Soot measurements in steady and pulsed ethylene/air diffusion flames using Laser-Induced Incandescence

Combustion-generated carbon black nano particles, or soot, have both positive and negative effects depending on the application. From a positive point of view, it is used as a reinforcing agent in tires, black pigment in inks, and surface coatings. From a negative point of view, it affects performance and durability of many combustion systems, it is a major contributor of global warming, and it is linked to respiratory illness and cancer. Laser-Induced Incandescence (LII) was used in this study to measure soot volume fractions in four steady and twenty-eight pulsed ethylene diffusion flames burning at atmospheric pressure. A laminar coflow diffusion burner combined with a very-high-speed solenoid valve and control circuit provided unsteady flows by forcing the fuel flow with frequencies between 10 Hz and 200 Hz. Periodic flame oscillations were captured by two-dimensional phase-locked LII images and broadband luminosity images for eight phases (0° – 360°) covering each period. A comparison between the steady and pulsed flames and the effect of the pulsation frequency on soot volume fraction in the flame region and the post flame region are presented. The most significant effect of pulsing frequency was observed at 10 Hz. At this frequency, the flame with the lowest mean flow rate had 1.77 times enhancement in peak soot volume fraction and 1.2 times enhancement in total soot volume fraction; whereas the flame with the highest mean flow rate had no significant change in the peak soot volume fraction and 1.4 times reduction in the total soot volume fraction. A correlation (fvRe-1 = a + b·Str) for the total soot volume fraction in the flame region for the unsteady laminar ethylene flames was obtained for the pulsation frequency between 10 Hz and 200 Hz, and the Reynolds number between 37 and 55. The soot primary particle size in steady and unsteady flames was measured using the Time-Resolved Laser-Induced Incandescence (TIRE-LII) and the double-exponential fit method. At maximum frequency (200 Hz), the soot particles were smaller in size by 15% compared to the steady case in the flame with the highest mean flow rate.

Soot Measurements in Steady and Pulsed Ethylene/Air Diffusion Flames Using Laser-Induced Incandescence

Combustion-generated carbon black nano particles, or soot, have both positive and negative effects depending on the application. From a positive point of view, it is used as a reinforcing agent in tires, black pigment in inks, and surface coatings. From a negative point of view, it affects performance and durability of many combustion systems, it is a major contributor of global warming, and it is linked to respiratory illness and cancer. Laser-Induced Incandescence (LII) was used in this study to measure soot volume fractions in four steady and twenty-eight pulsed ethylene diffusion flames burning at atmospheric pressure. A laminar coflow diffusion burner combined with a very-high-speed solenoid valve and control circuit provided unsteady flows by forcing the fuel flow with frequencies between 10 Hz and 200 Hz. Periodic flame oscillations were captured by two-dimensional phase-locked LII images and broadband luminosity images for eight phases (0°- 360°) covering each period. A comparison between the steady and pulsed flames and the effect of the pulsation frequency on soot volume fraction in the flame region and the post flame region are presented. The most significant effect of pulsing frequency was observed at 10 Hz. At this frequency, the flame with the lowest mean flow rate had 1.77 times enhancement in peak soot volume fraction and 1.2 times enhancement in total soot volume fraction; whereas the flame with the highest mean flow rate had no significant change in the peak soot volume fraction and 1.4 times reduction in the total soot volume fraction. A correlation (ƒv Reˉ1 = a+b· Str) for the total soot volume fraction in the flame region for the unsteady laminar ethylene flames was obtained for the pulsation frequency between 10 Hz and 200 Hz, and the Reynolds number between 37 and 55. The soot primary particle size in steady and unsteady flames was measured using the Time-Resolved Laser-Induced Incandescence (TIRE-LII) and the double-exponential fit method. At maximum frequency (200 Hz), the soot particles were smaller in size by 15% compared to the steady case in the flame with the highest mean flow rate.

Synthesis and Characterization of Photochromic Copolymers Containing 3-Indolylfulgides/Indolylfulgimides

Fulgides and fulgimides are important organic photochromic compounds and can switch between the open forms and the closed forms with light. The 3-indolylfulgides and 3-indolylfulgimides exhibit promising photochromic properties and have great potential in optical memory devices, optical switches and biosensors. Copolymers containing 3-indolylfulgides/indolylfulgimides synthesized via free radical polymerizations increase conformation changes and allow the photochromic compounds to be uniformly distributed in the polymer matrix. A trifluoromethyl 3-indolylfulgide and two trifluoromethyl 3-indolylfulgimides with one or two polymerizable N-stryryl group(s) were prepared. Copolymerization with methyl methacrylate provided two linear copolymers or a cross-linked copolymer. The properties of the monomeric fulgide/fulgimides and copolymers in toluene or as thin films were characterized. In general, the photochromic monomers and copolymers revealed similar photochromic properties and exhibited good thermal and photochemical stability. All compounds absorb visible light in both open forms and closed forms. The closed form copolymers were more stable than the open form copolymers and showed little or no degradation after 400 h. The photochemical degradation rate was less than 0.03% per cycle. In films, conformational restrictions were observed for the open forms suggesting that the preparation of films from the closed forms is advantageous. Two novel methyl 3-indolylfulgimides with one or two polymerizable N-stryryl group(s) were prepared. Copolymerization of acrylamide with the methyl indolylfulgimides or the trifluoromethyl indolylfulgimides yielded two aqueous soluble linear copolymers and two photochromic hydrogels. The closed form copolymers containing trifluoromethyl indolylfulgimides were hydrolyzed in aqueous solution by replacing the trifluoromethyl group with a carboxylic acid group. The resulting carboxylic copolymers were also photochromic. The copolymers containing methyl fulgimides were stable in aqueous solutions and did not hydrolyze. Both methyl and carboxylic copolymers exhibited good stability in aqueous solutions. In general, the open form copolymers were more stable than the closed form copolymers, and the copolymers revealed better stability in acidic solution than neutral solution. The linear copolymers displayed better photochemical stability in neutral solution and degraded up to 22% after 105 cycles. In contrast, the hydrogels showed enhanced fatigue resistance in acidic condition and underwent up to 60 cycles before degrading 24%.