The Premixed Charge Compression Ignition (PCCI) engine has the
potential to reduce soot and NOx emissions while
maintaining high thermal efficiency at part load conditions.
However, several technical barriers must be overcome. Notably ways
must be found to control ignition timing, expand its limited
operation range and limit the rate of heat release. In this paper,
comparing with single fuel injection, the superiority of
multiple-pulse fuel injection in extending engine load, improve
emissions and thermal efficiency trade-off using high exhaust gas
recirculation (EGR) and boost in diesel PCCI combustion is studied
by engine experiments and simulation study.
It was found that EGR can delay the start of hot temperature
reactions, reduce the reaction speed to avoid knock combustion in
high load, is a very useful method to expand high load limit of
PCCI. EGR can reduce the NOx emission to a very small
value in PCCI. At low engine load using high EGR, low soot, CO, UHC
and NOx emissions can be simultaneously achieved. There
are no significant differences in mixture formation before
ignition, emissions and thermal efficiency using single and
multi-injection at low load. At low load, with the increase of EGR
rate, smoke emission of PCCI doesn't increase obviously because
the homogeneous mixture avoids fuel-rich. At higher engine load
with high EGR, the localization of single injection in extending
operation range is the high soot, CO and UHC emissions; using
multi-injection mode, the CO and UHC emissions are decreased with
little expense of NOx emissions. Comparing with single
injection, multi-injection is more beneficial for lean and
homogenous mixture formation, especially at high load. With intake
boost using multi-injection, the engine load can be further
extended; despite the ignition time is advanced, the leanness and
homogeneity of the mixture are improved; the indicated thermal
efficiency is increased, and the CO and soot emissions are greatly
decreased with not large expense of NOx emissions. Using
PCCI with high EGR and boost, the IMEP of the engine can be further
extended to 1.01 MPa, while keeping near to zero emissions and high
thermal efficiency up to 47%.