Sub-23 nm Particle Measurement and Assessment of Their Volatile Fraction at Exhaust of a Four Cylinder GDI Engine Fueled with E10 and E85 Under Transient Conditions

In view of the new emission regulations seeking to lower the particle cut-off size down to the current 23 nm, an extensive comprehension on the nature of sub-23 nm particles is crucial. In this regard, a new challenge lies ahead considering an even more massive use of biofuels.

The objective of this research study was to characterize the sub-23 nm particles and to evaluate their volatile organic fraction (VOF) from a high performance, 1.8 L gasoline direct injection (GDI) engine under the Worldwide harmonized Light vehicles Test Cycle (WLTC). Particle emissions were measured through an Engine Exhaust Particle Sizer (EEPS) capable of particle sizing and counting in the range 5.6 - 560 nm. The sampling and conditioning were performed by both a single diluter and the Dekati Engine Exhaust Diluter (DEED) a Particle Measurement Programme (PMP) compliant sample conditioning system. The temperature of the dilution air at the first dilution stage and of the evaporation chamber in the DEED were varied to promote nucleation and condensation phenomena thus allowing to distinguish the VOF. The effect of ethanol at 10 %v/v (E10) and 85 %v/v (E85) blend on particle emissions was analyzed. The weight of sub-23 particles on the total emissions was assessed at each phase of the cycle.

Main results highlighted that sub-23 nm particles give an important contribution to the total particle emissions. A strong reduction of particle concentration as the ethanol content in the fuel increases was observed. Moreover, the test performed at low dilution temperature showed a large number of su-23 nm particles thus revealing a large fraction of volatile components in specific phases of the cycle.