140 research outputs found
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Measurements of the structure of turbulent premixed and stratified methane/air flames
No full textThe influence of stratification on the structure of turbulent methane/air combustion is investigated using experimental data from laboratory scale burners: a weakly turbulent slot burner, and a higher turbulence co-annular swirl burner. The degree of stratification can be controlled independently of the overall fuel/air flow rate. The resulting measurements of scalar and velocity fields provide detailed test cases for existing and emerging turbulent flame models, covering a range of u'/sL from 1 to 10, turbulence intensities from 5% to 60%, and stratification ratios from 1 to 3.
Simultaneous Rayleigh/Raman/CO-LIF measurements of temperature and major species concentrations - CH4, CO2, CO, H2, H2O and O2 - along a line are used to investigate the structure of a series of flames in both the slot and swirl burners. Concurrent cross-planar OH-PLIF allows thermal gradients to be angle corrected to their three-dimensional values. Finally, non-reacting and reacting velocity fields complete the flame database.
The behavior of major species concentrations in the slot and swirl burner with respect to temperature is found to agree well on the mean with unstrained premixed laminar flame calculations. Scalar means conditioned on stoichiometry also show good agreement, aside from hydrogen which is enhanced under stratified conditions. Surface density function and scalar dissipation are lower than calculated values in all cases, suggesting that turbulence-induced thickening dominates the effect of increased strain.
Metrics commonly used to derive flame surface density (FSD) were investigated. FSD may be determined using a statistical method based on measurements of temperature and its gradient, or a geometric method based on 2D temperature or LIF imaging. A third metric, an extension of the geometric method, is proposed. Good agreement is observed between the three metrics.
The current database provides the first detailed high resolution scalar measurements for premixed and stratified flames. The data analysis provides insight into the physics of stratification: for the flames considered, the effects of stratification appear to be surprisingly small compared to those of turbulence, even at significant stratification ratios. The datasets provide a means of validating current and future computational turbulent combustion models
Fuel Distribution and Combustion Characteristics in a Direct-Injection, Spark-Ignited (DISI) Engine Under Stratified Operation
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Optical Diagnostic Equipment for Research on Critical Processes in Spark-Ignition Engines
No full textThe equipment requested under grant Contract No. DE-FG02-95TE00065 was used in several projects investigating the behavior of fuel in spark-ignition engines. It has been a crucial piece of these efforts in understanding how new direct-injected engine sprays behave, as well as a key part in the determination of how liquid fuel enters the engine during port-fuel injection
Explosion hazards of aluminum finishing operations
No full textMetal dust deflagrations have become increasingly common in recent years. They are also more devastating than deflagrations involving organic materials, owing to metals' higher heat of combustion, rate of pressure rise, explosion pressure and flame temperature. Aluminum finishing operations offer a particularly significant hazard from the very small and reactive aluminum particles generated, and thus require high attention to details of operation and explosion safety management. This paper presents available statistics on metal dust explosions and studies the specific explosion hazards of aluminum finishing operations. The analysis of seven case studies shows that the proper design, monitoring and maintenance of dust collection systems are particularly important. Furthermore, the isolation of deflagrations occurring in dust collection systems, as well as good housekeeping practices in buildings, are critical safeguards to avoid the occurrence of catastrophic secondary explosions.Fluid MechanicsChemE/Delft Ingenious Desig
Liquid Fuel Impingement on the Piston Bowl of a Direct-Injection, Spark-Ignited (DISI) Engine under Stratified Operation
No full textGas phase Raman spectroscopy: Comparison of continuous wave and cavity based methods
No full text© 2018 The Author(s). Comparison of cavity-enhanced Raman spectroscopy to continuous wave detection for gas phase molecules in air. We show continuous measurements with calculated emission and discuss the potential benefits (two orders more signal) of using a cavity
Measurements of laminar flame speeds of liquid fuels: Jet-A1, diesel, palm methyl esters and blends using particle imaging velocimetry (PIV)
No full textLaminar flame speeds of practical fuels including Jet-A1, diesel, palm methyl esters (PME) and blends of PME with diesel and Jet-A1 fuels are determined using the jet-wall stagnation flame configuration and particle imaging velocimetry (PIV) technique. The PME/Jet-A1 and PME/diesel blends are prepared by mixing 10%, 20% and 50% of PME with Jet-A1 and diesel fuels by volume respectively. The experiments are performed over a range of stoichiometries at elevated temperature of 470 K and atmospheric pressure under premixed conditions. The reference flame speed and imposed strain rates are determined from the two dimensional velocity profiles. Subsequently, laminar flame speeds are derived by extrapolating the reference flame speed back to zero strain rates. Experimental results are compared to experimental and simulation data from the literature for large n-alkanes and practical fuels. The results show that laminar flame speeds of Jet-A1 fuel are similar to those of n-decane and n-dodecane, indicating their potential use as surrogate fuels. Peak laminar flame speeds for diesel/air and PME/air mixtures at 470 K are similar, around 86.7 and 86.5 cm/s at equivalence ratios around 1.10 and 1.14 respectively, and that both mixtures exhibit lower flame speeds compared to n-decane and n-dodecane at fuel-leaner and stoichiometric conditions. Blending PME with Jet-A1 and diesel leads to reduced laminar flame speeds on the lean side but increased on the rich side
The effects of fuel volatility and operating conditions on sprays from pressure-swirl fuel injectors
No full textThesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 1999."June 1999."Includes bibliographical references (p. 205-208).Optimal design of modern direct injection gasoline engines depends heavily on the fuel spray. Most of the studies published regarding these fuel sprays involve cold bench tests or motored optical engines, neglecting the roles of the fuel volatility and temperature. This study, therefore, was designed to describe changes in the spray properties due to fuel volatility and operating conditions using a firing optically-accessible engine. Planar laser-induced fluorescence and planar Mie scattering imaging experiments were performed to show changes in the spray structure, including its radial and axial penetration. Phase-Doppler particle analysis experiments were included to track the droplet diameter and velocity at various points throughout the spray. A computational fluid dynamics model was also used to study the physics leading to the observed changes. The results show that the spray structure changes with not only ambient gas density, which is often measured, but also fuel temperature and volatility. The mean droplet diameter was found to decrease substantially with increasing fuel temperature and decreasing ambient density. Under conditions of low potential for vaporization, the observed trends agree with published correlations for pressure-swirl atomizers. As ambient density decreases and fuel temperature increases, the volatile ends of multi-component fuels evaporate quickly, producing a vapor core along the axis of the spray. Beyond a certain point, evaporation is violent enough to cause additional breakup of the droplets. A fit to this volatility-induced breakup data provides an additional correlation for determining the mean diameter of volatile sprays. Coincident with the volatility-induced breakup trend is an increase in the initial cone angle of the spray. However, the reduced droplet diameter and rapid vapor generation under these superheated conditions result in a narrow spray with increased axial penetration. In the process of performing these experiments, insights were found regarding the operation of these diagnostics in high-density sprays.by Brad A. VanDerWege.Ph.D
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