Formation of soot and nitrogen oxides in unsteady counterflow diffusion flames

Journal Article · Thu Oct 15 04:00:00 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, Journal Name: Combustion and Flame Journal Issue: 10 Vol. 156; ISSN CBFMAO; ISSN 0010-2180
• Country of Publication: United States
• Language: English

Related Subjects

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