46 PRODUCT PROFILE
Next-generation
CFC EGR coolers
BorgWarner’s new compact floating core (CFC) exhaust gas recirculation (EGR) coolers feature
a flexible water-cooled damper directly integrated into their inner core. This enables them
to withstand thermal stresses and reduces the impact of transients
VehicleDynamicsInternational.com •November/December 2019
FIGURE 1 (ABOVE):
CFC EGR coolers
– four standard
designs
FIGURE 2 (BELOW):
The cooling system
is optimised
make up the EGR cooler family (see
Figure 1), all of which are able to
operate at a gas flow of between
50% and 100%.
Effective thermal resistance
Boiling of coolant can be caused in
a number of ways, and it can cause
malfunctions to occur in an early phase
due to the high thermal stress inside
the cooler. There are usually no problems
with nucleate boiling, which involves
the formation of bubbles on the hot
››In-cylinder EGR emission control
technology generally inhibits
the formation of NOX. This is
done by recirculating part of the exhaust
gas back to the cylinders, mixing it with
intake air and re-introducing it into
the combustion process. For commercial
vehicles, their rough working conditions
and lengthy service life require EGR
systems to be highly durable.
For this reason, engineers focus on
the lifetime requirements of EGR coolers
for commercial vehicles during the
design process. The parts must be able to
operate for up to 1.5 * 106km or 20,000
hours in an environment displaying
the maximum temperatures achieved
by diesel engines – or even 800ºC in
compressed natural gas (CNG) systems –
in order to withstand the stresses
that occur in everyday operation.
The CFC solution that BorgWarner
developed to meet these high
demands accurately covers numerous
specifications and functions, no
matter how rough the conditions.
From a design viewpoint, the low
sales volumes in the commercial vehicle
market mean that it must be possible to
adapt the systems for use in different
applications, with the aim of reducing
costs. Thus CNG and other alternative
fuels were taken into account, in
addition to the usual diesel applications.
A minimum of four standard designs
skin of the cooler core components.
BorgWarner engineers’ long years of
experience tell them that areas located
very close to the hot side header and
the inner tubes are in more danger of
boiling, and in order to prevent the
film from boiling, sufficient coolant
has to flow round each section of the
cooler core.
For each of the four standard
cooler types, a scenario was created
on the basis of the worst operating
conditions imaginable, and the data was
/VehicleDynamicsInternational.com