“…However, the measurement time delay caused by the location of the UEGO sensor, consisting of combustion cycle delay and exhaust mixing transport delay, becomes an obstacle to the achievable performance by the feedback fuelling control. Various A/F control strategies have been developed to tackle the time delay from the fuel injectors to the A/F output, for example, sliding mode control, 10–14 internal model control, 15–18 gain-scheduling/linear parameter varying (LPV) control, 19–23 model predictive control, 24 the Smith predictor method, 25,26 , the estimate or predict-based method 27–29 and control approaches to systems with input time-delay. 30,31 However, there still exist challenges to more sophisticated and efficient solutions to accurate cylinder air charge estimation and suitable A/F feedback control strategy for online computation and implementation in a real engine regardless of nonlinearities, time-delay and uncertain parameters in engine dynamics.…”