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Abstract : The present work concentrates on the macro and microscopic study of the diesel sprays injected with high pressures by the Common-Rail injection system through an injector mono-hole of small diameter in an isothermal inert environment, avoiding the evaporation of fuel at high gas pressures. The results promote significantly the increase of knowledge on the diesel sprays completely atomized almost at the injector exit and present a solid data base for the validation of the computational codes (computational fluid dynamics: CFD). Two techniques are used: The shadowgraphy technique allows the macroscopic study of the diesel spray (penetration, cone angle and volume of the spray). However, the microscopic study is achieved with the phase Doppler anemometry (PDPA) (measures of the diameter and the velocity of the drops). The combination of the two techniques allows a quantification of the fuel concentration. The correlation of the macroscopic parameters adjusts perfectly well to penetration measurements after transition time without taking into account the cone angle of the spray. This semi-empirical correlation resembles the expression obtained by the dimensional analysis assuming a rectangular form for the mass flow rate. The penetration during the transition phase follows a linear law according to time. The taking into account of the cone angle of the spray in the correlation increases the adjustment. The cone angle of the spray is very depending on the density of surrounding gas. The value of the cone angle is of 36° for the surrounding gas density of 30 kg/m3. For the microscopic study, the spray is divided into three parts; leading edge, central part and trailing edge. The injection duration in this case is brought to 3ms instead of 1.5ms to lengthen the central spray part. The temporal evolutions of the mean velocity and rms of the longitudinal velocity show peaks. The peaks of the rms of longitudinal velocity are an indication of the strong dispersion, due to the phenomena of overtaking of braked drops by the fast ones and or secondary atomisation. The peak velocity is explained by an energy supply of the air pulled by the frontal vortices to the smallest drops. The decrease of longitudinal velocity on the axis in the central spray part resembles to that of the gas jets. However, the decrease of the rms of the longitudinal velocity is faster than that of the free gas jets. Coalescence is effective in all the spray parts for the low injection pressures closer to the injector. However, for high injection pressures, the coalescence in the leading edge acts only far from it. The longitudinal velocity and the concentration of the drops have homothetic radial profiles and the effective Schmidt coefficient < 1. However, close to the spray axis, the velocities are sometimes too high. The radial distribution of the intensity of turbulence is homothetic, but it is similar to that of the free gas jet in r/r0,5< 1 and higher beyond. The intensity of turbulence in the leading edge is higher than in the central part and the trailing edge; and it has values of 40-60%. The pdfs of drop velocity are asymmetric (Su>0 or Su<0) and narrow (Fu>3) or flattened (Fu<3) in the leading edge, but they are Gaussians in the rest. However, the pdfs of drop diameters are narrow (Fd>3) and quasi-symmetrical (Sd≈0) in all the spray parts. The virtual origin of the spray at the beginning of the injection is variable and stabilizes afterwards in the interval 11-15 mm. In this spray region, the spray is dense and measurements by PDA system are impossible. The dynamic cone angle of the spray is approximately 32°.The virtual origin and the cone angle are independent on the injection pressure.
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Contributor : Abdelkader Doudou <>
Submitted on : Thursday, October 6, 2011 - 5:31:04 PM
Last modification on : Friday, October 7, 2011 - 10:02:15 AM
Long-term archiving on: : Tuesday, November 13, 2012 - 3:20:19 PM


  • HAL Id : tel-00629877, version 1


Abdelkader Doudou. ETUDE MACRO/MICROSCOPIQUE DES SPRAYS DIESEL INJECTES PAR LE SYSTEME COMMON RAIL AVEC LA TECHNIQUE D'OMBROSCOPIE ET L'ANÉMOMÈTRE PHASE DOPPLER. Sciences de l'ingénieur [physics]. Faculté des Sciences de Kenitra, 2007. Français. ⟨tel-00629877⟩



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