RESUMO
Soot particles can be formed in hydrocarbon flames as a result of an inefficient combustion process. The particles are near-spherical, and at later stages in the soot growth process, they form chainlike sparse aggregates. When applying optical diagnostic methods, this aggregation influences the evaluation of soot properties based on assumptions of isolated particles. In this paper an efficient and accurate method for calculating scattering of light from these structures is presented. The method can handle aggregates with several hundred subparticles with no restrictions on shape, internal structure, or coagulation of the subparticles. The basic idea is that the induced dipole moments of the subparticles are determined from the solution of a quasi-static problem that can be solved with high accuracy by, e.g., the finite element method.
RESUMO
Formaldehyde (CH2O) is an important intermediate species in combustion processes and it can through laser-induced fluorescence measurements be used for instantaneous flame front detection. The present study has focussed on the use of the third harmonic of a Nd:YAG laser at 355 nm as excitation wavelength for formaldehyde, and different dimethyl ether (C2H6O) flames were used as sources of formaldehyde in the experiments. The investigations included studies of the overlap between the laser profile and the absorption lines of formaldehyde, saturation effects and the potential occurrence of laser-induced photochemistry. The technique was applied for detection of formaldehyde in an internal combustion engine operated both as a spark ignition engine and as a homogenous charge compression ignition engine.