Fuel Sprays for Premixed Compression Ignited Combustion - Characteristics of Impinging Sprays

For homogeneous charge compression ignition (HCCI) engines with direct-injected fuel (also called PCI, Pre-mixed Compression Ignition), it is important to achieve a lean and homogeneous mixture before ignition. For this purpose, impinging diesel sprays have proven to be useful. In this study, an evaluation of the overall air/fuel ratio of such sprays was made in a test rig. The test rig consists of a pressurized vessel with optical access and a Common Rail (CR) fuel injection system. The investigation was made for impinging spray nozzles with different impingement angles and orifice diameters. Three gas back pressures and three injection pressures were evaluated. The evaluation was based on images of the fuel sprays taken in the test rig. The fuel spray images were automatically processed using in-house developed software. The results of the investigation points out some important factors to obtain a lean spray, (a high air/fuel ratio). The investigation also points out some factors that give a low spray penetration for a certain injected mass of fuel.