Ozone, the main component of photochemical smog, is formed when hydrocarbons in the atmosphere oxidize in the presence of sunlight and nitric oxide. Ozone causes health problems, damages crops and disrupts natural ecosystems. Despite remarkable progress over the past 30 years, automobiles continue to be a major source of hydrocarbon emissions and ozone pollution. Numerous studies have shown that variable valve actuation (VVA) can reduce engine fuel consumption and nitric oxide emissions. The objective of this study is to evaluate whether VVA controlled exhaust valve opening (EVO) and exhaust valve closing (EVC) can also be used to reduce hydrocarbon emissions.; An automotive gasoline engine was set up and tested with different EVO and EVC timings under steady-state and start-up conditions. Crank angle based hydrocarbon measurements were taken at the exhaust valve, in the exhaust manifold and at the entrance and exit of the close-coupled catalyst. Hydrocarbon speciation was performed to gain insight into combustion and post-flame oxidation processes and to estimate local ozone production (LOP) attributable to exhaust hydrocarbons. The methodology to estimate LOP, which accounts for local atmospheric conditions, was developed specifically for this purpose. A carefully validated engine cycle simulation was utilized to identify promising EVO and EVC timings and to simulate crank angle based exhaust mass flow that was used with measured hydrocarbon concentrations to calculate hydrocarbon mass flow.; The first strategy tested on the engine utilizes early EVO with standard EVC. Although this strategy increases exhaust gas temperature and reduces catalyst light-off time, the rapid drop in cylinder temperature increases cylinder-out hydrocarbons to such a degree that a net increase in hydrocarbon emissions and LOP results.; The second strategy investigated on the engine utilizes early EVO with early EVC. This strategy reduces hydrocarbon emissions and LOP. Early EVO reduces catalyst light-off time by increasing exhaust gas temperature and early EVC retains the hydrocarbon-rich exhaust gas from the piston crevice in the cylinder for reburning in the next cycle. Start-up hydrocarbon emissions are reduced by 27% and start-up LOP is decreased by 25%.
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