1996-02-01

The Influence of Hydro Grinding at VCO Nozzles on the Mixture Preparation in a DI Diesel Engine 960867

The hydro grinding process can be used for valve covered orifice (VCO) nozzle production. A comprehensive numerical and experimental investigation was performed to determine the influence of hydro grinding (HG) at VCO nozzles on the mixture preparation in pressure charged high speed direct injection diesel engines.Samples of five hole VCO nozzles with defined grades of HG and different sprayhole diameters were selected to ensure a constant mass flow at a fixed feeding pressure for comparable engine tests. The simulation of the internal flow shows a more symmetrical velocity profile indicating less shear flow and lower turbulence intensities at the orifice with increased HG grade. From these results an enhanced atomization at further penetration depth and reduced atomization close to the nozzle could be expected. This was confirmed by measuring the spray momentum distribution and spray tip speed by mechanical and optical probes in high pressure vessels. The experiments at an optical access high s peed direct injection (HSDI) engine confirmed these results under dynamic engine pressure and temperature conditions and additionally exhibited changes in wall impingement. Experiments at a charged HSDI single cylinder engine showed a significant improvement in smoke emissions with increasing HG grade at a full load high speed operation point.From our results we can conclude that the modified spray features due to the HG process meet the demands of pressure charged HSDI engines for mixture preparation.

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