Abstract
A complementary computational and experimental study is carried out on the formation of ultrafine particulate matter in premixed laminar methane air flames. Specifically, soot formation is examined in premixed stretch-stabilized flames to observe soot inception and growth at relatively high flame temperatures common to oxygen enriched applications. Particle size distribution functions (PSDF) measured by mobility sizing show clear trends as the equivalence ratio increases from Φ = 2.2 to Φ = 2.4. For a given equivalence ratio, the measured distribution decreases in median mobility particle size as the maximum flame temperature increases from approximately 1,950–2,050 K. The median mobility particle size is 20 nm or less for all flame conditions studied. The volume fraction decreases with increasing flame temperature for all equivalence ratio conditions. The Φ = 2.2 condition is close to the soot inception limit and both number density and volume fraction decrease monotonically with increasing flame temperature. The higher equivalence ratio conditions show a peak in number density at 2,000 K which may indicate competing soot inception processes are optimized at this temperature. Flame structure computations are carried out using detailed gas-phase combustion chemistry of the Appel, Bockhorn, Frenklach (ABF) model to examine the connection of the observed PSDF to soot precursor chemistry. Agreement between measured and computed flame standoff distances indicates that the ABF model could provide a reasonable prediction of the flame temperature and soot precursor formation for the flames currently studied. To the first order, the trends observed in the measured PSDF could be understood in terms of computed trends for the formation of benzene, naphthalene and other soot precursors. Results of the current study inform particulate matter behavior for methane and natural gas combustion applications at elevated temperature and oxygen enriched conditions.
Highlights
Particulate matter formation is a crucial factor for combustion applications affecting performance (Heywood, 2018), emissions regulations (Jacobson, 2001) and public health (Jacobson et al, 2000)
The current study examines soot formation in premixed methane—enriched air flames using modeling and experimental approaches
Studies on flame structure effects (Xu et al, 1997; Alfè et al, 2010), parent fuel effects (Slavinskaya and Frank, 2009; Sirignano et al, 2011; Russo et al, 2013), and soot inception (Desgroux et al, 2017; Mouton et al, 2013; D’Anna et al, 2008) have been reported for premixed methane flames but the current study focuses on ultrafine (
Summary
Particulate matter formation is a crucial factor for combustion applications affecting performance (Heywood, 2018), emissions regulations (Jacobson, 2001) and public health (Jacobson et al, 2000). Oxygen enriched conditions are often used with natural gas to optimize heat transfer and emissions performance (Shaddix and Williams, 2017). The current study examines soot formation in premixed methane—enriched air flames using modeling and experimental approaches. Studies on flame structure effects (Xu et al, 1997; Alfè et al, 2010), parent fuel effects (Slavinskaya and Frank, 2009; Sirignano et al, 2011; Russo et al, 2013), and soot inception (Desgroux et al, 2017; Mouton et al, 2013; D’Anna et al, 2008) have been reported for premixed methane flames but the current study focuses on ultrafine (
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