Improving Diesel Engine Performance Using Low and High Pressure Split Injections for Single Heat Release and Two-Stage Combustion 2010-01-0340

This study explores an Adaptive Injection Strategy (AIS) that employs multiple injections at both low and high pressures to reduce spray-wall impingement, control combustion phasing, and limit pressure rise rates in a Premixed Compression Ignition (PCI) engine. Previous computational studies have shown that reducing the injection pressure of early injections can prevent spray-wall impingement caused by long liquid penetration lengths. This research focuses on understanding the performance and emissions benefits of low and high pressure split injections through experimental parametric sweeps of a 0.48 L single-cylinder test engine operating at 2000 rev/min and 5.5 bar nominal IMEP. This study examines the effects of 2nd injection pressure, EGR, swirl ratio, and 1st and 2nd injection timing, for both single heat release and two-peak high temperature heat release cases.

In order to investigate the AIS concept experimentally, a Variable Injection Pressure (VIP) system was developed. The VIP system is capable of both low and high pressure injections (~300 bar and ~1200 bar respectively) through one injector in the same cycle. For both the single heat release and TSC experiments, optimal operating conditions were found. The single heat release cases tended to have better fuel economy and lower emissions than the TSC cases. However, the peak pressure rise rates (PRR) for the single heat release cases were typically above 6 bar/deg whereas TSC peak PRR were typically under 3 bar/deg. Further, for the single heat release cases, it was found that high EGR rates sufficiently suppressed the first stage of combustion allowing the combustion phasing to be controlled by the second injection. The TSC combustion phasing of both heat releases could be controlled with injection timing and EGR. Emission and engine performance trade-offs were observed over the injection timing ranges for all cases. Variable pressure injection was also compared to a highly dilute (~67% EGR) low temperature combustion (LTC) and was found to produce slightly higher emissions while maintaining the same engine performance at a lower EGR rate (~55%).