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In the present study, we developed a reduced TRF-PAH chemical reaction mechanism consisted of iso-octane, n-heptane and toluene as gasoline surrogate fuels for GDI (gasoline direct injection) spark ignition engine combustion simulation. The reduced mechanism consists of 85 species and 232 reactions including 17 species and 40 reactions related to the PAHs (polycyclic aromatic hydrocarbons) formation. The present mechanism was validated for extensive validations with experimental ignition delay times in shock tubes and laminar flame speeds in flat flame adiabatic burner for gasoline/air and TRF/air mixtures under various pressures, temperatures and equivalence ratios related to engine conditions. Good agreement was achieved for most of the measurement. Mole fraction profiles of PAHs for n-heptane flame were also simulated and the experimental trends were reproduced well. The vapor-phase and particulate-bound PAHs existed in GDI engine exhaust were sampled and analyzed by GC-MS.

Gasoline-fueled small engines have been developed predominantly for power by using fuel-rich combustion, and unburned HC is usually a consequence of inadequate mixing and combustion of the charge. In principle, a straightforward way to reduce HC emissions is to run at an almost stoichiometric air-fuel ratio while NOx emission become problematic, namely a tradeoff exists between the amount of HC and NOx emission, especially at high engine loads. Cooled exhaust gas recirculation (EGR) is a common way to control in-cylinder NOx production when burning stoichiometric or even leaner mixture. In this paper, experimental investigations were conducted on a small off-road gasoline engine to study the effect of EGR system on the engine-out emission especially the unburned HC and NOx.