Diesel fuel jet lift-off stabilization in the presence of laser-induced plasma ignition

Pickett, Lyle M.; Kook, Sanghoon; Persson, Helena; Andersson, Öivind

doi:10.1016/j.proci.2008.06.082

Cited by 99 publications

(65 citation statements)

References 16 publications

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“…Up until 1.6 ms aSOI, the lift-off location steadily progresses downstream, although evidently much slower compared to the local spray velocities. This observation is consistent with results by Pickett et al [37], where forced laser ignition was used to decrease the liftoff length.…”

Section: Second Injectionsupporting

confidence: 93%

Transient Flame Development in a Constant-Volume Vessel Using a Split-Scheme Injection Strategy

Maes

Bakker

Dam

et al. 2017

SAE Int. J. Fuels Lubr.

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Multiple-injection strategies are characterized by a complex and transient interplay between high-and low-temperature reactions. Tracking low-temperature reaction products such as formaldehyde (CH2O) is particularly important to understand ignition phenomena and the so-called "combustion recession" that is observed in experiments. Experimentally, it is often difficult to discriminate between formaldehyde and other species such as poly-aromatic hydrocarbons, which is why a selective excitation approach is used in this work. Simultaneous high-speed imaging of the chemicallyexcited hydroxyl radical (OH*) is used to improve indication of flame location and second stage ignition. During experiments in a constant-volume vessel, two 0.5-ms injections of n-dodecane, separated by 0.5-ms dwell time, are injected into a 900-K ambient. The global flame development is characterized based on high-speed diagnostics, followed by an investigation into the spatial distribution of formaldehyde at four different times after start-of-injection (aSOI). Results show significant influence of the first injection on characteristics of the second. Ignition delay and lift-off location of the second injection are prominently reduced, while flame penetration is greatly enhanced by the wake of the first injection. Formaldehyde structure is observed during both end-of-injection transients, reaching as far upstream as 6 mm from the nozzle. Even after the second injection, the flame structure still appears to be influenced by the first, with a shorter lift-off length and compressed formaldehyde structure. Based on the selective excitation procedure, it becomes clear that the interpretation of laser-induced fluorescence (LIF) images obtained by 355-nm excitation alone is prone to ambiguity.

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Section: Second Injectionsupporting

confidence: 93%

Transient Flame Development in a Constant-Volume Vessel Using a Split-Scheme Injection Strategy

Maes

Bakker

Dam

et al. 2017

SAE Int. J. Fuels Lubr.

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“…Dashed lines on this figure are the experimental values of lift-off length for two different fuel injection pressures. The results are in good agreement with those from other researchers who experimentally showed that a flame remains lifted at a fixed location during the entire steadystate combustion process (Pickett et al, 2005;Pauls et al, 2007;Idicheria and Pickett, 2007;Pickett et al, 2009). However, both LES and RANS underpredicted the lift-off length at the temperature 1600 K and overpredicted it at the temperature 2200 K.…”

Section: Air Entrainment and Mixingsupporting

confidence: 91%

Large-eddy simulation of air entrainment during diesel spray combustion with multi-dimensional CFD

Azimov

Kim

2011

Int.J Automot. Technol.

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Large-Eddy Simulation (LES) was used to perform computations of air entrainment and mixing during diesel spray combustion. The results of this simulation were compared with those of Reynolds Averaged Navier Stokes (RANS) simulations and an experiment. The effect of LES on non-vaporizing and vaporizing sprays was evaluated. The validity of the grid size used for the LES analysis was confirmed by determining the subgrid-scale (SGS) filter threshold on the turbulent energy spectrum plot, which separates a resolved range from a modeled one. The results showed that more air was entrained into the jet with decreasing ambient gas temperatures. The mass of the evaporated fuel increased with increasing ambient gas temperatures, as did the mixture fraction variance, showing a greater spread in the profile at an ambient gas temperature of 920 K than at 820 K. Flame lift-off length sensitivity was analyzed based on the location of the flame temperature iso-line. The results showed that for the flame temperature iso-line of 2000 o C, the computed lift-off length values in RANS matched the experimental values well, whereas in LES, the computed lift-off length was slightly underpredicted. The apparent heat release rate (AHRR) computed by the LES approach showed good agreement with the experiment, and it provided an accurate prediction of the ignition delay; however, the ignition delay computed by the RANS was underpredicted. Finally, the relationships between the entrained air quantity and mixture fraction distribution as well as soot formation in the jet were observed. As more air was entrained into the jet, the amount of air-fuel premixing that occurred prior to the initial combustion zone increased, upstream of the lift-off length, and therefore, the soot formation downstream of the flame decreased.

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“…Pickett et al in [33] observed that the assumed quasi-steady state of the flame is somehow contradictory with the fact that the injection history may change the lift-off length during the injection, moving the final lift-off length location upstream from the first auto-ignited region. In fact, when the ignition is induced by plasma generation on the upstream region [38], tests showed a very long time period (> 10ms) to reach the same lift-off observed in a natural ignition test. Furthermore, there are some indications that nozzles used by the ECN community (like the one used in this experiments [28]) have a needle that oscillates [39].…”

Section: Figure 9 Oh Images and Instantaneous Schlieren Contours (Yementioning

confidence: 60%

Schlieren Methodology for the Analysis of Transient Diesel Flame Evolution

Pastor¹,

Payri²,

García-Oliver³

et al. 2013

SAE Int. J. Engines

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Schlieren/shadowgraphy has been adopted in the combustion research as a standard technique for tip penetration analysis of sprays under diesel-like engine conditions. When dealing with schlieren images of reacting sprays, the combustion process and the subsequent light emission from the soot within the flame have revealed both limitations as well as considerations that deserve further investigation. Seeking for answers to such concerns, the current work reports an experimental study with this imaging technique where, besides spatial filtering at the Fourier plane, both short exposure time and chromatic filtering were performed to improve the resulting schlieren image, as well as the reliability of the subsequent tip penetration measurement. The proposed methodology has reduced uncertainties caused by artificial pixel saturation (blooming). Additionally, an algorithm to calculate Lift-off length from schlieren images has been developed and compared to the more conventional OH* imaging technique.By means of the improved setup, the analysis of transient diesel flame has been performed throughout the ignition and early combustion phases. When compared to a non-reacting vaporizing spray, the temporal evolution of the reacting case departs from the inert one at the start of combustion, when expansion in both axial (i.e. spray tip increase) and radial direction are observed. After that, the tip penetration progressively decreases on a clear transient period where the flow tries to re-organize itself in response to the induced reaction zone. Eventually, the spray undergoes an acceleration period where the reacting spray tip progresses above the nonreacting one. A parametric study has been conducted for three injection pressure levels to investigate the influence of this parameter upon transient flame evolution.

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Diesel fuel jet lift-off stabilization in the presence of laser-induced plasma ignition

Cited by 99 publications

References 16 publications

Transient Flame Development in a Constant-Volume Vessel Using a Split-Scheme Injection Strategy

Transient Flame Development in a Constant-Volume Vessel Using a Split-Scheme Injection Strategy

Large-eddy simulation of air entrainment during diesel spray combustion with multi-dimensional CFD

Schlieren Methodology for the Analysis of Transient Diesel Flame Evolution

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