AAAR 37th Annual Conference October 14 - October 18, 2019 Oregon Convention Center Portland, Oregon, USA
Abstract View
Laser-induced Incandescence: Need to Revisit
IGOR ALTMAN, Fengshan Liu, Naval Air Warfare Center Weapons Division, USA
Abstract Number: 30 Working Group: Instrumentation and Methods
Abstract Laser-induced incandescence (LII) is currently being considered a powerful tool for characterization of the condensed phase in combustion diagnostics of two-phase systems [1]. The interpretation of LII experiment is based on two main postulated statements: the light emission from the laser irradiated particles is related to the Planck blackbody radiation, as a result of particle temperature rise by laser energy absorption, and the particle heat transfer to the environment determines the emission decay after the laser pulse. These two statements seem so obvious that, in our knowledge, have never been deeply analyzed except the old attempt to challenge the LII fundamentals [2].
Recently, LII practitioners have faced a couple of issues [3] that they could not resolve based on the existing LII theory [4]. They found that the laser energy in the experiment is not enough to heat the particle up to a temperature, at which it can emit a detectable LII signal, and the energy deficit far exceeds 10 at some conditions. Besides the unexplained issues, LII predictions of the energy accommodation coefficient in the range of 0.1-1 need to be challenged as well [5, 6]. Then, there seems more than enough evidence to introduce some alternative LII scenario.
The essence of our explanation of the LII occurrence is the thermal isolation between the systems of electrons and phonons in the laser irradiated particles during and after the laser pulse, whose possible mechanism is described in [7]. Based on this thermal isolation we are able to reconcile all major LII issues. The LII scenario we introduce does necessarily lead to the need to revisit the LII results in their entirety.
[1] H.A. Michelsen, C. Schulz, G.J. Smallwood, S. Will, Prog. Energy Comb. Sci. 51, 2 (2015). [2] I.S. Altman, M. Choi, J. Aerosol Sci. 32, S619 (2001). [3] T.A. Sipkens, N.R. Singh, K.J. Daun, Appl. Phys. B 123: 14 (2017). [4] S. Talebi Moghaddam, K.J. Daun, Appl. Phys. B 124: 159 (2018). [5] I.S. Altman, J. Phys. Stud. 3, 456 (1999). [6] D. Allen, N. Glumac, H. Krier, Combust. Flame 161, 295 (2014). [7] E.D. Belotskii, S.N. Luk’yanets, P.M. Tomchuk, Sov. Phys. JETP 74, 88 (1992).