The mechanism by which CH2O and H2O2 additives affect the autoignition of CH4/air mixtures

Manias, Dimitris M.; Tingas, Efstathios-Al.; Frouzakis, Christos E.; Boulouchos, Konstantinos; Goussis, Dimitris A.

doi:10.1016/j.combustflame.2015.11.008

Cited by 60 publications

(50 citation statements)

References 41 publications

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“…On the other hand, negative J n k indicates that the k-th reaction reinforces the dissipative character of τ n . The use of TPI has been already used in a large number of reacting flow, biological and pharmacokinetics problems in order to identify the driving processes [22,[33][34][35][35][36][37][38][39][40][41][42][43][44][45][46][47].…”

Section: The Csp Methodsologymentioning

confidence: 99%

“…After t = ∼0.75 s , temperature is identified by Po to be the variable mostly related to the explosive dynamics. The stage where temperature is not strongly pointed by CSP is defined as the chemical runaway and emerges in the initial portion of the explosive stage [22,29,42]. On the other hand, when the temperature is pointed strongly, then the system undergoes the thermal runaway, which usually develops in the last part of the explosive stage [22,29,42].…”

Section: Autoignition Of Ammoniamentioning

confidence: 99%

“…The stage where temperature is not strongly pointed by CSP is defined as the chemical runaway and emerges in the initial portion of the explosive stage [22,29,42]. On the other hand, when the temperature is pointed strongly, then the system undergoes the thermal runaway, which usually develops in the last part of the explosive stage [22,29,42]. In previous studies relating to the autoignition of H 2 /air, CH 4 /air, n-hexane/air, n-heptane/air, DME/air, and ethanol/air mixtures, it was shown that chemical runaway regime practically occupies all the explosive stage, while the thermal runaway regime only appears at the very final portion of the explosive stage [22,34,37,38,41,43,44,46,[52][53][54][55][56].…”

Section: Autoignition Of Ammoniamentioning

confidence: 99%

“…The use of CSP Pointer, as an indicator of probable additives in the starting fuel/air mixture from the set of intermediate species, has been successfully employed in previous works [42,43,45,57]. This tool was shown most successful when employed during the chemical runaway regime, where the explosive activity is chemically driven.…”

Section: Autoignition Of Ammoniamentioning

confidence: 99%

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Algorithmic Analysis of Chemical Dynamics of the Autoignition of NH3–H2O2/Air Mixtures

et al. 2019

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The dynamics of a homogeneous adiabatic autoignition of an ammonia/air mixture at constant volume was studied, using the algorithmic tools of Computational Singular Perturbation. Since ammonia combustion is characterized by both unrealistically long ignition delays and elevated NO x emissions, the time frame of action of the modes that are responsible for ignition was analyzed by calculating the developing time scales throughout the process and by studying their possible relation to NO x emissions. The reactions that support or oppose the explosive time scale were identified, along with the variables that are related the most to the dynamics that drive the system to an explosion. It is shown that reaction H 2 O 2 (+M) → OH + OH (+M) is the one contributing the most to the time scale that characterizes ignition and that its reactant H 2 O 2 is the species related the most to this time scale. These findings suggested that addition of H 2 O 2 in the initial mixture will influence strongly the evolution of the process. It was shown that ignition of pure ammonia advanced as a slow thermal explosion with very limited chemical runaway. The ignition delay could be reduced by more than two orders of magnitude through H 2 O 2 addition, which causes only a minor increase in NO x emissions.

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Section: The Csp Methodsologymentioning

confidence: 99%

Section: Autoignition Of Ammoniamentioning

confidence: 99%

Section: Autoignition Of Ammoniamentioning

confidence: 99%

Section: Autoignition Of Ammoniamentioning

confidence: 99%

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Algorithmic Analysis of Chemical Dynamics of the Autoignition of NH3–H2O2/Air Mixtures

et al. 2019

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“…In the current study, tools generated on the basis of CSP, were employed in order to (i) obtain physical understanding about the roles of specific reactions in the ignition process, and (ii) identify the variables that govern the dynamics of ignition. The following CSP tools were employed: (i) the time scale participation index (TPI), which measures the contribution of each reaction to the time scale of each CSP mode [34], and (ii) the CSP Pointer, which identifies the variables that mostly relate to each CSP mode [35,36]. The CSP basis vectors were approximated by the right and left eigenvectors of the Jacobian of the chemical source term [33,37].…”

Section: Computational Singular Perturbation (Csp) Toolsmentioning

confidence: 99%

Three-stage heat release in n-heptane auto-ignition

Sarathy

Tingas

Nasir

et al. 2019

Proceedings of the Combustion Institute

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Colloquium: REACTION KINETICS / INTERNAL COMBUSTION ENGINES Word Count (Method 1): The total word count (exclusive of title page, abstract) is: 5793 words Word Count (Performed from automatic counting function in MS Word plus References/Tables/Equations/ Figures) Abstract: 235 words, not included in word count Equations: 0 words (0 equations, single column) Figures: 1030 words (4 figures with captions) 3 single 50(+10) 132 4 double 52(+10) 273 Captions 116 Total: 6055 words Supplemental Materials: One supplemental material is available. AbstractMulti-stage heat release is an important feature of hydrocarbon auto-ignition that influences engine operation. This work presents findings of previously unreported three-stage heat release in the autoignition of n-heptane/air mixtures at lean equivalence ratios and high pressures. Detailed homogenous gas-phase chemical kinetic simulations were utilized to identify conditions where two-stage and threestage heat release exist. Temperature and heat release profiles of lean n-heptane/air auto-ignition display three distinct stages of heat release, which is notably different than two-stage heat release typically reported for stoichiometric fuel/air mixtures. Concentration profiles of key radicals (HO2 and OH) and intermediate/product species (CO and CO2) also display unique behavior in the lean autoignition case. Rapid compression machine measurements were performed at a lean equivalence ratio to confirm the existence of three-stage heat release in experiments. Laser diagnostic measurements of CO concentrations in the RCM indicate similar concentration-time profiles as those predicted by kinetic modeling. Computational singular perturbation was then used to identify key reactions and species contributing to explosive time scales at various points of the three-stage ignition process.Comparisons with two-stage ignition at stoichiometric conditions indicate that thermal runaway at the second stage of heat release is inhibited under lean conditions. H+O2 chain branching and CO oxidation reactions drive high-temperature heat release under stoichiometric conditions, but these reactions are suppressed by H, OH, and HO2 radical termination reactions at lean conditions, leading to a distinct third stage of heat release.

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Screening gas‐phase chemical kinetic models: Collision limit compliance and ultrafast timescales

Yalamanchi

Tingas

et al. 2020

Int J of Chemical Kinetics

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Detailed gas‐phase chemical kinetic models are widely used in combustion research, and many new mechanisms for different fuels and reacting conditions are developed each year. Recent works have highlighted the need for error checking when preparing such models, but a useful community tool to perform such analysis is missing. In this work, we present a simple online tool to screen chemical kinetic mechanisms for bimolecular reactions exceeding collision limits. The tool is implemented on a user‐friendly website, cloudflame.kaust.edu.sa, and checks three different classes of bimolecular reactions; (ie, pressure independent, pressure‐dependent falloff, and pressure‐dependent PLOG). In addition, two other online modules are provided to check thermodynamic properties and transport parameters to help kinetic model developers determine the sources of errors for reactions that are not collision limit compliant. Furthermore, issues related to unphysically fast timescales can remain an issue even if all bimolecular reactions are within collision limits. Therefore, we also present a procedure to screen ultrafast reaction timescales using computational singular perturbation. For demonstration purposes only, three versions of the rigorously developed AramcoMech are screened for collision limit compliance and ultrafast timescales, and recommendations are made for improving the models. Larger models for biodiesel surrogates, tetrahydropyran, and gasoline surrogates are also analyzed for exemplary purposes. Numerical simulations with updated kinetic parameters are presented to show improvements in wall‐clock time when resolving ultrafast timescales.

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The mechanism by which CH2O and H2O2 additives affect the autoignition of CH4/air mixtures

Cited by 60 publications

References 41 publications

Algorithmic Analysis of Chemical Dynamics of the Autoignition of NH3–H2O2/Air Mixtures

Algorithmic Analysis of Chemical Dynamics of the Autoignition of NH3–H2O2/Air Mixtures

Three-stage heat release in n-heptane auto-ignition

Screening gas‐phase chemical kinetic models: Collision limit compliance and ultrafast timescales

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