Genetic algorithm optimization of fuel economy for PFI engine with VVT-VCR

This research is focused on the fuel economy benefit issues for gasoline engines under emission performance constraints. New technologies are to be implemented on a PFI engine throughout physical operating ranges of the testing vehicle. The objective is to create a complementary scheme that offers an optimal fuel consumption performance. Fuel economy is to be optimized in a city drive cycle. The values from speed-load regions in city drive cycles with no VVT and VCR are used as the baseline. Then, variable valve timing (VVT) and variable compression ratio (VCR) techniques can be applied on 1.8 L four-cylinder engine for fuel economy improvement. The inter-cooled engine is supercharged to achieve efficiency benefits so that a smaller boosted engine can reach similar performance to that of a larger replacement regular engine. The influences of both VVT and VCR on various operating regions are studied to identify the actual outcome of fuel economy improvement by the integration of compression ratio and valve timing technologies so as to optimize the engine operation at a part load region and to prevent engine knock at a full load region. The results show that the two technologies can be collaborated to achieve an overall fuel economy benefit at some typical operating regions despite of overlapping. The speed-load points for potential maximal and minimal fuel economy benefit via technology synergy are determined by genetic algorithm optimization.