Applications and evaluation of two-line atomic LIF thermometry in sooting combustion environments

Abstract

Temperature measurements using planar laser-induced fluorescence (PLIF) are most often associated with experimental challenges. In addition, no PLIF technique is generally applicable in all kinds of environment. Especially under sooting conditions problems are prone to arise, which limits the use of these techniques. In this paper the two-line atomic fluorescence (TLAF) technique was investigated in sooting environments. Indium atoms were used as thermometry species and seeded into the combustion region. Data from two-dimensional measurements are often difficult to analyse, because of problems with treating noise. A statistical analysis method for correction of laser fluctuations was developed to increase the precision of the temperature calculations. The results show that TLAF holds promise for temperature measurements in rich combustion, such as diesel engines, where other techniques have proven to fail. Drawbacks with the TLAF technique are that the probe volume is biased towards the post-flame zone and that seeding is required. The statistical analysis improved the precision considerably and is suitable for evaluation of other two-dimensional thermometry techniques. This paper also presents a critical review and comparison with alternatives, such as OH and NO thermometry.

Solvent effects on two-line atomic fluorescence of indium

“…LIF thermometry has most commonly been employed to probe in situ flame radical OH or seeded NO [7][8][9]. However, the narrow range of temperature and mixture fraction over which OH exists in a flame limits its general application for thermometry [10]. Likewise, NO-LIF has limitations because it can suffer from background interferences in the presence of soot [9].…”

Development of temperature imaging using two-line atomic fluorescence

“…Of the naturally occurring species within a flame, the OH radical is one of the most commonly used [8,[14][15][16]. In nonpremixed flames, OH only exists over a small range of temperature and mixture fraction, and so is not well suited for general measurements [17]. Furthermore, in fuel-rich flames, the OH concentration is low so that it is poorly suited to simultaneous measurements with soot, which is typically found in the fuel-rich side of the reaction zone [18].…”

“…Indium has good sensitivity over the temperature range ∼800-2800 K [29] and both wavelengths are in the visible (namely, 410 and 450 nm), where interferences are less pronounced than in the UV range, where many spectral species need to be excited. Recent feasibility studies [17,27] have shown that TLAF with indium holds promise for temperature measurement in a highly sooting environment. The indium is introduced to the system as indium chloride, which is dissolved in water.…”

“…The theory was first evaluated by Alkemade [30] and has subsequently been the interest of other studies [17,24,27,29,31,32]. The TLAF technique is based on the optical excitation of two electronic transitional energy states and the sequential detection of the spectrally shifted emission.…”

Vapor phase tri-methyl-indium seeding system suitable for high temperature spectroscopy and thermometry

“…Inherently, indium signal can only be obtained from the post combustion region of the flame. 4 The use of liquid seeding systems in flame measurements introduces various complications to the combustion system. Aspirating seeders generate a range of droplet sizes, only some of which successfully join the carrier gas stream; excess must be drained off to diminish problems of clogging and condensation on instrument surfaces.…”