Effect of n-dodecane decomposition on its fundamental flame properties

Smolke, Jennifer; Carbone, Francesco; Egolfopoulos, Fokion N.; Wang, Shuangfeng

doi:10.1016/j.combustflame.2017.11.009

Cited by 25 publications

(3 citation statements)

References 28 publications

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“…In this scenario, hydrocarbon fuel in the cooling channel absorbs heat from the walls via convection. When the fuel reaches a certain temperature, it will undergo the thermal cracking process to form gaseous components such as hydrogen, methane, and ethylene, and thereby greatly affects the overall atomization, ignition, and flame propagation characteristics. , The precise details of how these gases are formed and the impact on system characteristics remain unclear. Moreover, aromatic hydrocarbons contained in the cracked fuel are the most important precursors for coke and soot formation in the combustor .…”

Section: Introductionmentioning

confidence: 99%

Experiment and Modeling on Thermal Cracking of n-Dodecane at Supercritical Pressure

et al. 2018

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A comprehensive understanding of the thermal cracking behavior of hydrocarbon fuels is important for thermal protection applications and investigations into the combustion of thermally cracked fuels. In the present study, n-dodecane is selected as a surrogate for aviation kerosene and it is subjected to a series of thermal cracking experiments at supercritical pressure. According to variations in chemical heat sink, fuel-conversion rate, and gas-production rate, the thermal cracking of ndodecane is divided into three regions: primary, secondary, and severe. In the primary cracking region, the fuel-conversion rate is lower than 13%, and the liquid products contain only chain alkanes and alkenes. Owing to the mass fraction of main products being proportional to the fuel-conversion rate, a one-step global reaction kinetics is constructed. The secondary cracking region is characterized by rapidly increasing chemical heat sink, fuel-conversion rates, and gas-production rates with increasing fuel temperature, and the appearance of monocyclic aromatic hydrocarbons (MAHs) and cycloalkenes. A kinetic model containing three reactions is proposed for this region. This also considers the thermal decomposition of chain alkanes and alkenes, which result in the formation of MAHs and cycloalkenes. Severe cracking is observed for fuel-conversion rates above 71% where a rapid increase in the concentration of monocyclic and polycyclic aromatic hydrocarbons (PAHs) occurs. The increasing rate of chemical heat sink slows in this region which is characterized by the formation of MAHs, PAHs, and coke. A three-dimensional numerical model is built for the primary and secondary cracking regions, taking the effects of the flow, heat transfer, and thermal cracking of n-dodecane into consideration. Predicted values for the outlet temperature, fuel-conversion rate, and distribution of the main species in all tested cases agree well with the experimental results, validating the numerical model and kinetics for the primary and secondary thermal cracking of n-dodecane.

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Section: Introductionmentioning

confidence: 99%

Experiment and Modeling on Thermal Cracking of n-Dodecane at Supercritical Pressure

et al. 2018

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“…the distributions of density and mixture fraction are given by 𝜌=𝜌1exp(−𝜅𝜉),𝑍=𝑍1exp(−𝛽𝜉), (7) where the index 1 denotes the variable at the flame initiation position. It is worth noting that by proper curve fitting on the kinetic results of mass fractions, derived by USC-Mech II [60], the exponential variation of mass fraction was verified in the narrow region of the n-dodecane-air flame. For the flow under investigation, a linear relation exists between the mixture fraction and mass fraction [59].…”

Section: 𝑑𝑒=𝑇𝑑𝑠+𝑝𝑑𝜌𝜌2−𝑖=1𝑁𝜇𝑖𝑀𝑊𝑖𝑑𝑌𝑖mentioning

confidence: 90%

Dynamics of entropy wave generation in a simplified model of gas turbine combustor: A theoretical investigation

2020

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Entropy noise remains as a largely unexplored mechanism of combustion generated noise. Currently, little is known about the production sources of entropy waves in flames. To address this issue, the present work puts forward a theoretical investigation of the generation of entropy waves in a one-dimensional, ducted flow. A linear theory is developed for the dynamic responses of different sources of unsteady entropy generation including thermal, hydrodynamic, pressure, and chemical irreversibility. For the first time in the literature, dynamics of chemical sources of unsteady entropy generation are investigated extensively. It is found that the mixture fraction fluctuations are responsible for the production of almost all unsteady chemical entropy and the effect of chemical potential is negligibly small. For the Strouhal numbers less than unity, fluctuations in pressure are the most significant source of the overall generation of unsteady entropy. However, at higher frequencies, mixture fraction fluctuations dominate the generation of entropy wave. The cut-off frequency for the generation of entropy wave is shown to depend not only on the thermal and hydrodynamic characteristics of the flame but also on the chemical properties of the downstream gases. It is further argued that the transfer function of entropy generation for a thin flame may feature an unrealistically high amplitude. This study shows that neglecting the chemical sources of an entropy wave can result in wrong predictions of the combustor acoustics and impede the suppression of combustion instabilities and noise.

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“…Such understanding can be achieved by using experiments and theory to decouple the pyrolysis of the fuel from the oxidation of relatively small individual hydrocarbon fragments and their radicals formed as a result of the pyrolysis. On the basis of sophisticated chemical models, Wang et al − provided compelling evidence that the pyrolysis of hydrocarbon fuels such as JP-8 and JP-10 requires a few tens of microseconds, such as around 20 μs for the decomposition of dodecane. Since the oxidation of the hydrocarbon fragments occurs on a time scale of typically a few 100 μs and the ignition engages at normally close to 1000 μs, the pyrolysis stage can be decoupled from the oxidation chemistry of the hydrocarbon fragments and their radicals.…”

Section: Introductionmentioning

confidence: 99%

Computational Study on the Unimolecular Decomposition of JP-8 Jet Fuel Surrogates III: Butylbenzene Isomers (n-, s-, and t-C₁₄H₁₀)

2018

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Ab initio G3(CCSD,MP2)//B3LYP/6-311G(d,p) calculations of potential energy surfaces have been carried out to unravel the mechanism of the initial stages of pyrolysis of three CH isomers: n-, s-, and t-butylbenzenes. The computed energy and molecular parameters have been utilized in RRKM-master equation calculations to predict temperature- and pressure-dependent rate constants and product branching ratios for the primary unimolecular decomposition of these molecules and for the secondary decomposition of their radical fragments. The results showed that the primary dissociation of n-butylbenzene produces mostly benzyl (CH) + propyl (CH) and 1-phenyl-2-ethyl (CHCH) + ethyl (CH), with their relative yields strongly dependent on temperature and pressure, together with a minor amount of 1-phenyl-prop-3-yl (CH) + methyl (CH). Secondary decomposition reactions that are anticipated to occur on a nanosecond scale under typical combustion conditions split propyl (CH) into ethylene (CH) + methyl (CH), ethyl (CH) into ethylene (CH) + hydrogen (H), 1-phenyl-2-ethyl (CHCH) into mostly styrene (CH) + hydrogen (H) and to a lesser extent phenyl (CH) + ethylene (CH), and 1-phenyl-prop-3-yl (CH) into predominantly benzyl (CH) + ethylene (CH). The primary decomposition of s-butylbenzene is predicted to produce 1-phenyl-1-ethyl (CHCHCH) + ethyl (CH) and a minor amount of 1-phenyl-prop-1-yl (CH) + methyl (CH), and then 1-phenyl-1-ethyl (CHCHCH) and 1-phenyl-prop-1-yl (CH) rapidly dissociate to styrene (CH) + hydrogen (H) and styrene (CH) + methyl (CH), respectively. t-Butylbenzene decomposes nearly exclusively to 2-phenyl-prop-2-yl (CH) + methyl (CH), and further, 2-phenyl-prop-2-yl (CH) rapidly eliminates a hydrogen atom to form 2-phenylpropene (CH). If hydrogen atoms or other reactive radicals are available to make a direct hydrogen-atom abstraction from butylbenzenes possible, the CH radicals (1-phenyl-but-1-yl, 2-phenyl-but-2-yl, and t-phenyl-isobutyl) can be formed as the primary products from n-, s-, and t-butylbenzene, respectively. The secondary decomposition of 1-phenyl-but-1-yl leads to styrene (CH) + ethyl (CH), whereas 2-phenyl-but-2-yl and t-phenyl-isobutyl dissociate to 2-phenylpropene (CH) + methyl (CH). Thus, the three butylbenzene isomers produce distinct but overlapping nascent pyrolysis fragments, which likely affect the successive oxidation mechanism and combustion kinetics of these JP-8 fuel components. Temperature- and pressure-dependent rate constants generated for the initial stages of pyrolysis of butylbenzenes are recommended for kinetic modeling.

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Effect of n-dodecane decomposition on its fundamental flame properties

Cited by 25 publications

References 28 publications

Experiment and Modeling on Thermal Cracking of n-Dodecane at Supercritical Pressure

Experiment and Modeling on Thermal Cracking of n-Dodecane at Supercritical Pressure

Dynamics of entropy wave generation in a simplified model of gas turbine combustor: A theoretical investigation

Computational Study on the Unimolecular Decomposition of JP-8 Jet Fuel Surrogates III: Butylbenzene Isomers (n-, s-, and t-C₁₄H₁₀)

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Effect of n-dodecane decomposition on its fundamental flame properties

Cited by 25 publications

References 28 publications

Experiment and Modeling on Thermal Cracking of n-Dodecane at Supercritical Pressure

Experiment and Modeling on Thermal Cracking of n-Dodecane at Supercritical Pressure

Dynamics of entropy wave generation in a simplified model of gas turbine combustor: A theoretical investigation

Computational Study on the Unimolecular Decomposition of JP-8 Jet Fuel Surrogates III: Butylbenzene Isomers (n-, s-, and t-C14H10)

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Computational Study on the Unimolecular Decomposition of JP-8 Jet Fuel Surrogates III: Butylbenzene Isomers (n-, s-, and t-C₁₄H₁₀)