Fuel Chemistry Impacts on Gasoline HCCI Combustion with Negative Valve Overlap and Direct Injection 2007-01-4105
Homogeneous Charge Compression Ignition (HCCI) combustion has the potential to produce low NOx and low particulate matter (PM) emissions while providing high efficiency. In HCCI combustion, the start of auto-ignition of premixed fuel and air depends on temperature, pressure, concentration history during the compression stroke, and the unique reaction kinetics of the fuel/air mixture. For these reasons, the choice of fuel has a significant impact on both engine design and control strategies. In this paper, ten (10) gasoline-like testing fuels, statistically representative of blends of four blending streams that spanned the ranges of selected fuel properties, were tested in a single cylinder engine equipped with a hydraulic variable valve train (VVT) and gasoline direct injection (GDI) system. By using VVT and GDI, re-compression early injection (RCEI) HCCI combustion was implemented, in which exhaust valve closes much earlier than normal valve timing to trap burnt gases into the combustion chamber to promote auto-ignition of fuel at the end of compression stroke. In the study, fuel chemistry impacts on HCCI combustion are investigated at three steady-state points with 50% mass fraction burned location (CA50) fixed at 5 degrees after top dead center (ATDC). A stepwise multiple regression method, in which fuel properties are correlated with combustion and emissions, is employed to understand the fuel effects on HCCI combustion. Results demonstrate that fuel sensitivity, distillation temperature T10, and percentages of i-paraffins, n-paraffins, and aromatics strongly affect engine emissions (HC, CO, NOx), fuel consumption, and combustion stability.