(2-19) Real-Time Engine Control Using a Combustion Model for Lean Boost Engines((SI-6)S. I. Engine Combustion 6-Modeling)

Abstract

The combination of physical models including a combustion model of an advanced engine control system (Fig. A-1) was proposed to obtain sophisticated combustion control in lean mixture combustion and high boost engines, including homogeneous charge compression-ignition and activated radical combustion with variable intake valve timing and a supercharger. Physical intake, engine thermodynamic, and combustion models predicted mass flow rate and exhaust gas recycle rate in the intake system, and temperature and pressure in the cylinder, based on the signals of an air flow sensor and a pressure sensor. Then, These models determined control variables such as air mass, fuel mass, exhaust gas recycle valve opening, intake valve timing and combustion start crank angle, resulting in combustion improvement in the above conditions. The combustion characteristics and auto-ignition parameters in the combustion model were investigated, and compared with some experimental data. Fig. A-2 shows air mass G_a, fuel mass G_f, and combustion start crank angle θ_i versus indicated mean effective pressure P_<mi> to attain optimum combustion. When p_<mi> was low, G_a/G_f was 20 and the mixture was lean, When the p_<mi> was high, G_a/G_f=15, mixture was stoichiometric. When p_<mi> became high enough, the stroke volume was decreased by using late intake valve closing, and knock tendency decreased. Therefore, p_<mi> increased by ignition timing advance (decrease in θ_i). 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.