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This paper presents a model-based design approach to feedback air-fuel ratio control for SI engines during fuel injection path changing. For the SI engines, emission performance during transient mode is remarkably influenced by air-fuel control, and to improve the efficiency of combustion engines, the fuel injection path is frequently changed from port-injection to direct injection or reverse. Therefore, how to describe the dynamics during the fuel path changes and to compensate the fuel injection are important issues to achieve good transient performance of air-fuel ratio. In this paper, a feedback control scheme with a mode changing command triggered feedforward compensation is proposed, and experimental validation on a six cylinders engine will be demonstrated.

For spark-ignition gasoline engines, the air-fuel ratio during transient operation is an important index concerning the emission performance and the torque generation quality, and the challenge is from the dynamics of air intake path, the fuel injection path and the sensor delay. This paper presents a simple model of intake dynamics-based air-charge estimation for the individual cylinder air charge. Then, with the model, a feed-forward based air-fuel ratio control law is developed in which the intake dynamics and the sensor delay are taken into account by introducing the cylinder air-charge prediction. The proposed control strategy is validated by the experiment results conducted on a commercial vehicle-used six-cylinder gasoline engine control test-bench.

The spark ignition-controlled auto-ignition (SI-CAI) hybrid combustion is promising in achieving smooth transition between SI and CAI combustion but, it is limited by the combustion cyclic-variation at late combustion phasing to avoid too high pressure rise rate (PRR). In this paper, to stabilize the combustion and reduce PRR, the in-cylinder fuel-stratification strategy is investigated in a gasoline engine, equipped with port fuel injection combined with single pulse direct injection (PFI-DI). Experimental results confirm the benefits of employing PFI-DI in comparison with PFI and single-pulse DI strategy. The influence of DI timing (Start of injection, SOI) on the combustion process is found to be quite complicated, in terms of combustion phasing, combustion stability, PRR and thermal efficiency. It makes the optimal-SOI calibration time-intensive, since complex trade-off between PRR and thermal efficiency is needed.