Particulate Characteristics for Varying Engine Operation in a Gasoline Spark Ignited, Direct Injection Engine 2011-01-1220

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.