Laminar flame propagation and nonpremixed stagnation ignition of toluene and xylenes

Abstract

Using the constant-pressure expanding spherical flame and nonpremixed stagnation pool experiments, the laminar flame speeds and nonpremixed ignition temperatures of toluene and the xylenes were experimentally determined at atmospheric and elevated pressures. The experimental situations were then computationally simulated using the kinetic models of Metcalfe et al. and of Narayanaswamy et al., and interrogated through sensitivity, reaction path and chemical explosive mode analyses. For the laminar flame speed study, both present and literature experimental results show that the toluene flame propagates faster than the xylene flames at all pressures, while the computation analyses show that this is primarily due to the fuel chemistry, with the attendant controlling reaction paths identified. For the nonpremixed stagnation ignition, experimental results show that toluene has lower ignition temperatures than the xylenes, and numerical analysis identifies that it is mainly due to the higher fuel diffusivity of toluene. Furthermore, the ignition temperatures of o-xylene are lower than those of m-and p-xylenes, and are suggested to be due to the formation of dimethylphenyl radicals with isolated H abstraction sites, which react with O 2 for further chain branching. The computed ignition temperatures for all fuels are consistently higher than the experimental values, and chemical explosive mode analysis shows that the C 1 /H 2 chemistry plays the dominant role in the ignition.

Exploring pyrolysis and oxidation chemistry of o-xylene at various pressures with special concerns on PAH formation

“…Recently, Kukkadapu et al [15] measured the ignition delay times of o-xylene in a rapid compression machine (RCM) at pressures of 25-45 atm, temperatures of 850-1000 K and equivalence ratios of 0.5-1.0. The laminar flame speeds of o-xylene were also measured by Ji et al [13] at the initial pressure (Pu) of 1 atm and initial temperature (Tu) of 353 K and by Han et al [14] at Pu = 1-2 atm and Tu = 353 K. Furthermore, Han et al [14] also measured the ignition temperatures of o-xylene at 1-3 atm using a counterflow ignition apparatus.…”

“…Previous studies of o-xylene combustion either focused on the speciation in the oxidation or flames at low-to-atmospheric pressures [4][5][6][7][8], or were dedicated on the measurements of global combustion parameters [5,[9][10][11][12][13][14][15]. Among the speciation experiments, Emdee et al [4] investigated the flow reactor oxidation of o-xylene at 1 atm and 1150 K. The mole fractions of some major products were measured using gas chromatography (GC).…”

The origin of CEMA and its relation to CSP

“…i.e., now the indices are by definition all positive, in contrast with the results displayed in [35]. Later on, the absolute value in the numerator was removed, so that P I k could be positive or negative [42], as with the equivalent CSP quantity P i k in Eq. 7.…”

“…Regarding journal papers, CEMA was first introduced in the 2010 Combustion and Flame paper by Liu et al [35] and later in the same year in the Journal of Fluid Mechanics paper by Lu et al [36]. Since its introduction, CEMA has been employed for the analysis of a large number of combustion processes, including autoignition, flames and turbulent reacting flows; e.g., [37][38][39][40][41][42][43].…”

Effects of branch structure of alkylbenzenes on spray auto-ignition of n-decane and alkylbenzenes blends

“…3–6 Therefore, when researchers developed surrogates to study the combustion chemistry of practical transportation fuels, simple alkylbenzene molecules were usually selected as a key component to emulate the real aromatic hydrocarbons. 5,7–9 Typical alkylbenzene molecules include C 7 H 8 (toluene), C 8 H 10 (xylenes and ethylbenzene), C 9 H 12 (trimethylbenzenes and propylbenzenes), and C 10 H 14 (butylbenzenes). The existence of aromatic compounds in practical fuels has significant impacts on fuel auto-ignition behaviors, which are especially important in advanced combustion engines featuring highly premixed charge and compression ignition.…”