Air/Fuel Ratio and Residual Gas Fraction Control Using Physical Models for High Boost Engines with Variable Valve Timing

The combination of physical models including a combustion model of an advanced engine control system was proposed to obtain sophisticated air/fuel ratio and residual gas fraction control in lean mixture combustion and high boost engines, including homogeneous charge compression-ignition and activated radical combustion with a variable intake valve timing and a turbocharger or supercharger. Physical intake, engine thermodynamic, and combustion models predicted air mass and residual gas fraction at the beginning of compression in the cylinder, on the basis of signals from an air flow sensor and an in-pressure sensor. Then, these models determine control variables such as air mass, fuel mass, exhaust gas recycle valve opening, intake valve timing and combustion start crank angle, to attain an optimum air fuel ratio (A/F), optimum residual gas fraction, and high efficient low nitrogen oxides combustion without power degradation in the above conditions. The control variables were investigated in simulation.

Total calculation times per intake stroke depended on the time step of the intake model and the crank angle step of the combustion model. A calculation time within 5ms was attained.