Control Re-Optimization of a Series-Parallel Hybrid Powertrain Fueled with High-Octane Gasoline

High-octane gasoline has the potential to improve engine efficiency but has been reported to marginally reduce and even increase vehicle fuel consumption. The objective of this study is to evaluate the fuel-saving effect of high-octane gasoline on series-parallel hybrid electric vehicles (HEVs) under the re-optimized powertrain control, including engine control and energy management. Firstly, a bench test was conducted on a spark ignition engine fueled with three fuels with research octane numbers of approximately 92, 95, and 98, named 92#, 95#, and 98#. Then the engine control parameter (i.e., spark advance) was re-optimized for maximum engine efficiency and acceptable particle number emissions with the knock constraint. Finally, the energy management was re-optimized for a series-parallel hybrid powertrain equipped with the engine. It was found that 95# and 98# even increased vehicle fuel consumption by 0.2% and 0.6% without the re-optimization of powertrain control compared with 92#, but reduced the fuel consumption by 2.1% and 3.8% with the re-optimization. The results indicated high-octane gasoline can reduce HEV fuel consumption but requires the re-optimization of powertrain control. The engine control re-optimization for high-octane gasoline increased the maximum torque and expanded the high-efficiency area toward higher torque in the engine efficiency map. Then the energy management re-optimization shifted the engine operating points to area with higher engine efficiency and reduced powertrain operation under low-efficiency series mode. The fuel-saving analysis indicated that, under the condition of re-optimizing only the control, high-octane gasoline is suitable for application in parallel or series-parallel HEVs rather than in series HEVs.