Turbocharger for an exhaust temperature of 1050°C
is also becoming more and more accepted in connection with the gasoline engine.
The advanced charging technique will cause the percentage of turbocharged vehicles
to steadily increase. The exhaust temperatures of future turbocharged gasoline engines
will increase. The air ratio ? at the rated output point is currently about ?=0.75–0.85
since a portion of the fuel is used to cool the inside of the engine. If the air
ratio is increased to a value between ?=0.9-1.0, then a potential fuel savings of
up to 20% can be attained. However, this leads to an increase in the exhaust temperature
of up to 1050°C and places new demands on the turbocharger, among other things.
Turbochargers for exhaust temperatures of 1050 °C require a material for the turbine
housing that will withstand such high component temperatures during the entire service
life of the vehicle. Heat-resistant cast steel is ideal for this purpose. Turbine
housings made of heat-resistant cast steel are already being used today by BorgWarner
Turbo Systems for mass-produced customer engines.
In addition to the turbine housings, the increased exhaust temperatures also result
in extreme conditions for the turbine wheels. In this case, as well, BorgWarner
Turbo Systems can provide a solution thanks to continuous refinement of the materials
and connecting technologies previously in use. The bearing housing was redesigned
with a highly efficient water cooling system in mind. The V-band clamp was introduced
to ensure a secure connection between the bearing housing and the turbine housing
at high temperatures.
The thermal inertia of the turbine housing is of great significance to very low
emission vehicles. Due to the low level of thermal inertia, the temperature in the
catalytic converter during the cold-start phase of the engine rises quickly. The
conversion of the pollutants in the exhaust starts early in this case. The thermal
inertia and the surface area of the turbine housing are to be kept as small as possible
to keep emissions low.
The thin-walled turbine housing
The complexity of the manufacturing and machining processes for turbine housings
made of cast steel and the high costs arising in connection with them has raised
the question of what benefits the customer derives from these technologies. Thin
walls are desired to significantly reduce the weight of the turbine housing and
simultaneously reduce the thermal inertia of the turbine housing. This leads to
faster activation of the catalytic converter during the cold-start phase of the
engine, which in turn significantly improves the emission levels of the vehicle.
The sheet-metal turbine housing
Another promising solution can be found in the form of an sheet-metal turbine housing.
It consists of several stamped sheet-metal parts that are welded together. The turbine
housing can have a single-flow or double-flow construction with air-gap insulation.
The turbine housing in the exhaust system of the engine can be connected to its
exhaust manifoldes by a flange or the pipes can be welded on. As a result of this,
it is possible to have continuous air-gap insulation for the flow of exhaust from
the cylinder head all the way down to the catalytic converter. Heat resistant sheet
metal is available as a material that permits exhaust temperatures of up to 1050°C.
Aluminum turbine housings are just as good as cast turbine housings in terms of
their efficiency and throughput, yet they have much less thermal inertia and therefore
allow the catalytic converter to be activated faster during a cold start.
The newest generation of charging systems from BorgWarner Turbo Systems fulfills
the higher demands of future gasoline engine generations in regards to turbocharging
and provides the customer with solutions for all gasoline engine applications.