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The air fuel mixing process of a small direct injection (d.i.) diesel engine, equipped with two different re-entrant combustion chambers and two nozzles having unlike spray angles, has been studied by integrated use of in-cylinder laser Doppler velocimetry (LDV) measurements, engine tests, and KIVA simulations. The LDV measurements have been carried out in an engine with optical access motored at 2200 rpm. The engine tests have been performed on a similar engine at the same speed, at fixed start of combustion, and different air-fuel ratio. The KIVA-II simulations have been made using as initial conditions the parameters determined by LDV and engine tests. The re-entrant bowl with higher levels of air velocity and turbulent kinetic energy at the time of injection gives the best performance. The nozzle having a spray angle of 150° which injects the fuel into the regions at higher turbulent kinetic energy lowers the smoke emission levels.

The capabilities of the Taylor analogy breakup (TAB) and wave breakup (WB) spray models, already existing in the literature, were evaluated in KIVA-II code. Also, a novel droplet deformation and breakup (DDB) model that takes into account the nonlinear effects which manifest at large deformation of the drops was incorporated and tested in KIVA-II. The assessment of the three models was performed by using experimental measurements of tip penetration, spray cone angle and Sauter mean radius (SMR) in a cylindrical optically accessible closed vessel at room temperature and high gas density. High speed photography and laser light extinction techniques were simultaneously used to detect data along a n-heptane jet coming out from a single hole nozzle of 0.20 mm diameter supplied by PE-Bosch injection pump operating in single shot by electro-hydraulical device. The KIVA calculations with TAB model in terms of penetration and SMR do not predict accurately the experiments.