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The paper discusses investigations into improving the full-load and transient performance of the Ultraboost extreme downsizing engine by the application of the SuperGen variable-speed centrifugal supercharger. Since its output stage speed is decoupled from that of the crankshaft, SuperGen is potentially especially attractive in a compound pressure-charging system. Such systems typically comprise a turbocharger, which is used as the main charging device, compounded at lower charge mass flow rates by a supercharger used as a second boosting stage. Because of its variable drive ratio, SuperGen can be blended in and out continuously to provide seamless driveability, as opposed to the alternative of a clutched, single-drive-ratio positive-displacement device. In this respect its operation is very similar to that of an electrically-driven compressor, although it is voltage agnostic and can supply other hybrid functionality, too.

An experimental study has been performed to analyse and compare the effects on performance and emissions of two forms of Internal Exhaust Gas Recirculation (IEGR) systems. Variable valve event phasing, specifically increasing intake and exhaust event overlap, through control of the intake camshaft, has been used as an IEGR control mechanism and for increased full load performance. Port throttling in combination with long valve event overlap periods has been used to increase peak torque and power and when allied to a single upstream throttle, IEGR control has been demonstrated. Barrel throttles have been used for the port throttled variant and this type of port throttle is responsible for some of the benefits found.