In the port injected Spark Ignition (SI) engine, the single greatest part load efficiency reducing factor are energy losses over the throttle valve. The need for this throttle valve arises from the fact that engine power is controlled by the amount of air in the cylinders, since combustion occurs stoichiometrically in this type of engine.
In WEDACS (Waste Energy Driven Air Conditioning System), a technology patented by the Eindhoven University of Technology, the throttle valve is replaced by a turbine-generator combination. The turbine is used to control engine power. Throttling losses are recovered by the turbine and converted to electrical energy. Additionally, when air expands in the turbine, its temperature decreases and it can be used to cool air conditioning fluid. As a result, load of the alternator and air conditioning compressor on the engine is decreased or even eliminated, which increases overall engine efficiency.
A model and validating experiment both indicate throttle losses of about 1.25 kW in a modern 2 liter engine at common operating points. On the same engine in a different operating point, an automotive turbocharger is used in another experiment to recover 1.1 kW of these throttling losses. Based on these measurements, a simulated MVEG-A drive cycle predicts a fuel efficiency improvement of 15 to 19%.
