Investigating Soot Morphology in Counterflow Flames at Elevated Pressures

Practical combustion devices such as gas turbines and diesel engines operate at
high pressures to increase their efficiency. Pressure significantly increases the overall
soot yield. Morphology of these ultra-fine particles determines their airborne lifetime and
their interaction with the human respiratory system. Therefore, investigating soot
morphology at high pressure is of practical relevance.
In this work, a novel experimental setup has been designed and built to study the
soot morphology at elevated pressures. The experimental setup consists of a pressure
vessel, which can provide optical access from 10° to 165° for multi-angle light scattering,
and a counterflow burner which produces laminar flames at elevated pressures.
In the first part of the study, N2-diluted ethylene/air and ethane air counterflow
flames are stabilized from 2 to 5 atm. Two-angle light scattering and extinction technique
have been used to study the effects of pressure on soot parameters. Path averaged soot
volume fraction is found to be very sensitive to pressure and increased significantly from
2 to 5 atm. Primary particle size and aggregate size also increased with pressure.
Multi-angle light scattering is also performed and flames are investigated from 3
to 5 atm. Scattering to absorption ratio is calculated from multi-angle light scattering and
extinction data. Scattering to absorption ratio increased with pressure whereas the number
of primary particles in an aggregate decreased with increasing pressure.
Practical combustion devices such as gas turbines and diesel engines operate at
high pressures to increase their efficiency. Pressure significantly increases the overall
soot yield. Morphology of these ultra-fine particles determines their airborne lifetime and
their interaction with the human respiratory system. Therefore, investigating soot
morphology at high pressure is of practical relevance.
In this work, a novel experimental setup has been designed and built to study the
soot morphology at elevated pressures. The experimental setup consists of a pressure
vessel, which can provide optical access from 10° to 165° for multi-angle light scattering,
and a counterflow burner which produces laminar flames at elevated pressures.
In the first part of the study, N2-diluted ethylene/air and ethane air counterflow
flames are stabilized from 2 to 5 atm. Two-angle light scattering and extinction technique
have been used to study the effects of pressure on soot parameters. Path averaged soot
volume fraction is found to be very sensitive to pressure and increased significantly from
2 to 5 atm. Primary particle size and aggregate size also increased with pressure.
Multi-angle light scattering is also performed and flames are investigated from 3
to 5 atm. Scattering to absorption ratio is calculated from multi-angle light scattering and
extinction data. Scattering to absorption ratio increased with pressure whereas the number
of primary particles in an aggregate decreased with increasing pressure.