Redjem Hadef

LASER-BASED INVESTIGATION OF SOOT FORMATION IN LAMINAR PREMIXED FLAMES AT ATMOSPHERIC AND ELEVATED PRESSURES

ABSTRACT An experimental investigation into soot formation in laminar premixed flames at atmospheric and elevated pressures (1–5 bar) has been conducted. The flames were produced in a dual-flame burner enclosed in a pressure housing. Quantitative soot volume fraction measurements were obtained using laser-induced incandescence coupled with a quasi-simultaneous absorption measurement for calibration; the data were corrected for signal trapping using an “onion peeling” algorithm. Temperature measurements were obtained using shifted vibrational coherent anti-Stokes Raman scattering, which yields well-resolved, accurate temperature measurements in sooting and nonsooting environments. Results are presented for stable homogeneous flames using air as oxidizer and ethylene, propylene, and toluene as fuels. The variation of soot volume fraction and temperature with height above burner and as a function of fuel, equivalence ratio, and pressure are presented and discussed. The present soot data are well represented by a first-order growth rate law. The data identify trends and features useful for the validation of numerical models of soot formation.

Comparison of laser-induced incandescence method with scanning mobility particle sizer technique: the influence of probe sampling and laser heating on soot particle size distribution

We present a simple method for comparing particle size measurements, obtained with laser-induced incandescence (LII) and a scanning mobility particle sizer (SMPS) in a premixed laminar sooting flame. A quartz cell was installed in line with the SMPS probe to allow LII measurements within the SMPS sample line. In this configuration, the LII and SMPS measurements gave similar results in terms of mean particle size. After the probe, the soot particles appear to be made of tight compact particles. In addition, with this experimental configuration, the influence of the probe in the flame is studied for different particle size ranges by applying LII before and after the probe. Application of SMPS with and without LII in the quartz cell shows that laser heating during LII measurements has an influence on the soot particle size distribution. The method could be used to improve probe sampling of particulate matter in reactive fields as well as to validate the interpretation of relevant physical mechanisms involved in the LII process.

Soot Formation and Flame Characterization of an Aero-Engine Model Combustor Burning Ethylene at Elevated Pressure

Swirl-stabilized, non-premixed ethylene/air flames were investigated at pressures up to 5 bars to study the effect of different operating parameters on soot formation and oxidation. Focus of the experiments was the establishment of a data base describing well defined flames, serving for validation of numerical simulation. Good optical access via pressure chamber windows and combustion chamber windows enables application of laser-induced incandescence to derive soot volume fractions after suitable calibration. This results in ensemble averaged as well as instantaneous soot distributions. Beyond pressure, parameters under study were the equivalence ratio, thermal power and amount of oxidation air. Latter could be injected radially into the combustor downstream of the main reaction zone through holes in the combustion chamber posts. Combustion air was introduced through a dual swirl injector whose two flow rates were controlled separately. The split of those air flows provided an additional parameter variation. Nominal power of the operating points was approximately 10 kW/bar leading to a maximum power of roughly 50 kW, not including oxidation air.Copyright