Measurement of Cyclic Variability in a Diesel Engine Using a Single Cycle Sampler

A system that allows collection and analysis of all of the exhaust from individual engine cycles has been built. Its development and performance are described. The system was used to study the cyclic variability of a 0.7 liter direct injection diesel cylinder operating at 1500 rpm and an equivalence of 0.6. Particulate emissions exhibited the greatest variability. The cyclic variability (standard deviation) of particulate emissions associated with in-cylinder processes was found to be about 40% of the mean. The variability of NO_x emissions that could be associated with in-cylinder processes was much lower, only about 6% of the mean. The variability of pressure development in the combustion process itself, as indicated by IMEP, was very low, less than 2% of the mean. The high variability of particulate emissions may be due to high sensitivity of the formation/oxidation balance to small changes in the combustion process, to in-cylinder surface deposition/resuspension processes, or to some combination of the two. Of course other unidentified phenomenon may play a role.