Bruno IMBERT - Academia.edu (original) (raw)
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Papers by Bruno IMBERT
Le Centre pour la Communication Scientifique Directe - HAL - Université de Nantes, 2003
International audienc
Journal of Rheology, 2013
Being able to model at what point a yield stress material starts to flow under its own weight is ... more Being able to model at what point a yield stress material starts to flow under its own weight is of great importance for many practical applications. However, describing the deformation of yield stress fluids under gravity is anything but a simple exercise due to the feedback between the shape of the deposited material and the locally acting stresses. In this article, we concentrate on a specific aspect of this problem: What is the maximum height of a pile of a yield stress fluid which can be obtained under gravity? For this purpose we use the example of liquid foams in which the yield stress is strongly coupled to the bubble size and the liquid fraction. We show that a good agreement between models and experiments is obtained over a wide parameter range in two limiting cases: When the yield stress is either higher or much lower than the normal stresses encountered in the material. V
Journal of Propulsion and Power, 2004
ABSTRACT Ignition time measurements of lean, stoichiometric, and rich n-heptane/oxygen/argon mixt... more ABSTRACT Ignition time measurements of lean, stoichiometric, and rich n-heptane/oxygen/argon mixtures have been studied behind reflected shock waves in the temperature range 1300-1600 K and pressure range 2-4 atm. The experimental data were compared to previously published results and have been found to be consistent with them. The experimental data were compared to ignition delay predicted using some of the kinetic models available in the literature. Discrepancies have been interpreted kinetically, thus leading to a slightly modified detailed kinetic model able to predict accurately high-temperature ignition delay such as encountered in the heptane/oxygen detonation wave.
Fuel, 2009
ABSTRACT A novel ignition concept based on autoignition in an unscavanged prechamber is currently... more ABSTRACT A novel ignition concept based on autoignition in an unscavanged prechamber is currently being developed at the Laboratory for Industrial Energy Systems (LENI). On a single cylinder test engine a series of experimental runs (CR=8.5-14, =1-1.6, RPM=1150/1500 min−1) have been realized with natural gas as fuel, comparing the new ignition concept to standard spark ignition. The comparison is based on fuel efficiency and exhaust emissions (CO, THC, NOx). The feasibility of operating the engine in auto-ignition mode has been demonstrated, and the potential of prechamber autoignition, in particular in the lean combustion regime, is indicated by the trends in fuel efficiency and emission concentration. The resistive heating of the prechamber walls has been shown to be an effective mean to trigger ignition. The prechamber could clearly be identified as primary ignition location. A reduction of the cycle-by-cycle variations - due to mixture fluctuations - is necessary to exploit the full potential of this engine concept.
Le Centre pour la Communication Scientifique Directe - HAL - CEA - Commissariat à l’énergie atomique, 2005
International audienc
Combustion and Flame, 2008
This article is part of the project to model the kinetics of high-temperature combustions, occurr... more This article is part of the project to model the kinetics of high-temperature combustions, occurring behind shock waves and in detonation waves. The "conventional" semi-empirical correlations of ignition delays have been reformulated, by keeping the Arrhenius equation form. It is shown how a polynomial with 3 N coefficients (where N ∈ [1, 4] is the number of adjustable kinetic parameters, likely to be simultaneously chosen among the temperature T , the pressure P , the inert fraction X Ar , and the equivalence ratio Φ) can reproduce the delays predicted by the Curran et al. [
Le Centre pour la Communication Scientifique Directe - HAL - Université de Nantes, 2003
International audienc
Journal of Rheology, 2013
Being able to model at what point a yield stress material starts to flow under its own weight is ... more Being able to model at what point a yield stress material starts to flow under its own weight is of great importance for many practical applications. However, describing the deformation of yield stress fluids under gravity is anything but a simple exercise due to the feedback between the shape of the deposited material and the locally acting stresses. In this article, we concentrate on a specific aspect of this problem: What is the maximum height of a pile of a yield stress fluid which can be obtained under gravity? For this purpose we use the example of liquid foams in which the yield stress is strongly coupled to the bubble size and the liquid fraction. We show that a good agreement between models and experiments is obtained over a wide parameter range in two limiting cases: When the yield stress is either higher or much lower than the normal stresses encountered in the material. V
Journal of Propulsion and Power, 2004
ABSTRACT Ignition time measurements of lean, stoichiometric, and rich n-heptane/oxygen/argon mixt... more ABSTRACT Ignition time measurements of lean, stoichiometric, and rich n-heptane/oxygen/argon mixtures have been studied behind reflected shock waves in the temperature range 1300-1600 K and pressure range 2-4 atm. The experimental data were compared to previously published results and have been found to be consistent with them. The experimental data were compared to ignition delay predicted using some of the kinetic models available in the literature. Discrepancies have been interpreted kinetically, thus leading to a slightly modified detailed kinetic model able to predict accurately high-temperature ignition delay such as encountered in the heptane/oxygen detonation wave.
Fuel, 2009
ABSTRACT A novel ignition concept based on autoignition in an unscavanged prechamber is currently... more ABSTRACT A novel ignition concept based on autoignition in an unscavanged prechamber is currently being developed at the Laboratory for Industrial Energy Systems (LENI). On a single cylinder test engine a series of experimental runs (CR=8.5-14, =1-1.6, RPM=1150/1500 min−1) have been realized with natural gas as fuel, comparing the new ignition concept to standard spark ignition. The comparison is based on fuel efficiency and exhaust emissions (CO, THC, NOx). The feasibility of operating the engine in auto-ignition mode has been demonstrated, and the potential of prechamber autoignition, in particular in the lean combustion regime, is indicated by the trends in fuel efficiency and emission concentration. The resistive heating of the prechamber walls has been shown to be an effective mean to trigger ignition. The prechamber could clearly be identified as primary ignition location. A reduction of the cycle-by-cycle variations - due to mixture fluctuations - is necessary to exploit the full potential of this engine concept.
Le Centre pour la Communication Scientifique Directe - HAL - CEA - Commissariat à l’énergie atomique, 2005
International audienc
Combustion and Flame, 2008
This article is part of the project to model the kinetics of high-temperature combustions, occurr... more This article is part of the project to model the kinetics of high-temperature combustions, occurring behind shock waves and in detonation waves. The "conventional" semi-empirical correlations of ignition delays have been reformulated, by keeping the Arrhenius equation form. It is shown how a polynomial with 3 N coefficients (where N ∈ [1, 4] is the number of adjustable kinetic parameters, likely to be simultaneously chosen among the temperature T , the pressure P , the inert fraction X Ar , and the equivalence ratio Φ) can reproduce the delays predicted by the Curran et al. [