Boris F. Kock

In-cylinder sizing of diesel particles by time-resolved laser-induced incandescence (TR-LII)

Laser-induced incandescence (LII) is a technique allowing particle-size distribution measurement and quantifying in an extremely short time. It is especially attractive for rapidly varying conditions as in diesel engine combustion. A special variant is the time-resolved method (TR-LII), which yields almost instantaneous particle-size information. In the present work, the application of particle sizing in the combustion chamber of a diesel engine is demonstrated. The measuring equipment was adapted to a one-cylinder, two-stroke engine with a specially designed cylinder head, yielding highly reproducible signals for particle thermal emission after rapid heatup by a pulsed laser. The characteristic time constant τ m of the exponential signal decrease is a measure for the particle size. TR-LII signals for different crank angles and varying motor conditions were measured. A strong dependence of the characteristic emission time constant τ m during particle cooling from the measured crank angle and the engine load could be determined. Specialties in signal evaluation due to the higher pressure level during diesel combustion are discussed, and size parameters, such as the count median diameter and the geometric standard deviation of an assumed lognormal size distribution, were determined from the measured optical signals. A comparison of in situ TR-LII particle sizing with the well-established ex situ differential mobility particle-sizing technique was performed. The results are in good agreement.

Shock wave induced carbon particle formation from CCL4 and C3O2 observed by laser extinction and by laser-induced incandescence (LII)

Abstract The formation of carbonaceous particles from the hydrogen-free precursors CCl 4 and C 3 O 2 , both diluted in argon was studied behind reflected shock waves in the temperature range 1400 K ≤ T ≤3700 K and at pressures 1.3 bar ≤ p ≤ 4.5 bar. The appearance of particles was measured by laser light extinction (LLE) and by laser induced incandescence (LII). Also, some time and spectrally resolved emission measurements were performed. The LLE experiments are sensitive to the optical density of the post-shock gas-particle mixture and show a time-dependent increase, depending on the detailed reaction conditions. The evaluation of the experiments at a reaction time of t = 1 ms results in a double, bell-shaped temperature dependency of the optical density. The LII-experiments, which are sensitive to the particle size, provide particle growth curves determined from several “identical” shock tube experiments with delayed triggering of the LII heat-up laser. Particle sizing experiments at a reaction time of t = 1 ms after shock-induced heat-up of the initial gas mixtures also clearly yield a double, bell-shaped temperature dependency of the particle diameter and confirm the optical density experiments. The shock tube was also equipped with a molecular beam system allowing supersonic beam probing from the shock-heated gases. Particles were collected on TEM grids and visualized by HR-TEM. The sizes of these images more or less confirm the LII sizing.

Nanoparticle formation from supersaturated carbon vapour generated by laser photolysis of carbon suboxide

Particle formation and growth from condensation of supersatd. carbon vapor was investigated. At. carbon vapor was generated under well-controlled conditions from UV-laser pulse photolysis of C3O2 at 193 nm. Particle formation and growth were studied in a wide range of conditions with varying carbon vapor concn., bath gas compn., and pressure. The formation of particulate matter was obsd. as a function of time by laser light extinction. Particle sizes were detd. in situ by time-resolved laser-induced incandescence and ex situ by transmission electronic microscopy. The characteristic time of particle growth was 20-1000 micro s. The final particle size was 5-12 nm, increased with pressure, and depends on bath gas compn. We propose a simple model for the description of carbon vapor condensation that assumes condensation of individual atoms on the cluster surface as the main growth mechanism. The comparison of expts. and simulations provides information about the initial concn. of carbon clusters for the different mixt. conditions.