A systems approach is implemented to fully optimize the overall performance of a gasoline SIDI two-valve “small block” engine. The objective is to maximize fuel economy while achieving significant improvements in idle stability, cold-start emissions, and torque and power performance relative a baseline port-fuel-injected (PFI) engine. The scope includes the optimization of the fuel injector, piston, cylinder head, cams, in-cylinder charge motion, and the intake-manifold. The results show that the SIDI engine provides the potential to achieve 6.5% better fuel economy; a result of higher efficiency when implementing a higher geometric compression ratio and significantly better combustion performance. A multiple fuel-injection strategy is examined to provide lower HC emissions at a representative cold-start operating condition. The engine’s idle stability is improved by a factor of three; the individual contributions from a better combustion system design and from multiple fuel injections are identified. The new SIDI engine concept demonstrated significantly better wide-open-throttle (WOT) performance, including up to 10% higher torque and 6% more power when using premium fuel. This document further demonstrates the performance sensitivity to engine design variables while emphasizing the importance of using a systems approach to achieve optimized performance for the direct-injection engine technology.

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