Homogeneous charge compression ignition (HCCI) combustion mode is a promising combustion strategy for range extension of hybrid electric vehicles, due to its high thermal efficiency at specific load conditions. However, the fuel combustion in HCCI mode is triggered by fuel auto-ignition kinetics, and a comprehensive understanding of fuel oxidation kinetics is essential for HCCI combustion modulation. In pursuit of this, experimental studies were performed on a modified Cooperative Fuels Research (CFR) engine to investigate the oxidation characteristics of a practical gasoline and five gasoline model fuels: PRF (n-heptane/iso-octane), TRF-30T and TRF-20T (n-heptane/iso-octane/toluene), TRFD-20D (n-heptane/iso-octane/toluene/diisobutylene), and TRFDC (n-heptane/iso-octane/toluene/diisobutylene/cyclopentane), which have identical research octane number (RON). The experimental results revealed that the same-RON gasoline fuels displayed distinct oxidation reactivities: generally, practical gasoline was the most reactive, followed by PRF > TRF-20T > TRF-30 T > TRFD-20D > TRFDC. To analyze the compositional effect on the oxidation reactivity of gasoline model fuels, we developed and validated a gasoline chemical kinetic mechanism. Kinetic modeling indicated that the addition of toluene or a mixture of toluene and diisobutylene to PRF, forming the TRF or TRFD-20D, reduces the blended fuel reactivity through OH radical consumption through hydrogen abstraction reactions. They are, for toluene, C6H5CH3 + OH = C6H4CH3 + H2O and C6H5CH3 + O2 = C6H5CH2 + HO2, and for diisobutylene, IC8D4 + OH = IC8D4-5R + H2O. The addition of cyclopentane to TRFD-20D, forming TRFDC, reduces reactivity by depleting highly reactive species and consuming OH radicals through H2O2-forming reactions.
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