Effects of Multiple Injections on Engine-Out Emission Levels Including Particulate Mass from an HSDI Diesel Engine

The effects of multiple injections on engine-out emissions from a high-speed direct injection (HSDI) diesel engine were investigated in a series of experiments using a single cylinder research engine.

Injection sequences in which the main injection was split into two, three and four pulses were tested and the resulting emissions (NO_x, CO HC and particulate matter), torque and cylinder pressures were compared to those obtained with single injections. Together with the number of injections, the effects of varying the dwell time were also investigated. It was found that dividing the main injection into two parts lowered the engine-out particulate and CO emissions and increased fuel efficiency. However, it also resulted in increased NO_x emissions. Further, using double injections reduced the peak rate of heat release (RoHR) and increased RoHR in the later stages of the combustion without changing the combustion duration, resulting in a more even distribution of RoHR during the combustion, which is believed to be the main reason for the changes in fuel consumption and engine-out emission levels. When the number of injections was increased to three or four and the dwell time was prolonged the RoHR decreased, the combustion duration increased and the CA50 was retarded. Consequently, NO_x emissions were reduced but the fuel efficiency also declined, and emissions of particulate mater, CO and HC rose.