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The part-load fuel consumption potential of unthrottled engine operation using variable valve actuation is evaluated for a single-cylinder version of the GM 3.4 L DOHC engine. The investigation focuses on evaluating the practical range of the early-intake-valve closing (EIVC) variable valve actuation strategy, which includes intake-valve-opening positions ranging from 360 to 420 crank-angle degrees ATDC, intake-valve durations ranging from 54 to 226 crank-angle degrees, and peak intake-valve lifts ranging from 0.75 to 4.5 mm. In addition to the experimental investigation, a one-dimensional simulation evaluation is completed to examine the potential of enhanced in-cylinder charge motion when implementing variable-valve actuation. A 7 % fuel consumption improvement is achieved for unthrottled engine operation when implementing the EIVC variable valve actuation strategy.

A numerical and corresponding experimental study was undertaken to identify the ability to accurately predict combustion performance using our 3-D numerical tools for a direct-injection homogeneous-charge engine. To achieve a significant range of combustion rates, the evaluation was conducted for the engine operating with and without enhanced charge motion. Five charge motion configurations were examined, each having different levels of swirl and tumble flow leading to different turbulence generation and decay characteristics. A detailed CFD analysis provides insight into the in-cylinder flow requirements as well as the accuracy of the submodels. The in-cylinder air-fuel distribution, the mass-averaged swirl and tumble levels along with mean flow and turbulent kinetic energies are calculated throughout the induction and compression processes.

A 2.0L twin-scroll turbocharged SIDI engine was used to evaluate low-pressure loop water-cooled external EGR at operating conditions between 1000 rpm 75 Nm and 3000 rpm 250 Nm. The engine compression ratio was increased from 9.3 to 10.9. The maximum fuel consumption reduction potential, the boost pressure requirements, and the optimized external EGR calibration were determined. Combination of higher compression ratio and external EGR achieved 5-7% better fuel economy over mid-load region when using the twin-scroll turbocharger. A similar (4-6%) better fuel economy was observed over much of the higher-load region, including peak torque condition at 1000rpm, when the required boost pressure was provided by an externally-driven auxiliary boost system (not connected to the engine). The power consumption of auxiliary boost system (supercharger loss) was estimated and considered in fuel economy assessment. The fuel consumption reduction mechanisms of EGR were also analyzed.