A Review of Fundamental Studies Relevant to Flame Lift-off in Diesel Jets

Venugopal, Rishikesh; Abraham, John

doi:10.4271/2007-01-0134

Cited by 38 publications

(21 citation statements)

References 11 publications

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“…Since the stoichiometric mixture fraction is higher for oxygenated fuels, the flame position is expected to occur closer to the center of the fuel jet [17], and the flame length will also be less [18]. With the flame closer to the center of the fuel jet there is still limited information in the literature that quantifies LOL's for reacting biodiesel sprays and the mechanisms governing the lift-off stabilization are still unclear to make good predictions [19]. Limited reports, such as [20], have shown biodiesel to have a longer LOL F o r P e e r R e v i e w 3 than a conventional European diesel for a large range of charge-gas (ambient) temperatures, but there is still not a widespread conclusion on the LOL behavior of biodiesel.…”

Section: Introductionmentioning

confidence: 99%

Fundamental spray and combustion measurements of soy methyl-ester biodiesel

Nerva

Genzale

Kook

et al. 2012

International Journal of Engine Research

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Nerva, J.; Genzale, CL.; Kook, S.; García Oliver, JM.; Pickett, LM. (2013) soy methyl-ester biodiesel is injected into a constant-volume combustion facility. A range of optical diagnostics is performed, comparing biodiesel to a conventional #2 diesel at the same injection and ambient conditions. Schlieren imaging shows virtually the same vapor-phase penetration for the two fuels, while simultaneous Mie-scatter imaging shows that the maximum liquid-phase penetration of biodiesel is higher than diesel due to their different boiling-point temperatures. But the different liquid-phase penetration does not affect overall mixing rate and downstream vapor-phase penetration because each fuel spray has similar momentum and spreading angle. The ignition delay and lift-off length are only slightly less for biodiesel compared to diesel, consistent with the CN. Because of the similarity in lift-off length, the differences in equivalence ratio distribution at the lift-off length are mainly affected by the fuels oxygen content. For biodiesel, the equivalence ratio is reduced, which, along with the fuel molecular structure and oxygen content, significantly affects soot formation downstream. Spatially-resolved soot volume fraction measurements obtained by combining laser extinction measurements with planar laser-induced incandescence imaging show that the soot concentration can be reduced by an order of magnitude for biodiesel. These integrated measurements of spray mixing, combustion, and quantitative soot concentration provide new validation data for the development of CFD spray, combustion, and soot formation models suitable for the latest biofuels. AbstractThough biodiesel has begun to penetrate the fuel market, its effect on injection processes, combustion, and emissions formation under diesel engine conditions remains somewhat unclear. Typical tailpipe measurements from engines running biodiesel indicate that PM, CO and UHC are decreased, whereas NO X emissions tend to be increased. However, these observations are the result of complex interactions between physical and chemical processes occurring in the combustion chamber, for which understanding is still needed.To characterize and decouple the physical and chemical influences of biodiesel on spray mixing, ignition, combustion and soot formation, a soy methyl-ester biodiesel is injected into a constant-volume combustion facility under diesel-like operating conditions. A range of optical diagnostics is performed, comparing biodiesel to a conventional #2 diesel at the same injection and ambient conditions.Schlieren high-speed imaging shows virtually the same vapor-phase penetration for the two fuels, while simultaneous Mie-scatter imaging shows that the maximum liquid-phase penetration of biodiesel is higher than diesel. Differences in the liquid-phase penetration are expected because of the different boiling-point temperatures of the two fuels. But the different liquid-phase penetration does not affect overall mixing rate and downstream vapor-phase penetration because each...

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Section: Introductionmentioning

confidence: 99%

Fundamental spray and combustion measurements of soy methyl-ester biodiesel

Nerva

Genzale

Kook

et al. 2012

International Journal of Engine Research

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“…Hence, understanding lift-off, and the development of predictive computational tools for diesel jet flames are important. Recent attempts in literature 3 to numerically predict diesel flame lift-off with conventional Reynolds-averaged Navier-Stokes ͑RANS͒-based modeling approaches, such as steady diffusion flamelets 4 and perfectly stirred reactors 5 have met with only limited success. RANS models are also inadequate in reproducing the mixing and entrainment characteristics in the jet-near-field region where lift-off occurs.…”

Section: Recent Experimentsmentioning

confidence: 99%

Numerical studies of vortex-induced extinction/reignition relevant to the near-field of high-Reynolds number jets

Venugopal

Abraham

2009

Physics of Fluids

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This work is motivated by the need to understand physical mechanisms governing near-field phenomena, such as flame lift-off, in high-Reynolds number jet flames. Numerical studies of vortex-induced flame extinction/reignition are performed for conditions representative of the near field of high-Reynolds number ͑ϳ100 000͒ jets under high pressure and temperature conditions. The governing equations for compressible, viscous, and reacting flows are solved along with a single-step irreversible chemical kinetic model for gaseous n-heptane oxidation. Extinction/ reignition phenomena, influenced by unsteady and curvature effects, are observed. Unsteady flamelet/progress variable models are shown to accurately describe the flame response during extinction/reignition observed in the flame-vortex studies. Furthermore, while unsteady effects on extinction/reignition are found to diminish with weaker vortices and relatively strong flames, curvature effects are found to increase with relatively thicker flames. The observed flame-vortex interaction regimes are summarized on an outcome diagram, which is useful to understand the nature of localized flame dynamics in the near field of jet flames.

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“…Different modeling approaches were addressed to compute the diesel lift-off length [11][12][13][14][15][16][17][18][19][20], as was mentioned earlier. In this paper, the lift-off length is modeled based on flame surface density and the flame extinction concept.…”

Section: Flame Lift-off Length Modelingmentioning

confidence: 99%

“…Lehtiniemi et al [13] modeled the lift-off length using detailed chemistry and the progress variable approach. Venugopal and Abraham [14,15] modeled the lift-off length and correlated it with flame extinction. For the range of conditions explored, adequate agreement was obtained between the numerical results and the measurements for varying injection pressures, ambient densities, ambient temperatures and ambient O 2 concentrations.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the Flame Lift-off Length in Diesel Spray Combustion Based on Flame Extinction

Azimov

Kawahara

Tomita

et al. 2010

JTST

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The interaction of spray and combustion processes forms a complex system of physical phenomena undergoing in IC engines. Studying this interaction is important to determine strategies for simultaneously reducing soot and NOx emissions from diesel engines. Spray combustion interactions are evaluated by the flame lift-off length -the distance from the injector orifice to the location of hydroxyl luminescence closest to the injector in the flame jet. Various works have been dedicated to successful simulations of lifted flames of a diesel jet by use of various combustion modeling approaches. In this work, flame surface density and flamelet concepts were used to model the diesel lift-off length. Numerical studies have been performed with the ECFM3Z model and n-Heptane fuel to determine the flame lift-off length under quiescent conditions. The numerical results showed good agreement with experimental data, which were obtained from an optically accessible constant volume chamber and presented at the Engine Combustion Network (ECN) of Sandia National Laboratories. It was shown that at a certain distance downstream from the injector orifice, stoichiometric scalar dissipation rate matched the extinction scalar dissipation rate. This computed extinction scalar dissipation rate correlated well with the flame lift-off length. For the range of conditions investigated, adequate quantitative agreement was obtained with the experimental measurements of lift-off length under various ambient gas O 2 concentrations and ambient gas densities.

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A Review of Fundamental Studies Relevant to Flame Lift-off in Diesel Jets

Cited by 38 publications

References 11 publications

Fundamental spray and combustion measurements of soy methyl-ester biodiesel

Fundamental spray and combustion measurements of soy methyl-ester biodiesel

Numerical studies of vortex-induced extinction/reignition relevant to the near-field of high-Reynolds number jets

Evaluation of the Flame Lift-off Length in Diesel Spray Combustion Based on Flame Extinction

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