The impacts of mid-level biofuel content in gasoline on SIDI engine-out and tailpipe particulate matter emissions

The influences of ethanol and iso-butanol blended with gasoline on engine-out and post three-way catalyst (TWC) particle size distribution and number concentration were studied using a turbocharged spark-ignition direct-injection engine. Particle size distribution in the range of 5.6 to 560 nm was measured. U.S. federal certification gasoline (E0), two ethanol-blended fuels (E10 and E20), and 11.7% iso-butanol blended fuel (BU12) were tested at 10 selected steady-state engine operation conditions. Bi-modal particle size distributions were observed for all operating conditions with peak values at particle sizes of 10 nm and 70 nm. Idle and low-speed/low-load conditions emitted higher total particle numbers than other operating conditions. At idle, the engine-out particulate matter emissions were dominated by nucleation mode particles. The TWC reduced these nucleation mode particles by more than 50%; the accumulation mode particle distribution was unchanged. At an engine load higher than 6 bar net mean effective pressure, accumulation mode particles dominated the engine-out particle emissions, and the TWC had little effect. Compared to E0, E10 did not significantly change PM emissions, while E20 and BU12 reduced PM emissions. Isobutanol was observed to impact PM emissions more than ethanol, with up to 50% reductions at some conditions.