Abstract
Some different injection strategies and nozzle designs were tested in a transparent engine in order to investigate on their influence on spray and combustion evolution. The engine was a single cylinder research engine equipped with a common-rail injection system. A classic elongated piston and a quartz window acting as bowl bottom were used for diagnostic applications into the combustion chamber. The system configuration tested in the present work corresponds to a four-cylinder engine of 1930 cc of displacement chosen as representative in the class of light duty DI diesel engines. The injection system can be controlled in real time by a special ECU interfaced via Electronic Emulator Unit (EMU) with a PC. The hardware and software of the injection system were provided by Fiat Research Center. Spray and combustion evolutions were visualized through a high-speed CCD camera synchronized with a copper vapor laser acting as a light source. Tests were performed at fixed engine speed and with a fixed injected fuel mass but varying different injection parameters as rail pressure, fuel mass quantity of different injections and injector configuration (holes number and size). As expected experiments have shown the great influence of injection parameters and nozzle characteristics on spray and combustion behavior and in particular on liquid penetration, hole to hole spray asimmetry, auto-ignition locations and flame propagation.
Pilot and main injections show a very different evolution. Spray distribution of the main injection greatly depends on pilot injection parameters and nozzle configuration. Further investigations on different injection strategies are needed in order to optimize the combustion process and as a consequence engine emission.