Papers by Georges Descombes
international journal of energy and environmental engineering, Oct 31, 2014
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Machines hydrauliques, aérodynamiques et thermiques, 2021
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International Journal of Engineering and Technology, 2018
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Energy, 2014
ABSTRACT Reducing fuel consumption is a prime objective in order to meet regulatory and customer ... more ABSTRACT Reducing fuel consumption is a prime objective in order to meet regulatory and customer demands. Given this context, an original port fuel injected engine featuring variable valve actuation was initially investigated when operating at idle with low intake valve lift. An improvement of both fuel economy and engine cycle-to-cycle variability was recorded at idle operation, which is a prominent feature of real world driving, especially in congested city traffic. To complete the picture, however, results concerning the engine's internal aerodynamics are necessary. In the present study, the internal aerodynamics and gas exchange phenomena of the engine are examined when using low intake valve lift. For this purpose, a 3D CFD (computational fluid dynamics) dynamic simulation of the motored engine at a speed corresponding to idle operation has been adopted. Experimentation was also performed to obtain data to set the initial and boundary conditions and to calibrate and validate the CFD model. The results provide important insights into the effects of operating the engine with low intake valve lift: increased flow velocity, turbulence and swirl intensity and reduction of internal EGR (exhaust gas recirculation). Thus, this CFD study confirmed our previous work recorded phenomena mentioned as the cause of the engine's idle operation improvement.
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Proceedings of the Institution of Mechanical Engineers, Part D: Journal of Automobile Engineering, 2006
ABSTRACT An improvement in automotive fuel consumption has been for many years the most important... more ABSTRACT An improvement in automotive fuel consumption has been for many years the most important challenge in engine development. In a century of automotive spark ignition engine development, only two parameters were subject to automatic control: the air-fuel ratio and spark advance. Ever since, a wide range of technologies has been developed in order to improve fuel economy further. The following strategy was used: the identification of the sources of losses in the conventional spark ignition engine and then the attempt to reduce them one by one. The potential of these technologies needs to be evaluated by a cost and consumption benefit trade-off and all these, of course, without affecting the power level. In this context, the authors are about to develop a variable geometrical compression ratio engine, in order to overcome the main drawback of the spark ignition engine: the continuous variation of the real rate of compression, caused by the load control. The concept of the variable geometrical compression ratio (VCR) engine is the subject of a patent and consists of a hinged mechanism. It is an intrinsic, automatic self-regulation system with a fast response time and at the same time is a natural development of the classic engine. So far, two prototypes have been designed and tested. The paper presents some specific features regarding hinge position choice. The following are taken into consideration: the upper block rotational angle, added angle of the piston, tipping torque, and relative motion of the camshaft with respect to the crankshaft.
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Energies, 2013
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Colloque francophone sur l’énergie, l’environnement, l’économie et la thermodynamique - COFRET'16, Jun 29, 2016
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International Journal of …, 2001
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Dans le secteur des transports des pays développés, les automobiles constituent le plus grand con... more Dans le secteur des transports des pays développés, les automobiles constituent le plus grand consommateur de pétrole et la source principale d'émission de CO 2 ,, gaz en grande partie responsable de l'effet de serre. Pour l'évaluation et la validation des automobiles dès la phase de conception les simulations des cycles de conduite sont utilisées fréquemment. L'article présente les approches de modélisation utilisées dans ce domaine, ainsi qu'un exemple de simulation d'un cycle de conduite à l'aide du logiciel Advisor.
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Exergy for A Better Environment and Improved Sustainability 1
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Les compresseurs centrifuges presentent, a faible debit et fort taux de compression une zone de f... more Les compresseurs centrifuges presentent, a faible debit et fort taux de compression une zone de fonctionnement tres dangereuse se caracterisant par d'importantes fluctuations du debit et du taux de compression .(Figure 1) Ces instationnarites (observees a des frequences de quelques dizaines de hertz) de l'ecoulement interne dans le compresseur se manifestent egalement par des vibrations et un bruit intense mais aussi par une temperature compresseur qui ne se stabilise jamais. Des tentatives (voulues ou non voulues) de fonctionnement sous ce regime conduisent rapidement a une deterioration du compresseur et du circuit qui lui est associe. Durant ce regime prohibe car dangereux le point de fonctionnement decrit une boucle plus ou moins etendue qui caracterise l'intensite de ce phenomene appele « pompage du compresseur ». Sur la figure 2, on montre la boucle de pompage relevee experimentalement sur un compresseur centrifuge « en pompage » pour un regime de rotation de 100 0...
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Often a turbocharger is led to run at low speeds. A better knowledge of turbocharger characterist... more Often a turbocharger is led to run at low speeds. A better knowledge of turbocharger characteristics at low speeds is needed in order to improve the engine running in this area. As regard friction losses at the turbocharger's shaft, although these are generally small, they have a greater importance in this case of lower speeds. So, in order to have more information on the mechanical efficiency of the turbocharger, a special torquemeter has been fitted in our test bench, affording a speed limit up to 120000 rpm. This device allows the power measurement on the turbocharger's shaft. Applying the first law of thermodynamics, power given to the airflow is calculated and then power losses in the turbocharger's bearings are deducted. This paper presents the first experimentation conducted on the test bench and comments on the results obtained.
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When talking about diesel engine, it cannot be cons idered as a true competitor of the gasoline e... more When talking about diesel engine, it cannot be cons idered as a true competitor of the gasoline engine without the turbocharging. The most obvious drawbac k of the engine-turbocharger assembly is the operat ion of these two machines with highly different laws. T his calls for a tuning of their characteristics. Running at low speeds, which is often encountered i n automotive applications, is generally not an optimum range for the turbocharger. Moreover, in th is area, the compressor map is not given by the turbocharger’s manufacturer. So, a better knowledge of turbocharger characteristics at low speeds is n eeded to obtain the improvement of the engine running. In order to perform this study, a special torquemet er has been fitted in our standard test bench, affo rding measurements from 30000 rpm to 120000 rpm. The expe rimental results, which will be presented in this paper, show the combined effect of the lubricating oil temperature and pressure on power demand of the compressor an...
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Positive Displacement Machines
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En Europe le developpement des Mooc (cours en ligne gratuits et accessibles a tous) est recent. F... more En Europe le developpement des Mooc (cours en ligne gratuits et accessibles a tous) est recent. Fort de son experience en formation a distance pour les adultes, le Conservatoire national des arts et metiers a investi massivement dans cette nouvelle modalite de diffusion des connaissances avec 18 MOOCS realises en deux ans. En energetique, il existait peu de MOOCs francophones alors que ce sujet lie au rechauffement climatique concerne tout un chacun. Le Cnam a donc propose un MOOC intitule « Defis energetiques et risques sanitaires dans les transports ». Celui-ci a ete labellise COP21 a l’occasion de la 21e conference des parties de la convention cadre des Nations Unies dont le but est de limiter le rechauffement climatique. L’objectif du MOOC est de fournir au grand public sous une forme synthetique des outils les plus recents de sensibilisation a la dimension energetique, economique et sanitaire des differents modes de transports. L’article presente les moyens technologiques et l’...
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This article first gives a brief review of heat engines designed for terrestrial transportation s... more This article first gives a brief review of heat engines designed for terrestrial transportation since the 1900s. We then outline the main developments in the state of the art and knowledge about internal combustion engines, focusing on the increasingly stringent pollution constraints imposed since the 1990s. The general concept of high-energy performance machines is analyzed from the energy and public health point of view and illustrated with typical examples of clean energy production and zero emissions. The article concludes with some perspectives for the emergence of an economic model that could be applied to land-based transport systems in the framework of energy transition by 2030.
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Turbo charging is a way for car manufacturers to meet the major challenge of fuel economyand redu... more Turbo charging is a way for car manufacturers to meet the major challenge of fuel economyand reduction of the CO2 emissions. The aim is to replace current engines with a downsized engine in order to improve its fuel consumption. This requires higher specific power and torque especially at very low engine speed. The wide functioning area required for this technique leads to an operation of compressors at low air flow rate and high compression ratio characterised by the occurrence of surge phenomenon. On the engine, it can be intensified by the fuel flow rate pulses consecutive to air flow rate pulses leading to torque oscillations. In fact, surge is an aerodynamic instability that affects both the compressor and its associated network which results in strong pressure and mass flow rate oscillations describing a surge cycle in the compressor map. The surge limit of a centrifugal compressor and its frequency are highly dependant on the geometrical configuration of its associated networ...
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This study presents a comprehensive analysis of the effect of a waste heat recovery (WHR) system ... more This study presents a comprehensive analysis of the effect of a waste heat recovery (WHR) system using the Rankine cycle on passenger car engine fuel consumption. In reciprocating engines more than 60% of fuel energy is lost as heat. The engine studied here is a 2.0liter four-cylinder direct injection diesel engine developed for a passenger car. The maximum engine output power is 101kW at 4000rpm and the maximum torque is 320Nm at 2000rpm. An engine computational model built with the advanced simulation code AVL Boost was used to estimate the engine output power and exhaust gas parameters over the whole operating range. A physical model of the Rankine cycle was also developed, comprising a discretized 0D model of the heat exchanger. Based on the model, a computational code was developed in Python (x,y). The working fluid parameters were determined with the open-source platform CoolProp. The Rankine cycle simulation was conducted over the engine operating map with water as the workin...
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Papers by Georges Descombes