Effects of a Combined
Diesel Particle Filter-DeNOx
System (DPN) on Reactive Nitrogen Compounds Emissions: A Parameter
Study
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Abstract
The impact of a combined diesel particle filter-deNO<sub><i>x</i></sub> system (DPN) on emissions of reactive nitrogen
compounds
(RNCs) was studied varying the urea feed factor (α), temperature,
and residence time, which are key parameters of the deNO<sub><i>x</i></sub> process. The DPN consisted of a platinum-coated
cordierite filter and a vanadia-based deNO<sub><i>x</i></sub> catalyst supporting selective catalytic reduction (SCR) chemistry.
Ammonia (NH<sub>3</sub>) is produced in situ from thermolysis of urea
and hydrolysis of isocyanic acid (HNCO). HNCO and NH<sub>3</sub> are
both toxic and highly reactive intermediates. The deNO<sub><i>x</i></sub> system was only part-time active in the ISO8178/4
C1cycle. Urea injection was stopped and restarted twice. Mean NO and
NO<sub>2</sub> conversion efficiencies were 80%, 95%, 97% and 43%,
87%, 99%, respectively, for α = 0.8, 1.0, and 1.2. HNCO emissions
increased from 0.028 g/h engine-out to 0.18, 0.25, and 0.26 g/h at
α = 0.8, 1.0, and 1.2, whereas NH<sub>3</sub> emissions increased
from <0.045 to 0.12, 1.82, and 12.8 g/h with maxima at highest
temperatures and shortest residence times. Most HNCO is released at
intermediate residence times (0.2–0.3 s) and temperatures (300–400
°C). Total RNC efficiencies are highest at α = 1.0, when
comparable amounts of reduced and oxidized compounds are released.
The DPN represents the most advanced system studied so far under the
VERT protocol achieving high conversion efficiencies for particles,
NO, NO<sub>2</sub>, CO, and hydrocarbons. However, we observed a trade-off
between deNO<sub><i>x</i></sub> efficiency and secondary
emissions. Therefore, it is important to adopt such DPN technology
to specific application conditions to take advantage of reduced NO<sub><i>x</i></sub> and particle emissions while avoiding NH<sub>3</sub> and HNCO slip