Autoignition of Hydrocarbon/Air Mixtures in a CFR Engine: Experimental and Modeling Study

Blin-Simiand, N.; Rigny, R.; Viossat, V.; Circan, S.; Sahetchian, Krikor

doi:10.1080/00102209308947243

Cited by 42 publications

(19 citation statements)

References 20 publications

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“…Gas temperature rise results from the exothermic character of the reaction process. From 560 to 580 K initial reactor temperature, n-heptane and the PRF mixtures begin to show some conversion, with reactivity peaking from 600 to 625 K due to the decomposition of ketohydroperoxide species and the formation of a second reactive hydroxyl radical, resulting in chain-branching [23,40,48]. At lower initial temperatures, no fuel conversion is observed because ketohydroperoxide decomposition has a high activation energy barrier of approximately 43 kcal/mol.…”

Section: Methodsmentioning

confidence: 99%

Oxidation of automotive primary reference fuels at elevated pressures

Curran

Pitz

Westbrook

et al. 1998

Symposium (International) on Combustion

238

121

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March 1999This is a preprint of a paper intended for publication in a journal or proceedings. Since changes may be made before publication, this preprint is made available with the understanding that it will not be cited or reproduced without the permission of the author. Automotive engine knock limits the maximum operating compression ratio and ultimate thermodynamic efficiency of spark-ignition (SI) engines. In compression-ignition (CI) or diesel cycle engines, the premixed burn phase, which occurs shortly after injection, determines the time it takes for autoignition to occur. In order to improve engine efficiency and to recommend more efficient, cleaner-burning alternative fuels, we must understand the chemical kinetic processes that lead to autoignition in both SI and CI engines. These engines burn large molecular-weight blended fuels, a class to which the primary reference fuels (PRF) n-heptane and iso-octane belong. In this study, experiments were performed under enginelike conditions in a high-pressure flow reactor using both the pure PRF fuels and their mixtures in the temperature range 550-880 K and at 12.5 atm pressure. These experiments not only provide information on the reactivity of each fuel but also identify the major intermediate products formed during the oxidation process. A detailed chemical kinetic mechanism is used to simulate these experiments, and comparisons of experimentally measured and model predicted profiles for O 2 , CO, CO 2 , H 2 O and temperature rise are presented. Intermediates identified in the flow reactor are compared with those present in the computations, and the kinetic pathways leading to their formation are discussed. In addition, autoignition delay times measured in a shock tube over the temperature range 690-1220 K and at 40 atm pressure were simulated. Good agreement between experiment and simulation was obtained for both the pure fuels and their mixtures. Finally, quantitative values of major intermediates measured in the exhaust gas of a cooperative fuels research engine operating under motored engine conditions are presented together with those predicted by the detailed model. PREPRINT

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Section: Methodsmentioning

confidence: 99%

Oxidation of automotive primary reference fuels at elevated pressures

Curran

Pitz

Westbrook

et al. 1998

Symposium (International) on Combustion

238

121

View full text Add to dashboard Cite

show abstract

“…Recent works with motored engines [5][6][7][8] showed that ketohydroperoxides play a key role in the ignition process of fuel/air mixtures since the decomposition of these species gives two radicals. Computer modeling studies performed with reduced chemical mechanisms [7,[9][10][11] enabled a fairly good reproduction of the experimental results. As shown recently in a comprehensive modeling study of n-heptane oxidation [12], the introduction of isomerization reactions and the formation of ketohydroperoxides are necessary in the modeling of alkane fuel oxidation, and, moreover, they permit a reduction of the whole number of required reactions.…”

Section: Introductionmentioning

confidence: 99%

Isomeric hexyl‐ketohydroperoxides formed by reactions of hexoxy and hexylperoxy radicals in oxygen

Jorand

Heiss

Perrin

et al. 2003

Int J of Chemical Kinetics

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Isomerization reactions of peroxy radicals during oxidation of long-chain hydrocarbons yield hydroperoxides, and therefore play an important role in combustion and atmospheric chemistry, because of their action as branching agents in these chain reaction processes. Different formation mechanisms and structures are involved. Three isomeric hexyl-ketohydroperoxides are formed via isomerization reactions in oxygen of either hexoxy RO or hexylperoxy RO 2 radicals. In the temperature range 373-473 K, 2-hexoxy (C 6 H 13 O) radical in O 2 /N 2 mixtures gives 2-hexanone-5-hydroperoxide via two consecutive isomerizations. The second one is a H transfer from a HC(OH) group occurring via a seven-membered ring intermediate:Its rate constant has been determined at 453 and 483 K, and the general expression can be written as k = (1.8 ± 1) × 10 10 × exp[−(14300 ± 700)/RT] s −1 (E a in cal mol −1 ) Hexylperoxy C 6 H 13 O 2 radical, present in n-hexane oxidation by oxygen/nitrogen mixtures in the temperature range 543-573 K, gives 2-hexanone-4-hydroperoxide, 3-hexanone-5-hydroperoxide, and 2-hexanone-5-hydroperoxide. The first two are formed through an

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“…The first stage could be detected by studying the blue light, a characteristic color for the emission of HCHO* (Figure 2), formed during this step [10,11,12]. Depending on the fuel chemistry, in some cases at a given pressure and for some low initial temperature (lower than 750 K), the oxidation process slows down whereas the temperature increases.…”

Section: H Machrafi Et Almentioning

confidence: 99%

Reduced chemical reaction mechanisms: experimental and HCCI modelling investigations of autoignition processes of iso-octane in internal combustion engines

Machrafi

Lombaert

Cavadias

et al. 2005

Fuel

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A semi-reduced (70 species, 210 reactions) and a skeletal (27 species, 29 reactions) chemical reaction mechanism for iso-octane are constructed from a semi-detailed isooctane mechanism (84 species, 412 reactions) of the Chalmers University of Technology in Sweden. The construction of the reduced mechanisms is performed by using reduction methods such as the quasi-steady-state assumption and the partial equilibrium assumption. The obtained reduced iso-octane mechanisms show, at the mentioned conditions, a perfect coherence with another more detailed iso-octane mechanism of ENSIC-CNRS (2411 reactions and 473 species) and the semi-detailed iso-octane mechanism of Chalmers. The validity of this mechanism with regard to the ignition delay is determined for several engine parameters adhering to HCCI conditions : inlet temperature (303-363 K), equivalence ratio (0.2-0.7) and compression ratio (10-16). The ignition delay is found to be decreased by an increase in the inlet temperature, H. Machrafi et al. a decrease in the equivalence ratio and an increase in the compression ratio. In order to validate the effects of the inlet temperature, compression ratio on the auto-ignition delay, experiments are performed on a CFR engine. A good agreement is obtained between experimental results and calculations.

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Autoignition of Hydrocarbon/Air Mixtures in a CFR Engine: Experimental and Modeling Study

Cited by 42 publications

References 20 publications

Oxidation of automotive primary reference fuels at elevated pressures

Oxidation of automotive primary reference fuels at elevated pressures

Isomeric hexyl‐ketohydroperoxides formed by reactions of hexoxy and hexylperoxy radicals in oxygen

Reduced chemical reaction mechanisms: experimental and HCCI modelling investigations of autoignition processes of iso-octane in internal combustion engines

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