Simultaneous imaging of soot volume fraction, PAH, and OH in a turbulent n-heptane spray flame

Mulla, Irfan; Renou, Bruno

doi:10.1016/j.combustflame.2019.08.012

Cited by 25 publications

(5 citation statements)

References 47 publications

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“…Both LIF and LII signals are spectrally collected through a bandpass filter of bandwidth 360–430 nm (LaVision GmbH, Goettingen, Germany) fixed in front of the camera objective. The detection of PAH-LIF signal in the spectral range of 350–400 nm indicates the presence of smaller PAH (primarily of two to four-ringed) [ 23 , 24 , 44 ]. It is worth highlighting that the interpretation of PAH from their LIF signal and their isolation is not straightforward due to overlap between the excitation and emission spectra of different classes (rings) of PAH [ 11 ].…”

Section: Description Of the Experimentsmentioning

confidence: 99%

“…However, the intensifier gain is reduced by nearly 5% here compared to the first measurement to avoid camera saturation. To detect OH fluorescence, the selected optical filter is well adapted and it is sufficiently narrow to reduce the interference with the PAH fluorescence signal, which occurs over a broader band of wavelengths (that is also excitable at 283.5 nm) [ 24 ]. The overall contribution of PAH-LIF to the optical signal in the spectral range of the optical filter is expected to be negligible compared to that of the OH-LIF signal.…”

Section: Description Of the Experimentsmentioning

confidence: 99%

“…For simultaneously imaging multiple species in flames, a combination of multiple lasers and several cameras (which are time-gated and/or equipped with different spectral filters) is required—making the optical setup complex and resource-intensive [ 21 , 22 , 23 , 24 ]. For example, Sjöholm et al [ 21 ] utilized three pulsed lasers to generate four different wavelengths of 266 nm, 309 nm, 355 nm, and 431 nm to excite fluorescence of toluene, OH, CH 2 O, and CH, respectively, in a methane jet flame.…”

Section: Introductionmentioning

confidence: 99%

“…Franzelli et al [ 23 ] performed simultaneous imaging of soot, PAH, and OH in a turbulent methane diffusion flame using 284 nm as the excitation wavelength of a dye laser and three high-speed intensified CMOS cameras. In a recent study, Mulla et al [ 24 ] conducted instantaneous soot-PLII and PLIF of PAH and OH in a turbulent n-heptane jet spray flame. The optical setup consisted of two pulsed lasers at 283 nm (to excite both PAH- and OH-LIF) and 1064 nm (for LII) and three intensified CCD cameras including two pulse generators to synchronize the lasers and cameras.…”

Section: Introductionmentioning

confidence: 99%

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Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera

Mishra

Boggavarapu

Chorey

et al. 2020

Sensors

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In this article, the application of the FRAME (Frequency Recognition Algorithm for Multiple Exposures) technique is presented for multi-species measurements in symmetric and asymmetric ethylene/air diffusion flames. Laminar Bunsen-type and swirled diffusion flames are investigated to gain a better understanding of sooting combustion. For this purpose, simultaneous imaging is conducted in terms of Laser-Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAH) and Laser-Induced Incandescence (LII) of soot particles. Subsequently, the approach is utilized for simultaneous imaging of hydroxyl (OH)-LIF and soot-LII. Here, the modulated LIF- and LII-signals are acquired together as a single sub-image—with a single exposure utilizing the full sensor size of a single camera. By employing the frequency-recognition algorithm on the single image, the LIF- and LII-signals are spectrally isolated—generating two individual LIF- and LII-images. The flame luminosity and out-of-focus light such as reflected surrounding laser light are detected as non-modulated signals in the unprocessed image. These unwanted signals are suppressed using the image post-processing, and, therefore, the image contrast of the two resulting images is improved. It is found that PAHs mainly exist in the inner region near the burner and are surrounded by soot. The majority of the OH is distributed on the outer edges of the flame—representing the reaction zone and soot-oxidation region of the flame.

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Section: Description Of the Experimentsmentioning

confidence: 99%

Section: Description Of the Experimentsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera

Mishra

Boggavarapu

Chorey

et al. 2020

Sensors

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“…For the pure CH 4 /air flames, however, unexpected signals between two OH layers are observed, which are not found for the flames with high x a,f (=0.4). Thus, the unexpected signals seem to be originated from the existence of polycyclic aromatic hydrocarbons (PAHs) which are considered as a soot precursor since soot can be emitted in conventional hydrocarbons/air nonpremixed flames. , In fact, the LIF technique has been widely used to investigate the characteristics of PAH and soot formation in the previous studies. ,− The PAH has a broad absorption range in the ultraviolet (UV) region, and the signals from the PAH, which could be induced by LIF, also include a broad wavelength range depending on its structure and molecular weight. In general, PAHs with higher molecular weight emit light of longer wavelength. , In order to clearly confirm if the signals in Figure a are induced from the PAH, the laser sheet-beam that is tuned to 282.5 nm slightly different from the wavelength for OH-PLIF signals (282.92 nm) is passed through the flames so that the PAH having a broad range of absorption wavelengths, unlike the OH radicals, can be excited.…”

Section: Resultsmentioning

confidence: 88%

Combustion Characteristics for the Stabilization of Nonpremixed Methane-Ammonia/Air Coflow Flames through Their Visualization

Kim,

Ku,

Kwon

2024

Energy Fuels

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In order to confirm the possible use of methane (CH 4 )ammonia (NH 3 ) blends as a low carbon fuel, the fundamental combustion characteristics for the stabilization of nonpremixed CH 4 − NH 3 /air flames using the coflow jet flame configuration are experimentally studied, observing the flame behaviors by the direct imaging, shadow-graph, and OH radical visualization systems. Two types of flames, attached and lifted flames, are observed, and extinction (blowout) occurs as the injection velocity of fuel u fuel increases. The occurrence of blowout for pure CH 4 /air flames depends on u fuel regardless of the injection velocity of coflow air u coflow , while it considerably depends on u coflow for CH 4 −NH 3 /air flames. The OH radical visualization reveals that NH 3 addition affects the overall reaction intensity and mechanism but does not reduce the average reaction region near the injector lip. Also, the addition of NH 3 reduces the formation of polycyclic aromatic hydrocarbons (PAHs) as a soot precursor. Direct images confirm the effects of NH 3 addition, u fuel , and u coflow on the flame length, and the liftoff height. The measured NO x emissions exhibit that the fuel NO x from NH 3 is dominant and the NO x emissions are considerably affected by the flame intensity and fluctuation.

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Low-pressure ethylene/air laminar premixed flames: characterisations and soot diagnostics

et al. 2023

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In this work, the structure of laminar premixed ethylene/air flat flames at low pressure are studied experimentally. The aim of the work is to exploit the spatial expansion of laminar 1D flames and advanced laser techniques to better understand the conditions and precursors affecting soot particles inception. Soot volume fraction (fv) profiles were measured using laser-induced incandescence (LII), while spatial distribution of the CH* and C2* radicals was measured using spatially resolved emission spectroscopy. Spatially resolved laser-induced fluorescence has been used to record emission from 2–3 rings, 3–4 rings and > 5 rings. The temperature of soot particles (Ts) was evaluated through fitting the spectrally resolved soot luminosity, while flame gaseous temperature (Tg) was measured using a fine thermocouple. The laminar flow velocity was modeled and used to evaluate the reaction time at each HAB. Taking advantage of the expanded flame structure at low pressure, the profiles of CH*, C2*, soot and temperatures, as a function of the height above the burner, were well resolved. It was found that CH* and C2* chemiluminescence overlap in space. The thickness of CH* layer is larger than that of C2*, and it peaks at slightly different location, CH* appears approximately 1 mm before C2*. The distance between the two peaks decreases linearly with the increase in pressure. The lowest value of the initial soot volume fraction (fv) was 0.19 ppb, measured at pressure 27 kPa. It was found that fv scales with the pressure following a power function of the form fv α Prn, where n is 2.15 ± 0.7. It was observed that, in all the flames investigated, the initial soot particles first appear at a common critical inception temperature, Tinception, of 1465 ± 66 K. It was found that the Tinception is lower than the maximum flame temperature, Tmax, by ~ 45° and appeared ~ 1 mm further than the location of Tmax. Using the Lagrangian quantity dfv/dt and fv, it was possible to reveal the soot growth rate, kSG. At pressure of 27 kPa, the value of kSG was evaluated as 20 s−1.

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Simultaneous imaging of soot volume fraction, PAH, and OH in a turbulent n-heptane spray flame

Cited by 25 publications

References 47 publications

Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera

Application of FRAME for Simultaneous LIF and LII Imaging in Sooting Flames Using a Single Camera

Combustion Characteristics for the Stabilization of Nonpremixed Methane-Ammonia/Air Coflow Flames through Their Visualization

Low-pressure ethylene/air laminar premixed flames: characterisations and soot diagnostics

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