Abstract
Diesel engine particle emissions during transient operations, including
emissions during FTP transient cycles and during active
regenerations of a NOx adsorber, were studied using a fast Engine
Exhaust Particle Sizer (EEPS). For both fuels tested, a No. 2 certification
diesel and a low sulfur diesel (BP-15), high particle concentrations
and emission rates were mainly associated with heavy
engine acceleration, high speed, and high torque during transient
cycles. Averaged over the FTP transient cycle, the particle number
concentration during tests with the certification fuel was 1.2e8/cm3,
about four times the particle number concentration observed during
tests using the BP-15 fuel. The effect of each engine parameter
on particle emissions was studied. During tests using BP-15, the
particle number emission rate was mainly controlled by the engine
speed and torque, whereas for Certification fuel, the engine
acceleration also had a strong effect on number emission rates.
The effects of active regenerations of a diesel NOx adsorber on
particle emissions were also characterized for two catalyst regeneration
strategies: Delayed Extended Main (DEM) and Post 80 injection
(Post80). Particle volume concentrations observed during
DEM regenerations were much higher than those during Post80 regenerations, and the minimum air to fuel ratio achieved during
the regenerations had little effect on particle emission for both
strategies. This study provides valuable information for developing
strategies that minimize the particle formation during active
regenerations of NOx adsorbers.