In order to further reduce NOx emissions in increasing HP EGR
cooler performance, several OEMs have decided to use a secondary
cooling loop dedicated to bring cold water (around 35°C) to the HP
EGR heat exchanger. Nevertheless, strongly cooled EGR gases can
condensate in the cooler-producing acidic liquids which can corrode
some parts in the loop. It is therefore necessary to define EGR
components compatible with such kind of environment and
constraints.
Testing was performed on a 2.0-liter EU4 diesel engine, using a
large panel of current fuels including neat biodiesels from
soybean, rapeseed or palm, as well as low and high sulfur
petroleum-based diesels. In order to cover all existing cycle
conditions, the HP EGR is cooled from 20°C to 90°C independently
from the engine coolant circuit. In the aim to perform a fair
comparison among biodiesels and diesels, injection and air mass
flow setpoints coming from the serial EU4 calibration were adapted
to achieve same torque and similar NOx emissions for all fuels.
As expected, at a constant air mass flow setpoint, a strong EGR
cooling allows a noticeable reduction of NOx emissions due to a
significant increase of the EGR rate. Volumes and acidity of
condensates were measured: as calculated and correlated by means of
psychrometric charts, and depending on the calibration, tests show
that condensation occurs for gas temperatures below 50°C and
represent up to 400 ml/h at 20°C ambient temperature. Condensate
acidity is similar for all tested fuels and stays within an
acceptable range for products in series.