMPS are able to measure the particle size distribution functions with good resolution. PIMS is favorable in detecting the smallest particles ( 2 nm and > 3 nm, respectively). LII offers t...
TL;DR: In this article, an overall stability diagram was obtained and a specific rigid standing wave regime was observed between the upstream and downstream propagating regimes, whereas only one standing wave point existed in other ordinary porous media.
Abstract: Filtration combustion of lean methane-air mixtures in inert, high-porosity micro-fibrous media was studied experimentally in quartz tubes with different diameters. First, an overall stability diagram was obtained. Between the upstream and downstream propagating regimes, a specific rigid standing wave regime was observed, whereas only one standing wave point existed in other ordinary porous media. A specific instability phenomenon of a combustion wave splitting into two or more parts during wave propagation downstream was also observed in smaller diameter tubes at high filtration velocities. In principle, the results of a conventional two-temperature 1D analytical model captured the main feature of the process obtained in the experiment, but failed to explain the process of flame anchoring to the porous carcass that was observed under variation of the mass flow rate. The possible causes of the failure of the conventional modeling approach were presented.
TL;DR: In this paper, the authors investigated the transition between the conventional spark ignition combustion and HCCI combustion and developed the control strategies for optimized mode switch, which can be stably achieved around the boundaries of HCCC operation region through the rapid and effective control of the in-cylinder residual gas concentration by a Four Variable Valve Actuation Syst...
Abstract: Homogeneous charge compression ignition (HCCI) combustion, also known as controlled autoignition (CAI) combustion, has been realized over a range of engine speed and load conditions in a single cylinder four-stroke gasoline engine equipped with a 4VVAS mechanical variable intake and exhaust valve lift and timing devices system. The engine has the capability to operate either in the spark ignition (SI) or HCCI combustion in order to cover the complete engine operational range. Therefore, smooth switching between SI and HCCI modes is required. In this work, a systematic investigation has been carried out to study the transition between the conventional spark ignition combustion and HCCI combustion and develop the control strategies for optimized mode switch. Results show that dynamic transitions between HCCI and SI can be stably achieved around the boundaries of HCCI operation region through the rapid and effective control of the in-cylinder residual gas concentration by a Four Variable Valve Actuation Syst...
TL;DR: Tanaka's reduced chemical kinetic model for a commercial gasoline fuel with an RON of 95 has been modified and applied in both burned and unburned zones incorporated with the LUCKS (Loughborough University Chemical Kinetics Simulation) code as discussed by the authors.
Abstract: High load performance and fuel economy of gasoline engines are limited by knocks. Such limitations are becoming worse when the engine is heavily super-charged for high BMEP outputs. Spark ignition timing retardation has been an efficient method to avoid knock but results in reduced engine performance and poor fuel economy. A better understanding of knock, which could be used to optimize the engine design, and ignition timing optimization in particular, is important. In this research, a simulation model for SI engine knock has been developed. The model is based on a three-zone approach (i.e., unburned, burning, and burned zones). Tanaka's reduced chemical kinetic model for a commercial gasoline fuel with an RON of 95 has been modified and applied in both burned and unburned zones incorporated with the LUCKS (Loughborough University Chemical Kinetics Simulation) code. Both post-flame heat release and pre-flame autoignition have been simulated. The burning zone uses equilibrium combustion thermodynamic model...
TL;DR: In this article, the effects of ethanol addition to ethylene on soot emissions were investigated using a suite of laboratory devices that included a shock tube, a well-stirred reactor, a premixed flat flame, an opposed-jet diffusion flame, and a high pressure turbulent reactor.
Abstract: The impact of a variety of non-metallic fuel additives on soot was investigated in a collaborative university, industry and government effort. The main objective of this program was to obtain fundamental understanding of the mechanisms through which blending compounds into a fuel affects soot emissions. The research team used a suite of laboratory devices that included a shock tube, a well-stirred reactor, a premixed flat flame, an opposed-jet diffusion flame, and a high pressure turbulent reactor. The work reported here focuses on the effects of ethanol addition to ethylene on soot. The addition of ethanol led to substantial reductions in soot in all of the devices except for the opposed-jet diffusion flame. Modeling of the premixed flame and opposed-jet diffusion flame was used to obtain insights into the mechanism behind the opposing effects of ethanol addition in these two flames.
TL;DR: In this article, a modified thickened flame (TF) model based on large eddy simulation (LES) methodology is used to investigate premixed combustion, and the model predictions are evaluated by comparing with the piloted premixed stoichiometric methane-air flame data for Reynolds numbers Re = 24,000 (flame F3) and Re = 52,000(flame F1).
Abstract: A modified thickened flame (TF) model based on large eddy simulation (LES) methodology is used to investigate premixed combustion, and the model predictions are evaluated by comparing with the piloted premixed stoichiometric methane-air flame data for Reynolds numbers Re = 24,000 (flame F3) and Re = 52,000 (flame F1). The basic idea of the TF approach is that the flame front is artificially thickened to resolve on the computational LES grid while keeping the laminar flame speed ( ) constant. The artificially thickening of the flame front is obtained by enhancing the molecular diffusion and decreasing the pre-exponential factor of the Arrhenius law. Because the flame front is artificially thickened, the response of the thickened flame to turbulence is affected and taken care of by incorporating an efficiency function (E) in the governing equations. The efficiency function (E) in the modified TF model is proposed based on the direct numerical simulations (DNS) data set of flame-vortex interactions. The pred...
TL;DR: In this paper, an experimental investigation of laminar smoke points of candle flames is presented, where adjustable wicks with diameters of 1.7-7.3mm were used to measure smoke points in quiescent air for 14 different waxes.
Abstract: An experimental investigation of laminar smoke points of candle flames is presented. Adjustable wicks with diameters of 1.7–7.3 mm were used to measure smoke points in quiescent air for 14 different waxes. The measured smoke points increased with wick diameter. Smoke points interpolated to a wick diameter of 4.5 mm varied from 41–80 mm and increased from commercial waxes (candelilla, carnauba, beeswax, paraffin) to normal alkanes (hexatriacontane, octacosane, tetracosane) to primary alcohols (octadecanol, docosanol, hexadecanol) to carboxylic acids (stearic, palmitic, lauric, myristic). Wax smoke points decreased with increasing carbon number. Alkane and alcohol smoke points decreased with increasing fuel C/H ratio and correlated with past measurements of liquid fuels and polymers. Soot emission was not possible for any fuel when wick diameter was below 1.7 mm or when wick length was below 5.9 mm.
TL;DR: By using molecular beam sampling mass spectrometry, the structure of a NH3/H2/O-2/Ar flat premixed flame burning at 50 mbar and with an equivalence ratio equals to one has been determined as discussed by the authors.
Abstract: By using molecular beam sampling mass spectrometry, the structure of a NH3/H-2/O-2/Ar flat premixed flame burning at 50 mbar and with an equivalence ratio equals to one has been determined. Simulated mole fraction profiles have been obtained by using the kinetic mechanisms of Konnov (2000), Bian et al. (1990), Lindstedt et al. (1994), and Smith (1999), but only the first two give results in agreement with the experimental ones. Furthermore, an initial study on a spark ignition engine has been performed to define which parameters must be applied to reach the best possible efficiency and reduce the formation of pollutants when ammonia is used as fuel in engines.
TL;DR: In this article, an experimental study of flame blowoff phenomenon in a bluff body stabilized flame confined in a cylindrical duct is presented, where the blowoff equivalence ratio was determined for two approach velocities and three different upstream equivalence ratios profiles (uniform, inner and outer fuel enrichment) in the absence and presence of imposed upstream velocity oscillations.
Abstract: An experimental study of flame blowoff phenomenon in a bluff body stabilized flame confined in a cylindrical duct is presented. Blowoff equivalence ratios were determined for two approach velocities and three different upstream equivalence ratio profiles (uniform, inner, and outer fuel enrichment) in the absence and presence of imposed upstream velocity oscillations. The results were compared with those for the unconfined flame configuration as well. It is found that the blowoff equivalence ratios exhibit somewhat different trends for different approach velocities. For the uniform mixture profile, blowoff equivalence ratio first increases with increasing excitation frequency and then decreases at higher frequencies for the approach velocity of 5 m/s. For the 11 m/s approach velocity, the trend is different, and the blowoff equivalence ratio continuously increases with increasing excitation frequency. The blowoff equivalence ratios are higher for the confined flame configuration. An empirical correlation o...
TL;DR: An approximate model of chemical equilibrium in heterogeneous mixtures of a combustible gas with chemically inert solid or liquid particles has been suggested in this article, which includes explicit algebraic formulas for the calculation of the molar mass of the gas, internal energy, and heat capacities of gas-particles mixture, and ordinary differential equations for the description of isentropic compression and adiabatic index of the system.
Abstract: An approximate model of chemical equilibrium in heterogeneous mixtures of a combustible gas with chemically inert solid or liquid particles has been suggested. It includes explicit algebraic formulas for the calculation of the molar mass of the gas, internal energy, and heat capacities of gas-particles mixture, and ordinary differential equations for the description of isentropic compression and adiabatic index of the system. The model can be also useful for the rough estimations of thermodynamic parameters of gaseous mixtures with particles of soot. As an example of a possible application of the suggested model of chemical equilibrium, parameters of stationary one-dimensional detonation wave in gas-particles mixtures are calculated. The algorithm of estimation of detonation cell size in such heterogeneous mixtures is presented. Detonation wave parameters and cell size in the stoichiometric hydrogen-oxygen mixture with particles of W, Al2O3, and SiO2 have been calculated. The results of the calculations o...
TL;DR: In this article, the combustion characteristics of biodiesel produced from karanja oil and its blends with diesel and gasoline were investigated using porous sphere technique, and the visible flame shape was analyzed with the help of digital flame image.
Abstract: Experiments employing porous sphere technique are carried out to investigate the combustion characteristics of biodiesel produced from karanja oil and its blends with diesel and gasoline. Biodiesel or its blend is transpired to porous sphere surfaces, where it burns. Porous spheres are placed in an air stream blowing with a uniform velocity at atmospheric pressure and temperature under normal gravity conditions. At low air velocities, a flame envelops the entire sphere. Fuel feed rates are recorded for various sphere sizes and air velocities. Overall, the visible flame shape is analyzed with the help of digital flame image. At a particular air velocity, the flame will not envelope the sphere, but establish near the rear region of the sphere and the same is recorded for different sphere sizes. Theoretical correlations are proposed for burning rate as a function of effective Reynolds number and for Damkohler number as a function of Froude number.
TL;DR: In this article, the pyrolysis and burning kinetic models of different fuels were implanted into the WBSF-PCC2 (wall burning and slag flow in pulverized co-combustion) computation code, and then the slagging and cocombion characteristics of different solid fuels and their effects on the whole burning behavior in the cylindrical combustor at different mixing ratios under the condition of keeping the heat input samewere simulated numerically.
Abstract: Numerical analysis was used to study the deposition and burning characteristics of combining co-combustion with slagging combustion technologies in this paper. The pyrolysis and burning kinetic models of different fuels were implanted into the WBSF-PCC2 (wall burning and slag flow in pulverized co-combustion) computation code, and then the slagging and co-combustion characteristicsespecially the wall burning mechanism of different solid fuels and their effects on the whole burning behavior in the cylindrical combustor at different mixing ratios under the condition of keeping the heat input samewere simulated numerically. The results showed that adding wood powder at 25% mass fraction can increase the temperature at the initial stage of combustion, which is helpful to utilize the front space of the combustor. Adding wood powder at a 25% mass fraction can increase the reaction rate at the initial combustion stage; also, the coal ignitability is improved, and the burnout efficiency is enhanced by about 5% of suspension and deposition particles, which is helpful for coal particles to burn entirely and for combustion devices to minimize their dimensions or sizes. The results also showed that adding wood powder at a proper ratio is helpful to keep the combustion stability, not only because of the enhancement for the burning characteristics, but also because the running slag layer structure can be changed more continuously, which is very important for avoiding the abnormal slag accumulation in the slagging combustor. The theoretic analysis in this paper proves that unification of co-combustion and slagging combustion technologies is feasible, though more comprehensive and rigorous research is needed.
TL;DR: In this paper, a large eddy simulation (LES) model is used to predict water sprinkler spray interaction with a fire environment and the results of the computations compare favorably to measurements from full-scale fire tests reported in the literature, indicating good accuracy of LES approach in application to practical fire design problems.
Abstract: A large eddy simulation (LES) CFD model is used to predict water sprinkler spray interaction with a fire environment. The emphasis is on computing gas temperatures and velocities induced by sprinkler discharge onto the ceiling jet flow. Results are presented for two different water discharge rates, in addition to simulation of free-burning fire. Extensive variation of physical and numerical parameters is performed to investigate the robustness of the predictions. The results of the computations compare favorably to measurements from full-scale fire tests reported in the literature, indicating good accuracy of LES approach in application to practical fire design problems. Results are also compared with the earlier treatment of the same problem using the Reynolds-averaged Navier–Stokes (RANS) approach.
TL;DR: In this paper, a comprehensive theoretical/numerical model was developed to investigate the transient combustion response of AP/HTPB composite propellant to acoustic excitation in a rocket-motor environment.
Abstract: A comprehensive theoretical/numerical model is developed to investigate the transient combustion response of AP/HTPB composite propellant to acoustic excitation in a rocket-motor environment. The work extends our previous analysis of AP/HTPB combustion at steady-state to include flow oscillations and their subsequent influence on the flame structure and propellant burning behavior. Detailed information about the flame-zone physiochemistry near the propellant surface is obtained at different locations in the motor for the first three modes of longitudinal acoustic waves. In addition, various mechanisms dictating the characteristics of the propellant combustion response, including microscale motions in the flame zone and macroscale motions in the bulk flow, are explored. The effects of mean and oscillatory flowfields in determining the propellant combustion response are also examined. Furthermore, a large flow velocity fluctuation often leads to a nonlinear response of the heat feedback to the propellant su...
TL;DR: In this article, the variation of flame propagation velocity with rising explosion pressure for methane-air mixtures was investigated in an explosion chamber with a volume of 1.25 m3.
Abstract: Results are presented for the variation of flame propagation velocity with rising explosion pressure for methane-air mixtures. The experiments were carried out in an explosion chamber with a volume of 1.25 m3. Photos of the flame propagating during the explosion processes were obtained through a window in the middle of the front cover of the chamber. The influence of the methane concentration on the time delay between the flame front approaching the chamber wall and the moment when the pressure inside the chamber reached its maximum is also discussed.
TL;DR: In this paper, the authors described the production of chars from loquat stones in a tube furnace at carbonization temperatures of 600°C, 700°C and 800°C in a nitrogen flow at a heating rate of 10°C/min.
Abstract: This paper describes the production of chars from loquat stones in a tube furnace at carbonization temperatures of 600°C, 700°C, and 800°C in a nitrogen flow at a heating rate of 10°C/min. The physical and chemical structures of the stones and chars were investigated by FTIR spectrometer, X-ray diffractometer, and SEM, as well as the combustion reaction and kinetic parameters based on the TG-DTG graphs obtained by thermogravimetric analysis. The combustion reaction was carried out at a heating rate 10°C/min and an oxygen flow rate of 50 ml/min up to 700°C. The kinetic parameters were calculated using the methods by Arrhenius; Coats and Redfern; Horowitz and Metzger; and Ingraham and Marier.
TL;DR: In this paper, a two-phase valveless pulse detonation engines (PDEs) with inner diameters of 50mm and 120mm were investigated for different operational cases.
Abstract: This paper addressed the ignition and detonation initiation investigation of two-phase valveless pulse detonation engines (PDEs) in different operational cases. To quantify the ignition and detonation initiation performance, the parameters detonation initiation time and deflagration-to-detonation transition (DDT) distance were examined. Detonation initiation time was defined as the time between the times when the spark plug received the ignition signal and when detonation initiated by DDT, which was the sum of the ignition time and DDT time. In order to observe the effects of ignition energy, operating frequency of the PDE, liquid fuel type, and inner diameter of the PDE on detonation initiation characteristics, proof–of-principle experiments of PDEs with inner diameters of 50 mm and 120 mm were carried out. Gasoline and kerosene were used as the liquid fuels of PDEs. A conventional Schelkin spiral is used to obtain DDT in liquid fuel/air mixtures. The results indicated that the ignition energy, operating...
TL;DR: A methodology for computing steady turbulent reacting flows in complex shape combustors with special emphasis to nitrogen oxides is described, using a 3-D computational fluid dynamics (CFD) proprietary code properly coupled with a numerical tool called Kinetic Post-Processor (KPP).
Abstract: An advanced low-NOx combustor is studied experimentally in the frame of the recent European Program EEFAE (Efficient and Environmentally Friendly Aero-Engine) for the CLEAN (Component vaLidator for Environmentally-friendly Aero-eNgine) demonstrator. The experimental measurements are compared with model predictions obtained using a 3-D computational fluid dynamics (CFD) proprietary code properly coupled with a numerical tool called Kinetic Post-Processor (KPP). One of the aims of this paper is also to describe a methodology for computing steady turbulent reacting flows in complex shape combustors: the thermo-fluid dynamics results of the CFD code are processed by the KPP with the use of detailed kinetics for predicting pollutant emissions, with special emphasis to nitrogen oxides. The comparisons between experimental measurements and model predictions indicate the current limitations of the procedure but also the possibilities of this powerful tool. From the kinetics point of view, the need for accurate hi...
TL;DR: In this article, a Lagrangian framework is proposed for non-premixed flames stabilization in high-velocity reactive flows where compressibility effects, turbulent mixing, and chemical kinetics processes are competing.
Abstract: The present study is devoted to the computational modeling of non-premixed flames stabilization in high-velocity reactive flows where compressibility effects, turbulent mixing, and chemical kinetics processes are competing. The characterization of the unsteady features of such turbulent reactive flows is still a difficult task, from both experimental and numerical points of view, so that the evaluation of numerical models capabilities remains essentially performed through the comparisons of steady-state solutions with the corresponding experimental data. The Reynolds averaged Navier-Stokes (RANS) strategy still provides the most suitable framework to obtain such steady-state solutions for flows at a high Reynolds number, especially for design and optimization purposes. In turbulent non-premixed flames, the competition between molecular diffusion effects—namely, micromixing or scalar dissipation—and chemical kinetics must be taken into account. In the present work, a Lagrangian framework, able to represent...
TL;DR: In this article, a novel tabulation procedure for reactive scalar statistics based on one-dimensional turbulence (ODT) is implemented to study extinction and reignition in piloted methane-air jet diffusion flames.
Abstract: A novel tabulation procedure for reactive scalar statistics based on the one-dimensional turbulence (ODT) is implemented to study extinction and reignition in piloted methane-air jet diffusion flames. The formulation is based on constructing the scalar statistics from stand-alone temporal jet simulations using ODT. The statistics are correlated in terms of two parameters based on a single transported variable: the mean mixture fraction, which measures the extent of mixing between the fuel and oxidizer streams, and the centerline mixture fraction, which measures the extent of entrainment into the fuel jet or the jet evolution downstream. The evolution of momentum and passive scalars is computed using a Reynolds-Averaged Navier-Stokes (RANS) formulation, which uses the 2D table for look-up of the mean density. Other reactive scalars' profiles are obtained from the 2D table and the computed momentum and scalar fields from RANS. Comparison of the computed and the experimental statistics for momentum and scala...