M. Ribaucour - Academia.edu (original) (raw)

Papers by M. Ribaucour

Proceedings of the Combustion Institute, 2000

Experiments in a rapid compression machine were used to examine the influences of variations in f... more Experiments in a rapid compression machine were used to examine the influences of variations in fuel molecular structure on the autoignition of isomers of pentane. Autoignition of stoichiometric mixtures of the three isomers of pentane were studied at compressed gas initial temperatures between 640 K and 900 K and at precompression pressures of 300 and 400 torr. Numerical simulations of the same experiments were carried out using a detailed chemical kinetic reaction mechanism. The results are interpreted in terms of a low-temperature oxidation mechanism involving addition of molecular oxygen to alkyl and hydroperoxyalkyl radicals. Results indicate that in most cases, the reactive gases experience a two-stage autoignition. The first stage follows a low-temperature alkylperoxy radical isomerization pathway that is effectively quenched when the temperature reaches a level where dissociation reactions of alkylperoxy and hydroperoxyalkylperoxy radicals are more rapid than the reverse addition steps. The second stage is controlled by the onset of dissociation of hydrogen peroxide. At the highest compression temperatures achieved, little or no first-stage ignition is observed. Particular attention is given to the influence of heat transfer and the importance of regions of variable temperature within the compressed gas volume. Implications of this work on practical ignition problems are discussed.

International Journal of Chemical Kinetics, 2007

ABSTRACT This study describes a new technique of reduction of detailed mechanisms for autoignitio... more ABSTRACT This study describes a new technique of reduction of detailed mechanisms for autoignition. It is based on two analysis methods. An analysis of reaction rates is coupled to an analysis of reaction sensitivity for the detection of redundant reactions. Thresholds associated with the two analyses have a great influence on the size and efficiency of the reduced mechanism. Rules of selection of the thresholds are defined. The reduction technique has been successfully applied to detailed autoignition mechanisms of two reference hydrocarbons: n-heptane and isooctane. The efficiency of the technique and the ability of the reduced mechanisms to reproduce well the results generated by the full mechanism are discussed. A speedup of calculations by a factor of 5.9 for n-heptane mechanism and by a factor of 16.7 for isooctane mechanism is obtained without losing accuracy of the prediction of autoignition delay times and concentrations of intermediate species. © 2007 Wiley Periodicals, Inc. 39: 181–196, 2007

Fuel, 2006

ABSTRACT This article reports a detailed reaction mechanism able to predict our experimental data... more ABSTRACT This article reports a detailed reaction mechanism able to predict our experimental data obtained for methane/benzene and n-heptane/benzene mixtures at low and high temperature. The high temperature data consist in mole fraction profiles of stable and reactive species measured in low-pressure (5.19×10−2 bar) stoichiometric premixed CH4/O2/N2 and CH4/1.5%C6H6/O2/N2 flames by coupling MB/MS and GC/MS techniques. The low temperature data consist in cool flame and autoignition delay times of a 50%n-heptane/50%benzene/air mixture measured in a rapid compression machine in the ranges 620–885K and 4.63–8.87bar. Intermediate oxidation products were also analyzed. The proposed mechanism includes our previous GDF-Kin®2.0 mechanism developed for natural gas oxidation, a low and high temperature literature submechanism of n-heptane oxidation, and a high temperature submechanism of benzene oxidation. Predicted mole fraction profiles measured in methane and methane/benzene flames are in reasonable agreement with experimental profiles for most molecular species. Reaction path analyses were performed to interpret the effect of benzene on the analyzed chemical species in the methane/benzene flame. The proposed mechanism reproduces well the evolution of both delay times versus temperature. Local sensitivity analyses show that, in the low temperature range, benzene plays a non-significant role in the reactivity of the n-heptane/benzene mixture and acts more as a diluent than as a chemical inhibitor.

Combustion and Flame, 1995

n-Heptane oxidation and auto-ignition in a rapid compression machine is studied in the low and in... more n-Heptane oxidation and auto-ignition in a rapid compression machine is studied in the low and intermediate temperature regimes at high pressures. Experimental ignition delay times and some phenomenological aspects related to knock in engines are presented, ...

Combustion and Flame, 2011

ABSTRACT

Combustion and Flame, 1999

The pre-autoignition chemistry of n-pentane and 1-pentene was studied by rapid compression in the... more The pre-autoignition chemistry of n-pentane and 1-pentene was studied by rapid compression in the low temperature range (600 -900 K). The pressure traces, light emissions, intensities of cool flames, autoignition delays, and hydrocarbon conversions before final ignition indicate that there are similarities of behavior, but a lower reactivity of 1-pentene over the whole temperature range. Chemical analysis of the stable intermediate species after the cool flame, but before final ignition, shows marked differences in selectivities for Oheterocycles and aldehydes. Relatively high amounts of propyloxirane and butanal in the oxidation of 1-pentene suggest additions of oxidizing radicals to the double bond. The classical low temperature peroxidation scheme of alkanes can be applied, not only to n-pentane, but also to 1-pentene, if the higher reactivity of the allylic hydrogens and direct addition of OH and HO 2 radicals are taken into account. Some peroxy radicals are common to both fuels and are responsible for their similar features of pre-autoignition chemistry. However, oxidation of 1-pentene is still deeply marked by the presence of an olefinic bond.

Combustion and Flame, 2001

The oxidation and auto-ignition of cyclohexane, cyclohexene, and cyclohexa-1,3-diene have been st... more The oxidation and auto-ignition of cyclohexane, cyclohexene, and cyclohexa-1,3-diene have been studied by rapid compression between 600 K to 900 K and 0.7 MPa to 1.4 MPa to identify the low-temperature pathways leading to benzene from cyclohexane. Auto-ignition delay times were measured and concentration-time profiles of the C 6 intermediate products of oxidation were measured during the auto-ignition delays. Cyclohexane showed two-stage ignition at low temperatures, but single-stage ignition at higher temperatures, and a well-marked negative-temperature coefficient. By contrast there was neither a cool flame, nor a negativetemperature coefficient for cyclohexa-1,3-diene. Cyclohexene behaved in an intermediate way without a cool flame, but with a narrow, not very marked negative-temperature coefficient. The identified C 6 products belong to three families: the bicyclic epoxides and cyclic ketones, the unsaturated aliphatic aldehydes, and the conjugated alkenes, which are always the major products. The formation of C 6 products from cyclohexane is explained by the classical scheme for low-temperature oxidation, taking into account addition of O 2 to cyclohexyl radicals and the various isomerizations of the resulting peroxy radicals. Most of the C 6 products from cyclohexene are predicted by the same scheme, beginning with the formation of the allylic cyclohexenyl radical. However, addition of HO 2 to the double bond has to be included to predict the formation of 1,2epoxycyclohexane. For cyclohexa-1,3-diene, the classical scheme is not valid: the C 6 oxygenated products are only formed by addition of HO 2 to the double bond. For all three hydrocarbons, the pathways to benzene are those leading to conjugated alkenes, and they are always more efficient than those producing oxygenated products, either by adding HO 2 to double bonds, or by addition of O 2 to the initial cyclic radical.

Fuel, 2008

The ignition delay times of CH 4 =C 2 H 6 =C 3 H 8 mixtures representative of an average natural ... more The ignition delay times of CH 4 =C 2 H 6 =C 3 H 8 mixtures representative of an average natural gas composition have been measured in a rapid compression machine (RCM) at the University of Lille. The pressure at the end of compression (EOC) varied from 13 to 21 bar and the core gas temperature ranged from 850 to 925 K. Zero-dimensional modelling starting from the EOC was used to reproduce the experimental ignition delay times taking into account heat losses during the pre-ignition phase. The experimental database served as basis for the development of a reaction mechanism suitable for HCCI like autoignition simulations on a stationary co-generation engine with a prechamber, which is under development at the laboratory. Different mechanisms for natural gas oxidation and combustion have been tested and their low temperature simulation ability investigated, showing difficulties to properly reproduce the low temperature ignition delay times. Starting from the GRI3.0 mechanism with an additional submodule improving the low temperature chemistry representation, a sensitivity analysis was performed to determine the most influential reactions. The rate constants of these reactions were then optimised within their range of uncertainty using a multi-objective strategy. The resulting optimised mechanism led to a strong improvement of the agreement between simulation and experimental RCM data. The optimised mechanism was also tested on experimental shock tube data between 900 and 1250 K and gave satisfying results within the temperature range where the optimisation was performed on. Therefore, the applied optimisation technique showed its efficiency.