Abstract
To examine the feasibility of improving performance through highly flexible fuel injection, a series of experiments were performed using a single-cylinder diesel engine with a dual injector system, which included two sets of common-rail injection systems. The injectors were installed around the center of the cylinder to simulate flexible injection with a single nozzle configuration. This system enabled different injection rates in each injection pulse and a wide dwell range between injection pulses, i.e., even a negative injection dwell could be performed. Experiments with multi-stage injection were conducted using a single-cylinder metal engine, and the behaviors of the sprays and flames were observed in an optically accessible single-cylinder engine with an extended bottom-view piston. Based on a double pilot injection strategy, the effects of the injection pressures, injection timings, and injection quantities of split injection were investigated. The results showed that the dual injector system tended to increase smoke emissions because of a lack of symmetry in the combustion system. The heat release rates were hardly affected by switching from one injector to another for the main injection, whereas the smoke emissions were markedly reduced. A higher main injection pressure with lower pilot injection pressures reduced the smoke emissions with no increase in the CO emissions. A split-main injection with zero injection dwell increased the thermal efficiency under high injection-pressure conditions. A negative injection dwell markedly increased the smoke emissions.
