Air-Fuel Ratio Control of Spark Ignition Engines with Unknown System Dynamics Estimator: Theory and Experiments

This paper addresses the emission reduction of spark ignition engines by proposing a new control to regulate the air-fuel-ratio (AFR) around the ideal value. After revisiting the engine dynamics, the AFR regulation is represented as a tracking control of the injected fuel amount. This allows to take the fuel film dynamics into consideration and simplify the control design. The lumped unknown engine dynamics in the new formulation are online estimated by suggesting a new effective unknown system dynamics estimator. The estimated variable can be superimposed on a commercially configured, well-calibrated gain scheduling like PID control to achieve a better AFR response. The salient feature of this proposed control scheme lies in its simplicity and the small number of required measurements, i.e., only the air mass flow rate, the pressure and temperature in the intake manifold, and the measured AFR value are used. Practical experiments on a Tata Motors Limited 2-cylinder gasoline engine are carried out under a realistic driving cycle. Comparative results show that the proposed control can achieve an improved AFR control response and reduced emissions.