References of "Machrafi, Hatim"
     in
Bookmark and Share    
Full Text
Peer Reviewed
See detailUsing time-dependent reference profiles for an instability analysis of an evaporating binary liquid layer
Machrafi, Hatim ULg; Rednikov, Alexey; Colinet et al

in Proceedings of the International Conference on Multiscale Comples Fluid Flows and Interfacial Phenomena, 16 (2010)

This study treats an evaporating horizontal binary-liquid layer (aqueous solution of 10 % wt ethanol) in contact with air with an imposed transfer distance. Solutal and thermal Rayleigh-B´enard-Marangoni ... [more ▼]

This study treats an evaporating horizontal binary-liquid layer (aqueous solution of 10 % wt ethanol) in contact with air with an imposed transfer distance. Solutal and thermal Rayleigh-B´enard-Marangoni instabilities are taken into account together with the Soret effect. The critical times with corresponding liquid thicknesses are calculated, showing that a critical liquid thickness can be found under which no instability can occur. [less ▲]

Detailed reference viewed: 23 (14 ULg)
Peer Reviewed
See detailBénard instabilities of a binary liquid layer evaporating into an inert gas: stability of quasi-stationary and time-dependent reference profiles
Machrafi, Hatim ULg; Rednikov, A.; Colinet, Pierre et al

in Proceedings of the 5th Conference of the International Marangoni Association “Interfacial Fluid Dynamics and Processes” (2010)

Detailed reference viewed: 39 (14 ULg)
Full Text
Peer Reviewed
See detailLinear stability analysis of an evaporating binary liquid layer with fully transient reference profiles
Machrafi, Hatim ULg; Rednikov, Alexey; Colinet, Pierre et al

in Bulletin of the American Physical Society, Vol. 55, n°16 (2010)

Detailed reference viewed: 19 (13 ULg)
Full Text
Peer Reviewed
See detailInfluence of fuel type, dilution and equivalence ratio on the emission reduction from the auto-ignition in an Homogeneous Charge Compression Ignition engine
Machrafi, Hatim ULg; Cavadias, Simeon; Amouroux, Jacques

in Energy (2010), 35(4), 1829-1838

One technology that seems to be promising for automobile pollution reduction is the Homogeneous Charge Compression Ignition (HCCI). This technology still faces auto-ignition and emission-control problems ... [more ▼]

One technology that seems to be promising for automobile pollution reduction is the Homogeneous Charge Compression Ignition (HCCI). This technology still faces auto-ignition and emission-control problems. This paper focuses on the emission problem, since it is incumbent to realize engines that pollute less. For this purpose, this paper presents results concerning the measurement of the emissions of CO, NOx, CO2, O-2 and hydrocarbons. HCCI conditions are used, with equivalence ratios between 0.26 and 0.54, inlet temperatures of 70 degrees C and 120 degrees C and compression ratios of 10.2 and 13.5, with different fuel types: gasoline, gasoline surrogate, diesel, diesel surrogate and mixtures of n-heptane/toluene. The effect of dilution is considered for gasoline, while the effect of the equivalence ratio is considered for all the fuels. No significant amount of NOx has been measured. It appeared that the CO, O-2 and hydrocarbon emissions were reduced by decreasing the toluene content of the fuel and by decreasing the dilution. The opposite holds for CO2. The reduction of the hydrocarbon emission appears to compete with the reduction of the CO2 emission. Diesel seemed to produce less CO and hydrocarbons than gasoline when auto-ignited. An example of emission reduction control is presented in this paper. (C) 2010 Elsevier Ltd. All rights reserved. [less ▲]

Detailed reference viewed: 40 (0 ULg)
Full Text
Peer Reviewed
See detailBénard instabilities in a binary-liquid layer evaporating into an inert gas
Machrafi, Hatim ULg; Rednikov, Alexey; Colinet, Pierre et al

in Journal of Colloid & Interface Science (2010), 349

Detailed reference viewed: 28 (11 ULg)
Full Text
Peer Reviewed
See detailThe development and experimental validation of a reduced ternary kinetic mechanism for the auto-ignition at HCCI conditions, proposing a global reaction path for ternary gasoline surrogates
Machrafi, Hatim ULg; Cavadias, Simeon; Amouroux, Jacques

in Fuel Processing Technology (2009), 90(2), 247-263

To acquire a high amount of information of the behaviour of the Homogeneous Charge Compression Ignition (HCCI) auto-ignition process, a reduced surrogate mechanism has been composed out of reduced n ... [more ▼]

To acquire a high amount of information of the behaviour of the Homogeneous Charge Compression Ignition (HCCI) auto-ignition process, a reduced surrogate mechanism has been composed out of reduced n-heptane, iso-octane and toluene mechanisms, containing 62 reactions and 49 species. This mechanism has been validated numerically in a OD HCCI engine code against more detailed mechanisms (inlet temperature varying from 290 to 500 K, the equivalence ratio from 0.2 to 0.7 and the compression ratio from 8 to 18) and experimentally against experimental shock tube and rapid compression machine data from the literature at pressures between 9 and 55 bar and temperatures between 700 and 1400 K for several fuels: the pure compounds n-heptane, iso-octane and toluene as well as binary and ternary mixtures of these compounds. For this validation, stoichiometric mixtures and mixtures with an equivalence ratio of 0.5 are used. The experimental validation is extended by comparing the surrogate mechanism to experimental data from an HCCI engine. A global reaction pathway is proposed for the auto-ignition of a surrogate gasoline, using the surrogate mechanism, in order to show the interactions that the three compounds can have with one another during the auto-ignition of a ternary mixture. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 34 (0 ULg)
Peer Reviewed
See detailStability analysis of the evaporation of a binary liquid into an inert gas, considering solute/thermal and gravity/surface tension effects
Machrafi, Hatim ULg; Rednikov, A.; Colinet, P. et al

in Proceedings (CD) of the EUROTHERM Seminar Nr. 84 “Thermodynamics of phase changes”, Namur (Belgium), May 24-27, 2009 (2009)

Detailed reference viewed: 26 (9 ULg)
Peer Reviewed
See detailStability analysis of an evaporating binary mixture
Machrafi, Hatim ULg; Rednikov, Alexey; Colinet, Pierre et al

in Bulletin of the American Physical Society, Vol. 53, n°15 (2008, November 01)

Rayleigh-Bénard-Marangoni instabilities in an evaporating binary mixture, consisting of a solvent and a solute of weak concentration, are studied theoretically. Local thermodynamic equilibrium is assumed ... [more ▼]

Rayleigh-Bénard-Marangoni instabilities in an evaporating binary mixture, consisting of a solvent and a solute of weak concentration, are studied theoretically. Local thermodynamic equilibrium is assumed at the flat gas-liquid interface. Solvent evaporation and air absorption in the liquid are neglected. At a certain height above the interface, the temperature and the concentration are fixed. One of the goals of the study is to track down the effects of this artifact on the results. Non-linear quasi-stationary basic profiles (due to evaporation) of the temperature and the solute concentration in the gas phase are considered, while the temperature distribution in the liquid is assumed to be linear and quasi-stationary. For the solute concentration in the liquid phase, two variants of the reference solution are studied, one just linear and quasi-stationary, whereas the other involves a fully transient non-linear profile. The latter is a more realistic option, given the relatively slow diffusion time in the liquid. A linear stability analysis is then carried out numerically, and illustrated for an aqueous solution of ethyl alcohol. [less ▲]

Detailed reference viewed: 18 (4 ULg)
Full Text
Peer Reviewed
See detailAn experimental and numerical analysis of the HCCI auto-ignition process of primary reference fuels, toluene reference fuels and diesel fuel in an engine, varying the engine parameters
Machrafi, Hatim ULg; Cavadias, Simeon; Gilbert, Philippe

in Fuel Processing Technology (2008), 89(11), 1007-1016

For a future HCCI engine to operate under conditions that adhere to environmental restrictions, reducing fuel consumption and maintaining or increasing at the same time the engine efficiency, the choice ... [more ▼]

For a future HCCI engine to operate under conditions that adhere to environmental restrictions, reducing fuel consumption and maintaining or increasing at the same time the engine efficiency, the choice of the fuel is crucial. For this purpose, this paper presents an auto-ignition investigation concerning the primary reference fuels, toluene reference fuels and diesel fuel, in order to study the effect of linear alkanes, branched alkanes and aromatics on the auto-ignition. The auto-ignition of these fuels has been studied at inlet temperatures from 25 to 120 degrees C, at equivalence ratios from 0.18 to 0.53 and at compression ratios from 6 to 13.5, in order to extend the range of investigation and to assess the usability of these parameters to control the auto-ignition. It appeared that both iso-octane and toluene delayed the ignition with respect to n-heptane, while toluene has the Strongest effect. This means that aromatics have higher inhibiting effects than branched alkanes. In an increasing order, the inlet temperature, equivalence ratio and compression ratio had a promoting effect on the ignition delays. A previously experimentally validated reduced surrogate mechanism, for mixtures of n-heptane, iso-octane and toluene, has been used to explain observations of the auto-ignition process. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 23 (0 ULg)
Full Text
Peer Reviewed
See detailAn experimental and numerical analysis of the influence of the inlet temperature, equivalence ratio and compression ratio on the HCCI auto-ignition process of Primary Reference Fuels in an engine
Machrafi, Hatim ULg; Cavadias

in Fuel Processing Technology (2008), 89(11), 1218-1226

In order to understand better the auto-ignition process in an HCCI engine, the influence of some important parameters on the auto-ignition is investigated. The inlet temperature, the equivalence ratio and ... [more ▼]

In order to understand better the auto-ignition process in an HCCI engine, the influence of some important parameters on the auto-ignition is investigated. The inlet temperature, the equivalence ratio and the compression ratio were varied and their influence on the pressure, the heat release and the ignition delays were measured, The inlet temperature was changed from 25 to 70 degrees C and the equivalence ratio from 0.18 to 0.41, while the compression ratio varied from 6 to 13.5. The fuels that were investigated were PRF40 and n-heptane. These three parameters appeared to decrease the ignition delays, with the inlet temperature having the least influence and the compression ratio the most. A previously experimentally validated reduced surrogate mechanism, for mixtures of n-heptane, iso-octane and toluene, has been used to explain observations of the auto-ignition process. The same kinetic mechanism is used to better understand the underlying chemical and physical phenomena that make the influence of a certain parameter change according to the operating conditions. This can be useful for the control of the auto-ignition process in an HCCI engine. (C) 2008 Elsevier B.V. All rights reserved. [less ▲]

Detailed reference viewed: 27 (0 ULg)
Full Text
Peer Reviewed
See detailAn experimental and numerical investigation on the influence of external gas recirculation on the HCCI autoignition process in an engine: Thermal, diluting, and chemical effects
Machrafi, Hatim ULg; Cavadias, Simeon; Guibert, Philippe

in Combustion & Flame (2008), 155(3), 476-489

In order to contribute to the solution of controlling the autoignition in a homogeneous charge compression ignition (HCCI) engine, parameters linked to external gas recirculation (EGR) seem to be of ... [more ▼]

In order to contribute to the solution of controlling the autoignition in a homogeneous charge compression ignition (HCCI) engine, parameters linked to external gas recirculation (EGR) seem to be of particular interest. Experiments performed with EGR present some difficulties in interpreting results using only the diluting and thermal aspect of EGR. Lately, the chemical aspect of EGR is taken more into consideration, because this aspect causes a complex interaction with the dilution and thermal aspects of EGR. This paper studies the influence of EGR on the autoignition process and particularly the chemical aspect of EGR. The diluents present in EGR are stimulated by N-2 and CO2, with dilution factors going from 0 to 46 vol%. For the chemically active species that could be present in EGR, the species 0 and 170 ppm, while that of CH2O alters between 0 and 1400 ppm. For the investigation of the effect of the chemical species on the autoignition, a fixed dilution factor of 23 vol% and a fixed EGR temperature of 70 degrees C are maintained. The inlet temperature is held at 70 degrees C, the equivalence ratios between 0.29 and 0.41, and the compression ratio at 10.2. The fuels used for the autoignition are n-heptane and PRF40. It appeared that CO, in the investigated domain, did not influence the ignition delays, while NO had two different effects. At concentrations up until 45 ppm, NO advanced that ignition delays for the PRF40 and at higher concentrations, the ignition delayed. The influence of NO on the autoignition of n-heptane seemed to be insignificant, probably due to the higher burn rate of n-heptane. CH2O seemed to delay the ignition. The results suggested that especially the formation of OH radicals or their consumption by the chemical additives determines how the reactivity of the autoignition changed. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved. [less ▲]

Detailed reference viewed: 18 (0 ULg)
Full Text
Peer Reviewed
See detailThree-stage autoignition of gasoline in an HCCI engine: An experimental and chemical kinetic modeling investigation
Machrafi, Hatim ULg; Cavadias, Simeon

in Combustion & Flame (2008), 155(4), 557-570

The alternative HCCI combustion mode presents a possible means for decreasing the Pollution with respect to conventional gasoline or diesel engines, while maintaining the efficiency of a diesel engine or ... [more ▼]

The alternative HCCI combustion mode presents a possible means for decreasing the Pollution with respect to conventional gasoline or diesel engines, while maintaining the efficiency of a diesel engine or even increasing it. This paper investigates the possibility Of using gasoline in an HCCI engine and analyzes the autoignition of gasoline in such an engine. The compression ratio that has been used is 13.5, keeping the inlet temperature at 70 degrees C, varying the equivalence ratio from 0.3 to 0.54, and the EGR (represented by N-2) ratio from 0 to 37 vol%. For comparison, a PRF95 and a Surrogate containing 11 vol% n-heptane, 59 vol% iso-octane, and 30 vol% toluene are used. A previously validated kinetic surrogate mechanism is Used to analyze the experiments and to yield possible explanations to kinetic phenomena. From this work, it seems quite possible to use the high octane-rated gasoline for autoignition purposes, even Under lean inlet conditions. Furthermore, it appeared that gasoline and its Surrogate, unlike PRF95, show a three-stage autoignition. Since the PRF95 does not contain toluene, it is Suggested by the Kinetic mechanism that the benzyl radical, issued from toluene, causes this so-defined "obstructed preignition" and delaying thereby the final ignition for gasoline and its surrogate. The results of the kinetic mechanism supporting this explanation are shown in this paper. (C) 2008 The Combustion Institute. Published by Elsevier Inc. All rights reserved. [less ▲]

Detailed reference viewed: 28 (1 ULg)
Full Text
Peer Reviewed
See detailExperimental validation of a kinetic multi-component mechanism in a wide HCCI engine operating range for mixtures of n-heptane, iso-octane and toluene: Influence of EGR parameters
Machrafi, Hatim ULg

in Energy Conversion And Management (2008), 49(11), 2956-2965

The parameters that are present in exhaust gas recirculation (EGR) are believed to provide an important contribution to control the auto-ignition process of the homogeneous charge compression ignition ... [more ▼]

The parameters that are present in exhaust gas recirculation (EGR) are believed to provide an important contribution to control the auto-ignition process of the homogeneous charge compression ignition (HCCI) in an engine. For the investigation of the behaviour of the auto-ignition process, a kinetic multi-component mechanism has been developed in former work, containing 62 reactions and 49 species for mixtures of n-heptane. iso-octane and toluene. This paper presents an experimental validation of this mechanism, comparing the calculated pressure, heat release, ignition delays and CO2 emissions with experimental data performed on a HCCI engine. The validation is performed in a broad range of EGR parameters by varying the dilution by N-2 and CO2 from 0 to 46vol.%, changing the EGR temperature from 30 to 120 degrees C, altering the addition of CO and NO from 0 to 170 ppmv and varying the addition of CH2O from 0 to 1400 ppmv. These validations were performed respecting the HCCI conditions for the inlet temperature and the equivalence ratio. The results showed that the mechanism is validated experimentally in dilution ranges going up to 21-30 vol.%, depending on the species of dilution and over the whole range of the EGR temperature. The mechanism is validated over the whole range of CO and CH2O addition. As for the addition of NO, the mechanism is validated quantitatively up to 50 ppmv and qualitatively up to 170 ppmv. (C) 2008 Elsevier Ltd. All rights reserved. [less ▲]

Detailed reference viewed: 25 (2 ULg)
Full Text
Peer Reviewed
See detailA parametric study on the emissions from an HCCI alternative combustion engine resulting from the auto-ignition of primary reference fuels
Machrafi, Hatim ULg; Cavadias, Simeon; Amouroux, Jacques

in Applied Energy (2008), 85(8), 755-764

The homogeneous charge compression ignition is an alternative combustion technology that can reduce automobile pollution, provided that the exhaust emission can be controlled. A parametric study can be ... [more ▼]

The homogeneous charge compression ignition is an alternative combustion technology that can reduce automobile pollution, provided that the exhaust emission can be controlled. A parametric study can be useful in order to gain more understanding in the emission reduction possibilities via this new combustion technology. For this purpose, the inlet temperature, the equivalence ratio and the compression ratio are changed, respectively, from 30 to 70 degrees C, 0.28 to 0.41 and 6 to 14. Also the diluting, thermal and chemical effects of exhaust gas recirculation were studied. The emission of CO, CO2, O-2 and hydrocarbons has been measured using primary reference fuels. It appears that an increase in the inlet temperature, the EGR temperature, the equivalence ratio and the compression ratio results into a decrease of the emissions of CO and the hydrocarbons of up to 75%. The emission of CO2 increased, however, by 50%. The chemical parameters showed more complicated effects, resulting into a decrease or increase of the emissions, depending on whether the overall reactivity increased or not. If the reactivity increased, generally, the emissions of CO and hydrocarbons increased, while that of CO2 increased. The increase of CO2 emissions could be compensated by altering the compression ratio and the EGR parameters, making it possible to control the emission of the HCCI engine. (c) 2008 Elsevier Ltd. All rights reserved. [less ▲]

Detailed reference viewed: 12 (0 ULg)
Full Text
Peer Reviewed
See detailHCCI engine modeling and experimental investigations - Part 2: The composition of a NO-PRF interaction mechanism and the influence of NO in EGR on auto-ignition
Machrafi, Hatim ULg; Guibert, Philippe; Cavadias, Simeon

in Combustion Science And Technology (2008), 180(7), 1245-1262

This article presents an investigation of the effect of NO in EGR on HCCI auto-ignition, by means of experiments and a NO-PRF interaction mechanism. The influence is investigated both numerically and ... [more ▼]

This article presents an investigation of the effect of NO in EGR on HCCI auto-ignition, by means of experiments and a NO-PRF interaction mechanism. The influence is investigated both numerically and experimentally. The numerical part is effected by a composition of a NO submechanism and the subsequent addition of this sub mechanism to a reduced validated n-heptane/iso-octane PRF mechanism, the latter of which is presented in a previous article, named article 1 (Machrafi et al., submitted 2006). The experimental part is effected on a CFR engine, operating at HCCI conditions, with an inlet temperature of 70 degrees C and a compression ratio of 10.2. Hereby n-heptane and PRF40 are used as the fuels, using different equivalence ratios in order to extend the interpretation domain. The NO adding concentration is experimentally varied between 0 and 160 ppm. The results showed that adding NO at low concentrations advances the ignition delays, the promoting reactions being more reactive than the inhibitory ones. The promoting effect seems to be at its maximum at an addition of 45 ppm concerning the fuel PRF40. At higher adding concentrations of NO the promoting effect becomes less and the inhibitory reactions become more reactive. The effect of NO on the auto-ignition of n-heptane seemed, however, to be unsignificant. The effect of NO was qualitatively well represented by the mechanism, while quantitatively the mechanism predicted a lower effect of NO at an addition of 45 ppm. [less ▲]

Detailed reference viewed: 34 (0 ULg)
Full Text
Peer Reviewed
See detailHCCI engine modeling and experimental investigations - Part 1: The reduction, composition and validation of a n-heptane/iso-octane mechanism
Machrafi, Hatim ULg; Guibert, P.; Cavadias, S. et al

in Combustion Science And Technology (2007), 179(12), 2561-2580

A certain possible approach for the control of HCCI chemistry is to use kinetic chemistry mechanisms. This opens a field of interest that lead to the composition of a validated reduced PRF chemistry ... [more ▼]

A certain possible approach for the control of HCCI chemistry is to use kinetic chemistry mechanisms. This opens a field of interest that lead to the composition of a validated reduced PRF chemistry mechanism. For this purpose a skeletal chemical reaction mechanism for n-heptane and for iso-octane are constructed from a detailed n-heptane and iso-octane mechanism of the Chalmers University of Technology. Subsequently these two mechanisms are forged into one reduced chemical reaction mechanism for mixtures of n-heptane and isooctane (39 species and 47 reactions). This mechanism is numerically validated against the Chalmers mechanisms, respecting the HCCI application range. The reduced mechanism is also successfully numerically validated against another more detailed mechanism provided by LLNL. Engine experiments are performed validating this mixture mechanism with respect to the fuel composition containing n-heptane and iso-octane. The influence of the compression ratio and the equivalence ratio is also studied and used to validate the reduced PRF mechanism. [less ▲]

Detailed reference viewed: 30 (0 ULg)