Experimental Investigation of Multiple Injection Effects on Combustion of a Diesel Engine with a Unit Injector,

The aims of this study were to investigate the effects of multiple injections (pilot, split, and, post injection) on the combustion process and specific NOx and soot engine-out emissions fm Heavy-Duty DI diesel engine (displacement 2.02 l), equipped with an advanced two-actuator, Electronic Unit Injector (EUI) system. Investigated parameters were the amount of fuel injected during each injection pulse, the dwell time between the injection pulses, and the start of injection (SOl). Two engine loads (25 % and 75 %) at 1200 rpm, conforming to European Stationary C (ESC) measuring points, were selected for the experiments. Both "conventional" measuring techniques and flame imaging using the AVL VisioScopeTM system were used. A key characteristic of the EUI system is that the injection pressure increases during the injection (ramp shape) which allows the second injection to be injected at a higher injection pressure than the first. It was found that a reduction in soot emission could be obtained at low load with a long dwell between the and second pulses. In contrast, at high load the multiple injections did not show any improvement, and soot emissions were even worse with very late injection