Mapping optimization for partial loads of common rail diesel piston engines

Theoretically, from a control design point of view, modern diesel engines are dynamic, nonlinear, MIMO (multiple-input and multiple-output) systems. This paper demonstrates that this assumption is not correct and a suitable model for predictive control (MPC) of power (torque), NOx and soot emissions based on temperature feedback is perfectly possible on SCR (Selective Catalytic Reduction) CRDITDs (Common Rail Direct Injection Turbocharged Diesel). The method optimizes the temperature at a selected point of the engine exhaust. This reference point is the turbocharger intake for Euro 0 (aircraft). For Euro 6+/US Tier 3a+ SCR diesels, the reference point is the intake of the "emission control system" usually at the outlet of turbocharging system. The traditional five-inputs are only theoretically independent. In fact, fuel injection duration depends on torque (load) and efficiency. Fuel advance is retarded to obtain the required reference temperature. HPEGR (high pressure exhaust gas recirculation) is adopted only when the emissions cannot be controlled by the fuel advance. VGT (variable geometry turbo) valve positions and low pressure LPEGR maximize the air flow (efficiency) at the engine intake. On the outputs, peak pressure and peak pressure derivative should be kept within structural limits. Soot and NOx are two faces of the same problems. In fact, high NOx means low soot and good combustion efficiency. Temperature and air flow are the keys to obtain optimum engine performance. Air flow is controlled by the turbocharger, while temperature depends on injection. This paper demonstrates that CRDITDs mapping is much easier when the fundamentals of diesel combustion and SCR are simplified to basic concepts. The strategy to retard the injection advance increases efficiency of 30% over traditional LPP (Optimal Location of Peak Pressure)- mapping at low loads.