Laser-induced incandescence: Particulate diagnostics for combustion, atmospheric, and industrial applications

Abstract

The understanding of soot formation in combustion processes and the optimization of practical combustion systems require in situ measurement techniques that can provide important characteristics, such as particle concentrations and sizes, under a variety of conditions. Of equal importance are techniques suitable for characterizing soot particles produced from incomplete combustion and emitted into the environment. Additionally, the production of engineered nanoparticles, such as carbon blacks, may benefit from techniques developed. This review discusses considerations for selection of laser and detection characteristics to address application-specific needs. The benefits of using LII for measurements of a range of nanoparticles in the fields mentioned above are demonstrated with some typical examples, covering simple flames, internal-combustion engines, exhaust emissions, the ambient atmosphere, and nanoparticle production. We also remark on less well-known studies employing LII for particles suspended in liquids.An important aspect of the paper is to critically assess the improvement in the understanding of the fundamental physical mechanisms at the nanoscale and the determination of underlying parameters; we also identify further research needs in these contexts. Building on this enhanced capability in describing the underlying complex processes, LII has become a workhorse of particulate measurement in a variety of fields, and its utility continues to be expanding. When coupled with complementary methods, such as light scattering, probe-sampling, molecular-beam techniques, and other nanoparticle instrumentation, new directions for research and applications with LII continue to materialize.

Experimental assessment of the sudden-reversal of the oxygen dilution effect on soot production in coflow ethylene flames

“…Since soot exhibits a fairly short lifetime in the atmosphere on the order of days to weeks, the mitigation of soot emission has been considered as a near-term climate-change approach to gain time for implementations of long-term strategies [2]. As soot emitted by Internal Combustion (IC) engines contributes significantly to PM pollution in the air, innovative technologies especially designed for the reduction of soot emission have been a hot topic in IC engine related research in the last few decades [3][4][5].…”

Use of the Single Particle Soot Photometer (SP2) as a pre-filter for ice nucleation measurements: effect of particle mixing state and determination of SP2 conditions to fully vaporize refractory black carbon

“…It is interesting to note that this minimum power to vaporization is over twice the value outlined by Schwarz et al (2010) needed to detect 0.7 fg rBC particles with uniform efficiency. Thus, particles can be detected in the SP2 with uniform detection efficiency without vaporizing them, similar to pulsed laser-induced incandescence techniques (Michelsen et al, 2007(Michelsen et al, , 2015. For all subsequent SP2 exhaust results, data were taken at an absolute laser power of at least at 930 nW/(220 nm PSL).…”

Sequential signal detection for high dynamic range time-resolved laser-induced incandescence

“…Time-resolved laser-induced incandescence (TiRe-LII) is a well-established in situ measurement method for soot particle concentration and primary particle-sizes [1][2][3]. Twocolor (2C) pyrometry is frequently used for detecting the particle temperature by measuring the ratio of LII signals in two wavelength bands [2][3][4][5][6].…”

“…Twocolor (2C) pyrometry is frequently used for detecting the particle temperature by measuring the ratio of LII signals in two wavelength bands [2][3][4][5][6]. The signal-to-noise ratio (SNR) of LII measurements strongly decreases with signal duration because of the exponential decay of the signal intensity following the initial heat-up of the gas-borne particles with a pulsed laser.…”