Diesel engine has a good fuel economy and high durability and
used widely for power source such as heavy duty in the world. On
the other hand, it is required to reduce NOx (Nitrogen Oxides) and
PM (Particulate Matter) emissions further from diesel exhaust gases
to preserve atmosphere. The urea-SCR (Selective Catalytic
Reduction) system is the most promising measures to reduce NOx
emissions. DPF (Diesel Particulate Filter) system is commercialized
for PM reduction. However, in case that a vehicle has a slow speed
as an urban area driving, a diesel exhaust temperature is too low
to activate SCR catalyst for NOx reduction in diesel emissions.
Moreover, the diesel exhaust temperature becomes lower as a future
engine has less fuel consumption.
The purpose of this study is reduction of NOx emission from a
heavy-duty diesel engine using the Urea SCR system at the low
temperature. The performance of NOx reduction especially at low
temperature was investigated to the influence of NOx/NO ratio at
the inlet of Urea-SCR catalyst and the effect of NH₃ adsorption on
the Urea-SCR catalyst. The SCR catalysts were coated by the zeolite
with different active metals. The performance of NOx reduction at
low temperature was observed by the effect of NOx/NO ratio at the
inlet gas of Urea-SCR catalyst and the NH₃ adsorption on the
Urea-SCR catalysts.
The NOx reduction efficiency was tested using simulated gas
experiment. In this study, the improvement of NOx reduction
catalyst at the low temperature is discussed about tested new
material catalysts. These catalysts were selected from the
viewpoints of NH₃ and NO adsorption amounts. Drastic NOx reduction
efficiency improvement at low temperature (around 200 degree C)
would be achieved using copper zeolite catalyst. The next step,
emissions reduction effect was discussed from the results of the
engine experiments under steady-state and transient conditions. The
latest results and problems were reported with the results from the
simulated gas experiments and engine experiments.