Turbocharging allied to gasoline direct injection will become more common as OEMs tight to reduce CO{sub}.2. Bownsizing gasoline engines is part of most OEMS' powertrain strategy. Direct injection (GDI) and turbocharging, together with cam phasing, will give fuel efficiency more similar to diesel. Most GDI turbo engines favour output. Further downsizing and downspeeding is needed to obtain the desired fuel economy without affecting low speed torque and transient response. Part- and full-load efficiency must also improve but technologies must be affordable if gasoline is to stay cheaper than diesel. "We want 130g/km CO{sub}2," says Giinter Fraidl, AVL's executive director of gasoline engines. "The turbo is not seen as a measure to reduce consumption but GDI turbo is an essential combination to reach this target and to retain a 'fun-to-drive' character." Downsized engines improve economy through reduced throttling losses. But as downsizing ratio and boost pressure increase, knocking occurs, limiting compression ratio and thus efficiency.
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