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In the work, the combustion regimes of iron particles (d10 = 4.7 µm) in a laminar pre-mixed flame (LPF) and in an axisymmetric laminar diffusion flame (LDF) are studied. For (LPF), we studied the effect of variations in gas suspension of the concentrations of fuel Cf = 0.4 ÷ 0.6 kg/m3 and oxygen CO2 = 21 ÷ 40%, and for (LDF), pure oxygen blowing and variation in the iron concentration Cf = 0.4 ÷ 1.5 kg/m3. The results of particle temperature measurements in the combustion zone of LPF and LDF, the dispersed and phase composition of the combustion products (depending on the concentration of fuel and oxidizer) are presented. It is shown that, under certain conditions, iron particles in LPF switch to a "high-temperature" diffusion mode of combustion. This mode is accompanied by intensification of gas-phase reactions and leads to a two-mode particle size distribution of combustion products. In this mode of combustion of a gas suspension (at temperatures much lower than the boiling point of iron), the mass yield of a nanoscale fraction of combustion products reaches tens of percent and increases with increasing oxygen concentration in LPF. This mode of iron particles combustion was not observed in LDF. The features of the thermal structure of the diffusion dust flame are analyzed. It is shown that in LDF the burning time of metal particles in the diffusion mode is proportional to the particle radius r p ( \~ r p in the kinetic mode), and should depend on the concentration of fuel and the size of the burner. [ABSTRACT FROM AUTHOR]

Attempts were made to reproduce the laboratory measurements of flameless combustion systems using numerical simulation tools, for different chambers designs. In many cases, a significant discrepancy is reported between the experimental measurements and the numerical results. In this work, we have successfully reproduced the reported experimental results (velocity field, temperature field, and the outlet dry NOx emissions) of the "FOUR" MILD combustion facility (proposed by C. Rottier). An acceptable accuracy was achieved in two reference test cases. A concise discussion is presented on the available literature on the subject of numerical modeling for the flameless combustion mode. The use of two turbulence models was explored (standard k-ε, and modified k-ε), along with two kinetic mechanisms (a global 2-step CH4 combustion mechanism, and the more detailed KEE-58 mechanism). The commercial ANSYS FLUENT® software was used in these simulations. The results of seven different modeling setups are presented, comparing the predictions of temperature fields, and NOX emissions. Features such as the onset of premature ignition and the reactants entrainment ratio are also discussed. Our results show that the most accurate model setup employs the following: SKE – KEE-58 – EDC with a reduced volume fraction constant. In regards to reproducing the measurements from the "FOUR" facility, we are not aware of a similar research that runs a concise discussion on the predictions of such broad and different modeling setups. [ABSTRACT FROM AUTHOR]

This paper presents experimental results of the effects of CO2 and H2O dilution on CH4-air flames enriched by oxygen. The study focuses on pollutant emissions, flame stability through the determination of liftoff heights and flow fields by LDV measurements. Different parameters of the burner are studied such as the swirl number, the global equivalence ratio, and the fractions of O2, H2O, and CO2 in the mixture. The fraction of diluents varies from 0% to 20%, O2 enrichment from 21% to 30% (in vol.), and the swirl number from 0.8 to 1.4. The experiments are carried out on a coaxial swirled burner placed in a vertical combustion chamber. The flame is visualized by the chemiluminescence technique on OH* in order to locate the flame front. Measurements of combustion products such as NOx, CO, and CO2 are done using a HORIBA PG250 multi-gas analyzer. Flow fields are measured by LDV measurement for the longitudinal velocity component and its fluctuations. Results show that the CO2 and H2O dilution influences significantly the flame characteristics. With dilution the liftoff height increases but the flame remains stabilized. With O2 enrichment the liftoff height decreases and flame stability is enhanced. If we therefore want to dilute more, we should enrich with oxygen. The increase of dilution rate induces a decrease in NOx emission and exhaust gas temperature and an increase in CO emissions. LDV measurements showed the longitudinal velocity distribution of flow and its fluctuations in reactive and non-reactive conditions. Note that the presence of the flame induces an increase in the longitudinal velocity downstream of the flow due to the expansion of gases. [ABSTRACT FROM AUTHOR]

The frontal propagation of smolder combustion of thin solid fuel in airflow in a narrow channel is considered. It is shown that the governing process that determines the propagation of the smolder combustion front is the diffusion of oxygen in flow and its absorption by the front. A two-dimensional thermodiffusion model of propagation of the smolder combustion front is considered and the equations describing the front propagation have been obtained. The solution of the equations was obtained in general form that allows constructing an algorithm for the numerical simulation. The stability of the planar smolder combustion front is investigated. It is shown that diffusion of oxygen and thermal conductivity in airflow are competing processes and can play either a stabilizing or destabilizing role depending on the mutual direction of airflow and the propagation of the smoldering front. So, if airflow occurs against the propagating smoldering front, the diffusion of oxygen in airflow plays a destabilizing role while the thermal conductivity is a stabilizing factor. If, however, airflow and the propagation of the smoldering front occur in the same direction, the phenomenon will be reversed. The diffusion of oxygen in airflow is a stabilizing factor while the thermal conductivity plays a destabilizing role. [ABSTRACT FROM AUTHOR]

A method and application of measuring the soot volume fraction, H2O concentration, and its temperature simultaneously in an ethylene/air premixed flame environment based on tunable diode laser absorption spectroscopy technique is presented in this article. Only one distributed feedback diode laser with a center wavelength at 1397.83 nm combined with a scanned-wavelength direct absorption spectroscopy technique was used during measurements. The attenuation of laser intensity caused by soot extinction and H2O gas absorption after transmitting through the flame region was detected and distinguished, respectively. Soot volume faction was inferred from the light extinction with Rayleigh limit assumption. The absorption signals of two H2O spectral lines were acquired during one scanning, thus both the H2O concentration and its temperature can be retrieved. Measurements have been taken in ethylene/air premixed flat flames on a standard bronze McKenna burner at different cold-gas velocities (5.9 cm/s and 4.4 cm/s) and equivalence ratios (φ= 2.3, 2.1, and 1.9). The gradient tendencies of soot volume fraction, H2O concentration, and temperature along the vertical direction and the variations in different flames were well demonstrated. The results were in good agreement with the values measured using other techniques and studies. The proposed method is proved to be suitable and accurate for measuring oot volume fraction together with gas concentration and temperature. This multipurpose measuring method with high accuracy exhibits great potential in combustion diagnostics and soot study. [ABSTRACT FROM AUTHOR]

Measuring and monitoring the cylinder pressure in relation to the instantaneous cylinder volume allows the engineer to gain a great deal of information about the quality and efficiency of the energy conversion process taking place inside the cylinder. Many useful metrics can be derived or extracted from the pressure curve and these parameters are well established. This article forms the basis to propose a set of basic combustion data metrics that can be used to establish the quality of measured data. The proposed indicators can be used to establish fitness for purpose of the proposed system set-up for various measurement applications, prior to undertaking the critical measurement task. In addition, these metrics can be used or monitored during system run time, to ensure consistent data quality throughout short- or long-term test procedures, in addition to allowing identification of measurement drift or step change factors that could affect data quality over time. This article shows the application of DoE-based testing and a model-based approach in order to establish the response of newly developed metrics when stimulated with target error variations. The output could be used to understand the variation and interactions of the newly developed metrics, and also to understand if they would be usable for the application suggested. It was found that not all of the results that were tested could be utilized, but the test and measurement environment, plus the unique application of model-based testing, facilitated an efficient working environment to support future development work. [ABSTRACT FROM AUTHOR]

The behavior of the early phase of combustion in spark-ignition (SI) engines is very crucial, since cycle-by-cycle dispersion in combustion, and hence pressure development, originates during this phase. A fundamental experimental study has been undertaken to understand and establish the behavior of early quasisteady premixed laminar flames, or generally called, early flames that exist in practical SI engines. A new, specially designed, closed-volume, spherical vessel test cell with central ignition and optical access was designed, built, and used to undertake experimental measurements for laminar premixed flame growth. A novel multiple-zones mathematical model was implemented to develop a new method for calculating the key properties of early flame behavior inside a closed vessel. Laminar premixed combustion experiments were undertaken to measure, quantify, and decouple the effects of initial fuel mixture equivalence ratio (φ = 0.8to φ = 1.4), pressure (0.5 bar, 1 bar, 2 bars, and 3.5 bars), and temperature (298 K and 425 K) on the key characteristics of early laminar flame kernel such as timing (t) and rate of change of first 5% mass fraction burned (MFB –X5%), flame radius (Rf), flame growth rate (dRf/dt), laminar burning velocity (Su), flame stretch (α), flame cellularity, and unburned gas temperature and pressure. The study showed that the timings ofX5%and the rate of mass fraction burned (dX/dt) had been significantly affected by the variation in equivalence ratio, initial temperature, and pressure. Flame stretch rates during early flame growth were very high but were found to decline nonlinearly to lower, steadier values afterRf > 2.5 cm. The onset of cellularity or autoturbulence was found to trigger at a critical radius (Rfcr) in the laminar premixed flames causing rapid increase in itsSuanddRf/dt. [ABSTRACT FROM AUTHOR]

Focuses on a study related to the dependence of magnetically induced change in OH distribution in a methane-air premixed flame on equivalence ratio. Significance of combustion control by magnetic field; Utility of planar laser-induced fluorescence measurements; Change in OH fluorescence intensity distribution.