Turbocharger for an exhaust temperature of 1050°C

The turbocharger 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.

 

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