Study of carbonaceous nanoparticles in premixed C2H4–air flames and behind a spark ignition engine

Abstract

Study of carbonaceous nanoparticles in premixed C 2 H 4 -air flames and behind a spark ignition engine, Combust. Flame 156 (2009) 791-800.The original publication is available at www.elsevier.com http://dx. AbstractNanoparticle size distributions and their concentrations were studied in atmospheric premixed ethylene/air flames using photo ionization mass spectrometry (PIMS) and total organic carbon (TOC) calibration supplemented by differential mobility analysis (DMA). Focus of this study is the evolution of nanoparticles as a function of height above burner (HAB) and of the C/O ratio of the unburned gases. It was found that especially particles of the cluster type exhibit a sharp concentration drop by more than two orders of magnitude within a narrow C/O window which is close to the sooting threshold. Using DMA a decline by two orders of magnitude was found. These results suggest that at best only small concentrations of nanoparticles should be formed significantly below the sooting threshold. As these conditions prevail in a homogeneously charged IC engine no or only very small nanoparticle emissions are expected in the exhaust gas. This was indeed found for a small Otto engine driving a power generator unit. Using flame nanoparticle profiles as standard, absolute concentrations for their emissions could be deduced. These data were supported by additional DMA measurements. The calibration using TOC did not completely match the one based on the condensation particle counter of the DMA apparatus.Contrary to this clear evidence of nanoparticles it is much more under debate whether a minimum C/O ratio comparable to the sooting threshold is required for the formation of these particles. In a series of papers by D'Alessio and coworkers [3, 16 -19] premixed ethylene/air flames (C/O = 0.4 to 0.9) were studied. For these flames the yellowish luminosity occurs for C/O >~ 0.6. By contrast, nanometer-sized particles, called transparent soot, were reported to

Understanding the ignition mechanism of high-pressure spray flames

“…Experimental evidence suggests that there are at least two types of incipient particles [51,52,56,57,[61][62][63][64][65]. The first type (1) absorbs in the UV but is transparent at visible and IR wavelengths [59,[66][67][68][69][70], * The term "nascent" is often used to describe young, freshly nucleated soot particles, but this term is also used within the atmospheric research community to label mature soot freshly emitted from the combustor.…”

“…(2) fluoresces predominantly in the UV [56,57,71], (3) is less than ~3 nm in diameter [51,52,56,57,62,63,65], (4) is formed under relatively fuel-lean conditions [51,52,[62][63][64][65], and (5) appears to be composed of randomly ordered aromatic structures combined with some aliphatic content [51,52,64,65]. This type of particle may be consistent with the macromolecular clusters predicted by Violi and coworkers [72][73][74] or the particles predicted by Frenklach [34] to be formed by processes that are not entirely thermodynamically controlled.…”

“…The second type of incipient particle (1) absorbs in the visible and IR regions [64,66], (2) fluoresces in the visible [56,57,64], (3) is ≥~3nm in diameter [33,54,62,63,68,[75][76][77], (4) is formed under fuelrich conditions [51,52,[62][63][64][65], and (5) appears to be composed of nucleated [38,76,78,79], stacked [64,80] PAH structures held together by van der Waals forces [64]. This second type of particle may be consistent with structures predicted by Frenklach [34] to be formed at high temperatures by the Habstraction-C 2 H 2 -addition (HACA) driven mechanism, which generates clusters of physically bound stable PAHs.…”

Photoionization mass spectrometry for the investigation of combustion generated nascent nanoparticles and their relation to laser induced incandescence

“…This apparatus is used mainly for atmospheric flame measurements and for engine exhaust gases. It has been recently described in some detail 29 . Its main features are as follows.…”

Bay-capping reactions: Kinetics and influence on graphene-edge growth

“…One of the biggest unknowns, particle inception, received substantial attention in recent years [1][2][3][4][5][6][7][8][9][10][11][12][13] and its mechanistic picture steadily advances toward a unified theory [1,13]. Another part of the mechanism, surface growth, has transformed from an empirical rate law [14] to a simple elementaryreaction model [15], to a complex, multi-step process [9,10,[16][17][18][19].…”