Formation of soot and nitrogen oxides in unsteady counterflow diffusion flames

Journal Article · Thu Oct 15 00:00:00 EDT 2009 · Combustion and Flame

DOI:https://doi.org/10.1016/J.COMBUSTFLAME.2009.06.023· OSTI ID:21227403

Cuoci, A; Frassoldati, A; Faravelli, T; Ranzi, E ^[1]

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1. Dipartimento di Chimica, Materiali e Ingegneria Chimica ''G. Natta'', Politecnico di Milano, P.zza Leonardo da Vinci 32, 20133 Milano (Italy)

The formation of pollutant species in turbulent diffusion flames is strongly affected by turbulence/chemistry interactions. Unsteady counterflow diffusion flames can be conveniently used to address the unsteady effects of hydrodynamics on the pollutant chemistry, because they exhibit a larger range of combustion conditions than those observed in steady flames. In this paper, unsteady effects on the formation of soot (and its main precursors) and nitrogen oxides (NO{sub x}) are investigated by imposing harmonic oscillations on the strain rate of several counterflow diffusion flames fed with propane. Numerical results confirm that the dynamic response of each species is strongly affected by the strain rate oscillations and the characteristic time governing its chemistry. At low frequencies of imposed oscillations the soot and NO{sub x} profiles show strong deviations from the steady-state profile. At large frequencies a decoupling between the concentration and the velocity field is evident. In particular, the formation of soot and NO{sub x} is found less sensitive to velocity fluctuations for flames with large initial strain rate. The significant increase of soot and NO{sub x} concentrations in unsteady conditions appears to be a function of both forcing frequency and flame global strain rate. Moreover, the cut-off frequency, defined as the minimum frequency above which the strain rate oscillations have negligible effects on the formation of each species, was found to be strongly dependent on the chemical characteristic time and the flame global strain rate, but only marginally affected by the amplitude of imposed oscillations. (author)

• OSTI ID: 21227403
• Journal Information: Combustion and Flame, Vol. 156, Issue 10; Other Information: Elsevier Ltd. All rights reserved; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
NITROGEN OXIDES
SOOT
FLAMES
STRAIN RATE
DIFFUSION
OSCILLATIONS
PROPANE
COMBUSTION
HYDRODYNAMICS
FLUCTUATIONS
SYNTHESIS
TURBULENCE
VELOCITY
COUNTERFLOW SYSTEMS
AMPLITUDES
DECOUPLING
FREQUENCY DEPENDENCE
PRECURSOR
COMBUSTION KINETICS
Turbulence-chemistry interactions
Unsteady flames
Oscillating flames
Flame dynamics