Assessment of the New Features of a Prototype High-Pressure “Hollow Cone Spray” Diesel Injector by Means of Engine Performance Characterization and Spray Visualization

摘要

The application of more efficient compression ignition combustion concepts requires advancement in terms of fuel injection technologies. The injector nozzle is the most critical component of the whole injection system for its impact on the combustion process. It is characterized by the number of holes, diameter, internal shape, and opening angle. The reduction of the nozzle hole diameter seems the simplest way to promote the atomization process but the number of holes must be increased to keep constant the injected fuel mass. This logic has been applied to the development of a new generation of injectors. First, the tendency to increase the nozzle number and to reduce the diameter has led to the replacement of the nozzle with a circular plate. The vertical movement of the needle generates an annulus area for the fuel delivery on 360 degrees, so controlling the atomization as a function of the vertical plate position. Second, on the base of the obtained results, the authors have introduced a new nozzle configuration. This is characterized by a hybrid fuel injection concept, composed of five preferential fuel jets, generated via a specific design of the internal nozzle geometry, and an additional circle-shaped fuel injection, with the aim of using the air between the jets. The experimental investigation has been performed on a single-cylinder metal engine to assess the new concept injector performance by varying the main control parameters (electrical command, nozzle tip protrusion, test point, etc.). Then a deeper investigation of the injector characteristics in different conditions has been performed in an optical single-cylinder diesel engine via digital imaging to catch information on its functioning. A better control of the fuel delivery has been observed compared to the previous injector configuration. Images of the injection process showed that the fuel assumed a good symmetric shape at the nozzle exit for both the jets and the circular plume. A better utilization of the available volume is granted by the new concept injector. The improved mixing quality has shown advantages in terms of combustion efficiency and engine-out emissions.