A 2.5-liter light-duty diesel van certified to Euro 4 emission
standards was tested in a chassis dynamometer test cell, which
included a modal FTIR exhaust gas analyzer with the capability of
measuring 22 separate gas species. The engine was equipped with a
cooled Exhaust Gas Recirculation (EGR) system, which controls the
nitrogen oxide emissions (NOx) to less than the 390 mg/km limit
required by Euro 4 regulations. The vehicle was tested by
dynamometer with the New European Drive Cycle (NEDC) sequence, and
found to exceed the 390 mg/km NOx limit. The FTIR was applied as a
diagnostic tool for the engine EGR function.
The FTIR monitored N₂O, NO, NO₂, and NH₃ over the NEDC test
cycles. The linear-control EGR valve failed abruptly during a
subsequent test, and the relative concentration of the reduced and
oxidized nitrogen species showed significant changes. The nitrous
oxide increase in concentration preceded the increase in NO and NO₂
by several seconds, which suggests the EGR system failure could
generate both reducing and oxidizing conditions in the LDD engine.
The increase in nitrous oxide emission is interesting because it is
typically an insignificant fraction of the total nitrogen mass
emissions, so more nitrous oxide emitted during EGR failure is
unexpected. Nitrous oxide is also of interest because it is a
priority greenhouse gas that has recently been considered for
regulation.
After the EGR system was repaired, tests yielded NOx emissions
near the 390 mg/km limit. The modal gas concentrations of the
nitrogen species are shown during the EGR failure, and after the
EGR repair, which resulted in low NOx and N₂O concentrations. This
demonstrated the FTIR analyzer was capable of diagnosing EGR
problems, and it demonstrated the value of monitoring unexpected
exhaust components when an engine has failing emission control
components, poisoned catalysts, or any unconventional emission
problem.