Experimental and numerical study of chemiluminescent species in low-pressure flames

Abstract

Chemiluminescence has been observed since the beginning of spectroscopy, nevertheless, important facts still remain unknown. Especially, reaction pathways leading to chemiluminescent species such as OH * , CH * , C * 2 , and CO * 2 are still under debate and cannot be modeled with standard codes for flame simulation. In several cases, even the source species of spectral features observed in flames are unknown. In recent years, there has been renewed interest in chemiluminescence, since it has been shown that this radiation can be used to determine flame parameters such as stoichiometry and heat release under some conditions. In this work, we present a reaction mechanism which predicts the OH * , CH * (in A-and B-state), and C * 2 emission strength in lean to fuel-rich stoichiometries. Measurements have been performed in a set of low-pressure flames which have already been well characterized by other methods. The flame front is resolved in these measurements, which allows a comparison of shape and position of the observed chemiluminescence with the respective simulated concentrations. To study the effects of varying fuels, methane flame diluted in hydrogen are measured as well. The 14 investigated premixed methane-oxygen-argon and methanehydrogen-oxygen-argon flames span a wide parameter field of fuel stoichiometry (φ = 0.5 to 1.6) and hydrogen content (H 2 vol% = 0 to 50).The relative comparison of measured and simulated excited species concentrations shows good agreement. The detailed and reliable modeling for several chemiluminescent species permits correlating heat release with all of these emissions under a large set of flame conditions. It appears from the present study that the normally used product of formaldehyde and OH concentration may be less well suited for such a prediction in the flames under investigation.

The influence of charge stratification on the spectral signature of partially premixed combustion in a light-duty optical engine

“…This increase can be related to the influence of combustion temperature; locally higher equivalence ratios result in higher combustion temperature, and this elevated temperature can be the cause of enhanced chemiluminescence. However, the exact chemical processes behind chemiluminescence are not sufficiently well known to provide definitive answers to the phenomena, particularly at elevated pressure [12,25]. Time-resolved results for various species are presented in Fig.…”

“…The chemiluminescence yield due to specific molecules varies for different combustion regimes, and this can provide information about the nature of the chemistry involved [9][10][11]. Because chemiluminescence is the direct product of exothermic chemical reactions, it marks the location of the initial combustion reactions, both temporally and spatially [10], although reaction pathways leading to chemiluminescent species are under debate [12]. In practical implementation, a drawback is that the collected light is integrated along the line of sight of the detector.…”

Towards Identifying Flame Patterns in Multiple, Late Injection Schemes on a Single-Cylinder Optical Diesel Engine

“…Therefore, C2 * chemiluminescence images can provide information about reacting fuel-rich zones, predominately originating from premixed areas of the flame (e.g. Kohse-Höinghaus, 1994), as has also been substantiated in studies of fundamental premixed flames (Kathrotia et al, 2012) and diesel engines environment (Anders et al 1999). Exited OH * species are mainly formed through reaction of molecular oxygen with CH (e.g.…”

Experimental and Numerical Study of Chemiluminescence Characteristics in Premixed Counterflow Flames of Methane based Fuel blends

“…The chemical kinetics mechanism used in this work consisted of GRI-Mech 3.0 35 , as the basic hydrocarbon mechanism, with an additional chemiluminescence sub-model adopted by Kathrotia et al 1,27 . The 4,28 was included in the chemiluminescence sub-model.…”