Authors: R P C Zegers M Yu C Bekdemir N J Dam C C M Luijten L P H de Goey
Publish Date: 2013/03/20
Volume: 112, Issue: 1, Pages: 7-23
Abstract
Planar laserinduced fluorescence LIF of toluene has been applied in an optical engine and a highpressure cell to determine temperatures of fuel sprays and incylinder vapors The method relies on a redshift of the toluene LIF emission spectrum with increasing temperature Toluene fluorescence is recorded simultaneously in two disjunct wavelength bands by a twocamera setup After calibration the pixelbypixel LIF signal ratio is a proxy for the local temperature A detailed measurement procedure is presented to minimize measurement inaccuracies and to improve precision nHeptane is used as the base fuel and 10 of toluene is added as a tracer The toluene LIF method is capable of measuring temperatures up to 700 K above that the signal becomes too weak The precision of the spray temperature measurements is 4 and the spatial resolution 13 mm We pay particular attention to the construction of the calibration curve that is required to translate LIF signal ratios into temperature and to possible limitations in the portability of this curve between different setups The engine results are compared to those obtained in a constantvolume highpressure cell and the fuel spray results obtained in the highpressure cell are also compared to LES simulations We find that the hot ambient gas entrained by the head vortex gives rise to a hot zone on the spray axisThe authors to thank Bert van Bakel for his efforts in applying toluene LIF in the optically accessible engine Gabrielle Tea Gilles Bruneaux and Robin Devillers from IFPEN are kindly acknowledged for providing the spectral data The project “Towards clean diesel engines” was funded by the Dutch Technology Foundation STW DAF Trucks NV Shell Global Solutions Wärtsilä TNO and Delphi Diesel Systems are also acknowledged for their contributions to the projectThe LES code used in this study is the fully compressible AVBP solver codeveloped by IFP Energies Nouvelles and CERFACS for structured and unstructured meshes 20 The second order centred Lax–Wendroff convective scheme 21 is combined with an explicit time advancement Unresolved subgridscale turbulence is modeled by a Smagorinsky model 22 with constant coefficient The dispersed liquid phase is resolved using a mesoscopic Eulerian formalism 23 The region close to the injector dominated by high volumetric ratios of liquid fuel and breakup effects is not included in the simulations The DIturBC injector model 24 is used to bridge that region by imposing physical flow conditions at a distance approximately 10 nozzle diameters downstream of the injector outflow plane Its principle is to impose boundary conditions for the two phase flow at a distance downstream of the injector nozzle in regions where the flow has been dispersed by breakup phenomena and can be addressed by a diluted mesoscopic Eulerian formalismThe LES has been run on a computational mesh which represents a closed combustion vessel with slightly larger dimensions than the HPC 1123 versus 1083 mm3 It consists of a tetrahedral mesh with local refinement The mesh size near the nozzle exit is 80 μm and gradually increases to 800 μm toward the other end of the domain yielding approximately 07 million nodes and 43 million cells All boundaries except for the injection plane are taken as adiabatic walls which have negligible influence on the spray internal structure This mesh has been chosen on the basis of spray formation results presented in 25The results of the LES are also given in Fig 19 velocity vectors are colored with the corresponding temperature at that point Furthermore the contour of the fuel spray Y fuel = 0001 is indicated with the solid black line The LES results reveal heavy mixing in a pulsating fashion due to sprayinduced vortices at the edge resulting in hot spots of ambient air enclosed in the spray core region The LES predicts temperatures in the order of 500 K for the inner spray areas whereas the experimental results are much closer to the ambient condition of 590 K Possible reasons might be the averaging effect in the experiment due to the laser thickness
Keywords: