A New Validation of Spray Penetration Models for Modern Heavy Duty Diesel Fuel Injectors 2017-01-0826
The performance of five positive k-factor injector tips has been assessed in this work by analyzing a comprehensive set of injected mass, momentum, and spray measurements. Using high speed shadowgraphs of the injected diesel plumes, the sensitivities of measured vapor penetration and dispersion to injection pressure (100-250MPa) and ambient density (20-52 kg/m3) have been compared with the Naber-Siebers empirical spray model to gain understanding of second order effects of orifice diameter. Varying in size from 137 to 353μm, the orifice diameters and corresponding injector tips are appropriate for a relatively wide range of engine cylinder sizes (from 0.5 to 5L). In this regime, decreasing the orifice exit diameter was found to reduce spray penetration sensitivity to differential injection pressure. The cone angle and k-factored orifice exit diameter were found to be uncorrelated.
Measurements of injector rate shape, orifice discharge coefficients, spray cone angle, and vapor penetration have also been reconciled with one-dimensional transient computational simulations (Musculus and Kattke) to assess fuel injector tip performance and to evaluate predictive capability. A constant cone angle offset (i.e. reduction) of 2°, applied to all data is required to reconcile measured and simulated spray vapor penetration. A judicious choice of time after injection to determine cone angle is necessary to distinguish effects of ambient density for all injectors considered in this work. Over a wide range of ambient conditions, vapor penetration measurements agree with simulated values to within 0.6% mean error, bolstering confidence in the model, particularly for larger orifice diameters. The measurements in this work constitute a crucial data set for understanding the performance of heavy-duty diesel injectors and for validating spray models at relevant conditions.