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Showing papers in "Combustion Science and Technology in 2013"


Journal ArticleDOI
TL;DR: In this article, the effects of dissipation and dispersion of the entropy waves on the stability of a combustor were investigated in aero-engine combustors, and four combustor configurations were discussed: a stable combustor that may be destabilized due to the presence of entropy noise, an unstable combustor which may be stabilized by indirect combustion acoustics, an instability that experiences a “mode switch” to oscillations at a different frequency, and a combustionor that is driven to instabi...
Abstract: Thermoacoustic instability can be a major problem for aero-engine combustors, particularly lean-premixed burners designed for low NOx emissions. The instability is caused by the interaction between unsteady heat release and acoustic waves within the combustion chamber. Unsteady combustion generates acoustic waves directly, as well as entropy fluctuations that are quiescent. The subsequent acceleration of these entropy waves at the combustor exit creates further acoustic waves known as indirect combustion noise. In this article, a thermoacoustic model is extended to study the effects of dissipation and dispersion of the entropy waves on the stability of the combustor. Four combustor configurations are discussed: a stable combustor that may be destabilized due to the presence of entropy noise, an unstable combustor that may be stabilized by indirect combustion acoustics, an unstable combustor that experiences a “mode switch” to oscillations at a different frequency, and a combustor that is driven to instabi...

115 citations


Journal ArticleDOI
TL;DR: In this paper, numerical simulations of soot formation of n-heptane autoigniting spray in a constant-volume vessel under diesel engine conditions with different ambient densities (14.8 and 30 kg/m3) and ambient oxygen concentrations (8-21% O2 mol fraction) were performed using two-dimensional, first-order conditional moment closure (CMC).
Abstract: Numerical simulations of soot formation of n-heptane autoigniting spray in a constant-volume vessel under diesel engine conditions with different ambient densities (14.8 and 30 kg/m3) and ambient oxygen concentrations (8–21% O2 mol fraction) were performed using two-dimensional, first-order conditional moment closure (CMC). Soot formation was modeled with a semiempirical two-equation model that considers simultaneous soot particle inception, surface growth, coagulation, and oxidation by O2 and OH. Soot radiation was accounted for with an optical-thin formulation. Results are compared to experimental data by means of ignition delay time, lift-off length, and soot volume fraction distribution. Good predictions of ignition delay and lift-off for all nine cases are achieved. High volume fraction soot location and semi-quantitative distribution have been well described even with this comparatively simple soot model. The findings suggest that the conditional moment closure approach is a promising framework for ...

79 citations


Journal ArticleDOI
TL;DR: In this article, an unsteady flamelet progress variable (UFPV) model is evaluated for modeling autoignition and flame lift-off in diesel jets, where changes in injection pressure, orifice diameter, ambient temperature, density, and O2 concentration are considered.
Abstract: An unsteady flamelet progress variable (UFPV) model is evaluated for modeling autoignition and flame lift-off in diesel jets. Changes in injection pressure, orifice diameter, ambient temperature, density, and O2 concentration are considered. In implementing the model in a Reynolds-averaged Navier–Stokes (RANS) code, a look-up table of reaction source terms is generated as a function of mixture fraction Z, stoichiometric scalar dissipation rate χst and progress variable Cst by solving the unsteady flamelet equations. It is assumed that the probability density functions (pdfs) of Z, χst, and Cst are statistically independent, and presumed functions are employed for the pdfs. Comparisons with experimental results show that the model is able to predict ignition delay and flame lift-off with reasonable accuracy in the RANS simulations. The quantitative agreement between computed and measured results depends on the definitions employed to quantify autoignition time and lift-off height, but, in general, the agre...

75 citations


Journal ArticleDOI
TL;DR: In this paper, a premixed swirl burner was designed to experimentally study the impact of the spark location on successful ignition and to detail the scenario from ignition to flame stabilization, and the results showed that no correlation between local turbulent kinetic energy and ignition probability was observed.
Abstract: Optimization of the ignition location is of crucial importance for many combustion systems and requires advanced knowledge of the ignition process for both fundamental and applied configurations. In this article, a premixed swirl burner was designed to experimentally study the impact of the spark location on successful ignition and to detail the scenario from ignition to flame stabilization. Two swirl numbers were investigated to evaluate their impact on the ignition process. Particular attention was paid to providing accurate data on cold flow velocity field statistics (obtained by stereoscopic particle image velocimetry) as well as on ignition conditions. Ignition probability maps were obtained for a constant level of deposited energy. Contrary to previous studies, no correlation between local turbulent kinetic energy and ignition probability was observed, and a deeper analysis of the temporal evolution of the flame kernel within the combustion chamber is required. Coupling fast flame visualization with...

56 citations


Journal ArticleDOI
TL;DR: In this article, an experimental study was conducted to understand the combustion behavior of polytetrafluoroethylene (PTFE)/boron-based solid fuels for future hybrid rocket motor applications.
Abstract: An experimental study was conducted to understand the combustion behavior of polytetrafluoroethylene (PTFE)/boron–based solid fuels for future hybrid rocket motor applications. Fuels were loaded with 10–40% boron powder (w/w). Two different types of PTFE were examined in this study, while a single type of boron powder was considered. No significant differences in the decomposition mechanisms for PTFE and a candidate solid fuel mixture were observed by differential scanning calorimetry (DSC) and temperature-jump (T-jump)/Fourier transform infrared (FTIR) experiments. Diffusion flame studies between solid fuels and gaseous oxygen were carried out to measure regression rates and to develop a fundamental understanding of the combustion behavior. The fuels with the lowest boron content readily extinguished upon removal of the supplemental oxygen flow. The fuels with the highest loadings of boron self-propagated after ignition. X-ray diffraction on postcombustion residue of the self-propagating material reveale...

48 citations


Journal ArticleDOI
TL;DR: In this paper, a passive mixing enhancement strategy of using inclined struts along with a flow guide vane is presented and experimentally tested at atmospheric pressure conditions, and results show excellent mixing and consequently low values of the combustor exit pattern factor in the range of 0.1 and small flame lengths (57 times the main-duct depth).
Abstract: Previous studies on a single-cavity, compact trapped vortex combustor concept showed good flame stability for a wide range of flow conditions. However, achieving good mixing between cavity products and mainstream flow was still a major challenge. In the present study, a passive mixing enhancement strategy of using inclined struts along with a flow guide vane is presented and experimentally tested at atmospheric pressure conditions. Results show excellent mixing and consequently low values of the combustor exit pattern factor in the range of 0.1 and small flame lengths (57 times the main-duct depth). The pressure drop is small in the range of 0.35%, and NOx levels of the order of 12ppm are achieved. The flame stability is excellent, and combustion efficiency is reasonable in the range of 96%. The effectiveness of the proposed strategy is explained on the basis of in-situ OH chemiluminescence images and prior numerical simulations of the resulting complex flow field. The flow guide vane is observed to lead to a counterclockwise cavity vortex, which is conducive to the rise of cavity combustion products along the inclined struts and subsequent mixing with the mainstream flow.

46 citations


Journal ArticleDOI
TL;DR: In this article, the computational domain is extended below the exit plane of the fuel tube to account for the flame preheating effect, which increases the contribution by polycyclic aromatic hydrocarbon (PAH) condensation to computed soot volume fractions.
Abstract: Previous attempts to model elevated-pressure coflow laminar flames have been hindered by neglecting the preheating within the burner, caused by downward heat transfer to the burner. In the present work, the computational domain is extended below the exit plane of the fuel tube to account for the flame preheating effect. Conjugate heat transfer (CHT) is implemented by the harmonic mean method to model the heat transfer between the fluid streams and solid fuel tube. This extension of the domain allows for solutions to a high pressure ethane/air data set from 2 to 33 atm, which is an improvement over previous attempts where only pressures below 15 atm could be modeled. The extended model more accurately predicts centerline soot formation than the truncated model due to capturing fuel pyrolysis that occurs below the exit plane of the fuel tube. This increased fuel pyrolysis increases the contribution by polycyclic aromatic hydrocarbon (PAH) condensation to computed soot volume fractions. For pressures above 2...

45 citations


Journal ArticleDOI
TL;DR: In this article, the effects of nano-aluminum powder (nAl, nominal size of particles 50nm and 100nm), obtained by electrical explosion of wires, was passivated by air and coated by several different organic reagents.
Abstract: Nanoaluminum powder (nAl, nominal size of particles 50 nm and 100 nm), obtained by electrical explosion of wires, was passivated by air and coated by several different protective organic reagents to assess the effects on ballistics of nAl-loaded hydroxyl-terminated polybutadiene (HTPB)-based solid fuel with respect to pure HTPB baseline. The nAl samples were characterized by transmission electron microscopy (TEM), Brunauer–Emmett–Teller (BET), and chemical analysis on active aluminum content (Al°) content and added to HTPB-based solid fuels for hybrid propulsion. Combustion tests were carried out burning central-perforated single-port cylindrical samples in a 2D radial burner. Data analysis was performed to obtain a continuous time-resolved regression rate. Coated nAl particles may significantly improve the ballistics of HTPB + nAl formulations burning in gaseous oxygen, with respect to pure HTPB. All investigated formulations with nAl exhibit increase of instantaneous regression rate (up to 89% maximum),...

44 citations


Journal ArticleDOI
TL;DR: In this article, a comparison of different turbulence and combustion models and different chemical reaction mechanisms is reported, and the results are validated using experimental data obtained in a small-scale combustor fired with methane.
Abstract: Flameless combustion in a laboratorial combustor is numerically simulated. A comparison of different turbulence and combustion models and different chemical reaction mechanisms is reported. The results are validated using experimental data obtained in a small-scale combustor fired with methane. The calculations show that the different turbulence models employed do not yield significant differences, as far as the mean temperature and major species are concerned. Combustion models based on the flamelet concept predict a steep rise in temperature and CO2 molar fraction along the combustor axis in comparison with the experimental data, even though they yield satisfactory predictions elsewhere. In contrast, the eddy dissipation concept along with a detailed reaction mechanism yields rather good predictions, particularly if the most detailed reaction mechanism is employed. The N2O mechanism is responsible for most of the predicted NO molar fraction, which is of the order of 10 ppm, clearly exceeding the experim...

43 citations


Journal ArticleDOI
TL;DR: In this article, a direct-injection spark-ignition optical research engine on ethanol and butanol was tested with a multihole injector, located centrally in the combustion chamber, was used with all fuels.
Abstract: Future automotive fuels are expected to contain significant quantities of bio-components. This poses a great challenge to the designers of novel low-CO2 internal combustion engines because biofuels have very different properties to those of most typical hydrocarbons. The current article presents results of firing a direct-injection spark-ignition optical research engine on ethanol and butanol and comparing those to data obtained with gasoline and iso-octane. A multihole injector, located centrally in the combustion chamber, was used with all fuels. Methane was also employed by injecting it into the inlet plenum to provide a benchmark case for well-mixed “homogeneous” charge preparation. The study covered stoichiometric and lean mixtures (λ = 1.0 and λ = 1.2), various spark advances (30–50° CA), a range of engine temperatures (20–90°C), and diverse injection strategies (single and “split” triple). In-cylinder gas sampling at the spark-plug location and at a location on the pent-roof wall was also carried o...

37 citations


Journal ArticleDOI
TL;DR: In this article, the forced response of swirl-stabilized turbulent flames to upstream flow disturbances was investigated in an industrial scale gas turbine combustor operating with natural gas fuel and CO2/air.
Abstract: Experimental investigations of the forced response of swirl-stabilized turbulent flames to upstream flow disturbances were performed in an industrial scale gas turbine combustor operating with natural gas fuel and CO2/air. We measured flame transfer functions (FTFs) for a wide range of forcing frequency over a broad range of operating conditions with 50–120 kW thermal power. A sensitivity analysis was then performed in order to identify the key dimensionless parameters controlling the forced swirl flame dynamics. Two different dimensionless parameters, S t 1 = (fδ sw )/U and S t 2 = (f L f )/U, are used as dimensionless frequencies, while the dependence of the FTF gain on the turbulent flame speed is taken into account using a dimensionless flame length, ξ = L f /D c . The implementation of the nondimensionalization strategy using several time and length scales reveals that all FTFs are well characterized by either S t 1 or S t 2, but the best result is obtained from a combination of S t 1 and S t 2, whic...

Journal ArticleDOI
TL;DR: In this paper, the impact of fuel composition on auto-ignition in homogeneous charge compression ignition (HCCI) engines was investigated in order to develop a future metric for predicting fuel performance in future HCCI engine technology.
Abstract: The purpose of this research is to investigate the impact of fuel composition on auto-ignition in homogeneous charge compression ignition (HCCI) engines in order to develop a future metric for predicting fuel performance in future HCCI engine technology. A single-cylinder, variable compression ratio engine operating as an HCCI engine was used to test reference fuels and gasoline blends with octane numbers (ON) ranging from 60 to 88. Correlations between fuel composition, ON, and two existing methods for predicting fuel auto-ignition in HCCI engines (Kalghatgi's octane index and Shibata and Urushihara's HCCI index) are investigated. Results show that octane index and HCCI index poorly predict the impact of fuel composition on auto-ignition for fuels with the same ON. The effect of ethanol in delaying auto-ignition depends on the composition of the original gasoline blend; the same is true for the addition of naphthenes. Low-temperature heat release (LTHR) correlates well with auto-ignition for gasoline fue...

Journal ArticleDOI
TL;DR: In this article, the authors computed statistically spherical expanding turbulent premixed flames using an unsteady Reynolds-averaged Navier-Stokes (URANS) approach, which is able to capture the measured growth rate of a methane-air turbulent flame ball.
Abstract: Statistically spherical expanding turbulent premixed flames are computed using an unsteady Reynolds-averaged Navier–Stokes (URANS) approach. Mean reaction rate is closed using strained and unstrained flamelet models and an algebraic model. The flamelets are parametrized using the scalar dissipation rate in the strained flamelet model. It is shown that this model is able to capture the measured growth rate of methane–air turbulent flame ball, which is free of thermo–diffusive instability. The spherical flames are observed to accelerate continuously. The flame brush thickness grows in time and the role of turbulent diffusion on this growth seems secondary compared to the convection due to the fluid velocity induced by the chemical reaction. The spherical flames have larger turbulent flame speed, the leading-edge displacement speed st, compared to the planar flames for a given turbulence and thermochemical condition. The computational results suggest with 0.57 ≤ n ≤ 0.58, where Re t is the turbulence Reynold...

Journal ArticleDOI
TL;DR: In this article, an experimental investigation on the oxidation behavior of diesel particulate matter (DPF) collected from a DPF test system connected to the exhaust stream of a 1.9l, 4cylinder, light-duty diesel engine is reported.
Abstract: Diesel engines generally employ diesel particulate filter (DPF) systems to meet increasingly stringent emissions regulations. The development of optimum methodologies for DPF regeneration requires detailed information on the oxidation characteristics of diesel particulate matter (PM) that accumulates on the DPF under realistic engine conditions. An experimental investigation on the oxidation behavior of diesel PM collected from a DPF test system connected to the exhaust stream of a 1.9 L, 4-cylinder, light-duty diesel engine is reported. A thermogravimetric analyzer (TGA) was used to measure the instantaneous sample mass and the rate of mass loss during its oxidation for a wide range of conditions, which include initial sample mass, amount of volatile components of soluble organic fraction (SOF) in the sample, oxygen concentration, and various heat treatment schemes in both the inert and oxidizing environments. The global kinetic parameters, i.e., the reaction orders of soot and oxygen, activation energy,...

Journal ArticleDOI
TL;DR: In this paper, the effects of turbulent Reynolds number on the transport of scalar dissipation rate of reaction progress variable in the context of Reynolds averaged Navier-Stokes simulations have been analyzed using three-dimensional simplified chemistry-based direct numerical simulation (DNS) data of freely propagating turbulent premixed flames with different values of Re t.
Abstract: The effects of turbulent Reynolds number, Re t , on the transport of scalar dissipation rate of reaction progress variable in the context of Reynolds averaged Navier–Stokes simulations have been analyzed using three-dimensional simplified chemistry-based direct numerical simulation (DNS) data of freely propagating turbulent premixed flames with different values of Re t . Scaling arguments have been used to explain the effects of Re t on the turbulent transport, scalar–turbulence interaction, and the combined reaction and molecular dissipation terms. Suitable modifications to the models for these terms have been proposed to account for Re t effects, and the model parameters include explicit Re t dependence. These expressions approach expected asymptotic limits for large values of Re t . However, turbulent Reynolds number Re t does not seem to have any major effects on the modeling of the term arising from density variation.

Journal ArticleDOI
TL;DR: In this article, a novel automatic feature extraction (AFE) technique, based on data registration using the dual-tree complex wavelet transform, was used to identify multiple flame-flame interactions in premixed combustion, and their influence on the flame area was extracted using AFE.
Abstract: Multiple flame–flame interactions in premixed combustion are investigated using direct numerical simulations of twin turbulent V-flames for a range of turbulence intensities and length scales. Interactions are identified using a novel automatic feature extraction (AFE) technique, based on data registration using the dual-tree complex wavelet transform. Information on the time, position, and type of interactions, and their influence on the flame area is extracted using AFE. Characteristic length and time scales for the interactions are identified. The effect of interactions on the flame brush is quantified through a global stretch rate, defined as the sum of flamelet stretch and interaction stretch contributions. The effects of each interaction type are discussed. It is found that the magnitude of the fluctuations in flamelet and interaction stretch are comparable, and a qualitative sensitivity to turbulence length scale is found for one interaction type. Implications for modeling are discussed.

Journal ArticleDOI
TL;DR: In this paper, the formation of planar flames in preheated mesoscale channels of various divergent angles and aspect ratios is investigated. And the effect of various parameters such as channel aspect ratio, divergence angle, and heating rate on the formation and prediction of laminar burning velocity of various fuel-air mixtures at high temperatures are discussed.
Abstract: Flame stabilization studies of preheated mesoscale channels of various divergent angles and aspect ratios are reported in this article. Flame propagation modes such as planar flame and negatively and positively stretched flames were observed for a range of mixture flow rates and equivalence ratios. The present investigation is focused on the formation of the planar flames in these channels. The effect, of various parameters such as channel aspect ratio, divergence angle, and heating rate on the formation of planar flames and thereby on the prediction of laminar burning velocity of various fuel–air mixtures at high temperatures are discussed. Detailed investigations show that stretch-free planar flames can be stabilized in high-aspect-ratio channels with linear velocity and temperature gradient in the axial direction. Detailed numerical simulations confirm a negligible effect of heat loss on the burning velocity due to external preheating of the channel walls. Apparatus independence of the burning velocity...

Journal ArticleDOI
TL;DR: In this article, a comparison of several detailed kinetic models describing the ignition and combustion of hydrogen/air mixture in a supersonic flow is conducted, and the possible uncertainties in the rate constants of principle reactions responsible for the chain mechanism development in the H2/O2(air) mixture are inspected.
Abstract: Comparative analysis of the prediction ability of several modern detailed kinetic models describing the ignition and combustion of hydrogen/air mixture in a supersonic flow is conducted. The possible uncertainties in the rate constants of principle reactions responsible for the chain mechanism development in the H2/O2(air) mixture are inspected. Special attention is paid to matching the lengths of ignition and energy release zones and combustion completeness predicted by considered kinetic models in both one-dimensional homogeneous premixed flow and two-dimensional non-premixed flow in a scramjet model combustor. It is demonstrated that, while the difference in the induction zone length predicted by considered kinetic models does not exceed 30%, the discrepancy in the calculated values of energy release zone length may be as large as a factor of 4. As a consequence, different reaction mechanisms give distinguished magnitudes of combustion completeness at the combustor exit.

Journal ArticleDOI
TL;DR: In this article, a sol-gel combustion synthesis has been adopted by using sucrose as a fuel and nitric acid as an oxidizer to synthesize wollastonite.
Abstract: Wollastonite is a bioactive material (molecular formula of CaSiO3) that belongs to the class of calcium silicate. It is widely used as a bone regenerative material and as a drug delivery carrier due to its high bioactivity and biocompatibility. A novel sol-gel combustion synthesis has been adopted by using sucrose as a fuel and nitric acid as an oxidizer to synthesize wollastonite. Calcium nitrate and tetraethyl orthosilicate were taken as the source of calcium and silicate. The obtained powders were characterized by powder X-ray diffraction to check the phase formation and Fourier transform infrared (FT-IR) spectroscopy for the identification of the characteristic functional group. The average particle size calculated by using Scherer's formula is 51.7 nm, and the lattice parameter values are found to be a = 15.4301 A, b = 7.3242 A, and c = 7.017 A. The phase transformation studies were carried out by using a thermogravimetric analyzer. The morphology of the pure wollastonite was imaged by using scanning...

Journal ArticleDOI
TL;DR: In this article, the universal behavior of propagation rate variation with air superficial velocity (V-s) in a packed bed of a range of biomass particles in reverse downdraft mode was studied.
Abstract: This article aims at seeking the universal behavior of propagation rate variation with air superficial velocity (V-s) in a packed bed of a range of biomass particles in reverse downdraft mode while also resolving the differing and conflicting explanations in the literature. Toward this, measurements are made of exit gas composition, gas phase and condensed phase surface temperature (T-g and T-s), and reaction zone thickness for a number of biomass with a range of properties. Based on these data, two regimes are identified: gasificationvolatile oxidation accompanied by char reduction reactions up to 16 +/- 1cm/s of V-s and above this, and char oxidationsimultaneous char oxidation and gas phase combustion. In the gasification regime, the measured T-s is less than T-g; a surface heat balance incorporating a diffusion controlled model for flaming combustion gives and matches with the experimental results to within 5%. In the char oxidation regime, T-g and T-s are nearly equal and match with the equilibrium temperature at that equivalence ratio. Drawing from a recent study of the authors, the ash layer over the oxidizing char particle is shown to play a critical role in regulating the radiation heat transfer to fresh biomass in this regime and is shown to be crucial in explaining the observed propagation behavior. A simple model based on radiation-convection balance that tracks the temperature-time evolution of a fresh biomass particle is shown to support the universal behavior of the experimental data on reaction front propagation rate from earlier literature and the present work for biomass with ash content up to 10% and moisture fraction up to 10%. Upstream radiant heat transfer from the ash-laden hot char modulated by the air flow is shown to be the dominant feature of this model.

Journal ArticleDOI
TL;DR: In this article, the role of water vapor in the combustion process was investigated via simulating an opposed diffusion flame and a laminar premixed flame with pyrolysis gases as the fuel and air as the oxidizer.
Abstract: The role of water vapor, originated from the moisture content in vegetation, on the combustion process was investigated via simulating an opposed diffusion flame and a laminar premixed flame with pyrolysis gases as the fuel and air as the oxidizer. The fuel was mixed with water vapor, and the simulation was repeated for various water mole fractions. In both of the diffusion and premixed flames, the smaller the water mole fraction, the higher the maximum temperature. No reactions occurred when the water mole fraction was 0.65 or larger in the diffusion flame, and 0.70 or larger in the premixed flame. The maximum energy release rate and the flame speed decreased with the increase of the water mole fraction in the premixed flame. In both flames, O2 and H were the components that showed dramatic changes with the change of the water mole fraction.

Journal ArticleDOI
TL;DR: In this article, the impact of heat transfer between the flame and the flameholder on the dynamic stability characteristics of a 50-kW backward-facing step combustor was investigated, and it was shown that with the ceramic flameholder, the onset of instability is significantly delayed in time and, for certain operating conditions, disappears altogether.
Abstract: In this article, we investigate the impact of heat transfer between the flame and the flame-holder on the dynamic stability characteristics of a 50-kW backward-facing step combustor. We conducted a series of tests where two backward step blocks were used, made of ceramic and stainless steel, whose thermal conductivities are 1.06 and 12 W/m/K, respectively. Stability characteristics of the two flame-holder materials were examined using measurements of the dynamic pressure and flame chemiluminescence over a range of operating conditions. Results show that with the ceramic flameholder, the onset of instability is significantly delayed in time and, for certain operating conditions, disappears altogether, whereas with the higher conductivity material, the combustor becomes increasingly unstable over a range of operating conditions. We explain these trends using the heat flux through the flame-holder and the change in the burning velocity near the step wall. Results suggest a potential approach using low-therma...

Journal ArticleDOI
TL;DR: Experimental results obtained show that the KPCA method outperforms the traditional PCA in discriminating between the normal and abnormal combustion conditions, even in cases where the number of training samples is limited.
Abstract: This article presents a methodology for the diagnosis of abnormal conditions in a combustion process through flame imaging and kernel principal component analysis (KPCA). A digital imaging system is used to capture real-time flame images and radiation signals, from which flame characteristics such as flame area, brightness, non-uniformity, and oscillation frequency are quantified. These characteristics are used as the variables to establish the KPCA model of the combustion process. With the use of Hotelling's T2 and Q statistics, the monitoring of abnormal conditions of the combustion process is achieved. Unlike the traditional principal component analysis (PCA) method, the KPCA method is capable of dealing with nonlinear data via nonlinear mapping, which projects the original nonlinear input space into a high-dimensional linear feature space. The effectiveness of the methodology is demonstrated by applying the approach to processing the data obtained on a 9MWth heavy oil fired combustion test facility. E...

Journal ArticleDOI
TL;DR: In this paper, an n-heptane mechanism is combined with a detailed polyaromatic hydrocarbon (PAH) mechanism to simulate diesel spray combustion and emissions formation, and the mechanisms are validated against experimental data of ignition delays and flame speeds.
Abstract: Numerical modeling of soot formation and oxidation in diesel sprays was conducted using a multistep soot model coupled with reaction mechanisms for fuel oxidation and polyaromatic hydrocarbon (PAH) formation. As new combustion strategies such as low-temperature combustion emerge, the demand for accurate numerical models has also increased to predict the effects of subtle changes in the operating conditions on combustion and exhaust emissions. Accurate prediction of soot emissions from diesel engines remains challenging, particularly for low-temperature combustion conditions with massive exhaust gas recirculation. Soot emissions from the engine are highly sensitive to local temperature and chemical compositions. In this article, an n-heptane mechanism is combined with a detailed PAH mechanism to simulate diesel spray combustion and emissions formation. The mechanisms are validated against experimental data of ignition delays and flame speeds. The overall reaction mechanism consists of 68 species and 145 re...

Journal ArticleDOI
TL;DR: In this article, the response of bluff-body stabilized flames subjected to transverse acoustic waves was investigated at flow velocities of 50 and 100m/s with inlet air temperatures ranging from 475 to 750k.
Abstract: This article describes measurements of the response of bluff-body stabilized flames subjected to transverse acoustic waves. It is the first of a two-article series. The objective of this work was to extend prior studies of this nature to much higher Reynolds numbers and more severe environments that more closely mimic conditions encountered in applications. To this end, experiments were performed at flow velocities of 50 m/s and 100 m/s with inlet air temperatures ranging from 475–750 K. Two different modes of acoustic excitation were applied, corresponding to velocity and pressure nodes/antinodes along the combustor centerline. High-speed imaging and phase-locked particle image velocimetry (PIV) were used to characterize the spatio-temporal flame front and velocity field response. The data show that the disturbance field and the flame front response amplitude exhibit a nonmonotonic spatial distribution with interference patterns. The phase of the flame front response at the forcing frequency varies nearl...

Journal ArticleDOI
TL;DR: In this paper, the authors investigated the validity of corrections developed for methane to the combustion of other fuel classes (e.g., alcohols, unsaturated hydrocarbons, and aromatics), and proposed a methodological approach for the development of generic correlations.
Abstract: There is considerable interest in formulating practical correlations for the quantification of heat-release rate in flames via appropriate chemical markers, mainly due to difficulties in obtaining a direct estimation of the former Experimental and numerical studies performed in methane-air flames have identified corrections between suitable kinetic information and heat-release rate The present work investigates the validity of corrections developed for methane to the combustion of other fuel classes (eg, alcohols, unsaturated hydrocarbons, and aromatics), and proposes a methodological approach for the development of generic correlations Numerical assessment of such correlations and their underlying methodology is performed on the basis of experimental data from 24 laminar premixed flames, utilizing a single, in-house, recently published C1–C6 detailed chemical kinetic model It is shown that the proposed correlations are valid for methane-based fuels but they are largely inadequate for unsaturated fu

Journal ArticleDOI
TL;DR: In this article, a chemical kinetic mechanism for a three-component fuel composed of iso-octane/n-heptane/ethanol was developed, consisting of 51 species and 204 elementary reactions, and validated results show that the predictions using the present mechanism are in good agreement with the experimental ignition delay time and laminar flame speed.
Abstract: A chemical kinetic mechanism for a three-component fuel composed of iso-octane/n-heptane/ethanol has been developed. The mechanism consists of 51 species and 204 elementary reactions. Two elementary reactions that significantly affect laminar flame speed are subjected to sensitivity analysis. The validated results show that the predictions using the present mechanism are in good agreement with the experimental ignition delay time and laminar flame speed. Both the chemical reaction and the transportation process are accurately reproduced by the simulation using the present model in iso-octane/air premixed flames and in n-heptane/air counterflow partially premixed flames. The chemical kinetic mechanism is applicable to multidimensional computational fluid dynamics simulations of the combustion of gasoline surrogates or the cocombustion of primary reference fuels (PRF) with ethanol because of its smaller number of species and fewer reactions.

Journal ArticleDOI
TL;DR: The one-dimensional character of sooting premixed porous-plug (McKenna) burner flames has been examined in this paper, motivated by recent investigations where the one-dimensionality has been questioned.
Abstract: The one-dimensional character of sooting premixed porous-plug (McKenna) burner flames has been examined, motivated by recent investigations where the one-dimensionality has been questioned. The examination employs laser diagnostic techniques to measure different characteristics: temperature using rotational coherent anti-Stokes Raman spectroscopy (CARS) and soot properties using laser-induced incandescence and elastic light scattering. Special attention has been paid to the influence of an outer shroud gas flow of either nitrogen or air. The nitrogen shroud gas leads to flame cooling at the outer edge, whereas the air shroud results in heating through the oxidation of CO/H2/soot. This generally results in a more inhomogeneous spatial particle size profile for the nitrogen shroud flame, with smaller particle sizes at the flame edge. The present results emphasize the need to characterize burner and operating conditions accurately, and also, regarding parameters that at first glance seem less relevant, such ...

Journal ArticleDOI
TL;DR: In this paper, the authors describe thermochemical properties and ignition characteristics of pyrotechnic compositions consisting of TiH2+KClO3, TiH 2+KCLO4, andTiH 2−+Ba(NO3)2.
Abstract: This study describes thermochemical properties and ignition characteristics of pyrotechnic compositions consisting of TiH2 + KClO3, TiH2 + KClO4, and TiH2 + Ba(NO3)2, where titanium hydride is used as fuel and KClO3, KClO4, and Ba(NO3)2 act as oxidants. Differential thermal analysis (DTA) and thermogravimetry (TG) techniques have been employed to elucidate the reaction process of these pyrotechnic systems. TG/DTA analysis of pure titanium hydride indicates that this compound decomposes at 535 °C. By replacing KClO3 with KClO4 as oxidizer in a titanium hydride–fueled mixture, the sensitivity of the mixture decreases. A TiH2 + KClO3 pyrotechnic mixture has a fusion temperature around 358 °C and ignition temperature around 472 °C. A TiH2 + KClO4 pyrotechnic system decomposes at 541.5 °C. However, replacing KClO4 with Ba(NO3)2 in this mixture, increases the ignition temperature of the mixture by at least 30 °C to ∼ 570 °C, which is a safe temperature for preventing activation of the mixture by accidental fact...

Journal ArticleDOI
TL;DR: In this article, a two-zone combustion model was used to study the effect of air-fuel ratio (AFR) on the temporal variation of charged species concentration in a spark-ignited methane/air mixture using the equilibrium constant method.
Abstract: Identifying charged species and their relative concentrations as a function of initial mixture composition, temperature, and pressure can play an important role in the diagnostics and control of combustion devices. This article aims to identify important charged species and their temporal variation in a spark-ignited methane/air mixture using the equilibrium constant method. The equilibrium composition of 20 neutral and seven charged species [(e−), CHO+, H3O+, NO+, OH−, , O−] was obtained using a novel adaptation of the Newton–Raphson method for highly stiff nonlinear system of equations. A two-zone combustion model was used to study the effect of air–fuel ratio (AFR) on the temporal variation of charged species concentration. Temporal variation of the current computed from the equilibrium concentration of charged species was found to compare well with experimental data for several AFRs.