Identification and air-fuel ratio control of a spark ignition engine

Accurate control of the air-fuel ratio in a spark-ignition engine is critical to satisfying future federal and California emissions regulations. The goal of this research is to explore the use of adaptive control as a means of precisely controlling the air-fuel ratio. A control-oriented, physics-based engine model, in which the sampling rate is based on crank-angle instead of time, has been utilized to construct a feedforward/feedback control scheme to regulate air-fuel ratio. The derived control law, however, requires the values of time constants, delay times, and other model parameters that must be experimentally determined. Since these parameters can possibly change over time, a method for estimating them online is preferred. A nonlinear least squares identification technique is used to accurately determine the model parameters using normal engine operating data. These parameter values are then employed in an estimator based controller to demonstrate cycle-to-cycle air-fuel ratio regulation on a single-cylinder laboratory engine (CFR) during various throttle transients