The objective of this research is a detailed investigation of
particulate sizing and number count from a spark-ignited,
direct-injection (SIDI) engine at different operating conditions.
The engine is a 549 [cc] single-cylinder, four-valve engine with a
flat-top piston, fueled by Tier II EEE. A baseline engine operating
condition, with a low number of particulates, was established and
repeatability at this condition was ascertained. This baseline
condition is specified as 2000 rpm, 320 kPa IMEP, 280 [°bTDC] end
of injection (EOI), and 25 [°bTDC] ignition timing.
The particle size distributions were recorded for particle sizes
between 7 and 289 [nm]. The baseline particle size distribution was
relatively flat, around 1E6 [dN/dlogDp], for particle diameters
between 7 and 100 [nm], before dropping off to decreasing numbers
at larger diameters. Distributions resulting from a matrix of
different engine conditions were recorded. These varied parameters
include load, air-to-fuel ratio (A/F), spark timing, injection
timing, fuel rail pressure, and oil and coolant temperatures. Most
conditions resulted with uni-modal type distributions usually with
an increase in magnitude of particles in comparison to the
baseline, with the exception of lean operation with retarded
ignition timing. Further investigation revealed high sensitivity of
the particle number and size distribution to changes in the engine
control parameters. There was also a high sensitivity of the
particle size distributions to small variations in A/F, ignition
timing, and EOI. Investigations revealed the possibility of
emissions oxidation in the exhaust and engine combustion
instability at later EOI timings which therefore ruled out late EOI
as the benchmark condition. Attempts to develop this benchmark
revealed engine sensitivity to A/F and ignition timing, especially
at later EOI operation.