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Combustion of NG + H2 fuel mixtures in a non-premixed swirl burner with radial fuel injection
No full textExperimental analysis of the precessing vortex core in a free swirling jet
No full textAn experimental analysis of the Precessing Vortex Core (PVC) instability in a free swirling jet of air at ambient pressure and temperature is performed by means of Laser Doppler velocimetry (LDV) and Particle Image Velocimetry (PIV). Two parametric studies are considered, varying the swirl parameter and the Reynolds number. The range of parameters considered allowed to study conditions
of strong precession as well as the inception and settlement
of the instability. Mean velocity and standard deviation pro files, power spectral density functions and probability density functions for the axial and tangential velocity components are presented. Average as well as instantaneous PIV maps are considered in the characterization of the flowfield structure and detection of the instantaneous position of the vortex center. Joint analysis of velocity PDFs and power spectra shows that the PVC contribution to the global statistics of the velocity field can be properly separated from the
contribution of the true flow turbulence, giving additional
insight to the physics of the precession phenomenon. The
results obtained in the explored range of conditions indicate that the true turbulence intensity is not dependent on
the swirl parameter
Thermal and chemical efficiencies of a meso-scale combustor for propulsive or power generation systems
No full textAnalysis of hydrogen enriched flames by laser diagnostics
No full textThe flame structure and flow field modifications induced in a confined lean non-premixed natural gas swirled flame by hydrogen addition were experimentally investigated using non-intrusive laser based diagnostic techniques: PIV and LDV were used for a comprehensive analysis of the velocity field and
the Rayleigh scattering technique for the local temperature distribution. Measurements were performed on a straight exit laboratory burner with no quarl cone; the flame was stabilized at the end of two concentric pipes with the annulus supplying swirled air and the central pipe delivering the fuel. In order to improve the mixing between reactants, the fuel mixture was injected transversally toward the swirling air flow.
Experiments were carried out at varying hydrogen content in the range 0% - 100% of the total volumetric fuel flow rate. The analysis of vorticity maps and velocity PDFs underlined that in the region located between the Central Toroidal Recirculation Zone (CTRZ) and the Corner Recirculation Zone (CRZ) took place an intense mixing process between reactants coming from the burner outlet and hot products from recirculation zones. Also temperature PDFs analysis revealed bimodal distributions in the same regions. Considering each bimodal
distribution as the overlap of two distinct Gaussian distributions, it was possible to evaluate the temperature of each stream in the mixing layer and to characterized the mixing process
Characterization of Pollutant Emissions in Diffusion and Premixed Natural Gas Burners
No full textThis paper describes the measurement of pollutant emissions (nitric oxides and carbon monoxide) in different natural gas burners: particularly, a swirl burner with different fuel injection typologies (co-axial and radial injection, with respect to the rotating air stream) and a premixed burner have been taken into account. As for the premixed burner, pollutant emissions have been related with thermal characterization of the reactant zone performed by
thin thermocouples. In this case, a strong correlation with temperature and equivalence ratio has been observed. At the contrary, the swirl burner presents a strict dependence from the value of the air stream swirl number, which plays an important role for flame stabilization and fluid dynamic mixing process in the primary flame zone. Moreover, the radial injector in the swirl burner contributes to a general decrease of pollutant emissions, behaving similarly to the premixed burner, also as for the trend of CO and NOx emissions versus the equivalence
ratio
Stability and Combustion Efficiency of a Meso-Scale Combustor Burning Different Hydrocarbon Fuels
No full textIn the last decade the interest in the development of meso-scale combustors (i.e. combustor having a characteristic dimension of the order of the quenching diameter) has grown due the
interest in the development of portable power generation systems and small scale propulsion systems. Micro systems based on combustion are appealing because energy density of liquid
hydrocarbons fuels is much higher than those of currently available top chemical batteries (~40-45 MJ/kg vs. ~1.2 MJ/kg). Moreover macro systems based on combustion show high
reliability and efficiency, thus their miniaturization offers the potential to realize very efficient micro systems. Nevertheless when dealing with combustion at such small scale, problems related to heat losses, residence time and mixing became increasingly important and they will significantly affect the combustor performances. The objective of the present work is to experimentally investigate stability limits, efficiencies
and pollutant emissions of a meso scale swirl combustor when burning different hydrocarbon fuels (methane, propane and butane)
Advanced sequential dual evaporator domestic refrigerator/freezer: System energy optimization
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Near field flow structure of isothermal swirling flows and reacting non-premixed swirling flames
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