ID 219

Investigation on a Simple Model to Predict Spray Cone Angle for Sac Type Diesel Injectors

 

Abstract:

This presentation will describe a simple model that can predict rate of fuel injection and spray cone angle in order to use combustion simulations for modern automotive diesel engines with common rail systems. Major focus of the presentation is calculation for fuel injection events with low needle lift. Temporal change of sac volume pressure can be calculated from difference of volumetric flow rate of fuel between entrance and exit of the sac volume with consideration of unsteadily compressible flow inside the sac volume. Spray cone angle can be estimated from total discharge coefficient of the injector because of experimental results that lower needle lift causes reduction of the total discharge coefficient and increase of the spray cone angle. The total discharge coefficient of the injector is defined as pressure difference between the entrance and the exit of the injector. Empirical formulas of discharge coefficient of the needle seat gap and loss coefficient of pressure due to flow orientation from direction of a narrow needle seat gap to each hole direction inside the sac volume are incorporated into a sub-model to predict the total discharge coefficient of the injector. Additionally discharge coefficient of the each hole, which is set to a constant value, incorporated into the sub-model. The total discharge coefficient calculated by using the sub-model are compared to total discharge coefficient, which can be provided by pressure measurement inside a 10 times large-scaled injector.