Pressure and temperature effects on fuels with varying octane sensitivity at high load in SI engines

Szybist, James P.; Splitter, Derek

doi:10.1016/j.combustflame.2016.12.002

Cited by 127 publications

(66 citation statements)

References 38 publications

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“…The endgas ahead of the flame front was compressed and heated; this T-P was representative of the endgas before auto-ignition. Experiments from Szybist et al showed unburnt mixture temperatures in this range for RON tests, depending on the compression ratio of the engine [53]. A relatively lower temperature (compared to previous publications), coincided with the higher pressure, placing the mixtures in the NTC region, where the RON of fuel blends has been correlated with IDT previously [25][26][27].…”

Section: Methodsmentioning

confidence: 80%

Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels

et al. 2019

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The synergistic octane blending behavior of ethanol with gasoline and its surrogates has been observed by many researchers. The non-linear octane boosting tendency is observed at mid and high molar blends of ethanol in primary references fuels. The present work aims to provide chemical insight into this non-linear blending behavior of ignition processes when ethanol is blended with primary reference fuels. To this end, ignition delay time calculations, using a wellvalidated mechanism, were performed for several fuel blends of iso-octane, n-heptane, and ethanol. Temperature and pressure values were found, correlating experimentally measured octane numbers and simulated homogenous batch reactor ignition delay times. The temperature and pressure conditions obtained, were then used to study the evolution of heat release and reactivity before the onset of auto-ignition in a homogeneous premixed reactor. Markers of low and high temperature reactivity (OH and HO2) were analyzed for various molar blends of n-heptane with ethanol/iso-octane. Ethanol was observed to be better at radical scavenging than iso-octane at higher mole fraction. A computational singular perturbation analysis was conducted for a selection of blends to clarify the reactions responsible for the synergistic blending behavior of ethanol in nheptane. The role of the H-abstraction reactions was highlighted during the first ignition stage; reactions related to n-heptane were found to compete with the H-abstraction reactions of iso-octane or ethanol. Notably, the H-abstraction path of ethanol was more favored than that of the iso-octane, as a result of the smaller activation energies of the related reactions in the ethanol. The competition of the H-abstraction paths resulted in a smaller radical pool in the n-heptane-iso-octane-air case, and an even smaller pool in the n-heptane-ethanol-air. In all the cases considered, the second stage was dominated mainly by hydrogen-related reactions, regardless of the initial mixture, with the H2O2 (+ M) → 2OH (+ M) and H + O2 → O + OH playing the most important roles. This work employed a novel approach to examine specific reactions responsible for auto-ignition in ethanol blends, which can be used for fuel design, primarily around the generation/consumption of radical pool intermediates by interaction with fuel components.

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Section: Methodsmentioning

confidence: 80%

Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels

et al. 2019

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“…Two-stage heat release is a feature of alkane auto-ignition [15][16][17] that has attracted significant research interest in both fundamental [18] and practical [19] applications. This phenomenon is characterized by a low-temperature heat release (LTHR) regime that raises the system temperature and results in the first stage (1) ignition delay time (IDT).…”

Section: Introductionmentioning

confidence: 99%

“…Auto-ignition phenomena with more than two stages of heat release have been seldom reported in the literature. Intermediate-temperature heat release (ITHR) has been observed in engines [19,21,22]; however, this is not a distinct stage of heat release because it is typically merged with the HTHR and the controlling chemistry is attributed to traditional competition between alkyl peroxy radical chain branching, propagation, and termination pathways. Yamamoto et al [23] reported three-stage oxidation of n-heptane/air in a micro-flow reactor with controlled temperature profile.…”

Section: Introductionmentioning

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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“…100-300 • C with an internally cooled metallic base) [15][16][17]. Theories developed in this field indicate that TBCs can have additional benefits such as an increase in mean combustion temperature, reduction in heat loss to the cooling system, increase in the coefficient of thermal efficiency of the engine and enhancement in the fuel consumption rate [18][19][20][21][22][23][24][25]. Several techniques/methods are developed by researchers such as…”

Section: Introductionmentioning

confidence: 99%

Modelling Thermal Conductivity of Porous Thermal Barrier Coatings

2019

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Thermal conductivity of porous thermal barrier coatings was evaluated using a newly developed five-phase model. It was demonstrated that porosities distributed in coating strongly affect thermal conductivity. The decisive reason for this change in thermal conductivity can be traced back to defect morphology and its orientation, depending on the coating deposition technique and process parameters used during deposition. In this paper, the Bruggeman’s two-phase model was used as a reference, and a five-phase model was developed to evaluate the thermal conductivity of porous coatings. This approach uses microstructural details of the shape, size, orientation and volumetric fraction of defects of coatings as input parameters. The proposed model can predict thermal conductivity values better than the previous two-phase model.

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Pressure and temperature effects on fuels with varying octane sensitivity at high load in SI engines

Cited by 127 publications

References 38 publications

Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels

Chemical Ignition Characteristics of Ethanol Blending with Primary Reference Fuels

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

Modelling Thermal Conductivity of Porous Thermal Barrier Coatings

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